Black holes might end their lives by transforming into their exact opposite — ‘white holes’ that explosively pour all the material they ever swallowed into space, say two physicists. The suggestion, based on a speculative quantum theory of gravity, could solve a long-standing conundrum about whether black holes destroy information.
The theory suggests that the transition from black hole to white hole would take place right after the initial formation of the black hole, but because gravity dilates time, outside observers would see the black hole lasting billions or trillions of years or more, depending on its size. If the authors are correct, tiny black holes that formed during the very early history of the Universe would now be ready to pop off like firecrackers and might be detected as high-energy cosmic rays or other radiation. In fact, they say, their work could imply that some of the dramatic flares commonly considered to be supernova explosions could in fact be the dying throes of tiny black holes that formed shortly after the Big Bang.
Albert Einstein’s general theory of relativity predicts that when a dying star collapses under its own weight, it can reach a stage at which the collapse is irreversible and no known force of nature can stop it. This is the formation of a black hole: a spherical surface, known as the event horizon, appears, shrouding the star inside from outside observers while it continues to collapse, because nothing — not even light or any other sort of information — can escape the event horizon.
Because dense matter curves space, ‘classical’ general relativity predicts that the star inside will continue to shrink into what is known as a singularity, a region where matter is infinitely dense and space is infinitely curved. In such situations, the known laws of physics cease to be useful.
Many physicists, however, believe that at some stage in this process, quantum-gravity effects should take over, arresting the collapse and avoiding the infinities.
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