Time travel could actually be possible in real life, physicist Barak Shoshany of Canada's Brock University has suggested in an article for The Conversation. However, there's a small twist.
First of all, there is a prosaic issue: in order to create a time machine, one would need a lot of exotic matter — matter with negative energy. All matter on Earth has positive energy, and even though quantum mechanics suggest that exotic matter can, in theory, be created, it would be in too small quantities and for too short periods of time.
Secondly, according to Shoshany, time travel could escape the pages of science fiction, but only when parallel timelines are involved. This is due to the time paradox, or consistency paradox.
In movies and books, time travellers are warned against interacting with their past selves or making any dramatic changes to history — because if, for instance, they kill their own grandfather for some reason, it would logically prevent them from being born in the first place, let alone travel back in time.
These paradoxes point to the impossibility of time travel. But if parallel timelines existed, allowing a time-traveller to jump across into an alternative history leading to an alternative present, then there would be no paradox.
Shoshany argues that this means time travel can be possible if our universe allows multiple histories to somehow co-exist. This is an issue for a whole other study, which the physicist is already conducting with the help of his students.
"My students and I are currently working on finding a concrete theory of time travel with multiple histories that is fully compatible with general relativity. Of course, even if we manage to find such a theory, this would not be sufficient to prove that time travel is possible, but it would at least mean that time travel is not ruled out by consistency paradoxes," Shoshany said in his article.
He noted that quantum mechanics imply the possibility of what some dub a "multiverse". One well-known example is the paradox of Schrödinger’s Cat. In one timeline the cat in the box dies, while in another, parallel one it survives.
So it would seem that if our universe can actually handle multiple histories, then we might really be able to travel through time — even though we still would be more of spectators than actors, given that nothing could be changed.