Black hole channel could send messages to past

A new study calculates how much information could be transmitted from the future to the past using exotic spacetime paths known as closed timelike curves—scenarios general relativity says could form around a spinning black hole.

For decades, time travel has lived in movies and paradoxes. Now, a new study is doing something stranger and more precise: it’s asking a quantitative question about whether information can be sent backward in time—if the universe allows closed timelike curves.

The work begins with the physics that’s already on the books. Einstein’s general theory of relativity predicts that closed timelike curves may form in regions where space and time are intensely bent and rotating. such as around a spinning black hole. In that kind of warped geometry. the study’s co-author Seth Lloyd describes the unsettling idea that “spacetime can curve around so much that you can be innocently going forward in time and then you meet yourself in the past.”.

What makes the scenario plausible isn’t that anyone has observed time travel. It’s that black holes are common, and most of them spin. Lloyd argues that means these structures could exist: “So they might very well exist.”

In general relativity’s picture of a rotating black hole. the singularity at the center—normally described as a point of infinite density—is instead treated as a one-dimensional ring. Closed timelike curves would arc around it. No one knows whether these spacetime pathways truly exist in our universe, but researchers say they are physically plausible.

The new study, published recently in Physical Review Letters, calculates how much information could be sent backward through time via closed timelike curves. It traces its inspiration to an unlikely place: a film.

“In early 2025 I watched the film Interstellar,” said Kaiyuan Ji, a graduate student at Cornell University. Ji worked on the research with his advisor Mark Wilde and with Lloyd. Ji said the movie’s setup was mathematically equivalent to a question the team had already posed in earlier research—how to use closed timelike curves to transmit information between the future and the past.

The researchers’ focus wasn’t just whether a message could travel. It was what kind of communication strategy could survive real-world complications—especially noise.

Ji described how the logic differs from ordinary time-forward communication. In their model, the sender in the future has memory of what happened in the past. That memory. Ji said. “causes a causal loop.” With that loop in place. the team found the sender can “bend the probability of success. ” using knowledge of the past to counteract interference that otherwise prevents the maximum amount of information from passing.

Lloyd offered a concrete way to think about the problem. If you “drop a message into a black hole in the future and it emerges from the same black hole in the past. ” the message might be corrupted or parts of it could be lost. In a noisy channel. the receiver in the past could respond: “Hey. if you’re going to send me a message last Tuesday. I know the closed timelike curve was super noisy then. Can you send multiple copies or try on Wednesday?”.

That possibility—feedback from the past shaped by the future sender’s remembered history—is at the heart of what the study is quantifying.

Giulio Chiribella. a quantum information scientist at the University of Hong Kong who was not involved in the research. said the implications could extend beyond speculative time travel. He has studied ways to simulate closed timelike curves in laboratory settings on Earth. “We don’t know if [these curves] exist in our universe. but we do know that if they exist. they have powerful consequences. ” he said. In his view. closed timelike curves would create “radically new scenarios where the order of events becomes indefinite. ” potentially allowing quantum computation and quantum communication to go beyond the limits of conventional setups.

The team also lands on a boundary where time travel fantasies usually break. Past studies have found that closed timelike curves can’t be used for paradoxical time travel. A laboratory experiment described in a 2011 paper co-authored by Lloyd simulated these pathways and effectively sent a photon—a particle of light—back in time by less than a second. Researchers then examined whether such a setup could enable a “grandfather paradox. ” essentially whether the past could be destroyed—like killing a grandfather. preventing the traveler’s own birth.

The conclusion was that quantum physics permits only self-consistent versions of time travel. “In other words, you can visit the past, but you can’t change the future—no grandfather murder allowed.”

In this new work, the paradox avoidance still hangs in the background. But the focus has shifted toward a more unsettling kind of possibility: even if a causal loop must remain self-consistent. information might still be transmitted backward—and the study now puts numbers on what that could mean when the channel is noisy.

Whether the universe actually allows closed timelike curves is still an open question. But the study makes the mystery concrete enough to matter. If such spacetimes exist around spinning black holes, the way they reshape causality could become more than a philosophical puzzle. It could become a tool—one that bends not just time, but the limits of information itself.

closed timelike curves black holes time travel quantum information general relativity Physical Review Letters Seth Lloyd Kaiyuan Ji Mark Wilde Giulio Chiribella Interstellar