The light doesn't get affected directly at all. It's just travelling on its own merry way, runs into the curve in space caused by the gravity and follows that.
Let me think of another analogy...
Ok, you're travelling slowly along a narrow river in a boat (which represents our beam of light) and there's a weir to the right hand side. The presence of the weir has absolutely no direct effect on your boat whatsoever (ie. there's no force from the weir that is pulling your boat) - it's just keeping going forward.
However the weir is
moving the water that your boat is floating on and therefore your boat will veer to the right.The weir isn't affecting your boat
itself though, just the water it travels on.
As for photons having mass and other such nasty questions. A physics textbook will tell you they have negligable mass (same as electrons and things like that). Now, bear in mind that negligable doesn't actually mean zilch, just really really tiny.
Another of Einstein's famous equations E=mc^2 tells us that anything with energy and velocity will have a mass of sorts, even if it is ridiculously tiny.
I was visiting
Cern and got to watch this visitor telling the particle physicist that electrons didn't have mass. Well, the response was that it
did have a mass. For normal people its so ridiculously tiny it doesn't really matter, but for these guys I guess it starts to be a bit more important.
Once again though, the fact it has even a token mass has
nothing to do with it appearing to be bent by gravity - the gravity is affecting the space it travels in, not the light itself.
[ 04-11-2005, 03:52 PM: Message edited by: shamrock_uk ]