One classic way of detecting aliens is by detecting stellar-scale engineering projects. If aliens could spread out 100 million light years and recycle 90% of UV/visible light from those stars into IR in order to power their civilization, we’d probably notice—it would be a mysterious patch in cosmological maps that people would probably stop to think about.
Unless they’re in the plane of the Milky Way, of course, then we’d never notice.
One classic way of detecting aliens is by detecting stellar-scale engineering projects. If aliens could spread out 100 million light years and recycle 90% of UV/visible light from those stars into IR in order to power their civilization, we’d probably notice—it would be a mysterious patch in cosmological maps that people would probably stop to think about.
Unless they’re in the plane of the Milky Way, of course, then we’d never notice.