Light is affected by gravity which means light has got mass. Quantum theory tells us that light consists of discrete quanta of energy, which we call photons. These photons have a rest mass of zero (as a consequence of special relativity), but a "moving photon" (I don't know whether that notion is stupid) has got some mass.
According to Planck, a photon travelling with a frequency ϑ will be associated with an energy
$$
E=hϑ.
$$
Since the same photon is travelling at the speed of light, it should hold valid for relativity also. In relativistic theory, the energy of a photon is given by
$$
E=pc
$$
for a photon $p=mc$ where $m$ is the relativistic mass of the photon.
Hence $E=mc^2$
Comparing both equations,
$$
hϑ=mc^2$$
or
$$m=hϑ/c^2$$
which means the mass of a photon is dependent on its frequency. This is the cause of redshift of light in a gravitational field. But how frequency account for mass? Is it a direct evidence that light and matter are not distinct entities of the universe, but matter is nothing but condensed energy?
3 Answers
There is a great misunderstanding here. The photon is an elementary particle (the gamma in the table is the photon) of spin one and mass zero. This has been validated innumerable times in nuclear physics, atomic physics and particle experiments. There is no question about it.
Special relativity treats the four-vector of a particle. In this framework the masses of all particles are the four vector dot product, called the invariant mass and does not change, hence the name.
In General Relativity the total four vector follows the geodesics of the four dimensional space time , it is the total four-vector that bends in space time , whether a massive particle or a massless one.
All the rest is misuse of formulas , due to fundamental misunderstanding of special relativity.
Light is a gravitational wave of bent space, it travels at the velocity of C, where time slows down. At that velocity (with time dilation) it makes a gravity wave into the photon. Mass is nothing more than the potential energy of a gravity wave of relativistic bent space. because it is traveling relativistic-ally it is slowing time and bending space. So when the time dilation of a photon or a "micro-gravity wave" travels through a gravitational part of space, like the side of the planet, the planet's time dilation adds to the sin wave of the light's frequency of time dilation causing it to bend along the planet's time dilation gravity gradient. Where ever mass is, there shall you Always find slower time. I like this question it gets to the real facts fast!
I think the answer could be just as simple as that mass of any body i just a projection of that system vibrating. Consider a particle vibrating about a fixed position which starts gaining speed but first when it had zero speed or small vibration frequency its body vibrations were restricted to small particle area but when it start vibrating its projection disperses to a relatively bigger area and when it approaches "c" it completely vanishes. So i think you get the idea that what i am saying.
