Can the speed of light be affected? Can we cause it to slow, by heat, cold, wind or other outside forces?

Answer 1

Actually, the speed of light can be affected by all of them, and the reason for that is because light travels through things like air or glass, which are mediums with an index of refraction which can be affected by heat, cold, wind, and other forces. In fact, non-linear optics is a burgeoning field today, and through interesting tricks, the speed of light can be made to slow down to a crawl, or be made to go even FASTER than the speed of light! Check the link below.

When light is in a vacuum not in the presence of forces other than gravity, its speed remain a constant. Even when massive gravitional bodies bend the path of light, the instantaneous speed of light at any point is still the same.

Answer 2

Why do u think black holes are given that name. that is becasue they really are that black, so black that thier gravational pull even pulls light back. Thats why we can't see black holes, light can't escape them. This is just one example.
And source of gravity slows down light and also bends it. Technically the forces you mentioned above can not slow light, but they do because those forces bend and somewhat manipulate light thus making it have a larger distance to travel than it would through those forces. However we do not have any accepted theory that proposes that light can go faster than its original speed. However many scientists do not rule it out.

Answer 3

The speed of light is slower in materials with high refractive index: v = c/n

Also, you can consider group velocity and phase velocity... it is possible to produce "slow light" in some conditions... search for "slow light"

Answer 4

correction to someone's answer: black holes aren't necessary black they are invisible but they are related terms since black is an absence of light.