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The Question

(Submitted February 14, 1997)

I am a junior and have a passion for space. I just read in a Popular Science about someone doing an experiment with a satellite. Inside the satellite, will be a vacuum ten times stronger then that of space. It is being built to test Einstein's theory that a body such as the earth, drags space\time along with it. I had asked an astrophysicist at some collage via E-mail if a black hole was planer. She told me that a black hole has four dimensions. Three of space and one of time. Now, since all objects in the Universe revolve around something, that means its moving through space time. What I'm asking you is when the hole moves through space, does it drag time along with it, or does it tear it temporarily? What is you theory of what happens?

The Answer

You've got the right idea. Yes, a black hole does move through "space-time". It certainly moves through space, just like any other star in the galaxy. And everything moves through time. Since Einstein's theory predicts a dragging of space-time by massive bodies, a black hole could also be expected to drag space-time.

This dragging of space-time, however, is usually discussed in terms of rotating bodies. The experiment you read about aims to measure the dragging near the Earth due to the Earth's rotation, not due to its motion around the Sun. But this "frame dragging" (as it's called) also occurs around rotating black holes. In fact, frame dragging becomes so extreme as you approach the event horizon of a rotating black hole that at a certain distance (the "static limit"), all bodies **must** orbit a rotating black hole. (That is, no amount of rocket power could keep you from orbiting, as seen from a great distance). The effect intensifies until at the horizon itself, there's no place to go but into the hole.

However, the dragging is smooth, just as the motion through the galaxy would be smooth. As far as I know, the "tearing" of space-time (or just time) is more of a science fiction idea. The notion of tearing may come from taking the analogy of the "fabric of space time" too seriously.

Jim Lochner

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