Until his death on 14 March, Stephen Hawking mulled the problem that vexed him for decades: How does information that falls into a black hole get back out so that it isn’t lost forever? This week, Hawking’s collaborators on his final work—Malcolm Perry of the University of Cambridge in the United Kingdom and Andy Strominger of Harvard University—summarized the group’s theory in a paper posted to the arXiv preprint server and titled “Black Hole Entropy and Soft Hair.” The paper, whose lead author is Cambridge graduate student Sasha Haco, describes how information might linger on the surface of a black hole in the arrangement of subtle charges, stanching the information loss that would otherwise undermine quantum mechanics. Those charges constitute the soft hair, without which a black hole would be an inscrutable orb described by just its mass and spin. The speculative idea likely isn’t the last word on the problem.
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