## Sidney on progress in theoretical physics.

[This edition is for the **tribe**. I will elaborate this so that even those who have not taken calculus will understand it. In short, I will cause the blind to see and the deaf to hear. To those of you in need of such miracles, y’all come back now hear?]

Half way through Physics 253, Quantum Field Theory, after introducing vacuum diagrams Sidney would observe:

In Classical Mechanics, you can only solve the two-body problem exactly. The rest is approximation. In General Relativity, you can only solve the one-body problem exactly. The rest is approximation. In Quantum Field Theory you can’t even solve the no-body problem exactly. This is progress?

I don’t know when he started telling this story. Probably before String Theory had its Cambrian explosion of vacua. I think I heard him ad lib on this point, but I never heard it worked into his routine. Maybe somebody else did?