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Thursday, September 11, 2008

What Happens if You Fall Into a Black Hole?You die.

Illustration by Robert Neubecker. Click image to expand.

The world's largest scientific instrument, the Large Hadron Collider, was switched on in Switzerland on Wednesday. A few people worried that the LHC would cause the world to be swallowed up by a black hole, especially when it starts to operate at full force in the spring. What would happen if you fell into a black hole?

Your body would be shredded apart into the smallest possible pieces. Neil deGrasse Tyson, director of the Hayden Planetarium at the American Museum of Natural History, who wrote the definitive account Death by Black Hole, imagined the experience as "the most spectacular way to die in space."

A black hole is a place where the force of gravity is so powerful that you would need to be traveling at a speed faster than the speed of light to escape its pull. Since nothing in the universe is faster than the speed of light, nothing that falls into a black hole can ever escape. The border at which gravity becomes strong enough to create that phenomenon is known as the "event horizon"; it marks the outer boundary of the black hole. (Until the 1940s, some scientists believed that matter crusted up on the event horizon and didn't fall in.)

Closer to the center, gravity is even stronger. If you were caught by the pull of a black hole, you would be sent into free fall toward its center. The pulling force would increase as you moved toward the center, creating what's called a "tidal force" on your body. That is to say, the gravity acting on your head would be much stronger than the gravity acting on your toes (assuming you were falling head-first). That would make your head accelerate faster than your toes; the difference would stretch your body until it snapped apart, first at its weakest point and then disintegrating rapidly from there as the tidal force became stronger than the chemical bonds holding your body together. You'd be reduced to a bunch of disconnected atoms. Those atoms would be stretched into a line and continue in a processional march. As Tyson described it, you would be "extruded through space like toothpaste being squeezed through a tube." No one knows for certain what happens to those atoms once they reach the center, or "singularity," of a black hole.

In a small black hole—like the one predicted by the LHC doomsayers—this dissolution would occur almost immediately. In fact, for all but the largest black holes, dissolution would happen before a person even crossed the event horizon, and it would take place in a matter of billionths of a second.

The more matter—and people—a black hole gobbled up, the bigger it would get. That could have the effect of making it less spectacularly deadly. As a black hole increases in size, the differences in gravitational force inside become less dramatic. If you fell into a truly gigantic black hole, the rate of change—and resulting tidal force—might not be enough to rip your body apart until after you'd crossed the event horizon.

If you fell into a large enough black hole, your last moments would be a little bit like being on the inside of a distorted, one-way mirror. No one outside would be able to see you, but you'd have a view of them. Meanwhile, the gravitational pull would bend the light weirdly and distort your last moments of vision.

Got a question about today's news? Ask the Explainer.

Explainer thanks Ted Bunn of the University of Richmond and Edwin Taylor of MIT.

Original here

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