[Physics] why can’t the missing mass (evidence for dark matter) be matrioshka brains/dyson spheres


i know that the claim is that nucleosynthesis models say that the observed abundance of deuterium is too high for dark matter to be baryonic, but couldn't deuterium be a waste product of civilizations? you say that postulating civilizations is not the simplest explanation, but isn't it far more complex to postulate that we are unique (or an invisible form of matter with exotic physics for which we have no evidence)? even from a single seed civilization, galactic colonization times are in the hundred million year range, so we should expect some evidence of environmental manipulation everywhere we look. given the need for civilizations to hide from predators, isn't eliminating EM interactions/emissions the best strategy?

Best Answer

Physically, if you look at the low level of CMB anisotropy and the BAO power spectrum, you need some sort of mass that interacts gravitationally but is decoupled from the photons before recombination (i.e. - dark matter). Otherwise there would be no way to seed the galaxy formation that we see occuring at lower redshifts. That is to say, dark matter needs to be primordial, so that it can dodge Silk Damping and provide the graviational "cores" around which galaxies form.

Which would also imply that dark matter cannot be the construct of an alien civilization.

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