White Holes: The Death of a Black Hole Gives Rise to Its Perfect Inverse?
Does a black hole explode into a "white hole" when it dies? Where a black hole is essentially an enormous vacuum from which nothing, not even light, can escape, two physicists have theorized that the death of a black hole may transform it into its exact opposite: a "white hole" that pours all of the contents of a black hole into space.
According to extrapolations from Einstein's theory of relativity, when a star begins to die, it undergoes a process called gravitational collapse, in which the star's temperature drops to the point that it is no longer able to support its own weight. When the gravitational collapse reaches a certain point, the mass is so compact that it deforms spacetime and deforms a black hole. The black hole contains an event horizon, or a "point of no return" in which no matter or radiation can escape its gravitational pull. Within the event horizon, a gravitational singularity forms, a point at which spacetime is infinitely curved and the laws of physics cease to have meaning. However, many physicists believe that this account of black holes given by classical mechanics is incomplete, as it is incompatible with quantum mechanics in several different ways. In order to make the theory of black holes compatible with quantum mechanics, some mechanism would need to arrest the collapse of the black hole before the infinities occurred.
[Credit: Alain R]
One proposed solution is the idea of looped quantum gravity. According to this theory, gravity and spacetime consist of interwoven loops that are so tiny, an outside observer would only perceive smooth spacetime. Today, physicists Carlo Rovelli and Hal Haggard have published research which postulates that this looped gravity would sufficiently arrest the collapse of a black hole. As a result, the singularity would not be surrounded by a true event horizon, which is incompatible with quantum mechanics, but an "apparent horizon" that would eventually dissolve and release the absorbed, and now scrambled, information, a phenomenon which was first predicted by Stephen Hawking. This theory leads to the conception of a "white hole," in which a black hole releases all of its contents into space in explosive fashion. When completely compressed, the loops would exert external pressure, which would transform a black hole into a white hole. According to current theories, this transformation would take place directly after the formation of a black hole, but since gravity dilates time, it would look like trillions of years to the outside observer.
This theory may solve a long-pondered paradox regarding the apparent loss of physical information in black holes. According to the classical theory of black holes, physical information is destroyed within the event horizon as matter devolves into a particular physical state. But one of the fundamental tenets of quantum mechanics, called unitarity, postulates that physical information is encoded into a system's wave function, and therefore is conserved in the quantum sense. If information is eventually released upon the transformation into a white hole, then this paradox could potentially be resolved. According to theoretical physicist Steven Giddings of the University of California, Santa Barbara, "Understanding how information escapes from a black hole is the key question for the quantum mechanics of black holes, and possibly for quantum gravity itself."