[Doctor Stochastic]

But in order to have momentum, mass is required.

But not rest mass. A photon may have finite momentum but zero rest mass. Photons aren't heavy, they're light.

[The_Victor]

But not rest mass. A photon may have finite momentum but zero rest mass. Photons aren't heavy, they're light.

I posted a link at post 116 with an essay about science being unable to confirm the zero rest mass of a photon. It is interesting that the equations allow for the zero rest mass, but do not confirm it.