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timtyler comments on The Popularization Bias - Less Wrong
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Re: One is that black holes have entropy quadratic in mass, and therefore are ideal entropy dumps (or equivalently, negentropy mines).
What would anyone want a black hole entropy dump for? If you are in orbit around a star, you can just let entropy radiate off as heat. Compared to that sending it into the nearest black hole would probably require a lot of energy. This seems like a bad idea - so what is the proposed point?
The point is that a black hole is much colder than interstellar space, and its temperature decreases as its mass increases. This coldness implies that it takes much less energy to dump a certain amount of entropy into a black hole than into interstellar space. Of course you probably don't want to ship that entropy across interstellar distances before dumping. That would likely wipe out any savings. You'd create a black hole close by, or build your civilization around an existing one.
It still doesn't seem to make sense. Buiding a black hole anywhere near a sentient agent seems like a really, really bad idea. Orbiting around one doesn't help you drop things into it much - because of orbital inertia. The suggestion seems rather like proposing that we dump the planet's excess heat into the Sun - as opposed to radiating it off in all directions. Yes, we could build a heat ray and point it at the sun - but if you think about that for a moment, you will realise why it wouldn't help get rid of entropy, and would actually just make things worse.
The tiny relative temperature difference between the surface of the hole and interstellar space hardly makes much difference if you are many millions of miles away from it. Also, the hole is likely to be surrounded by extremely hot stuff in orbit around it. Are you sure that you have thought this idea through?
By the time your civilisation is taking advantage of black holes, it's large enough that even a small temperature difference can scale to quite a bit of negentropy. Further, you don't have to be in orbit, you can build a Dyson shell around the hole at such a distance that the surface gravity is one g. (Or several shells, if people prefer different levels of gravity.) Then there's no orbital velocity to deal with. (And in any case, you could brake by tidal friction and extract some entropy that way.) Or to be shorter, why are you objecting to the practical details of a thought experiment? Nothing about the game theory relies on black holes or the particular exponent 2; it could just as well be mass^1.5, and the analysis would remain the same although the numbers would change a bit.
Regarding this discussion, I'm totally confused what people are talking about. It sounds like you want to take some of your excess energy and throw it into a black hole. Wouldn't it be smarter to give it to me? How can energy be "excess"?
Eliezer has a post that explains some of the background assumed here: http://lesswrong.com/lw/o5/the_second_law_of_thermodynamics_and_engines_of/.
I have just finished reading this article. I still have no idea what it is that you intend to do with the black hole, or why it's useful. Seriously, not even an inkling. And I seem to be unique in this regard, which sucks.
The only way that I can think of for a black hole to reduce entropy is if you throw things into it. Give them to me.
Tilba, Wei's earlier post pointed to this article:
http://weidai.com/black-holes.txt
You might also need to know that computation can be done in principle almost without expending energy, and the colder you do the computation, the less energy is wasted. Hence being cold is a good thing, and black holes are very cold.
I didn't get it right away, but now that I do, it's pretty ingenious. Let me see if I got it right. Build a big ball in space. If the ball was empty, starlight and cosmic background would heat it up, the inner surface would emit photons, and they would bounce around the shell - so you're back to square one. But the black hole at the center can absorb those photons without becoming hot. And the photons are unusable because they are ambient.
On the other hand, there is now a temperature difference between the inside and the outside. Can it be used to make usable energy?
Not energy, entropy. Energy is useful - entropy is useless.
+1; indeed, this is interesting from an scifi-itch-scratching viewpoint, but I guess we have the next 10^6 years to worry about the details.
Anyway, I like LW for bringing such things to my attention (thanks Wei_Dai!), but apart from being interesting, this seems not like an idea that need mass-popularization, or?
You ask a fair question, I think. Here are some potential short-term implications of black-hole negentropy: