My personal fantasy tech for subspace is that it functions as an absolute zero heat sink. So heat engines can use absolute zero as the ultimate heat sink to bu

My personal fantasy tech for subspace is that it functions as an absolute zero heat sink. So heat engines can use absolute zero as the ultimate heat sink to build a Carnot contradiction: They don't actually sink any heat at all, and can extract all of the heat energy as work. Quantum mechanics forces them to actually sink a tiny amount of heat proportional to process entropy. Those tiny fluctuations are the "subspace signatures" that get detected anyway. Its still more fantasy than science, but hey, so are warp drive, hyperspace, and all that jazz :)