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September 12

If the LHC created a black hole...

Or more generally, if a black hole were to appear on or near Earth's surface(presumably a small one, but let's say it's just big enough to avoid collapsing into Hawking radiation), how long would it take to swallow up the entire planet? And what would happen to the rest of the solar system? 68.123.238.140 (talk) 02:10, 12 September 2008 (UTC)

Longer than the expected life of the solar system, and no effect. Even if it swallowed the Earth in a day, the solar system would be fine -- you'd still have an Earth-ish mass orbiting the sun. — Lomn 02:25, 12 September 2008 (UTC)

Another related question: how big would a black hole need to be in order for there to be exactly 24 hours before the earth was gone? Nadando (talk) 04:07, 12 September 2008 (UTC)

Cannot be computed exactly. In fact, a silly question (do you need a 24h message in advance?). Next black hole question, please. --Ayacop (talk) 08:00, 12 September 2008 (UTC)

So you could use a vacation day, of course... --- OtherDave (talk) 10:40, 12 September 2008 (UTC)

It's amazing how ill-informed scientific reports, scare stories and other paper selling drivell is generating an unprecedented interest into an amazing scientific work that might have gone unnoticed outside of the ususal aficionados. 190.244.186.234 (talk) 11:47, 12 September 2008 (UTC)

I think the scientific community has underestimated how well a little irrational fear can benefit them if they spin it right. --98.217.8.46 (talk) 12:42, 12 September 2008 (UTC)

"Nice planet, mate. Awful shame if somethin' bad happened to it ..." Gandalf61 (talk) 13:52, 12 September 2008 (UTC)

Rather a high level of WP:BITE here: please avoid pejoritives such as "silly," "drivell (sic)," and "irrational" in responses. Lomn has the right idea in providing a reasoned and informative response without insulting the questioner. Edison (talk) 19:01, 12 September 2008 (UTC)

Have any scientists calculated the beam energy scale where we would actually say "Hmm, maybe we better not try that"? Could it be the next machine after the SHLC? Franamax (talk) 19:27, 12 September 2008 (UTC)

Probably somewhere around the Overwhelmingly Large Hadron Collider, which I think comes after the Ginormous Hadron Collider. -- Coneslayer (talk) 19:32, 12 September 2008 (UTC)

I don't know how higher energies are likely to cause problems, regardless of how high they get (assuming the equipment is built to handle that much energy - obviously if the machine explodes that would be undesirable! It wouldn't destroy the planet though, just Switzerland. ;) ). All the fear with black holes is nonsense, it doesn't matter how much energy is involved, black holes just don't behave in ways that would swallow the Earth like that. --Tango (talk) 21:22, 12 September 2008 (UTC)

Yes, I'm not that interested in the MBH hypothesis, for one thing, we now have an experiment underway to test it :)

However, to take a ridiculous example, if you collided two particles with the same energy as the Big Bang, you would end up with a new expanding universe in your lab, which could have undesirable results. Somewhere between there and here must be a line where problems could result.

Wouldn't there be an energy where you made a black hole big enough that it would be a problem? Or a sufficiently energetic strangelet or powerful magnetic monopole that they would do whatever bad things they might do?

How many orders of magnitude are we away from those energies? Franamax (talk) 23:15, 12 September 2008 (UTC)

The energy has to come from somewhere, you would need to extract all energy from the whole universe in order to create an explosion with the same energy as the big bang (and even then, it wouldn't be a big bang - the big bang involved space expanding, not just matter exploding). --Tango (talk) 08:38, 13 September 2008 (UTC)

Well, I suppose I shouldn't have postulated the ridiculous case of the Big Bang. (Though I'm reminded somewhat of an Asimov story where the first computer was asked "can the end of the universe be prevented?" and the last computer solved it, and "the cosmic AC said 'Let there be light' - and there was light").

I will persist in my question though - is anyone aware of scientific calculations as to the energy scale of a collider which could produce particles or states of matter which could pose a planetary threat? I'm pretty sure that every accelerator ever built has had just such a risk assessment - so what was the risk based against? In fact, in the 60's and 70's, I think there was a specific named committee to examine new accelerators.

And as a secondary question, what are the energy scales where we could possibly produce a more stable phase of matter, a cosmic Ice-9 as it were? Obviously these would be theoretical answers - has anyone done the theory? Franamax (talk) 10:27, 13 September 2008 (UTC)

Even in less extreme cases, the energy still has to come from somewhere. I don't think putting lots of energy into a few subatomic particles is going to be any more dangerous that releasing the same amount of energy with a bomb, so you would need to get an amount of energy into the particles comparable to the energy released by several large nuclear bombs - that's very difficult to do. As for your second question, more stable than what? Regular matter is pretty stable... --Tango (talk) 11:21, 13 September 2008 (UTC)

Water bears on Mars

We hear about the harsh conditions on Mars, and how unlikely it is to find life. But Water bears (Tardigrades) have been shown to survive (for 10 days)[1] conditions far harsher than those seen by recent Mars probes, including the vacuum of outer space, temperature extremes, and intense UV radiation.. They can survive ten years without water, temperatures from about absolute zero to 151 Celsius, and 1,000 times the radiation which would kill humans. Could terran Tardigrades survive and reproduce in the Martian polar areas, given that there seems to be liquid water sometimes? (after 6 "database locked" error messages)Edison (talk) 05:16, 12 September 2008 (UTC)

I don't think there's ever liquid water on Mars (currently, that is), the most it does is sublimate. Also, according to this Wired article: "Tardigrades may even provide insights into adaptations necessary for survival in off-Earth colonies, though they could not live actively in the extreme and nutrient-poor environments of Mars or the moon." -- MacAddct  1984 ^{(talk • contribs)} 05:44, 12 September 2008 (UTC)

See Extremophile. Even the limited spectrum of life seen on this planet shows that there is probably no environment too harsh for life to develop. There is a very real chance that space itself is liberally populated by micro-organisms which could very well seed planets, satellites, asteroids and comets with the first steps on the way to macro-organisms - I deliberately avoid use of the word "higher" or "more advanced", as being very subjective. 196.2.124.253 (talk) 06:47, 12 September 2008 (UTC)

The bacteria that can survive in space usually do so by becoming dormant, they need less extreme conditions to actually reproduce. I don't think the surface of Mars ever has conditions suitable for terrestrial life to reproduce, although somewhere underground theoretically could. --Tango (talk) 10:32, 12 September 2008 (UTC)

Maybe deinococcus radiodurans would be a better candidate. -- MacAddct  1984 ^{(talk • contribs)} 14:16, 12 September 2008 (UTC)

If there is never liquid water, coult sometning like a tardigrade live in the water ice layer a few inches below the Martian surface, dormant most of the time, but active and reproducing when conditions are least harsh? Desert plants and animals remain dormant for a year or longer on earth and use the rare less harsh conditions to do their business. Edison (talk) 18:55, 12 September 2008 (UTC)

Earth-derived life seems to requre exactly two things to flourish: liquid water, and an energy source. We've never found life where one or the other is missing, and everywhere we've looked that has both, we've found life. --Carnildo (talk) 21:35, 12 September 2008 (UTC)

If one is speculating about the forms that life might take, then there is no reason to suppose that water is a prerequisite for life to develop or exist. 196.2.124.253 (talk) 19:56, 12 September 2008 (UTC)

There is somewhat of a difference between lasting 10 years and 100000000 years between ice melting. Radiation damage would be far more severe, and any way what is there to eat for those tardigrades on Mars? The perchlorate would poison them anyway! Being animals they also need to respire oxygen . Graeme Bartlett (talk) 22:48, 12 September 2008 (UTC)

Water on Mars? They also recently found wet rivers that dried up I think.

~AH1^(TCU) 23:48, 12 September 2008 (UTC)

Gamma ray bursts and black holes

Gamma ray bursts are a very large release of energy. Assuming black holes have a limited lifetime because of an upper limit to the mass that they can contain, would an explosive release of that mass be of the same order of energy as observed gamma ray bursts? 196.2.124.253 (talk) 06:31, 12 September 2008 (UTC)

Much bigger. Who cares, it will never happen. Next black hole question, please. --Ayacop (talk) 07:56, 12 September 2008 (UTC)

Since no existing theory predicts an upper limit to the mass of black holes, there's nothing we can really say about what would happen when a black hole hit such a limit. Algebraist 09:46, 12 September 2008 (UTC)

Black holes don't explode... very small ones evaporate by Hawking radiation pretty explosively, but all black holes will evaporate at the same rate in their last X seconds of life, regardless of their starting mass (bigger ones will just take longer to get there). --Tango (talk) 10:30, 12 September 2008 (UTC)

This possibility has been explored by scientists, but not for black holes formed from stars since they last very very long, but for smaller black holes created in the big bang. I can't find any references but I think they studied what the signature flash would be like. No sightings so far. EverGreg (talk) 16:03, 12 September 2008 (UTC)

As mentioned, there is no known upper limit, but presumably if a black hole evaporated for long enough, at some point (the Chandrasekhar limit?), gravity would not be strong enough to resist the various forces of matter that enjoy a little lebensraum and it would explode. --Sean 16:40, 12 September 2008 (UTC)

As far as I know, degeneracy pressure doesn't count for anything once it's collapsed into a black hole - there isn't really any matter left, there's just a singularity (of course, our understanding of black holes isn't really up to explaining what happens to the matter). Current theories don't include any kind of lower limit under which black holes explode, there's just Hawking radiation (which grows exponentially, so the last fraction of a second would seem rather explosive). --Tango (talk) 17:42, 12 September 2008 (UTC)

Radioactive decay in materials. Schrodinger's cat

The degree of decay in a given radioactive material is measured in half-life. If this is so, then surely it should be possible to predict the point in time at which a material has sufficiently decayed to an extent that it will trigger the release of a poisonous gas, thus killing an imprisoned cat? —Preceding unsigned comment added by 78.32.39.90 (talk) 08:13, 12 September 2008 (UTC)

Half-life is a measure of a quantity of atoms, i.e., statistical. No way to predict the behaviour of a single atom which is random. Those gedanken experiments you are referring to (see Schrödinger's cat) always involve a single atom, not a quantity. --Ayacop (talk) 08:30, 12 September 2008 (UTC)

The half-life is basically an average, there is plenty of deviation from that average for either small amounts of the isotope or small periods of time. --Tango (talk) 10:27, 12 September 2008 (UTC)

As the others say, the problem is that if it is a single atom you have no way of predicting when it will or won't decay. Half-life does not tell you about that. --98.217.8.46 (talk) 12:37, 12 September 2008 (UTC)

Instead of providing a solution, the statistical nature of half-life is actually what causes the problem. If you have a large quantity of a radioactive material, after one half life 50% of that material will have decayed. Therefore, there is a 50% probability that any individual atom in that material will decay. According to quantum mechanics, that atom actually exists in a superposition of states (decayed/radioactive) until we observe it, at which point our observation collapses the wave function into one state or other. The point of the schrodinger's cat thought experiment was that by including the cat in the system, the cat itself should be thought of as entagled with the atom and therefore as existing in a superposition of states (dead/alive) until we observe it, which is extremely counter-intuitive. Schrodigner originally meant the experiment as a discusison of QM's flaws, but subsequent interpretations of the thought experiment have been used to illustrate how other interpretations of QM operate. Read our article on it, it's not bad. --Shaggorama (talk) 14:18, 12 September 2008 (UTC)

Unsailable Dead Sea

Our Dead Sea article states that the "salinity makes for a harsh environment where animals cannot flourish and boats cannot sail". Why is that? Is it due to high buoyancy or the effect of the salt on the hull of the boats? Or something else? -- MacAddct  1984 ^{(talk • contribs)} 15:12, 12 September 2008 (UTC)

No... I suspect that the article is wrong. Plasticup ^T/C 16:00, 12 September 2008 (UTC)

I've dropped it from the article. Such a surprising claim certainly needs a supporting citation. ike9898 (talk) 16:28, 12 September 2008 (UTC)

Animals not being able to flourish is certainly true (hence the name Dead Sea), but I can't see any reason why boats would have any difficulty, the added buoyancy should make things easier, not harder. --Tango (talk) 17:44, 12 September 2008 (UTC)

The very salty water might promote corrosion of metal hulls, but that's hardly the same as "boats cannot sail". --Anon, 22:06 UTC, September 12, 2008.

The Israel Museum certainly thinks it's possible to sail: [2] Now, they're just showing old anchors, so it's technically possible that all you can do is anchor a boat in the Dead Sea. ;) I would think though that the greater buoyancy would decrease draft and maybe make it much harder to control the boat. You might need so much ballast that your boat would be too heavy for the wind to push. Franamax (talk) 23:00, 12 September 2008 (UTC)

I was thinking that - I think you just need to change the shape of the boat so it has a flatter bottom, that should stabilise it (I've not done much sailing, so I'm guessing here). --Tango (talk) 08:35, 13 September 2008 (UTC)

This convention center advertising touts "sailing on the Dead Sea itself". Clarityfiend (talk) 02:03, 13 September 2008 (UTC)

And in case there's any doubt left at all... Site Matt Deres (talk) 15:25, 13 September 2008 (UTC)

Electroforming solution

Is there anywhere where i can find some recipes for a coppor electrioforming solution. I know that the main components are distilled water, copper suphate and various acids but cannot find any information about quantaties of each. Any help would be very much appreciated. regards Kirk uk —Preceding unsigned comment added by 87.82.79.175 (talk) 16:04, 12 September 2008 (UTC)

here you go. Watch yourself with those acids! Fribbler (talk) 17:53, 12 September 2008 (UTC)

Patella/knee jerk reflex

I've knocking my knees every which way with a finger-long hammer (toy, tool? I know not which) and I'm getting no reflex. I've seen the graphics but can't find the spot. Argh. Imagine Reason (talk) 17:40, 12 September 2008 (UTC)

I think it's just below the knee cap, there's a soft bit. Make sure your knee is bent and you should feel a dip between the knee cap and the top of the lower leg bone (I'm sure someone will tell me what that bone is called, but I don't really care!). I can trigger the reflex by hitting that spot with the side of my hand. --Tango (talk) 17:46, 12 September 2008 (UTC)

Yes, the patellar tendon is the spot, like tango says (above the tibia). You can also try to enhance the reflex by clenching your teeth or trying to pull your clasped hands apart. Fribbler (talk) 17:49, 12 September 2008 (UTC)

Huh. What's that based on? I mean, what makes it work like that? -- Captain Disdain (talk) 17:59, 12 September 2008 (UTC)

Shhhh Captain! :-) Telling you how it works will likely remove some (but not all) of it's effectiveness. It sure works though. I use it regularly. Fribbler (talk) 18:08, 12 September 2008 (UTC)

Oh, good old misdirection. I dig. -- Captain Disdain (talk) 00:11, 13 September 2008 (UTC)

It works better if someone else does it to you. Graeme Bartlett (talk) 22:38, 12 September 2008 (UTC)

chemistry - glassware

I have been working in labs for a couple of years, but I never have understood exactly the qualifications for volumetric glassware to called class "A." Does anyone know what the requirements are? —Preceding unsigned comment added by 204.214.74.84 (talk) 18:12, 12 September 2008 (UTC)

See Volumetric flask. Strawless (talk) 18:56, 12 September 2008 (UTC)

I have read that article but I was wondering if there is a more precise definition of the classifications -- all the article says is that the graduation mark is placed more accurately. This begs the question, to what degree of accuracy? —Preceding unsigned comment added by 204.214.74.84 (talk) 19:55, 12 September 2008 (UTC)

Have a look at this pdf file. It contains a table of how accurate the graduations must be. Fribbler (talk) 20:01, 12 September 2008 (UTC)

PHEV Battery Economics

How can I calculate the following:

• Cost of Plug-in Hybrid Electric Vehicile (PHEV) vs. Internal Combustion Engine (ICE) in cents/mile?
• Total lifetime operating cost of PHEV-vs-ICE, including the decrease in battery capacity and resistance to re-charge with time, as well as the difference in maintenace costs between PHEV and ICE technologies?

Also: Can the batteries proposed for PHEV's be used as a storage system for homes using wind or photo-voltaic power systems? 146.18.173.73 (talk) 18:51, 12 September 2008 (UTC)EC

The Tennessee Valley Authority had a wind generator which charged battery powered vehicles as a demonstration project over 30 years ago, so clearly wind generated electricity could be used to charge the batteries of a plug-in hybrid vehicle. Any source of electricity could be used to charge any batteries, with varying cost effectiveness. As for the other question, experience may not exist yet for lifetime operating cost. What is the lifetime of a vehicle these days? Edison (talk) 01:06, 13 September 2008 (UTC)

angular momentum

Is angular momentum just a manifestation of linear momentum (ie you can treat angular momentum as the combination of thelinear momenta of each of the rotating object's particles)? There's a follow-up question. —Preceding unsigned comment added by 65.92.231.82 (talk) 21:04, 12 September 2008 (UTC)

Short answer, yes. I think it also works the other way around - linear momentum is just angular momentum taken around a point at infinity (don't quote me on that, though!). --Tango (talk) 21:25, 12 September 2008 (UTC)

This is probably a silly question -- I'm trying to make my quota for the week. If linear momentum is angular momentum taken around a point at infinity, is that point on the line of the linear motion, off to the right, downstage left, or?? Wanderer57 (talk) 21:46, 12 September 2008 (UTC)

I haven't heard this interpretation before, but it seems like it ought to be the point at infinity at right angles to the line (which of these two points you choose will just introduce a minus sign somewhere). Algebraist 21:52, 12 September 2008 (UTC)

Wouldn't any point not on the line of motion yield a linear momentum? i.e. hold your reference point steady then allow the mass to continue moving, it's no longer at a right angle but the momentum is still linear. -- Mad031683 (talk) 22:03, 12 September 2008 (UTC)

Yes, but not a constant one. An object moving in a circle does have a linear momentum, but it changes direction as it moves round. If the point is at infinity (and I did have an infinity at right angles in mind, yes) then that change in direction becomes zero (a radius of curvature of infinity corresponds to a straight line). I'm not sure how rigorous all that is, I haven't really heard it before in this context, but it makes sense intuitively (I have heard of translations being thought of as rotations about infinity - momenta are a natural extension of that, I think). --Tango (talk) 08:32, 13 September 2008 (UTC)

Okay, there's a reason I asked this question. If I push against a vertical wall, I will gain linear momentum, right? But the earth in response will start spinning. Isn't the sum of the linear momenta of a rotating body equal to 0 (every point has corresponding point going in the opposite direction). So how is linear momentum conserved? Is the question even valid (a force is acting on each of the rotating particles to keep them in uniform circular motion)? —Preceding unsigned comment added by 65.92.231.82 (talk) 21:57, 12 September 2008 (UTC)

In considering the momentum changes when two bodies interact, you have to use a reference frame based on their common center of gravity. When the objects are you and the Earth, that will be near enough to the center of the Earth. When you push against a wall, you set the Earth spinning and you also set yourself rotating around that center of gravity. The momentum you gain only seems linear because your motion is constrained to be parallel to the Earth's surface and you move a small enough distance that the Earth seems flat. But angular momentum is conserved. --Anon, 22:17 UTC, September 12, 2008.

No. Gravity does not have to have to be intoduced. Besides, you can push strongly enought to surpass the earth's escape velocity. Anyway, even in your example linear momentum wouldn't be conserved. —Preceding unsigned comment added by 65.92.231.82 (talk) 23:26, 12 September 2008 (UTC)

• I did not mention gravity, I mentioned the center of gravity, also called the barycenter or center of mass. My apologies for confusing you by my choice from the three synonyms. --Anon, 21:08 UTC, September 13, 2008.

Ignoring gravity, you push on a wall on Earth's surface and fly off into space. Your push gives Earth some angular momentum (around its center of mass) and also some linear momentum (its center of mass moves away from you as it spins around it). -- BenRG (talk) 10:23, 13 September 2008 (UTC)

Missiles on Main Battle Tanks

Are there any MBT's that mount missiles? Is there a reason why most (if any) don't mount missiles? ScienceApe (talk) 21:36, 12 September 2008 (UTC)

Missile tank. Dragons flight (talk) 21:51, 12 September 2008 (UTC)

Price is a factor: a TOW missile appears to have a unit cost (the missile, not the launcher) of $38,000. The M256 round an M1 Abrams MBT fires costs around $4000. The two rounds have comparable weight and lethality (although the TOW has greater range). That cheaper round means you can have more in inventory and thus don't have to be so careful in deciding what to shoot at (and so can shoot at lower-value targets). -- Finlay McWalter | Talk 21:56, 12 September 2008 (UTC)

Yea, I've considered the costs. Missiles cost so much which is why railguns are so appealing in the future. But missiles can do things that cannons can't. Like being guided. Such a thing would be useful against attack helicopters and such. I would think that kind of extra protection would justify the extra costs. ScienceApe (talk) 22:14, 12 September 2008 (UTC)

But cannon shells can be guided.[3] Once again expense enters into the equation. Rmhermen (talk) 23:48, 12 September 2008 (UTC)

It's always tempting (to generals in particular) to keep adding stuff on (until they've build an Apocalypse Tank). But you get much more flexibility if you build the antiaircraft capability separately, so you can a) defend what you like with it and b) it can be a mile or so behind the dynamic tank battle and still give effective AA protection. The jack of all trades is the (super expensive) master of none. -- Finlay McWalter | Talk 22:33, 12 September 2008 (UTC)

Additionally, you don't really want all your big expensive fragile (and explosive) stuff outside the tank's armor. Even if its destruction won't harm the tank, it's highly vulnerable to soft kills and endangers exposed crew or nearby troops. — Lomn 23:19, 12 September 2008 (UTC)

Eh. I've considered that too, but I would think there would at least be some more experimentation with such a tank. I guess we could assume it would become a jack of all trades, master of none, but without actual testing it's a little presumptuous. ScienceApe (talk) 03:26, 13 September 2008 (UTC)

According to IT-1, "The large deadzone around the tank created by the missiles' minimum range combined with the limited amount of ammunition carried made it unpopular with the military." Clarityfiend (talk) 08:10, 13 September 2008 (UTC)

England MD/MBBS info

Hello every one.I need imformation about England Medical College/Universities for MD/MBBS courses.Please any body tell me the Tuition Fee,Living Fee,visa and other requirement for international students and also scholarship availibility.Any help will be much appreciated.OR someone wantto directly contact me are most wellcomed. thax —Preceding unsigned comment added by 202.125.143.76 (talk) 23:13, 12 September 2008 (UTC)

Hi 202, I googled here[4] then my eyes decided to swim in opposite directions so it's over to you – but it's a start until someone who knows comes by. Julia Rossi (talk) 07:27, 13 September 2008 (UTC)

Hi. Individual medical schools in the United Kingdom all charge different tuition fees, the only way to tell is to look at the individual schools themselves. Try looking at List of medical schools in the United Kingdom, picking a few that sound interesting to you, and going to their websites. They always give details of their international rates, and usually give you an idea of living costs. —Cyclonenim (talk · contribs · email) 08:19, 13 September 2008 (UTC)

This website [5] run by the British Council, has a number of search options for courses, scholarships etc. It would also be worth contacting the British Council, either through the website or through the branch nearest you. DuncanHill (talk) 12:11, 13 September 2008 (UTC)

September 13

Unidentified Plant

File:UnkFlwr.jpg

Pic1

Pic2

Can you help me identify this plant? What I know: It has feathery light green leaves, 5 petal bloom with yellow centre, perennial, flowers are pink or white, grows tall, seems to spread easily, grows in southern Ontario.

Thanks, *Max* (talk) 00:09, 13 September 2008 (UTC).

Floated the two photos --antilived^{T | C | G} 02:33, 13 September 2008 (UTC)

Is it a form of Cosmos (plant)? Especially Cosmos bipinnatus for the leaves. If you google images "cosmos plant" you'll find some more like it. The volume of petals varies from a simple variety to hybrids. Julia Rossi (talk) 07:20, 13 September 2008 (UTC)

F-16 Fuel consumption

Quoted from a local paper:

"Depending on thrust and altitude, an F-16 burns anywhere from 200 to 400 kilos of fuel a minute"

Is this true?

