Andrew Strominger

So a black hole is defined, theoretically, as a region of space-time from which light can never escape.

Therefore, it's black.

Now, that's just the starting point.

Many weird things follow from that basic definition, but that is the basic definition.

What is light that can't escape from a black hole?

Well, light is the stuff that comes out of the sun, that stuff that goes into your eyes.

Light is one of the stuff that disappears when the lights go off, the stuff that appears when the lights come on.

Of course, I could give you a mathematical definition or a physical mathematical definition, but I think it's something that we all understand very intuitively.

what is light.

Black holes, on the other hand, we don't understand intuitively.

They're very weird.

And one of the questions is about black holes, which I think you were alluding to, is why doesn't light get out?

Or how is it that there can be a region of space-time from which light can't escape?

It definitely happens.

We've seen those regions.

We have spectacular pictures, especially in the last several years of those regions.

They're there.

In fact, they're up in the sky, thousands or millions of them.

We don't yet know how many.

But the proper explanation of why light doesn't escape from