Question

Question #d6f72

Answer 1

Photons are packets of energy and are not matter, therefore they have no mass.

Answer 2

As far as we know, photons are actually massless.

Explanation:

According to special relativity , you can either have mass or travel at the speed of light but not both.

We have done experiments to check whether this is the case, and we have set a fairly strict upper limit on how much mass a photon could have and still be consistent with what is observed experimentally ( `< 10^{-14}` eV/`c^2)`. However it is impossible to prove experimentally that its mass is exactly equal to zero.

See Experimental checks on photon mass from the Wikipedia

Interestingly, there is another particle, the neutrino, that we thought had zero mass. We now know that they just very light and travel at almost, but not quite, the speed of light. This discovery won this year's Nobel prize in physics.