freecounterpoint: Not bad 96

Saturday, April 19, 2008

Not bad 96

12 comments:

Tecumseh said...: Not bad, not bad. You met the guy?; 4/19/2008 7:52 AM
Arelcao Akleos said...: Never.... I'd always thought he had to be older, because Feynman was taught by him at Princeton. It turns out that, even so, he was barely older than Feynman.
A "Very American" physicist, in the same sense Linus Pauling was a Very American chemist, and Buckminster Fuller a Very American architect.
Damn, as we descend into the Pepean swamps of base and torpid dhimmitude, we're going to miss such optimistic, life-loving, endlessly daring and creative American thinkers...
These men, in truth, are the ones who deserve "Peace Be Upon Him".; 4/19/2008 12:18 PM
Mr roT said...: Yes, AA. Someone reminded me of the question Wheeler asked Feynman that led to the path-integral formulation of quantum. Here it is. Are you ready?

Suppose there's just one electron in the whole universe.

OK. That's it.; 4/19/2008 1:14 PM
Tecumseh said...: What's the question, JJ?; 4/19/2008 2:31 PM
Tecumseh said...: More: Feynman continued: “Wheeler used advanced waves to get the reaction back at the right time...”. Wheeler then considered the phase shift of the retarded waves going through a medium of absorber electrons forward in time. Wheeler, according to Feynman, made the adhoc postulate that the advanced waves do not suffer a similar phase shift as they propagate backward in time so that “there will be a gradual shifting in phase between the [advanced] return and the original [retarded] signal so that we would only have to figure that the contributions act as if they come from only... the first wave [Fresnel] zone ...” Wheeler told Feynman to figure out how much advanced and retarded waves are needed to get the right answer for radiation resistance. Feynman told Merhra, “I found that you get the right answer if you use half-advanced and half-retarded [potentials] as the field generated by each charge. That is, one has to use the solution of Maxwell’s equations which is symmetrical in time and the reason why we got no advanced effects at a point close to the source in spite of the fact that the source was producing an advanced field is” that advanced waves from the future absorbers exactly cancel the advanced wave from the source on a test charge close to the source. Feynman and Wheeler concluded “we could account for the radiation resistance as direct action of the charges of the absorber acting back by advanced waves on the source.”

The Wheeler-Feynman model solved the classical electron self-energy problem because electrons did not act directly on themselves. They also eliminated the infinite number of classical degrees of freedom, i.e., “modes”, in the electromagnetic force field getting a direct advanced and retarded delayed Lagrangian between a finite number of source electrons. Their idea was to eliminate the infinite zero point energy of the electromagnetic quantum vacuum fluctuations. The experimentally observed Casimir electromagnetic zero-point force would have to be a purely finite boundary effect, but it was not easy to make a quantum theory of this.; 4/19/2008 2:38 PM
Arelcao Akleos said...: I'm goint to have to get Mehra's books on the history of quantum physics. They are history of science which does honestly the science in that history; 4/19/2008 2:47 PM
Arelcao Akleos said...: Ever read parts of his Gravitation blockbuster? I used to think it was roccoco and overkill, but now it strikes me as a masterpiece of technical exposition. You can bloody teach yourself from that thing, and just be an average FCP plodder such as myself. And it's fun, to boot [by way of contrast, compare it with Wald's text, or the the piece of scheit by Carrol ].; 4/19/2008 2:52 PM
Arelcao Akleos said...: Or is it "rococco"??

Bah, sue me if I got it wrong.; 4/19/2008 2:52 PM
Tecumseh said...: Neither. It's Rococo (a French compression of rocaille and barocco).; 4/19/2008 3:18 PM
Mr roT said...: Gravitation, a.k.a. the phonebook, is very easy to read and learn from, particularly if you don;t know any differential geometry. It's annoying probably in the Wheelerian parts ("bongs of the bell" means the value of a dual vector on a vector) but the physics is explained very beautifully.
It's also very helpfully divided into tracks so the first reading is actually quite short.; 4/19/2008 3:21 PM
Mr roT said...: racaille?; 4/19/2008 3:22 PM
Tecumseh said...: Rocaille comes from rocks, racaille has something to do with spit. Just one vowel can make a ton of difference, JJ. It's like physics -- just think of one electron.; 4/19/2008 6:51 PM

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