PostHeaderIcon What is Hawking Radiation?

Hawking Radiation is the process by which black holes evaporate. Usually only small black holes actually evaporate, though Hawking Radiation is believed to happen to all black holes.

Background Information:

In spite of conservation of matter, we can assume that matter can be created from nothing, as long as it disappears quickly enough for the universe “not to notice.”

If you imagine that a particle is created from nothing, you can get away with it if its antiparticle (like a positive number and a negative number) is also created from nothing right next to it. The two particles immediately combine – going back into nothingness ((+1) + (–1) = 0). These imaginary particles are “virtual particles,” and their appearances and disappearances are called Vacuum Fluctuations.

An Instance of Hawking Radiation:

I’m going to write this in steps.

1. A black hole exists. Anything that ends up within the black hole’s event horizon ultimately falls into the black hole, adding its mass to that of the black hole. It can never escape.

2. A virtual particle pair springs into existence RIGHT ON the event horizon.

3. Before the two particles can annihilate (combine and disappear) one falls into the black hole’s event horizon. OH NO!

4. The second virtual particle is stuck! It can’t disappear anymore since its pair (its soulmate if you will) is gone forever!

5. The universe “notices” the existence of an extra particle by the black hole.

6. The extra particle is outside the black hole’s event horizon, and it’s a real particle now, not a virtual one because it existed for too long and the universe noticed.

7. But wait! You’re NOT ALLOWED to create something from nothing, so this particle had to come from somewhere.

8. The universe asks its bookkeepers where this extra particle came from.

9. The bookkeepers scramble. (They’re being audited.) Ummm… no one will notice if we take a little of the energy from the black hole, will they?

10. Clearly the energy for this new particle must have come from inside the black hole.

11. The black hole is now down one particle’s worth of energy. (Another way to think of this is that the virtual particle that fell in had “negative” energy – absorbing some energy from the black hole).

If you weren’t following all this anthropomorphizing of the universe, it looks like a particle is now beside the black hole, and the black hole is a little smaller.

In effect, the black hole has evaporated a little bit. Big black holes are sucking in so much mass that this tiny evaporation doesn’t have any effect. Tiny black holes, on the other hand, evaporate faster than they can suck in matter. So if there were a one-atom black hole created on Earth, one might be afraid that it would suck in the atoms next to it, and the molecules next to that, and get bigger and bigger until it sucked in the Earth. Luckily a one-atom black hole would evaporate before that happened. At least, so say the physicists in Geneva who are trying to create tiny black holes.

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Where’d I Get My Info?

Astronomy classes at Whitman College

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