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Currently Playing: Quantum Field Theory 2b - Field Quantization II

Here we complete the "quantum field theory" of a vibrating string. (Note: My voice is lower and slower than normal - I was coming down with a cold.) Errors: At 0:42 I say "minus c-squared times q-k..." I should have said, "minus c-squared times quantity k pi over L squared, times q-k..." At 6:00 the last two "kets" on the lower right should have n_k in place of n_k+1. The number operator does not change the photon occupation numbers.