Can Black Holes be the Dark Matter? Seems to fit the definition: interacts with gravity, doesn’t radiate energy (except Hawking Radiation) and could create gravity lensing without absorbing very much of the light.
Could 80% of the original matter created in the Big Bang have ended up in lots of black holes thereby giving us the amount of mass to balance the universes gravity?
Kent
 A: This is impossible for several reasons.


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*Each black holes would have to be insanely massive.


A black hole the size of a proton (which Hawking radiates pions like crazy) already has the mass of a mountain. The radius and mass of a black hole are proportional, and at 1 Planck length of 10^{-34} m, it has 10^{-5} g of mass. At 10^{-15}m, you have 10^11 Kg. But this is nonsense, the black holes would have to be bigger than the wavelength of visible light at least, to avoid Hawking radiating visible light, which is another factor of 10^8, which means that each one would have the mass of 10^{20} Kg, the mass of a small celestial body. They would clump matter around them gravitationally, and you couldn't miss them.


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*Black holes are not weakly interacting


Such massive black holes have strong gravitational scattering of other objects, they don't pass right through. It is implausible that they would form spherical clouds around galaxies, they would have strong scattering and friction with galactic gas and dust, and they would end up in the galactic disk along with everything else.


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*Black holes explode


The few black holes which are small enough to decay would lead to signature Hawking explosions at the end stages, which were searched for and not found.


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*Black holes can't be the end-product of inflation


When you have an inflating universe, the end of inflation is gravitationally homogenous for good reason--- it is coming from the maximum entropy state, the deSitter state, of a positive cosmological constant universe. Any black holes will be diluted by inflation, which can be viewed as the black hole falling into the cosmological horizon. When inflation ends, the end is graceful and not sufficiently inhomogenous to clump matter into black holes, at least not until after some time has passed for the matter to clump in the ordinary way.
