Talk:Julian Schwinger

Renormalization due to Schwinger?

The article contains an imprecise statement when it attributes the renormalization concept to Schwinger. The renormalization is usually credited to Victor Weisskopof. Anyways, Victor and Bethe already employed renormalization even before Schwinger had a Ph.D.

References on the work of Victor and Bethe can be found in standard textbooks on quantum field theory, such as Weinberg's.

I'm sure that Schwinger did contribute to the development of the renormalization theory but he was certainly not the one who invented it.

I believe that the idea was originally conceived by Kramers. Ty8inf (talk) 03:51, 2 November 2009 (UTC)

War Work

It is possible that Schwinger chose not to work at Los Alamos during WWII because of his personal dislike of the unpleasant J.R. Oppenheimer.64.12.116.131 16:48, 25 March 2006 (UTC)Lestrade

• According to R. Rhodes, in "The Making of the Atomic Bomb," I.I. Rabi refused to work at Los Alamos, saying (more or less) "I'm serious about this war. We could lose it without adequate radar." Schwinger may simply have chosen to work with his old mentor. MWS 22:11, 15 August 2006 (UTC)

In Climbing the Mountain, by Mehra and Milton, Schwinger did not go to Los Alamos because he felt that the bomb was essentually an engineering problem. The book also indicates that Schwinger did not dislike Oppenheimer, but felt uncomfortable around him. Ty8inf (talk) 03:51, 2 November 2009 (UTC)

Minor Edits

Corrected for neutral perspective. Comments about quality of UCLA physics department have no place in a biographical article.

I dunno how to add a comment to the talk page, but the article is erroneous in saying Schwinger didn't use an explicit regulator. He used an infrared cutoff to regulate the integral of cos(w)/w from 0 (he set it to w0) to infinity, which appeared in his calculation of both the vacuum polarization and the electron matter field's self-energy. —Preceding unsigned comment added by 137.158.152.207 (talk) 20:18, 25 August 2009 (UTC)

Schwinger effect

The Schwinger effect redirects here, and this page links to the Schwinger effect. Would be nice to have a separate stub. I believe it has to do with dielectric breakdown of the vacuum. —Preceding unsigned comment added by Lionelbrits (talk • contribs) 18:19, 22 March 2008 (UTC)

It would also be nice to have an article on his source theory and more on why it was not acceptable to his colleagues. Xxanthippe (talk) 02:44, 10 December 2009 (UTC).

Schwinger's picture

I've seen that picture a hundred times--- I am pretty sure that there aren't copyright issues with it. It's the photograph he puts in books and whatnot, it's supposed to be used for stuff like this. Unfortunately, this is all from vague memory, so I can't verify it. I think that for photographs of academics, taken from university archives, the copyright issues are probably nonexistent. I can see how for photos of Brittany Spears there could be issues, but does that mean that we have to find out what anonymous photographer took a picture of a dead scientist forty years ago?Likebox (talk) 19:17, 11 September 2008 (UTC)

Differential form of the path integral

I find the statement "He expressed the Feynman path integral in differential form" to be misleading in the sense that it implies that Schwinger started with the path integral and rewrote it in differential form. However this is not at all the case. Rather Schwinger's differential formulation of QFT was later found (by Dyson) to be equivalent to Feynman's path integral approach. Ty8inf (talk) 03:51, 2 November 2009 (UTC)

In fact, it is exactly true that Schwinger started with the path integral and rewrote it in differential form. To clarify: the thing that Dyson did is to show that the Feynman diagrams (not the path integral) could be derived from the standard time-dependent perturbation theory. This is not a surprise, in hindsight, because the time-dependent perturbation theory is just the form that the path-integral takes when you work with an "integral" over transitions between discrete energy levels. But dyson explicitly showed that Schwinger's equations of motion and the perturbation series that he used would come out of time dependent perturbation theory, which was a standard tool. This allowed physicists to learn Feynman diagram methods without using the path integral. That was historically important for the acceptance of the new methods, but it has nothing directly to do with the Schwinger variational principle.

What Schwinger was after was something altogether different. He wasn't trying to formulate diagrams, he wanted the equations of motion and canonical commutation relations for fields to come from an obviously relativistically invariant Lagrangian formulation. Feynman had completely solved the problem for bosonic fields--- the path integral is the answer--- but he couldn't handle Fermions the same way. When Feynman dealt with Fermions, he formulated their theory with diagrams for the particle paths, but didn't give a path-integral for their fields.

The reason is that the theory of the path-integral of Fermionic fields required a mathematical innovation, called Grassman integration. Grassman variables and Grassman integration were invented in the 1956 by David John Candlin in the west, and by Felix Berezin in the east a little later. Both started from the known Feynman diagram expansion for Fermi fields, and developed the same formalism. Berezin went farther with it then Candlin, but Candlin came first.

Anyway, Schwinger's action principle predated both Candlin and Berezin. Schwinger didn't know how to integrate over Fermionic fields, so he decided that it wasn't necessary to integrate at all！ His idea was to replace the integral in the path-integral by a set of differential identities which would be equivalent to the path integral, and could replace it. The idea was to consider a Lagrangian with extra source terms coupled to different operators, and then to differentiate with respect to the sources. This would pull down different operators in the integral. Then you could make rules for how the derivatives of the path integral behaved without dealing with the integral itself. This formal trick allowed Schwinger to recast the path-integral as a set of differential identities which include the equations of motion for the operators and the commutation relations.

