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Wei_Dai comments on The Popularization Bias - Less Wrong
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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.