A Straight Dope Classic from Cecil's Storehouse of Human Knowledge

What would happen if you were swallowed by a black hole?

August 7, 1981

Dear Cecil:

Please, Cecil, answer my questions and put my mind to rest. (1) What would happen theoretically if the earth was swallowed by a black hole? (2) How would we, i.e., mere mortals, experience this? Would we know it was coming in advance or would it just zap us? Please, our very lives might depend on this!

Cecil replies:

Tranquilize yourself, laddie. Most black holes are thought to arise from the collapse of very large stars--at least ten times larger than the sun. What happens, as you may recall, is that the star, having begun to run out of gas, expands to red-giant size and then explodes as a supernova. Whatever's left over then collapses into a very small, very dense core. If by the time you get down to neutron-star stage (very very dense) you find your mass is still three times that of the sun, then you continue to collapse into a black hole, where the pull of gravity is so great that even light cannot escape.

This won't happen to our sun, but that's no cause for comfort. Life As We Know It will be extinguished during the red-giant stage (if not sooner), which most stars go through sooner or later.

However, suppose you are just tootling around the galaxy in your cosmic Cadillac and you happen to trip over a black hole that's already there. What happens? Basically you are sucked irresistibily into the black hole's "accretion disc," a whirlpoollike mass of gas and dust surrounding the hole. As you get closer and closer to ground zero, the temperature gets higher and higher. At 100 miles away you're heated up to 2,000,000 degrees Kelvin. Needless to say this is Snuff City as far as your caboose is concerned.

But let us suppose further that you had brought the all-time mother air conditioner with you. Then what? Here we must enter the murky swamps of conjecture. In your classic black hole, all matter eventually contracts to a single point called a "singularity," where density and pressure are infinite and space and time have no meaning. Some think that as you were drawn into this point both time and space would contract for you (i.e., you would go slower and slower), so that as far as you were concerned, you would never arrive at the bottom of the well--you would fall forever.

Possibility number two is that the black hole would so warp the space-time continuum that something called a "wormhole" or an "Einstein-Rosen bridge" would be formed. You would be sucked into this wormhole and spat out the other side, in a different place in space and time. Say, Mattoon, Illinois, last Tuesday night. Hardly worth the trouble, to my way of thinking.

Possibility number three (you may want to sit down for this) is as follows. For reasons that I confess are not entirely clear to me, when a black hole grows to enormous mass, it becomes less dense.

If our entire galaxy collapsed into an ebony aperture (I am getting tired of typing black hole), said BH would be about ten billion light years across, with the average density of a thin gas. If we take this to its logical conclusion, it is possible that the known universe is itself a black hole, with us living in it. Wherefore, it seems to me, the obvious question is: how the hell do we get out of here? The casual attitude of our public officials toward this baleful possibility is nothing short of scandalous.

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