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February 23

Does the brain control the heart also?

or the heart is exception and it doesn't control the heart? I'm asking it because according to what I know there are no nerves in the heart. 93.126.88.30 (talk) 00:31, 23 February 2017 (UTC)[reply]

See Heart#Nerve_supply. The heart normally beats on its own, but the rate is influenced by the brain. However, trauma to the brain alone can cause cardiac arrest, though our articles do not explain the mechanism. Someguy1221 (talk) 00:38, 23 February 2017 (UTC)[reply]

Think you'll find the most important is the Vagus nerve. Beta blockers work by damping down the brains control.--Aspro (talk) 00:41, 23 February 2017 (UTC)[reply]

Then the brain controls the heart. Isn't it? Now I'm holding a booklet of the Red Cross organization which states (translated) about the brain that it "activating and supervising on the lungs" while the brain "supervising and regulating the heart". The use different terms for the lungs and for the heart. They don't say about the heart the it's activating by the brain. I'd like to know what is the explanation for these different terms regarding to the brain and the heart. 93.126.88.30 (talk) 01:08, 23 February 2017 (UTC)[reply]

Well, it depends on what you mean by control. And brain. The normal function of the heart is primarily controlled by the Cardiac pacemaker without direct continuous input from the brain. But there can be things that happen in your brain that influence the function of your heart. --Jayron 32 01:29, 23 February 2017 (UTC)[reply]

I think the reason for the difference in description is the nature of the "control". Muscle contractions that lead to breathing are caused by continuous nerve impulses from the brain. That is not the case for the heart, even if the brain can modulate its rate, and the heart cannot beat indefinitely with no input from the brain. Controlled, but not micromanaged? Semi-independent? Someguy1221 (talk) 01:31, 23 February 2017 (UTC)[reply]

I'd note that while translated, the word which seems to confuse the OP is "activating". I'd suggest removing "activating" is a fair call for the heart. The heart is supervised and regulated by the brain and does need input from the brain long term, but it isn't really activated by it. It "activates" itself by the cardiac pacemaker which is part of the heart. The lungs do need to be "activated" by the brain, if they don't receive a signal they don't work. The Pre-Bötzinger complex is part of the brainstem, not the lungs. Of course control and regulation of these organs is complicated, as with most things, we you should always be wary of reading too much into words whether English or some other language and with no disrespect to the Red Cross, I'm sure it isn't intended to be a scientific text book. Nil Einne (talk) 01:56, 23 February 2017 (UTC)[reply]

Exactly. The difference between the lungs and heart is that the heart contains its own pacemaker, and the lungs do not. No brain = no breathing, but the heart will beat autonomously... for a very brief time. - Nunh-huh 02:19, 23 February 2017 (UTC)[reply]

A very rough analogy would be the difference between driving a car and riding a bike - in the car, you control the rate the engine turns by pressing the accelerator, but don't directly affect the details of the motion (analogous to the brain's control of the heart - it can change the rate, but the heart controls the details of the movement). On a bike, your feet are turning the wheels, and there is a 1-to-1 correspondence between the movement of your foot and the movement of the bike (assuming fixed gears - this is like the brain's control of the lungs, where it will send a signal for each breath in and out). MChesterMC (talk) 10:33, 23 February 2017 (UTC)[reply]

The heart does not require a signal from the brain to function on a basic (as opposed to regulated) level, see SA Node and Fibers of Purkinje. The lungs will entirely fail to function without a brain signal. This is called a "central apnea since the failure originates in the central nervous system. μηδείς (talk) 03:51, 23 February 2017 (UTC)[reply]

The autonomic nervous system controls heart rate.
Sleigh (talk) 19:42, 23 February 2017 (UTC)[reply]

Sudden unexpected death in epilepsy (SUDEP) is a recognized clinical event, though its causes aren't well-understood at present - but it's definitely a case where the brain controls the heart. "Cardiac arrest associated with epileptic seizures: A case report with simultaneous EEG and ECG", Fatemeh Fadaie, et al, Epilepsy & Behavior Case Reports Volume 2, 2014, Pages 145–151 reports on two patients who experienced asystole after epileptic seizures. In the 1970s, I witnessed what may have been a similar case, a young lady who presented at the hospital emergency room where I worked (as a non-medical employee) experiencing what appeared to be drug-related seizure activity which ended with cardiac failure, after which cardioversion failed and she died. loupgarous (talk) 21:58, 23 February 2017 (UTC)[reply]

Isn't the brain also involved here by sending signals such that in the absence of the signal the heart rate would rapidly increase to about 100 bpm? I remember reading somewhere that this allows for rapid stress responses. Count Iblis (talk) 22:28, 23 February 2017 (UTC)[reply]

Our article on the vagus nerve's function explains that. A properly functioning right vagus nerve does down-regulate the heart beat by controlling the sino-atrial node. The vagus nerves and spinal ganglionic nerve keep the heart rate down to normal levels in healthy people. When the vagus nerves are hyperstimulated bradyarrhythmias, pathologically slow heart beat, can result. Hyperstimulation of the left vagus nerve can cause conduction block at the sino-atrial node.

One correct answer to the OP is that in healthy people the brain does routinely help regulate heart rate through the parasympathetic nervous system - though even after a vagotomy the heart continues beating, still controlled by its internal pacemakers. The control, however, doesn't respond to external stimuli as responsively as when the vagus nerves are left intact. loupgarous (talk) 22:57, 23 February 2017 (UTC)[reply]

Ratio of circumference to diameter

Could the ratio of a circle's circumference to its diameter be possibly different in an alternate universe?

Then it wouldn't be a circle. --DHeyward (talk) 09:27, 23 February 2017 (UTC)[reply]

(edit conflict) Everything is possible in an unspecified alternate universe, so yes.

Outside the realm of speculation, you can try reading about Non-Euclidean geometry, where such a ratio is not even constant. For instance, a circle on the Earth's surface of small dimensions compared to the Earth's curvature will have about the same properties as in planar geometry, whereas a circle on the equator has a perimeter of four times its radius (= the pole-equator distance) (assuming a spherical Earth, which is not exactly true), so that ratio is 4 rather than 2π. Tigraan^{Click here to contact me} 09:28, 23 February 2017 (UTC)[reply]

"Pi is approximately 3.1415927, given Euclidean geometry" appears to be a true statement regardless of the nature of the universe. If we lived in a universe that was obviously non-Euclidean, we would still be able to imagine a world that was not. As Tigraan mentions, certain non-Euclidean worlds give non-constant values of pi (pi here being not mathematical pi, but the circumference-to-diameter ratio of an arbitrary real circle). You could even imagine a universe in which particle movement was restricted to triangular or square grid lines on a physically realized spacetime, and wind up with pi of exactly 3 or 4, respectively. But then we could still imagine a Euclidean world, and calculate pi ~ 3.1415927. In logic this is called a logical truth, a statement that (given its underlying assumptions) appears to be true no matter what (in the words of philosophers, in every possible universe). Whether logical truths really exist, and what they mean, has been debated for millennia. Though most people just go about their day and don't worry about it. Someguy1221 (talk) 09:44, 23 February 2017 (UTC)[reply]

In Pratchett's Going Postal there´s a machine in which pi = 3. The inventor was really annoyed that pi was so "messy". As a consequence, the machine bends time and space. Gråbergs Gråa Sång (talk) 10:24, 23 February 2017 (UTC)[reply]

The USA tried that too: Indiana Pi Bill Andy Dingley (talk) 14:45, 23 February 2017 (UTC)[reply]

It's different on this planet too.

Pi's value doesn't depend on the universe, but rather the geometry. If you have a non-Euclidean geometry, then pi doesn't have the same value one would expect for a flat plane. Nor do the angles of a triangle add up to 180º.

You can demonstrate this with a large spherical ball (easy to find), or the alternate of a hyperbolic surface (a bit harder to find physical examples of - a Pringle or a trumpet bell are sometimes used to make museum displays). With an exercise ball, some whiteboard pens and flexible tape measure and protractor you can do classroom demonstrations with measurements. As the radius is measured along the curved plane of the ball's surface it is "longer" than you might expect for a circle of such diameter, thus the value of pi is smaller than for a flat Euclidean plane. Andy Dingley (talk) 10:47, 23 February 2017 (UTC)[reply]

Minor nitpick: that supposes you define π as the ratio of circumference to diameter. Many people define it as the half-period of the cosine function, or a similar definition from calculus; you can prove that the cosine, defined as a power series, has a period without involving geometric arguments. See Pi#Definition. Tigraan^{Click here to contact me} 13:12, 23 February 2017 (UTC)[reply]

Well, that still leaves the same basic question, but worded differently "Under what mathematics systems does the half-period of the cosine function NOT equal the ratio of the diameter to the circumference of the circle?" The symbol used to represent those two concepts is identical under the mathematics we all know and love, but that's merely convention. What if they were different numbers? --Jayron 32 13:15, 23 February 2017 (UTC)[reply]

The broader question is whether mathematics (so maybe try the Maths desk) works the same in an alternate universe, a question that has been asked here many times, most recently here.--Shantavira|^{feed me} 12:27, 23 February 2017 (UTC)[reply]

The OP's question amounts to the tautology "If math were different would math be different." The simple answer is "of course it would, you've already stipulated that it was different". The more interesting questions come from asking "If math were different in this specific way how would that one change propagate through the entire system to change other things." Entire fields of mathematics are dedicated to answering that question. Besides the alternative geometries mentioned above in non-Euclidian geometry there are things like Alternative algebra or Non-associative algebra or Non-standard model of arithmetic the like in which some fundamental axiom of a mathematical system is changed, and then further implications are studied. --Jayron 32 13:05, 23 February 2017 (UTC)[reply]

Newly discovered earth-size planets at nearby star 40 light years away.

This cnn.com[1] page states: "Standing on the surface of one of the planets, you would receive 200 times less light than you get from the sun, but you would still receive just as much energy to keep you warm since the star is so close." It does not make any sense to me. --AboutFace 22 (talk) 13:21, 23 February 2017 (UTC)[reply]

Compare a candle to a bonfire. To get the same heat energy from the candle as from the bonfire, you'd have to stand MUCH closer to the candle than you would the bonfire. --Jayron 32 13:22, 23 February 2017 (UTC)[reply]

(EC with below) I imagine the OP's question is why you receive much less light but just as much energy (since both are referring to a planet that is very close). The CNN story doesn't explain very well, but I imagine they are talking about visible light. Since TRAPPIST-1 is an ultra-cool dwarf, the energy in what's visible light to us would be significantly reduced even on a relative basis. Of course any life evolved there would be adapted to that spectrum. Nil Einne (talk) 13:46, 23 February 2017 (UTC)[reply]

There are multiple effects at play here, and the article seems to be mixing them up awkwardly.

Obviously, the closest from the star you are, the more energy flux (by surface area) you receive. However, that energy is transferred by radiation, and is thus distributed among the radiation spectrum according to Planck's law. This law involves temperature in two ways:

The hotter a body, the more radiation it emits overall (see Stefan-Boltzmann law).
The hotter a body, the more the bulk of the radiation is shifted to the short ("blue") wavelengths (see Wien's displacement law).

The important point is that "light" refers to the portion of energy that falls within the visible spectrum, where the Sun emits most of its radiation (which is not coincidential: life forms evolved optical sensors called "eyes" to have sensitivity in the domain where there was stuff to see).

My guess is that the star discussed in the article is cooler than the Sun, thus emitting less energy overall and having a peak emission at longer wavelengths (in the infrared domain) than the Sun. Because it is closer, it compensates for the first effect (overall energy flux), but it still emits more at non-light wavelengths. Tigraan^{Click here to contact me} 13:42, 23 February 2017 (UTC)[reply]

Is it possible that the article really meant that the star was 200 times less bright than the Sun? They actually wrote "200 times less light", but maybe they were just confused. You could get comparable amounts of light from a much dimmer star, if its disk is much larger in the sky.

