>>Me:
>>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.
>Hara Ra <harara@shamanics.com>
>There's an easy fix to this. Use a telescope. What telescopes do is
>enlarge the amount of sky seen by the telescope's magnifying power.
>Using a very low f ratio means your radiator can see a lot of black
>hole in the sky, at a reasonable distance. Just focus the telescope
>on the black hole and put the radiator on the focal point.
That won't work. A lens (or curved mirror) can only bring light to a focus if
the wave front is parallel or nearly so, and that can only happen if the lens
is small and far from the light source. The wave front of the blackbody
radiation near a heat radiator would be almost spherical and so will not
focus for the same reason a lage magnifying glass placed right next to a
light bulb will not focus. To work you'd have to place your telescope at a
large distance from the radiator where the wave front has become almost
parallel, and then only a very small percentage of the heat radiation would
intersect with the lens.
Another way to see this is that If it were not true you could make a
perpetual motion machine, just focus the waste heat from a steam engine
and run another steam engine with it, then do the same thing with that steam
engine.
John K Clark johnkc@well.com
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