Scrambling is the same in essence, but much stronger: You can’t distinguish two scrambled systems even if you look not just locally but at correlations across both systems. “Scrambling is a very strong form of thermalization,” Yao says. “It is the delocalization of quantum information.”

“It’s a quantum analogue of shuffling,” says Adam Brown, a physicist at Google and Stanford University. “If you start off with an ordered pack of cards, you say it’s shuffled if you look at the cards and say there is no obvious pattern left in them. This is not the same as saying that you’ve made it entirely random—it’s sufficiently mixed up that you have to be very sophisticated to know that it’s not random. It happens much sooner than genuine randomness.”

“Almost any many-body quantum system is eventually going to scramble,” he adds. But black holes are special. Just as the rate at which a pack of cards gets shuffled depends on the technique you use, the scrambling rate of a system depends on the details of how the particles in that system interact. These details are described mathematically by a function called a Hamiltonian. And it turns out that the Hamiltonian governing black holes means they scramble quantum information at the fastest rate possible.

And that’s what leads to Hayden and Preskill’s conclusion. Black holes act like fast quantum-scrambling circuits, so once they are sufficiently entangled with their own Hawking radiation, any new information entering them shows up very quickly in that radiation.

All the same, you’ll have to wait until the black hole and its Hawking radiation are entangled enough—that is, until it is half-evaporated—before this happens.

But there’s a faster alternative for getting at the information: Entangle the black hole maximally with something else—such as another black hole. That’s the proposal put forward in 2016 by Ping Gao and Daniel Jafferis of Harvard, working with Aron Wall of the Institute for Advanced Study in Princeton, New Jersey. If you could entangle a pair of black holes this way, they said, then a qubit swallowed by the first black hole would be registered in the other. Gao and colleagues showed how, by adding a further coupling between the black holes, you could make the transfer of quantum information between them formally identical to the process called quantum teleportation. Here, the entanglement between two particles is used to transfer the quantum state of one of them to the other. The target particle ends up looking identical to the initial one—in fact, there is no meaningful way to say it is not the same particle, vanished from one part of space and reconstituted in another. “Their entanglement acts like a bridge” for the information, Yao says.

Systems with the dynamics of black holes, Yao explains, “allow teleportation on the fastest possible timescale.” That’s because any information that enters one of them is quickly shared among all its particles—and thus, because of the entanglement with the second black hole, it’s shared quickly with that one too.