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#1 2003-05-31 20:00:10

Alexander Sheppard
Member
Registered: 2001-09-23
Posts: 178

Re: Hawking radiation - Cheap anti-matter source?

I was just thinking, Hawking radiation should be equally matter and anti-matter. Of course, it would only come in significant quantities from a small black hole--perhaps even one small enough to haul along in a starship. Assuming that it is feasible from an engineering standpoint to in some way haul a small black hole along in a starship, it would seem possible to generate unlimited amounts of antimatter. One could envision Hawking drive ramscoops, whereby hydrogen is harvested from the interstellar medium, fed in a controlled fashion into a small black hole, and then, once the mass reappears as anti-matter in form of Hawking radiation, harvest it to use in a photon rocket.

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#2 2003-05-31 23:05:21

RobertDyck
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From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 7,930
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Re: Hawking radiation - Cheap anti-matter source?

I should be possible to contain a very small charged black hole in a magnetic field. The real engineering problem is how to create a black hole.

Science fiction about a half a century ago talked about using a contained black hole as a power source. The idea was to dump matter into it. As the matter gets close to the event horizon it emits massive amounts of energy, primarily x-rays. That energy is used to heat reaction mass which propels the rocket. How well will x-rays heat cryogenic hydrogen? I don't know. Actually the science fiction stories talked about using water as reaction mass, and some of that water was dumped into the black hole. That means you only need to harvest water from an asteroid to collect fuel. Let's let the engineers argue the merits of water vs. cryogenic hydrogen for specific impulse and tank size. The principle is the same as a nuclear thermal rocket, but a small black hole will only get larger as you use it, the nuclear fuel will never run out.

Hawking radiation is more complicated. I believe you are talking about virtual particle pairs. These pairs are theoretically created spontaneously from the random "foam" of space on the scale of the Plank constant. The particles would be one matter and the other negative matter. Negative matter theoretically is composed of negative energy so the energy of matter and negative matter cancel out to nothing. Such a particle pair can be made from nothing, but normally they will re-merge back into nothing. The extreme gravity at the edge of the event horizon of a black hole should permit the particles to separate. The particle that enters the event horizon will never get out, the other one will escape. If a negative matter particle enters the event horizon, it will reduce the total mass of the black hole. Stephen Hawking calculated that for very small black holes, on average more negative matter particles would enter the event horizon that positive matter particles. The opposite particle of the pair would effectively carry away mass from the black hole. This means that any black hole smaller that a critical size would "evaporate" until it could no longer hold itself together. When it reduced in size to a smaller critical mass, it would explode. However, the constant influx of matter from use as a power source would increase the size of the black hole. As long as the influx was greater than the mass loss due to Hawking radiation, the tiny black hole would not reduce in size. In fact, Hawking radiation could help prevent the black hole from becoming too big due to accumulation of fuel it had "swallowed".

This means that matter radiated as Hawking radiation would be positive matter as apposed to negative matter. But positive matter could be either normal matter or anti-matter. Here I am defining anti-matter as having its charge reversed: anti-protons with a negative charge, positrons with a positive charge, and anti-neutrons with a magnetic field oriented backward. Anti-matter is still composed of positive energy. The fact that both normal matter and anti-matter could be expected as Hawking radiation, means that if you can slow it down to react this would be a great source of energy. Containing it within a medium such as water or liquid hydrogen would cause that reaction.

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#3 2003-06-01 12:05:12

Alexander Sheppard
Member
Registered: 2001-09-23
Posts: 178

Re: Hawking radiation - Cheap anti-matter source?

Yes, that is what I was thinking of. So the potential is massive assuming it is possible from an engineering standpoint to generate a small black hole. All you have to do is balance the incoming mass with the mass of the outgoing Hawking radiation. Then you have an unlimited energy source.

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