I originally wrote this after having a discussion with some folks on an internal chat about Physics. I captured the text of that conversation and then converted it into a blog entry. I had my particle physicist friend review it and she corrected me on a few things. I don't claim to be a physicist or a mathematician, but I do have a fairly good grasp on the concepts behind all of this. If I am saying anything wrong, it's my doing, and you should let me know so that I learn and I can fix it.
As most people know, black holes suck in stuff like a vacuum. Most people don't understand why though. They get the overall concept that gravity gets so strong that even light can't escape. But light doesn't have mass. So how does light get sucked into a black hole?
In reality, it doesn't. Not really. The problem though is with that word sucked. It kind of implies that the black hole is directly interacting with the light. It isn't though. What Einstein discovered with General Relativity is that gravity actually bends space. Now you may ask yourself, what does it mean to bend space? I can give you a 2d analogy.
Imagine you live in flatland. You are a 2 dimensional being that only knows how to go up down left or right. You are basically stuck in a universe that consists of a flat plane. Now imagine that somehow, that plane gets bent in our 3 dimensional space. You will be unaware of the bending, as you can only see the space in that plane we are bending. The fact that we bend it in 3d is invisible to you. You can still move up down left or right on the plane just like before, and you can't see anything except things that are in that horizontal plane.
Now what does that mean for us 3d beings? It means that our space is being bent in other dimensions. There is some uncertainty, however, about what those dimensions might be. Physicists studying String theory believe there could be dozens of dimensions, although most of them are curled up in spacetime so small that they are basically invisible to us. But it could also be some other physical dimension that we just aren't aware of, just like how in flatland you would be unaware of the third spacial dimension, even though a 3 dimensional being can see them all clearly.
Light moves through all these dimensions. How do we know about these other dimensions? Things like light move differently depending on how space is bent. Some physicists believe that if you could see all the dimensions, you would see that light is actually traveling in a straight line through them all, but because our space is being bent in other dimensions, the light appears to curve to us in our 3 dimensions.
What causes this curvature of space? Gravity. Depending on the strength of gravity, the curve gets steeper and steeper. Black holes are just the point at which space gets bent so much that it basically folds in on itself, and there is no longer a path that light can travel in our 3 dimensions that doesn't exist within the black hole itself. Thus, light can't escape.
But this isn't about why black holes are black. You knew that already. It's about how they aren't entirely black. What does that mean? To really explain it, I'm going to have to explain a few deeper concepts within Physics. I've already started with one of them, General Relativity. I'm going to touch on that one and then touch on Special Relativity and Quantum Mechanics as well. When it is all said and done, you will understand why black holes aren't actually so black.