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Inverted Dyson Spheres
Adam Crowl has suggested a peculiar form of black hole civilisation; a supermassive black hole is a nice heat sink, and if it is rotating fast enough the infalling light from the rest of the universe (including the CMBR) would be blue-shifted and highly energetic. An inverted Dyson Sphere could be built to catch this light.

The downside is that time dilation could be ferocious. This was brought up in connection with the M87 picture, but it could be located around any large SMBH with plenty of rotation.

The Xeelee (in Stephen Baxter's novels) apparently like to live in huge ringworlds that orbit superrmassive blackholes, rotating at nearly the speed of light- I wonder if even magmatter would be strong enough for that (Xeelee use domain walls, if I recall correctly).

A reference for the technically-minded; Life under a Black Sun
Dave was working on an S5 update around the concept of using a black hole as a heat sink, sadly he's dropped off again.
OA Wish list:
  1. DNI
  2. Internal medical system
  3. A dormbot, because domestic chores suck!
Stellar-mass black holes are fairly commonplace- there are probably many in the Terragen Sphere, undetected and undetectable except by gravitational lensing. They could be a good place for a moderatively secretive archailect to hide out, hidden from anyone with 21st-century-level tech.
I'm thinking that a good place to locate a detectable inverted Dyson swarm could be the Sombrero Galaxy; a well-known object, and the closest billion-sun-mass SMBH to Sol.
How efficient would the extraction of energy be if it were beamed out against the same forces that made it come in?
Coming inwards, the blueshifted radiation would arrive from all directions, covering 4 x pi steradians. (Actually, it is less than that, since the black hole itself covers up to half the sky as seen from an object in orbit around it).

A beam coming out of the inverted dyson could be much smaller in subtended angle, so it would be much more powerful (in the dyson rest frame). However this beam would be red-shifted as it left the dyson, so it would end up no more powerful than the light going in at normal wavelengths (i.e. not very powerful at all). To get the most benefit from the blueshifted energy, you have to pay the penalty of being on a fast-track to the future.
(05-15-2019, 10:07 PM)stevebowers Wrote: have to pay the penalty of being on a fast-track to the future.

That's also the motto of the self-driving truck industry.
(05-15-2019, 10:07 PM)stevebowers Wrote: To get the most benefit from the blueshifted energy, you have to pay the penalty of being on a fast-track to the future.

Note that some number of sophonts in the setting would likely consider that fast track to be a feature, not a bug.

Some sophonts might see this option as a way to 'time travel' - either jumping ahead to some specific date for some reason or seeking to 'fast-track to the future' to see the distant future or migrate into deep time or the like.

Given OA tech, they might also not need to wait to find natural black holes. Rather, they could convert stars into black holes and then built inverted dysons around them.


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