It is important to realize that in physics today, we have no knowledge of what energy is. We do not have a picture that energy comes in little blobs of a definite amount. It is not that way. -Feynman

All these fifty years of conscious brooding have brought me no nearer to the answer to the question, “What are light quanta?” Nowadays every Tom, Dick, and Harry thinks he knows it, but he is mistaken. - Einstein

Why all scientists forgot their quotes? 

What is quantum/quanta/photon/EM wave/radiant energy/light? Particle or wave? Where it comes from? How photons are emitted? How photons move? In a straight line or not? Does a photon have mass? Are red and blue photons have the same mass? How exactly photons interact with solar cells to produce electricity? What exactly is photon made of? What is photon's/EM wave's frequency? Does photon vibrate or wave? What mechanism?

If a photon has mass then gravity can accelerate and decelerate photon speed. If a photon has no mass then light has no momentum to produce current in solar cells.

If the light is photon particles that move outward at light speed from light sources/stars, then photons direction must parallel to the direction of gravity so that photons can move in a straight line. If photons can move at a constant speed, then gravity must not able to influence photon speed.