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So I’m doing a science project and I’m trying to understand why the photon is massless. I’ve learned that neutrinos were thought to be massless at first, but then physicists found 3 types of neutrinos and established that they have mass. So what if the photon has mass and there’s 3 different types of photons regarding their type of wave. And can we accelerate the photon.

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marked as duplicate by Emilio Pisanty, Qmechanic Sep 20 '18 at 14:39

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    $\begingroup$ Possible duplicate of Why don’t photons interact with the Higgs field? $\endgroup$ – Stéphane Rollandin Sep 20 '18 at 14:16
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    $\begingroup$ Possible duplicate of Why can't photons have a mass?, and of questions linked therein. $\endgroup$ – Emilio Pisanty Sep 20 '18 at 14:36
  • $\begingroup$ Is not true that you cannot accelerate a photon, at least nominally. The speed of photons in a refractive medium is given by $\frac{c}{n}$, with n the refractive index of the medium. If you build a refractive material with a carefully engineered gradient of the refractive index, you can make light to accelerate or decelerate within it $\endgroup$ – lurscher Sep 20 '18 at 14:45
  • $\begingroup$ There is acceleration as soon as the velocity vector change its orientation, not just its norm. Thus, when light deviates from the straight path, there is light acceleration. Gravity alone can induces deviation of light around a massive object. Light is accelerating in vacuum, in this case (deflexion of rays). $\endgroup$ – Cham Sep 20 '18 at 14:49