**Ask a monkey a physics question thread**

[OngBonga]

Light is light. Photons are photons. They behaved the same then as now. They mediate the electromagnetic interactions. By mediate, I mean they are the exchange particles which express transfers of momentum. Changes in momentum over time are forces, recall. F = dp/dt, where F is force, dp is a small change in momentum, dt is a small change in time, and dp/dt is the incremental change in momentum over an incremental change in time.

Ok, but what I wanted to know is if light still travels at c in the EW universe. I don't think it will, but not because EM is different, rather because gravity will be truly immense.

[MadMojoMonkey]

Ok, but what I wanted to know is if light still travels at c in the EW universe. I don't think it will, but not because EM is different, rather because gravity will be truly immense.

Light always travels at c. It even does so when the Index of Refraction is not exactly 1, but the QM is trickier to understand than the classical approximation of just assuming it moves slower by a factor of the IoR.

Gravity doesn't change the speed of light, only the wavelength of the light.... and the stuff you know about directions and geodesics. Block holes don't trap light by slowing it down. They trap light by red-shifting it to the limit of infinite red shift, which has infinite wavelength, and therefore 0 energy. If it has 0 energy, it's not really a photon, it's been wholly absorbed by the black hole and its energy is converted to ... IDK... heat? It's a black hole... anything else it would be heat. With black holes, I'm not sure what heat means.