White hole

In astrophysics, a white hole is the theoretical time reversal of a black hole. Whilea black hole acts as a vacuum, sucking up 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 reversalFact|date=July 2008, so both black and white holes attract matter. The only potential difference between them is in the behavior at the horizon.Fact|date=July 2008

Black hole event horizons can only "suck up" 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 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 equilibrium state is time reversal invariant, Hawking argued that the time reverse of a black hole in thermal equilibrium is again a black hole in thermal equilibrium. [cite journal
author = Hawking, S. W.
year = 1976
title = Black Holes and Thermodynamics
journal = Physical Review D
volume = 13
pages = 191–197
doi = 10.1103/PhysRevD.13.191 ] 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, [cite paper
first = Igor R.
last = Klebanov
title = TASI lectures: Introduction to the AdS/CFT correspondence
version =
publisher =
date = 19 May 2006
url = http://arxiv.org/abs/hep-th/0009139v2
id = hep-th/0009139 v2
accessdate = 2007-08-29] 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 our universe may connect to white holes elsewhere, in reality, this is untrue, 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. [http://casa.colorado.edu/~ajsh/collapse.html#kruskal]

The existence of white holes that are not part of a wormhole is doubtful, as they appear to violate the second law of thermodynamicsFact|date=May 2008.

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 solution.

Recent speculations

A more recently proposed view of black holes might be interpreted as shedding some light on the nature of classical white holes. Some researchers proposed that when a black hole forms, a big bang occurs at the core, which creates a new universe that expands into extra dimensions outside of the parent universe. [cite journal |author= E. Fahri and A. H. Guth |title= An Obstacle to Creating a Universe in the Laboratory |journal= Physics Letters | volume= B183 |pages= 149 |year= 1987] See also Fecund universes.

The initial feeding of matter from the parent universe's black hole and the expansion that follows in the new universe might be thought of as a cosmological type of white hole. Unlike traditional white holes, this type of white hole would not be localized in space in the new universe, and its horizon would have to be identified with the cosmological horizon.

The problem with white holes is that they violate the Second Law of Thermodynamics, which states that any ordered system becomes more disorganized (if you drop an egg, it will become a disordered mess, but a disordered mess will never spontaneously form a perfect egg), and so a system which adds order to a system is not possible. This is why many believe that a white hole can not exist.

ee also

*Black Hole
*Wormhole
*White holes in fiction

References

External links

* [http://curious.astro.cornell.edu/question.php?number=108 Ask an Astronomer: "What is a White Hole?"]
* [http://casa.colorado.edu/~ajsh/schww.html Schwarzschild Wormholes]
* [http://casa.colorado.edu/~ajsh/schwwbig_gif.html Schwarzschild Wormhole animation]
* [http://www.space.com/scienceastronomy/white_hole_030917.html New Theory: Universe Was Born in a Black Hole]
* [http://www.pnas.org/cgi/content/full/100/20/11216 Shockwave cosmology inside a Black Hole]
* [http://education.guardian.co.uk/academicexperts/story/0,,1419424,00.html Michio Kaku: Mr Parallel Universe]
* [http://math-science-tit-bits.blogspot.com/2008/02/white-hole-did-i-say-them-in-199798-you.html End of Black Hole Is Starting of Big Bang - Discussed in Newsgroup in 1999]
* [http://groups.google.com/group/sci.astro/browse_thread/thread/153d3dc9f209647d/551eaa4623f4f4f5?lnk=st&q=sunils+blackhole#551eaa4623f4f4f5 End of Black Hole Is Starting of Big Bang - Discussed in Newsgroup in 1999]