For a particle moving at a small fraction of the speed of light, momentum is just rest mass times velocity, and since the rest mass doesn't vary, uncertainty in momentum is equivalent to uncertainty in velocity...but what would uncertainty in momentum mean for a photon? Would it be uncertainty about the frequency, or uncertainty about the distance the photon will have moved between two successive position measurements? Maybe you'd need quantum field theory to deal with this question, and I don't know if the uncertainty principle has the same form in quantum field theory as it does in nonrelativistic QM...(adsbygoogle = window.adsbygoogle || []).push({});

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# How does uncertainty princ. apply to photons?

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