No one has yet managed to travel through time – as far as we know – but the question of whether such an achievement would be theoretically possible continues to fascinate scientists.
Like movies like The Terminator, Donnie Darko, Back to the future and many others show that moving in time poses many problems for the fundamental rules of the universe: if you go back in time and, for example, prevent your parents from meeting, how can you exist to go back in time ? in the first place?
It’s a monumental head-scratcher known as the ‘grandfather paradox’, but last September, a physics student Germain Tobar, from the University of Queensland in Australia, said he has figured out how to ‘divide’ the numbers to make time travel feasible . without the paradoxes.
“Classical dynamics says that if you know the state of a system at a particular point in time, it can tell us the entire history of the system,” Tobar said in September 2020.
“Einstein’s general theory of relativity, however, predicts the existence of time loops or time travel – where an event can be in the past as well as in the future – turning the study of dynamics on its head in theory.”
What the calculations show is that space-time can potentially adapt itself to avoid paradoxes.
To use a current example, imagine a time traveler traveling to the past to prevent a disease from spreading – if the mission were successful, the time traveler would have no disease to go back in time to defeat .
Tobar’s work suggests that the disease would still escape in a different way, by a different route or by a different method, thus dispelling the paradox. Whatever the time traveler did, the illness was not going to be stopped.
Tobar’s work is not easy for non-mathematicians to dig into, but it looks at the influence of deterministic processes (without any arbitrariness) on any number of regions in the space-time continuum, and shows how both timelike curves (as predicted) by Einstein) fit within the rules of free will and classical physics.
“The math is right – and the results are science fiction,” said University of Queensland physicist Fabio Costa, who oversaw the study.
Fabio Costa (left) and Germain Tobar (right). (Ho Vu)
The new research mitigates the problem with another hypothesis, that time travel is possible, but that time travelers would be limited in what they did, to avoid creating a paradox. In this model, time travelers have the freedom to do whatever they want, but paradoxes are not possible.
While the numbers may add up, it remains difficult to bend space and time to get to the past – the time machines that scientists have devised so far are so sophisticated that they currently exist only as calculations on a page.
We could one day get there – Stephen Hawking certainly thought it was possible – and if we do, this new research suggests that we would be free to do whatever we wanted to do with the world in the past: it would adjust itself accordingly.
“Try however you could to create a paradox, the events will always adjust themselves to avoid inconsistencies,” says Costa. “The set of mathematical processes we discovered show that free will time travel is logically possible in our universe without any paradox.”
The research is published in Classic and quantum gravity.
A version of this article was first published in September 2020.