Time travel is possible!

the time travel. Admit it, it makes you dream a little too. The opportunity to repair a mistake made in the past. Or to take a look at the future. Science fiction has been enjoying it for a long time. But what does science say? This is what Barak Shoshany, a Brock University physicist (Canada).

Let us first recall that it is the theory of general relativity posed by the physical German Albert Einstein (1879-1955) which defines, for more than 100 years, the links between space and time. This gives us a complex explanation of the principle of causality. And it turns out she authorizes writing equations which consistently describe time travel. “But equations don’t make sense if they don’t correspond to anything in reality”emphasizes Barak Shoshany, a The conversation.

Is that to say? Well, first, let’s keep in mind that to build a time machine, equations would have used physicists subject matter with negative energy. However, negative energy is not found in every corner. In the current state of our knowledge, there are almost none Quantum mechanics which allows us to expect to be able, in theory in any case, to manufacture it in very small quantities and for extremely short time. But Barak Shoshany wants to be optimistic: “This problem could simply be a limitation of our current technology or our understanding of the Quantum mechanics. »

Difficulties to overcome to go back in time

We will therefore sweep away the problem of matter with negative energy. However, another important obstacle remains. What we’ve all heard before. That of the paradox of coherence. The physicist sets a striking example. He imagines himself using a time machine he has just built to go back five minutes in time. There he destroys the machine. However, the destroyed machine should not allow you to use it five minutes later to return five minutes earlier and destroy it. If it is when it is, it must mean that the time machine has not been destroyed. And you can use it to go back in time and destroy it. In other words, here is a time machine that is destroyed if and only if … it is not destroyed. go! Do you see the inconsistency?

He science fiction it deals with the matter by advising its travelers in time to avoid intervening in the past. Or to get to know themselves. Problem solved. Except that in physics, a paradox corresponds to a purely theoretical concept. Understand that it reveals an inconsistency in the theory itself. And hell! This is how time travel becomes impossible eyes science.

Impossible, right? Not necessarily, according to some researchers. Russian theoretical physicist Igor Dmitriyevich Novikov is one of them. She conjecture of self-coherence was imagined to solve the paradoxes of time travel. Simply forbidding time travelers … to change the past. Really forbidding. With laws of physics that somehow conspire to prevent Barak Shoshany from destroying his time machine five minutes before entering it. But then what good is it? Isn’t it the point to go back to the past precisely to be able to change it?

End the paradoxes of the coherence of time travel

In addition, the work done by Barak Shoshany shows that the conjecture of self-coherence does not eliminate all the paradoxes of time travel. So let’s get back to the case of one? With time travel impossible? Well, not at all, the physicist tells us.

The ultimate solution would be to create multiple stories. Or parallel timelines. That means ? Simply, when the time traveler leaves his machine, he enters a timeline independent of his original timeline. In this new timeline, he is free from everything. Even destroying your time machine. And this, without any impact on what will happen, a little later, in the timeline from which it comes. This is the end of the paradoxes. And science that reconciles with science fiction, which was already fond of stories of parallel chronologies.

“I have been working on the paradoxes of time travel for the last three years and I am becoming more and more convinced that time travel could be possible.says Barak Shoshany. But only if our universe can allow multiple stories to coexist. » Which, of course, raises a new question: Can our universe accept parallel timelines?

Quantum mechanics seems to lean inward. The theory of multiple worlds imagined by Hugh Everett, an American mathematician (1930-1982), predicts this. The story could be divided. To allow the Schrodinger’s cat to be alive in one new story and dead in the other.

Barak Shoshany’s team is currently working to establish a concrete theory of time travel with multiple stories consistent with Albert Einstein’s general relativity. A theory that would not yet prove that time travel is possible, but at least that it is not made impossible by coherence paradoxes.