This issue made for a difficult problem to solve at the Moon article, which claims that the Moon is second only to the Sun in terms of brightness as visible from Earth. Literally, that's false (Venus is about 10x brighter, as you can easily see when they're close to one another in the sky). But the article text goes on to explain that this is as measured by illuminance. I'm not entirely happy with the solution there but I'm not sure I have a better suggestion. --Trovatore (talk) 23:17, 23 February 2017 (UTC)[reply]

The stellar magnitude of Venus can be as much as -4.6, and that of the moon -13. The sun's is -27. A unit decrease in magnitude represents an increase in brightness of approximately 2.5. The absolute magnitude of stars is calibrated by lining them up at a distance of 32.6 light - years - for planets and asteroids the distance is a more useful one earth - orbit radius. 80.5.88.48 (talk) 08:49, 24 February 2017 (UTC)[reply]

You're missing the point. The Moon delivers more light to the Earth; there's no question about that. But Venus is brighter. Brightness is the amount of light per unit solid angle as seen by an observer, and Venus subtends a much smaller solid angle. (Relative) magnitude doesn't measure brightness, but rather illuminance.

This sounds abstract, but it really isn't. Next time Venus is close to the Moon on a clear night, just look at them. You can easily see that Venus is brighter. --Trovatore (talk) 09:03, 24 February 2017 (UTC)[reply]

sub-Q - Is CO2 a greenhouse gas?

I gotta ask... a "Venus-like atmosphere" has not been ruled out for the inner planets of the star. But if they are heated almost entirely by infrared radiation, is a Venus-like CO2-intense atmosphere a greenhouse gas for them, or does it actually make them cooler, or does it more or less cancel out? Wnt (talk) 13:46, 23 February 2017 (UTC)[reply]

Can you explain more why you think it might not be a "greenhouse gas", due to the spectrum of radiant heat? Somewhat relevant: you may enjoy this [2] critique of the word greenhouse gas, as it is a terribly misleading metaphor. An actual greenhouse acts to keep the inside warm by limiting convective transport. An actual greenhouse would keep the inside warmer than the outside, no matter what the spectrum of light. SemanticMantis (talk) 15:59, 23 February 2017 (UTC)[reply]

The thought is correct (if the star emits in the infrared, the CO2 will absorb more of the incoming radiation), but even a red dwarf has an effective surface temperature of 2300K to 3800K, while the planet would have a temperature about an order of magnitude lower. Wien's displacement law tells us that a planet at 300K will have its maximal emissions at 9.6μ, while a red dwarf at 3000K will have the maximum at 0.97μ. CO2 mainly absorbs at 2-3μ, around 4μ, and from ~~8-20~~~13-~16μ. So while the greenhouse effect would be a bit weaker than for earth, it would still contribute to warming the planet, not to cooling it. --Stephan Schulz (talk) 16:37, 23 February 2017 (UTC)[reply]

An aside on real greenhouses, and how they work. Not terribly relevant to either question above, interesting though it may be. SemanticMantis (talk) 17:08, 23 February 2017 (UTC)[reply]

My understanding is that in a physical greenhouse the windows allow the visible and ultraviolet to get inside, the latter warm the plants and the soil. The latter emit low frequency infrared light which the windows do not allow to pass, thus the energy is trapped inside. --AboutFace 22 (talk) 16:21, 23 February 2017 (UTC)[reply]

That effect is tertiary at best. Actual greenhouses keep the inside warm by keeping that air in one place, while allowing light in. This is is explained more clearly by a Dr. Fraser at the link I posted above. If you could magically make the walls of a greenhouse permeable to air while keeping the exact same optical properties, it wouldn't be able to keep the inside warm in the winter. Likewise, if you contain a volume of air, butlet the IR back out, you get pretty much the same warming, as illustrated by the quote below. SemanticMantis (talk) 16:33, 23 February 2017 (UTC)[reply]

(ec) One way an actual greenhouse works is that the glass is almost 100% transparent to visible light, but less so to infrared. Therefore, light enters, hits things like plants, is converted to infrared, but then reflects off the glass and stays inside. If the same is true of the greenhouse effect, then this Q would come up, if there's little visible light. StuRat (talk) 16:23, 23 February 2017 (UTC)[reply]

Stu, if you'd read what you yourself just linked, you'd see that's not the relevant part at all. It's also explained in my link, and I also explained why greenhouses and the greenhouse effect are not very similar. Since you can't be bothered to read the article, Let me help you and and do some of your homework for you:

“

However, R. W. Wood in 1909 constructed two greenhouses, one with glass as the transparent material, and the other with panes of rock salt, which is transparent to infrared. The two greenhouses warmed to similar temperatures, suggesting that an actual greenhouse is warmer not because of the "greenhouse effect", but by preventing convective cooling, not allowing warmed air to escape.

”

Next time read and think a bit before you type up whatever you happen to recall from your distant school days. SemanticMantis (talk) 16:31, 23 February 2017 (UTC)[reply]

Far am I from defending Stu (usually), but the greenhouse effect, while not the primary explanation for the warming of greenhouses, is measurable and even significant - see Greenhouse_effect#Real_greenhouses and Greenhouse#Design. Wood's experiment is interesting, but was rather crude by today's standards. --Stephan Schulz (talk) 16:42, 23 February 2017 (UTC)[reply]

Sure it's measurable, but significance is... debatable at best. Do you have any sources showing it as contributing to warming in a real greenhouse in anything over small percentages? Because 8% is an interesting footnote, not the thing that we explain if we only get to explain one thing. Saying a greenhouse keeps the interior warm due to the greenhouse effect is like saying "an airplane flies by pushing air down with its wings, and that pushes the airplane up". Yeah, we have Ground_effect_(aerodynamics), but the offered explanation is still very bad and misleading, even though some aircraft can take advantage of this downward push in some circumstances. When we explain things, we should explain the bits that are important, not the bits that are not important. Anyway, I'm sorry I brought it up at all, none of this is terribly relevant to OP or Wnt's question. SemanticMantis (talk) 17:05, 23 February 2017 (UTC)[reply]

SemanticMantis, I said "One way an actual greenhouse works..", not that this is the only way, or even the main way. The source I provided backs up what I said, and I said that to explain the term "greenhouse effect", since it refers to that portion of the way a greenhouse works. You owe me an apology for misrepresenting what I said. StuRat (talk) 18:16, 23 February 2017 (UTC)[reply]

Convenience link: CO2 transmittance in the IR range. For the answer to the question, see Stephan Schulz's post, although I believe their "8-20μ" indication of an absorption window in the far infrared to be erroneous (going by the spectrum I linked, it is more like 13-17μm). And yes, in theory, the "greenhouse" effect could lead to cooling rather than heating. Tigraan^{Click here to contact me} 17:10, 23 February 2017 (UTC)[reply]

Also see anti-greenhouse effect. --Stephan Schulz (talk) 17:16, 23 February 2017 (UTC)[reply]

And you are right about the absorption - I was going by a bad web source. This is better. Note that this is maintained by the NIST, but they still claim copyright. That sounds doubly wrong to me... --Stephan Schulz (talk) 20:54, 23 February 2017 (UTC)[reply]

A very interesting and well-referenced post that was not asked for by anyone above. If you would like to read why it is unlikely that you will get to travel to one of these planets, and find it a hospitable world of easy wealth, read on.

Reality check

A science fiction artist has been at work painting "What the TRAPPIST-1 planetary system may look like" of which 2-3 of the 7 planets resemble our own watery blue marble. This imaging is entirely imaginary, in the tradition of the sci-fi illustrator Chesley Bonestell 1888 - 1986. All that can be said reliably is that existence of 7 probable Exoplanets has been deduced from obscurations of a little star in Aquarius (constellation) designated TRAPPIST-1, 3 of them may be in "Goldilocks" habitable orbits, which is a factor that the speculative Drake equation uses to estimate the chances of Extraterrestrial life, but the reality is that we as yet are less able to image the TRAPPIST-1 planets properly than Sciaparelli was in 1877 to draw the Mars that he could actually see. So to you eager futurists who are already planning to terraform a TRAPPIST-1 planet, already counting the wealth in untouched natural resources to be extracted, already imagining yourselves as colonists of an extraterrestrial utopia, already imagining exquisite sunset scenes where nobody can say for sure whether there are atmospheres or that the planets are spherical, and even planning to build a Dyson sphere or two, I offer the following reality check on your dream: Suppose a long-lost relation leaves you $1 million with which you may buy the fastest car possible - it must be a model in production (but the budget allows you to tune it for higher performance). Now, disregarding little problems like refuelling, let's suppose you drive to TRAPPIST-1 at the car's full speed. Please answer here below 1) your car model, 2) your speed, and 3) your age when you finally arrive at TRAPPIST-1. Blooteuth (talk) 20:46, 23 February 2017 (UTC)[reply]

EXTRATERRESTRIAL TRAVELS TO OTHER STARS ARE IMPOSSIBLE. That car of yours will take millions of years to get there. --AboutFace 22 (talk) 21:36, 23 February 2017 (UTC)[reply]

Only under current technology. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:51, 23 February 2017 (UTC)[reply]

There will be no technology for interstellar travels in a million years. You are up against the laws of physics in there. --AboutFace 22 (talk) 22:26, 23 February 2017 (UTC)[reply]

We don't necessarily know all the laws of physics, nor all the possible ways to get from point A to point B. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:32, 23 February 2017 (UTC)[reply]

I think the ref desk has work within the known parameters of physics as we understand it. It's all very well to claim we can be reborn as unicorns or we can travel at 8 million times the speed of light or Donald Trump isn't orange, but most of that is just stuff of fiction right now. Answering questions at the Ref Desk assumes that you're going to respond within the known known parameters, not the known unknown parameters. The Rambling Man (talk) 22:45, 23 February 2017 (UTC)[reply]

The poster claimed interstellar travel is impossible. I don't think there is universal agreement on that. Keep in mind that in 1902 the poster might have said that about airplanes. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:14, 23 February 2017 (UTC)[reply]

If you need to send a file to someone, you attach it in your email and send it electronically. You don't need to book a flight and bring a computer with you that has the file on its hard drive. Similarly, I think that advanced civilizations will have made the transition to a machine civilization who travel electronically by uploading themselves to machines at the destination via radio communications (or perhaps using lasers as they'll have a larger bandwidth ). That way you can travel at the speed of light without needing a spacecraft. This only works as long as there are suitable machines at the point of destination, so different civilizations may travel to each other, but travel to locations without technology will be more difficult. Count Iblis (talk) 22:56, 23 February 2017 (UTC)[reply]

Why are you talking about art? Did someone ask about art? Why are you talking about terraforming? Pretty sure that has not been asked about here either. Can you explain to me why this post of yours, in a whole new section, is anything other than WP:SOAP? We are WP:NOTAFORUM. I don't really disagree with anything you said, but I know this is a reference desk, and not a place to post our tangential grievances with how some people may misinterpret news of scientific findings. SemanticMantis (talk) 23:08, 23 February 2017 (UTC)[reply]

My launchpad and first link is this cnn report introduced by the OP. Have you noticed how much of it is artwork? Have you noticed the amount of artwork that enhances our TRAPPIST-1 article? It even has a video simulation. Those who remember the Golden Age of Science Fiction (you may not) understand the importance of conjectural art as the only way we (excepting the odd astro- or cosmonaut) will ever perceive things in space. But without a clear idea of what is fact and fiction, the artwork used in NASA's announcement can blind some to the fact that today's status of extrasolar exploration is comparable to that of the makers of Early world maps who decorated unknown lands (which in 1566 meant most of North America) with art to say "Here be dragons". NASA have good reason to popularize their work because education is the only answer to misinformed accusations of criminal, nay "lunatic" conspiracy that somehow persist among Americans who need to be persuaded by this better informed opinion: "Right now, NASA’s annual budget is half a penny on your tax dollar. For twice that—a penny on a dollar—we can transform the country from a sullen, dispirited nation, weary of economic struggle, to one where it has reclaimed its 20th century birthright to dream of tomorrow."[3]. If there are aliens with a Radio telescope on a TRAPPIST-1 planet who follow Earth affairs, they are getting news of a new US President (named Carter), the test flight of Space Shuttle Enterprise, an air collision on Tenerife and the opening of George Lucas's movie Star Wars; on audio they hear the US debut of Pavarotti and the last concerts of The Supremes and Elvis Presley; and the aliens may be delighted to receive news of the Wow! signal event, and may know who sent it. Blooteuth (talk) 02:38, 24 February 2017 (UTC)[reply]

Ok. That's all fine. I would not have balked at or collapsed a brief comment clarifying that the OP's link contained a lot of speculative art. The thing is, nobody asked for an essay on the value of art in science communication, or to comment on their fantasies. Yet that's what you're doing here. If you have a problem with NASA, take it up with them, but nobody here was even talking about flying to these planets or what they look like. OP and the rest of us were talking about the actual science and physics of exoplanets.

