In astrophysics, a White Hole is the time reversal of a black hole. While a black hole acts as an absorber for any matter that crosses the event horizon, a White Hole acts as a source that ejects matter from its event horizon. The sign of the acceleration is invariant under time reversal, so both black and white holes attract matter. The only potential difference between them is in the behavior at the horizon.
Black hole horizons can only absorb matter, while white hole horizons ostensibly recede from any incoming matter at the local speed of light, so that the infalling matter never crosses. The infalling matter is then scattered and reemitted at the death of the white hole, receding to infinity after having come very very close to the final singular point where the white hole is destroyed. The total proper time until an infalling object encounters the singular endpoint is the same as the proper time to be swallowed by a black hole, so the white hole picture does not say what happens to the infalling matter. Ignoring the classically unpredictable emissions of the white hole, the white hole and black hole are indistinguishable for external observers.
In quantum mechanics, the black hole emits Hawking radiation, and so can come to thermal equilibrium with a gas of radiation. Since a thermal equilbrium state is time reversal invariant, Hawking argued[2] that the time reverse of a black hole in thermal equilibrium is again a black hole in thermal equilibrium. This implies that black holes and white holes are the same object. The Hawking radiation from an ordinary black hole is then identified with the white hole emission. Hawking's semi-classical argument is reproduced in a quantum mechanical AdS/CFT treatment[3], where a black hole in Anti De Sitter space is described by a thermal gas in a gauge theory, whose time reversal is the same as itself.
Origin
White holes appear as part of the vacuum solution to the Einstein field equations describing a Schwarzschild wormhole. One end of this type of wormhole is a black hole, drawing in matter, and the other is a white hole, emitting matter. While this gives the impression that black holes in this universe may connect to white holes elsewhere, this turns out not to be the case for two reasons. First, Schwarzschild wormholes are unstable, disconnecting as soon as they form. Second, Schwarzschild wormholes are only a solution to the Einstein field equations in vacuum (when no matter interacts with the hole). Real black holes are formed by the collapse of stars. When the infalling stellar matter is added to a diagram of a black hole's history, it removes the part of the diagram corresponding to the white hole
The existence of white holes that are not part of a wormhole is doubtful, as they appear to violate the second law of thermodynamics.
Quasars and active galactic nuclei are observed to spew out jets of matter. This is now believed to be the result of polar jets formed when matter falls into supermassive black holes at the centers of these objects. Prior to this model, white holes emitting matter were one possible explanation proposed.
See also
| Black holes suck in objects but -- according to Einstein's general theory of relativity that time reversal is possible -- objects that travel through black holes could theoretically be spewed out of other holes. Such holes are called white holes. The tunnels that connect black and white holes are known as wormholes. The space-time tunnels of another world Black holes are the final stage of a star's development. But in extraordinary times, such as the start of the Universe, wormholes could be created. If the changing nature of space and time is considered, it's better to think that wormholes appear and disappear. By thinking closely about wormholes, it's possible to understand that there is a different world to the one we live on. If we consider both these worlds as being parallel, wormholes are like a space-time tunnel that joins our world to the other. Wormholes present time travel opportunities Kip Sone, a relative theorist, devised a theory where wormholes could act as time machines. He believed that, according to the principles of quantum mechanics, if a space ship was strong enough to travel at something near light speed through a wormhole, time would travel backwards. By following the principles of the special theory of relativity that say time moves slower for objects traveling at the speed of light, it would be possible to travel in time. Stephen Hawking has dismissed the possibility of creating time machines There are a number of factors working against the theory of creating a time machine and it's better at this stage to consider its construction impossible. Stephen Hawking has often said that if the effects of quantum mechanics are considered, the construction of a time machine is not possible in the real world. |
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