The concept of **time travel** It has fascinated mankind for millennia. However, the idea has had a special rise 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. We have all surely dreamed of the infinite possibilities of time travel, even if it is 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 assistant 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 (1879-1955). 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, the “**space time**“, and offers an extraordinarily intricate explanation, according to Shoshany, of how they both work, on 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 **they don’t make sense if they don’t correspond to anything in reality,” says Shoshany. Why then would these equations be unreal?

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### Two big problems with time travel

First, according to the physicist, to build a time machine, the equations would require scientists to use exotic matter with negative energy. However, the **negative energy** it is not available on 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.

Is time travel really possible in our universe, or is it just science fiction?

### consistency paradoxes

Aside from exotic matter, the other main problem is the observation that time travel seems to contradict logic in the form of consistency paradoxes. To explain it, the physicist gives a striking 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 as soon as I reach the past. Now that I have destroyed the time machine, I would be unable to use it.” five minutes later, Shoshany explains.

This means that if you are at the moment you are, you cannot **go back in time** and destroy it, implying that the time machine has not 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?

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

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

Theoretical physicist Igor Dmitriyevich Novikov attempted to resolve the question 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, 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 for multiple histories (or in more familiar terms, parallel timelines) can resolve paradoxes that the Novikov conjecture cannot. In fact, it can resolve any paradox that is thrown at it,” says the physicist.

According to his theory, when a person steps out of a time machine, he lands in a **different timeline**, where you can do whatever you want, including destroying your time machine five minutes before you’re supposed to 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 actually traveled back in time with, there’s no paradox,” says Shoshany.

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

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### Quantum mechanics seems to lean towards yes

According to Shoshany, the division into multiple **plot lines** It is entirely possible in **quantum mechanics**. “Quantum mechanics seems to imply that it does, at least if you subscribe to Everett’s interpretation of the** ‘many worlds’**in which a story can be ‘split’ into multiple stories, one for each possible measurement outcome, for example, whether Schrödinger’s cat is alive or dead, or whether or not I reached the past,” he says.

#### Today, Shoshany continues to work intensively with his students on developing a concrete theory of time travel on different timelines that adheres to the law of general relativity.

##### Of course, even if we do 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 is not ruled out by consistency paradoxes.” in your article.

Source: DW