I understand your points, I am somewhat sympathetic, and you really have provided some nice references. But I think you may be missing the point, which is that this is not a place to post unsolicited essays. That's called soap-boxing, and while it's good fun in real life and in some internet fora, we have explicit rules against it here. If you and Wnt want to keep talking about it, that's fine, I'll leave you to it. SemanticMantis (talk) 22:42, 24 February 2017 (UTC)[reply]

Realistically, it is at least conceivable to make a Voyager-like probe that leaves the Solar system on a slow trajectory toward these worlds. If we could make a sufficiently durable probe, it would be possible that it could be loaded with certain very long-lived microorganisms with intent of dispersing them on arrival, polluting those planets and changing them. (Caveat: I don't know about the relative velocity of that system, and if it is too much all these ideas get ever more unlikely) This might permit Earth style life to endure, for better or worse, for a thousand times longer than it would otherwise. So it is not, even with near-present technology, particularly unrealistic to think about them.

Now as for looking at them - we're getting better telescopes all the time, and their atmospheres are part of the transits of the stars. It may be very difficult but it is by no means impossible to figure out what compounds are in them, their approximate temperature, maybe even look for so-called signatures of life.

And then... there are the very brave or very foolhardy people who like to send radio signals at things beyond our comprehension. Wnt (talk) 11:45, 24 February 2017 (UTC)[reply]

Foolhardy yes, because like Lucy we may have some 'splainin' to do. The awesome introduction to "Contact" (video) plays the babble we have already transmitted in a sphere of radius 123 Light-years (counting from Guglielmo Marconi's transmissions in 1894) that is still expanding. See History of radio. Blooteuth (talk) 15:02, 24 February 2017 (UTC)[reply]

Can a human house provide shelter for the animals, and in return, the animals provide food for humans?

Spiders and insects can somehow come into the human-constructed house. Termites can chew on the wood. Rats can enter the house through the toilet or a rat hole in the structure. Then, there are the intentional animals, like cats and dogs and chickens. Some humans live in a rural area, so chickens can enter the house and get on the furniture. While cats and dogs and chickens probably cannot survive on their own, other animals can enter and leave at will. It seems that the human house functions like a little world. If the house provides shelter for these animals and attract animals because of food, then can humans take advantage of that and use the house to lure animals in instead of going after the animals in another place? 66.213.29.17 (talk) 16:58, 23 February 2017 (UTC)[reply]

Sure. Just leave the doors and windows open, and shoot anything edible that comes in. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:06, 23 February 2017 (UTC)[reply]

What sorts of references were you looking for? I'm unclear as to what additional information you want us to provide for you. --Jayron 32 17:14, 23 February 2017 (UTC)[reply]

Yes, the human house is a little world. You might be interested in reading about Commensalism. Things like house centipede and house fly house mouse and flour beetle basically only exist in human-made environments. Flour beetles are edible, but usually considered a pest. Our article on entomophagy lists some other human commensal species, and if you'd like to learn more about bug eating, see this excellent article from the FAO [4], which describes how eating bugs can increase our food security. Some people do eat mice [5]. If you try attracting mice to your house to eat, let us know how that goes! SemanticMantis (talk) 17:19, 23 February 2017 (UTC)[reply]

A traditional Swiss chalet, and many other vernacular architectures, was a form of farmhouse where dairy animals were kept inside the same building for at least part of the year. They would also need to be fed: this was done by fattening them through the Summer on good pastures outside, then keeping them indoors over Winter on stored hay or silage. They food they provided though would mostly be in the form of cheese - this was produced from the animals during the good feeding season, then could be stored for consumption during the hard Winter. Some animals (not just under this Swiss model) would also be consumed at Christmas feasts, in the earlier part of the hard Winter, and could then be either eaten at a last feast, removed from needing to be fed through the Winter, or could be preserved as hams, sausages etc.

The problem comes down to a food supply: many farming societies have kept animals in the same house during Winter, but they've not been able to feed them there, other than from stored food. I can't think of clear examples where the animals are kept "in the house" year-round, as there's no way to produce their food in-house too. Chickens or birds in a dovecot might be "indoors" year round, but they'd need to be fed on high-value cereals too.

Could you eat termites? Only if they're eating your house too. If I eat spiders, how do I get the flies to feed my spiders? My houseflies disappear in the Winter. Andy Dingley (talk) 17:24, 23 February 2017 (UTC)[reply]

Yeah, you run into basic energetics problems with closed system that's too small. Metabolic_theory_of_ecology may be of interest to anyone pursing such plans. (My desktop salticids seem happy year-round, and never have to leave throughout the winter. They don't need to eat that often. If I were concerned, I'd just leave some old bananas around ;) SemanticMantis (talk) 17:38, 23 February 2017 (UTC)[reply]

My grandfather used to keep livestock in the basement, which served as pets for my mother and her siblings, until holiday dinner. μηδείς (talk) 22:49, 23 February 2017 (UTC)[reply]

I wonder if a set of beehives can be built around a small house, providing free heat and well-nigh unbeatable security. ;) But no one I know of has much experience training guard bees, you'd need broad vents for the summer, and you probably have to make your whole property a flower garden. Still, there must be a place to put one in a sufficiently whimsical work of fiction... Wnt (talk) 11:58, 24 February 2017 (UTC)[reply]

This is a quite common system, called "rented flat". Nowadays, most of the animals pay cash or even by money transfer, but paying in kind is not unknown. --Stephan Schulz (talk) 12:54, 24 February 2017 (UTC)[reply]

They do. --IEditEncyclopedia (talk) 15:27, 24 February 2017 (UTC)[reply]

Intensive farming can be of many forms. But for the OP's " It seems that the human house functions like a little world." there is a problem - these intensive farming practices require food to be brought into the "house" from outside. For dairy, this is often high value food too, grown and manufactured at some cost. Andy Dingley (talk) 16:05, 24 February 2017 (UTC)[reply]

Kinetic energy, Momentum

Is there a Conservation of kinetic energy?

For example: An object $m_{1}=2kg$ moving at a constant velocity $3{\frac {m}{s}}$ , elastically collides with a resting object $m_{2}=1kg$ .

Let us say now that $m_{1}$ is resting and $m_{2}$ is moving at a constant velocity $6{\frac {m}{s}}$ . We get

m_{1}{\vec {v}}_{1}=m_{2}{\vec {v}}_{2}\ \Rightarrow \ 2\cdot 3=1\cdot 6

but

{\frac {m_{1}v_{1}^{2}}{2}}={\frac {m_{2}v_{2}^{2}}{2}}\ \not \Rightarrow \ {\frac {2\cdot 3^{2}}{2}}={\frac {1\cdot 6^{2}}{2}}

This is impossible. Where was I wrong? יהודה שמחה ולדמן (talk) 17:53, 23 February 2017 (UTC)[reply]

What is your basis for concluding that it's wrong? Akld guy (talk) 18:18, 23 February 2017 (UTC)[reply]

You assumed the final velocities are 0 and 6 m/s. As you found above, those assumptions are not consistent with an elastic collision. Dragons flight (talk) 18:26, 23 February 2017 (UTC)[reply]

Looking at elastic collision might help. Dragons flight (talk) 18:29, 23 February 2017 (UTC)[reply]

I still don't get it. יהודה שמחה ולדמן (talk) 18:42, 23 February 2017 (UTC)[reply]

Why would you think that ${\vec {v}}_{2}>>{\vec {v}}_{1}$ ?

We don't know

{\vec {v}}_{2}

and it's hard to predict, without understanding details of the collision, such as the elasticity of the masses. This isn't trivial in theoretical kinematics, it's near impossible for practical experiments, except by making empirical measurements. But we do know that momentum is conserved and that the KE must be reduced: it can't increase, it can't even stay constant except for a theoretical and perfectly elastic collision. So we can put an upper limit on

{\vec {v}}_{2}

{\frac {m_{1}v_{1}^{2}}{2}}>{\frac {m_{2}v_{2}^{2}}{2}}\ \Rightarrow \ {\frac {2\cdot 3^{2}}{2}}>{\frac {1\cdot v_{2}^{2}}{2}}

{\vec {v}}_{2}<{\sqrt {2\cdot 3^{2}}}\approx 4.24

Andy Dingley (talk) 19:05, 23 February 2017 (UTC)[reply]

But for the conservation of momentum we get that

v_{2}=6{\frac {m}{s}}

. So why does the kinetic energy smaller? יהודה שמחה ולדמן (talk) 19:11, 23 February 2017 (UTC)[reply]

Sorry, can't typeset that quickly!

My

{\vec {v}}_{2}

limit above is for the case you describe where

m_{1}

is left at rest afterwards. What this proves is that

m_{1}

cannot be at rest afterwards, from this collision. You can't set up any physical case where all momentum is transferred and the initial mass stops dead. Andy Dingley (talk) 19:15, 23 February 2017 (UTC)[reply]

You have two boundary conditions, which you can now solve for a possible physical case: momentum is conserved (it's conserved as a principle), energy is conserved (it need not be, but that establishes a boundary) but there is no axiom that one mass ends up stationary, and we've just shown that for masses like these it's not even possible for it to do so.

To solve this, and establish both

{\vec {v}}_{1}

and

{\vec {v}}_{2}

after the collision, solve the simultaneous equations that you have for momentum and energy. But don't assume

{\vec {v}}_{1}=0

Andy Dingley (talk) 19:18, 23 February 2017 (UTC)[reply]

I think Andy Dingley has covered it, but I had to write it out a different way to really see it. Maybe this will help OP as well.

One problem is that you (the OP) have overconstrained the system by specifying both an elastic collision and the final velocities. By specifying an elastic condition, you have assumed that kinetic energy is conserved. In this case, use energy equivalence (and momentum equivalence) to calculate the final velocities. If instead you specify the final velocity, use this to calculate the final kinetic energy.

A second problem is that the final velocity that you have specified results in an increase in kinetic energy of the system, which is impossible without an additional input of energy. That some final velocities for m1 are impossible is a valuable result of the thought experiment IMHO.

