The time travel. Admit it also makes you dream a little. An opportunity to fix a mistake made in the past. Or to get a glimpse into the future. Science fiction has always enjoyed it. But what does science say about it? This is what Barak Shoshani proposes to us today to understand, a Brock University physicist (Canada).

Let us first remember that it is his general theory of relativity physical German Albert Einstein (1879-1955) that defined, for more than 100 years now, the bonds that unite space and time. In doing so, he presents us with a complex explanation of the principle of causation. It turned out that she was authorized to write Equations which describe time travel coherently. “But equations have no meaning if they don’t correspond to anything in reality.”confirms Barak Shoshani, in Conversation.

that by saying? Well first, let’s note that to build a time machine the equations would make physicists use negative energy stuff. However, there is no negative energy on every street corner. In the current state of our knowledge, it is rarely found Quantum mechanics Which gives us the hope of being able, in theory anyway, to manufacture it in very small quantities and for very short times. But Barak Shoshani wants to be an optimist: “This problem could simply be a limitation of our current technology or our understanding of Quantum mechanics. »

Difficulties to overcome to go back in time

So let’s sweep the matter problem with negative energy. However, there is still another major hurdle. Which we’ve all heard about before. That is the paradox of cohesion. The physicist gives a stark example. He imagines using the time machine he just made to go back in time by five minutes. There he destroys the machine. However, the destroying machine must not allow him to use it after five minutes to return five minutes earlier and destroy it. If it is when it is, then that means the time machine hasn’t been destroyed. He can use it to go back in time and destroy it. In other words, this is a time machine that is destroyed if and only if… it is not destroyed. Wonderful! Do you see the contradiction?

The Science Fiction He deals with the matter by advising time travelers to avoid interfering with the past. or to meet themselves. Problem solved. Except in physical, the contradiction corresponds to a purely theoretical concept. Understand that he enters light A contradiction in the theory itself. And hell! This is how time travel becomes simply impossible for him eyes Science.

Really impossible? Not necessarily, according to some researchers. Among them is the Russian theoretical physicist Igor Dmitrievich Novikov. His self-consistency conjecture is designed to solve time travel paradoxes. Quite simply by preventing time travelers from…altering the past. Really forbidden. With the laws of physics that somehow conspire to prevent Barak Shoshani from destroying his time machine five minutes before he enters it. But then, what’s good? Isn’t the point of going back to the past precisely to be able to change it?

Ending the paradoxes of interconnectedness in time travel

In addition, the work of Barak Shoshani shows that self-consistency guesswork does not make it possible to eliminate all paradoxes of time travel. And that goes back to square one? With time travel becoming impossible? Well, not quite, as the physicist tells us.

The ultimate solution would be to create multiple stories. or parallel schedules. what does it mean ? Quite simply, when a time traveler gets off his devices, he enters a timeline separate from his original timeline. In this new timeline, he is free from everything. Including destroying his own time machine. And that is, without any bearing on what will happen, shortly, in the timeline from which it comes. This is the end of the ironies. A science in line with science fiction that was already fond of parallel chronologies.

“I’ve been working on the paradoxes of time travel for the past three years and I’ve become more and more convinced that time travel might be possible.As Barak Shoshani says. But only if the files being It can allow multiple stories to coexist. » Which of course raises a new question: Can our universe accept parallel timescales?

Quantum mechanics seems to lean toward yes. Envisioned by the many-worlds theory imagined by the American mathematician Hugh Everett (1930-1982). The story can be divided. to allow Schrödinger’s cat To be alive in a new story and dead in the other.

Barak Shoshani’s team is currently working on creating a concrete theory of time travel with multiple histories consistent with Albert Einstein’s general relativity. The theory still hasn’t been able to prove that time travel is possible, but at least it’s not impossible due to coherence paradoxes.