So according to QFT, fundamental particles are just excitations in their underlying fields.(adsbygoogle = window.adsbygoogle || []).push({});

So the photon would correspond to an oscillation of the EM field.

But it takes energy to excite this field. And E=mc^2. So therefore the photon should have some mass. Energy was put in to create it. That energy has to be concentrated somewhere.

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# B Why are Photons Massless?

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