The F-16 article doesn't answer the question as far as I can tell. Thanks. Wanderer57 (talk) 00:21, 13 September 2008 (UTC)

Yes, that's about right. You can google for "F-16 fuel consumption" to verify. There's an interesting table comparing the fuel consumption of different fighter variants. The consumption depends heavily on the mission, the payload at takeoff, the speed and altitude flown, etc. ~Amatulić (talk) 00:36, 13 September 2008 (UTC)

The table indicates a loiter time of 145 minutes, which would imply a fuel weight of at least (145 min)×(200 kg/min) = 29,000 kg or so, but F-16 indicates a dry weight of 8,670 kg and a maximum weight of 19,200 kg. I conclude, therefore, that the 200 kg/min figure is not actually a lower bound, and the burn rate could be a lot lower during cruise. Maybe 200-400 kg/min is a typical range, not an absolute range. -- Coneslayer (talk) 01:01, 13 September 2008 (UTC)

Kinetic energy revisited

Hi. Sorry if it looks like I'm being naïve again, but a few months ago I asked a question about kinetic energy, and I remember the following formula. This is not homework. kE=mv²; v=t•a; d=t²•a/2. Sorry I'm not good at LaTex, t= time, a= acceleration, d= distance. Anyway, here's the problem. An apple with a mass of 100g dropped from 1 metre has kE of roughly 1 joule. However, if I follow the distance formula, 1 = t²•5; t=~0.45, v=~4.47, kE=2. It should equal 1, so something isn't working. I'm not going to speculate by assuming that d=t²•a instead of d=t²•a/2, because that is probably wrong. Again, this is not homework, I would like to remind myself for myself. Thanks. ~AH1^(TCU) 00:29, 13 September 2008 (UTC)

Wait, or is it d=t²•a/2 and not d=t²•(a/2)? Oops. ~AH1^(TCU) 00:33, 13 September 2008 (UTC)

Those two expressions are equal. Your mistake is in your first formula: kinetic energy is one half of mass times velocity squared. Algebraist 00:35, 13 September 2008 (UTC)

Algebraist is (of course) correct. But you can also avoid finding or using the final velocity of the apple if you remember that energy gained = net force x distance (in direction of force). In this case the apple starts from rest and experiences a force of 0.1 kg x 10 ms^-2 (if we take g to be 10 ms^-2) over a distance of 1m, so its final kinetic energy is 0.1 x 10 x 1 = 1 J. Gandalf61 (talk) 11:02, 13 September 2008 (UTC)

Turtle Bites and Salmonella

Can you get salmonella from a turtle bite if you didn't bleed? The skin is starting to peel off, but I never started bleeding. Thanks. Nick (talk) 01:09, 13 September 2008 (UTC)nicholassayshi

You should consult a physician, because we cannot give medical advice here. Keep in mind that salmonella can enter through the mouth, for example, which is why you need to practice very good hygiene any time you're handling reptiles. If you've been distracted by a bite, it's easy to imagine touching your face or eyes without realizing or remembering it, or touching objects or surfaces that you don't think to sanitize later. -- Coneslayer (talk) 01:21, 13 September 2008 (UTC)

Agreed. Have you seen the article Salmonella especially this bit[6]? It breifly mentions contracting it through handling iguanas and turtles with a reference. Julia Rossi (talk) 05:55, 13 September 2008 (UTC)

It appears many reptiles have bad mouth flora: see for example Komodo_Dragon#Venom_and_bacteria. --Ayacop (talk) 07:58, 13 September 2008 (UTC)

Sort of an extreme example though. Komodo dragons are sort of a special case. --98.217.8.46 (talk) 08:12, 13 September 2008 (UTC)

Bird identification request

At the memoriam to deceased Wikipedian Jeffpw, there is a request to identify the birds in this photo. Please identify the birds in the photo and post the results here. Thanks. -- Suntag (talk) 04:35, 13 September 2008 (UTC)

You might find something here at Buzzards and Eagles of Thailand[7]. Julia Rossi (talk) 05:51, 13 September 2008 (UTC)

The larger bird is probably an immature White-bellied Sea-Eagle (Haliaeetus leucogaster) and the two smaller birds are probably Brahminy Kites (Haliastur indus).--Eriastrum (talk) 17:25, 13 September 2008 (UTC)

electrical circuit solving

1.why is the power transfer curve for a load resistor in a simple electrical circuit(battery,source resistor,load resistor),is not symmetrical over resistance. 2.why thevinen's theorem for solving complex circuits apply only on linear circuits 116.71.183.222 (talk) 10:58, 13 September 2008 (UTC)

These appear to be homework questions. If you have specific things you don't understand about the questions, you'll probably have better luck getting an answer, but we're not going to do your homework for you. -- Captain Disdain (talk) 12:52, 13 September 2008 (UTC)

transistor

In a transistor we observe base -collector resistance less then the other b-e junction.why?116.71.183.222 (talk) 11:03, 13 September 2008 (UTC)

See the answer to your previous question. -- Captain Disdain (talk) 12:52, 13 September 2008 (UTC)

These appear to be college-level homework questions that you want to avoid learning the answers to. I assume you're not on a scholarship, so I have to ask what is it that you're paying for? --Sean 20:16, 14 September 2008 (UTC)

Houston muscle

Is the Houston muscle present in all men, or is it only present in some? Thank you in advance for your answer. Leptictidium (mt) 13:41, 13 September 2008 (UTC)

What is the houston muscle? I've never heard of it, unless it has a more common name. Fribbler (talk) 13:56, 13 September 2008 (UTC)

Its more common name is the compressor venae dorsalis penis. DuncanHill (talk) 13:58, 13 September 2008 (UTC)

Aha, yup found it. My Google search was missspelled. Anyhoo, it's a variant of the bulbospongiosus muscle and being a variant, only some men will have it. Couldn't find percentages on how many, though. Fribbler (talk) 14:06, 13 September 2008 (UTC)

ice caps of the earth

I have seen long ago in a childrens program that if you fill a glass of water half way, and fill the glass to the brim using ice;the question being: will the glass overflow if the ice melts? the answer is no. Would'nt the same rule aply with the Earth?; if the mass of the continents is already in the equasion of the Earths oceans? —Preceding unsigned comment added by 68.114.246.137 (talk) 17:50, 13 September 2008 (UTC)

By analogy to the example you give, floating ice (like the north polar ice) will have negligible effect, but ice that sits on land and slides into the ocean can have a profound effect. --Scray (talk) 17:57, 13 September 2008 (UTC)

Glaciers being the main example of such ice. --Tango (talk) 18:11, 13 September 2008 (UTC)

Ice has a different volume than liquid water. It is not a question of mass. In the example you give, I imagine the reason it doesn't overflow has to do with surface tension, not the fact that the ice and the liquid have the same total volume, as they do not (which you can easily see if you put a fixed amount of liquid into a small container and then freeze it—it'll burst). --98.217.8.46 (talk) 18:02, 13 September 2008 (UTC)

No, it's nothing to do with surface tension. In order for the ice to float it has to displace an amount of water with the same mass as it (see Archimedes principle). When it melts, it will have the same volume as the water it displaced, so will just take the place of the part of the ice cube that was underwater and the water level won't change. --Tango (talk) 18:10, 13 September 2008 (UTC)

Huh, I guess my brain isn't working today. --98.217.8.46 (talk) 19:37, 13 September 2008 (UTC)

I'm not sure quite what you're asking, but the continents aren't floating on the ocean. There is no water underneath, just the Earth's mantle. --Tango (talk) 18:10, 13 September 2008 (UTC)

The Arctic polar ice cap is frozen ocean and so is indeed floating on sea water Jdrewitt (talk) 20:27, 13 September 2008 (UTC)

But the ice caps on Greenland and Antarctica are largely on land, so melting of this ice would indeed act to raise sea level. That is the main reason for the concern over global warming causing low-lying land to flood. More detailed discussion at Sea level rise#Glaciers and ice caps. --Anonymous, 21:10 UTC, September 13, 2008.

And don't forget Post-glacial rebound. Wisconsin is still rebounding. Saintrain (talk) 22:33, 13 September 2008 (UTC)

The raising of the sea levels has as much to do with the thermal expansion of the existing water as it does to do with melting glaciers. Plasticup ^T/C 02:26, 14 September 2008 (UTC)

Another issue not accounted for in the ice in the cup analogy is that the ice caps are bright white, and liquid ocean is dark, so a lot more sunlight is reflected off into space when there's ice than there will be in nearish future when the arctic ice cap is only visible in history books. This increased heat will cause more thermal expansion. See albedo. --Sean 20:12, 14 September 2008 (UTC)

Storage

I am in the process of sketching out a new invention, which I unfortunately cannot discuss the details of (for obvious reasons). However, my invention has certain storage requirements that I am hoping somebody could assist me with. Basically, I need a form of storage with sufficient capacity to store the exact location, and state, of every atom in a adult human's body. Can anybody suggest a form of storage which would have this capacity? If you can help with this, please let me know. Thanks John. —Preceding unsigned comment added by Jbsouth1971 (talk • contribs) 19:05, 13 September 2008 (UTC)

Um, no. You're talking about something that needs a minimum of like 10²⁷ bits of information, but probably even more than that (that's just the number of atoms in the body—so add to that some sort of x,y,z coordinate system, plus all that can go into "state", e.g. which element, ions, etc., how it is bonded with other atoms into molecules, etc., and you're increasing the total amount of data by five or six times at a minimum). To give you an idea of how much that is, Google's total capacity is more than 10 orders of magnitude (10 million times) smaller than that. In an imaginary science fiction universe the best way to store that sort of information would be in directly making an exact duplicate of the body. --98.217.8.46 (talk) 19:47, 13 September 2008 (UTC)

are you building, a "teleportation" device? Coolotter88 (talk) 19:30, 13 September 2008 (UTC)

Hi John. Maybe the guys over at archive.org could help. They need an extra 20TB of space every month.78.148.226.73 (talk) 19:51, 13 September 2008 (UTC)

Doesn't this run into a major issue with the Heisenberg uncertainty principle? Exact location and state would seem entirely impossible. — Lomn 20:07, 13 September 2008 (UTC)

There's no such thing as exact when you measure a real quantity with a finite number of bits. But there's some resolution beyond which it doesn't matter, functionally. —Tamfang (talk) 07:20, 15 September 2008 (UTC)

OK, many thanks for all your help. It would seem that looking at the atomic level was a little too ambitious! I have thought about this further and I think that just storaging the location and type of each cell would be OK. Is there a form of storage that could handle that? Thanks again! Jbsouth1971 (talk) 20:20, 13 September 2008 (UTC)

According to Cell (biology), there's about 10¹⁴ cells in the human body, that's 100,000 billion cells. A typical large harddrive currently for sale can store about one terabyte of data, ie, 10¹² bytes, so you would need several hundred of those to store meaningful data. Equendil Talk 21:28, 13 September 2008 (UTC)

OK, so this is starting to look doable. I guess I would need about 100 drives just to store a list of the cells, and more to store other information. Thanks. Jbsouth1971 (talk) 00:07, 14 September 2008 (UTC)

Well, 10¹⁴ cells, each of which need location coordinates, not just "a byte of info". Think how big a cell is, and then you know how accurately you have to specify each one's (x,y,z) coordinates. And both exact position and cell↔cell contact information are critical if you're hoping to (re)create some sort of viable organism from the data. Gotta get the right nerves talking to the right muscles, etc. DMacks (talk) 03:31, 14 September 2008 (UTC)

Thanks. So if it would need this extra information, can anybody suggest how to figure out how much information would be required to create an accurate representation of an adult human? Along with the compression I mentioned before, it is likley that each cell would only need its location to be defined relative to its neighbours, so I am not sure if that helps minimise the information to be stored (i.e. I am not sure which representation would work best). Jbsouth1971 (talk) 14:50, 14 September 2008 (UTC)

Without knowing what you will do with the info, there's no way anyone can tell you what info you will need or how accurate it has to be. DMacks (talk) 15:52, 14 September 2008 (UTC)

I can't really go into exactly what it does but, suffice to say, that it would need to be enough information that, if a human were asembled from the information, they would be identical and alive and well. Jbsouth1971 (talk) 20:12, 15 September 2008 (UTC)

How much detail do you need on the "type" of cell? How many cell types are there? I am pretty sure we don't have a clue, if you include the state of the cell. What about each cell's contact with its neighbors? There are innumerable details that contribute to the state of the organism. --Scray (talk) 21:36, 13 September 2008 (UTC)

Be still my heart. And don't breathe! Saintrain (talk) 22:30, 13 September 2008 (UTC)

I think that it will probably just need the type of cell in terms of skin, blood, brain etc. Of course, there will be sub-types of those cells, but I guess that all of the types are known. I don't think it will need the contact information, just the exact location at a given point in time. It may well be that there could be some compression here too, I think. For example, if there is a block of identical cells (e.g. all liver cells) then you would just need to store the position of the boundaries, if you see what I mean. Thanks Jbsouth1971 (talk) 00:07, 14 September 2008 (UTC)

Just warn us before you test your mass teleportation device. Plasticup ^T/C 02:24, 14 September 2008 (UTC)

Also, before you decide a teleporter is a good idea (since that's pretty much the only thing any of us can imagine you are thinking about, except for maybe soylent tostito dip) watch The Prestige (film) or read the introduction to the book The Mind's I. --Shaggorama (talk) 07:12, 14 September 2008 (UTC)

Maybe he just needs a lot of storage space and is disguising its purpose by implying teleportation. --Bowlhover (talk) 15:31, 14 September 2008 (UTC)

Thanks for all of that info, it was very enlightening. Unfortunately I really can't discuss what the invention actually is, at least not at this stage of the process. Once the whole thing is a little more advanced I will be able to unveil it. Thanks again. Jbsouth1971 (talk) 14:50, 14 September 2008 (UTC)

Assuming it's a teleporter or cloning device you're inventing, rather than, say, simulating a human on a computer, you may be interested in tissue engineering. Also, google organ printing. That is for how you'd assemble the cells. Note that it takes so long to do this that if you're not printing a rather small organ, it will die as it's being built. Also, it would be impossible to build a brain with such a machine, partially because you'd have no way of wiring the axons, and because AFAIK there's information stored on a sub-cellular level. Anyway, why start with humans? Shouldn't you make a prototype for some simple multi-celled organism, like moss, and work up from there? — DanielLC 15:51, 14 September 2008 (UTC)

Thanks. Again, without going into the details of the invention, I do think that your idea of targeting a simpler organism is a good one. I can see some problems with proving the viability of the invention, but I could work on those. Using your example of moss, what kind of simplification do you think we would get over a human? Jbsouth1971 (talk) 20:12, 15 September 2008 (UTC)

If you are creating a clone, you should get the "look and feel" of your copy working with the just genetic code. ... However, I'd assume that you would not just want a walking, talking dummy/another person but a clone who has experienced what the master copy has already experienced, and knows what the master copy knows. ... Sounds quite a bit of a challenge already. I chime in with the others who are asking you to try small[er], and simple[r] organisms. Kushal (talk) 11:05, 20 September 2008 (UTC)

Nuclear waste into space

With the problem of nuclear waste being as long lasting as it is, would not the best option be to chuck the stuff into the sun. Chemical rockets and their occasional explosions would make that into a self-inflicted dirty bomb, but, would not a rail-gun type of launch into space be practical? —Preceding unsigned comment added by 68.193.8.247 (talk) 19:46, 13 September 2008 (UTC)

See Nuclear_waste#Space_disposal. Sure, if you came up with a totally reliable way of launching it into space, that might work. But we're pretty far away from such an option. And personally I'm still dubious that launching it into space is the "best" option. A carefully managed underground repository in a remote area would still probably be easier and cheaper to deal with. --98.217.8.46 (talk) 19:49, 13 September 2008 (UTC)

Given science fiction technology, we may as well just annihilate our radioactive waste, and not bother with sending stuff into space. "Railguns" applied to space launch ain't practical, we don't have that kind of technology. Besides, cost considerations more so than technology dictate how we can realistically dipose of radioactive waste. Equendil Talk 21:41, 13 September 2008 (UTC)

Disposing of nuclear waste in space may be worth considering, and has been suggested, but chucking it into the sun would take an enormous amount of fuel (unless you waited until you can get great gravitational assists from various planets). In order to hit the sum you need to get rid of all orbital velocity you've inherited from Earth, a tiny bit left and you'll just loop round the sun and come back. --Tango (talk) 22:46, 13 September 2008 (UTC)

If you put nuclear waste in a rocket, there is a chance that the rocket can explode and send back the waste to Earth. 72.136.110.93 (talk) 23:10, 13 September 2008 (UTC)

Or blow the Moon out of orbit. What happens if we figure out how to recover and reuse that material? --—— Gadget850 (Ed) ^talk - 00:01, 14 September 2008 (UTC)

• I think we can all learn a valuable lesson from Futurama. -- MacAddct  1984 ^{(talk • contribs)} 03:08, 14 September 2008 (UTC)

Why don't we (America) just sell it to nations that are willing to reprocess it, or better yet, fix our broken nuclear policy and reprocess it ourselves? — DanielLC 15:29, 14 September 2008 (UTC)

Selling it to other nations to reprocess is sort of a political non-starter, even if one thought it was a good idea to increase worldwide plutonium inventories. Can you imagine the headlines? "US selling plutonium to Russia (or India, or China, or France)"? The only place I could imagine even contemplating getting away with it would be the UK and even that seems unlikely. --98.217.8.46 (talk) 20:13, 14 September 2008 (UTC)

Why is the UK any better than any of the other existing nuclear powers? Selling it to a country that doesn't already have nuclear weapons might be an issue, but all the countries you list have them already, so what difference does it make? Of course, you can't completely reprocess it - you're still going to have radioactive waste left, just less of it. --Tango (talk) 13:09, 15 September 2008 (UTC)

Because the IAEA won't allow that. Otherwise nuclear waste could be exported to developing countries and disposed of on the cheap, at great risk to the locals.

(edit to clarify) The UK's THORP plant is supposed to be capable of receiving and reprocessing foreign spent fuel, but you get an equivalent amount of radioactive material in return.AlmostReadytoFly (talk) 13:57, 15 September 2008 (UTC)

Nuclear explosion and X-Ray lasers

The blast element of a nuclear explosion is mostly caused by the sudden release of x-rays correct? So if we were to create an X-Ray laser like the bomb pumped x-ray laser proposed during the 80s, and it was fired relatively close to the ground, what would the effect look like? The X-rays themselves I know are invisible, but I'm assuming we would see something because the X-rays would create blast when they are absorbed by the atmosphere. ScienceApe (talk) 20:34, 13 September 2008 (UTC)

A nuclear blast has three devises that cause damage: the blast itself/expansion of gases, intense heat, and nuclear radiation. Nuclear radiation traditionally consists of alpha particles, beta particles, and gamma rays (not X-rays.) I don't think you would see much if you released a bunch of X-ray's, just like you can't see anything when they are used to photograph your teeth or bones. Unless by some chance they excite the atmosphere, which I don't think is possible. X-rays are not well absorbed by the earth's atmosphere. --Russoc4 (talk) 20:43, 13 September 2008 (UTC)

I think you are confused a little. I'm not referring to the total effects of a nuclear explosion, just the blast effects, which is different. The effects of a nuclear explosion consist of,

    Blast—40-50% of total energy
    Thermal radiation—30-50% of total energy
    Ionizing radiation—5% of total energy
    Residual radiation—5-10% of total energy

Now, I'm only referring to the blast effects, not the other three. With that in mind according to, http://en.wikipedia.org/wiki/Effects_of_nuclear_explosions#Blast_damage, blast is indeed mostly caused by the x-rays. It says "shock wave is inside the surface of the developing fireball, which is created in a volume of air by the X-rays.". Additionally the the particles and the gamma rays you mentioned appear to be associated with ionizing radiation, which is another effect that I'm not asking about. ScienceApe (talk) 20:57, 13 September 2008 (UTC)

That article is rather weak on the actual physical mechanism whereby soft X-rays actually form the fireball, saying only (of the air) "this radiation interacts with and rapidly heats it". How this actually happens is better described in this article. What's not clear to me is what proportion of the visible spectrum light is due to direct incandescence of the superheated atmosphere atoms (I confess to not really understanding what "heating" an atom really means) and what proportion is photoelectric fluorescence. This paper discusses atmospheric fluorescence due to the x-ray emissions of nuclear explosions. I guess in answer to your "what would it look like" the answer is going to lie somewhere between "discrete death beam" and "terrifying glowing blurry death sausage". Either way it's not going to reach very far (perhaps a mile). Russoc4: as these papers show, X-rays are very much absorbed by the atmosphere, the first paper saying "the X rays are absorbed in the immediate vicinity of the burst, and they heat the air to high temperatures. This sphere of hot air is sometimes referred to as the "X-ray fireball." -- Finlay McWalter | Talk 21:48, 13 September 2008 (UTC)

Interesting off-topic factoid that you should not try to verify: if your eyes are well-adjusted in a darkened room and you look at a strong X-ray source, you can see a ghostly gray light, according to Röntgen. --Sean 20:42, 14 September 2008 (UTC)

Not making nutrients as an evolutionary "tactic"

While stirring my grits this morning and thinking about incomplete proteins (no, really) it occurred to me that, as omnivores, we didn't need to make many of our "secondary" nutrients since we could just harvest them. What is the cost of making vitamins? Would such a cost-avoidance provide a significant evolutionary benefit? Thanks Saintrain (talk) 21:05, 13 September 2008 (UTC)

I'm not sure what you are talking about. There are lots of things that we evolved that we didn't "need" or there are better alternatives to what we have. I don't know the cost of making vitamins, but I do know that just taking vitamins without food, tends to not be assimilated properly. You usually need to take vitamins with food in order to absorb the vitamins correctly. Could you clarify what you are asking a little more? ScienceApe (talk) 21:16, 13 September 2008 (UTC)

I'm talking about the "old days". What is the metabolic cost of making, say, vitamin C. Did avoiding the cost of making vitamin C provide a significant evolutionary benefit? Saintrain (talk) 21:34, 13 September 2008 (UTC)

If the diet provides all of the vitamin C (your example) needed, then there would be no incremental benefit in developing the mechanisms to synthesize it. So, the question becomes how much our inability to make vitamin C limited our fitness. --Scray (talk) 21:45, 13 September 2008 (UTC)

(ec) Maybe it did. The other possibility is simply genetic drift: given a diet rich in Vitamin C, our ancestors had no need to produce it, and thus no selection pressure against mutants with inactive L-gulonolactone oxidase. Apparently, the haplorrhini, including humans, all descend from a lineage with such a mutation. —Ilmari Karonen (talk) 21:49, 13 September 2008 (UTC)

To emphasize what was just said, it isn't that losing the ability to make vitamin C was beneficial, it was that there wasn't any selective pressure to keep the synthesis genes. When random mutations knock out the gene's function, the animal can still survive, and pass on the "dead" gene to its offspring - it's not better than one who can, but it's not dead, either. This was how the essential amino acids were explained to me. Since humans have historically gotten enough of most of the amino acids in the diet, there isn't any pressure to keep the synthesis genes around, and you slowly lose their function. The pathways which require more genes to make are lost first, as there is more chances that one of the genes will be knocked out by random mutation. -- 128.104.112.147 (talk) 22:00, 13 September 2008 (UTC)

There's a thread on the "Darwin-L Message Log" on this very topic but it, too, was just hand waving and diarrhea and polar bear livers(!?). Noone answered the question "What is the metabolic cost of making vitamin C".

The best that several variations of google(metabolic cost liver ascorbic "vitamin c" synthesis site:.edu) turned up was that vitamin C was so common in other species were the suppositions were that it was very important and/or very cheap to make. (Lots of veterinary schools because humans don't make it. (Calves can make it by day 7!)) Lots of taking Dr. Pauling's name in vain, too, 'til I added the "site:.edu". What's a better set of search terms? Saintrain (talk) 01:09, 14 September 2008 (UTC)

You might want to look at the papers linked from the pertinent page on OMIM. - Nunh-huh 01:17, 14 September 2008 (UTC)

That is a very cool site. Thanks! There's all kinds of info there. Never realized how universally important vitamin C is, even to yeast. (There's even a speculation that the lack of vitamin C resulted in a higher oxidant-related mutation rate in Hominids!) But it's hard to find the cost of v-C biosynthesis in humans ('cause we don't do it). I'm about to give up. There is a reason why I didn't study biology. :-) Saintrain (talk) 00:33, 15 September 2008 (UTC)

Your best bet may be to look at vitamin C synthesis in presimians, as they are the most closely related creatures to humans in which the pathway may have been studied. - Nunh-huh 03:31, 16 September 2008 (UTC)

OMIM is very cool, and since he died recently I'd like to point out that OMIM was created and largely written by Victor McKusick, widely regarded as the father of medical genetics (and a wonderful human being who will be sorely missed). --Scray (talk) 00:23, 16 September 2008 (UTC)

Thanks for pointing out our article. I've fulfilled my "learn something new every day" obligation... - Nunh-huh 03:33, 16 September 2008 (UTC)

Only marginally related to the discussion, but reading the heading I thought that perhaps among plants being made of hard to digest fiber and some species offering low nutritional value, maybe that was an advantage to not being eaten up. Well until something evolves to eat them; food sources rarely stay unexploited.

Why is 16:9 superior to 4:3?

I look at screens all day. So do most people I know. It seems we have made a choice as a society to go with a wider, shorter resolution rather than the more square-like box. I can think of 2 reasons why this doesn't make sense:

1) We are tall, thin beings. A wider resolution impedes caturing our counteance on screen. It is disturbing to see so much landscape left and right of a human figure in the center. 2) Reading is always easier when done vertically. If a line becomes too wide it is too easy to get lost when trying to find the next line, and, far more importantly, it hinders speed reading. Sucking up short phrases is easily done in a vertical newspaper format, no inner voice required. Sappysap (talk) 22:40, 13 September 2008 (UTC)

It is not. 16:9 is a compromise TV aspect ratio between standard 4:3 and 2.35:1 movie aspect ratios. It is already not a very good solution for TV broadcast, because now you have black-bars everywhere, and when you apply it to computer monitors it's even worse. Sure now you could watch movies with less black bars but as you have said reading web pages become much more painful and whatever you have gained in less black bars when watching movies you have lost it in fixed-sized web pages that leave 50% of your monitor blank. It's mostly a fad (and this can be extended to those 16:9 cameras), and IMHO what you lose (precious vertical resolution) is much more important than what you gain (less black bars when watching movies, which I hardly ever do anyway). --antilived^{T | C | G} 23:47, 13 September 2008 (UTC)

Some computer monitors (have have a rather nice Dell one) allow you to rotate a 16:9 through 90 degrees, making it a stringy 9:16. At least for text-based stuff like web-browsing and word processing that turns out to be rather nice. -- Finlay McWalter | Talk 23:52, 13 September 2008 (UTC)

Isn't our natural range of vision more oblong? Presumable the most acute portion of our vision is an ellipse inside the larger ellipse of our total range, and the largest quadrilateral that can be inscribed in that ellipse is a rectangle. Plasticup ^T/C 03:10, 14 September 2008 (UTC)

It's better for pictures as it corresponds more to how we view the world - up and down aren't as important as left and right. Holding my fingers up I can see about two and a half times as much or more sideways with both in view at the same time as I can up and down. But yes I agree, for reading it's no good currently. There is a proposal to support columns of text better in HTML so one automatically gets one, two or more to fit the screen complete with text flowing between them. At the moment doing that is a pain which is why it isn't done more frequently. Dmcq (talk) 09:22, 14 September 2008 (UTC)

I've actually held off on buying a new laptop partly for this reason. I'm hoping that the fad will blow over, but maybe I'm deluding myself. I've always suspected that part of the reason is that screens are marketed by diagonal instead of area. A 16:9 screen with a given diagonal is about 11% smaller than a 4:3 screen with the same diagonal and correspondingly cheaper to manufacture. It's a good thing digital cameras are marketed by an areal unit (megapixels) or we might be deluged with widescreen digicams also. -- BenRG (talk) 11:47, 14 September 2008 (UTC)

It's unlikely to "blow over", seeing as how 16:9 has very wide support from the LCD TV industrial base. But I think the change to 16:9 is actually a good thing; I've owned five 4:3 laptops and two 16:9 laptops and I find the 16:9 laptops much more esthetically-pleasing. For one thing, the screen much more closely approaches the golden ratio (being 1.78 rather than 1.33, and the golden ratio being 1.62). Also, when opened, the entire "height" of the laptop (screen height plus base depth) is much less than the far-"oversquare" effect you get with a 4:3 laptop. I'm not sure I'd want to go any wider, but I'm very pleased with the transition to 16:9.

Atlant (talk) 16:31, 15 September 2008 (UTC)

Good or bad, I can't imagine it blowing over. Not only is 16:9 closer to the natural aspect ratio of a keyboard, it's more like the movies, and nowadays, it's more like TV. For better or worse, I think that those are unstoppable forces in marketing and fads. APL (talk) 03:12, 16 September 2008 (UTC)

Masturbation

At what average age do girls start masturbating? —Preceding unsigned comment added by BellyGrease (talk • contribs) 22:41, 13 September 2008 (UTC)

See Masturbation#Masturbation frequency, age and sex (fourth paragraph). Zain Ebrahim (talk) 22:49, 13 September 2008 (UTC)

end of the world : december 2012?

hi guys, i am curious about what is the concensus among scientists about all the predictions that the world may end on 2012 because of all the clues that point to that happening, like the sun spot cicle ending, poles shifting, the mayan prophecy, global warming...and all that...and also the LHC possibly creating a black hole!!! thank you! —Preceding unsigned comment added by 24.91.11.185 (talk) 22:52, 13 September 2008 (UTC)

See Wikipedia:Reference desk/Archives/Science/2008 August 15#about 20 dec 2012. There are some links to older questions in there too. Zain Ebrahim (talk) 23:00, 13 September 2008 (UTC)

Grooooaaaaaaan. See [8], [9], [10], [11],[12], and [13]. --Bowlhover (talk) 23:21, 13 September 2008 (UTC)

lol, thanks guys. but also...i think it is too much of a coincidence that the mayan calendar ends in 2012, terrence mckenas' whatever diagram ends in 2012 too, (the one that is based on the i ching), the LHC poses a minimal threat of creating a dangerous mini black hole and nostradamus has a prophecy about this machine, look it up on youtube. also the sun ending its current sun spot cicle, the solar system aligning itself with the center of..the galaxy i think. so there is a lot of stuff that seems correlated with that date. i am a skeptic too...but the world just seems so close to ending...i mean, the war in irak and stuff...i bet a bunch of countries hate the US and are planning evil things against it. like a nuclear attack , a viral attack and what not. —Preceding unsigned comment added by 24.91.11.185 (talk) 23:57, 13 September 2008 (UTC)

The Mayan's did not predict that the world would end in 2012. That is a total fabrication. I spoke to Dr. Mary Miller about this just a couple years ago, and she is widely regarded to be the foremost authority on pre-Columbian Mesoamerica. Plasticup ^T/C 00:01, 14 September 2008 (UTC)

as far as i know their calendar abruptly ends in december 2012...but i mean, i don't want the world to end. so if all this is just pseudoscience then i'm glad.

thank u guys for all your answers! —Preceding unsigned comment added by 24.91.11.185 (talk) 00:06, 14 September 2008 (UTC)

Also, the sunspot cycle repeats every 11 years, so this wouldn't be the first time. ~AH1^(TCU) 00:39, 14 September 2008 (UTC)

OK, let's go:

• sun spot cycle ending

The Sun has a 9-14 years cycle of activity. It's not really precise, and if one were to end in 2012 it would be just a coincidence.

