In August 2013, dozens of renowned theoretical physicists gathered in Santa Barbara, California, to discuss a crisis. Their tenuous understanding of black holes was falling apart. Viewed from afar, as if through a telescope, a black hole should behave like a planet, a star, or any other conglomerate of elementary particles. But if the physicists believed the work of Albert Einstein, as most of them did, then impossible consequences came about when they considered the black hole from the viewpoint of someone just inside its boundary.
A thought experiment the previous year had sharpened this clash of perspectives, abruptly ending a two-decade armistice between those who believed the exterior view to be the fundamental one and those who focused on the view from inside. Suddenly, all manner of sacrosanct physical beliefs were up for debate. Those behind the thought experiment suggested, desperately, that black hole interiors might simply not exist — that space-time ended at the edge of the black hole in a literal wall of fire.
As an extension of that thinking, one attendee at the conference even suggested, largely in jest, that the paradox seemed to imply that the known laws of physics might just break down everywhere all the time, an observation that earned a Comedy Cellar–worthy laugh. One of the more junior participants, Daniel Harlow, took the mic and reacted with a single incredulous “Dude,” before guiding the conversation back to less heretical ground.
“There was just a flurry” of brainstorming, said Patrick Hayden, a computer scientist turned physicist at Stanford University. “People’s willingness to go out on a limb with crazy ideas was shocking.”
After another decade of arguing and calculating, Harlow, now a senior physicist at the Massachusetts Institute of Technology, believes that he and a team of up-and-coming theorists have finally found the way, or at least a way, of squaring the exterior and interior views. In doing so, they have established something of a détente between the warring worlds of relativity and quantum theory. Their resolution, which weaves together far-flung ideas from quantum information theory and breakthrough calculations from 2019, is a headache-inducing and hard-won attempt to have the outside and keep much of the inside too.
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