# A Physicist Has Worked Out The Math That Makes ‘Paradox-Free’ Time Travel Plausible

So far as we know, no one has been able to travel through time, but scientists are still interested in the question of whether or not it would be possible in theory.

Movies like The Terminator, Donnie Darko, Back to the Future, and many others show that moving around in time breaks a lot of the basic rules of the Universe. For example, if you go back in time and stop your parents from meeting, how can you even exist to go back in time?

It’s called the “grandfather paradox,” and it’s a huge puzzle. But in September of last year, an Australian physics student named Germain Tobar from the University of Queensland said he had figured out how to “square the numbers” to make time travel possible without any paradoxes.

Tobar said in September 2020, “Classical dynamics says that if you know the state of a system at a certain time, you can figure out its whole history from that.”

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

The math shows that space-time might be able to change so that paradoxes don’t happen.

Imagine a time traveler going back in time to stop the spread of a disease. If the mission was successful, the time traveler wouldn’t have to go back in time to stop the disease.

Tobar’s work suggests that the disease would still get out some other way, through a different route or by a different method. This takes away the paradox. No matter what the time traveler did, he or she couldn’t stop the disease.

Tobar’s work is hard for people who aren’t mathematicians to understand, but it looks at how deterministic (non-random) processes affect any number of regions in the space-time continuum. It also shows how both closed timelike curves (which Einstein predicted) and the rules of free will and classical physics can work together.

“The math works out, and the results are like something out of science fiction,” said Fabio Costa, a physicist at the University of Queensland who oversaw the study.

The new research solves the problem with a different idea: that time travel is possible, but time travelers would be limited in what they could do so they wouldn’t create a paradox. In this model, time travelers can do whatever they want, but they can’t get themselves into a paradox.

Even though the math might work, scientists have not yet found a way to bend space and time to go back in time. The time machines they have come up with are so far-fetched that they only exist as numbers on a page.

We might get there someday; Stephen Hawking thought it was possible. If we do, new research suggests that we could do whatever we wanted to the world in the past, and it would fix itself.

“No matter how hard you try to make a paradox, things will always change to keep things consistent,” says Costa. “The different mathematical processes we found show that time travel with free will is logically possible in our universe without any paradox.”

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