Germain Tobar and Fabio Costa say that if we did travel to the past, any actions taken would not change anything.

Movies, Television shows, comics and just about every other form of entertainment have played with the idea of time travel. Each has its own rules and usually there are grave consequences. The biggest issue is if you change the past what will happen in the future. It's a monumental head-scratcher known as the 'grandfather paradox', but now a physics student Germain Tobar, from the University of Queensland in Australia, says he has worked out how to "square the numbers" to make time travel viable without the paradoxes.

"Classical dynamics says if you know the state of a system at a particular time, this can tell us the entire history of the system," says Tobar.

"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 future of itself – theoretically turning the study of dynamics on its head."

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

To use a topical example, imagine a time traveller journeying into the past to stop a disease from spreading – if the mission was successful, the time traveller would have no disease to go back in time to defeat.

Tobar's work suggests that the disease would still escape some other way, through a different route or by a different method, removing the paradox. Whatever the time traveller did, the disease wouldn't be stopped.

"The maths checks out – and the results are the stuff of science fiction," says physicist Fabio Costa from the University of Queensland, who supervised the research.

If time travel is possible – Stephen Hawking certainly thought it was possible – and if we do then this new research suggests we would be free to do whatever we wanted to the world in the past: it would readjust itself accordingly.

"Try as you might to create a paradox, the events will always adjust themselves, to avoid any inconsistency," says Costa. "The range of mathematical processes we discovered show that time travel with free will is logically possible in our universe without any paradox."

The research has been published in Classical and Quantum Gravity.

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