Does Light have mass?

The confusion has to do with the little-known fact that mass doesn't have the same meaning in general relativity (GR) as it does in Newtonian mechanics. In GR, light follows straight lines in Minkowski 4D space-time. It doesn't change direction and has no mass to be attracted by gravity; instead, gravity warps the space-time.

In Newtonian mechanics, gravity is a force field in 3D space, rather than a warping of 4D space-time. So light is attracted by gravity and changes direction when passing a strong gravity field. Because the direction of a photon is changed, its momentum is changed. If momentum is conserved, then an equal and opposite change of momentum must be imparted to the source of the gravity. Therefor, in Newtonian 3D space photons have gravitational mass, and other masses are gravitationally attracted to passing photons.

I doubt if most physics PhD's are aware of the fact that mass has different meanings in different contexts. They are so indoctrinated in GR that they become angry when anyone suggests that photons have mass.

sources used are from the top down:

Light is in the Electromagnetic Spectrum...

because light is in the EM spectrum it emits Radiation Pressure upon hitting a surface

Because light exerts Radiation Pressure upon hitting a surface, it must have energy (and kinetic at that) further proving the E=MC^2 theory... Because if Light had no mass, it couldnt have energy (0*anything) = 0

therefore the Solar Sails are a possibility :)

Light does not have mass. It does have energy and momentum. It is effected by gravity.