• poles shifting

Completely unpredictable when it will happen.

• Mayan prophecy and calendar

The prophecy is a fabrication and this has been debunked several times.

• Global warming

2012 has no relation to global warming.

• LHC creating a black hole

Pretty much debunked. There's nothing to fear.

• Nostradamus prophecy

Nostradamus is a joke. There's no "prophecy" worth bothering. They're always found in hindsight and are usually passages vague enough to fit a lot of situations - just like bible and other prophecies.

• the solar system aligning itself with the center of the galaxy

This makes no sense. Two points are always "aligned". Planets alignment are worthless too.

• the world just seems so close to ending

Nah, we've been through much worse times. We're in a relatively peaceful time, really, and throughout history there has always been people claiming "the world is just about to end, you just have to look at the signs". Yet, nothing ever happened. Why do people always forget failed predictions? For example, Christians have been thinking the Second coming was going to happen within their lives for centuries.

So you see, this is not even pseudoscience. It's bullshit. Just move on and don't bother with these apocalypse fears, because they have always been wrong throughout history. But if someday you see scientists reporting an actual natural threat, then you have reasons to believe them. — Kieff | Talk 02:08, 14 September 2008 (UTC)

If you look hard enough, any year has peculiarities that, if isolated, seem surprising. I can easily claim that 2009 is going to be the best year on record by pointing to the 1909 article. Just look at what happened during that one short year! The People's Republic of China was established, and it was this party that ended 2000 years of monarchy in China. Dessau became the first radio broadcaster. Robert Peary became the first person to reach the north pole. The Pearl Harbor base was founded in November. The person accused of setting fire to the Reichstag was born. All of these events are much more well-known than the "predictions" involving 2012! Who doesn't know about the ROC? Who doesn't know about radio broadcasts, Peary, the Reichstag fire, or Pearl Harbor? But who, without having read about the "apocalypse", would know about some obscure Mayan text or McKennas' graph?

It's true that the events I mentioned do not make it more likely that 2009 will be the best year on record, but celestial alignments, the LHC, the solar maximum, and pole shifts don't increase the likelihood of an apocalypse either.

I assume that this is the Youtube video you're referring to. The Nostradamus prophecy, which does not mention the year 2012, reads:

"All should leave Geneva. Saturn turns from gold to iron. The raypoz will exterminate everything. There will be signs in the sky before this."

Only the first sentence suggests the LHC; "raypoz" is not a French word and is not always interpreted as "positive ray". This website, for example, believes it means "Christ". The poem might as well be construed as a prediction of a war in which Switzerland is taken. As for the other passages the video quotes, none of them accurately describe an engulfment of Earth by a black hole. --Bowlhover (talk) 05:14, 14 September 2008 (UTC)

From a scientific standpoint, which plant is the most important?

By "important" I mean what species of plant has the most value from a guys in a lab coat researchable, medicinal, and physical law standpoint? Which lends itself best to the most rigorous scientific tests, yet can still make and cure just about anything?Sunburned Baby (talk) 22:58, 13 September 2008 (UTC)

I'll nominate arabidopsis thaliana aka thale cress. Google Scholar returns 680,000 hits for "arabidopsis", that's a lot of scholaring! It's widely considered a model organism. Doesn't really cure stuff though. Franamax (talk) 01:43, 14 September 2008 (UTC)

Interesting question. On a whim, I checked soybean and got 996,000 hits. Of course, since oak gives us more than a million hits, I'm not sure how good a gauge Scholar really is. Wheat gives us two million hits. Matt Deres (talk) 02:08, 14 September 2008 (UTC)

Heh. Turns out there are a lot of people named Wheat doing research out there; forget that one! Matt Deres (talk) 02:09, 14 September 2008 (UTC)

Maybe so, but all those people named Wheat are undoubtedly descendants of wheat farmers, so if not for wheat we would have a HUGE loss of valuable researchers. Therefore, those hits still definitely count! --Scray (talk) 04:55, 14 September 2008 (UTC)

But why are the people named Potato being discouraged from going into scientific research fields? Systemic bias? Franamax (talk) 17:09, 14 September 2008 (UTC)

It very much depends on how you define important. Arabidopsis was the first plant to have its genome sequenced and widely used in genetics studies. (And there are no researchers named Mr. Arabidopsis) Important food crops such as soybean, maize, rice and wheat attract attention from agronomists because of their importance to the world, and also from geneticists because of their very complex genomes. And by historical scientific importance, you could think of the pea also, since that's where Gregor Mendel first studied genetic inheritance. Franamax (talk) 17:09, 14 September 2008 (UTC)

The effects of Ocean Nuclear Bomb Testing

What are the effects of the Nuclear Bomb Testing on the Pacific Ocean environment? Some water is now radioactive, so how long does it takes for the radioactive water to become non-radioactive water? 72.136.110.93 (talk) 23:04, 13 September 2008 (UTC)

If the water had become radioactive then more by taking up products of the fission, less by being irradiated. Anyway, the water soon mixes. The problem is the island soil that took up long-lived fission products. See that article for some ideas. On a similar note, there are still forests round Munich where collecting of mushrooms for culinary purposes is still discouraged, twenty years since Chernobyl, and more to the east it must be worse. --Ayacop (talk) 14:01, 14 September 2008 (UTC)

Our article, Pacific Proving Grounds, does not mention water contamination for the reasons stated above. More precisely, you need to define "radioactive water" and "non-radioactive water" before you can proceed. Seawater is water (Oxygen and Hydrogen) with many disolved substances (ions and some non-ionic molecules.) The readiosctivity results from radioactive isotopes of some of the atom in the water or in the disolved substances. There is a natrual background of radioactive isotopes, so one answer to your question is "never." If you define "non-radioactive" as the point at which the water near the testing ground is at or very near the background radiation, I would guess that this happens within weeks due to radioactive dacay and dilution.If you ar worried about health effects, you will need to analyze individual elements like iodine, but even these will drop to background quickly due to dilution. -Arch dude (talk) 14:23, 14 September 2008 (UTC)

The water isn't the problem—the ocean is just too vast not to dilute such effects to the level of background radiation within a short amount of time. --98.217.8.46 (talk) 15:31, 14 September 2008 (UTC)

September 14

Thallium Stress Test (Side Effects)

I am wondering if anyone has had a Thallium Stress Test ? If so; did you have any side effects ?

My cousin just had a test and since then has had terrible discomfort in his chest area that he never had before.

Thank You . —Preceding unsigned comment added by 74.235.199.159 (talk) 00:29, 14 September 2008 (UTC)

Well, it is a stress test. It stresses the heart, and most people who take the test either have known or suspected heart disease. So a report of discomfort following such a test needs to be made to a doctor, not to the Wikipedia reference desk! If your cousin has chest pain, he needs to call his doctor, so that it can be determined if he's suffering a heart attack or not! - Nunh-huh 00:49, 14 September 2008 (UTC)

Contact the doctor. That is what they are there for.--mboverload@ 02:18, 14 September 2008 (UTC)

No, call for an ambulance unless there is a doctor right at hand. "Terrible discomfort in the chest area" is an emergency situation! --Anonymous, 05:10 UTC, September 14, 2008.

If you had a stress test they must have give you an emergency contact number. Use it. Plasticup ^T/C 02:30, 14 September 2008 (UTC)

Chemical Name

I'm trying to figure out the name of a molecule, but I'm out of combinations. It looks like cyclopentane, but there is a nitrogen atom in place of one of the carbon atoms. No, this is not homework or anything, I'm just curious.CalamusFortis 04:54, 14 September 2008 (UTC)

Perhaps Pyrrolidine? You don't mention how saturated the molecule is, but maybe this helps. --Scray (talk) 05:02, 14 September 2008 (UTC)

That was it exactly. Thank you. Forgive me for neglecting to mention saturation.CalamusFortis 05:18, 14 September 2008 (UTC)

For future, you can search google or wikipedia for the chemical formula ("C4H9N" in this case) for many organic compounds and find their name and relevant articles. ChemSpider is another good free chemical search engine. DMacks (talk) 15:49, 14 September 2008 (UTC)

For browsing according to structure, the WikiCommons compounds tree is near perfect. --Ayacop (talk) 16:02, 14 September 2008 (UTC)

Swimming Pool (Hydrochloric) Acid

What is the gravelly, grinding noise that can be heard when pool acid is poured from the bottle into another vessel, or swirled in its own bottle ? It sounds as if there is a layer of gravel scratching around the bottom of the plastic container. --196.207.47.60 (talk) 05:00, 14 September 2008 (UTC)

I don't know about that, but a minor correction. It's Chlorine. Not Hydrochloric Acid (often wrongly called Hydraulic or Hydrolic acid). Hydrochloric Acid would irritate your skin to a point where you would have to get out because it stung so much. OK? OK. See also: Chlorine and Hydrochloric Acid.--Editor510 ^{drop us a line, mate} 17:08, 15 September 2008 (UTC)

Er, hydrochloric acid (concentrated HCl, often labeled "muriatic acid") is used in pools also to lower pH (all that chlorine is pretty alkaline). DMacks (talk) 17:11, 15 September 2008 (UTC)

Oh, actually maybe I do know.

1. In the swimming pool, that'll be the ripples from when you pour it in slapping around in the little open venty thingys on the sides of the pool.
2. The bottle? My only guess is some trapped air inside there...

--Editor510 ^{drop us a line, mate} 17:18, 15 September 2008 (UTC)

I think that the disinfectant used is sodium hypochlorite. This leads to precipitation of calcium carbonate inside the bottle. Axl ¤ [Talk] 12:55, 19 September 2008 (UTC)

Dark matter

wat is meant by dark matter? —Preceding unsigned comment added by Donlesnar (talk • contribs) 05:47, 14 September 2008 (UTC)

see dark matter. --Shaggorama (talk) 06:52, 14 September 2008 (UTC)

Name for animals that can change colour

Does anyone know what the scientific name for this capability among animals is? We have a list at Category:Animals that can change colour and a request to fill in this missing information. (Can;t seem to link to it but it's there in fact) Thanks, Julia Rossi (talk) 11:46, 14 September 2008 (UTC)

It's at Category:Animals that can change color. DuncanHill (talk) 11:53, 14 September 2008 (UTC)

(edcon) yes it is thanks DuncanHill, Julia Rossi (talk) 11:58, 14 September 2008 (UTC)

For the edification of other readers, you link to a Category (or Image) like so: [[:Category:Animals that can change color]] Plasticup ^T/C 16:08, 14 September 2008 (UTC)

The mechanisms responsible for colouration strategies differ between species depending upon the nature of the pigment, the control over pigment distribution and the time frame over which pigments change. If different species do it in different ways, there may not be a catch-all phrase. Plasticup ^T/C 16:11, 14 September 2008 (UTC)

Oh, I was hoping for something like "changer of colour" or "environment mimic" in Latin, but never mind. Thanks anyway, Julia Rossi (talk) 10:05, 15 September 2008 (UTC)

Things that weigh on Milligram.

What are some common things that weigh one milligram? —Preceding unsigned comment added by 80.148.22.232 (talk) 12:30, 14 September 2008 (UTC)

There's one at Orders of magnitude (mass). Fribbler (talk) 12:51, 14 September 2008 (UTC)

(For those who don't want to click through, it is a mosquito) Plasticup ^T/C 16:06, 14 September 2008 (UTC)

Five grains of table salt.--Stone (talk) 17:03, 14 September 2008 (UTC)

VEGA LAUNCHER

My cousin (a nuclear enginneer) said that Vega can be used also as military rocket.Which distance is it able to do? Thanks. —Preceding unsigned comment added by Vindobona (talk • contribs) 14:02, 14 September 2008 (UTC)

Not sure what you're refering to. Do you mean Vega (launcher), Lockheed Vega, or Percival Vega Gull? --Ayacop (talk) 14:26, 14 September 2008 (UTC)

Given that the title of his question is "Vega Launcher", it seems a safe bet that he is referring to Vega (launcher). All of your questions are answered in that article. The first launch is scheduled for 2009. Plasticup ^T/C 16:04, 14 September 2008 (UTC)

If you realy want you can use the space shuttle or any other rocket. For military the liquid stage especialy LOX LH2 stage is stupid, you can not leave it in the silo for long an fueling the thing costs time, so most military nuclear rockets are solid fuel and the last upper stage of Vega is only for orbit insertion. So yes, but for which country? France und GB have already what they want, and the other ESA members have no nuces.--Stone (talk) 17:00, 14 September 2008 (UTC)

Italy has (like other EU contries) is able to build a nuke actually very quickly.It doesn't build because he decided to do not build it and so itself decided it! My cousin teaches nuclear physics in Milan.He says that country like Italy officially haven't the nuke because of NPT,but Italian Army did several years ago what it wanted.It had nuclear research centres only for military aims.Vega derives from Scout so he said it's very good for military aims(it's also too much!).He told me also that EU (by a small law wanted by Italy and Germany;at that time EU didn't exist)can declare itself nuclear power.The same thing i heard by the Italian ambassador in UN.I think they know more than us. PS Nowhere is written that you have to keep the rocket in a silo especally if you set it on something moving. Thanks. —Preceding unsigned comment added by Vindobona (talk • contribs) 18:41, 14 September 2008 (UTC)

To build a nuce is not much of a poblem if you have a HEU research reactor. But to declare to be a nuclear power would make you a nation nongrata in europe. One thing is you have to get all the others helping you to build the Vega for you, and France and GB for sure will not give you the Vega parts they provide for a rocket. To have a a couple of Vegas somewhere else than Koru makes only sense if you build them for military purpose. The silo or on a truck does not matter the -200°C liquid will give you trouble.--Stone (talk) 20:54, 14 September 2008 (UTC)

In UK are built no parts of Vega. Italy builds the 65% of launcher and it's able to build everithing it wants.Be sure!I haven't yet received an answer about its distance on Earth! —Preceding unsigned comment added by Vindobona (talk • contribs) 09:53, 15 September 2008 (UTC)

Since, from the article, it can put 2 tonnes into polar orbit, it can hit anywhere. Saintrain (talk) 14:17, 15 September 2008 (UTC)

This isn't a rational answer.The rocket can also landing!The problem is going up and not landing!It's also too strong !Certainly it 's able to cover many many thousands Km.Also Stone said "Yes it can be used!".Thanks. —Preceding unsigned comment added by Vindobona (talk • contribs) 14:52, 15 September 2008 (UTC)

Thyrotropin Releasing hormone in Gastrointestinal tract

What does TRH do in the gastro-intestinal tract? can someone give further links to reading sources? 117.97.145.59 (talk) 14:06, 14 September 2008 (UTC)

According to de:Thyreoliberin, any effects are indirect, i.e., through stimulation of nerves in the brain. We have (no references, sorry)

• through the vagus, stimulation of stomach acid production and peristalsis
• through the sympathetic nerves, stimulation of insulin secretion
• stimulation of exocrine function of the pancreas

--Ayacop (talk) 14:35, 14 September 2008 (UTC)

Dog ESP

I went to my friend's home with him. His home is in another city, some 7 hours away by train. He was away from his home for several weeks. When we got there their dog was waiting at the gate for him. His dad told us that the dog had been standing outside and waiting all day long, as if he knew my friend was coming. He said it happens every time he's about to come home. Any scientific explanation for this? ReluctantPhilosopher (talk) 14:22, 14 September 2008 (UTC)

I'm willing to bet it's more a matter of confirmation bias and the father just ignores all the other days when the dog is waiting by the gates. -- MacAddct  1984 ^{(talk • contribs)} 15:12, 14 September 2008 (UTC)

Or the dog picks up on changes in the father's behavior on the days when the father expects a visit. Or both. - Nunh-huh 15:19, 14 September 2008 (UTC)

I'd go with what MacAddct and Nunh-huh are saying. I'd also like to add that this is a classic case of anecdotal evidence, which is unreliable. There are all sorts of reasons why the premise -- that the dog always waits for him all day -- could be wrong: perhaps the father exaggerates (consciously or otherwise), because it makes for a good story, or because it reinforces the idea of a loving and loyal dog, or because he knows it makes your friend feel good, for example. In order for us to even begin honestly entertaining the idea that the dog is actually doing this (and I think the other explanations are far more likely), there should be some kind of actual evidence of the dog really standing by the gate all day long on the days your friend is coming home (and not doing so on any other day). -- Captain Disdain (talk) 15:34, 14 September 2008 (UTC)

My dog always knows when my wife and I are about to go on a trip—all day long she frets about us leaving in a very distinct way. She also knows when people are going to be visiting and is similarly antsy. How does she know these things? She's not psychic (she's many things, but it's clear she's not that!). She knows we are going to go on a trip because she sees us doing things we don't usually do (e.g. packing). Before people come over, we are always cleaning things up that usually we don't bother with. The dog observes us, and can pick up on very subtle changes in activity and emotion. The dog always knows when one of us is sick. She isn't psychic, she's just able to tell when we're doing things we don't normally do. Dogs are very capable of noticing routines (including the much beloved "time for dinner!"), and are very keen to what differences in them mean. One of the things we love about our dog is that after seven years or so we all understand each other very well. We can tell what she is thinking and feeling just as well as she can tell what we are thinking and feeling. It's not ESP, it's empathy. --98.217.8.46 (talk) 16:14, 14 September 2008 (UTC)

Another possibility is that your friend's Dad told the dog he was coming home, mentioned his name, opened the door to his bedroom, things like that. When my Mom tells her dog I'm coming to visit, he insists on staying out in the yard with his eyes on the gate until I get there. I bring doggie treats for him you see and pat him a lot. He knows exactly what my name means when it's linked with "is coming". Franamax (talk) 17:39, 14 September 2008 (UTC)

Thank you all guys, that was very helpful. ReluctantPhilosopher (talk) 15:34, 15 September 2008 (UTC)

I remember hearing that one of the suggestions for the Longitude prize (essentially for timekeeping at sea) was that litters of puppies were raised together, and then distributed to ships with one being left at home. Exactly at midday the dog left at home would be jabbed with a sharp object: the theory was that all the other dogs in the litter would howl at the same time. I don't have a reference to show it really was proposed, but it makes a good story. It didn't win. DJ Clayworth (talk) 21:38, 15 September 2008 (UTC)

There have been scientific studies of the phenomenon: http://en.wikipedia.org/wiki/Sheldrake#Seven_Experiments_That_Could_Change_the_World

What's it called when...

You look at a lamp or the sun and it leaves an imprint in your eye, which discolours what you are looking at, making it purple, black-and-white, or just false colour?--Editor510 ^{drop us a line, mate} 16:56, 14 September 2008 (UTC)

It is called an after-image. DuncanHill (talk) 17:01, 14 September 2008 (UTC)

Help identifying flowers

Hi. I'm trying to identify the species of a couple of plants from my mother's garden. For geographical/climate information, these plants are growing in North Texas.

The first is a vine with bright pink flowers that bloom at night. (These photos are taken during the day):

• 
• 
• 

These others are delicate purple blooms:

• 
• 
• 

If they turn out to be pictures we could use, I'll re-upload them with more useful file names. Thanks in advance to anyone who can help. -GTBacchus^(talk) 19:12, 14 September 2008 (UTC)

Do the pink flowers have a sweet scent? They look like a honeysuckle to me. DuncanHill (talk) 19:32, 14 September 2008 (UTC)

I think the pink night-bloomer might be Angel's Trumpet (Datura). According to our article on that, it comes in pink, is shaped like the flowers in your picture and blossoms at night. 128.239.177.28 (talk) 13:26, 15 September 2008 (UTC)Hana

The blue ones could be are Ruellia brittoniana and the article (needs pictures) has a link to a French language site with similar pix. The pink one is Four o'clock flower or Mirabilis jalapa and the article could use pix like yours for its different states.Julia Rossi (talk) 09:54, 16 September 2008 (UTC)

Wonderful, thank you! I will re-upload the pictures with proper names, and add them to the articles. -GTBacchus^(talk) 19:24, 19 September 2008 (UTC)

Ornithopters

Lets say we want to turn the F-22 into an ornithopter. Its empty mass is about 19,700 kg. If we assume its wing area remains the same (840 ft² (78.04 m²)), how fast does it have to flap in order to hover? I'm aware of the technological limitations of such things, but for this thought experiment, lets just ignore how we could build such a thing. ScienceApe (talk) 19:36, 14 September 2008 (UTC)

Simply flapping flat wings won't produce any lift at all, since you're doing a symmetrical motion on both up and down strokes. The wings would have to bend somehow, and the rate of flapping required will depend on how that bending is done. --Sean 12:58, 15 September 2008 (UTC)

That's not true actually. The upstroke does not cancel out the downstroke. Bending the wing on the upstroke helps, but it's not required. Check out http://www.ornithopter.org/how.wing.shtml. In short the angle of attack allows for the wing to constantly gain lift, even on the upstroke. So both the upstroke and downstroke create lift. 98.221.85.188 (talk) 14:06, 15 September 2008 (UTC)

The problem is that flapping flight depends on "wing loading" - how many kilograms of weight is there per square meter of wing area? The problem with making things bigger is that when you double the size of something, you typically quadruple its area and octuple it's weight. So when you double the size of a flying machine, you double the wing loading. So tiny insects fly really well and seemingly without much effort. Small birds also work pretty well - but as birds get bigger, they have more and more unwieldy wings and rely more and more on gliding and less and less on flapping. So ornithopter flight is inherently difficult for "human sized" flying machines. I don't know how fast an ornithopter the size and weight of an F22 would have to flap - but I'm pretty sure it's impossible. There comes a point with flapping flight where the wing would start to "cavitate" - that is to say that the air pressure beneath it would drop to zero - and at that point, flapping faster wouldn't win you any additional lift because you're essentially just pumping vacuum...I suspect that would happen before you got to that scale - but I don't know how to calculate that.

There have been efforts to make light-aircraft-sized ornithopters - but so far, none of them have worked - they are probably right on the edge of what's possible.

SteveBaker (talk) 15:25, 16 September 2008 (UTC)

That's also not true. There have been working examples of ornithopters that are plane sized. Your vacuum hypothesis doesn't seem any more likely than a helicopter would create a vacuum. Big birds do not glide. They soar. That's a completely different flight mechanism. We do know that it's possible to create a large ornithopter because we know large animals that can fly. Specifically pterosaurs. Hatzegopteryx in particular is probably one of the largest animals ever that was fully capable of flying through flapping and soaring. Therefore, if biology can achieve this, then it's entirely possible to create a machine that can do the same. 98.221.85.188 (talk) 22:18, 16 September 2008 (UTC)

It would probably be dependant on wing dimensions and hence the F22 probably isn't a very good choice. Something like a B2 Spirit (due to its massive wingspan compared to the body) or a C-130 because presumably from its ability to take off from very small runways it must create a lot of lift, and be light. 88.211.96.3 (talk) 13:07, 18 September 2008 (UTC)

Inverse Compton effect and nuclear weapons

I was told by someone who was very much involved in the US H-bomb program that in the 1950s the inverse Compton effect was regarded as a big secret because it had major implications for hydrogen bomb design.

Can someone more literate in physics explain to me why this might be so? And if the Compton effect is relatively common, would it be much to expect that someone scientifically literate would not happen upon the likelihood that the inverse Compton effect would exist and have relevance to such an endeavor? The article on Compton scattering didn't really help me in wrapping my mind around this question, other than indicating that the inverse effect seems pretty rare under Earth conditions (i.e. it seems like it only takes place in regards to astrophysics, and presumably in nuclear weapons though it doesn't say that). --98.217.8.46 (talk) 20:10, 14 September 2008 (UTC)

If you google h-bomb and inverse compton effect, there's some documentation to be found. For instance according to [14] the i.c.s. effect created a problem for the H-bomb by cooling the electrons, but the challenge was more in doing the calculations surrounding this, and they may have been kept a secret. I believe i.c.s in itself must have been well known in the 1950s. EverGreg (talk) —Preceding undated comment was added at 21:57, 14 September 2008 (UTC).

The fellow who told me about it said that it wasn't well-known at all at the time, though he conceded that if you thought about it, it wasn't too hard to imagine that it would exist (he thought the idea of trying to keep something like that a secret was stupid). I interpreted this as meaning that it's the sort of effect that really doesn't come up under earth regimes, and so would be counterintuitive unless you were really trying to figure out things in extreme regimes (like the idea that solid plutonium can be compressed under extreme pressure regimes, which only occurred to Edward Teller because he had been working with Gamow on things relating the core of the earth).

What I'm asking for, basically, is a straightforward explanation by someone who understands the physics, for a non-scientist. --98.217.8.46 (talk) 22:56, 14 September 2008 (UTC)

Oh, an explanation! :-) That's actually very easy. The compton effect is all about a photon (light) and an electron colliding. These hit each other like billiard balls and recoil in opposite directions. In typical situations, it is the electron that speeds up after the collision and the photon looses energy. It still moves at the speed of light, but with a longer wavelength. "Typical" as in typical photon energies and typical electron speeds. But in some situations, like in astrophysics, some physics experiments and the H-bomb, the electron is moving so fast it is the photon that gains energy after the collision. For an H-bomb this seems to have been a bad thing because the energy "leaked out" of the process with the photons. But I'm not familiar with the details here. If you like, you could perhaps edit the compton effect article to provide a better-worded lay-man explanation. EverGreg (talk) 08:19, 15 September 2008 (UTC)

Why is gold leaf opaque when it is only one atom thick and each atom is mostly empty space?

Please could someone explain why it is not easy to see through gold leaf, when the material is only one atom thick? It is possible to see through the material if you hold it close but it is not transparent in the same way that air or many types of glass are.

My understanding of the scale of the atom is that if the nucleus was the size of the circle at the centre of Wembley Stadium, then the electons would be vastly smaller and whizzing around within a cloud the size of the whole stadium.

I also understand that gold has 79 electrons, but these are so, so small then surely, even as a fast-moving cloud I cannot believe that they could form the illusion of a solid space to the human eye.

Using the same argument, I also struggle to understand why it is possible to see through vast volumes of air. On a clear day, from a reasonable height, it is possible to see around 20 miles (and much further from the top of some skyscrapers). When looking this far, the observer is looking through a block of air. I would have thought that, as sparse as the atoms/molecules in air are, over this distance the chances are that there would be many atoms or molecules 'obstructing' the observer's line of sight - yet he or she can still see through.

