
Black Holes as a cooling system for advanced civilisations? - zx76
http://weidai.com/black-holes.txt
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michaelpinto
That's like saying making a star go supernova is a great way to generate
energy for an advanced civilization — there are some huge leaps in logic in
making sweeping assumptions of that scale. It would be like someone in the
Victorian era predicting that we'll farm whales for their oil...

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hugh3
_It would be like someone in the Victorian era predicting that we'll farm
whales for their oil..._

That actually sounds like a pretty cool idea. Would it be possible to keep
whales alive on land indefinitely?

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michaelpinto
They won't be actual whales — we'll use their genetics "or something like
that"

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yaks_hairbrush
There's a problem with this approach: black holes evaporate, which would yield
a useful-life ceiling of 10^100 years. I know I'd like my machines to work
longer than that.

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geuis
I think
10,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000
years would be a pretty usable amount of up time.

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albemuth
you're thinking like a human, I reckon 640kb of memory would be enough too ;)

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bfe
You're going to have some major practical trade-offs with this choice of
cooling system. For one thing, any data you get out of this computer when
you're positioned further away from the event horizon is going to be red-
shifted down to a lower data rate.

For another thing, the electrical and magnetic fields generated by your
computing and data transmitting hardware are going to induce a Lorentz force
on the event horizon and torque it into rotation, which in turn produces both
gravitational frame dragging and dissipation. Now it's a lot hotter than if it
were just a Schwarzchild black hole emitting only Hawking radiation.

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lifefundr
I think science fiction writer Arthur C. Clarke said it best "Any sufficiently
advanced technology will indistinguishable from magic." I paraphrased so don't
hurt me if I didn't get it word for word. I have to agree with him that any
civilization that was advanced as the essay speculates, would seem like real
magic to our relatively young civilization.

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n-ion
When you cool something down to near absolute zero it can turn into a
Bose–Einstein condensate (BEC). <http://en.wikipedia.org/wiki/Bose-
Einstein_condensate> For example at 1.7×10^-7K rbidium turns into a BEC. At
10^-8K perhaps that would turn normal matter into a BEC. Then you would have
to be able to get useful information out of a state of matter where every
possible value exists at once, and the tool your using to read values warms
the condensate past the point of being one. Hey - I think you just invented a
quantum computer. Congrats.

On a site note I think lasers are the advanced cooling system of the future!

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aphyr
_I think lasers are the advanced cooling system of the future!_

They're the advanced cooling system of the present!
<http://en.wikipedia.org/wiki/Magneto-optical_trap>

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hugh3
I'm confused. How is radiating your heat into a black hole better than
radiating your heat into space?

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fletchowns
The theoretical limit for your thermal efficiency is going to be based on the
temperature of whatever you are cooling and the temperature of the environment
you exhaust the waste heat into. Minimizing the latter is what he seems to be
talking about here.

 _Since these equipment cannot operate with perfect efficiency, they will need
to eliminate waste heat._

Who says it has to operate at perfect efficiency? I would imagine that any
slight improvement you get by incorporating a black hole into your cooling
system (however the hell that would work) would be negated by the fact that a
cooling system that involves a black hole is probably a bit expensive.

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aphyr
It might not be. Assuming you could find a black hole which is not actively
engaged in swallowing something (and hence spewing out huge amounts of heat
and relativistic particle jets), you could surround it with mirrors to create
an internal volume with a very low photon temperature at relatively (in
astronomical terms) mild expense.

Obviously a spherical shell would be unstable, but you don't need a contiguous
shell to lower the internal temperature. A rotating ring (or easier, an
orbiting series of small, overlapping satellites) would be stable (not in the
orbital sense, but in that they wouldn't need to hold themselves up) and could
use the thermal gradient between their sides to power their station-keeping.
You could construct additional rings at greater distances, each with a
different inclination, to cover more of the angular area.

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colanderman
That's a really good idea.

Come to think of it, could black holes actually be used as an energy source? A
setup like the one he describes would create a temperature gradient, and it's
easy to extract power from that.

That would only make sense if this process somehow "depleted" the black hole;
otherwise one could reverse entropy. IANA theoretical physicist so I don't
know which mechanisms would be at work here.

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geuis
I wonder if black holes might be usable as cosmic-scale batteries. Suppose
your civ was preparing to settle in for long-term survival into the super
distant future. You might not need high amounts of energy, just a low constant
supply for incredibly long amounts of time. You could drop a good percentage
of a galaxy's mass into a black hole, then use the evaporated Hawking
radiation over cosmological time scales to power your civ.

Suppose that the entities living inside this civ are simulations. A second to
us might be tens of thousands of years to them, because their hardware
processing runs very slowly because of the low amounts of available energy.

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neolefty
Or for young whipper-snapper civilizations who want to live faster, you could
turn that black hole + galaxy-sized mass into a really big hydro-electric
plant -- that is, power your civ from the potential energy.

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phreeza
Theres a more thorough exploration of using a black holes in a reversible
Carnot Cycle here: <http://dx.doi.org/10.1088/1674-1056/18/3/015>
unfortunately behind a paywall.

