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When it comes to black holes, we are caught between a rock and a hard place. In the 1970s, Stephen Hawking showed that all black holes give off thermal radiation(热辐射)and eventually evaporate(蒸发). In doing so, they seemed to be destroying information contained in the matter that fell into them, therefore going against a rule of quantum mechanics(量子力学): information cannot be created or destroyed.

Some argued that the outgoing “Hawking radiation” preserved the information. However, if this were the case, then given certain assumptions, the event horizon(视界)—— the black hole’s boundary of no return—— would become intensely energetic, forming a firewall. But such firewalls go against the theory of general relativity, which says that space-time near the event horizon should be smooth. The black hole firewall paradox was thus born.

Now, Sean Carroll at the California Institute of Technology and his colleagues have shown that the paradox disappears when the evolution of black holes is understood in the context of the many-worlds interpretation of quantum mechanics.

The quantum state of the universe is described by something called the global wave function(全局波函数). According to traditional quantum mechanics, whenever there are many possible outcomes for physical process, this wave function ”collapses“ to represent one outcome. But in the many-worlds Interpretation, the wave function doesn’t collapse-rather, it branches, with one branch for each outcome. The branches evolve independently of each other, as separate worlds.

In this way of thinking, the formation of a black hole and its evaporation due to Hawking radiation lead to multiple branches of the wave function. An observer monitoring a black hole also splits into multiple observers, one in each branch.

The new work shows that from the perspective of an observer in a given branch, space-time behaves as described by general relativity and the black hole has no firewall.

But does that imply loss of information? No, says team member Aidan Chatwin-Davies, also of Caltech. That is because the principle of preservation of information applies to the global wave function and not to its individual branches, he says. Information is preserved across all branches of the global wave function, but not necessarily in any one branch. Given this case, a black hole that doesn’t lose information and yet has a smooth, uneventful event horizon without a fire wall isn’t a contradiction.

Yasunori Nomura at the University of California at Berkeleyy has independently arrived at some similar conclusions in his work. He agrees that the many-worlds approach resolves the paradox around information loss from black holes. “Many worlds should be taken seriously,” he says.