So...what property of materials makes us able to see though some and not others (oher than their depth)? Thank you Jilly (talk) 20:21, 14 September 2008 (UTC)

One thing that comes to mind is that your gold leaf is thin but it is tightly packed, and the atoms aren't moving. In the air, you have a very low density collection of atoms that are constantly moving about. It would seem to me to be the equivalent of shooting bullets at a tight-knit chain link fence in the case of gold, whereas air would be more like setting up a long tennis court with a bunch of constantly bounding balls. In the latter case you are likely to hit one every once in awhile but a constant spay would make it through pretty well; in the former case each shot has a pretty high chance of getting scattered in the same general area. But this is obviously a very off-the-cuff sort of reasoning. And it doesn't take into account transparent solids like glass, obviously, though I would guess that glass is more like the chain linked fence, but with very wide linkages. --98.217.8.46 (talk) 20:34, 14 September 2008 (UTC)

A few things here:

• Is there actually gold leaf one atom thick ?
• Light interacts with matter through electrons that absorb and reemit certain wave lengths (so basically, what we "see" is the electrons really).
• Regarding air, not all light makes it through, that's why for instance the sky is blue (as some wave lengths are absorbed), some light is scattered (things become blurry in the distance), ultimately, it's just a matter of distance and density of the air, it just so happens the atmosphere on earth is not "thick" enough to block/scatter light entirely (whereas visible light on Venus is too scattered for us to see anything of the surface). Equendil Talk 20:59, 14 September 2008 (UTC)

(edit conflict with Gandalf61) I am extremely skeptical that someone could make gold leaf that was just one atom thick. Our article on Goldbeating says that "The finished leaf forms an unbroken sheet of gold with a thickness of 1/250,000 of an inch." Now, that's really amazingly thin, absolutely, but nonetheless, the leaf is still 0.0000001016 meters thick. That's pretty hefty compared to the "size of a typical atom, which is 0.000000001 meters across", according to this RHIC physics primer. That's plenty of room for a whole bunch of atoms to be stacked on top of each other. -- Captain Disdain (talk) 21:27, 14 September 2008 (UTC)

Our goldbeating article says that gold leaf is 1/250,000 of an inch thick - that's about 10^-7 m or 100 nanometres. Typical atomic radius is 0.1 nanometre, so gold leaf is hundreds of atoms thick. Gandalf61 (talk) 21:19, 14 September 2008 (UTC)

When you get gold leaf extra thing it does permit light to move through and becomes nearly transparent when really thin. Graeme Bartlett (talk) 21:28, 14 September 2008 (UTC)

Indeed. Most space suits for extra-vehicular activity have their outer visor coated in a thin layer of gold, to protect the occupant from the intense sunlight. The astronauts actually look through the gold layer. (I'm having a hard time finding a WP article that says so explicitly, the best I can come up with is Krechet - note the gold-colored viewing bubble.) -- 128.104.112.147 (talk) 21:52, 14 September 2008 (UTC)

Well, the article does say, "The outer visor was coated in gold for reflectivity." That's pretty explicit! -- Captain Disdain (talk) 22:00, 14 September 2008 (UTC)

The outer visor is coated in gold. Not gold leaf. - Nunh-huh 22:53, 14 September 2008 (UTC)

Gold leaf is just an extremely thin layer of gold. What distinction are you trying to draw here? Algebraist 00:30, 15 September 2008 (UTC)

Possibly the distinction between rolling/beating (to form gold leaf) and methods like vacuum deposition to place a thin layer of metal onto a substrate. I'm not sure that the latter would be called "leaf". -- Coneslayer (talk) 14:14, 15 September 2008 (UTC)

Well, yes, it would make absolutely no sense to apply a visor coating as gold leaf. There'd be no way to make it as uniform as it needs to be. Gold leaf is not just "an extremely thin layer of gold". It's a thin sheet of hammered (or rolled) gold; it's applied by hand; it's difficult to accurately approximate the sheets without overlapping, etc. all of which make it unsuitable for visors. Which of course it is anyway, because it's opaque! - Nunh-huh 22:47, 15 September 2008 (UTC)

While the "diameter" of an atom is about 100,000 times that of its nucleus(!), it's the (outside) electrons that interact with the light rays. The distance between gold atoms in its crystal structure is about 270 picometres. (Gold remains a crystal even after you beat the crap out of it, that's why it's done so much.) Visible light has wavelengths that vary between about 400 (blue) and 700 (red) pm (less than an octave!).

See-through gold (visors etc.) is "sputtered" on to the surface. It's not a continuous crystal layer but a bunch of dots with lots of space in between (if you're a photon).

Transparent materials like glass don't "allow" light to "pass through" (silicon and oxygen atoms, the principle components of glass, are (about) the same size as gold and as tightly packed and made of exactly the same stuff.) The atoms "relay" (I know. I know. I can't think of a better word.) the light all the way through. Saintrain (talk) 01:52, 15 September 2008 (UTC)

I think the physics of light on the atomic scale is more complicated than the simple model I have in my head. I understand electron transitions releasing light but I'm struggling with objects that do not emit light themselves. Could you tell me a bit more about how the wavelengths and electron interactions affect what we see (or point me in the direction of an article where I can learn more?). I've never understood how solid things are made up of tightly packed 'things' of mostly empty space and I think this is the lead I was looking for. Thank you all for all of the answers so far. 90.211.244.242 (talk) 21:06, 15 September 2008 (UTC)

Practically speaking, there are several easy ways to see that very thin layers of metal can be quite transparent. One way is to find an old piece of cut glass (a wine goblet, etc.) that is decorated with gold leaf. You'll often find that if you hold the glass up to a bright light, you can see through the gold. If you have a gold-metalized CD, that's a more-uniform, thinner layer (sputtered, not leaf) and you'll definitely be able to see through that. (Aluminized CDs show a similar effect and are far more common, of course.) Switching to other metals, if you're looking at this article on a LCD, you're looking through transparent Indium tin oxide electrodes within the LCD panel. And if your car (like many Fords) has a transparent, electrically-heated front windshield/windscreen, again, you're looking through transparent ITO (I think). And then there are always mirrored sunglasses.

Atlant (talk) 19:23, 15 September 2008 (UTC)

Prostate Treatment

The articles on Prostatitis and on BPH don"t mention treatments such as ejaculation, eating radishes, drinking cranberry juice. Is this type of treatment addressed somewhere? They do mention avoiding caffeine as a prevention. Also, if antibiotics such as cipro and doxycycline alleviate symptoms for a period of months is there an antibiotic that offers longer relief? Bigprostate (talk) 20:35, 14 September 2008 (UTC)

You can edit article to improve them, this is wikipedia the encyclopedia you can edit. We cannot offer medical advice here though. I have linked your words in case someone want to check out the articles. Graeme Bartlett (talk) 21:40, 14 September 2008 (UTC)

Do you have any sources that suggest that those treatments are commonly used, or effective? Wikipedia articles need reliable sources to back up their claims, and in this instance I'd say a medical journal would be about the level required. Confusing Manifestation(Say hi!) 23:41, 14 September 2008 (UTC)

Having a bit of knowledge about effects of cranberry juice, that only works as preventative of infections where it actually touches the skin/mucus. You couldn't prevent or even heal prostatitis. --Ayacop (talk) 13:54, 15 September 2008 (UTC)

The Merk online medical resource [15] mentions frequent ejaculation as a relief for prostatitis but does not mention radishes or cranberry juice. Treatment for benign hypertrophic prostate does not mention either frequent ejaculation, cranberries or radishes. Cranberry juice has scientifically been shown to alleviate mild urinary infections (sorry, no refs) and by association may have been included to alleviate prostatic patholgies. I would expect Merk to make reference to any accredited treatments. There are many references on the internet regrading radishes and protatitis, and many of these seem to be rehashes of this bizarre specimen. [16], which seems to have no valid scientific backing but sources back to a Chinese address. Richard Avery (talk) 13:53, 15 September 2008 (UTC)

Parallel universes

I parallel universes exist, is it possible to communicate or travel between them? —Preceding unsigned comment added by 79.76.164.210 (talk) 22:03, 14 September 2008 (UTC)

Well, it depends what definition you give to "universe" and "parallel universe" really, then the answer is pretty much in the definition. If you define "universe" as "everything that exists anywhere", then by definition, there is no "parallel universes". You might want to check the article on existence here. Equendil Talk 23:29, 14 September 2008 (UTC)

You might find time travel[17] in the article Many-worlds interpretation stimulating. As if my mind doesn't branch enough, along comes your question, so I am stepping inside and may be gone for some time. Julia Rossi (talk) 23:26, 14 September 2008 (UTC)

Also see Multiverse; there are various ways and senses in which there could be multiple universes. --Allen (talk) 04:31, 15 September 2008 (UTC)

It's impossible to know whether there ARE parallel universes. In my personal opinion, the theory of multiverses is much more understandable than alternative interpretations of bizarre quantum theory effects. If we can't possible know whether they exist - it's very premature to ask whether we could travel between them. My best guess is "No" - but it's a guess. SteveBaker (talk) 18:10, 15 September 2008 (UTC)

So, an aging rockstar has taken so much speed and cocaine over the decades...

...that it has somehow permanently altered his entire blood chemistry, meaning that a transfusion of normal, healthy blood would kill him - and turned his own blood so toxic that if transfused into another person, it would kill them instantly.

Urban legend/toughguy publicity posturing or genuine possibility? Not naming any names, a) due to WP:BLP, b) I've heard the same story attached to at least three different people. --Kurt Shaped Box (talk) 23:10, 14 September 2008 (UTC)

Definitely sounds like urban legend/pathetic boasting. Even people with a long history of heavy polysubstance abuse will clear the drugs from their blood within days. Obviously the addiction lasts longer, but their blood is not toxic per se (assuming no HIV, hepatitis C, etc of course). If they have liver, kidney, or other disease, then some things might be out of whack, but not enough to be fatal with the usual volume of a blood transfusion. --Scray (talk) 23:47, 14 September 2008 (UTC)

So, file alongside 'singer has pair of ribs removed to aid autofellatio' and 'singer hospitalized after swallowing 5 pints of semen' (hilariously, I can think of two singers who've had both these stories circulated about them)? --Kurt Shaped Box (talk) 00:18, 15 September 2008 (UTC)

Presuming any of that drug use was does intravenously, it seems a moot point since they'd be banned from donating blood by most or all blood collection agencies Nil Einne (talk) 17:12, 15 September 2008 (UTC)

Why is it always "singer"? It's never "drummer"...but they are way more crazy in my experience. SteveBaker (talk) 18:07, 15 September 2008 (UTC)

Probably because many drummers - unless they're particularly remarkable are seen (by fans) as to rock bands what redshirts are to Star Trek... ;) Cue all the bad jokes about 'the musicians and the drummer', groupies that were so desperate/stupid/drunk that they had sex with the *drummer*, etc.... --Kurt Shaped Box (talk) 21:02, 15 September 2008 (UTC)

I can only think of one for the drugs, and two for the ribs/stomach pump. DuncanHill (talk) 21:16, 15 September 2008 (UTC)

Why? as a scientific question

Is "why" a valid question in science. For example, "Why is there a universe, rather than none?" or "Why does the apple falls?" or "Why does the atomic nucleus does not integrate?" etc.

Please provide examples from scientific papers and the academia.

Is "Why" a valid of question of science? —Preceding unsigned comment added by 98.97.102.6 (talk) 23:12, 14 September 2008 (UTC)

Yes, certainly. 'Why' asks for an explanation, and one of the purposes of science is to explain things. Exactly what constitutes a scientific explanation is a big topic in the philosophy of science. There's some information at philosophy of science#Scientific explanation. Algebraist 23:42, 14 September 2008 (UTC)

Why is the sky blue? Why do objects appear to fall straight towards the center of the planet? Why is there so much variety in species? Why is just fine. It might not always be answerable at the moment (like your "Why is there a universe", which is at the moment beyond our understanding), but that doesn't make them non-scientific. --98.217.8.46 (talk) 23:48, 14 September 2008 (UTC)

Perhaps how is a better-accepted scientific question in general, because it leads more directly to a mechanistic answer rather than a teliological or philosophical one. --Scray (talk) 23:51, 14 September 2008 (UTC)

Why? ;) --Kurt Shaped Box (talk) 00:04, 15 September 2008 (UTC)

Isn't there a school of thought in philosophy of science that would answer "no" to the OP's question, and say that science can only describe, not explain? I can't remember the name of that position or the people promoting it, but I'm pretty sure they exist. --Allen (talk) 00:46, 15 September 2008 (UTC)

Facts describe. Theories explain. That objects fall straight towards the earth is a straightforward descriptive fact. That they do so because of a mysterious force called gravity, or because that is the path-of-least-resistance in spacetime due to the warping of spacetime by the mass of the earth, is a theory. It is an explanation. Tentative, but legitimately scientific. --98.217.8.46 (talk) 01:00, 15 September 2008 (UTC)

I can't think of any such people offhand either, but one can normally find a philosopher willing to espouse any given position. Such people would, however, be opposed by the vast majority of philosophers of science and all practicing scientists. Algebraist 01:00, 15 September 2008 (UTC)

All practicing scientists seems extreme to me. In my experience, it seems like a lot of practicing scientists do their work with little attention to its philosophical underpinnings. And among those who think about the philosophy, I think at least some of them would try to construe their work as fundamentally descriptive, even if they use explanatory language as shorthand. --Allen (talk) 04:14, 15 September 2008 (UTC)

Well, it's the sort of doctrinaire sort of thing that certain philosophers and scientists might like to impose, but any attempt to demarcate what exactly is science and what isn't is going to run into a million practical problems (ergo the demarcation problem, which is no closer to being solved today than it was two hundred years ago). --98.217.8.46 (talk) 02:03, 15 September 2008 (UTC)

I'm pretty sure it was Richard Feynman who drummed this into my head - that science can tell us how the sky is blue, but not why. It's a subtle but important point - the mechanisms (the how) are much more tractable for research than the reasons (the why). --Scray (talk) 01:44, 15 September 2008 (UTC)

Except that linguistically speaking why is often about mechanisms as much as how is. And why does the apple fall to earth is much more straightforward and unambiguous than how is it that the apple falls to earth. --98.217.8.46 (talk) 02:01, 15 September 2008 (UTC)

If you look up why and how in a dictionary (I just did in 3 of them) I think you'll find why wrapped up in 'cause, reason, intention' and how equated with the 'manner' in which something falls. The latter is amenable to analytical approaches, whereas the former is not. I'll agree that the distinction has been blurred by common usage. --Scray (talk) 04:12, 15 September 2008 (UTC)

Richard Feynman also said [I wonder why]... manya (talk) 03:56, 15 September 2008 (UTC)

No, it is not valid at all. --proficient (talk) 04:50, 15 September 2008 (UTC)

It's okay to question, to propel inquiry, perchance to dream but doesn't guarantee there'll be valid answers. Julia Rossi (talk) 10:18, 15 September 2008 (UTC)

Yes, of course "why" is a valid question in science. Open-ended "why" questions have driven far more fundamental discoveries in science than closed-ended "how" questions. For example, to answer "how does an apple fall to Earth" you observe the paths of falling objects under various conditions and conclude that "a falling object experiences a constant vertical acceleration which is independent of its mass and of its velocity" (you might then go on to correct this initial conclusion to take account of drag forces and terminal velocity). This bit is easy - Galileo knew this in the 17th century.

But answering "why does an apple fall to Earth" in a scientific way is much harder. Newton's answer was "because each object in the Universe exerts a gravitational force on all other objects which is proportional to the product of their inertial masses". This then leads to "why is the force of gravity proportional to inertial mass" - as has been pointed out, answering one "why" question often leads to more "why" questions. The answer to this second "why" question had to wait for Einstein and general relativity. Then you have the question "why do objects even have inertial mass ?", and we are still trying to answer that question - this brings us to the Higgs boson and the LHC. If scientists had not been interested in the "why" questions we would not have advanced beyond Galileo's understanding of "how". Gandalf61 (talk) 10:44, 15 September 2008 (UTC)

Good points, but along the lines of what Julia said, "why" questions could be valid in the sense of being useful to the social and creative progress of science, without being valid in the sense of science truly being able to explain things. --Allen (talk) 16:29, 15 September 2008 (UTC)

But my point is that answering "why" questions provides a deeper level of explanation than just answering "how" questions. Not necessarily an ultimate level of explanation, but that may not be achievable anyway - reality may be "turtles all the way down", as they say. Gandalf61 (talk) 16:37, 15 September 2008 (UTC)

I see now; thanks. --Allen (talk) 17:54, 15 September 2008 (UTC)

When an apple falls from a tree - science says "How" is because there is this gravitational field, curved earth, etc. In that case, the "Why" is because it simply can't do anything else. "Why" isn't a problem for things that are already well-explained. Why is only a serious problem for the "end point" questions. "Why" does mass produce a gravitational field is a question we can't answer because we don't know the "How" part (yet). Perhaps studies in the LHC of the Higgs Boson will explain where mass comes from and perhaps that'll explain "Why" masses produce gravity. If we knew HOW gravity was produced then we'd probably say "Why" is (again) because it can't do otherwise. So it seems to me that once we know "How" - then in a predominantly mechanistic universe, the answer to "Why" is that things couldn't possibly have turned out any differently. Things are perhaps a little different at the quantum level because things can often turn out in multiple ways - seemingly at random. In that case - we can ask "Why did Schrodinger's cat die when we did the classic thought experiment?" - or "Why did it survive?" - the answer is "because the radioactive atom either did or didn't emit a neutron" - but we can just ask "Why did/didn't the atom do that?"...and now, we don't know "Why" because it could just as easily have done the opposite. But even in those cases, we might hypothesise the "Many worlds" interpretation in which the cat dies in one version of the universe and not in another. When you do that, the question "Why did the cat die?" boils down "Because we are in the universe in which it dies and not in the one where it survives."...then you ask "Why are we in that universe" and the answer is..."We're in both universes at the same time".

So I think we can always boil down any "Why" question into an explanation of "How" (assuming we know) - followed by "...and that's the only possible way things could have turned out." - which answers the "Why" part. SteveBaker (talk) 18:06, 15 September 2008 (UTC)

September 15

Somewhere theres music

Somewhere thers music, how faint the tune
Somewhere theres heaven, how high the moon?
But exactly where is Heaven? —Preceding unsigned comment added by 79.76.225.5 (talk) 00:22, 15 September 2008 (UTC)

It's underneath Charing Cross station. DuncanHill (talk) 00:24, 15 September 2008 (UTC)

It is a place [18] where Fred dances forever with Ginger, and Louis sings forever with Ella [19]. Note that Ginger does everything Fred does, except backwards and wearing high heels. Edison (talk) 02:28, 15 September 2008 (UTC)

For Ginger's Heaven, wouldn't it be Fred who was in high heels and dancing backwards? Clarityfiend (talk) 04:11, 15 September 2008 (UTC)

And maybe having top billing. Julia Rossi (talk) 10:10, 15 September 2008 (UTC)

Ummm, top billing? In Heaven? Saintrain (talk) 14:24, 15 September 2008 (UTC)

The mind is its own place, and in itself, can make heaven of Hell, and a hell of Heaven. --- OtherDave (talk) 12:22, 15 September 2008 (UTC), channelling Milton.

Triple point

Do all compounds have a triple point? Nadando (talk) 04:42, 15 September 2008 (UTC)

I don't believe helium does. Does that count as a compound or would that be just an element? --Bennybp (talk) 11:27, 15 September 2008 (UTC)

(conflict) Helium is a weird one, but according to this diagram I found it still has a triple point. --Shaggorama (talk) 20:03, 15 September 2008 (UTC)

Yes, sort of. To clarify, it doesn't have a triple point between solid, liquid, and gas. The triple point is between solid, liquid, and superfluid. Because superfluid is also "liquid", helium doesn't really have a triple point like all other elements. ~Amatulić (talk) 20:29, 15 September 2008 (UTC)

Copper Sulfate decomposes by losing water at 110° and 150° and decomposing at 650°

No, many compounds decompose when heated and do not form a liquid, instead they turn into a other compounds. Graeme Bartlett (talk) 21:32, 15 September 2008 (UTC)

CO2 goes from gas to solid and back to gas again. I don't think you can ever have liquid CO2 (certainly not at normal atmospheric pressures). SteveBaker (talk) 01:23, 16 September 2008 (UTC)

But at elevated pressure, liquid CO2 is quite common at room temperature. A triple point need not be "at 1 ATM". See Image:Carbon dioxide pressure-temperature phase diagram.svg DMacks (talk) 01:29, 16 September 2008 (UTC)

How do we know there will be no problems with the LHC?

If it created a black hole, wasn't it supposed to grow gradually? It's only been a week, so it might be only the size of a pinhole or so. I'm afraid in about a month or two from now one of those scientists might be saying "Hey, what's that black spot over there? Charlie, you've got to be more careful with that marker, this machine is expensive! Here, I'll wipe it off.....uh,oh." Dr. Carefree (talk) 05:03, 15 September 2008 (UTC)

First, the LHC hasn't collided anything yet, and it shouldn't operate with energies larger than of existing accelerators until next year.

Now, our current theories predict that black holes evaporate through Hawking radiation, and small black holes should evaporate faster. We have no experimental evidence of this, but we're pretty confident on it. See the article for more details. If we are correct, the black holes created by the LHC, if any, should evaporate almost instantly.

If the LHC created a stable black hole, it would be extremely tiny (in fact, smaller than Planck length), and it would have a terribly small - practically nil - gravitational pull. The only chance it could accrete more mass would be direct contact with other particles which, given its size and the fact atoms are 99,99% vacuum, it wouldn't happen very often. There are probably some quantum effects that need to be taken into account here, but I haven't read anything about it yet.

Such a black hole would fall immediately towards the center of the Earth and orbit it. It would probably take millions of years for it to be of any concern. But again, chances are no such black holes will be produced.

Also, we can be pretty confident the LHC is safe because we have natural phenomena (cosmic rays) that replicates the experiments we're doing, even with much larger energies. There's a counter argument you'll see around that these natural collisions could produce "fast black holes", and the LHC would be creating "stationary black holes". This is sort of true, but it wouldn't matter. Neutron stars have huge densities and gravitational fields, and such particles or black holes wouldn't get through them. The fact that there are ancient Neutron stars everywhere in the Universe strongly suggests that there is no threat from such collisions. — Kieff | Talk 05:28, 15 September 2008 (UTC)

Unless I got my math wrong, a black hole of 100kg evaporates in about 8e-11 seconds. A black hole on the order of 1000 proton masses would evaporate in 4e-79 seconds. In that time it could move less than 1.2e-68cm. Now that time is shorter than the Planck time, and the distance is shorter than the Planck length. Things don't get more "instanteneous" than that. --Stephan Schulz (talk) 10:31, 15 September 2008 (UTC)

Black holes would only be produced at the LHC if there are large extra dimensions. If there are large extra dimensions then the value of G that we measure is just a long-distance effective value and the real G is much larger. The Planck units and the black hole evaporation time depend on G, so they change also. -- BenRG (talk) 14:22, 15 September 2008 (UTC)

I DONT BELIEVE ANY OF YOU- WERE ALL GONNA DIE! AAAAHHHH!!! I kid (only a little), but really- should scientists be messing around with this sorta thing? Is it that important to recreate the conditions of the Big Bang? What practical knowledge could we get from this anyways? Everytime science starts pokin around tryin to learn stuff that we have no real need to know, and has great potential to be dangerous, I'm reminded of my favorite quote by HP Lovecraft that goes ""The most merciful thing in the world, I think, is the inability of the human mind to correlate all its contents... some day the piecing together of dissociated knowledge will open up such terrifying vistas of reality, and of our frightful position therein, that we shall either go mad from the revelation or flee from the light into the peace and safety of a new Dark Age." --Dr. Carefree (talk) 17:48, 15 September 2008 (UTC)

Yes, it is that important. The question of the origin of everything has occupied mankind since humans learned to record their thoughts. We already have a multitude of incompatible answers from various religions. If it is a valid question to religion, it is certainly also a valid question for science. We do have a real need to know. Your comment reminds me of when horse-drawn carriages still outnumbered automobiles, when people feared that a person couldn't breathe if he traveled over 50 mph. Ignorance is no excuse for remaining willfully ignorant. ~Amatulić (talk) 20:24, 15 September 2008 (UTC)

We have an article on this. Among things, strangelet production will be less likely as collider energies increase apparently (ie. the LHC will be safer in this respect), there's a number of papers documenting why the blackhole production is not going to happen, and there's enormously powerful cosmic rays that smack into the Earth and other bodies in the solar system without collapsing the Universe.

You know we also can't say for certain that your posting this on the Wikipedia won't perturb the exact right part of the vacuum in the exact right way to trigger a transition to a new vacuum state or completely collapse the whole deal, right? 24.76.161.28 (talk) 00:00, 16 September 2008 (UTC)

To re-phrase your question: "Isn't it enough to know that gravity works? Why do we have to understand it?" Plasticup ^T/C 02:23, 16 September 2008 (UTC)

Dont get me wrong. I love science. But I'm talking practical science. Let's cure cancer science. Let's let math be the light that shines the way to truth science. We can study gravity, basic physics, and all that without too much trouble. But when we start messing with forces that's way beyond our grasp, especially when we don't need to, I think we're asking for trouble. I even like theoritical physics. Such as mathematical dimensions, black holes, strangelets, etc. as long as we dont create one. I'm not sure what a strangelet is (even after reading your article) but it doesn't sound friendly. This whole "Well it's pretty unlikely we'll create a black hole that wont go away, or some other wierd force that'll eat the planet. No guarantee mind you, but yeah, I wouldn't worry about it" attitude scares me. This is not child's play here. We're talking forces that we don't completely understand. Some of the math backs those Chicken Little scientists up, and I wouldn't dismiss them too easily. But they didn't build a multi billion dollar paperweight here, so I'm sure they're gonna use it. But before they start smashing atoms up(at 99.999% of the speed of light, yet! Yeah, that doesn't sound dangerous. Isn't something that moves at the speed of light supposed to have infinite mass? There's not much wiggle room here.) that were minding thier own business (being "atomy") they should consider the following:

• What if they create a God knows what particle that eats us from the inside out? And it drives us mad as it lays its particle "eggs" inside our helpless bodies and uses our nervous system for it's own agenda to propogate it's DNAless "species"? Plants, ameobas, and animals all have thier own agendas and are all radically different, so why couldn't this be the next stage of "life"?....if we let it.

• Or simply transforms matter into something mathematically indefinable that changes us into, uh....something we wouldn't like.

• What if it brings to this planet some creature, now freed from his atomic prison, something that's many levels beyond our worst nightmare!?

• Or God Himself! Think about that one. Now, wouldn't He be pissed? A:Because we yanked Him out of his bubble bath for an unscheduled visit. And B:Man outsmarted Him!