Schwinger could easily do this for bosonic fields, because of the path integral. After he dealt with bosons, he found that the same formal rules worked without any problem in the case of Fermionic fields too. This was a surprise, and for this reason (I think) he suggested that the differential form of the action principle is more fundamental than the path integral. The reason, in hindsight, is because there is a consistent fermionic integration, but Schwinger didn't know that. The formalism Schwinger used was the first Lagrangian formulation which could deal with Fermions and Bosons on equal footing. Feynman felt uncomfortable with path-integrals well into the sixties because he was not sure how to deal with Fermions. A lot of other people did too. Path integrals only became mainstream in the 1970s, as Grassman integration became a standard part of the physicists toolkit.

Schwinger disguised the path-integral origin of the action principle to some extent. Maybe it was the rivalry with Feynman, maybe it was because he felt that the path integral was only heuristic (a lot of people felt that way back then), or maybe he felt that a quantum mechanical formalism that didn't allow for Fermionic fields was essentially incomplete. I don't know the reason. But the Schwinger variational principle is historically important because it did allow many people to do something equivalent to Grassman integration before Grassman integration was defined.Likebox (talk) 05:12, 19 January 2010 (UTC)

Statistical Atom and the Thomas-Fermi Model

There is no mention of Schwinger's work on the Thomas-Fermi model that he carried out in the early 1980s. Here I quote from Schwinger's biography, Climbing the Mountain by Mehra and Milton:

"It is interesting that this work not only is regarded as important
in its own right by atomic physicists, but has led to some
significant results in mathematics.  A long series of substantial
papers by C. Fefferman and L. Seco has been devoted to proving his
conjecture about the Z dependence of the ground state energy of large
atoms.  As Seth Putterman has remarked, it is likely that, of all the
work that Schwinger accomplished at UCLA, his work on the statistical
atom will prove the most important."

Ty8inf (talk) 18:09, 26 November 2009 (UTC)

Schwinger's Quote Regarding Feynman

About this quote:

"Like the silicon chips of more recent years, the Feynman diagram was bringing computation to the masses."

I am reminded of a quote attributed to Newton about how he (Newton) stood tall merely because he stood on the shoulders of giants. Most of the time, that quote is used to imply a humility on Newton's part; that implication, however, is incorrect. Newton was actually referring to a rival of his (a German, I believe) who was known for his physically short stature.

I mention this because James Gleick in Genius states explicitly that Shwinger was being anything but respectful with that line; that in fact that he (Schwinger) considered it pedagogical tool, not a scientific tool. I believe that another line should be added to emphasize this point.

<br. />—NBahn (talk) 03:55, 25 July 2010 (UTC)

Schwinger and Infinite Energy Magazine

interesting how Schwinger worked with Eugene Mallove of Infinite Energy Magazine. Schwinger spoke at Mallove's conferences. 66.194.104.5 (talk) 14:59, 9 June 2011 (UTC)

Immigrate versus migrate

Hi, I think there is a misunderstanding at work here. The term to "immigrate" is used in relation to a country to mean that a person relocates to that country. To "emigrate" is used in relation to a country to mean that someone leaves that country. Therefore, no matter from which perspective it is viewed, the term is clear for international readers, and the meaning of the sentence is that the person moved to the US from another place. Moreover, to "migrate" does not have the exact same meaning, and, while it not wrong to use the term, it is less precise in this situation. Silvrous ^Talk 10:13, 23 February 2013 (UTC)

Yes, there is a misunderstanding at work here - and I think it is you who are misunderstanding. One action of relocating one's life from Poland to the US can be described with 3 variants of the same verb

• Emigrate
• Immigrate
• Migrate

The only distinction between the verbs is that 'Emigrate' implies the country from which they departed according to the implied location of the author, 'Immigrate' implies the country in which they arrived again according to the implied location of the author and 'Migrate' makes no implication as to the perspective of the author, requiring origin and destination to be specified explicitly. The implications of author location translate into assumptions that the readers share the same location as the author

There is indeed a tautology in saying "immigrated to America" for US readers, because America is stated once and implied once, although this is consistent for those readers. This is a jarring contradiction for readers from all other locations because their own location is implied, but America is stated. The jarring conflict is only resolved by concluding that the author is based in the US. I note that you rejected the alternative "emigrated to America", which would be consistent for Polish readers, because Poland is both stated and implied but jarring for readers from all other locations unless they conclude that the author is based in Poland,

As I understand it, Wikipedia is neutral in author perspective - articles are not written from a US perspective and should strive to avoid this. That being the case 'migrate' is the correct word to use to preserve that neutral perspective. 'Alternately' (for users of US English and 'Altenatively' for users of UK English), if you insist on using the 'word 'Immigrate', it has to read:

Julian Seymour Schwinger was born in New York City, to Polish Jewish parents Belle (Rosenfeld) and Benjamin Schwinger, a garment manufacturer,[1][2] who had 'immigrated' (for US located readers, 'emigrated' for readers located in Poland and 'migrated' for all other readers) to America.

Please show some respect for non US users. The verbs 'Emigrate' and 'Immigrate' both imply author location and assume reader location, forcing readers from any other location to evaluate location unnecessarily. 'Migrate' reads equally well for all readers and rightly retains focus on the content rather than extraneous questions of location and perspective. --78.32.68.244 (talk) 11:36, 23 February 2013 (UTC)

Concerning the edit to 'emigrate', this is, of course, a valid way of describing the move made by the Schwinger family for readers based in Poland. In reverting from 'emigrate', user Silvrous states 'As explained on the talk page, it is gramatically incorrect to state that someone emigrates to a country'. This of course is false. Implicit in the context is the fact that the emigration was from Poland and the destination is explicitly specfied as the US. All emigrations and immgrations are from somewhere to somewhere else. There is no grammar error. This is not a syntactic issue, it is semantic. And to portray it as grammatic is a complete misrepresentation of the issue (coming back to this after I have eaten) --78.32.68.244 (talk) 12:52, 23 February 2013 (UTC)