Can we really time travel? Here's what award-winning physicist Brian Cox says

Time travel usually sounds like something straight out of a sci-fi movie, but what if that’s not really all? According to famous physicist Brian Cox, who recently won the 2026 Stephen Hawking Medal for Science Communication, some forms of time travel are actually allowed by physics.

Speaking at the British Science Festival, the University of Manchester professor explained what Einstein's theories really say about traveling through time and where they draw a hard line. Here's what he had to say.

According to Cox, “the answer is yes, you can go into the future.” But he added that once you are in the future, you will have “almost total freedom of movement." Einstein's general theory of relativity shows that time doesn't pass at the same rate for everyone.

To explain this, Cox shared on ABC News (Australia), "The protons go around the Large Hadron Collider at 99.999999% the speed of light. At that speed, time passes 7,000 times more slowly for the protons than it does for the experimenters watching them." Similarly, when anyone who flies to the Moon comes back, they age slightly less than the people who stayed on Earth.

Based on what physicists already know, forward time travel requires extreme speed. You would have to move close to the speed of light. Cox explained that the closer you get to the speed of light, the slower your personal clock runs compared to everyone else's. 

“Moving clocks run slow relative to stationary ones. So if you were to run across this studio now and run back and sit down, and we measured the time on your watch very accurately, your watch relative to mine would have run slower…That's true, and that's Einstein's theory,” he added.

Traveling into the future is possible, but there's a catch. You can't really come back and tell us that you have actually made it. Moving forward in time only works one way, and anyone who "arrives" thousands of years ahead has no way to return to where they started. 

Cox explained that a time traveler (like the Doctor from Doctor Who) would need a wormhole, which is a theoretical shortcut through space-time that can return you to an earlier point. But no wormhole has ever been proven to exist. Even if we found one, scientists aren't sure it could be used this way.

Cox cited physicist Stephen Hawking's "chronology protection conjecture" as the biggest obstacle to backward time travel. "Most physicists doubt it," he noted. The idea is that the laws of nature may always block travel into the past and prevent paradoxes like meeting your own parents before you were born. 

“So there's a conjecture that the laws of nature will always be such that time travel into the past is forbidden…I think most theoretical physicists would say, as Stephen Hawking does, that the physics protects the past”, he added.

On ABC News (Australia), mathematician Nalini Joshi pushed back on the idea that the past is completely off-limits. "Well, I don't know about whether there's an arrow that prevents you from going to the past or only into the future, but mathematically I think that there are many, many possible answers to these questions," she said. 

To illustrate, she described compressing a three-dimensional cube down into a flattened hexagon. She added that new dimensions can reveal new possibilities: "There are many, many possible structures in many, many dimensions which could give rise to time travel if you knew how to navigate around symmetries."