Sweet dreams.Dr. Carefree (talk) 06:15, 16 September 2008 (UTC)

This is basic science, not applied research, engineering, or "let's make a better mousetrap" work. I direct your attention to several previous science ref-desk discussions about what the goals are (in lay terms). As to your concerns, scientists who understand the possibilities have already analyzed the risks and it's been through a jillion reviews by experts. You can "what if" yourself into staying in bed with the drapes closed all day if you like, but you'll wind up pretty miserable. Every day you (every "you") do things that work for reasons you don't understand based on principles you haven't studied and you take for granted that a possible alternative "very bad thing" isn't going to happen:) I'd say most people may not completely (or even at all) understand what the LHC science is all about, but that's why it was reviewed by people who do. It's fine to be scared of the unknown, but let's not let ignorance (in the "don't know" not "you idiot!" sense) and fear drive society. Get concerned, but then do research enough to decide if there really is an actual problem, or ask someone who has. It's funny (in a sad way) that if popular press hadn't gotten ahold of "OMG they might make a black hole and swallow us all!" nobody would have cared...heck, even if they'd just used really complex scientific terms instead of scary Star Trek terms instead. Okay, I'll stop ranting now. DMacks (talk) 06:42, 16 September 2008 (UTC)

"Ugh not smash rocks together. Rocks may make fire. Fire burns. Maybe rock fire different from wood fire, rock fire burns rocks, burns everything! Ugh, Orgh and Ruma all die in quantum singularity! Grunt! Grunt!" --Stephan Schulz (talk) 07:10, 16 September 2008 (UTC)

Okay, that argument has been discussed to death elsewhere as well. [20] for instance (a CERN scientist arguing it). -- Consumed Crustacean (talk) 14:29, 16 September 2008 (UTC)

TURN IT AROUND. WHY would there be a problem with the LHC? Do you understand nuclear physics better than the guys running the LHC? What is so special about the LHC to you? --mboverload@ 06:57, 16 September 2008 (UTC)

You know, guys, feeding trolls just makes them hungrier. Saintrain (talk)

views of Thuria and Cluros

Moons of Barsoom. NASA/JPL

Astronomy on Mars doesn't say: Other than transits, have the hurtling moons of Barsoom ever been photographed from the ground? —Tamfang (talk) 07:11, 15 September 2008 (UTC)

That question sounds suspiciously ER Burroughs'ish. Anyway, the answer is yes: [21]. Franamax (talk) 08:02, 15 September 2008 (UTC)

Yeah, someone freecycled a big bag of ERB books my way; I'm on #4. —Tamfang (talk) 04:04, 16 September 2008 (UTC)

Hydrogen gas - analytical test???

Is there any analytical method to detect hydrogen gas? The pop test just tells qualitatively. can hydrogen gas be converted through cheical reaction so that it can be detected easily in lab scale.....? ....Venki —Preceding unsigned comment added by 218.248.46.116 (talk) 08:22, 15 September 2008 (UTC)

You could burn it like in the pop test, and find a way to get the mass of the water. From there, it's stoichiometry. It would be tricky, since the burning would vaporize the water, and would tend to shoot it all over the place. --Bennybp (talk) 11:30, 15 September 2008 (UTC)

de:Wasserstoff says that NMR spectroscopy is frequently used for that purpose in laboratories. --Ayacop (talk) 14:01, 15 September 2008 (UTC)

Burn a known amount it in a closed container, then all the water is still in there. That's the basis for elemental analysis, a standard way of determining "how much mass of each element is in this sample of stuff?". Also could use a mass spectrometer: add a known amount of some other gas and you will find the ratio of amounts of hydrogen vs that other gas. DMacks (talk) 18:41, 15 September 2008 (UTC)

One more - Use a calorimeter (something completely sealed like a bomb calorimeter). Given a heat of reaction, you should be able to tell how much burned by looking at the temperature. You have to make sure you don't have anything else flammable - just pure hydrogen (and oxygen, in excess). --Bennybp (talk) 00:06, 16 September 2008 (UTC)

Why Is Electromagnetic Wave Sine Wave?

There are many kind of waves such as saw wave, square wave, triangle wave etc. But why is electromagnetic wave always depicted as sine wave? How to prove that? - Justin545 (talk) 11:34, 15 September 2008 (UTC)

Good question. The reason is that circle functions like sinus are the solutions of differential equations that describe damped movement. I'm not able to say which equations and why but I remember that was the reason. --Ayacop (talk) 14:05, 15 September 2008 (UTC)

Undamped surely? Damped motion decays exponentially IIRC, but undamped motion, such as Simple harmonic motion, results in nice sinusoidal motion.

I would guess it's also related to the fact that, through Fourier Analysis, all of those other waves can be represented by adding sinusoidal waves of different frequencies. AlmostReadytoFly (talk) 14:16, 15 September 2008 (UTC)

PS: See Electromagnetic wave_equation#Solutions to the homogeneous electromagnetic wave equation. AlmostReadytoFly (talk) 14:22, 15 September 2008 (UTC)

A non-sine wave (a squarewave say) is the sum of a number of different sine waves at different frequencies. A square wave is the sum of a wave at some frequency ('f'), plus another at 3f, another at 5f, 7f, 9f...and so on. So if (for example) you had a light that emitted square waves, it might be emitting mostly red light - with some at three times that frequency, some more at five times and so on. Well, three times and five times the frequency of red light is ultraviolet light - and seven and nine times times red light is in the X-ray spectrum and so on. So you could in principle make square-wave "light" by carefully arranging an exact set of visible light, UV light and X-ray emitters. It wouldn't look much different from red light...except that it would irradiate your retinas pretty nastily!

It's certainly possible - but it doesn't tend to happen in nature because the processes that produce waves of such radically different frequencies are very different and their absorption in atmosphere is wildly different too.

SteveBaker (talk) 17:39, 15 September 2008 (UTC)

Hurricanes over warm water, meeting with freezing air over land, making snow?

Some of the rain from Hurricane Ike reached the middle of the U.S., and I recall one in Boston in 1991. So, I got to thinking during the windy remnants last night - suppose a hurricane or tropical storm hit in early November, while waters in the Atlantic Ocean were still warm, but while there was an unusually early cold snap and lows were below freezing over land. Would the foot of rain fall as maybe 10 feet or so of snow?

I'm guessing not, because after reading the article here, it seems like the water would have to be warm enough to warm the air around it to above freezintg - but that the interaction of warm and cold air would be such as to produce some *very* violent thunderstorms. However, I wanted to post the question here, too, to learn more and in case anyone else wondered.Somebody or his brother (talk) 12:17, 15 September 2008 (UTC)

See Halloween Blizzard ("the perfect storm"). Saintrain (talk) 14:35, 15 September 2008 (UTC)

LEDs or LASERs penetrating the body

Is there any LED or LASER that penetrates the body? —Preceding unsigned comment added by 117.196.163.244 (talk) 13:03, 15 September 2008 (UTC)

A pulse oximeter functions by shining a LED through the body (e.g. the fingertip). -- Coneslayer (talk) 13:10, 15 September 2008 (UTC)

Ophthalmologists use LASERs all the time to treat conditions of the lens and retina, both of which are truly internal structures. Dermatologists use LASERs for a variety of purposes, though the penetration is not very deep. Cardiologists use LASERs to remove endocardial plaque, though they do this using a catheter so most of the penetration is mechanical rather than optical. My guess is that neither of these is what you were looking for, though. ;-) --Scray (talk) 15:34, 15 September 2008 (UTC)

Carbon dioxide lasers can penetrate the body, but not in a good way. — DanielLC 16:46, 15 September 2008 (UTC)

Well actually:

They are also very useful in surgical procedures because water (which makes up most biological tissue) absorbs this frequency of light very well. Some examples of medical uses are laser surgery, skin resurfacing ("laser facelifts") (which essentially consist of burning the skin to promote collagen formation), and dermabrasion. Also, it could be used to treat certain skin conditions such as hirsuties papillaris genitalis by removing embarrassing or annoying bumps, podules, etc.

Nil Einne (talk) 17:06, 15 September 2008 (UTC)

Semiconductor diode

What happens to the current when you apply 0.7 volt to a semiconductor diode?

http://static.howstuffworks.com/gif/diode-graph.gif

The current reaches infinity or what?-Abhishek (talk) 13:24, 15 September 2008 (UTC)

The picture you provide is an ideal approximation. The actual curve of diode is non-linear and should be more or less like this

When 0.7 volt is applied, the current should be large but not infinity. And the overcurrent could break the diode. See Semiconductor diodes for more - 219.70.173.218 (talk) 13:52, 15 September 2008 (UTC)

Trains and Trucks running on gasoline instead of diesel

Would they run properly if they ran on gasoline engines instead of diesel? How would their performances compare? 98.221.85.188 (talk) 14:05, 15 September 2008 (UTC)

Would they run as-is? No. Diesel engines are not compatible with gasoline and vice versa. Could you put a gasoline engine in a train? You could, but diesels are significantly more fuel efficient than their gasoline counterparts. See our comparison of diesel to spark-ignition engines for more. — Lomn 14:49, 15 September 2008 (UTC)

As I stated in my original question, I was asking about trains and trucks running on gasoline engines, not gasoline in diesel engines. 98.221.85.188 (talk) 16:40, 15 September 2008 (UTC)

My mistake, but I hope you'll note that I answered that question as well. — Lomn 16:57, 15 September 2008 (UTC)

Gasoline locomotives would probably have more catastrophic fires and explosions due to fuel leaks or accidents than diesel locomotives. Such an event would not constitute "running properly," and would be a foreseeable consequence of a shift to gasoline. Edison (talk) 19:56, 15 September 2008 (UTC)

Nobody seems to consider that a gasoline powered car, equally or more prone to fire and explosion, 'doesn't run properly'. DJ Clayworth (talk) 03:45, 16 September 2008 (UTC)

Diesel has a flash point of >62°C (143°F), but gasoline has a flash point of <−40°C (−40°F). Most power boats under 35 feet have gas engines and most over 35 feet have diesel engines. Gasoline engines burn more fuel per hour than diesel engines of the same horsepower. Diesel engines are cheaper to operate, gasoline engines are cheaper to build, for the same horsepower. Economics of operation favor diesel, initial cost favors gasoline, safety favors diesel. [22]. In "Safety preparations for cruising" p71 it says "there is much less risk of fire and explosion" with diesel boat engines than gas engines. [23] It is hard to find that bald statement comparing gasoline and diesel locomotives, because no one uses gasoline engines in locomotives of railway size, in modern times, although it was considered in the 1920's [24] as an alternative to coal burning steam locomotives. I would expect that a diesel car is in fact less likely to burn up than a gasoline car, factoring in fuel spills while fueling or when fuel is spilled from a portable container, and fuel leaks from fuel lines, or fumes accumulating from spills/leaks in the garage.[25] Edison (talk) 15:52, 16 September 2008 (UTC)

If there are so many advantages to diesel, including overall cost in the long run, then why do most normal cars use gasoline (I'm aware of a few diesel cars). 98.221.85.188 (talk) 22:26, 16 September 2008 (UTC)

(unindent) As mentioned at Diesel engine#Diesel applications, historically diesel engines in the United States have not been popular as they "have been traditionally perceived as heavier, noisier, having performance characteristics which make them slower to accelerate, sootier, smellier, and of being more expensive than equivalent gasoline vehicles." Additionally until recently diesel fuel in the US was of a rather poor grade, with a high sulfur content. Old diesels, while easier to maintain, were also viewed as more finicky - some diesels had a problem with stopping/starting, especially in cold weather, so you had to leave them running - not a problem for industrial applications, but a nuisance for someone just stopping to get milk. And since there weren't a lot of diesels around, there weren't a lot of stations selling diesel fuel, so it was less convenient than gasoline. Of course, modern diesels escape many of those problems, driven mostly by improvements for use in European automobiles, where diesels have been historically popular. -- 128.104.112.147 (talk) 16:05, 17 September 2008 (UTC)

Statistics in research

Let's say you're using an instrument to detect the concentration of something, and you want the average and standard deviation of the measured concentration. You measure 5 times. Four of the times you measure a very low concentration, the fifth time you don't detect any. One the fifth time, it is not exactly as if the instrument is telling there is none, it's just that the concentration is below the level that the instrument can detect. When calculating average and standard deviation, should you A) treat this measurement as zero, B) exclude this measurement from the calculation, C) something else.

I realize this might make little practical difference in many cases, but I like to know what the right thing to do is, when being rigorous with the statistics and experimental method. Thx ike9898 (talk) 14:50, 15 September 2008 (UTC)

The most rigorous thing to do is to start again with an instrument that can detect lower concentrations. If that's not possible, the next best thing to do is to take further readings. Note that if you only have five readings, then there is little point in calculating the average and SD. You can and probably should just list all the readings. If you are taking a greater number of readings and you have the best possible instrument, then the answer to your question depends on whether you are sure you always know the difference between a "true" zero and a "below detection" zero. Itsmejudith (talk) 15:16, 15 September 2008 (UTC)

One common convention is to determine the lower limit of quantitation (LLQ), or the lower limit of detection (LLD), and then when none is quantitated or detected (depending on which you use) then the measurement is represented as a value half of the LLQ/LLD (on a graph the values below the LLQ/LLD can easily be distinguished). Because these values are not normally distributed, you should use a nonparametric test, like a Mann-Whitney or similar, to compare medians (rather than means and standard deviations). --Scray (talk) 15:40, 15 September 2008 (UTC)

You might find Detection limit useful as well. --Scray (talk) 15:45, 15 September 2008 (UTC)

I would not object to someone calculating the SD and AVG of 5 measurements. Consider that they might be making these 5 measurements for hundreds of different samples or conditions. There are ways of comparing the random variation within samples to the difference between conditions, such as Analysis of variance, and there are ways of designing the experiment to determine how many samples per condition are advisable. If I measured 2,3,1,2, and 0, I would see no basis for excluding the zero, unless you noticed the battery had failed at the time of the zero measurement or some other experimental blunder. The correct average of 5 measurements in my example would be 1.6, but if the fifth measurement of zero was excluded it would be 2.0, which would overstate the mean. The zero is not necessarily "artificial" or "incorrect." Let the data speak for itself.Edison (talk) 19:53, 15 September 2008 (UTC)

My concern is that inclusion of the zero artificially depresses the average. For example, the case where the lower limit of detection is 0.9 and the true value for the fifth measurement was 0.8.

I totally agree with your comment that there is no problem in reporting an average and standard deviation for 5 observations. This is common practice in some fields. ike9898 (talk) 21:07, 15 September 2008 (UTC)

Whereas an earlier response did make a generalization questioning the validity of calculating mean and SD for 5 observations, my point specifically was that the mean should not be used if the data are not known to be normally distributed. This latter point is an often-overlooked, very important assumption of such analysis. --Scray (talk) 23:50, 15 September 2008 (UTC)

I understand that many methods have underlying assumptions such as normal distribution, but that is a good point to bring up -- yes, many people forget this. ike9898 (talk) 01:41, 16 September 2008 (UTC)

To expand your hypothetical scenario a little, if your sample size was 100 and you got 99 positive results high above the detection threshold and one result of zero (i.e. below the detection threshold) then you could discard the datapoint as an outlier. Plasticup ^T/C 04:11, 16 September 2008 (UTC)

Sometimes experimenter doing ESP research have done selective retention of data and artificially produced significant results. But in careful lab work, such as at the US Bureau of Standards doing thousands of repetitive comparisons with official standards, there are some measurements found which are so far outside the distribution that they should not have been seen in millions of years. The trick is that a methodology of excluding outliers should be established in advanced and not adopted on the spot, since that might reflect experimenter bias and favor one hypothesis or another. Bogus positive results from areas such as ESP research have resulted from the experimenter excluding data he doesn't like. It is a poor lab practice for any experimenter to look at the data and decide on the spot which data points to exclude, without an a priori rule for excluding data, such as it being a certain number of standard deviations away from the mean. Otherwise leaving out certain measurements could be construed as fraud. Edison (talk) 15:32, 16 September 2008 (UTC)

Understood, but there are plenty of legitimate reasons to disregard outliers. Some estimators give undue weight to extreme values, possibly amplifying measurement error. Plasticup ^T/C 22:02, 16 September 2008 (UTC)

As Itsmejudith pointed out, you need different equipment. Common calibration numbers are for the middle of the measurement range. It would be extremely difficult to calibrate a machine for the conditions you describe. The values you are getting are probably inaccurate.

NIST has a very nice intro for Exploratory Data Analysis. Lots of graphical techniques. Saintrain (talk) 18:09, 16 September 2008 (UTC)

the flight of projectiles

If you were to depress the trigger of a standard modern day automatic weapon, an M16 on burst on an MP5 or something, I know Ican look up firing rates per minute but what would be the physical distance between the tip of one bullet and the tail of the one infront, assuming they all flew dead straight? And how does this vary compared to something extremely rrrrrapido like the gattling-minigun-type-things you can get on this thing found on the M167 VADSs or UH-60 helicopters? SGGH ^speak! 16:36, 15 September 2008 (UTC)

You need to know the rate of fire in rounds per minute (r), the muzzle velocity in m/s (v) and the length of each bullet in metres (l). The separation in metres (s) would then be $s={\frac {60v}{r}}-l$. Those numbers should all be easy enough to find - I expect the Wikipedia article for each weapon will give you them. --Tango (talk) 16:44, 15 September 2008 (UTC)

The gattling fires 100 a second, so thats 1/100 of a second between one bullet and the next, so the distance between the tip of one and the tip of the other would be the distance travelled in 1/100 of a second according to the muzzle velocity. Take the length of the bullet from that and you have the answer, right? SGGH ^speak! 16:58, 15 September 2008 (UTC)

For the M16 case, from AR-15 and 5.56 NATO I get r = 800 and v = 838. I can't find a WP:RS telling its length, but let's say l = 20mm = .02 m. So, $s={\frac {60*838}{800}}-.02=62.83m$ --Sean 17:24, 15 September 2008 (UTC)

That gives me, if the 20mm projectile is 125mm long (the longest of this typoe according to article) then that is 10.275 meters between each weapon. Does this sound reasonably? SGGH ^speak! 17:02, 15 September 2008 (UTC)

Actually that has to be correct. 100 in a second, a one second burst at 1km/s means 100 bullets spread across 1km, which is one every ten meters, so I guess that must be right. Sounds big though. SGGH ^speak! 17:07, 15 September 2008 (UTC)

Looks like you've calculated it correctly. It does look like a very large distance, but then 1 km/s is extremely fast! --Tango (talk) 17:18, 15 September 2008 (UTC)

If you ever saw one of those things firing tracer rounds - and remembering that typically one round in four or maybe one in six is a tracer round, I have no trouble at all believing the tracers are 40m to 60m apart - so 10m spacing for the bullets seems entirely reasonable. SteveBaker (talk) 01:17, 16 September 2008 (UTC)

New "unusual object" discovered

So:

"Hubble began seeing something brighten. It continued brightening for about 100 days and peaked at 21st magnitude in two near-infrared colors. It then faded away over a similar timescale, until nothing was left in view down to 26th magnitude. The object brightened and faded by a factor of at least 120, maybe more.

The mystery object did not behave like any known kind of supernova. It is not even in any detectable galaxy. "The shape of the light curve is inconsistent with microlensing," say the researchers. They recorded three spectra of it — and its spectrum, they write, "in addition to being inconsistent with all known supernova types, is not matched to any spectrum in the Sloan Digital Sky Survey database" of vast numbers of objects. "We suggest that the transient may be one of a new class."[26][27]

I, for one, am very excited. They've narrowed it down to being 120 light years to 11 billion light years away. Any thoughts? -- MacAddct  1984 ^{(talk &#149; contribs)} 16:56, 15 September 2008 (UTC)

Doesn't sound like the know much about it if they've 'narrowed' it down to between 120-11,000,000,000 light years away Nil Einne (talk) 17:01, 15 September 2008 (UTC)

If they successfully got a decent spectrum for it - they should be able to use redshift information to narrow the distance range down more tightly than that. If the spectrum is a crappy one for some reason - then how would they know that it didn't match anything? This is a bit suspect. SteveBaker (talk) 17:28, 15 September 2008 (UTC)

Plots of the spectrum are shown in the arXiv link above. The problem with getting a redshift is that you have to be able to identify the spectral features—they don't come with nametags saying "Lyα 1216" or whatever. In this case, the absorption lines are few (4–5) and broad (which gives your poor S/N in observed wavelength). Two hypotheses are tried in Section 3 of the paper; a z=0 hypothesis and a high-redshift hypothesis. In each case, there are extra unidentified lines and/or missing lines that you would expect to be there. If the source is at high redshift, you could also have absorption lines due to intervening systems at lower redshift, which further complicates the identification of spectral features. I can assure you that it's not amateur day on the author list or acknowledgments, so if they can't come up with a solid redshift, it's not due to either lack of effort or lack of competence. -- Coneslayer (talk) 17:45, 15 September 2008 (UTC)

At this point, this is an unexplained observation, not an unknown object. Which of these seems more likely, then: (i) a previously unknown object, or (ii) a known type of object with observations distorted by an unusual superposition of known phenomena? My nickel is on the latter because there are so many possibilities. Interesting either way, of course. --Scray (talk) 17:58, 15 September 2008 (UTC)

Redshift only gives you distance information if the object is moving with the rest of the universe. --Carnildo (talk) 21:31, 15 September 2008 (UTC)

Over large distances the fabric of the Universe is receding at more than the speed of light, which is a obviously much greater velocity than that of the object, so the object's motion becomes irrelevant. Plasticup ^T/C 22:44, 15 September 2008 (UTC)

If it's the exhaust plume of a nearby Bussard ramjet moving away from us at half the speed of light, the object's motion is quite relevant. --Carnildo (talk) 20:35, 16 September 2008 (UTC)

I know. I was just offering a counterexample to your claim that "redshift only gives you distance information if the object is moving with the rest of the universe" Plasticup ^T/C 21:59, 16 September 2008 (UTC)

Sounds like a lighthouse to me. Plasticup ^T/C 22:38, 15 September 2008 (UTC)

Are these comparisons acurate?

"The explanation for this [biological] diversity, the theory of evo- lution by natural selection, will form the backbone of your study of biological science, just as the theory of the covalent bond is the backbone of chemistry, or the theory of quan- tum mechanics is that of physics."

At first sight not all three "backbones" are really the backbones of these three sciences. What about other bonds - like the ionic bond - in the case of chemistry? And other physical theories like the theory or relativity in the case of physics? I also wouldn't say that the backbone of biology is the evolution theory. Isn't it the cell biochemistry? Mr.K. (talk) 18:23, 15 September 2008 (UTC)

Yeah, I think all 3 of those statements are rubbish. I'm not sure any of those fields have backbones, really, that's just not how science is structured. --Tango (talk) 18:42, 15 September 2008 (UTC)

Note that it is asking for the backbone of study, not the backbone of the discipline. For example, your study of ionic bonds could be based on an understanding of covalent bonds. In physics, quantum mechanics is rarely the backbone of study. Newton's laws are. But, the backbone of study changes from school to school and professor to professor. -- kainaw™ 18:47, 15 September 2008 (UTC)

Nothing in Biology Makes Sense Except in the Light of Evolution -- MacAddct  1984 ^{(talk &#149; contribs)} 18:54, 15 September 2008 (UTC)

I think the key phrase in that quote is "just as". It's probably fair to say that evolution is just as important to biology as quantum theory is to physics. That is to say - that it's right up there in the top five most important theories. But to pick a particular theory and call it number one is kinda silly. It depends on what you're trying to do. SteveBaker (talk) 01:12, 16 September 2008 (UTC)

I might rephrase it, "The theory of evolution is the underlying presupposition behind your study of biological sciences." Kristamaranatha (talk) 02:37, 16 September 2008 (UTC)

It's not a presupposition - there is plenty of evidence for it. SteveBaker (talk) 03:40, 16 September 2008 (UTC)

It is also hardly the underlying theory. Plenty of biology exists independent of evolution. Plasticup ^T/C 03:54, 16 September 2008 (UTC)

My point entirely - there is plenty of physics that's independent of quantum theory. So the importance of evolutionary theory to biology is comparable to (or "just as") the importance of quantum theory to physics...that is to say: It's incredibly important - but it's not the only thing. SteveBaker (talk) 15:08, 16 September 2008 (UTC)

I agree. I was replying to Kristamaranatha's "summary". Plasticup ^T/C 21:57, 16 September 2008 (UTC)

Czech Fingerprint Scientist

I recently came across a short note in a biology textbook about a Czech scientist who discovered the individuality of fingerprints or something like that. What was his name? I can't find anything about it on Wikipedia. Vltava 68 (talk contribs) 21:47, 15 September 2008 (UTC)

It was the anatomist Jan Evangelista Purkyně (but our article doesn't mention it!). Fribbler (talk) 22:30, 15 September 2008 (UTC)

I was about to say that! Also, the Chinese and Assyrians may have had a clue. Plasticup ^T/C 22:33, 15 September 2008 (UTC)

Demon's Egg

I wanted to ask about the scientific "accuracy" of this fantasy story. A bunch of British alchemists lead by Sir Issac Newton has "made a pact with the devil" and perfected a secret alchemic procedure for producing "Demon's egg".

The "Demon's egg" is a black spherical artifact which has the unusual property where

• It heats very quickly up when cooled

• It cools down when heated

• It grows when it is heated

• It shrinks when it is cooled

For practical usage, the egg must be kept in a brazier to keep it from shrinking and periodically it must be dunked in water to keep it from growing too large. It main usage is as a source of "instantaneous" heat. For example, it is used to bring a cauldron of cool water to boil quickly, by dunking the "Demon's egg" in it.

So is this an accurate description of an evaporating black hole?

How much energy can a 1 kilogram of "Demon's egg" hold?

What temperature must the brazier be to keep the 1 kilogram black hole from shrinking?

Thank you 202.147.44.80 (talk) 22:08, 15 September 2008 (UTC)

This is not an accurate description of an evaporating black hole. Black holes have no temperature. A 1 kilogram black hole would be so small as to be unnoticeable except as a source of hawking radiation. A black hole of any size would be impossible to hold up conventionally (though you probably could hold it up with magnetic levitation). The egg itself makes no sense. If it heats up when cooled and cools down when heated, that would just make it nearly impossible to heat or cool. It would effectively just keep everything around it at its neutral temperature, so I suppose if that's boiling then you could use it to boil stuff. You wouldn't need to do anything to keep it from growing to large or shrinking to small, as it would regulate its own temperature, and therefore size. — DanielLC 22:25, 15 September 2008 (UTC)

That's nonsensical. It loses heat when it gains heat? What does that mean? 24.76.161.28 (talk) 23:55, 15 September 2008 (UTC)

One weird property of black holes is that they have a negative specific heat: tossing more mass-energy into the hole reduces the Hawking temperature. "Heating" a black hole could mean adding heat (reducing the temperature), or "making it hotter" (increasing the temperature). So maybe if you were writing a riddle to which "black hole" was the answer, you could say that it "heats when cooled and cools when heated." But I would call that a deliberately misleading description, not an accurate one. For what it's worth, the temperature of a one-kilogram black hole would be about 10²³ degrees (Kelvin, Celsius or Fahrenheit) and it would radiate about 10³³ watts (about a million times the total power output of the Sun). (edit: But not for long, since 10³³ watts is about 10¹⁶ kg/second.) -- BenRG (talk) 00:26, 16 September 2008 (UTC)

It's really impossible - something that gains heat when you put it into a cool place is a straight up violation of the laws of thermodynamics - so no. SteveBaker (talk) 01:03, 16 September 2008 (UTC)

Assuming it doesn't contain a fuel source, of course. Or suck it's power from somewhere else. There are plenty of space heaters that will get hot when you put them in a cool place ... so long as their cord will reach. APL (talk) 03:03, 16 September 2008 (UTC)

Yes - that's true - but then we can't explain why it would cool down when heated...but at any rate, to (seemingly) cheat thermodynamics requires energy - and whatever internal source it had would soon run down. SteveBaker (talk) 15:04, 16 September 2008 (UTC)

Darn clever though. If this is an idea for a story you are writing don't let a little thing like physical impossibility put you off. DJ Clayworth (talk) 03:43, 16 September 2008 (UTC)

Yes - I adhere to the principle that any work of fiction is entitled to explore the consequences of ONE gross violation of known science...but no more. SteveBaker (talk) 15:04, 16 September 2008 (UTC)

importance of one engineering to the other

what are the relevance of engineering geology to the civil engineering industry?80.78.17.58 (talk) 22:38, 15 September 2008 (UTC)

The St. Francis Dam article may illuminate you. -- Finlay McWalter | Talk 22:45, 15 September 2008 (UTC)

Electrical grounding chemicals

while preparing an electrical earth certain chemical compounds are used as back fill material in the earth pit around earthing electrode which in turn increases the water retaintion capacity of the earth pit & increases the electrical conductivity of the earthing earth system.

