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• White_hole abstract "In general relativity, a white hole is a hypothetical region of spacetime which cannot be entered from the outside, although matter and light can escape from it. In this sense, it is the reverse of a black hole, which can only be entered from the outside, but from which nothing, including light, can escape. White holes appear in the theory of eternal black holes. In addition to a black hole region in the future, such a solution of the Einstein field equations has a white hole region in its past. However, this region does not exist for black holes that have formed through gravitational collapse, nor are there any known physical processes through which a white hole could be formed.Like black holes, white holes have properties like mass, charge, and angular momentum. They attract matter like any other mass, but objects falling towards a white hole would never actually reach the white hole's event horizon (though in the case of the maximally extended Schwarzschild solution, discussed below, the white hole event horizon in the past becomes a black hole event horizon in the future, so any object falling towards it will eventually reach the black hole horizon).In quantum mechanics, the black hole emits Hawking radiation and so can come to thermal equilibrium with a gas of radiation. Because a thermal-equilibrium state is time-reversal-invariant, Stephen Hawking argued 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, 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 holeThe possibility of the existence of white holes was put forward by I. Novikov in 1964. White holes are predicted as part of a solution to the Einstein field equations known as the maximally extended version of the Schwarzschild metric describing an eternal black hole with no charge and no rotation. Here, "maximally extended" refers to the idea that the spacetime should not have any "edges": for any possible trajectory of a free-falling particle (following a geodesic) in the spacetime, it should be possible to continue this path arbitrarily far into the particle's future, unless the trajectory hits a gravitational singularity like the one at the center of the black hole's interior. In order to satisfy this requirement, it turns out that in addition to the black hole interior region which particles enter when they fall through the event horizon from the outside, there must be a separate white hole interior region which allows us to extrapolate the trajectories of particles which an outside observer sees rising up away from the event horizon. For an observer outside using Schwarzschild coordinates, infalling particles take an infinite time to reach the black hole horizon infinitely far in the future, while outgoing particles which pass the observer have been traveling outward for an infinite time since crossing the white hole horizon infinitely far in the past (however, the particles or other objects experience only a finite proper time between crossing the horizon and passing the outside observer). The black hole/white hole appears "eternal" from the perspective of an outside observer, in the sense that particles traveling outward from the white hole interior region can pass the observer at any time, and particles traveling inward which will eventually reach the black hole interior region can also pass the observer at any time.Just as there are two separate interior regions of the maximally extended spacetime, there are also two separate exterior regions, sometimes called two different "universes", with the second universe allowing us to extrapolate some possible particle trajectories in the two interior regions. This means that the interior black-hole region can contain a mix of particles that fell in from either universe (and thus an observer who fell in from one universe might be able to see light that fell in from the other one), and likewise particles from the interior white-hole region can escape into either universe. All four regions can be seen in a spacetime diagram which uses Kruskal–Szekeres coordinates. see figure.In this spacetime, it is possible to come up with coordinate systems such that if you pick a hypersurface of constant time (a set of points that all have the same time coordinate, such that every point on the surface has a space-like separation, giving what is called a 'space-like surface') and draw an "embedding diagram" depicting the curvature of space at that time, the embedding diagram will look like a tube connecting the two exterior regions, known as an "Einstein-Rosen bridge" or Schwarzschild wormhole. Depending on where the space-like hypersurface is chosen, the Einstein-Rosen bridge can either connect two black hole event horizons in each universe (with points in the interior of the bridge being part of the black hole region of the spacetime), or two white hole event horizons in each universe (with points in the interior of the bridge being part of the white hole region). It is impossible to use the bridge to cross from one universe to the other, however, because it is impossible to enter a white hole event horizon from the outside, and anyone entering a black hole horizon from either universe will inevitably hit the black hole singularity.Note that the maximally extended Schwarzschild metric describes an idealized black hole/white hole that exists eternally from the perspective of external observers; a more realistic black hole that forms at some particular time from a collapsing star would require a different metric. 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 interior region. But because the equations of general relativity are time-reversible (they exhibit T-symmetry), general relativity must also allow the time-reverse of this type of "realistic" black hole that forms from collapsing matter. The time-reversed case would be a white hole that has existed since the beginning of the universe, and which emits matter until it finally "explodes" and disappears. Despite the fact that such objects are permitted theoretically, they are not taken as seriously as black holes by physicists, since there would be no processes that would naturally lead to their formation, they could only exist if they were built into the initial conditions of the Big Bang. Additionally, it is predicted that such a white hole would be highly "unstable" in the sense that if any small amount of matter fell towards the horizon from the outside, this would prevent the white hole's explosion as seen by distant observers, with the matter emitted from the singularity never able to escape the white hole's gravitational radius.".
• White_hole thumbnail Krukdiagram.svg?width=300.
• White_hole wikiPageExternalLink schww.html.
• White_hole wikiPageExternalLink schwwbig_gif.html.
• White_hole wikiPageExternalLink question.php?number=108.
• White_hole wikiPageExternalLink ForwardtotheFuture1.pdf.
• White_hole wikiPageExternalLink ForwardtotheFuture2.pdf.
• White_hole wikiPageExternalLink 0,,1419424,00.html.
• White_hole wikiPageExternalLink 551eaa4623f4f4f5.
• White_hole wikiPageExternalLink 11216.
• White_hole wikiPageID "240972".
• White_hole wikiPageRevisionID "606788399".
• White_hole hasPhotoCollection White_hole.
• White_hole subject Category:Black_holes.
• White_hole subject Category:General_relativity.
• White_hole subject Category:Hypothetical_astronomical_objects.
• White_hole type BlackHole109223177.
• White_hole type BlackHoles.
• White_hole type Location100027167.
• White_hole type Object100002684.
• White_hole type PhysicalEntity100001930.
• White_hole type Region108630039.
• White_hole type YagoGeoEntity.
• White_hole type YagoLegalActorGeo.
• White_hole type YagoPermanentlyLocatedEntity.
• White_hole comment "In general relativity, a white hole is a hypothetical region of spacetime which cannot be entered from the outside, although matter and light can escape from it. In this sense, it is the reverse of a black hole, which can only be entered from the outside, but from which nothing, including light, can escape. White holes appear in the theory of eternal black holes.".
• White_hole label "Agujero blanco".
• White_hole label "Biała dziura".
• White_hole label "Buco bianco".
• White_hole label "Buraco branco".
• White_hole label "Trou blanc".
• White_hole label "Weißes Loch".
• White_hole label "White hole".
• White_hole label "Wit gat".
• White_hole label "Белая дыра".
• White_hole label "ثقب أبيض".
• White_hole label "ホワイトホール".
• White_hole label "白洞".
• White_hole sameAs Weißes_Loch.
• White_hole sameAs Άσπρη_τρύπα.
• White_hole sameAs Agujero_blanco.
• White_hole sameAs Trou_blanc.
• White_hole sameAs Buco_bianco.
• White_hole sameAs ホワイトホール.
• White_hole sameAs 화이트홀.
• White_hole sameAs Wit_gat.
• White_hole sameAs Biała_dziura.
• White_hole sameAs Buraco_branco.
• White_hole sameAs m.01jzf3.
• White_hole sameAs Q131468.
• White_hole sameAs Q131468.
• White_hole sameAs White_hole.
• White_hole wasDerivedFrom White_hole?oldid=606788399.
• White_hole depiction Krukdiagram.svg.
• White_hole isPrimaryTopicOf White_hole.