The concept of time travel has fascinated humanity for millennia. However, the idea has had a special boom since the appearance of the science fiction genre, which has been taking advantage of it for a long time. And it was not for less. Surely we all have dreamed of the infinite possibilities of time travel, even if it’s just to have the opportunity to make amends for a mistake made in the past.
But beyond dreams and science fiction, How realistic is time travel in our universe? What does science say about it?
In an article published in The Conversation, the adjunct professor of Physics at Brock University (Canada ), Barak Shoshany, wrote about the possibility of time travel, proposing a possible solution to the different paradoxes that physicists have found in the different theories about time travel.
Current understanding of the principle of causality
Our current understanding of time and causality is based on the general theory of relativity of the German theoretical physicist Albert Einstein (100-1955). This theory – which has been around for more than 100 years and which physicists agree fairly accurately describes the causal structures of our universe – combines space and time into a single entity, “space-time”, and offers an extraordinarily intricate explanation, according to Shoshany, of how they both work, at a level that is unmatched by any other established theory.
According to Shoshany, the general theory of relativity has allowed physicists to write equations that describe time travel in a way that is coherent and compatible with relativity. “But the equations don’t make sense if they don’t correspond to anything in reality,” says Shoshany. Why then would these equations be unreal?
Two big problems with time travel
First of all, according to the physicist, to build a time machine, the equations would require scientists to use exotic matter with negative energy . 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 periods of time.
But Shoshany is optimistic , pointing out, among others, 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 says.
Paradoxes of consistency
Apart from the exotic matter, the other main problem is the observation that the trip in time seems to contradict logic in the form of paradoxes of consistency. To explain, the physicist gives a surprising example.
“For example, consider a scenario where I enter my time machine, use it to go back in time five minutes, and destroy the machine when I get to the past. Now that I’ve destroyed the time machine, it would be impossible for me to use it five minutes later, explains Shoshany.
This means that, if it’s in the moment it is, he can’t go back in time and destroy it, implying that the time machine hasn’t been destroyed. And you can use it to go back in time and destroy it. In other words, it’s a time machine that destroys itself if and only if… it doesn’t. Paradoxical, right?
“As it cannot be destroyed and not destroyed simultaneously, this hypothesis is inconsistent and paradoxical”, affirms the physicist, who adds that, unlike science fiction, where there is the misconception that paradoxes can be “created”, a paradox in physics is not an event that can actually occur. Thus, paradoxes, he adds, are a purely theoretical concept that points to an incoherence in the theory itself.
Does this then mean that time travel becomes simply impossible in the eyes of The science? Not necessarily, according to some researchers.
Theoretical physicist Igor Dmitriyevich Novikov tried to solve the question of the paradoxes of travel in the time 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 studied time travel and in recent work found that there are time travel paradoxes that the Novikov conjecture cannot solve.
Thus, Shoshany and his students proposed another approach to solve the paradoxes: the theory of parallel timelines.
“We show that allowing multiple histories (or in more family members, parallel timelines) can resolve paradoxes that Novikov’s conjecture cannot. In fact, it can solve any paradox that arises”, assures the physicist.
According to his theory, when a person leaves a time machine, he lands in a different time line, in which he can do whatever he wants, even destroy his time machine five minutes before he’s supposed to use it. In this theory, changes to this new timeline would have no effect on the original timeline.
“Since I can’t destroy the time machine in the original timeline that I actually traveled to the past, there is no paradox”, says Shoshany.
“After working on the paradoxes of time travel Over the last three years, I have become more and more convinced that time travel could be possible, but only if our universe can allow the coexistence of multiple histories”, he adds.
Quantum mechanics seems to lean towards yes
According to Shoshany, splitting into multiple plot lines is entirely possible in quantum mechanics. “Quantum mechanics seems to imply that it does, at least if you subscribe to Everett’s ‘many worlds’ interpretation, in which a story can ‘split up; in multiple histories, one for each possible measurement result, for example, whether Schrödinger’s cat is alive or dead, or whether or not I reached the past”, he stated.
Currently, Shoshany continues to work hard with her students to develop a concrete theory of time travel on different timelines that conforms to the law of general relativity.
“Of course, even if we manage to find such a theory, this would not be enough to prove that time travel is possible, but it would at least mean that time travel it is not ruled out by the paradoxes of consistency”, concludes Shoshany in his article.
Edited by Felipe Espinosa Wang.