In science fiction movies, like the saga of Back to the future, they usually show us time travel that amazes more than one viewer. This is no coincidence, since we have all wondered if it was possible to do so.

The answer to this question was provided by Barak Shoshany, professor of physics at Brock University (Canada), in an article published on the science news portal The conversation.

The Canadian expert wrote about the possibility that humans have of time travel, establishing a solution to the various paradoxes that physicists have discovered in the various theories related to this subject.

Current understanding of the principle of causality

Our current understanding of time and causation is based on the German theoretical physicist’s theory of general relativity Albert Einstein (1879-1955), which has existed for more than 100 years and whose experts agree in describing the causal structures of our universe quite precisely.

This theory combines space and time into a single entity, “spacetime”, and offers an extraordinarily complex explanation, according to Shoshany, of how the two work, on a level unmatched by any other established theory.

According to the Canadian professor, the general theory of relativity has allowed physicists to write equations that describe time travel in a way that is consistent and compatible with relativity. “But the equations don’t make sense if they don’t correspond to anything in reality,” Shoshany said.

In this sense, the question that arises is why then would these equations be unreal?

Two big problems with time travel

First, according to the physicist, to build a time machine, the equations would require scientists to use exotic negative-energy matter. However, negative energy is not available in every corner.

In the current state of knowledge, only quantum mechanics gives us hope, at least in theory, of being able to produce it in very small quantities and for extremely short durations.

Shoshany is optimistic and supports the possibility of discovering other equations that allow time travel without the need for exotic matter. “This problem could simply be a limitation of our current technology or our understanding of quantum mechanics,” he said.

coherence paradoxes

Besides exotic matter, the other main problem is the observation that time travel seems to contradict logic in the form of coherence paradoxes. To explain it, the physicist gives a surprising example.

“For example, imagine a scenario where I enter my time machine, use it to go back five minutes, and destroy the machine as soon as I get to the past. Now that I’ve destroyed the time machine, I wouldn’t be able to use it five minutes later, Shoshany explained.

This means that if you’re in the moment you’re in, you can’t go back in time and destroy it, implying that the time machine wasn’t destroyed. And you can use it to turn back time and destroy it. In other words, it’s a time machine that destroys itself if it doesn’t. Paradoxical, right?

“Since it cannot be destroyed and not destroyed simultaneously, this hypothesis is inconsistent and paradoxical,” said the physicist, who added that unlike science fiction, where it is mistakenly believed that paradoxes can to be “created”, physics is not an event. it can actually happen. Thus, paradoxes, he added, are a purely theoretical concept that points to an inconsistency in the theory itself.

Does this then mean that time travel simply becomes impossible in the eyes of science? Not necessarily, according to some researchers.

The theoretical physicist Igor Dmitriyevich Novikov attempted to resolve the issue of time travel paradoxes with a self-consistency conjecture, which “essentially states that you can travel to the past, but you cannot change it”.

The parallel world approach

However, Professor Shoshany, along with his students Jacob Hauser and Jared Wogan, have studied time travel and in recent work have found that there are time travel paradoxes that Novikov’s conjecture cannot. solve.

Thus, the Canadian expert and his students proposed another approach to resolve the paradoxes: the theory of parallel chronologies.

“We show that allowing multiple histories (or in more colloquial terms, parallel timelines) can resolve paradoxes that the Novikov conjecture cannot. In fact, it can resolve any paradox that arises,” the physicist stressed.

According to his theory, when a person exits a time machine, they land in a different timeline, where they can do whatever they want, including destroying their time machine five minutes before leaving. use it. In this theory, changes to this new timeline would have no effect on the original timeline.

“Because I can’t destroy the time machine in the original timeline that I traveled with in the past, there’s no paradox,” Shoshany said.

“After working on the paradoxes of time travel for the past three years, I am increasingly convinced that time travel could be possible, but only if our universe can allow multiple stories to coexist.” .

Quantum mechanics seems to lean towards yes

According to Shoshany, the division into several scenarios is entirely possible in quantum mechanics.

“Quantum mechanics seems to imply that it is, at least if you subscribe to Everett’s ‘many worlds’ interpretation, in which a story can be ‘split’ into multiple stories, one for each measurement outcome. possible, for example whether Schrödinger’s cat is dead or alive, or whether or not I have reached the past,” he said.

Currently, the Canadian professor continues to work intensively with his students on the development of a specific theory of time travel in different timelines that respects the law of general relativity.

“Of course, even if we manage to find such a theory, it would not be enough to prove that time travel is possible, but it would at least mean that time travel is not excluded by paradoxes of coherence “, he concluded. in his article.