1 Translation invariance and energy-momentum conservation We showed in class that translation invariance leads to the conservation of the stress-tensor Tv, given by eq. (2.17) in Peskin and Schroeder (PS) for a real Klein-Gordon field. We also showed that this leads to conservation of the energy (2.18) and momentum (2.19). Use the expansion of the Klein-Gordon field in creation and annihilation operators to compute the Hamiltonian, H, and momentum, P, operators, and show that they have the form we used in our discussion of canonical quantization (given in equations (2.31) and (2.33) in PS)