Well... what about Dyson Spheres?
I'm pretty confident that there's not a single Dyson Sphere anywhere in the universe.
Never mind stability or radiation issues, do you have any idea how much material would be required to build a Dyson Sphere around our sun of 1 AU radius and one mile thick?
I believe Freeman Dyson said there is enough material in our own solar system to build one.
but Dyson Spheres, or any other product of an artifact-building intellegence, are a scientific explanation of Dark Matter for reason already mentioned in this thread. only some natural, or fundamental aspect of the universe can reasonable explain it.
that said, the idea of some hyper-advanced alien civilization who has been building Dyson Spheres all over the universe sounds like an interesting work of fiction