The course in mathematical physics was taught by Herman, and one thing I remember about Herman's class, and that is that he assigned one day – and I've written about this also – he assigned one day a problem that consisted of proving by reflection of co-ordinates that parity is conserved. And I spent the weekend on the problem and no matter how I twisted it, I could not prove from mathematics alone that parity was conserved, and so I turned in a little note on Monday that said I don't believe that parity can… parity conservation can be proved by reflection of co-ordinates. It’s a matter of how the Hamiltonian behaves under reflection of co-ordinates and that’s a matter of the laws of physics, and it would be possible, to have… in principle… to have laws of physics that were not symmetrical. The actual electromagnetic theory is symmetrical, but some other theory might not be. So I was not one of those people who thought that parity had to be conserved. And there were others, I discovered. I discovered that Dick Feynman was not particularly impressed with the need to have parity conserved under all conditions, Fermi also, and Dirac. These were all people who felt that parity conservation was a property of certain laws and that you can have others. In fact, if you look back at Fermi's 1934 paper on beta decay you will discover that he adds… that he has a vector interaction for the… how does it work? A vector interaction for the neutron and proton multiplied… a vector current for the neutron and proton, multiplied by an axial vector current for the electron and neutrino, something like that.
[Q] I see, so he…
Now, that actually, because of the special properties of the mass-less neutrino and so on, and that actually doesn't have any parity-violating properties because you can transform it into the… into a parity conserving transformation just by defining a new neutrino which is gamma five times the old neutrino. But it indicates that Fermi was paying absolutely no attention to parity, and he never thought that it was a fundamental inviolable principle. So there were a number of people who didn't think it was an inviolable principle. But apart from that, I don't remember learning much from Herman.
