Here’s what you’ll learn when you read this story:

• Inspired by the movie Interstellar, a team of researchers figured out—at least hypothetically—how to send messages to the past.
• The researchers answered the question of how the movie’s protagonist could communicate to his daughter backwards in time by hypothesizing that his memory of the past is a vision of her future.
• Retrieving memories from someone else’s future and sending information based on them through a noisy time loop turns out to be more efficient than sending messages into the future.

In the sci-fi epic Interstellar, strange patterns appear in the dust on the floor of young Murph Cooper’s bedroom after a dust storm sweeps through the house. Murph thinks a ghost is responsible, but her father, former NASA pilot Joseph “Coop” Cooper (Matthew McConaughey), recognizes the patterns as a gravitational anomaly encoding binary coordinates. Years later, after Coop travels through a wormhole, he finds himself inside a tesseract—a higher-dimensional space constructed by future beings—where he can manipulate gravity across time. From there, he sends messages backward through time to Murph by creating the very gravitational anomalies they once observed together.

Because of time dilation, in which time slows down for an object moving at incredibly high speeds, years passed on Earth while only hours elapsed for Coop. From within the tesseract, he was able to send messages across time to his daughter—it turned out he had been the “ghost” behind the gravitational anomaly all along. It all makes for a great movie—but sending a message backward in time might not be as far-fetched as it seems. According to recent research in quantum physics, it really might be possible.

Time loops may provide a mechanism for sending messages into the past like Cooper did in Interstellar. General relativity allows for a closed timelike curve (CTC), which occurs when an object’s trajectory through spacetime takes it to the future and then back to the past. Another possible mechanism is quantum entanglement: If Cooper and Murph were quantum-entangled, they could share information backward through time. Particles that are quantum-entangled are always sensitive to each other’s state, so even if one gets catapulted through space so far and so fast that it ends up in the future, it’s still transmitting information to the one left behind in the past.

In fact, some physicists have suggested that the hypersensitivity between entangled particles actually comes from the one in the future sending messages back in time. Recently, Seth Lloyd and fellow researchers at the Massachusetts Institute of Technology wanted to make this very science fiction-seeming concept into a reality. While bending spacetime to build an actual CTC would require an almost unfathomable amount of energy, Lloyd had previously succeeded in using photons that were quantum entangled to simulate a CTC by sending one of them a few nanoseconds back in time. Now, inspired by Interstellar, they wanted to see if sending messages backwards was an option, too.

Though it may sound counterintuitive, the researchers discovered that for a CTC-like channel that’s full of noise—like the quantum mechanical version of phone static—it was actually easier to transmit a message to the past than to the future.

“Access to a noiseless CTC of one kind or the other has been shown to unleash stunning information-processing power,” they said in a study recently published in Physical Review Letters, adding that a CTC-like channel “[can be] represented by a quantum channel, in the sense that information traveling through the noisy [channel] effectively evolves as if passing through the channel, except for ending up in the past.”

Messages traveling through a noiseless CTC channel are being teleported to the past so long as no other actions are necessary to complete message transmission. It is because the channel is noiseless that the past and future versions of the time loop are the same. But in a noisy time loop, a message from the future is sent to the past through a channel whose noise affects its journey. The researchers see the communication channel between Cooper and his daughter as “some noisy mechanism” that defies the usual passage of time from the past to the future. What’s really surprising is that this is more efficient than using a channel that’s just as noisy to communicate forward in time.

The difference between sending a message forward and backward in time comes down to Cooper remembering past events that include Murph’s decoding of the messages, since this technically happens in his past. He was able to get through to her because he recalled her decoding the messages. So when sending those messages, he wrote them as he recalled them, so she’d be able to translate. The only thing that violates the usual chronological order of things in this arrangement is the time loop involved. Otherwise, if Cooper were somehow unable to consult his memory, nothing would be different from communication that travels from past to future. The team plans to model this setup with photons to see how they behave in a noisy time loop.

“The existence of CTCs could lead to perplexing consequences such as violation of causality and escape from a black hole,” they said.

Escaping the massive gravity of the tesseract, as Coop seeks to do in Interstellar, would be an entirely different problem.