Re: the ultimate refrigerator

Anders Sandberg (
15 Dec 1997 18:58:45 +0100

Wei Dai <> writes:

> Black holes emit Hawking radiation at a temperature of
> T=h*c^3/(16*pi*G*M). With the mass of the sun, the temperature of a black
> hole would be about 10^-8 K. At this temperature, erasing a bit costs only
> about 10^-31 J. If you build an insulating shell outside the event horizon
> of a black hole, everything inside the shell would eventually cool down to
> the temperature of the black hole.

This is a very neat idea! I like it a lot. The only problem might be
preventing the occasional speck of dust from falling into the hole,
releasing a troublesome burst of radiation.

Of course, the finite area available will limit the amount of entropy
per second dumped into the hole, but it is likely very large anyway.

> If it's true that the only efficient way to cool material down to near
> absolute zero is with black holes, we should expect all sufficiently
> advanced civilizations to live near them. However testing this prediction
> may be difficult to test since they would have virtually no radiation
> signatures.

<twilight zone music on>Remember the dark matter of the universe? :-)

Anders Sandberg                                      Towards Ascension!                  
GCS/M/S/O d++ -p+ c++++ !l u+ e++ m++ s+/+ n--- h+/* f+ g+ w++ t+ r+ !y