Q:

Do photons have mass?

A:

Quick Answer

As of 2014, there is still significant debate as to whether photons have mass. Traditional quantum mechanics dictate that photons are without mass because they exhibit qualities of waves. Photons, however, have discrete particle-like qualities that set up a duality.

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Full Answer

If photons do have mass, they would end up traveling at a speed somewhat below the measured, constant speed of light. Since light is composed of photons, the speed of light would not be a constant because a photon with mass would be affected by other forces. Experiments have determined an upper limit on photon mass, measured at 1 x 10^-18 electron volts. A lower limit cannot currently be determined experimentally, allowing for the possibility that photons do have a mass of zero.

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