Question

Did Feynman ever derive the Bragg equation using Feynman diagrams?

Answer 1

Since Feynman diagrams are about the interaction of subatomic particles, and the Bragg equation isn't really about subatomic interactions, but about the geometry of reflection of x-rays, I doubt it.

Feynman diagrams here feel like a spanner for a job the requires a hammer.

Answer 2

I agree. I asked Freeman Dyson and he couldn't recall it either. But, Feynman's lectures show Feynman diagrams for reflection and interference so one would think there is something in his notes about the Bragg equation. The real reason is that Feynman always viewed photon interactions as particle interactions and not as wave interactions ie no field, just particles. So there must be an alternate Feynman diagram representation for the Bragg equation if Feynman's premise is correct that photons can always be represented as a particle. No duality here.

Answer 3

It might well be. I've learnt the hard way to be careful to say never!

Answer 4

And sure enough, it looks like it's possible. This paper is a special case, but it'll get you started. Look of course at the references.

https://docs.google.com/viewer?a=v&q=cache:RzPD6Xf7Gi4J:ctp.itp.ac.cn/EN/article/downloadArticleFile.do?attachType%3DPDF%26id%3D14911+bragg+law+feynman+diagram&hl=en&gl=us&pid=bl&srcid=ADGEEShGcZwt4zFkxfE4K_KU45nUACP6ShMahqYoaRAm_eRMmc4-H4lQ7qN-Y6-ofJ_MzgWA47utr65lypqxDcU9q5coAaIvjTITcRBmi8agB3izpoFNkkcw4xi0m31S_BftXrvnmJor&sig=AHIEtbStklhptnMzyRlDigu4VaSNp85TlA

Answer 5

As you said, it is a start. But you would have thought Feynman would have done it somewhere.

Answer 6

Let me know if you find it.

Answer 7

I found several articles on photon acoustical coupling diagrams similar to what you found previously, but even those reference seem to not hit this nail on the head..as you said..sometimes if you have a hammer and not a spanner then all problems look like nails.

Answer 8

I shall keep looking and tell you if I found it. Maybe, one needs to just reconstruct it a priori.

Answer 9

This would be a good question for physics.stackexchange.com

Answer 10

I just wrote to David Hecht the first author on the paper you sent asking him the same question.
What is the physics.stackexchange.com?

Answer 11

I just posted it on physics.stackexchange.com. Thanks. Will keep you informed.

Answer 12

I see. Name dropper! ;-)

Answer 13

If you want name dropping, I actually published with one of Bragg's grand children students..a chap called Francis Crick, who aggravated Bragg no end and is known for some thing or other.