A third, and more minor, problem is notation. Since you have both initial and final velocities for m1 and m2, labeling velocities as simply v1 and v2 can be confusing. Using v1i, v1f, etc. might make things clearer-Wikimedes (talk) 01:54, 24 February 2017 (UTC)[reply]

In case it was unclear,

v_{2}=6{\frac {m}{s}}

with

v_{1}=0{\frac {m}{s}}

is one way to conserve momentum, but there are an infinite number of ways to conserve momentum. For any choice of v2, you can find a corresponding v1 that allows the total final momentum to be equal to the initial momentum. An elastic collision means finding the values for v1 and v2 that allow both momentum and kinetic energy to be conserved. Dragons flight (talk) 08:38, 24 February 2017 (UTC)[reply]

Let's pick a convenient frame of reference: the one in which the total momentum is zero. This is the centre-of-mass frame (CM-frame). As the mass ratio of

m_{1}:m_{2}

is 2:1, the speed ratio in the CM-frame must be 1:2, so

{\vec {v}}_{1}=1m/s

and

{\vec {v}}_{2}=-2m/s

, the CM-frame itself moving at

{\vec {v}}_{CM}=2m/s

. In case of an elastic collision, conservation of both energy and momentum dictates there are only two solutions: the initial velocities, or both velocities reversed. As the masses don't move through each other without interacting, we know that after the collision

{\vec {v}}_{1}=-1m/s

and

{\vec {v}}_{2}=2m/s

. Converting to the original frame of reference, we see that

{\vec {v}}_{1}=1m/s

and

{\vec {v}}_{2}=4m/s

. PiusImpavidus (talk) 10:01, 24 February 2017 (UTC)[reply]

To directly answer the boldfaced question "Is there a conservation of kinetic energy": No there isn't. Energy can be readily converted from one to another form. For example, if a ball is launched straight up, kinetic energy is created from some other form of energy in the launcher (chemical potential, mechanical potential, electromagnetic, whatever); as it slows and stops under gravity, the kinetic energy is converted to gravitational potential energy (and a little is converted to heat, through friction with the air); when it falls again, the gravitational potential energy is converted back into kinetic energy; and when it hits the ground, the remaining kinetic energy is converted into heat and sound energy. --76.71.6.254 (talk) 21:00, 24 February 2017 (UTC)[reply]

Alright, to start off with I'm not that clear on your collision calculation. An object at rest doesn't have kinetic energy in that frame... maybe one is before and one after ... I didn't follow it. Anyway, the easiest way to solve these I think is to go into a frame where the net momentum of the colliding objects is zero. So 2 kg and 1 kg collide with one another while converging at 3 m/s. The rate of convergence doesn't depend on frame unless you want to go relativistic, and right now you're not ready for warp speed. So to make the momentum equal we need 2 kg to approach the center of gravity at 1 m/s and 1 kg to approach it at 2 m/s; both have 1*2 kg m/s momentum. They bounce off each other elastically so they carry away equal energy, and their total momentum doesn't change either, so we know they move away from each other at 1 m/s and 2 m/s the same way they came in. Now if we shift the frame so that the 1 kg object started at "rest" (adding + 2 m/s to the right, assuming it was on the right), it ends up with a speed of 4 m/s, while the 2 kg object starts at 1 + 2 = 3 m/s (as you said) and ends at -1 + 2 = 1 m/s. So the kinetic energy for the two at the beginning in this frame was 0.5(2*3^2 + 1*0^2) = 9, and at the end it's 0.5(2*1^2 + 1*4^2) = 9. The kinetic energy is indeed conserved in an elastic collision when looked at in any one inertial frame of reference, assuming the objects involved aren't doing work against (or being accelerated by) any other sort of force like gravity or friction. However, viewed in another frame it will be different, just as every object at rest can be viewed in a frame where it is moving. Wnt (talk) 22:25, 24 February 2017 (UTC)[reply]

The solution with 1 m/s and 4 m/s assumes one dimension, i.e. that after the collision the objects are moving along the same line as before. This doesn't have to be the case. See Elastic collision#Two-dimensional. The speeds can become anything from 1 to 3 m/s for the large object, and 0 to 4 m/s for the small. They need 2v₁² + v₂² = 18 (m/s)² to conserve kinetic energy, and there is no solution conserving momentum if v₁ < 1 m/s or or v₂ > 4 m/s. PrimeHunter (talk) 00:34, 25 February 2017 (UTC)[reply]

Quantifying change in equilibrium compositions in gas phase reactions from halving/doubling reaction volume

Hi, I just have to double check this. If I halve the partial pressures in the Haber process gas phase equilibrium constant, do I end up square rooting the equilibrium constant? But how wouldn't this apply in say, the solution phase for acid-base equilibria? (Changing reaction volume should affect gas phase reactions but not solution phase.) Yanping Nora Soong (talk) 22:10, 23 February 2017 (UTC)[reply]

Note I am trying to quantify the change not merely note the direction. Yanping Nora Soong (talk) 22:11, 23 February 2017 (UTC)[reply]

The answer to your first question is "no"; the equilibrium constant is a constant (unless changing the volume or pressure causes a temperature change as well, or your gases are far enough from ideal that you need to take fugacity into account). The change in equilibrium concentrations or partial pressures caused by a change in initial pressures is a different matter, and I would recommend looking up "equilibrium calculations" in a freshman chemistry textbook to see how this is done. It's not hard, but it wasn't obvious to me how to do it before I saw it done.--Wikimedes (talk) 01:21, 24 February 2017 (UTC)[reply]

OK, looking at Haber process I see that the equilibrium constants K_p we give are based on partial pressure of the gases, unlike the more familiar K_c based on concentration, but they work the same way. There is a molar fraction x_A of each gas, and the partial pressure of each is that times the total pressure in the container. Then as with the concentration variant, the concentration is equal to the concentrations of all the products over all the reactants, where multiple molecules count multiple times, so it's the square of the ammonia concentration over the nitrogen multiplied by the cube of the hydrogen. The constant stays the same ... unless, as our table shows, the temperature is changed, because then the entropy term changes while the enthalpy stays the same. Wnt (talk) 22:09, 24 February 2017 (UTC)[reply]

February 24

Blood meal

The blood meal article says that the substance is useful for repelling garden pests such as rabbits. How does that work? Using Google, I found nothing more scholarly than http://creekbed.org/bandh/pest.html, which claims that rabbits smell the blood and are repelled by its scent. Nyttend (talk) 01:01, 24 February 2017 (UTC)[reply]

Right, I also find lots of ads and patents, but not much in the way of true scientific discourse. I did ultimately find this review of animal repellent studies, which includes a couple of studies that found "intermediate effectiveness" for blood meal as a deer repellent. Someguy1221 (talk) 01:16, 24 February 2017 (UTC)[reply]

One possible mechanism would be if the smell of blood indicates the possible presence of a predator nearby, and those prey animals which avoid such areas are more likely to survive and pass on those genes. StuRat (talk) 05:59, 24 February 2017 (UTC)[reply]

How to find references, for anyone who might be curious

Let me let you in on a secret. I don't have any references right now. I'm also not sure what the mechanism is. I don't know the answer, but I'm a smart person, and I have some ideas. But I'm not going to post anything. Let me do a little work, and I'll be back when I have references to share. SemanticMantis (talk) 20:35, 24 February 2017 (UTC)[reply]

Ok, I'm back. I searched google scholar, starting with /"blood meal" pest deterrent/. That search wasn't all that useful, because "blood meal" is also what they call it when a mosquito or bedbug gets a meal of blood, and there is tons of research on that stuff that has nothing to do with vertebrate pest repellent. So I though maybe putting a vertebrate in would help, and also maybe "pest". Take out the quotes on blood meal since that means a thing I don't want. So I searched /blood pest deter deer/ [6], which led me to three very good references, which together will give OP access to a lot of real scientific findings about if and how this works. SemanticMantis (talk) 20:49, 24 February 2017 (UTC)[reply]

And now I've skimmed the articles, pulled out some quotes, and added a few wikilinks. The post below has a few key features:1) it took me more than thirty seconds to do. In fact it probably took me at least twenty minutes, not counting this explanatory text and some other things I was up to in the intervening interval. 2) it contains relevant references both external reliable sources, and also to wikipedia. 3) It gives OP plenty of directions to go if they want to learn more 4) I offer no opinions.

Now, I'm not saying that you or anyone else has to do all this. In fact, nobody has to post here at all. However, I hope that by explaining my process, people can learn how to provide helpful and well-referenced responses here, because that is what this desk is for. While posting of opinions and memories and hazy recollections and possibilities and the-way-that-one-guy-thinks-things-work are all very different, all well-referenced posts here are ultimately very similar, in that they share the four traits that I outlined above. SemanticMantis (talk) 21:13, 24 February 2017 (UTC)[reply]

Here is a freely accessible comparative study, from 2010 [7]. It says "While urine and blood-based repellents were somewhat effective in short-term pen studies, they were less effective in field studies." So maybe not the best stuff, but blood does have some beneficial effect against deer.

For mechanism, this study [8] tested "Four repellents representing different modes of action (neophobia, irritation, conditioned aversion, and flavor modification)". The experimental "data support previous studies indicating that habituation to odor limits the effectiveness of repellents that are not applied directly to food, while topically-applied irritants and animal-based products produce significant avoidance. The paper discusses mechanisms in several places, with additional references. Finally, this short work is all about the concepts of how vertebrate repellents work, and is definitely worth a read: Vertebrate repellents: mechanisms, practical applications, possibilities. [9]. SemanticMantis (talk) 21:03, 24 February 2017 (UTC)[reply]

How much vitamin b12 fortified foods must be eaten as a replacement for animal products?

Drinking fortified plant milk at every meal? How long can a human live healthfully without them? 107.77.194.188 (talk) 16:50, 24 February 2017 (UTC)[reply]

US RDA of B12 for non-lactating non-pregnant adults is 2.4 micrograms per day. The German RDA is 3 micrograms per day. You would need to look at how much B12 there is in a serving of the milk you're drinking, and calculate accordingly. Vegans suggest that 3 servings of fortified foods per day usually gets you the RDA. - Nunh-huh 17:21, 24 February 2017 (UTC)[reply]

Or, the simple solution is to just take a B12 supplement. As our article on Vitamin B12 discusses, it's impossible to give a one-size-fits-all answer to "How long can a human live healthfully without them?", because the body can store a good deal of B12, so it depends on diet, genetics, history, etc. Obviously, if you have or suspect you have a B12 deficiency, consult a medical professional; deficiency can be caused by things other than lack of B12 in the diet, in which case oral supplementation often won't do anything to treat the deficiency. --47.138.163.230 (talk) 21:35, 24 February 2017 (UTC)[reply]

It's a matter of current research (i.e. no-one really knows) how important B12 is, and how frequently it needs to be administered. If you suffer from chronic fatigue, linked to a B12 deficiency, then you're likely to be prescribed a dietary supplement and if that doesn't have an effect, intramuscular B12 injections. Then opinions vary: there is some indication that some people (likely those suffering from the chronic fatigue) are unable to absorb B12 at the normal rate (and so the standard RDAs are too low for them) even if they're ostensibly getting an "adequate" supply. Also conventional models suggest intramuscular B12 at intervals of months, whereas those reporting the fatigue see a boost and tail off on a cycle of weeks, suggesting that more frequent doses are needed.

In general, B12 is available in a good diet in such quantities, and is only needed at such a low level, that there isn't a problem. But when there is a problem, this has been explained previously as a dietary shortage when there is now indication that it's also (and particularly so for the chronic fatigue cases) at least as much a metabolic issue of utilising what the diet does provide.

B12 is an obvious issue for vegans, and one of the very few real dietary issues for a decent Western vegan diet. Yet some doctors, particularly in the US, see this choice as tantamount to asking for poor health and will simply fail to engage with vegans, or tell them outright that a vegan diet is an inevitable cause of weakness and imminent death. The Vegan Society is a bit more balanced. https://www.vegansociety.com/resources/nutrition-and-health/vitamins-minerals-and-nutrients/vitamin-b12-your-key-facts/what-every-vegan-should-know-about-vitamin-b12 Andy Dingley (talk) 16:10, 25 February 2017 (UTC)[reply]

Why is human intention regarded as unnatural?

