Workshop on Weinberg's Quantum Theory of Fields Hi, I've just joined this forum. I've been reading Weinberg's Quantum Theory of Fields Vol I for a few years on and off, and I'm now on Chapter 10. While I found it to be the most enlightening approach to Quantum Field Theory, I found parts of it heavy going. If there is anyone out there who, like me, has some answers to offer to some of the tricky bits but still many questions, do you fancy joining me on Weinberg Workshop here? First question: Chapter 2, page 68: Why does Weinberg say "It is very important that when Lambda_mu^nu is an arbitrary 3-dim rotation R, the Wigner rotation W(Lambda,p) is the same as R for all p"? Is this just for convenience, otherwise the equations get too complicated? I see this is true for the particular choice he uses, but I don't see why it has to be true.