I am interested in knowing the chemical composition of this back fill material & its chemistery. —Preceding unsigned comment added by 59.161.66.131 (talk) 23:53, 15 September 2008 (UTC)

see this link [28] —Preceding unsigned comment added by 79.76.201.117 (talk) 02:14, 16 September 2008 (UTC)

I question whether such chemicals are widely used in utility grounding systems, since the ground rods are typically simply driven into the ground to an adequate depth to obtain the desired low resistivity. There is typically no excavation, so no opportunity to che,ically amend the composition of the soil. If the grounding electrode is in a location where there is shallow earth over bedrock, then there might be excavation and backfill with chemical additives, but I have not encountered that. Edison (talk) 02:44, 16 September 2008 (UTC)

If you are doing it yourself, you can add salt and ashes to the ground. However this will increase corrosion of the grounding rod, as well as the conductivity of the ground. These add ions to the water, but if there is no water around will not conduct. Graeme Bartlett (talk) 21:26, 16 September 2008 (UTC)

September 16

Where do I buy kudzu?

(Moved from Reference Desk - Computers)

Infestation of Kudzu in the United States.

Sirs,any help in finding live kudzu vines, suitable for transplanting ,would be greatly appreicated.05:06, 16 September 2008 (UTC)

It would help to know where you are, at least at the country level. In many parts of the U.S., kudzu is considered an invasive species. You can find vines by the mile choking native vegetation. The U.S. Department of Agriculture requires a federal permit for the movement of many items (plants, insects, produce), including kuzdu. Kudzu can act as a host for soybean rust, a fungus that can significantly damage soybean yield. --- OtherDave (talk) 10:55, 16 September 2008 (UTC)

Are there areas of the U.S. not overrun by kudzu (or wysteria)? Perhaps Alaska and Hawaii. When I drive across the country, it seems that I see kudzu everywhere. -- kainaw™ 13:27, 16 September 2008 (UTC)

It's pretty much a southeastern thing; see the map to the right. -- Coneslayer (talk) 13:30, 16 September 2008 (UTC)

Heehee. I guess my view of "across the country" is very skewed. -- kainaw™ 13:32, 16 September 2008 (UTC)

Or just a little displaced in time. -- Coneslayer (talk) 13:35, 16 September 2008

(UTC)

It's wisteria not wysteria. Caspar Wistar never spelt his name with a 'y'.Richard Avery (talk) 15:17, 16 September 2008 (UTC)

Never ever? Not once? Not even during that really weird phase? -- kainaw™ 18:41, 16 September 2008 (UTC)

Wilmington, NC area. Thank you for your help so far. 16:09, 16 September 2008 (UTC) —Preceding unsigned comment added by 70.144.127.128 (talk)

Then you ought to be able to find kudzu along any county road. And around any county telephone pole. And engulfing half the houses in the country. No offense, buy why on earth would you want kudzu, the weed that's eating the South? Take a look at kudzu as an invasive species. --- OtherDave (talk) 18:34, 16 September 2008 (UTC)

Perhaps to discover a useful control measure, develop tasty kudzu recipes, or breed kudzu-craving coypu? --Scray (talk) 00:35, 17 September 2008 (UTC)

From the article, one useful control measure is a bulldozer. Possibly one equipped with a flamethrower. --- OtherDave (talk) 14:46, 17 September 2008 (UTC)

I have a metal

Located in the garden, buried in the soil. It is silver in colour, (very silver and shiny) it is very light, it tinkers like coins do when you hit it, it doesn't float, nor melts in boiling water (not that I expected it to) and doesn't respond to magnets. It is shaped like a misshapen circular flat disc, seems to be all distorted slightly on one side, flat on the other. I can't bend it with my hands.

What is it? Or what other tests can I carry out to work out what it is? SGGH ^speak! 11:31, 16 September 2008 (UTC)

It looks like fourth from the left on the top row, but without the markings. [29] It isn't particularly flexible (cracked it in a vice with a hamkmer and it didn't bend much). The metal detector beeps at the silver section of its display when I sweep it but then I don't trust that very much. SGGH ^speak! 11:40, 16 September 2008 (UTC)

Can you scratch it with your fingernail? --Tango (talk) 13:12, 16 September 2008 (UTC)

No, its too tough to scrape anything off, When I placed it in the vice a part of it broke away partly and i was able to bend it off and snap it with my finger very easily. =The shard was flexible and had to be bent almost right the way around before it broke off. The newly exposed ends were very shiny. SGGH ^speak! 13:16, 16 September 2008 (UTC)

It could be silver (probably not pure, but silver coins are rarely pure). I'm not sure of the best way to test it for sure, but someone here probably does. --Tango (talk) 13:24, 16 September 2008 (UTC)

Wouldn't silver feel heavy rather than light ? SGGH, you said the newly exposed surfaces were especially shiny when you broke a piece off - did they retain that shine or did they tarnish quickly ? Silver will stay shiny if polished; if it tarnishes quickly, my guess (from the lightness) would be aluminium or an aluminium alloy. Gandalf61 (talk) 13:50, 16 September 2008 (UTC)

Gandalf, the recently exposed areas have remained very shiny. SGGH ^speak! 14:15, 16 September 2008 (UTC)

Then I think that kicks my aluminium theory into touch. Gandalf61 (talk) 14:24, 16 September 2008 (UTC)

"Kick into touch" means? Playing rugby union, the only wp article that uses the phrase, is ambiguous. Thanks. Saintrain (talk) 15:29, 16 September 2008 (UTC)

I means it's been taken out of the equation. In Rugby, if you kick a ball into touch you are kicking it off the field of play. SGGH ^speak! 16:30, 16 September 2008 (UTC)

My Grandfather thinks it is some sort of long lost Roman coin, and then spottted images of the Maine penny and announced that that was it. Seeing as I am doing history at University I informed him that the Maine penny was forged in Norway and lost in "Vinland" and it was unlikely to be the same thing, and also that my area of the UK is a bit outside of Norse expansion and settlement. It is possible that trade brought coins here but we have to actually establish it is a coin first. I'm still trying to find out what metal it is! Is there a definitive test for silver bar trying to melt it at 950 degrees C? SGGH ^speak! 14:34, 16 September 2008 (UTC)

If it's silver, it should be about 50% heavier than iron or steel - if this is a potentially valuable coin then the best way to test it would be to measure it's electrical conductivity (silver is VERY conductive). If it's still shiney after being buried for years - then it's almost certainly silver - there aren't many metals that wouldn't corrode or tarnish. SteveBaker (talk) 14:54, 16 September 2008 (UTC)

Silver goes black when buried. DuncanHill (talk) 17:35, 16 September 2008 (UTC)

In the 1950's (& 1960's?) France circulated large aluminum coins. (The southern UK is in the historical area of French "expansion and settlement" :-) Fresh aluminum will coat itself with an oxide preventing its further corrosion (see telescope mirrors). (You beat a priceless artifact in a vice? No "Attic" for you!) Saintrain (talk) 15:13, 16 September 2008 (UTC)

I think it is too warped to be that recent, the only thing that suggests it is not silver is it is pretty light. It is about an inch and a 1/4 in diametre andabout 5-6mm thick. I don't have the ability to weigh it, it is too light to register on the only scales in this house. SGGH ^speak! 16:30, 16 September 2008 (UTC)

I'd guess aluminum. Magnesium is also a possibility (it's even lighter than aluminum), but it tends to corrode, unlike aluminum. --Carnildo (talk) 20:59, 16 September 2008 (UTC)

Certainly sounds like aluminium. When melted by a fire you can get misshapen blobs in the ground. Another destructive test is to see if it is dissolved in a hot sodium carbonate solution, bubbles of hydrogen should appear. Graeme Bartlett (talk) 21:35, 16 September 2008 (UTC)

Could be zinc. The broken cross section would be very shiny with some crystal structure visible. The shape suggests it would be from molten metal dropped on a hard surface to make a coin-like shape. If it is zinc or aluminium heating the edge of it in a gas flame would melt it. Polypipe Wrangler (talk) 06:01, 17 September 2008 (UTC)

reading upside-down..

If I hold a book upside-down I can read it easily..I surprised myself! How is this possible? —Preceding unsigned comment added by 89.241.116.4 (talk) 12:55, 16 September 2008 (UTC)

It's probably akin to the trick where you scramble letter order in words (except the first and last letter) and retain something fairly readable -- you're looking at an unfamiliar pattern, but you have the foreknowledge that it maps to a familiar pattern (a known word in a grammatically correct sentence), so you can fill in the fuzzy spots quite quickly. Try taking something without that familiarity mapping, though (say, a base 64 encoding), and I expect it will be much more difficult to read. Go with something like "V2lraXBlZGlh" (the base 64 for "Wikipedia"), write it on paper, and try reading that upside down. — Lomn 13:18, 16 September 2008 (UTC)

(edit conflict) Your mind can recognise letters and words upside down, I wuold imangine its the smae as wehn yuor mind can raed senentces like tihs as long as the first and last letters are intact. I suspect quick reading upside down still requires good mental organisation. SGGH ^speak! 13:20, 16 September 2008 (UTC)

(ec) I don't have time to google for it, but there was at least one study in which participants were given glasses that inverted everything - so everything the participants saw was upside down. It didn't take long for them to go about normal activities without difficulty. Similarly, the experiment used lenses to make things appear further away or closer and one had a bug-eye look with the view broken into a mess of hexagons. No matter what they did, the brain quickly adapted and the person was able to continue normal activities. So, reading upside down is a natural thing for the brain to be able to adapt to. -- kainaw™ 13:23, 16 September 2008 (UTC)

I read about those studies too, and I think "not long" was a few hours or days, rather than the seconds it takes it get used to reading upside down. It may be related, but it's not the same. (Also, with those studies there were apparently difficulties when they took off the glasses - it took a while to get used to being back to normal. It doesn't take any time to get used to reading up the right was again.) --Tango (talk) 13:28, 16 September 2008 (UTC)

Yes, in the study I saw it took a week or so to get fully used to the inverted vision, such that the subject didn't even notice the vision was inverted. There were some strange intermediate effects where whether or not vision was flipped depended on what sort of visual cues were available (rising smoke and such). After the experiment, it took less time, but still more than a day, to get back to normal. Algebraist 14:35, 16 September 2008 (UTC)

It took longer than I remembered - but I can't place any of those studies in a time period. All I remember is that it was a while back. Perhaps I didn't even read the study. I may have only seen mention of it on some documentary show. -- kainaw™ 14:49, 16 September 2008 (UTC)

¡noʎ ɹoɟ uʍopǝpısdn pǝddı1ɟ ʇxǝʇ ɹnoʎ ǝʌɐɥ os1ɐ uɐɔ noʎ [30] -- macaddct1984 17:54, 16 September 2008 (UTC)

<long boring> well, when you think about it, why not? you see a chair rightside up, you see it upside down, you recognize it immediately. that goes for most objects. why not words? presumably, the language processing center of the brain is involved, and it is not as invariant for spacial transformations as the general object recognition functions are. but knock those out of the loop, and upside down isn't a problem as far as recognizing the word; you then need to tap it back into the language functions to interpret it.

language function is not symmetrical, it's on one side of the brain, which corresponds to most people being righthanded. what lefthanded people do is a question; it seems like how they do their language processing varies quite a bit, some with the normal language center in the normal location, some doing it with another part of the brain entirely; perhaps with different "algorithms".

that said, i know somebody lefthanded who had the most incredible spatial pattern recognition abilities as a toddler; could solve maze puzzles on sight at an early age, i.e. didn't have to navigate along with the finger from the beginning trying to avoid dead ends, would just look at it and see the correct path all at once. the corresponding vice versa being that she had a tough time learning to read; for a long time would recognize each word separately and haltingly. one day i noticed that she was doing this, with the book upside down. a couple of minutes of testing established that she could read at the same speed rightside up as upside down. this ties in with what i was talking about in the previous paragraph; if you're using your regular object perceptive apparatus, upside down means nothing; it's only a problem for the specific language apparatus, which she apparently wasn't using given her relatively large bias in abilities towards nonverbal visual perception. anyway, years later, this large asymmetry in abilities, relative to the average, has in fact meanstreamed quite a bit, with the reading ability rising to normal while the analytical direct perception, for lack of a better word, have dropped down to about normal; but she's still much more a visual-oriented person than verbal. </long boring> Gzuckier (talk) 19:50, 16 September 2008 (UTC)

Well, I can think of at least one other reason why recognizing a chair that's upside down is not the same as being able to read upside down (besides what you mention) and that is that an upside down chair is obviously upside down and easily flipped mentally while letters often form other letters or numbers when they get flipped. Getting used to that would be akin to not getting caught up in false friends when learning a new language. I imagine words with letters such as p, b, d, q w, or m are among the hardest to get used to, for this very reason. If most of the letters are symmetrical (l, o, z, s, etc.) or are at least completely different when flipped (f, Q, R, etc.) then you'd get used to it more quickly. Matt Deres (talk) 20:29, 16 September 2008 (UTC)

Shop Vac power

The Rigid 16gal shop vac advertises itself as having 6.5 peak HP. How is this possible? I get 12A * 120V = 1440W ... 1440W/746W/HP = 1.9 HP. --Duk 14:08, 16 September 2008 (UTC)

Those figures may be standard operation, and the peak through some sort of freak occurance when testing, or the advert/sales people don't talk to the people who built it, or know what they are talking about, perhaps? SGGH ^speak! 14:36, 16 September 2008 (UTC)

Short answer - you can't believe ANY of the numbers on any vacuum cleaner advert!

The magic word "peak" is the key here. [31] has all the ugly details:

"The rating for Peak Horse Power is found by taking the suction motor without its fans and adding as much load as possible without burning it out and then measuring the horse power using the formula which is based on torque per second. This results in a rating that is many times higher than the actual horse power of the motor. Keep in mind also that this motor rating does not take into account the number of fans which the motor is driving. An example of this is that a 4.0 PHP motor with two fans produces about 33% more suction than a 4.0 PHP motor with only one fan."

So Peak Horsepower is meaningless measurement...ignore it.

Sadly, the Ampere value is useless too - that only tells you how much the vacuum cleaner uses - that's like buying a sportscar based on how crappy it's fuel consumption is rather than looking at it's 0-60 time and top speed! A 12 Amp vacuum cleaner might be a powerful one that you'd want to buy - but it could also be a horribly inefficient one that you don't want to go anywhere near!

So the Ampere rating is worse than useless.

The best measure is something called "Air Watts" (although that too is a bit "open to interpretation") or something called the "Sealed Suction" rating... but I don't think I've ever seen those numbers given on a domestic vacuum cleaner.

Basically - you're on your own!

SteveBaker (talk) 14:41, 16 September 2008 (UTC)

The maximum work done in sucking air and dirt into a vacuum cleaner would logically be the thing you are interested in.Another factor is max amperage, since that is what would blow a fuse, or pop a circuit breaker, or cause wiring to fry. If the machine is not connected to a hose, but just sucking air in, it would move the maximum volume of air per second, but without doing the most work mechanically and without having the greatest electrical input to the motor. At some middle level of resistance, with the hose attached and lifting dirt and air through the resistance of the hose, it will have the highest electrical input to the motor and do the most work mechanically. If at the other extreme the end of the hose is burrowing into a pile of dirt so that flow is blocked, there is also no air moved and no work done, and the electrical input to the motor will also not be the highest. This condition is likely to destroy the motor, however, if the air flow is used to cool the motor. This last condition is counter-intuitive, since one expects the greatest amperage under "locked rotor" condition, but that the motor is not in locked rotor. Consumer Reports rates vacuum cleaners on performance, not amperage. They rate them on cleaning carpet, bare floors, on noise, ease of handling, and a few other factors.SonsumerSearch compiled some ratings of shop vacs at [32]. Edison (talk) 15:16, 16 September 20ConsumerSearch has some shop vac ratings and reviews at 08 (UTC)

Of the large size models, an independent research group gives the "Ridgid Pro Utility Vac WD1850" (16 gallons) a very good rating, ranking second; Kenmore being the top one (as it often is). -- MacAddct1984 ^{(talk &#149; contribs)} 18:45, 16 September 2008 (UTC)

Potting soil mixture

Below is a table of ingredient proportions for making potting soil. Is there a similar table for making Terra Preta?

Potting soil	minimum percent	lbs/cuft	lbs each
charcoal	33	13	6.16
sand	59	130	61.61
sludge	5	45	21.33
sawdust	2	17	8.06
perlite	1	6	2.84
total	100	211	100.00

Help me identify my vacation photos

Can anyone help me identify the breed/species/behaviors shown in these pictures?

• 
  Taken in the Cotswolds. They fly in beautiful synchronized patterns. No idea what color they are.
• 
  Taken in the Cotswolds.
• 
  Taken in Oxford. Grey heron? I thought it was a Great Blue, but our article says they're rarely found in England.
• 
  Also in Oxford.
• 
  Taken at Slea Head in Ireland. Herring Gull?
• Taken at Slea Head in Ireland. Cicindela campestris?
  Taken at Slea Head in Ireland. Cicindela campestris?
• 
  I assume this cow is just sleeping and not dead?

There are more pictures at the Humanities, Language and Miscellaneous desks. Thanks, BenRG (talk) 17:42, 16 September 2008 (UTC)

Concur on Grey Heron. The flock in silhouette looks like Corvids of some kind. -- Coneslayer (talk) 17:50, 16 September 2008 (UTC)

Carrion Crows, I'd say. Your basic common-or-garden English crow. --Kurt Shaped Box (talk) 23:48, 16 September 2008 (UTC)

Any chance they could be jackdaws like this one I saw a few hours later? -- BenRG (talk) 00:42, 17 September 2008 (UTC)

It's possible. It's difficult to determine scale from the photo. If they were about the size of Feral Pigeons, then they'll have been Jackdaws. Bigger, and you're dealing with CCs. The wing shape and length suggests more crow to me - though I'm not an expert in bird identification... --Kurt Shaped Box (talk) 00:55, 17 September 2008 (UTC)

The shaggy sheep are Cotswold sheep, so I suppose that shouldn't be too much of a surprise. Mikenorton (talk) 18:49, 16 September 2008 (UTC)

Thanks. I looked through a bunch of sheep articles trying to identify them, including Cotswold sheep, but I didn't recognize them from the picture there. Is it normal for them to be dreadlocked like that? Are this and this also Cotswolds, or do they just go to the same hairstylist? -- BenRG (talk) 00:42, 17 September 2008 (UTC)

There are more pictures of Cotswolds at [33], as for those two pics, the first one I'd say yes, the second - not sure, do Cotswolds ever have black faces? DuncanHill (talk) 11:08, 17 September 2008 (UTC)

The second one is a Wensleydale, I think. Mikenorton (talk) 13:12, 17 September 2008 (UTC)

The gulls look like Herring gulls to me, the cow is probably asleep, but you'd probably want to poke her with a stick to double check. DuncanHill (talk) 23:32, 16 September 2008 (UTC)

Yep, they're Herring Gulls (probably a mated pair, based upon the fact that they're stood next to each other without looking as though they want to have a fight). As for the cow - don't cows sleep standing up? I know that they can kneel down, if they want (as the creamy-coloured one is doing) - but AFAIK, an adult cow can't actually breathe when lying on its side, due to it's lungs being compressed by its own body weight. That one might actually be dead... --Kurt Shaped Box (talk) 23:45, 16 September 2008 (UTC)

I've seen living cows lying down like that. A thought - if those are her calves beside her, they look quite placid, which suggests that they have no concerns about their mother. If you've ever seen a calf with a dead mother, you are left in no doubt that she's dead. DuncanHill (talk) 23:49, 16 September 2008 (UTC)

It's just lying down! They do that. Also unlikely to be the mother of those calves, for one the cow is a Fresian and there appears no evidence of that breed in the calves and second the cow looks too young herself to be the mother of those two sturdy calves. Jdrewitt (talk) 21:18, 17 September 2008 (UTC)

Ah, okay then - I'll bow to your superior knowledge on this one. I just seem to remember reading somewhere that cows can't lie on their sides and breathe at the same time. Never mind. ;) --Kurt Shaped Box (talk) 00:00, 17 September 2008 (UTC)

That was sort of my thinking—healthy cows don't look like that, do they? But an unhealthy cow would provoke a bit more reaction in the others, wouldn't it? I'll assume it's okay, but I'm still a bit worried. -- BenRG (talk) 00:42, 17 September 2008 (UTC)

Are you anywhere near this cow at the moment? Just walking up to her would usually get a reaction, or as I said you could poke her (not hard) with a stick. It is a bit dodgy going near cows with their calves though, as they do get a bit aggressive if they think you are a threat to their young. If you do find any more cows which concern you, try to find the farm and let the farmer know - they will be very grateful for your concern. Calves bellow something heartbreaking when their mothers are dead or very ill, and other cows in the field will often behave oddly too. DuncanHill (talk) 01:30, 17 September 2008 (UTC)

I once saw a couple of dead horses who had been struck by lightning. They were lying on their sides like this cow, but the legs farthest from the ground were quite a way up in the air due to the distension of the abdomen from post-mortem changes. So this would have to be a recently-dead cow. Edison (talk) 02:06, 17 September 2008 (UTC)

So, anyway - I've taken the liberty of adding a cropped version of the cow image to our Cow tipping article. That may be a controversial change, considering the history of the article (really!) - but let's wait and see... --Kurt Shaped Box (talk) 22:36, 17 September 2008 (UTC)

The birds are more likely to be rooks, given the old country adage crows together are rooks and rooks by themselves are crows. The cow is unlikely to be dead given that there is a large blood vessel crossing her abdomen and this looks normal and is clearly indicating a level of blood pressure. It is a well known fact that blood pressure very often drops at death ;-) Richard Avery (talk) 07:30, 17 September 2008 (UTC)

How can something be smaller than Planck length?

The LHC might create black holes smaller than Planck length according to the first response to my question above. Huh? I thought Planck length, Planck temperature, Planck energy levels, etc. was the ultimate. That any other extreme measurement would be nonsense? I suppose with some fancy math that would make Einstein look like a retard you could make it happen, but geeez- This mind blowing science not only gets me worried, it's driving me insane!. (HP Lovecraft's beeper just went off) How the- how can something be more extreme than the ultimate!? Can something less than nothing actually be created? If that's the case, it probably could only exist in another dimension. Or, having nowhere else to go, the universe would go TILT, turn itself inside out, and then -the black hole would take up infinite space! AAAAHHHH!!!Dr. Carefree (talk) 19:00, 16 September 2008 (UTC)

The Planck scale isn't necessarily the smallest possible, it's just the smallest our current theories can understand. --Tango (talk) 20:13, 16 September 2008 (UTC)

That response in the previous thread was incorrect. It was based on the usual black hole formulas that you can find in articles like black hole, but the scenarios for black hole production at the LHC assume that those formulas are wrong and the black holes are much larger (but still extremely tiny by everyday standards). Obviously this is all very speculative and most likely no black holes will be produced. Also, as Tango said, the Planck length is more of a threshold of ignorance than anything else. Claiming that it's a "minimum length" is misleading since it implies that we have some idea what's going on at that scale. -- BenRG (talk) 21:42, 16 September 2008 (UTC)

This plank length business does not make sense. Planks come in different lengths. Wanderer57 (talk) 21:02, 16 September 2008 (UTC)

The point was that because it is too tiny to exist, it does not exist. Also it should last less time than a Planck time before it has decayed. When you apply Heisenburg's uncertainty principle something with a very tiny size has to have a highly uncertain energy or mass. Or if it has a very short lifetime, the same applies. Graeme Bartlett (talk) 21:50, 16 September 2008 (UTC)

Dr. Carefree needs to change his/her name (that or take a tranquilizer). Clarityfiend (talk) 21:54, 16 September 2008 (UTC)

Also, Planck units are not all extreme. The Planck mass, for example, is about the same as that of an ant. The Planck energy is about the same as that of a barrel of oil. Some of them are a little nutty, though. --Sean 23:48, 16 September 2008 (UTC)

Chaotic system is Chaotic

Hello! Could someone explain in layman's terms the second and third conditions for a system to be considered chaotic? I just can't get my head around those two! The article explains in several paragraphs what "sensitivity to initial conditions" means (which is like the easiest one to understand), has a single short paragraph for "must be topologically mixing" (which I don't understand), and says nothing about "its periodic orbits must be dense". I'm asking here and not at the mathematics desk because I would also like to understand what this means for real chaotic systems, like the weather. There is an explanation of these for the layman, right? Thanks in advance, Kreachure (talk) 19:44, 16 September 2008 (UTC) PS. If you think I'd get a better answer at the Math Desk nonetheless, please tell me. :)

I think there's a fair bit of crossover between the Maths and Science desks, so there shouldn't be a problem there. I'll try to tackle a layperson's explanation of topological transitivity, first. Quoting from Mixing (mathematics):

A continuous map $f:X\to X$ is said to be topologically transitive if, for every pair of non-empty open sets $A,B\subset X$, there exists an integer n such that

$f^{n}(A)\cap B\neq \varnothing$

So, a continuous map is just a continuous function where the domain and range (i.e. sets of possible inputs and outputs) are the same. Because of this, it is possible to iterate the function - i.e. take the output of the function and use it as a new input. The nth iterate of f(x) is $f^{n}(x)=f(f(...f(x)...))$. The definition of open sets in a topology gets a bit circular, but for example's sake consider the basic open set of the real line, the open interval (a, b), which is the set of all numbers x such that a < x < b (i.e. numbers between a and b, but not including a or b). Take any two of these open sets, and label them A and B, and suppose that the domain of our function is to be the real numbers. The image of A in f, f(A), is the set of all outputs you get when you use all elements of A as inputs to f. For example, if f(x) = 2x, then f(A) is the set of all numbers twice as big as the elements of A, and f²(A) is the set of all numbers four times as big as the elements of A, and so forth. If f is topologically transitive, then you can always find a number n such that the image of A in the nth iterate of f (i.e. the set you get when you feed all elements of A into f, and feed that output back into f, and so forth for n times) has a non-empty intersection with B - they overlap.

Let's see if f(x) = 2x is transitive. If you start with A = (0, 1) and B = (3.5, 4.6) you see that f(A) = (0, 2), and f²(A) = (0, 4). Clearly f²(A) and B overlap on the interval (3.5, 4), so that's ok. But what about the other way around? f(B) = (7, 9.2), f²(B) = (14, 18.4), and you can see that as you continue applying f to B, you're actually getting further away from A. Clearly, f(x) = 2x is not topologically transitive on the real numbers.