Natural selection is a different concept from artificial selection. Why are "natural" perceived as good, while unnatural is not good? Why are human culture and technology regarded as artificial while chimpanzee culture and technology are natural? Are the tools made by Homo erectus also artificial? Since everything made by humans stems from the human brain, and the brain is natural, shouldn't everything "artificial" or "synthetic" be natural? 107.77.192.233 (talk) 23:28, 24 February 2017 (UTC)[reply]

One possible way to resolve the dilemma is if artificial selection is viewed as a proper subset of natural selection. In other words, whatever people do is both natural and artificial. As to why they are normally considered to be mutually exclusive, remember that it's only quite recently (in terms of language development) that the Theory of Evolution was proposed, and it still is far from globally accepted. StuRat (talk) 23:39, 24 February 2017 (UTC)[reply]

It took natural selection 4 billion years to make humans. It took only 0.005 billion years for humans to surpass the natural record in many things like creature power, spe ed, game compl exity, cause the Sixth Mass Extinction, almost cause a worse one (nuclear winter), terraform much of the surface and maybe disassemble most of the observable universe with grey goo (though they could only dismantle the galaxy by 0.0001 billion years AD due to the speed of light) Sagittarian Milky Way (talk) 00:08, 25 February 2017 (UTC)[reply]

(edit conflict) Yes, technically speaking, everything humans do is part of nature, though we tend to set ourselves apart from the rest of the natural world for various reasons (nature is something to be conquered, humans are exceptional beings, etc.). There's a lot of discussion about why that is. Here's some further reading: [10], [11], [12]. See also environmental philosophy. clpo13_(talk) 00:12, 25 February 2017 (UTC)[reply]

(ec, or then again, someone here might just come through! Thanks Clpo13, looks interesting!) This seems like a very important but very difficult philosophical question. To some extent I would suspect it is cosmetic, but rooted in the tendency of life to optimize to a situation. A barren volcanic flow or a meteor impact seems less "natural" than a jungle. But to a large extent it might depend on the nature of free will itself, and its ability to create genuinely new things. It might depend more simply on the ability of cognition to recognize and favor novelty, but I'm skeptical that's the full explanation. You might have better luck (like properly referenced answers) on the Humanities desk, because this is the sort of thing Mephistopheles would say is not of his kingdom. You need something past science, I think. Wnt (talk) 00:19, 25 February 2017 (UTC)[reply]

"Natural" does not inherently equate to "good". ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:32, 25 February 2017 (UTC)[reply]

All-natural lava. Yummy! Sagittarian Milky Way (talk) 01:17, 25 February 2017 (UTC)[reply]

"Nature" in this context is a philosophical concept, it's an idea dreamed up by men. And "Nature" as used philosophically has several meanings. One of them is the inherent or defining properties of a thing. A thing (other than man) has inherent or defining properties not dependent on human action, so if one wants to know the "nature" of a thing one is necessarily studying that thing in the absence of human intervention. - Nunh-huh 01:31, 25 February 2017 (UTC)[reply]

Nature is neither good nor bad, it just is what it is. Woody Allen once described nature as "basically a gigantic restaurant." ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:05, 25 February 2017 (UTC)[reply]

This is related to the fact that people don't see themselves as biological machines subject to the laws of physics, many people are skeptical that machines could ever have human level intelligence. These feelings are not based on reality, but we do feel as if we're not part of Nature but rather are above it and are able to manipulate Nature as a sort of God. Count Iblis (talk) 03:39, 25 February 2017 (UTC)[reply]

Related to the myth that "natural" (whatever that means) is good, see naturalistic fallacy and appeal to nature. Someguy1221 (talk) 04:28, 25 February 2017 (UTC)[reply]

If you're talking about evolution specifically, there are important differences between natural selection and artificial selection. Natural selection has no goal - mutations arise at random, and some survive for various reasons (helping a creature to survive or reproduce is the main one, but there are weird effects like sexual selection and genetic drift happening too), but there's no final destination and no deeper reason. Birds didn't evolve wings so they could fly - instead, they seem to have been creatures that lived in a forest with lots of trees to jump off, and they gradually evolved featherier arms and stronger chest muscles because creatures that had these were better at hunting and escaping predators, until one day this jumping and gliding became actual flight. Artificial selection however usually has a goal - to maximise the size of grains, maybe, or produce dogs that are loyal and intelligent. A bulldog has a squat face because this makes it easier to bite into the side of a large animal, and bulldogs were selected by breeders to have this feature. Maybe from a godlike perspective this is the same thing (bulldogs evolved squatter faces because the ones that didn't got castrated by a species of hairless ape), but when analysing evolution from a human perspective, this is an important ontological difference. Smurrayinchester 10:17, 25 February 2017 (UTC)[reply]
- Artificial selection still operates within the "natural" genetics that the individuals already have. Compare that with genetically modified organisms, which involve really "playing God" by inserting genetic material that could never be there via cross-breeding within a species. That's an argument you'll see against GMO's vs. "conventional" breeding. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:14, 25 February 2017 (UTC)[reply]

Not really true. Artificial selection tends to be a key part of mutation breeding (including atomic gardening for example) where it's highly questionable to say you're referring to "natural" genetics the individual already have. I mean they have them sure, but only because you mutated the hell out of them to get it. Or to put it a different way, why is [13] (taken from [14]) so natural but any GMO isn't? Note that artificial selection and conventional breeding are not the same thing. Artificial selection is part of conventional breeding, but artificial selection may also be used as part of producing a GMO. Also GMO tends to cover both cisgenesis and transgenesis. Finally even with transgenetic organisms, this doesn't mean the genetic material could never be there ~~with~~edit: without GMO. Depending on the complexity of the change, it may be possible to produce this somehow, perhaps by mutagenesis or looking through a wide database. It has been suggested that GM could be used as proof of concept before you spend the incredible time and resources to produce the same thing via conventional breeding somehow. Technically there would still be some small differences, particularly if you a marker is still hanging around but this isn't what you referred to. Nil Einne (talk) 16:30, 25 February 2017 (UTC) edit: 15:13, 26 February 2017 (UTC)[reply]

How would you be able to get Bacillus thuringiensis genes into a maize embryo via conventional cross-breeding? ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:26, 25 February 2017 (UTC)[reply]

I never said you could in any specific case, but if your maize or a close relative already has a close analogue of whatever gene you're trying to introduce then you just have to mutate the gene until you get the version you want and the breed into into the maize you want. Remembering also as molecular biology techniques improve it's getting possible to successful crossbreed more dissimilar plants. A gene is just a gene. If you're referring to a specific gene without a close analogue in any plausible relative, e.g. the cry gene, then yes it's probably very difficult as I said "Depending on the complexity of the change". Note I said complexity of the change rather then mentioning gene for a reason, if you just plan to introduce an antisense gene you could reduce activity of the gene in other ways in conventional breeding (e.g. mutating it until it doesn't work properly) then breed it back into your common variants until they seem to function as you want them to (maybe with various molecular biology techniques to help speed up the process by tracking your mutated gene without having to do much growing) and hope in the process you didn't also breed something undesirable that was also mutated and didn't notice because you don't have to really test safety or anything else. Nil Einne (talk) 15:18, 26 February 2017 (UTC)[reply]

You wait for a plant to pick up the genes from the bacteria on its own. --47.138.163.230 (talk) 00:45, 28 February 2017 (UTC)[reply]

February 25

Feynman Lectures. Lecture 49. Ch.49-4. [15]

...
There would be, if there were no spring, a certain natural frequency ω0 for this one alone. The equation of motion without a spring would be
$m\,{\tfrac {d^{2}x}{dt^{2}}}=-m\omega _{0}^{2}x.$

— Feynman • Leighton • Sands, The Feynman Lectures on Physics, Volume I

How have he derived that? If we have a coordinate system with upward Y and rightward X , then:
$m{\tfrac {d^{2}}{dt^{2}}}x=-{\tfrac {x}{L}}T$
$m{\tfrac {d^{2}}{dt^{2}}}y=-{\tfrac {y}{L}}T-mg$
$x^{2}+y^{2}=L^{2}$
$T+mg{\tfrac {y}{L}}-{\tfrac {mv^{2}}{L}}=0$
Putting the 4th eq. to 1st :

$m{\tfrac {d^{2}}{dt^{2}}}x=-{\tfrac {x}{L}}(-mg{\tfrac {y}{L}}+{\tfrac {mv^{2}}{L}})=-mx({\tfrac {-gy+v^{2}}{L^{2}}})$
But I can't see that $\omega _{0}^{2}=({\tfrac {-gy+v^{2}}{L^{2}}})$ . Moreover if initial conditions are $x(0)=L,y(0)=0,v_{x}(0)=0,v_{y}(0)=0$ , then $\omega _{0}=0$ and at the bottom point ( $y=-L$ ) $\omega _{0}>0$ . Username160611000000 (talk) 09:39, 25 February 2017 (UTC)[reply]

Since Feynman talks about a single equation of motion, this suggests we simplify the problem to a one dimensional one. If we work in polar co-ordinates then the distance from the pivot, r, is constant (it is always L) and we have just one equation of motion in θ, the angle of the pendulum from the vertical. This is derived in our article pendulum (mathematics). Note the approximation for small θ which makes the equation linear.:

{\frac {d^{2}\theta }{dt^{2}}}=-{\frac {g}{\ell }}\theta

which has the same form as Feynmann's equation with

\omega _{0}^{2}={\frac {g}{\ell }}

This is an example of simple harmonic motion. Gandalf61 (talk) 10:24, 25 February 2017 (UTC)[reply]

Hm. Thank you. In the small angle approximation

({\tfrac {-gy+v^{2}}{L^{2}}})={\tfrac {+gL+({\tfrac {dx}{dt}})^{2}}{L^{2}}}

. And so we must put

({\tfrac {dx}{dt}})^{2}=0

. But is it correct? If x is small there is no guarantee that

({\tfrac {dx}{dt}})^{2}

is small.Username160611000000 (talk) 11:57, 25 February 2017 (UTC)[reply]

Taste of VX

I heard a report of VX (nerve agent) being tasteless and wondered how we could know. The article itself has a [further explanation needed] tag. Could you explain? --Error (talk) 15:43, 25 February 2017 (UTC)[reply]

Since treatment is possible, it may well be possible to ask the victims if they tasted anything. A more inexplicable case is in the article on radon, where Rn is described to be tasteless; although this is stated in some actual reliable sources, it still sounds rather silly because if there was enough Rn around to taste, the alpha radiation from its decay would presumably be much more significant. Double sharp (talk) 16:01, 25 February 2017 (UTC)[reply]

Since it's tasteless, "if there was enough Rn around to taste" is an impossible condition. Henry ^Flower 16:35, 25 February 2017 (UTC)[reply]

Well, being an unreactive noble gas, it is almost certainly tasteless, but what would be interesting to see how this could have been verified experimentally. Double sharp (talk) 16:41, 25 February 2017 (UTC)[reply]

There are plenty of reliable sources to confirm that it is tasteless, but nobody says how they know that, as far as I can tell. Alansplodge (talk) 18:25, 25 February 2017 (UTC)[reply]

The taste and smell of chemical weapons is a matter of some importance, as even human noses are a pretty good early warning system. Also practically every agent, even the post-war nerve agents, isn't that toxic - you can smell these things and survive, especially if you use the warning to run.

The taste/smell is known from a few sources: someone tasted it by accident and their last words were "tastes like chicken" (there are a few of these) or simply that they didn't notice any distinctive smell, the structure is close enough to less toxic analogues with recognisable smells that it can be inferred, or if the material's physical properties aren't volatile enough at ambient temperatures, it can be assumed to have little or no practical smell (it might smell of something if heated, or in concentration).

