Solving The Mystery of Evaporating Black Holes

Physicists at Michigan State University found that quantum information leaks back out of a black hole’s event horizon during the later stages of a black hole’s evaporation, solving a major black hole physics problem in the process.

Forty years ago Stephen Hawking, the world’s foremost expert on black holes, announced that black holes evaporate and shrink because they emit radiation. The discovery perplexed physicists because, if a black hole evaporates and shrinks, what happens to everything it devoured during its lifetime? [Objects Would Not Be Crushed By A Black Hole, Study Finds]


Image credit: ESO/ M. Kornmesser

“The issue was never laid to rest because Hawking’s calculation was not able to capture the effect that the radiation, called Hawking radiation, has on the black hole itself,” said MSU professor Chris Adami, who was co-author of a paper published in the Physical Review Letters. “Physicists assumed that the black hole would shrink in time as the Hawking radiation carries away the black hole’s mass, but no one could verify this through mathematical calculations.”

Some scientists suggested that the information and everything else inside the black hole simply vanishes. However, vanishing information is not consistent with the known laws of physics.

Adami, along with his colleague Kamil Bradler from the University of Ottawa, developed a new simulation that allowed them to follow a black hole’s life cycle over time. The model revealed something completely unexpected: whatever was hiding behind the black hole’s event horizon (the invisible boundary of a black hole) slowly leaked back out during the later stages of the black hole’s evaporation.

The team used a set of sophisticated mathematical tools and high-performance computers to evolve the black hole over sufficiently long times until they were able to find quantum information outside of the black hole.

The findings solve a long standing mystery in astrophysics about black holes. Scientists have argued that it was not possible that everything a black hole gobbled-up during its life cycle could remain hidden within the black hole when it shrunk to minute sizes. The study suggests that they were correct – before a black hole can shrink to such small sizes, the model shows that quantum information has already leaked back out.

Most surprising of all was the occurrence of so called “Page curves” within their calculations. Named after physicist Don Page, his theory predicted the curves that show the quantum information first entering, then exiting a black hole. Adams and Bradler’s model is the first to yield curves just like those Page had theorized.

The team says there are still many leads to follow up on. To produce the model, researchers had to guess how a black hole interacts with the Hawking radiation field. In principle, the team’s guess should follow from the yet-to-be-discovered fundamental unified theory of quantum gravity. The model may even give physicists hints on how a theory of everything could be constructed.

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