>A civilization that built a Dyson Sphere would have to go to great lengths to avoid detection, either by getting rid of its waste heat in some novel way, or by building massive radiators that give off heat so cool that it would be undetectable against the cosmic microwave background, the faint afterglow of the Big Bang.
So if a civilization were to completely mask itself in the EM spectrum, the only way to detect them would be to look for gravitational distortions assuming those can't be masked. A civilization might do this either to hide from others or because the maximum efficiency of their energy extraction system would occur when their waste heat matched the background ration. So a really advanced (and paranoid or efficient) civilization would be indistinguishable from dark matter.
This brings up another interesting hypothesis: dark matter is actually the computronium of all of the alien civilizations in the universe that have achieved a technological singularity. Unfortunately, this hypothesis can't be tested until humanity gets to the same level.
>This brings up another interesting hypothesis: dark matter is actually the computronium of all of the alien civilizations in the universe that have achieved a technological singularity.
Technological singularity describes the aftermath as an entity achieves an intelligence significantly superior to that of the average unaided human mind. The term gets thrown at a lot of things that don't seem to have anything to do with it. In this case I don't see why humans level intelligence is not enough to build a Dyson Sphere.
It looks really naive that civilizations so advanced to blot out an entire star for its energy can't even find a way to co exist in such a vast universe.
But looking at how fellow humans behave with each other. I would say that is definitely a possibility.
So if a civilization were to completely mask itself in the EM spectrum, the only way to detect them would be to look for gravitational distortions assuming those can't be masked. A civilization might do this either to hide from others or because the maximum efficiency of their energy extraction system would occur when their waste heat matched the background ration. So a really advanced (and paranoid or efficient) civilization would be indistinguishable from dark matter.
This brings up another interesting hypothesis: dark matter is actually the computronium of all of the alien civilizations in the universe that have achieved a technological singularity. Unfortunately, this hypothesis can't be tested until humanity gets to the same level.