What is "white hole"

n. (context idiomatic English) A theoretically possible but physically highly unlikely singularity from which matter and energy are able to escape; the antithesis of a black hole.

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 and from which matter and light cannot 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. No white hole has ever been observed. Also, the laws of thermodynamics say that the net entropy in the universe can either increase or remain constant. This rule is violated by white holes, as they tend to decrease entropy.

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). Imagine a gravitational field, without a surface. Acceleration due to gravity is the greatest on the surface of any body. But since black holes lack a surface, acceleration due to gravity increases exponentially, but never reaches a final value as there is no considered surface in a singularity.

In quantum mechanics, the black hole emits Hawking radiation and so can come to thermal equilibrium with a gas of radiation (not compulsory ). 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 may imply 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.

"White Hole" is the fourth episode of science fiction sitcom Red Dwarf Series IV and the twenty-second episode in the series run. It was first broadcast on the British television channel BBC2 on 7 March 1991. Written by Rob Grant and Doug Naylor, and directed by Ed Bye and Paul Jackson, the episode features the crew's attempt to escape the gravity pull of a white hole.

White hole, white-hole, or whitehole can mean:

• White hole, a theoretical relativity physics phenomenon related to black holes and wormholes.
• "White Hole" (Red Dwarf), an episode of the television series Red Dwarf
• A song by Christina Rosenvinge, from the 2006 Continental 62 album.
• White Hole, a band formed by Hanno Leichtmann and Nicholas Bussmann