A physicist discovers that “paradox-free” time travel is theoretically possible

No one has yet been able to travel through time – at least to our knowledge – but the question of whether or not such a feat is theoretically possible continues to fascinate scientists.

Like movies The situation or the end, Donnie Darko, Back to the future Many others show that moving through time creates a lot of problems for the basic rules of the universe: if you go back in time and prevent your parents from meeting, for example, how can you exist to go back in time? in the first place?

It’s a huge surprise known as the Grandfather Paradox, but a few years ago, physics student Jermaine Tobar, from the University of Queensland in Australia, figured out how to “square numbers” to make time travel viable without paradoxes.

“Classical dynamics says if you know the state of a system at a given time, that can tell us the history of the entire system.” Tobar explained back in 2020.

“However, Einstein’s theory of general relativity predicts the existence of time loops or time travel — where an event can be both past and future itself — theoretically turning the study of dynamics on its head.”

What the calculations show is that space-time can adapt itself to avoid paradoxes.

To use a topical example, imagine a time traveler traveling into the past to prevent a disease from spreading—if the mission is successful, the time traveler will have no disease to go back in time to defeat.

Tobar’s work suggested that the disease would still escape in another way, through a different route or in a different way, eliminating the paradox. No matter what the time traveler does, the disease will not stop.

It is not easy for non-mathematicians to delve into Tobar’s work, but he is investigating the effect Deterministic processes (without any randomness) on an arbitrary number of regions in the space-time continuum, and shows how both Closed time curves (As Einstein predicted) It could fit the rules of free will and classical physics.

“The mathematics has been verified – and the results are the stuff of science fiction.” said physicist Fabio Costa from the University of Queensland, who supervised the research.

Fabio Costa (left) and Jermaine Tobar (right). (ho fu)

The research settled the problem with another hypothesis, which was that time travel was possible, but time travelers would be restricted in what they did, to prevent them from creating a paradox. In this model, time travelers are free to do what they want, but paradoxes are not possible.

While numbers may work, bending space and time to reach the past is still a long way off — the time machines scientists have created so far are so high-concept that they currently exist only as calculations on a page.

We might get there one day — Stephen Hawking certainly thought it was possible — and if we do, this new research suggests we’ll be free to do what we wanted the world to do in the past: it will adjust itself accordingly.

“Try as you may to create a paradox, events will always adjust themselves, to avoid any contradiction.” Costa said.

“The set of mathematical operations we have discovered shows that time travel with free will is logically possible in our universe without any paradox.”

The research was published in Classical and quantum gravity.

A previous version of this article was published in September 2020.