Monday, October 11, 2010

The Black Hole and the Light Bulb

Walk into a dark room and turn on a light bulb. The light heads off in every direction - to all sides, up to the ceiling, down to the floor. Big whoop. After all, that's what light does.

But I think that very fact goes to heart of a misunderstanding that most of us have about what happens inside a black hole.

When we're told that a black hole's gravity is so strong that nothing can escape it, not even light, we naturally think of light trying to get out, but being overcome and falling back - much like a baseball thrown into the air or a failed rocket.

Unfortunately, that just isn't the way to think about it. Sorry.

Let's imagine our shining light bulb crossing the event horizon into a black hole. Suddenly, its light doesn't spread out in all directions anymore! It goes in only one direction - right smack toward the center of the black hole. It doesn't head in the direction of an escape route (only to fall back) because it literally has no direction that goes that way. (As the lecture I was watching this afternoon put it, "all roads lead to Rome."

The reason all roads lead to the center of the black hole is not gravity by itself, but the gravity's monstrously huge distortion of space-time that twists things in such a way that, for light and anything else, including the poor light bulb, there simply is no outward direction.

The lecture by Professor Benjamin Schumacher, an extremely accomplished physicist teaching a course for dummies like me, explains all this in terms of tilting "light cones," which is fine for those of us who are comfortable with light cones. But I just invented this light "bulb" method as a simpler way. Maybe it even helps.

No comments:

Post a Comment