Micro black hole

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A micro black hole, also called a quantum mechanical black hole and inevitably a mini black hole, is simply a tiny black hole for which quantum mechanical effects play an important role.

Explanation

The smallest mass it is believed a black hole could have is of the order of the Planck mass, which is about 2 × 10⁻⁸ kg or 1.1 × 10¹⁹ GeV/c². At this scale the black hole thermodynamic formulae predict the mini-black hole would have an entropy of only 4π nats; a Hawking temperature of T_P / 8π, requiring thermal energy quanta comparable in energy to almost the mass of the entire mini black hole; and a Compton wavelength equal to the black hole's Schwarzschild radius (this distance being equal to the Planck length). This is the point where a classical gravitational description of the object stops being retrievable with merely small quantum corrections, but in effect completely breaks down. The existence of black holes of this mass is purely hypothetical but if primordial black holes exist, they might reach this condition as the final stage of runaway evaporation due to Hawking radiation. Such an energy is orders of magnitude greater than can be produced on Earth in particle accelerators such as the Large Hadron Collider (maximum about 1.4 × 10⁴ GeV), or detected in cosmic ray collisions in our atmosphere. It is estimated that to collide two aggregates of fermions to within a distance of a Planck length with the currently achievable magnetic field strength would require a ring accelerator about 1000 light years in diameter to keep the aggregates on track. Even if it were possible, any collision product would be immensely unstable, and almost immediately disintegrate. Some string theorists have suggested that the multiple dimensions postulated by string theory might make the effective strength of gravity many orders of magnitude stronger at small distances (very high energies). This might effectively lower the Planck energy, and perhaps make black-hole-like descriptions valuable even at slightly lower masses. This higher-dimensional component to gravity is, however, highly speculative. Others have wondered about the basic assumptions of the quantum gravity program, and whether there is really a compelling case to believe in Hawking radiation[1]. It is only these quantum assumptions which lead to the crisis at the Planck mass: in classical general relativity, a black hole could in principle be arbitrarily small. Physicist Brian Greene has suggested that the electron may be a micro black hole; see black hole electron. Small black holes would look like elementary particles because they would be completely defined by their mass, charge and spin. On this view, the significance of the Planck mass is that it marks a transition where the Hawking semi-classical approximation breaks down, and a fully quantum mechanical description of the system becomes required. Gravitationally dominated "black hole"-like structures might still exist with these lower masses, but the emission of Hawking radiation would be suppressed by quantum effects, just as an electron constantly accelerating round an atom does not radiate, despite the apparent predictions of classical electrodynamics. All that can be said with certainty is that current predictions for the functioning of a black hole with a mass less than Planck mass are inconsistent and incomplete.

See also

• Black hole, a general survey

Classification by type:

• Schwarzschild, or still, black hole
• Kerr, or spinning, black hole
• Kerr-Newman and Reissner-Nordström, or charged and spinning, black holes

Classification by mass:

• Micro black hole and extra-dimensional black hole
• Primordial black hole, a hypothetical leftover of the Big Bang
• Stellar black hole, which could either be a static black hole or a rotating black hole
• Intermediate-mass black hole
• Supermassive black hole, which could also either be a static black hole or a rotating black hole

References

• Quantum Mechanical Black Holes: Towards a Unification of Quantum Mechanics and General Relativity -- http://citebase.eprints.org/cgi-bin/citations?id=oai:arXiv.org:quant-ph/9808020
• S.W. Hawking, Commun.Math. Phys. 43 (1975) 199 : the article it all began with !
• D. Page, Phys. Rev. D13 (1976) 198 : first detailed studies of the evaporation mechanism
• B.J. Carr & S.W. Hawking, Mon. Not. Roy. Astron. Soc 168 (1974) 399 : links between primordial black holes and the early universe
• A. Barrau et al., Astron. Astrophys. 388 (2002) 676 , Astron. Astrophys. 398 (2003) 403 , Astrophys. J. 630 (2005) 1015 : experimental searches for primordial black holes thanks to the emitted antimatter
• A. Barrau & G. Boudoul, Review talk given at the International Conference on Theoretical Physics TH2002 : cosmology with primordial black holes
• A. Barrau & J. Grain, Phys. Lett. B 584 (2004) 114 : searches for new physics (quantum gravity) with primordial black holes
• P. Kanti, Int. J. Mod. Phys. A19 (2004) 4899 : evaporating black holes and extra-dimensions
• D. Ida, K.-y. Oda & S.C.Park, [2]: determination of black hole's life and extra-dimensions
• Sabine Hossenfelder: What Black Holes Can Teach Us, hep-ph/0412265
• Jason Doukas, S. Rai Choudhury, G. C. Joshi: "Lepton number violation via intermediate black hole processes", [3]

External links

• A. Barrau & J. Grain, The Case for mini black holes : a review of the searches for new physics with micro black holes possibly formed at colliders
• Exit Mundi's micro black hole end of world scenario
• Mini Black Holes Might Reveal 5th Dimension - Space.com