We may be able to book our ticket to the future someday -- it'll just be a one-way trip.
"The central question is, can you build a time machine? The answer is yes, you can go into the future," the University of Manchester professor told the audience during his hour-long speech on Tuesday, according to The Telegraph. "You've got almost total freedom of movement in the future."
Cox detailed how time travel to the future is possible under Albert Einstein's general theory of relativity. Traveling hundreds, or even thousands of years into the future, could be accomplished if someone was traveling at an incredibly fast pace, close to the speed of light.
Discovery News equated the theory to the so-called "Twin Paradox:"
Imagine twins, one stays on Earth (Twin A) while the other (Twin B) boards a spaceship and flies off at relativistic speeds. Compared with Twin A’s timeframe, Twin B’s timeframe will slow. If time is running slower for Twin B, then he/she will return to Earth where a lot more time has passed and Twin A has aged significantly more than Twin B. The mechanism behind this is “time dilation” and it has a stronger effect as you travel closer and closer to the speed of light.
Coming back from the future or traveling to another point in the past is much less likely, according to Cox.
Relating his theory to the popular British science fiction show "Doctor Who," Cox explained that the time-traveling Doctor would need to find a wormhole in order to return to the past. The theoretical bridge, or shortcut through space-time, proposed under Einstein's general-relativity theory has never been proven to exist. And, even if a wormhole were discovered or created, there's no telling whether humans could actually use it to travel through time.
Cox isn't the only one to theorize that a wormhole could allow time-travelers to travel backward in time. Earlier this year, astrophysicist Eric W. Davis of the EarthTech International Institute for Advanced Studies said that a wormhole would be the best option for back-in-time travel. But, Davis acknowledged, it would "take a Herculean effort to turn a wormhole into a time machine."