A black hole may carry “soft hair,” low-energy quantum excitations that release information when the black hole evaporates.
Four decades ago, Stephen Hawking proposed that black holes could destroy information—a conclusion that is incompatible with standard laws of quantum physics. This idea started a controversy known as the “black hole information problem” that even now has not been resolved. A new study by Hawking himself and Malcom Perry, both at the University of Cambridge, and by Andrew Strominger at Harvard University shows that some of the assumptions that led to the information problem might be wrong [1]. Their results do not completely solve the problem, but point to a promising research direction that might lead to its long-awaited solution.
According to Einstein’s general theory of relativity, stationary black holes are completely determined by just three observable parameters: their mass, charge, and angular momentum. Almost none of the information about what fell into the black hole is visible from the outside. Physicist John Wheeler described this idea by saying that “black holes have no hair.”
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