Most nerve agents simply don't smell though - their function is to be hazardous at such low concentrations that they need not be odorous. Andy Dingley (talk) 19:51, 25 February 2017 (UTC)[reply]

Having fewer early-warning signs makes it a better weapon too. See for example Phosgene#Chemical warfare. Another article I remember mentioning that a certain chemical-weapons agent that had noticeable odor was doped with another easily-smelled chemical to mask the odor, leading to the opponent recognizing the innocuous odor as the sign of a chemical weapon attack, but I can't find the article at the moment. DMacks (talk) 21:47, 25 February 2017 (UTC)[reply]

The US Army's Edgewood Arsenal has infamously done several human volunteer trials on nerve agents. There are people who claim the UK's biological/chemical defense labs at Porton Down performed similar research in human volunteers. Smell and taste are phenomena which occur at chemical concentration levels much lower than lethal cholinesterase inhibition caused by nerve agents. For VX, the LCt₅₀ for inhalation is estimated to be 30–50 mg·min/m³.

So it's plausible, at least, that a human volunteer did indeed inhale a sub-milligram dose of VX and live to tell the tale. Or at least report his impressions before dying. loupgarous (talk) 01:48, 26 February 2017 (UTC)[reply]

Porton Down did do experiments on humans, see Ronald Maddison. Widneymanor (talk) 09:02, 26 February 2017 (UTC)[reply]

That was Sarin though, not the V agents. These are too toxic (V agents maybe 10× the G agents) for such skin exposure experiments and their development also post-dates the abandonment of such testing. Although remember that they were developed as insecticides: Amiton (it's good against mites) was sold as such in the early '50s.

The point here though is that even a skin drop exposure is considerably more exposure than a potential smell. Andy Dingley (talk) 11:29, 26 February 2017 (UTC)[reply]

Military development of nerve agents for Chemical warfare is concerned as much with lethality (typically gauged by Median lethal dose LD₅₀) as with measures for protecting and decontaminating friendly troops and non-combatants. Against VX exposure, antidotes Atropine, Pralidoxime (2-PAM) and injection of Diazapam are indicated, and a US Army source dead link? described a Nerve Agent Antidote Kit. Clearly such antidotes could have been tested only by trial exposure of human subjects who survived to report the experience. Incidentally, some forms of the Botulinum toxin that celebrities pay to have injected into their pretty faces have even lower LD₅₀ than VX. Blooteuth (talk) 14:21, 26 February 2017 (UTC)[reply]

The newly discovered 7 earth size planets II

I am beating a dead horse. It is about this Internet cnn article: [16].I want to describe my motivation. I don't believe there is another planet in the Galaxy with intelligent life. I think the development of such life here on Earth was a result of events with extremely low probabilities, like acquiring mitochondria by unicellular organisms, so I wonder why people are so optimistic about those 7 planets. I just posted here in this desk a couple of days ago [17] Now I have a different question though. Those planets are so close to the star they must experience significant tidal forces. The magnitude of them should affect the chance for any life to develop. Could they be calculated? Thanks, - --AboutFace 22 (talk) 16:42, 25 February 2017 (UTC)[reply]

Tidal forces may be able to be calculated, but we don't understand abiogenesis nearly well enough to calculate how any particular force would affect liklihood of it occurring. Also: I wouldn't say the scientists are "optimistic", I'd say they are excited about interesting new things to look at. Popular press coverage is often breathlessly excited hype with little grounding in science or reason. Blooteuth had a lot to say about that and some good refs in the previous post, look there for more on that. SemanticMantis (talk) 17:57, 25 February 2017 (UTC)[reply]

Why the assumption of rarity? Forgetting intelligent life (since we don't have a lot of examples to look at), endosymbiosis seems to have happened at least twice in Earth biological history. --OuroborosCobra (talk) 18:12, 25 February 2017 (UTC)[reply]

Indeed. According to endosymbiont, many times.--Wikimedes (talk) 19:49, 25 February 2017 (UTC)[reply]

Multiverse theories would suggest that we live in a universe where the probability of our existence is maximized. So, if creating life in the lab is hard then that's probably only because life arising in a too easy way would have interfered with the development of more complex life that could give rise to us. Count Iblis (talk) 19:25, 25 February 2017 (UTC)[reply]

I would like to know what the magnitude of the tidal forces on those planets are. It is all speculation on my part but most of the answers so far, e.g. about the multiverses, etc. are even more speculative. So, if the tidal forces are high then first, the planets may have a lot of internal heating occur. What's the surface temperature then? Suppose one of the planets has water oceans and some land mass. If the tidal waves are high, the oceans may easily roll over the land mass every other day or so. If this is true, if the tidal forces are problematic, a certain class of earth size planets could be ruled out of consideration.

I want to give a real life example for comparison, just to appreciate the "magnitude" of very, very low probability events. It concerns Sporadic Creutzfeldt-Jakob disease. It affects prions, the structural proteins in all living forms. Imagine how many cells are in a human body, and each cell has countless number of prion molecules. They are subject to dying and regeneration, plus during the earlier development billions of them are created. This process is flawless, ALMOST. Once in a billion billion replications a quantum tunneling occurs and bingo, a misformed prion is made. It has a terrible property to convert all neighboring similar prions into this misformed state and the individual dies. Different species apparently have different probability of such an occurrence but in humans it is very low. Now listen here. At the end of WWII when missioners penetrated inner parts of New Guinea they found a tribe where almost everyone had this disease but it was not sporadic. They infected each other. It was calculated that the first case happened in 1910 and it was sporadic. Those people lived there for thousands years and never had Creutzfeldt-Jakob. Each of them had billions of prions which for generations were normal. And all of a sudden in 1910 that incredibly low probability event occurred. My point is that acquiring the mitochondria could have been even a much lower probability event the true frequency of which we don't know.

Homo sapiens developed in Africa but not in the Americas. The Americas haven't even had apes. There is one ape species in Asia but not intelligent development beyond that. This is one more strange probability that may not happen elsewhere ever again. --AboutFace 22 (talk) 21:26, 25 February 2017 (UTC)[reply]

We can speak of tidal forces in the TRAPPIST-1 system but these may be only stresses in planetary rock material; ocean tides such as we see on Earth would only be possible if liquid water (possibly on any of the 3 planets in the "Goldilocks" zone) is confirmed. We have estimates of the individual planet masses and orbits but I do not see any solution of the 8-body system that would yield an orbital almanac or Ephemerides that would be the basis for calculating tidal forces. Individual orbital periods ("years") seem short at mostly under 20 days but if the orbits are not in a simple resonance, there may be much longer time between tidal maxima than the time we have been observing the system. Note that gravitational forces are inversely proportional to the square of the distance but tidal forces are inversely proportional to the cube of the distance; the significance is that if a TRAPPIST-1 system resident were observing Earth and wondering about our tides, (s)he/it would very likely miss our tiny Moon that due to its relative closeness exerts more than double the tidal force of our Sun. Actually the near equal inclination of all 7 TRAPPIST-1 orbits is consistent with the planets being the result of the breakup by tidal forces of a previous single body, and after such short observation we don't know whether we are looking at a stable orbital system. It is not possible to make statements about chances for life to arise without invoking one's own belief system. The scientific community favours a variety of Abiogenesis mechanisms followed by a hardly-to-be-questioned evolution of the species₁ that culminates in ourselves₂. That is the background of the sourced statement here "All seven planets are likely to be tidally synchronized (one day = one year) making the development of life there "much more challenging". To the implicitly assumed Western tenet that Abiogenesis precedes Consciousness I respond with the opposing view expressed in Tibetan Buddhism that conscious existence predates the existence of bodily life. To read further: Gentle Bridges - Conversations with the Dalai Lama on the Sciences of Mind 1992, Random House / Shambhala Publications. Quote: "Buddhists cannot accept (the scientist's view) that consciousness arises from a material cause." Blooteuth (talk) 21:50, 25 February 2017 (UTC)[reply]

Note that when the Moon formed it was ten times closer to Earth and the tidal forces were as a consequence a thousand times stronger than what they are today. Count Iblis (talk) 22:53, 25 February 2017 (UTC)[reply]

Tidal forces vary with the cube of the distance ? I would have expected the square. Do you have a source for that ? StuRat (talk) 04:32, 26 February 2017 (UTC)[reply]

Yes, tidal force is approximately inversely proportional to the cube of the distance, since it depends on the difference between the gravitational force between two points. See the last equation in our tidal force article.

It should be noted that some theories of abiogenesis suggest that tides were beneficial or even essential to the development of life on earth [18]. By these theories, "water rolling over the land every other day" is a good way to get life started, since the prebiotic chemicals get concentrated in the drying tide pools. CodeTalker (talk) 05:02, 26 February 2017 (UTC)[reply]

Thanks. Does that mean (water) tides would be 1000 times higher ? StuRat (talk) 05:09, 26 February 2017 (UTC)[reply]

Yes, but the initial distance between the Earth and the Moon is believed to have been more like 60% of the current distance, not 10% a good summary of the thinking here. So more like 4.6 times higher, rather than 1000 times higher. I'm pretty sure I'd have remembered something about kilometer high tides. Someguy1221 (talk) 09:29, 26 February 2017 (UTC)[reply]

I do actually remember hearing about mile-high tides shortly after the formation of the moon, but the source would have been Discover Magazine, most likely. Here, SciAm predicts the moon being twice as close, with 12-hr days. This forum says critically that the History Channel gave tides 1,000X today's height. μηδείς (talk) 03:28, 27 February 2017 (UTC)[reply]

See here: "It is not easy to estimate how far away from the Earth the Moon was when it formed, but simulations suggest is was about 3-5 times the radius of the Earth, or about 20 to 30 thousand kilometers. (The Moon is currently about 384,000 km or 60 Earth radii away from Earth, which is about fifteen times further away than it was when it first formed.) The Moon probably couldn't have formed closer than 3 Earth radii because tidal forces from the Earth would just pull it apart again, and it is unlikely that the impact could have ejected material further than 5 Earth radii. It's not a totally easy questions to answer though as it depends a lot on the (unknown) details of the impact and how the hot material behaved in space."

Also note that just after the Moon formed the enormous tides would have made the Moon recede from the Earth at a fast rate, thousands of times faster than the current rate. Oceans had not yet formed on Earth, the Earth's surface was much too hot. In fact, as pointed out here: "The moon, being much smaller than Earth cooled more quickly. Because the Earth and the moon were tidally locked from the beginning, the still hot Earth -- more than 2500 degrees Celsius -- radiated towards the near side of the moon. The far side, away from the boiling Earth, slowly cooled, while the Earth-facing side was kept molten creating a temperature gradient between the two halves." Count Iblis (talk) 05:33, 27 February 2017 (UTC)[reply]

There is unlikely any tidal force at all because the planets dont rotate around their own axis but are in Synchronous rotation aka Tidal locking to the sun, like our moon orbits earth, always showing the same side to us. In such narrow orbits this tidal locking is very likely. This is also assumed for the closest known exoplanet Proxima Centauri b. --Kharon (talk) 12:20, 26 February 2017 (UTC)[reply]

Io (moon) is in a locked orbit and it experiences significant tidal heating due to the excentricity of its orbit. To quote from the discovery paper: "The TRAPPIST-1 system ...represents a unique opportunity to thoroughly characterize temperate Earth-like planets that are orbiting a much cooler and smaller star than the Sun, and, notably, to study the impact of tidal locking, tidal heating, stellar activity and an extended pre-main-sequence phase on their atmospheric properties." Scientists are optimistic that all these things (including detection of signatures of life IF there is life) can be studied in the system, but the investigations have only begun. --Wrongfilter (talk) 12:47, 26 February 2017 (UTC)[reply]

@Kharon is correct that there are no tidal forces when only 2 bodies orbit circularly around their common center of mass, and each rotates once per orbit. That is a classic soluble Two-body problem. However each body (planet or sun) of the TRAPPIST-1 system is pulled by gravity to each of the other (known) 7 bodies. Nobody promises that Celestial mechanics is easy; Celestial mechanics#Perturbation theory suggests where the work is needed on this thorny n-body problem. The article Orbital mechanics gives specific mathematical solutions. You may however enjoy the beauty of some demonstrable multi-body orbital solutions of the choreographic kind, or sketch your own, on this Java page. Blooteuth (talk) 13:38, 26 February 2017 (UTC)[reply]

Extra visual colors via eye tracking?

