What assumption did Feynman see through about the electron?
December 14, 2006 10:31 AM   Subscribe

In one of Richard Feynman's books, he talks about solving a problem by finding that a 'fact' about (I think) the spin state of the electron was really an assumption. I recall that it could be one of two values, something like T or V, and everybody had assumed it was T without any evidence. I know I got that all wrong, so what's the reality behind it?
posted by Skorgu to Science & Nature (5 answers total)
The Feynman example isn't ringing a bell (the spin of the electron might be a red herring.) Are the T and V parts something that you're remembering from the problem? If so, it might have to do with treating something as a vector rather than a tensor -- perhaps this might have to do with his work in the 50s to try to explain parity violation in the weak sector.

A cleaner example from another field comes from the Crick/Watson choice of the keto forms over enol forms of adenine and thymine (if my memory serves correctly.)
posted by cgs06 at 11:35 AM on December 14, 2006

I think Skorgu is right about it being some kind of spin state, and I do remember verbatim: "it could be T, or it could be V" (swap T and V if necessary) from the book. If someone wants to look it up, it was "Surely You're Joking, Mr. Feynman".
posted by spaceman_spiff at 11:49 AM on December 14, 2006

Best answer:
Finally they get all this stuff into me, and they say, "The situation is so mixed up that even some of the stuff that they've established for years are being questioned - such as the beta decay of the neutron is S and T. It's so messed up Murray says it might even be V and A"

I jump up from the stool and say, "Then I understand EVVVVVERYTHING!"

They thought I was joking. But the thing I had trouble with at the Rochester meeting - the neutron and proton disintegration; everything fit but that, and if it was V and A instead of S and T, that would fit too. Therefore I had the whole theory!
posted by No Mutant Enemy at 12:09 PM on December 14, 2006

I would guess that you're talking about the form of the terms that enter the expressions for amplitudes of weak processes--whether they're tensor or vector terms.

If that is what you're talking about, here's a brief review with some history.
posted by dsword at 12:10 PM on December 14, 2006

Best answer: neutron-proton coupling, from Surely You're Joking:

I went to Professor Bacher and told him about our success, and he said, "Yes, you come out and say that the neutron-proton coupling is V instead of T. Everybody used to think it was T. Where is the fundamental experiment that says it's T? Why don't you look at the early experiments and find out what was wrong with them?"
I went out and found the original article on the experiment that said the neutron-proton coupling is T, and I was shocked by something. I remembered reading that article once before (back in the days when I read every article in the Physical Review -- it was small enough). And I remembered, when I saw this article again, looking at that curve and thinking, "That doesn't prove anything!"

You see, it depended on one or two points at the very edge of the range of the data, and there's a principle that a point on the edge of the range of the data -- the last point -- isn't very good, because if it was, they'd have another point further along. And I had realized that the whole idea that neutron-proton coupling is T was based on the last point, which wasn't very good, and therefore it's not proved. I remember noticing that!

And when I became interested in beta decay, directly, I read all these reports by the "beta-decay experts," which said it's T. I never looked at the original data; I only read those reports, like a dope. Had I been a good physicist, when I thought of the original idea back at the Rochester Conference I would have immediately looked up "how strong do we know it's T?" -- that would have been the sensible thing to do. I would have recognized right away that I had already noticed it wasn't satisfactorily proved.

Since then I never pay any attention to anything by "experts." I calculate everything myself.
posted by djb at 12:14 PM on December 14, 2006

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