Spinning Black Holes Might Actually Send Messages Back in Time
It started with a movie. In early 2025, a Cornell University graduate student named Kaiyuan Ji sat down to watch Interstellar, the science fiction film where an astronaut sends a message through a black hole to his daughter in the past. Most people watching would file that under "cool but impossible." Ji, who studies quantum information science, had a different reaction: he realized the plot was mathematically similar to a real problem he and his colleagues had already been investigating. That observation helped spark a genuine scientific study, recently published in the journal Physical Review Letters, about whether information could actually travel backward through time.
To understand how this might work, you need to know a little about black holes and how they warp space and time. According to Albert Einstein's general theory of relativity — his famous set of equations describing how gravity works — massive objects bend the fabric of spacetime, which is the combined structure of space and time woven together. A spinning black hole bends spacetime so severely that it can create what scientists call closed timelike curves. A closed timelike curve is a path through spacetime that loops back on itself, meaning something following that path could end up in its own past. Think of it like a circular slide that, instead of just going down, winds all the way around and deposits you at the top again — except the slide is made of time.
Inside a rotating black hole, the singularity — the point of unimaginably intense density at the center — is not a dot but a ring. Closed timelike curves can arc around that ring. Nobody has confirmed that these structures exist in our universe, but Einstein's equations permit them, and since we know most black holes spin, researchers like Seth Lloyd, a quantum information scientist at MIT, think they might be real. "So they might very well exist," Lloyd says.
The research team, which included Lloyd, Ji, and Ji's advisor Mark Wilde, set out to calculate exactly how much information could be sent backward through time using one of these curves. Communicating into the past turns out to have a very different structure than communicating forward. The interesting twist is that a sender in the future has memory of what already happened in the past, which creates a feedback loop. That memory becomes a powerful tool. If you know a particular timelike curve tends to scramble or lose parts of a message — the way a bad phone connection drops words — you can ask the receiver in the past to request that you send extra copies, or try at a less noisy moment. The future sender, remembering that request, can adjust accordingly. The researchers found this strategy significantly improves the odds of a message getting through clearly.
You might be wondering: could someone use this to cause a paradox — like traveling back in time to prevent their own birth? This puzzle even has a name: the grandfather paradox. If you went back and stopped your grandfather from meeting your grandmother, you would never have been born, so you could never have gone back in time in the first place. It's a logical loop with no solution. But here is the reassuring part: previous research, including a 2011 experiment co-authored by Lloyd, showed that closed timelike curves only allow self-consistent versions of events. In other words, quantum physics seems to automatically prevent paradoxes. You might be able to send information to the past, but you cannot use it to rewrite history in a way that contradicts itself. The timeline stays coherent.
Beyond the mind-bending time travel angle, these findings have practical implications for quantum computing — a type of computing that uses the rules of quantum physics to process information in powerful new ways. Giulio Chiribella, a quantum information scientist at the University of Hong Kong, noted that even simulating closed timelike curves in a lab on Earth could lead to breakthroughs. "They induce radically new scenarios where the order of events becomes indefinite," he said, "boosting quantum computation and quantum communication beyond the limits of conventional setups." In short, understanding how time loops handle information could help build faster and more powerful computers, even if we never actually find a real closed timelike curve in space.
Science often starts with something that sounds too strange to be true. The fact that physicists are doing serious mathematics on backward-in-time communication — and publishing it in respected journals — says a lot about how far our understanding of the universe has come, and how much further it might still go.
Source: Scientific American