A function which is topologically mixed goes even further. Not only can you find an n such that $f^{n}(A)$ overlaps with B, you can find an n such that for every m > n, $f^{m}(A)$ overlaps B. So $f^{n+1}(A),\ f^{n+2}(A),\ f^{n+1000000}(A)$ all have overlaps with B.

Does that make it clearer? Confusing Manifestation(Say hi!) 23:59, 16 September 2008 (UTC)

Oh boy... er, first of all, thank you very much for taking the time to write up this explanation. It certainly explains "topologically transitive" quite thoroughly. But to be honest, I was expecting a far simpler explanation. I guess there really isn't a simpler way to explain these concepts, huh... I was expecting to understand what it means in general for a chaotic system (the same way I understand what "sensitivity to initial conditions" means). Does the "periodic orbits must be dense" bit need an equally intricate explanation? Kreachure (talk) 19:16, 17 September 2008 (UTC)

Strangelets

A few days ago, somebody asked a question regarding how long a mini-black hole would take to destroy the Earth, if one were created by the LHC. I would like to know how long the Earth would take to be destroyed by the creation of strangelets, assuming that a runaway strangelet reaction could in fact occur. My understanding is that every particle a strangelet touches would become a strangelet, and that this would eventually have a domino effect across the whole earth. But how fast would this theoretically happen? Would it be fairly instantaneous, or would we initially have time to hear that "Switzerland has disappeared" on the news? Thanks Baked Bean Bob (talk) 22:31, 16 September 2008 (UTC)

I don't know, but lets both read the articles on strangelets and Safety of the Large Hadron Collider and return in a couple hours. Plasticup ^T/C 01:52, 17 September 2008 (UTC)

From strangelet: "even if the strange matter hypothesis were correct, nuclei would never be seen to decay to strangelets because their lifetime would be longer than the age of the universe." So there you have it. Also, the collisions that will take place in the LHC are similar to the millions (billions?) that take place every day when cosmic rays hit our atmosphere. So far our planet has not been reduced to strange matter. Plasticup ^T/C 01:58, 17 September 2008 (UTC)

I can't count the number of times I've said this...but one more time can't hurt: There is a VERY significant difference between cosmic ray collision and what happens in the LHC. A cosmic ray comes in at some large fraction ot the speed of light and smacks into a more or less stationary particle on the earth or in the atmosphere. Conservation of momentum has the resulting "stuff" (including - maybe Higgs Bosons, mini black holes, strangelets, etc) hurtling off at maybe half the speed of light. They aren't going to be around long enough to cause major problems. But the LHC takes particles around the ring in opposite directions and smacks them together at precisely equal and opposite velocities. It does this SPECIFICALLY so that the momentum of the incoming particles will cancel out leaving the resulting "stuff" being more or less stationary with respect to their detectors. If the particles disappeared at half the speed of light - they'd never detect them. If there were truly no difference between cosmic ray events and LHC events, we wouldn't have spent all of those billions of dollars building the darned thing - we could have simply set the detectors up somewhere outdoors and waited for cosmic rays to make Higgs Bosons for us! So this argument that if there were any nasty things produced at those energies then we'd have seen them already is really pretty bogus. The thing that makes it safe is that we really don't believe in strangelets and mini-blackholes will evaporate - or simply take so long to grow to earth-eating sizes, it'll never matter. SteveBaker (talk) 04:32, 17 September 2008 (UTC)

I am familiar with that argument. Yes, the results of collisions with cosmic rays have tremendous momentum, but there are a hell of a lot of them. They have been happening for billions of years. At some point one of the stranglets would have hit 1,000 baryons on its way through the Earth and slowed down enough to be captured. The majority would escape, I have no argument there, but the natural experiment has been running for so long that the small possibility of capture would have been realized. Plasticup ^T/C 05:37, 17 September 2008 (UTC)

For a long time, it was thought that the Tunguska event might have been caused by a mini-black hole or a strangelet or something. We now know that's not true - but the idea was sufficiently plausible to be seriously considered for a while. If statistically unlikely cosmic ray events were indeed causing disasters of that scale - at a timescale of (say) once per few thousand years - then it's not clear that we would have noticed them from ancient craters and so forth. But I reiterate - I'm not in the slightest bit bothered about risk due to LHC and the people who do believe it's going to be the end of the world are largely nut-jobs. I'm only saying that the argument that "It must be OK because cosmic rays do this all the time" is not the slam-dunk that LHC folks claim that it is. SteveBaker (talk) 13:36, 17 September 2008 (UTC)

If the LHC caused a Tunguska-like event it would be unfortunate (particularly for France and Switzerland), but it would not be the end of the world. The mini-black-hole and strangelet theories involve the end of the world, there is a big difference. It's entirely possible that cosmic rays do occasionally cause natural disasters on the scale of Tunguska and we might not have noticed, but if they caused end-of-the-world events, we wouldn't be here to not notice it, so we can be pretty certain they haven't happened. --Tango (talk) 13:57, 17 September 2008 (UTC)

Wouldn't your "it's going too fast to hit anything" objection apply to the original cosmic ray collision? Presumably after some amount of playing pachinko it will get down to a less ludicrous speed; even more so for cosmic rays hitting the Sun. --Sean 14:22, 17 September 2008 (UTC)

Right - that's Plasticup's argument - and it has great merit. The problem is that the probability of that series of collisions happening is small (it must be small or we'd already have detected Higgs Bosons bouncing around all over the place). We don't know how many "pachinko"-style collisions it might take to create conditions with enough energy to create a strangelet/mini-black-hole/whatever and yet to have the resulting particle(s) going slowly enough to do noticable amounts of damage before they fly off into the inky void. That means that we don't really know for sure whether:

1. These things are happening all the time in the atmosphere - many times per day over every square mile of the world - and the world hasn't ended - so we're OK - and we didn't detect any weird particles because there just aren't any and the LHC is going to be a huge disappointment - but isn't dangerous. ...OR...
2. These things happen only rarely - maybe just a few times each year. Rarely enough that we can't detect them but frequently enough that we'd know if they were dangerous. Hence we know that the consequences are benign - so the LHC is definitely safe and may well detect something interesting. (this is Plasticup's view, I think)...OR...
3. These things (statistically) happen only once every few thousand years and they don't wipe out the entire planet - but maybe might account for some of the mysterious mass extinctions or other "natural" events of disasterous proportions...in which case the LHC might indeed be insanely dangerous - but probably not the end of the world. (I very much doubt this - but it's possible)...OR...
4. These things are statistically so amazingly unlikely that happen only once or twice in the life of the universe - so we're safe from cosmic ray events but we don't know about artificially-induced events in the LHC (this is my view).

So which of those is it? We don't know. Hence it's a guess - and this isn't a valid proof that the LHC is safe. (Although, IMHO, there are other things that constitute valid proof.)

SteveBaker (talk) 17:07, 17 September 2008 (UTC)

That statement that "nuclei would never be seen to decay to strangelets" is actually talking about something different. The idea is that strange matter is a lower energy state than ordinary matter, and in quantum mechanics any transition from a higher to a lower energy state that doesn't violate any conservation laws will happen eventually. But there's an energy barrier between the states, i.e. the potential function looks like

       \      _        /
        \    / \      /
         \A_/   \    /
                 \B_/

Classically you can't get from A to B without an energy input to get you over the hump. Quantum mechanically you can and will get there by tunneling, but the half-life for the transition is exponential in the size of the barrier. So nucleons might decay to strangelets but very very slowly. But it's a different story if you already have some strange matter (produced by actually supplying the energy to get over the hump)—it might catalyze the production of more. Its proximity might, if you like, "tilt" the energy function so that you can roll down from A to B. There are a bunch of sci-fi disaster scenarios like this—vacuum decay, ice-nine and grey goo spring immediately to mind. Personally I don't lose sleep over any of them. A more realistic example is invasive plant or animal species that can spread easily if they're introduced from elsewhere, but are unlikely to appear by spontaneous mutation. -- BenRG (talk) 16:38, 17 September 2008 (UTC)

Having read the articles I am still none the wiser. However it does seem that nuclei decaying into strangelets is different from the process described here:

"If strangelets can actually exist, and if they were produced at LHC, they could conceivably initiate a runaway fusion process in which all the nuclei in the planet were converted to strange matter, similar to a strange star"

This is the reaction that I am interested in. I would like to say that I do not believe this would happen in the LHC, I would really just like to know how long this runaway process would take (regardless of the source of the strangelets). Thanks Baked Bean Bob (talk) 10:46, 17 September 2008 (UTC)

Building a Terminator

How far away in terms of technology are we from being able to build lifelike femmebots like Cameron from the Terminator TV series? —Preceding unsigned comment added by 84.69.108.42 (talk) 23:02, 16 September 2008 (UTC)

Here's something near the state of the art, which should give you an idea. --Sean 23:52, 16 September 2008 (UTC)

150 years, give or take a century. Plasticup ^T/C 23:53, 16 September 2008 (UTC)

Be aware that while robots and humans have decision tables in common only humans go to the trouble of reducing them to minimum form, converting them to classification tables and optimizing the tables to produce polychotomous keys. 71.100.15.15 (talk) 00:28, 17 September 2008 (UTC)

Take a look at Actroid and EveR-1 too (there's some good vids on YouTube too). Those can't walk, perform ballet, kill on command, hack into computer systems through streetlights, survive car bomb explosions or have brief moments of glassy-eyed self-reflection though. Yet. --Kurt Shaped Box (talk) 01:36, 17 September 2008 (UTC)

As far as we know... Plasticup ^T/C 01:50, 17 September 2008 (UTC)

I would've thought the cleverer the femme the less of a bot she's likely to be.  ;) Julia Rossi (talk) 02:36, 17 September 2008 (UTC)

"AMEE" Autonomous Mapping Evaluation and Evasion from the movie Red Planet (film) is not far away except for the power pack. 71.100.15.15 (talk) 11:03, 17 September 2008 (UTC)

Mass vs. size

I'm having a hard time with this problem: If the Earth were shrunken down to one tenth its size but its mass remained the same, what would the effect be on the Moon and its orbit? I think that there should be no effect because gravity is based only on mass, not "size." Therefore, the Moon would remain in the same orbit with the same speed. Is my thinking correct? Or where have I gone wrong and what do I need to consider that I've overlooked? Thank you!--El aprendelenguas (talk) 23:20, 16 September 2008 (UTC)

There would be no effect. The shell theorem implies that a spherically symmetric body, for the purposes of gravitational interaction with other bodies, can be considered to be a point mass at its centre. Algebraist 23:31, 16 September 2008 (UTC)

Yep, that's right. For example, if the sun collapsed into a black hole out orbit would remain unchanged, although things would get quite dark... Plasticup ^T/C 05:31, 17 September 2008 (UTC)

The shell theorm works for a perfect sphere, but not for the earth. We have tides, and the effects of the tides depend on the earth's diameter. A smaller earth will not transfer angualr momentum from earth's rotation to the moon as fast as a larger earth. -Arch dude (talk) 01:18, 17 September 2008 (UTC)

That's true - but the error would be pretty much negligable. SteveBaker (talk) 04:22, 17 September 2008 (UTC)

SteveBaker is correct, there would be an effect, but it would be very small. Raising tides on the Earth is causing the moon to gradually (very slowly!) move further and further away from Earth. If the Earth was shrunk the magnitude of this effect would change, but you would only see this is you were observing the Earth-Moon system for a very long time. — QuantumEleven 13:15, 17 September 2008 (UTC)

Yes the effect is small, but it is a real, measurable effect. The OP is clearly contemplating some major macro-engineering project, so we cannot know for sure how many aeons he has allocated for the work. I'd hate for him to come back in 4 billion years to discover that his intervention had prevented the moon from migrating to the L3 point if in fact he wss assuming that it would. -Arch dude (talk) 16:27, 17 September 2008 (UTC)

September 17

Simulation from first principles

How complex a process can modern computers simulate from first principles in our understanding of matter? I know we don't have a complete theory of matter because of tying gravity into QM, but gravity's negligible on small scales, so let's ignore that. What sort of processes can be simulated (not modeled!) just using the Standard Model? How about a single atom splitting? A grain of sand plinking another one? The first few collisions of a nuclear explosion? What can we actually calculate with no hand waving? Is the limiting factor one of computing resources or holes in the theory which cause the results to not match reality? I hope I expressed this clearly. Thanks. --Sean 00:03, 17 September 2008 (UTC)

Let's simplify this a bit. My computer has 2Gbytes of RAM - if we stored position and momentum to double precision for each particle - plus a couple of other bytes for particle type...that kind of thing - then we need 50 bytes per particle. So we have only enough space for 42 million particles in memory. If we simulated a bunch of hydrogen atoms - those are just one proton and one electron - we'd have room for 21 million atoms. Sadly there are 6x10²³ hydrogen atoms in just one gram of gas. So we can simulate about 1/3x10¹⁶th of a gram. You could store all of the particle data on disk - that would get you a couple more orders of magnitude...but certainly anything as complicated as grains of sand are completely out of the question! We could do similar estimates based on the time to do those calculations...I'm pretty sure the results would be just as depressing. SteveBaker (talk) 04:20, 17 September 2008 (UTC)

Here is an article about an IBM/LLNL research project in 2002 that researched deformation of metals by simulating the interactions of 1 billion individual atoms - this required 10 days computing time on a supercomputer. I don't think this is quite what you mean by first principles, as each atom was modelled as an indivisible particle. If you went down to the level of fundamental particles, i.e. quarks and electrons, you would be increasing the complexity by a factor of 100 to 1,000 (strong force interactions between individual quarks must be more difficult to model than the longer-range electromagnetic interactions between atoms). So probably around 1 to 10 million atoms is the upper limit for truly "first principles" simulation with current technology (which is in the same ballpark as SteveBaker's figure). Gandalf61 (talk) 09:47, 17 September 2008 (UTC)

Even a single proton—with its three quarks interacting via the eight gluon fields, which also interact nonlinearly with each other, the whole thing subject to quantum self-interference in a phase space of uncountably many dimensions—is far too complex to simulate exactly. All simulations are approximations. I'm not sure that modern physics even has first principles. There's no axiomatic formulation of the Standard Model; the path integral that it's based on doesn't seem to be mathematically well defined, and it can only be "evaluated" using various tricks. I guess there's an analogy with the calculus, which didn't get a rigorous formulation (the epsilon-delta limit stuff) until long after Newton successfully used it to do physics. But I think it's a fairly common view among particle physicists that the Standard Model will never be formulated rigorously because it really isn't rigorous—it's nothing more than a collection of approximation techniques (for the real, unknown physics) with no "exact approximation" at the core. -- BenRG (talk) 10:56, 17 September 2008 (UTC)

OK, thanks to all for the depressing answers. I knew it was bad, but I didn't know it was that bad! --Sean 13:33, 17 September 2008 (UTC)

I think you'd be fairly horrified about the state of computational physics even at the macro scale. There are many physics engines for performing nothing more complex than Newton's laws of motion on human-scaled objects under gravity and friction. You'd think that the superbly well-understood physics on simple bodies like a dozen or so cuboids would be child's play to simulate - yet even those super-simple things are VERY hard to get right. Even the very best simulations tend to be heavily restricted in what can be done - with a horrible tendency to blow up and generate ridiculous forces and accellerations.

The problem tends to be that time is a continuous function in the real world - but inside a computer it pretty much has to be quantised at a fairly gross level (like maybe 1/100th second increments). Also, in the computer, we don't have infinite precision and precision errors can "leak" energy.

Some current software that works in this area would fail if (for example) you simply made a large stack of cubes - like a tower maybe - stack the cubes perfectly and have them all completely stationary. The collision detection code would have small roundoff errors that would make the cubes vibrate because they were bouncing up and down under gravity at distances that were at the smallest that the computer could resolve. Those vibrations would "leak" energy from nowhere into the system and the whole pile of cubes would start jiggling and bouncing at large scales until the whole pile would collapse with no external forces being applied beyond simple gravity. We're getting better at fixing those problems - but it's generally via ugly kludges that show up under all sorts of subtle special-case conditions.

SteveBaker (talk) 16:07, 17 September 2008 (UTC)

I know what you mean about the game packages. I was amazed when I learned that you can have a whole company whose only product is software to make a person's body look natural when it's falling down, but now I see those kinds of things all the time. --Sean 17:36, 17 September 2008 (UTC)

Yep - absolutely. "Ragdoll physics" are very important to many games. When the character is running around and under "intelligent" control, you can pretty much prerecord animations in a motion capture suite - but when they die and just fall to the ground, they need to behave in a physically reasonable way or it looks laughable. Since in so many games, a large fraction of the "action" entails killing people - they'd better look realistic when they die. That stuff is a pain to set up with a solid body physics package - so if you can buy a chunk of middleware that'll handle that for you - then it's worth having. SteveBaker (talk) 21:37, 17 September 2008 (UTC)

Streamlined intergalactic ship

On a very hypothetical, sci-fi basis, would it make sense for a spaceship traveling at a meaningful percentage of the speed of light to be streamlined as, at these speeds, the near vacuum of the integalactic or interstelar space is experienced as quite dense? Does that makes sense? What could we compare it to that can be intuitively understood? Thank you. 190.244.186.234 (talk) 00:36, 17 September 2008 (UTC)

Probably not. You're right that the interstellar medium would be a real issue at relativistic speeds. However, it's an issue that would have to be solved regardless of ship geometry -- you can't plan for some chunk of your ship to be constantly bombarded by hard gamma rays. As such, once you've solved the problem, it's likely a solution that can be applied across the board -- something like a Bussard ramjet would work just as well for a Borg cube as the starship Enterprise. — Lomn 02:09, 17 September 2008 (UTC)

There must be a range of speeds at which streamlining would help - and the difference in speeds between what would require streamlining and what would need yards of lead shielding could maybe be the difference between (say) 95% of the speed of light and 99%...not a great deal in terms of getting where you want to go. SteveBaker (talk) 03:09, 17 September 2008 (UTC)

There has to be some benefit from having a smaller surface area exposed to vacuum. Plus it looks much cooler (or more intimidating if you run into potential unfriendlies out there). Clarityfiend (talk)

It's sci-fi. Who cares? If you want the ship streamlined, invent some science that articulates why it needs to be that way. If you want it shaped funny, write the science some other way. It's the beauty of suspension of disbelief. --Shaggorama (talk) 07:23, 17 September 2008 (UTC)

Presumably he cares. That's why he asked. APL (talk) 20:56, 17 September 2008 (UTC)

I don't believe that there is any speed you could travel at under which conventional compressive drag would occur (but see caveat later). For that a particle you hit has to rebound into some other particle(s) and then either it or they hit your ship again before you've moved out of the way (that in you're effectively compressing the fluid before you, and that compression pushes you back). In a dense medium like water that's overwhelmingly likely to occur, but in the ultra low density environment of intergalactic space I think you'll find that the initially incident particle is so incredibly unlikely to hit another particle in the timeframe involved that you'll get no rebound and thus no "drag". [Things would be different if you C wasn't a limit, and surely at some impossible hyper-duper-C speed then you'd be hitting so many particles that the rebound probabilies became inevitabilities.] But you still have to worry about collisions, and at near-C speeds hitting even tiny motes of matter is going to be like being shot with a tank shell. Being shot by a tank shell has two demerits - momentum transfer (in this case you slow down a bit) and physical damage (it hurts). The solution, one your spaceship will need, is the same as employed by tank designers - a sloping hull. The more sloping the more glancing the blow, the less momentum you lose, and the less damage you take. I don't think Clarityfiend's concern about surface-to-vacuum would be a concern, because there's no need for that pointy "impact plow" to be filled with air or otherwise be habitable. It's a lot like the sea hull of a submarine - the submariners live in an ugly squat sausage-shaped pressure hull, which is surrounded by the elegant but unpressurised sea hull. SteveBaker's feelings regarding shielding are, however, I think well founded. Blasting around the universe at near-C is like being the projectile in a CERN experiment - all kinds of scary science impacts are going to be happening on the surface of the impact plow, giving off heat (in the plow) and gamma radiation and probably all that stangelet-blackhole-darkmatter disaster stuff that won't happen to CERN but will to you. So that's the front of your ship designed - it's got a super-pointy impact plow (maybe 2 km long and 100m in diameter) filled up with DU. After that there's a 2km pole at the end of which is your living module (where you and your chums live in a colour-coded-unitard utopia). Now for the back end. Let's face it, you're not going anywhere fast with those lefty-wefty renewable sustainable bussard organic macrame power sources; if history shows us anything, it's that to get anywhere fast you have to burn lots of evil fuel and leave a big mess. So behind your living module is another long pole, at the end of which is the propulsion module, wherein some faustian science horror occurs (bashing white holes into black holes, sacrificing bunny souls to Legba, etc.). Armed with this you can happily blast around the universe, and you can probably even bash on through planetary space, sterilizing the planets of impressed natives with the hard x radiation from your engines. Just don't try turning a corner. -- Finlay McWalter | Talk 22:28, 17 September 2008 (UTC)

Awesome! A round of applause for Finlay please!

Within the Milky Way - there are about a million particles per cubic meter...and it's almost all hydrogen and helium. But here on earth there are 2.5x10²⁵ of them per cubic meter. (That's the Loschmidt constant BTW)...so (naively) to encounter the same number of particles per second as an earthbound airplane flying at (say) 100 kph, your starship would have to be moving at 100kph x 2.5x10²⁵ / 1,000,000 - which is 2.5 x 10²¹kph - however, the speed of light is only 10⁹ kph - so at first sight, we never need streamlining.

However, as your speed approaches that of light, relativity starts to cause distances along your line of flight to become compressed - and also to increase the mass of the particles you're encountering - so that there will indeed be a speed at which the tenuous particles of deep space will seem exactly as dense as air to a regular airplane. The closer you get to the speed of light, the denser that interstellar medium becomes.

The tricky point is at that the kinetic energy these little particles release when they hit your starship depends on your velocity as well as their mass. So the energy of those collisions with the skin of your starship start to cause unacceptable amounts of damage - does that happen before or after the aerodynamics of it kick in?

SteveBaker (talk) 05:55, 18 September 2008 (UTC)

Actually you start to get chemical reactions between impacting particles and the hull when the energy is a few tens of eV per particle. For hydrogen, that occurs at ~50 km / s, i.e. 0.01% of the speed of light. Beyond that it is basically impossible to design a hull that wouldn't be eroded by impacting particles. The space shuttle has similar issues on re-entry (it reaches ~8 km/s during the fastest part of re-entry), and the heat shield is specifically designed to survive the partial erosion during the trip. Incidentally, and in response to Finlay, the speed of sound in the galactic medium is "only" ~100 m / s. So to the extent that traditional drag matters in an environment with extremely low pressure, it certainly should start to matter before you cross the "sound barrier", though I would expect that drag would still be pretty negligible. Dragons flight (talk) 06:41, 18 September 2008 (UTC)

Zucchini and squash

I've been growing Zucchini and squash. I've noticed that ants (and some other insects) seem to be crawling on them. They also seem to have been attacked by Leaf Miners. Are they safe to eat? 67.150.174.6 (talk) 00:58, 17 September 2008 (UTC)

As Leaf miners are in the leaves they won't affect the fruit and ants etc can be washed off. Some green conscious solutions are squirting the fruit with detergent diluted in water + garlic juice to discourage crawling insects. The stub article suggests companion planting rather than insecticide to help the miners problem. Julia Rossi (talk) 02:33, 17 September 2008 (UTC)

Just wash em off and chop em up. Unless the food looks rotten, I wouldn't be too concerned. Ants are everywhere in Brazil; if you find any in your food the locals usually just laugh it off, saying "they're good for the eyes" before chowing down. --Shaggorama (talk) 07:21, 17 September 2008 (UTC)

minimum size for a planet

Part of the definition of a planet is that it be massive enough to form a sphere. Given the type of material that makes up the bodies beyond Neptune, what would be the minimum diameter for a planet? --Halcatalyst (talk) 01:44, 17 September 2008 (UTC)

The definition of a planet is a sphere? I've got a football in the back garden, and I am pretty sure it's not a planet.--ChokinBako (talk) 11:54, 17 September 2008 (UTC)

Did this ball aggregate under its own gravity to form a sphere? Remarkable! --Scray (talk) 15:25, 17 September 2008 (UTC)

Right - so the definition specifically DOESN'T specify a minimum mass. In fact, Pluto (that famous non-planet!) is sufficiently massive to form a sphere - but it's STILL not a planet because mass isn't the only criteria. It isn't a planet because it has failed the "Clearing the neighbourhood" test. (check out Plutino to understand why not).

If we discount the "clearing the neighbourhood" bit - then perhaps your question is "How large much an object be to have sufficient gravity to pull itself into a sphere?" - (well, technically "to reach hydrostatic equilibrium" - the Earth is not a perfect sphere) then I guess there is a different answer. The trouble here is that when a body is a liquid, it takes very little gravity to do the job - if it's made of solid ice or nickel-iron, then it takes a great deal more gravitation to do the job. Consider 4 Vesta - which is a mere 530km across and is believed to have gained hydrostatic equilibrium when it was still a molten blob, but which is now a very non-spherical shape due to meteor bombardment and cannot regain a spherical shape because it's now solidified. On the other hand, Ceres is still spherical and is 950km across. So I suppose we could say that for a SOLID body - the limit is somewhere between 530km and 950km diameter - but for a liquid body, the limit is less than 530km...arguably, there is no lower limit for a liquid body because even a single water droplet assumes a spherical shape in zero g (although it is the surface tension forces that dominate in that case).

