No one has ever managed to travel through time—at least to our knowledge—but the question of whether or not such a feat would be theoretically possible continues to intrigue scientists.
As films such as The Terminator, Donnie Darko, Back to the Future and many others show that movement in time creates many problems for the basic rules of the universe: if you go back in time and your parents prevent you from meeting, for example, how can you possibly exist to go back in time first of all?
It’s a monumental head-scratcher known as the “grandfather paradox,” but a few years ago, physics student Germain Tobar from the University of Queensland in Australia figured out how to “square the numbers” to make time travel viable without the paradoxes make.
“Classical dynamics says that knowing the state of a system at a given point in time can tell us the entire history of the system.” said Tobar.
“However, Einstein’s theory is that general relativity predicts the existence of time loops, or time travel—where an event can be both past and future—thus theoretically turning the study of dynamics on its head.”
What the calculations show is that spacetime may be able to adjust itself to avoid paradoxes.
To use a recent example, imagine a time traveler going back in time to stop the spread of a disease – if the mission was successful, the time traveler would not have a disease that they could travel back in time to stop it to defeat.
Tobar’s work suggested that the disease would still escape in another way, by a different route or method, thereby removing the paradox. Whatever the time traveler did, the disease would not be stopped.
Tobar’s work is not easy to understand for non-mathematicians, but it examines the influence of deterministic processes (without any randomness) to any number of regions in the space-time continuum and shows how both work closed time-like curves (as predicted by Einstein) can conform to the rules of free will and classical physics.
“The math works – and the results are science fiction”, said the physicist Fabio Costa from the University of Queensland, who supervised the research.
Fabio Costa (left) and Germain Tobar (right). (Ho-Vu)
The research smoothed the issue with another hypothesis that time travel is possible but that time travelers would be restricted in what they do to prevent them from creating a paradox. In this model, time travelers are free to do as they please, but paradoxes are not possible.
While the numbers might work, the actual bending of space and time to get to the past remains elusive – the time machines, the scientists have thought up so far are so high concept that they currently only exist as calculations on one page.
Maybe one day we’ll get there – Stephen Hawking definitely thought it possible — and if we do, this new research suggests that we would be free to do whatever we wanted with the world in the past: it would readjust accordingly.
“Try to create a paradox, events will always adjust to avoid any inconsistency.” said Costa.
“The range of mathematical processes we have discovered shows that free will time travel is logically possible in our universe without paradox.”
The research was published in Classical and Quantum Gravity.
A version of this article was published in September 2020.
