|
Micro black holes, also called quantum mechanical black holes or mini black holes, are hypothetical tiny black holes, for which quantum mechanics effects play an important role.〔B.J. Carr and S.B. Giddings, "Quantum black holes",(Scientific American 292N5 (2005) 30. )〕 It is possible that such quantum primordial black holes were created in the high-density environment of the early Universe (or big bang), or possibly through subsequent phase transitions. They might be observed by astrophysicists in the near future, through the particles they are expected to emit by Hawking radiation. Some hypotheses involving additional space dimensions predict that micro black holes could be formed at energies as low as the TeV range, which are available in particle accelerators such as the LHC (Large Hadron Collider). Popular concerns have then been raised over end-of-the-world scenarios (see Safety of particle collisions at the Large Hadron Collider). However, such quantum black holes would instantly evaporate, either totally or leaving only a very weakly interacting residue. Beside the theoretical arguments, the cosmic rays bombarding the Earth do not produce any damage, although they reach center of mass energies in the range of hundreds of TeV. == Minimum mass of a black hole == In principle, a black hole can have any mass equal to or above the Planck mass (about 22 micrograms). To make a black hole, one must concentrate mass or energy sufficiently that the escape velocity from the region in which it is concentrated exceeds the speed of light. This condition gives the Schwarzschild radius, , where ''G'' is the gravitational constant, ''c'' is the speed of light, and ''M'' the mass of the black hole. On the other hand, the Compton wavelength, , where ''h'' is Planck's constant, represents a limit on the minimum size of the region in which a mass ''M'' at rest can be localized. For sufficiently small ''M'', the reduced Compton wavelength (, where ''ħ'' is Reduced planck constant) exceeds half the Schwarzschild radius, and no black hole description exists. This smallest mass for a black hole is thus approximately the Planck mass. Some extensions of present physics posit the existence of extra dimensions of space. In higher-dimensional spacetime, the strength of gravity increases more rapidly with decreasing distance than in three dimensions. With certain special configurations of the extra dimensions, this effect can lower the Planck scale to the TeV range. Examples of such extensions include large extra dimensions, special cases of the Randall–Sundrum model, and string theory configurations like the GKP solutions. In such scenarios, black hole production could possibly be an important and observable effect at the large hadron collider (LHC).〔〔〔〔〔 It would also be a common natural phenomenon induced by the cosmic rays. All this assumes that the theory of general relativity remains valid at these small distances. If it does not, then other, presently unknown, effects will limit the minimum size of a black hole. Elementary particles are equipped with a quantum-mechanical, intrinsic angular momentum (spin). The correct conservation law for the total (orbital plus spin) angular momentum of matter in curved spacetime requires that spacetime is equipped with torsion. The simplest and most natural theory of gravity with torsion is the Einstein-Cartan theory.〔Dennis W. Sciama, ("The physical structure of general relativity" ). Rev. Mod. Phys. 36, 463-469 (1964).〕〔Tom W. B. Kibble, ("Lorentz invariance and the gravitational field" ). J. Math. Phys. 2, 212-221 (1961).〕 Torsion modifies the Dirac equation in the presence of the gravitational field and causes fermion particles to be spatially extended. The spatial extension of fermions limits the minimum mass of a black hole to be on the order of 1016 kg, showing that mini black holes may not exist. The energy necessary to produce such a black hole is 39 orders of magnitude greater than the energies available at the LHC, indicating that the LHC cannot produce mini black holes. But if black holes are produced, then the theory of general relativity is proven wrong and does not exist at these small distances. The rules of general relativity would be broken, as is consistent with theories of how matter, space, and time break down around the event horizon of a black hole. This would prove the spatial extensions of the fermions limits incorrect as well. The fermion limits assumes a minimum mass needed to sustain a black hole, as opposed to the opposite, the minimum mass needed to start a black hole, which in theory is achievable in the LHC.〔Stephen Hawking, ("new doomsday warning" )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Micro black hole」の詳細全文を読む スポンサード リンク
|