SteveBaker (talk) 03:00, 17 September 2008 (UTC)

It is very hard to say what would be the required mass, as, indeed, it depends both on the composition and on the conditions in which the said planet was formed. These things are almost impossible to predict. We don't know the internal composition of Trans-Neptunian objects, so theoretical predictions for the required mass may vary substantially. TNOs are also nearly impossible to optically observe with decent resolution, at least at the present state of technology, so we also do not know for sure which are round and which are not. It is, however, reasonable to assume, based on observations, that Eris and Sedna are round, as possibly are some smaller TNOs; (136108) 2003 EL61 is probably not round, but that may be due to its fast rotation. For the smaller objects the shape can not be determined with acceptable accuracy at present. That puts the upper limit on the required mass at the order-of-magnitude of (1-3)*10²¹ kg; but it may be lower than that. Hope this helps. --Dr Dima (talk) 03:39, 17 September 2008 (UTC)

As of today 2003 EL61 is called Haumea. Rmhermen (talk) 21:08, 17 September 2008 (UTC)

Regarding the "liquid body" suggestion - well, it is highly unlikely to find a drop of liquid in space, because it does not have enough gravity to prevent its vapor from escaping. Thus, the vapor pressure will be lower than the solid-liquid-gas triple point, and the drop will eventually boil out (or partially boil out and partially freeze - that depends on initial temperature and the final steady-state temperature). However, an aggregate of loose solid material may form a sphere at arbitrary low mass, if it remains unperturbed. That was not the original question. The original question was, as SteveBaker correctly noted, what is a smallest required mass for a compact but not spherical object with a solid surface at temperature of a few tens of Kelvin and density of a few g/cm³ to gravitationally produce enough internal pressure to be able to assume hydrostatic equilibrium. The inner parts of the object need not be solid in this process, though. They may be liquid or solid-liquid mixture due to residual heat, compression heat, radioactive decay, etc. --Dr Dima (talk) 04:05, 17 September 2008 (UTC)

Sebaceous gland

Apparently, a Pimple is when the Sebaceous_glandSebaceous Gland blocks usually from the skin thickening or something. However a Sebaceous_cystSebaceous cyst is the same. Is there any explanation for this? —Preceding unsigned comment added by 70.89.49.205 (talk) 03:36, 17 September 2008 (UTC)

A pimple is always infected whereas a sebaceous cyst need not be. The latter are larger and located deeper in the subcutaneous tissue whereas pimples are more superficial. --Scray (talk) 12:52, 17 September 2008 (UTC)

Gasoline/alcohol mixture

The other day as I was filling up my truck, I noted that the pump had "may contain up to 10% ethanol" on it. If I remember my high school science, alcohol burns cleaner than gasoline. So my question is twofold: first, what would be the optimum mixture of gasoline/ethanol to get the most efficient and clean burn? 10%? 25%? 50%? Second (local moonshine laws notwithstanding), could one simply add ethanol to their gasoline tank(i.e. mix it with the gasoline) and still run their vehicle? Can a gasoline engine run on "pure ethanol?" OK. My queery was three fold. :) Thanks —Preceding unsigned comment added by 216.154.17.110 (talk) 03:49, 17 September 2008 (UTC)

Ethanol#As a fuel says that Brazilian gasoline contains 25% ethanol and over 20% of cars there can run on 100% ethanol, using ethanol-only and flexible-fuel engines. Clarityfiend (talk) 04:35, 17 September 2008 (UTC)

Don't take Clarityfiend's comment as meaning that you can just pour everclear in your car and go for a drive. Cars that run on 100% ethanol have engines that were designed to accept ethanol as their primary fuel. Gasoline engines can tolerate some ethanol in the fuel mixture, but only so much. If you want to run your car on ethanol, you'll need to convert your engine. In Brazil, alcohol is cheap because of how much sugarcane they produce, so ethanol is available at most gas stations. I'm gonna guess that's not the case where you live, so you may want to stick with the gas/ethanol mixture from the pump. --Shaggorama (talk) 07:16, 17 September 2008 (UTC)

Ethanol produces a little less energy per gallon than gasoline - and in small doses, most modern cars tolerate it quite well. However, older cars suffer because ethanol dissolves rubber - which does bad things to rubber fuel lines. Ethanol also conducts electricity quite well (gasoline does not) - so some fuel pumps and fuel gauges that are immersed inside the gas tank will short out and fail. However, fixing those kinds of things isn't difficult. The most significant change that most engines need is to have their engine management computer adjusted (perhaps reprogrammed) to deal with the different mixture control you need in order to optimise performance. The biggest problem in Brazil is that their cars are generally poorly converted from gasoline to run on ethanol - and for some reason, their converted engines don't start well on ethanol. Hence most cars there have a small gas tank and a switch on the dash that lets you switch between gasoline and ethanol. So you put the switch into the gasoline position, start the engine - and when it gets up to operating temperature, you switch over to ethanol.

Most cars that claim to be able to run on Ethanol here in the USA are actually only able to run on "E85" - which is a mixture of 85% ethanol and 15% gasoline. I believe that E15 (15% ethanol 85% gas) is what we're currently limited to with "normal" cars. E100 is available only in a few countries - I know Brazil is one...I believe there are a handful of others.

I restore classic cars - and for me, even E15 is a major problem because some of my cars are old enough (1960's) to have rubber seals and rubber hoses all over the place - and running on E15 is going to gradually kill my cars. Rumors of having E25 in US gas stations is pretty worrying. I can usually replace those rubber parts with modern plastic seals and steel hoses - but then they won't be "authentic" or "original" anymore...sigh.

SteveBaker (talk) 13:13, 17 September 2008 (UTC)

Ethanol also preferentially absorbs atmospheric and liquid water, which I think may cause problems. A little bit is good, it will form an azeotrope with the contaminant water in the bottom of your fuel tank; but lots of it will start absorbing water from the air too. Franamax (talk) 09:00, 18 September 2008 (UTC)

Light

Is there a material that changes opacity/scatters more or less light when subject to electric field? How is that effect called? —Preceding unsigned comment added by 89.201.134.211 (talk) 03:51, 17 September 2008 (UTC)

Take a look at the Electro-optic effect with an affect called electroabsorption. Graeme Bartlett (talk) 04:57, 17 September 2008 (UTC)

Liquid crystals can be made to do that - what they do is to change the plane of polarization of the light when you apply a voltage to them - so if you stick a sheet of polarizing film in front or behind the liquid crystal, you can effectively block light or allow it through using small voltages. This is how all manner of displays work - everything from digital watches to flat screen TV's. SteveBaker (talk) 12:59, 17 September 2008 (UTC)

Some other designs of liquid crystals don't rotate polarization but instead become turbid under the application of an electric field. These are used in those windows that magically become translucent and then transparent again (as seen in The Sum of All Fears, although that may be a CGI effect and also at Disneyworld's Star Tours warm-up show). For more information, see our not-so-hot Dynamic Scattering Mode article.

Atlant (talk) 18:28, 17 September 2008 (UTC)

Crickets Chirping

I have a cricket chirping LOUDLY just outside my bedroom window. It's driving me nuts! How long will this likely go on? Weeks? Months? 168.103.225.108 (talk) 04:28, 17 September 2008 (UTC)jmic

I suggest bug spray. Those with more compassion for nature might suggest waiting a few hours. I think it is unlikely that the cricket will stay there for too long. Plasticup ^T/C 05:29, 17 September 2008 (UTC)

If you have a tape recorder, record the cricket chirping. Play it back from a safe distance away from the house; the cricket will eagerly jump towards you. --Kjoonlee 07:22, 17 September 2008 (UTC)

Outdoors, it may eventually go away - but if one gets indoors, it can be absolutely maddening. They are smart enough to stop chirping when you walk around nearby and it's almost impossible to figure out where they are in the room. They also seem to live for weeks without food before they finally "just die already" and stop the incessant racket. We've resorted to bug spray in desperation. SteveBaker (talk) 12:55, 17 September 2008 (UTC)

Lucky you don't live near rice fields. I get billions of frogs banging away all night during the mating season. Nothing I can do about them! (By 'banging away' I mean shouting, trying to attract a mate, not actually what I just said....).--ChokinBako (talk) 14:15, 17 September 2008 (UTC)

You don't have to live near rice fields. Here in New England, "peepers" will keep you up if you're sensitive to that sort of thing. Presumably, they're saying the same thing as their rice-loving cousins, but with a Bahstahn accent.

Atlant (talk) 22:19, 17 September 2008 (UTC)

How does business units monetize their AR with bank and what are the criteria to be met?

Every BU sells some goods on credit, however to meet their working capital demands, they need to influx money which they borrow from Financial institutions. The question is what is the process of Monetizing the Receivable? How is that different from Leverage? What are the nitigritties of monetization of the AR?

Answers will be highly appreciated.

Thanks —Preceding unsigned comment added by 203.201.226.253 (talk) 07:15, 17 September 2008 (UTC)

I only hear Crickets_Chirping in response to your question on this Science desk. Maybe Wikipedia:Reference_desk/Miscellaneous would be a better place to ask? --Scray (talk) 12:47, 17 September 2008 (UTC)

I think you're describing an example of an Asset-based loan. Basically, if the borrower pledges its accounts receivable as security for the loan, it will pay a lower interest rate. Also see Factoring (finance), which is basically a sale of AR. Btw, RD/H is probably better. Zain Ebrahim (talk) 13:43, 17 September 2008 (UTC)

H2O mixed with CO2

If the molecular weight of the first is 18 and of the second is 117, shouldn't CO2 go down?Mr.K. (talk) 12:10, 17 September 2008 (UTC)

Density is not determined by molar mass. --Scray (talk) 12:44, 17 September 2008 (UTC)

...and if you doubt that - think about how liquid water is denser than steam - and how ice floats on liquid water because it's less dense. All of those things are H2O - but they vary immensely in density. SteveBaker (talk) 12:51, 17 September 2008 (UTC)

Note that the exception to the above is if both are gases. If you're talking steam, then you're correct -- but a steam/CO₂ mix is an uncommon scenario. — Lomn 12:53, 17 September 2008 (UTC)

What about exhaust from burning hydrocarbons? (admittedly these will commonly be mixed with nitrogen and other gases) AlmostReadytoFly (talk) 13:37, 17 September 2008 (UTC)

Ummm, 12+16+16=4844? And yes CO2 is denser than H2O (Avogadro's law and all that) but when mixed, the molecules are moving around really fast (speed of sound), so, in usual circumstances, they're very well mixed. Saintrain (talk) 14:37, 17 September 2008 (UTC)

Yes, I meant CO2 is 44. Actually Co2 is 117....Mr.K. (talk) 15:28, 17 September 2008 (UTC)

What's Co2? 2 x ⁵⁹Co = 118? Or something else? Saintrain (talk) 16:24, 17 September 2008 (UTC)

The isotopes of cobalt range in atomic weight from 50 u (50Co) to 73 u (73Co).Mr.K. (talk) 17:29, 17 September 2008 (UTC)

Yup, it's always about density if the materials don't mix and it's also about diffusion and intermolecular attraction if they do. As a kid, I was always confused why humid air rises ("water is heavier than air!"). Except it's not liquid water vs (gaseous) air, but rather water vapor compared to air. Water weighs 18 g/mol, air is mostly nitrogen, which weighs 28 g/mol. A mole of any gas has approximately the same volume, so now it's obvious that the less dense water would tend to rise compared to the more dense air. DMacks (talk) 14:52, 17 September 2008 (UTC)

The humid air tends to be warmer, too? --Scray (talk) 15:02, 17 September 2008 (UTC)

Yes, but backwards. As air cools, the net amount of condensation will increase (taking water out of the air and depositing all over my car). Say, rather, that warmer air will tend to have more humidity. Matt Deres (talk) 20:31, 17 September 2008 (UTC)

Shards of pottery

I have noticed that in all of the pictures of exposed Terra Preta, such as Amazon Pit with Scientists the shards of pottery lie spaced and horizontal at various depths as if individually placed and them covered as opposed to piles with shards at different angles, as one might find in a garbage heap or Midden. From this I assume the use of the shards is intentional but for what purpose? 71.100.15.15 (talk) 14:22, 17 September 2008 (UTC)

I profess no special knowledge here, but would it be possible that the method of excavation favored retention of horizontal shards? Wouldn't pottery shards tend to be somewhat level in a pile anyway? --Scray (talk) 15:13, 17 September 2008 (UTC)

As you can see in the photo there are no piles. Individual pots could be represented but neither the pieces or the pots are one on top the other but rather spread out. If dumped with other garbage and trash the pieces would have a tendency to angle. 71.100.15.15 (talk) 21:55, 17 September 2008 (UTC)

Even within a midden, many of the pieces will horizontal. Let's look at the process involved (yes, I have been trained in archaeology): whether the shard gets tossed into a midden or simply gets left in the walkway or falls through floorboards in more modern sites, the pieces will come to rest just as you'd expect - lying flat. As dust, dirt (and in the case of middens, decomposing food) comes to build up on top the pieces, the effect of making the shards horizontal increases. Where you see vertical shards is when the midden is so full of something dumped all at once that there's no time for each piece to "find its level" or where a larger piece has been broken post deposition with enough dirt and junk around it to support it standing upright. Trying to leave pieces in that way intentionally would be time-consuming and a little pointless (as you alluded to) and would not likely fool a trained archaeologist for long. (On that last point, leaving those bits in place, even with them hanging like that, is the mark of someone who's doing the dig in a very thorough, "by the book" manner). Matt Deres (talk) 16:31, 17 September 2008 (UTC)

Terra preta seems to be more of an engineered soil than a garbage dump. It may be reasonable to expect that the potsherds would be systematically laid - if there was cultural knowledge on how to produce terra preta. Since this soil seems widespread in the presumptive area of cultural knowledge and has high productivity, the possibility remains that there was a defined and careful formula for how to make terra preta. Franamax (talk) 08:46, 18 September 2008 (UTC)

What weighs one centigram?

What are some common objects that weigh one centigram?

--80.148.22.232 (talk) 15:12, 17 September 2008 (UTC)

A large grain of sand. --Scray (talk) 15:16, 17 September 2008 (UTC)

A raindrop. (Assuming about 3 to 4mm diameter). SteveBaker (talk) 15:51, 17 September 2008 (UTC)

Might want to tell your friends about that Orders of magnitude (mass) page. Just a few days ago, someone from your same IP asked a very similar question...would be good for everyone to learn about the solution to this type of question rather than just the specific answer to a specific metric-prefix. DMacks (talk) 16:13, 17 September 2008 (UTC)

Why does depression affect concentration?

I've been told that trouble concentrating is a symptom of depression. So I've been wondering if depression's affect on concentration is a chemical symptom or something psychological, does anyone know why concentration is affected by depression? —Preceding unsigned comment added by Mr.K. (talk • contribs) 16:27, 17 September 2008 (UTC)

IMO the short answer is that the effect is "both" chemical and psychological. The longer answer is that they are the same thing, just seen from a different point of view. Wanderer57 (talk) 17:06, 17 September 2008 (UTC)

pls help me with these question

--203.199.213.67 (talk) 17:03, 17 September 2008 (UTC) this book became a minor internet phenomenon when it was reviewed by users of a forum some of whom described it as genrebreaking master piece,while others mentioned that they found it better than the davinci code.another claimed it may cure insomnia,while somebody stated that it provided him with the phone no. of his future wife,pls tell me what is this all about?

It could be anything - those are pretty generic comments that people routinely make about any number of books (other than the phone number bit - that's the only real clue, but I don't recognise it). You would be better off on the miscellaneous or entertainment desks, though - this isn't a science question. --Tango (talk) 18:21, 17 September 2008 (UTC)

Or Humanities... some of those folks appear to read books now and then. (BTW, where are you getting these claims from? That might be a clue.) -- Coneslayer (talk) 18:27, 17 September 2008 (UTC)

The Secret?Avnas Ishtaroth _{drop me a line} 01:35, 18 September 2008 (UTC)

It may cure insomnia? Doesn't exactly sound like a rave review. BTW, are you the same person who asked this [34] or is this question going around for some reason? As for the future wife thing, maybe this guy [35] can help you Nil Einne (talk) 09:16, 18 September 2008 (UTC)

over the counter medicatons

what over the counter medications contain benzoylecgonine?? —Preceding unsigned comment added by 24.17.22.80 (talk) 18:13, 17 September 2008 (UTC)

According to this, small amounts of cocaine are found in Health Inca Tea which can be purchased without a prescription. I guess that doesn't answer your question, but it's another way that benzoylecgonine might show up in the body. The article also says that cocaine is sometimes an ingredient for topical medications from ears/nose/throat doctors. Cocaine is metabolized into benzoylecgonine in the body, so it doesn't seem likely that benzoylecgonine would be a component of OTC medications. —Preceding unsigned comment added by 98.210.62.147 (talk) 20:55, 17 September 2008 (UTC)

Copper Sulphate

Copper sulphate is a white powder as a solid compound. Yet, when dissolved in water, why is its solution blue? Luthinya (talk) 20:37, 17 September 2008 (UTC)

When dehydrated (by heating for example), copper sulphate is white or grey. When it absorbs water, it turns bright blue. There are photos and more information in the article Copper(II) sulfate, for example in the section "Chemistry education". Wanderer57 (talk) 20:59, 17 September 2008 (UTC)

Needles in your thigh

I hope I've managed to ask this question in a way that makes it clear that I'm not asking for medical advice. If not, please delete the question.

I would like to know the correct term (for googling purposes) for a specific type of treatment that I've been subjected to. The treatment consists of a physiotherapist putting needles into trigger points in the iliotibial tract, supposedly for releasing tension in the muscles attached to it, for treating iliotibial band syndrome (yes, I've been running too much, too often, too fast, and increased the distance too soon). Sensing my scepticism, she assured me that it had nothing whatsoever to do with acupuncture. The treatment is given as a supplement to excersises that aim to stretch the lilotibial tract, and excersises that aim to strengthen the gluteal muscles. My questions are:

• what search terms will give me the most relevant hits for this treatment on google?
• ditto on pubmed?
• do we have a page on this treatment?
• is anyone aware of placebo-controlled studies on this treatment, for iliotibial band syndrome or other similar conditions?

Thanks, --NorwegianBlue ^talk 20:52, 17 September 2008 (UTC)

Do they run an electric current through the needles or just poking you with needles? --antilived^{T | C | G} 06:23, 18 September 2008 (UTC)

Sorry, should have mentioned that. This time, needles and no current. Next time, they're planning to run an electric current through. --87.54.16.18 (talk) 06:42, 18 September 2008 (UTC) (NorwegianBlue not logged in, from a hotel PC)

This sounds a lot like electro-stimulation. Myo-stimulation is not uncommon, they have a weight-loss deal that does the same sort of thing, only from the surface. The difference is skin penetration, which will dramatically lower the overall electrical resistance. You haven't mentioned the proposed penetration depth or voltage, and we're not able to adequately judge either. Asking for controlled study ref's is bordering on medical advice, or at least opens the possibility of POV's creeping in - which is part of the medadvice stricture, really. You might be better to ask your practitioner for references from the Medical Review Board which approved the procedure. Get some good names and numbers, then we can search the heck out of it. Franamax (talk) 08:20, 18 September 2008 (UTC)

Quote?

I need a good quote on technology, that has enough information to cite it fully in MLA. Can anyone help? I can't seem to find anything useful with google. —Preceding unsigned comment added by 99.237.213.17 (talk) 21:58, 17 September 2008 (UTC)

One Charles Lindberg goes "I have seen the science I worshiped, and the aircraft I loved, destroying the civilization I expected them to serve." I find it pretty fitting as a technology/sociology quote, though perhaps if you're thinking more positive-impacts it wouldn't be any good. ny156uk (talk) 22:28, 17 September 2008 (UTC)

What kind of "good" quote? Pro-technology? Anti-technology? Something else? Straightforward? Cryptic? Interesting? It would help us a lot if you would give some description of what it was to be used for and what you need it to be "useful" for. "Technology's essence is nothing technological," was Heidegger's classic take on it. --98.217.8.46 (talk) 23:32, 17 September 2008 (UTC)

There are so many great quotes to choose from. But I'd have to go with: "Any sufficiently advanced technology is indistinguishable from magic." - Arthur C Clarke.

Or maybe: "For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled." - Richard P. Feynman

May I also recommend our sister site "http://en.wikiquote.com" - type "Technology" into the search box...enjoy! SteveBaker (talk) 05:05, 18 September 2008 (UTC)

Side note: enjoy Wikiquote while you can, it might be gone soon. Franamax (talk) 08:04, 18 September 2008 (UTC)

Blood as an indicator of pain

I get the impression that my brain is 'hardwired' to associate blood/bloodyness with pain. My question is: How good a correlation is it? If I cut myself shaving or get a nosebleed it doesn't hurt yet it can look pretty brutal. If I get a nasty cut it can really hurt but not cause much blood. Is it just a failing in my brain that causes the association (a failing in everyone's brain?) or is blood (and blood volume) a good indicator of pain/danger? Obviously lots of blood loss is a bad thing so that's why i'm thinking "yes". ny156uk (talk) 22:28, 17 September 2008 (UTC)

I would not expect this to be strongly hard-wired, since humans are omnivores and fresh bloody meat was no doubt something to celebrate, at some point in our history at least. --Scray (talk) 00:11, 18 September 2008 (UTC)

I would say that the greater association is the appearance of blood with an expectation of pain. This may be learned/reinforced from childhood - if you show up covered in blood, your parents adopt a somewhat odd response, what with the screaming and "oh you poor thing" reactions. Evolution will also program you to be more aware of your own pain sensations when you see flowing blood, you have a compelling interest to be sure it's not your own. That said, I tend to get more supreme pain from paper cuts and that grass with the sharp edges (ragged cuts) whereas I've clean-cut myself to the finger-bone and been quite clinical about the affair. Franamax (talk) 07:59, 18 September 2008 (UTC)

Cell-biology experiments outside the cell

Is there an umbrella term to describe experiments performed outside the cell in the same way that in vitro describes those outside the complete body? ----Seans Potato Business 23:38, 17 September 2008 (UTC)

Perhaps cell-free is the term you're looking for (e.g. cell-free transcription/translation systems). By the way, ex vivo is used for experiments done outside the body, too - the distinction between that and in vitro is subtle. --Scray (talk) 00:05, 18 September 2008 (UTC)

We have a Cell-free_system page! --Scray (talk) 00:06, 18 September 2008 (UTC)

The problem with cell-free system is that it's typically used only where the process in question is usually assumed to take place inside a cell, and the author wants to explicitly flag to the reader that something special is going on. ('Cell-free translation system', per your comment, is a good example.) In vitro is often used to describe 'test tube'-type experiments outside cells as well as for experiments in petri dishes; the specific sense will vary from field to field and is usually (but unfortunately not always) clear from context. In describing in vitro experiments that take place inside cells, I've sometimes seen in cellulo used. (The term gets a few thousand Google hits, and is even showing up on PubMed now, in peer-reviewed research.) There's no opposite term I'd feel comfortable using in formal writing, however in casual conversation I've heard ex cellulo—usually accompanied by finger quotes and slightly raised eyebrows. TenOfAllTrades(talk) 01:50, 18 September 2008 (UTC)

Agreed on all accounts. For the OP's question, I wonder if the Community would accept extracellular and dispense with the pretend Latin? Seems simple and clear to me (lack of sophistication obvious, I suppose). --Scray (talk) 03:13, 18 September 2008 (UTC)

My concern with extracellular is that (in my experience, at least) it implies that cells are present, but the reaction or process just happens to be happening outside the cell membrane. A word like acellular might be a little better (emphasizing the absence of cells) but I don't think I've run across it being used that way in the wild. TenOfAllTrades(talk) 03:54, 18 September 2008 (UTC)

Agreed. Acellular if no cells are present in the same container, extracellular if they are present. --Scray (talk) 03:59, 18 September 2008 (UTC)

I'll agree with all that, but if an experiment is carried out with no functional cells present to modulate the reaction, either intra- or extra-, wouldn't it be called, I dunno, chemistry? Franamax (talk) 07:45, 18 September 2008 (UTC)

September 18

dous anyone know how a solar panal works without the who made it stuff?

The science fair is coming up soon and i cant find any info on a way that a solar panal works theres all these words that lead to another word that lead to another word isthere an easy explination ive checked everywhere and it says stuff about photons electrons and stuff and it dousnt say how the electricity is created if anybody can help me on this with an easy explination please answer —Preceding unsigned comment added by Arkamond (talk • contribs) 00:42, 18 September 2008 (UTC)

There's a quite plain-language "Simple explanation" in the "Theory" section of the Solar cell page. Remember that electricity is just flowing electrons. DMacks (talk) 00:48, 18 September 2008 (UTC)

You will need to understand what a Photon and an Electron is before you understand how a solar panel works. If you can't understand at least the introductions to those articles then you may prefer the Simple English Wikipedia. (Simple English articles on Photon and Electron ).

Hope this helps. APL (talk) 01:06, 18 September 2008 (UTC)

"Photons" are little packets of light. "Electrons" are little packets of electricity. Basically. The photons (light) from the sun hits the special materials. These materials are special because of photons of the right sort (those from the sun, for example) hit them, they will knock loose electrons from the atoms in the material. These loose electrons run through the material—and moving electrons are basically an electric current. This is then siphoned off and fed into an electrical system as generated power. Does that help at all? --98.217.8.46 (talk) 01:12, 18 September 2008 (UTC)

COCONUT SEEDS

WHAT HAPPENS TO A COCONUT SEEN IN THE WATER?

HOW DOES A COCONUT SEED'S ABILITY TO FLAT HELP A NEW COCONUT TREE TO GROW?

HOW MIGHT THE HARD SHELL OF A COCONUT HELP A NEW COCONUT TREE GROW? —Preceding unsigned comment added by 71.246.121.96 (talk) 00:55, 18 September 2008 (UTC)

I'm afraid you're going to have to do your own homework. But you might be interested in reading our article on Coconuts. APL (talk) 01:08, 18 September 2008 (UTC)

WHAT? - WE CAN'T HEAR YOU! Oh, that's better ;-) -hydnjo talk 02:25, 18 September 2008 (UTC)

(Meaning: please don't type in all capitals, it's often considered rude or angry on the internet:) If you have any questions after reading our article on Coconuts, please come back here and ask them. Franamax (talk) 07:38, 18 September 2008 (UTC)

Transparent and reflective at the same time !

Is there any kind of glass that is transparent to light rays when light incident on it from one side and reflect light rays when light is incident upon the glass from the opposite side ? —Preceding unsigned comment added by Shamiul (talk • contribs) 04:56, 18 September 2008 (UTC)

In theory no, the principle of reciprocity holds. But you can get semireflective mirrors that reflect 80% and let through 20%. When the other side is dark, like sunglasses, you can see out through it. But you can get different effects if the angle of incidence is different, as in total internal reflection. Graeme Bartlett (talk) 05:13, 18 September 2008 (UTC)

Two-way mirror? Clarityfiend (talk) 07:25, 18 September 2008 (UTC)

Also called a one-way mirror. Yes, that's what Graeme is talking about. --Anonymous, 09:15 UTC, September 18, 2008.

Lithium Batteries (Elephant Tripling)

I'm not coming to this pure, I just watched Colbert interview Bob Lutz, who kinda trashed his own battery vehicle , but it's a question I've been pondering. It seems that for hybrid and EV passenger cars to progress: lead-acid batteries won't cut it based on the power/weight ratio; NiMH is too limited (dendrification?); and lithium Lilon batteries are the way to go.

The question being, where does the lithium come from and is there enough of it to supply the massive demand for EVs? No question there's enough for cellphones and other small rechargeable batteries, but where is the source for really large demand? Let's say just a million vehicles per year and the amount of lithium in each battery is ?how much? I've found this, which is pessimistic, and I've also seen questions about lithium availability raised reliably. Does anyone have some good sources? Franamax (talk) 07:17, 18 September 2008 (UTC)

Edible fir cones / pine cones

I asked this question on the miscellaneous section but the answers were not satisfactory and I hope you scientists can help. Last week in Istanbul, Turkey, I noticed in food shops, bottles of fir cones for sale. All were closed (immature) but some as long as three inches and perhaps two inches wide. I presume they were in some sort of brine or vinegar. My question is - how can wood impregnated with resin be made edible? (I use fir cones as fuel.) If this is truly the case, a vast food source is going unharvested worldwide. With thanks. —Preceding unsigned comment added by 77.199.89.144 (talk) 08:56, 18 September 2008 (UTC)

Well pine nuts are certainly edible and are sold in the shops where I live. According to our pine cone article some species of cone are edible including some species of Podocarpaceae. SpinningSpark 09:14, 18 September 2008 (UTC)

In Korea you boil them and drink use the resulting water. --Kjoonlee 10:06, 18 September 2008 (UTC)

Conversion

What is the right conversion factor to be use in obtaining the volume of liquid CO2 from a pressure guage (pressure guage indicate the H2O content of the horizontal cylindrical tank).

   Note:  Dimension of the tank is known.