As I understand it, some of the VR applications? or other equipment coming out do eye tracking where they have a good idea of where the user is looking. It just occurred to me that maybe this isn't entirely for spying on people after all...

Suppose a reader frequently looks at a high resolution computer screen (or, ideally, set of binocular computer screens) that displays video content. The reader is color blind. A camera very closely tracks where he is looking, and superimposes a fine-grained pattern that goes wherever he is looking. The fineness of the grains depends on how accurately it can follow his gaze, the resolution of the system, and whether it's binocular. In half the superimposed pattern, the screen content is changed to exclude the green channel - in the other half, to exclude the red. As a result, there are small fixed regions within his vision, so long as he uses the computer, which are "red-sensitive" and others which are "green-sensitive" - perhaps with some degree of channel mixing to help them appear as one image; after all the red-green receptors themselves have overlap.

Now I've read that people can get used to looking at the world rotated 180 degrees, so I'm thinking maybe in time, supposing he has a heavy computer job for example, or the system is made a standalone prosthesis, that is all it takes to perceive different green and red color values. The person's eyes might learn to process the colors differently and he might even see them as different colors subjectively.

Some time after the experiment, I'd expect these regions to return to normal; if the experiment were repeated with a different set of random regions, I wonder if the person could relearn to see the difference between green and red in those new areas. Would green and red seem like different colors subjectively than they did the preceding time?

Of course, there's nothing in principle to keep the same experiment from being done by people who have normal 3-color vision who want to get a taste of the tetrachromat life.

Is there anything to back up any of this, and is anyone working on such lunacy? I take the X-mosaicism tetrachromats to support the idea of learning to link regions to colors can be done by simple random differentiation - is that sound, at least? Wnt (talk) 21:43, 25 February 2017 (UTC)[reply]

There's certainly work being done on representing colours via other senses: see e.g. this abstract. (Note however the mention of "low spatial resolutions"). I can't see the whole paper, but e.g. this article covers some of the same research and does say that the input can be perceived as colours (caveat again: the systems can take a long time to learn to use). Henry ^Flower 22:32, 25 February 2017 (UTC)[reply]

Eye tracking describes techniques for a real-time experiment. False color images can render non-visible parts of the Visible spectrum or simulate the effect of Color blindness. Blooteuth (talk) 22:54, 25 February 2017 (UTC)[reply]

I believe that eye-tracking has been used experimentally to stabilize images to generate the perception of impossible colors such as bluish-yellow and reddish-green. See https://www.ncbi.nlm.nih.gov/pubmed/17736657 -- The Anome (talk) 14:15, 26 February 2017 (UTC)[reply]

February 26

Stereochemistry

This question is the result of reading Oxcarbazepine and Carbamazepine, and noticing from the infobox imagery that O... seems to be C... with an extra oxygen attached to the central ring.

How do we determine the specific structural formulas of not-so-simple molecules? I remember from high-school chemistry that the empirical formula is derived from breaking down the molecule (e.g. electrolysis of water yields twice as much hydrogen as oxygen), and I suppose that the basic chemical formula can be derived from a ratio of the empirical formula to mass (e.g. hydrogen peroxide will be twice as massive as peroxide, despite producing the same hydrogen/oxygen ratio), but neither one tells us anything about the shape. Based on the comments about Pasteur in the stereochemistry article, I'm guessing that the theoretical shape is the result of directly observed physical properties, but with molecules the size of these two anticonvulsants, I wonder how adding one oxygen would produce a molecule with distinctly different physical properties that can be determined to be independent of its chemical properties. The article refers to Stereoisomerism, so maybe my answer is there, but the article's technical enough that I don't understand it. Nyttend (talk) 12:30, 26 February 2017 (UTC)[reply]

You're correct that "total molecular weight" and "empirical formula" together can be used to solve for the chemical formula (fairly simple algebra if you have good-quality data). For the connectivity of the atoms and the conformation, IR, NMR and X-ray crystallography are the three classical tools one uses. DMacks (talk) 15:18, 26 February 2017 (UTC)[reply]

Also Mass spectrometry. --Jayron 32 22:45, 26 February 2017 (UTC)[reply]

Just molecular weight and empirical formula usually can't solve the structure, see isomers. Fgf10 (talk) 08:14, 27 February 2017 (UTC)[reply]

@Nyttend:, so far we are answering about the chemical structure (approximate 3D location of each atom and to which other one(s) it is bonded). Are you also asking about actual physical properties such as density, melting point, optical rotation, color, etc? Or biochemical properties, such as ADMET, receptor target specificity and affinity, actual cellular or systemic effects, etc? DMacks (talk) 23:00, 26 February 2017 (UTC)[reply]

I got the impression that the beginnings of stereochemistry came from Pasteur's observation that different version of the same compound had different physical properties, which I'm guessing means that he produced some theory (still followed in its basic idea) that the two had identical chemical formulas but different shapes. That's the only reason why I mentioned the physical properties. I'm trying to understand how we get a sense of the structure; I don't have time to check the links that you and Jayron provided above (in a fast-food restaurant at the moment), but I'll look at them when I get home. Nyttend (talk) 01:27, 27 February 2017 (UTC)[reply]

My recollection from undergraduate organic chemistry is that in the days that these things were invented, the complicated structures were derived from "proof by synthesis". That is, if you can synthesize the molecule using well studied reactions that yield predictable products, you can show that your molecule must have a particular structure, given the synthesis protocol. You can further confirm this by decomposing the structure, again using predictable reactions, and showing that the expected products result. I haven't been able to find any particular reference work describing how to do this, though you'll find lots of papers from the 50s and 60s doing a particular molecule by searching for "proof by synthesis" and similar terms. Nowadays I guess you just stick the thing in an NMR and call it a day. Someguy1221 (talk) 08:46, 27 February 2017 (UTC)[reply]

How to hasten the separation of oil from peanut butter?

I made my own peanut butter by grinding up nuts but it's too thin. Apparently if you let it sit for a long time, the oil rises to the top and can be poured off, leaving something more viscous. How could this be easily hastened? Would vibration on top of a washing machine make it better or worse? I can't really strap it down inside the washing machine. ----Seans Potato Business 12:52, 26 February 2017 (UTC)[reply]

Anyone who would even think about taping a jar of peanut butter to the drum of a washing machine is a kindred soul. More practically, you might use a long piece of hosiery (or similarly shaped apparatus) as a makeshift centrifuge. Put the jar inside it oriented so that the bottom of the jar is at the bottom end of the sock or whatever, then swing it round and round. Shock Brigade Harvester Boris (talk) 15:20, 26 February 2017 (UTC)[reply]

I googled for [how to make peanut oil] and got lots of hits for several different methods at varying levels of sophistication or equipment. DMacks (talk) 15:28, 26 February 2017 (UTC)[reply]

Stick it in the refrigerator for a couple of days - it will thicken up. You have squeezed oil out of the nuts when grinding them - but the solids will reabsorb much of the oil. Wymspen (talk) 15:49, 26 February 2017 (UTC)[reply]

You could keep it in a sieve or a suspended muslin bag (jam/jelly bags are ideal) - the liquid oil will drip out. You probably want to do this at around 10°C - too cool and the peanut oil will wax; too warm won’t prevent it going rancid. LongHairedFop (talk) 16:50, 26 February 2017 (UTC)[reply]

Try squeezing the bag to hasten it further (have paper towels ready, but you will need to wash hands with soap to get them clean).

Also, the oil does become thicker at lower temps, so, if eating it cold is an option, then that approach will work.

Finally, if you intend too use the peanut butter in a recipe with butter, margarine, or oil, like baked goods, you could just reduce the amount of those. StuRat (talk) 17:34, 26 February 2017 (UTC)[reply]

A Centrifuge is the most common technical approach for such separations. This was already pointed out in the first post. --Kharon (talk) 11:04, 27 February 2017 (UTC)[reply]

How far ahead can the weather be predicted with reasonable accuracy?

With the best models in use today for weather forecasting, how far ahead can the weather be predicted with reasonable accuracy? --100.34.204.4 (talk) 14:15, 26 February 2017 (UTC)[reply]

Weather forecasting introduces the subject and Atmospheric model teamed with Numerical weather prediction details current techniques. Blooteuth (talk) 14:28, 26 February 2017 (UTC)[reply]

It depends what you mean by "resonable accuracy" as well as what part of the forecast and for what geographical areas, but the answer most people give is something from 48 hours (or perhaps next day) to 5 days although some say up to 9 or 10 days [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29]. There seems to be general agreement anything beyond 10 days is mostly useless. Nil Einne (talk) 14:42, 26 February 2017 (UTC)[reply]

It also depends on the current weather situation. Its a lot easier to predict weather if there is a stable situation than in a case of a quick sequence of alternating high and low pressure systems coming in. --Stephan Schulz (talk) 14:39, 26 February 2017 (UTC)[reply]

I made some changes after you replied, adding references and extending the period to up to 9 or 10 days and mentioning more that more than 10 days isn't generally considered useful. [30] Hope you don't mind as this doesn't I think affect anything you said. Nil Einne (talk) 14:44, 26 February 2017 (UTC)[reply]

No worries. --Stephan Schulz (talk) 15:00, 26 February 2017 (UTC)[reply]

Also the Huffingtonpost reference suggests predictions during winter are less accurate (I didn't look at it carefully so I'm not sure if this is for reasons like the inaccuracy of snow predictions or other such complications). Nil Einne (talk) 14:53, 26 February 2017 (UTC)[reply]

Nil, you're a smart guy and I agree with you 99.9% of the time, but -- Mother Mary an Jozef, you're using teh Huffington Post as a source for a scientific topic? Here are verification stats from ECMWF. You can drill down for lots of details, including comparisons to other centers. Here are stats from NCEP. Notice the numerical forecast centers tend to focus on things like 500 mb anomaly correlation, which are well suited to basic questions of predictability and prediction skill but aren't of much interest to the general public. Here NCEP has some statistics on surface weather elements. Shock Brigade Harvester Boris (talk) 15:09, 26 February 2017 (UTC)[reply]

That NCEP stats page is pretty awesome, thanks! But I don't fully understand it. Can you tell us how we can use it to confirm, deny, or even just investigate the claim that winter predictions are in some sense less accurate than those in other seasons? SemanticMantis (talk) 16:12, 26 February 2017 (UTC)[reply]

First you need to decide what "less accurate" means, which can be a non-trivial problem in itself. ECMWF stats for 500 mb anomaly correlation outside the tropics shows that winter predictions are more accurate than summer predictions. It's pretty well accepted that summertime forecasting is harder than for winter, because summertime weather is dominated by small-scale phenomena such as convective storms rather than larger, long-lived frontal systems and the like. (That's why I went marginally sub-orbital about the HuffPo article.) Shock Brigade Harvester Boris (talk) 16:34, 26 February 2017 (UTC)[reply]

Lots of detailed statistics from the UK Met Office here - http://www.metoffice.gov.uk/about-us/who/accuracy/forecasts - making the interesting point that the four day forecast now is as accurate as the 24 hour forecast was 30 years ago. Wymspen (talk) 15:53, 26 February 2017 (UTC)[reply]

February 27

Why are there so few jet engine manufacturers?

It seems that jetliners from different aircraft manufacturers almost always use jet engines from a small group of manufacturers: GE, Pratt & Whitney, and Rolls-Royce. What is it about designing and building jet engines that is so difficult or expensive that even big aircraft manufacturers don't want to develop their own? --100.34.204.4 (talk) 02:37, 27 February 2017 (UTC)[reply]

It was decided in the 1930s that United States antitrust law did not allow airplane manufacturers to make the own engines (or to own their own airlines, either—see United Aircraft and Transport Corporation). I presume this still applies and would also prevent non-US companies such as Airbus, Bombardier, or Embraer from selling planes to US airlines if they had made the engines for them. And I presume that without the US market, they would be unwilling to manufacture engines. But my presumptions could be wrong; citations welcome. As to how difficult it is, this answer seems to be based on actual knowledge.

