Re: the ultimate refrigerator

Wei Dai (
Wed, 17 Dec 1997 10:00:40 -0800

On Tue, Dec 16, 1997 at 11:03:18PM -0800, John K Clark wrote:
> I have thought of a problem with the Black Hole refrigerator idea however.
> You're going to have to put your heat radiators pretty close to the event
> horizon because Black Holes are small but they must fill a large part of the
> shy. When you get that close the huge gravitational field is going to blue
> shift light, including the ubiquitous cosmic microwave background radiation,
> except that it wouldn't be microwave radiation anymore, it will be infrared
> or beyond.

More worrisome is the fact that the closer you get to the event horizon,
the time dilation effect becomes stronger and the black hole appears
hotter. The blue-shift of the cosmic background radiation is actually a
benefit, since you can take advantage of its higher temperature to run a
heat engine between it and the black hole. A proper design for a black
hole refrigerator would definately have to take relativistic effects into

I think the formula I gave earlier for black hole temperature is the
temperature apparent to an observer far away from the event horizon. Can
anyone confirm this?