slow motion

[claymore]

Is it possible for gravity to slow down the speed of light?. We know it can stop it escaping from a black hole.

[fo3nix]

It can change the velocity of light easily, but not slow the speed except for some exceptional circumstances (such as the one you've already given).

However, since gravity will fairly easily deflect light (with a large enough object anyway), this can be perceived as a change in speed, since it'll take it longer to get to you. But it's going to same speed, just round a longer route.

[jake-the-peg]

Gravity bends the space time that light travels through.

If the distance between two stars is such that it takes light 100 years to travel the distance between and I now place a black hole between them such that the light grazes the black hole, then the light will take slightly longer to travel the distance as the light has no to go slightly further because space has been bent around the gravitational field.

However it ill still travel at the speed of light in at all points in the journey.

A bit like putting a new bend in a motorway - the cars still do 70mph but they now have a little bit further to go.

What does slow the speed of light is matter. the speed of light in air is much slower than in a vacuum and slower still in water.

If you force a prticle through a medium at speeds greater than the speed of light in that medium you get little flashes of light called Cherenkov radiation