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?



This is impossible for several reasons.

  • 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.

  • 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.

  • 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.

  • 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.

  • $\begingroup$ There have been speculations on string models with some large (mm) dimensions where black holes appear and are sought for through their thermodynamic decay to many particles at the LHC. This might imply that a model might be found where a stable mini black hole of TeV mass might be concocted ( reviving the scare for the LHC). Alternatively it could be called a stable solution of a quantum gravitational equation (no Hawking radiation). There are more things.... $\endgroup$ – anna v Jan 11 '12 at 6:21
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    $\begingroup$ @anna v: I consider large extra dimensions to be a form of scientific fraud. There is no reason to take such ideas seriously, they are already ruled out, and were ruled out before they were first proposed. As for stable black holes, If a black hole is stable, it is not a black hole, by definition, it is a particle. $\endgroup$ – Ron Maimon Jan 11 '12 at 14:59
  • $\begingroup$ Ron, you've said this before about Large Extra Dimensions - would you care to elaborate (are you grouping RS with ADD in this?)? Thanks. Out of interest, how much faith do you personally think we should put in Hawking radiation? $\endgroup$ – James Jan 11 '12 at 15:35
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    $\begingroup$ This seems like an interesting analogue wired.com/wiredscience/2010/09/hawking-radiation-in-the-lab , at least mathematically? $\endgroup$ – anna v Jan 11 '12 at 16:10
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    $\begingroup$ Could I go back to your comment about celestial-mass black holes being readily observable. Would this really the case? I mean an even distribution of black holes wouldn't cause clumping of stars distinct from the observed distribution of stars in the galaxy, would it? (Ignoring issues with how we actually observe DM to be distributed) $\endgroup$ – James Jan 11 '12 at 23:56

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