Concept# Black hole

Summary

A black hole is a region of spacetime where gravity is so strong that nothing, including light or other electromagnetic waves, has enough energy to escape it. The theory of general relativity predicts that a sufficiently compact mass can deform spacetime to form a black hole. The boundary of no escape is called the event horizon. Although it has a great effect on the fate and circumstances of an object crossing it, it has no locally detectable features according to general relativity. In many ways, a black hole acts like an ideal black body, as it reflects no light. Moreover, quantum field theory in curved spacetime predicts that event horizons emit Hawking radiation, with the same spectrum as a black body of a temperature inversely proportional to its mass. This temperature is of the order of billionths of a kelvin for stellar black holes, making it essentially impossible to observe directly.
Objects whose gravitational fields are too strong for light to escape were first consider

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In theories with a large number N of particle species, black hole physics imposes an upper bound on the mass of the species equal to M-Planck/root N. This bound suggests a novel solution to the hierarchy problem in which there are N approximate to 10(32) gravitationally coupled species, for example 10(32) copies of the standard model. The black hole bound forces them to be at the weak scale, hence providing a stable hierarchy. We present various arguments, that in such theories the effective gravitational cutoff is reduced to Lambda(G)approximate to M-Planck/root N and a new description is needed around this scale. In particular, black holes smaller than Lambda(-1)(G) are already no longer semiclassical. The nature of the completion is model dependent. One natural possibility is that Lambda(G) is the quantum gravity scale. We provide evidence that within this type of scenarios, contrary to the standard intuition, micro-black-holes have a (slowly fading) memory of the species of origin. Consequently, the black holes produced at LHC will predominantly decay into the standard model particles, and negligibly into the other species.

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