The Science Behind Time Travel
Time machines may seem more like a concept from science fiction than something that could exist in a physics lab, but experts suggest that this futuristic technology might one day become a reality. Researchers have uncovered how time travel could actually function by applying the principles of quantum physics.
Although this method won’t allow you to travel back to the time of the dinosaurs, scientists believe it could be possible to send messages into the past. This technique is similar to what was depicted in Christopher Nolan’s sci-fi film Interstellar, where an astronaut played by Matthew McConaughey sends a message to his daughter in the past by moving the hands on her watch.
While the real-world application wouldn’t be as dramatic as in the movie, the researchers argue that this “causal loop” mirrors how real time travel might work. Dr Kaiyuan Ji, a researcher at Cornell University, explained: “The father remembers how the daughter decodes his future message. So he can instruct himself on what is the best way to encode the message.”
It might come as a surprise, but there is nothing in the laws of physics as we currently understand them that makes time travel impossible. According to general relativity, which is our best description of the universe, everything moves through space and time along a fixed path. One such path is known as a closed time-like curve (CTC). A particle traveling on a CTC moves into the future before looping back on itself via the past to end up exactly where it started.
The laws of physics allow for these loops to form, but creating one on a large scale would require twisting spacetime with an infinite amount of energy. However, on a very small scale, structures like CTCs might naturally arise due to the rules of quantum physics.
On the quantum level, two particles can become “entangled,” meaning that what happens to one particle affects the other, even if they are light-years apart. One possible explanation for this phenomenon, which Einstein called “spooky action at a distance,” is that one particle is sending messages backwards in time to the other.
How to Send a Message Back in Time
To send a message back in time, you can create a quantum system with two entangled particles. These particles form a closed time-like curve. Altering one particle creates a change in the other, effectively sending information backwards through time.
If you remember how the message was decoded in the past, you can use this knowledge to adjust how you encode the message in the future. This allows for clear communication, regardless of how noisy the connection is. Instead of assuming the particles are part of a single massive system or that they are sending information faster than light, their sensitivity is explained by receiving messages in the past that tell them how to react later.
This idea might sound far-fetched, but in 2010, scientists came up with a way to mimic closed time-like curves using entangled particles. Professor Seth Lloyd, a quantum physicist from MIT, described it as “the equivalent of sending a photon a few nanoseconds backwards in time, and having it try to kill its former self.”
This setup is akin to a telephone with a direct line to another device just a few moments earlier. In theory, you could use something like this to pass messages back to yourself in the past. Just like a real phone line, the connection on a CTC isn’t always perfect, and noise or disruption can make it difficult to transmit information with complete accuracy.
Professor Lloyd said: “Nobody’s built an actual physical, closed time-like curve, and there are reasons to think it’s very hard to make one. But all channels are noisy.”
This is where the insight from Interstellar comes into play. In their new paper, accepted for publication in Physical Review Letters, Professor Lloyd and his co-authors wrote: “The father, who is in the future, may retrieve his memory of past events he has witnessed, even including the daughter’s decoding of the message which he is about to send! It would thus not be surprising that he will consult his memory of the daughter’s decoding when encoding his message, so as to maximize the efficiency of the communication.”
Essentially, if you’ve already seen someone struggle to decode your garbled message, you should know how to send it so that it’s easier for them to understand. Even with a noisy connection, a backward time-traveling message would still be legible.
The slightly strange conclusion of this research is that sending messages backwards in time is likely to be clearer than sending a message in normal time. Although no one has built a real closed time-like curve, Professor Lloyd believes it should be fairly easy to turn this idea into an experiment on the quantum level.
This could allow scientists to explore how information is transmitted through “noisy channels” and potentially improve real-life communication methods.