None of this addresses the question of why there are so few engine manufacturers. I think (here I go presuming again) it is because engines are so expensive and complicated nowadays that new companies don't want to compete against the existing ones. --76.71.6.254 (talk) 02:56, 27 February 2017 (UTC)[reply]

(edit conflict) And Rolls Royce isn't even making that much profit off its jet engines [31]. I can't fin the specific answer for you, but it's usually dictated by economies of scale. This is general background, and I'm not certain this is the case here: In brief, the output of a given firm, in terms of widgets per year, gets cheaper per widget to a point. Up to that point, a large firm can undercut the price of a smaller firm. If the most efficient scale of production is a third the size of the entire market, then three firms can turn a profit (or one firm can operate three factories). If the most efficient scale is larger than the market, only one firm can turn a profit. It is widely thought, for instance, that the global market for large commercial airplanes can only support a single firm, and the most efficient scale is unreachable [32]. That one firm would be Boeing, with Airbus only continuing to exist thanks to sponsorship by European governments and carriers, who don't like the idea of one company making every airplane. Someguy1221 (talk) 02:58, 27 February 2017 (UTC)[reply]

And forgot to mention, companies that try to enter the engine market tend to get purchased by an existing company [33]. Someguy1221 (talk) 02:58, 27 February 2017 (UTC)[reply]

That does not compute. Boeing gets bigger State subsides than Airbus ever did. [34] , [35]. So Boeing is able to undercut Airbus by selling at below 'true' cost without going bankrupt.--Aspro (talk) 17:31, 27 February 2017 (UTC)[reply]

Barriers to entry may be relevant. StuRat (talk) 03:04, 27 February 2017 (UTC)[reply]

Also Monopolistic competition. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:11, 27 February 2017 (UTC)[reply]

More of an oligopoly. StuRat (talk) 03:47, 27 February 2017 (UTC)[reply]

Monopoly isn't relevant when there's three major manufacturers. The above linked oligopoly is indeed correct. The aviation jet engine (don't forget about marine turbines etc) market is largely determined by the plane manufacturers, as they choose which engine, or choice of which engine, they offer with their planes. Fgf10 (talk) 08:12, 27 February 2017 (UTC)[reply]

Not monopoly, but monopolistic competition: A few large firms controlling the market. ←Baseball Bugs ^{What's up, Doc?} carrots→ 08:44, 27 February 2017 (UTC)[reply]

The jet engine market is weird, since the three companies often work together in mix and match ways - Engine Alliance is GE and P&W, International Aero Engines was originally RR and P&W, and RR and GE worked together on the (failed) General Electric/Rolls-Royce F136, and then there are other smaller companies like the German MTU Aero Engines and the Japanese Japanese Aero Engine Corporation, who manufacture engines for the big three. So it's not really that there are very few engine manufacturers, exactly, but rather, the planemakers and airlines didn't want to deal with so many competing engine standards, and so engine manufacturers coalesced. As for why no duopoly has emerged (like, for instance, how Boeing and Airbus now dominate airliner manufacturing), the manufacturers specifically try to ensure that engine manufacturers are always competing and avoid vendor lock-in by making at least two different engine types available for each model (and Boeing is now going further - Dreamliner engines are designed so that engines from Rolls Royce and GE can be swapped easily). There's a fairly detailed analysis of jet engine manufacturing industry here. Smurrayinchester 09:01, 27 February 2017 (UTC)[reply]

In the UK, there was only a single engine maker and a single large aircraft maker as the result of a deliberate government merger policy in the 1960s. Particularly for aircraft, this is generally seen as having had a bad effect overall, particularly for defence procurement.

In the engines field, this led to the dominance of one company and its approaches, abandoning several promising avenues of development as "not invented here". Bristol Siddeley in particular saw products that had achieved successful sales (the BS Pegasus) absorbed under the new banner but the next generation of development, the BS100 abandoned to save investment costs on a "foreign" site. The supposed advantages of avoiding duplication didn't happen as intended, and engines like the Armstrong Siddeley Viper still continued, alongside the superior BS Orpheus. This single organisation was supposed to increase its investment potential in new projects (such money actually came from a government pot anyway, and was handed out on the same per-project basis no matter who it went to). Yet it also made the whole edifice prone to a single-point failure, such as Rolls-Royce's bankruptcy after the RB211 fan blade problems. Some companies, such as de Havilland and their small helicopter turbooshafts, disappeared into licence building US designs.

Procurement of aircraft was particularly affected. The UK went from the 1950s and an era of innovation and competition between manufacturers to the monolithic doldrums of the 1970s when the answer to all military large aircraft designs was to stick some more new parts onto a Nimrod - which led to abandonment, abandonment and explosion, followed by buying from the US. Andy Dingley (talk) 10:17, 27 February 2017 (UTC)[reply]

While all that is true, the British aviation industry model of the early 1950s was not sustainable: "... there would be too many companies chasing a declining domestic market, and few had the potential to take on the American competition", from The Formation of the British Aircraft Corporation (BAC) 1957-61 (p. 2). That article is about the restructuring of the aircraft industry, but the aero engine sector was under the same pressures. The age when the RAF could purchase several types of aircraft to fulfil the same role had gone for ever. Alansplodge (talk) 13:43, 27 February 2017 (UTC)[reply]

But an industry based on two or three makers would still have supported some competition.

There was no problem post-war that there were "too many" makers, but rather that most of them were far too small. It was the small makers who needed to be merged, not Avro / Vickers / Handley Page / Shorts. What actually happened didn't even give one simple economic unit: the "factory in Belfast" was still known as Shorts and it was still thrown porkbarrel government contracts to keep the population sweet. Work was split between Brough or Warton according to political lobbying by unions and local MPs, not for some corporate economy of scale.

We got the worst of both worlds. Andy Dingley (talk) 15:04, 27 February 2017 (UTC)[reply]

To discuss the barriers to entry a bit more, starting up a new jet engine company would require a major influx of capital, with little promise of a quick return on investment. Compare this to starting a restaurant chain. You could start with just a hot dog cart, then upgrade to a hot dog stand, then one restaurant, then 2, etc., until you have a major chain. So, the initial investment can be quite modest, making for a low barrier to entry. This is one factor explaining why there are so many restaurant chains, relative to the number of jet engine manufacturers. StuRat (talk) 15:15, 27 February 2017 (UTC)[reply]

In the restaurant scenario, selling the same hotdog as everyone else can work. In the engine scenario, selling the same engine as everyone else won't work. There is no reason to contract with the new guy in the market unless he has a phenomenal new design or he has plenty of money, drugs, and women lined up as kickback. 209.149.113.5 (talk) 17:58, 27 February 2017 (UTC)[reply]

True, but being able to do it cheaper would also be a selling point, and being based in nation X, which lacks it's own jet engine manufacturer, may get you more sales in that nation. Still, those barriers to entry are rather substantial. StuRat (talk) 18:02, 27 February 2017 (UTC)[reply]

Here's a fantastic set of charts from the USC Department of Aerospace Engineering: Merger and Acquisition History of Major US Aerospace Companies.

Nimur (talk) 19:15, 27 February 2017 (UTC)[reply]

Can earthling plants live on martian soil?

How is martian soil different from earthling soil? 166.216.159.83 (talk) 15:07, 27 February 2017 (UTC)[reply]

Wikipedia has articles titled Martian soil (for Mars) and simply Soil (which covers Earth's soil). You can read those and arrive at your own conclusions. --Jayron 32 15:14, 27 February 2017 (UTC)[reply]

How is Earth different from Mars? Can earthling life be transported to Mars? Does Mars have indigenous life adapted to the current conditions on Mars? 166.216.159.83 (talk) 15:12, 27 February 2017 (UTC)[reply]

Life on Mars is Wikipedia's article on this subject. --Jayron 32 15:15, 27 February 2017 (UTC)[reply]

As far as current technology, we could only transport small life forms to Mars, such as plant seeds. Keep in mind that they need to be kept alive during the long trip, so may need some heat, even if those seeds are resistant to freezing. Small animals, like mice, would require additional care, such as food, water, oxygen, and removal of solid, liquid, and gas waste (carbon dioxide). Of course, this doesn't mean that those life forms would survive for long, once on Mars, but could be useful for experiments, to see if the transport method is safe. StuRat (talk) 15:23, 27 February 2017 (UTC)[reply]

Just to provide a link to what you're describing (ECLLS); life support system Fgf10 (talk)

Regarding differences, Mars has less gravity than Earth (37.6% as much), a very thin atmosphere (0.6% of the pressure on Earth - see Atmosphere of Mars) with little oxygen (but 96% CO₂), no bodies of (liquid) water (see Water on Mars), and 43% as much sunlight (see Climate of Mars). What little water there is seems to be mostly frozen in the soil and as ice at the polar caps (Martian polar ice caps). Temperatures also drop exceedingly low during the Martian night and winter, particularly in the southern hemisphere and poles. The thin atmosphere also allows radiation and micrometeors to pass through which are blocked by Earth's atmosphere. Of these differences, the lack of water is a major problem for all Earth life, and the lack of oxygen is a problem for Earth animals. Any plan to bring life to Mars should include both plants and animals, as they can together form a closed system, where the plants provide oxygen and food for the animals, which in turn provide fertilizer, pollination, and carbon dioxide for the plants. Far more plants would be needed than animals, both because of the higher metabolic rate of animals, but also because Mars has lots of carbon dioxide to start with, and little oxygen, so need many plants to convert it to O₂. This could also be done mechanically/chemically, but since the goal is to bring life to Mars, plants meet that goal better. Also see Terraforming of Mars and colonization of Mars. StuRat (talk) 15:28, 27 February 2017 (UTC)[reply]

Experiments meant to simulate Martian soil suggest that many plants could be grown on it. [36] You would need to provide water, more air, reasonable temperatures, and for most plants protection from ultraviolet light. So basically, you would have to bring the soil inside and keep it in some kind of greenhouse, but the soil itself appears to be a viable foundation for agriculture. Of course, that's based on what we think is in the soil based on the limited experiments we've sent over. There could still be surprises that make growing plants harder than expected. Dragons flight (talk) 16:02, 27 February 2017 (UTC)[reply]

Metallic Hydrogen, Deuterium

Could metallic deuterium be formed? How would its properties differ from metallic hydrogen? Granted that the initially much lower abundance, and the necessary concentration and purification make difficulties, would it be easier after getting a good sized sample of pure deuterium to form the deuterium kind instead of the hydrogen kind, like somewhat lower pressure and higher temperature?144.35.45.64 (talk) 23:56, 27 February 2017 (UTC)[reply]

Not that many people study metallic deuterium compared to the corresponding state in hydrogen, but it is suspected to also reach this state at appropriate temperatures and pressures. However, the physical properties are expected to be measurably different (thermal expansion coefficient, specific heat, etc.) [37]. Deuterium also, interestingly, has a different phase diagram from hydrogen [38]. Someguy1221 (talk) 00:18, 28 February 2017 (UTC)[reply]

This paper talks more about the difference between the two isotopes, but like the others, doesn't say whether one will form a metal easier than the other. Someguy1221 (talk) 00:26, 28 February 2017 (UTC)[reply]

This is an interesting question. I would think the kinetic isotope effect would stabilize deuterium metal as it stabilizes other deuterium compounds - the heavier molecules jiggle back and forth less under the same heat, so they stay closer to the optimal positions for bonding, as far as I know. But... I certainly don't know, so take that as a mere question. Wnt (talk) 00:44, 28 February 2017 (UTC)[reply]