No one has yet managed to time travel – at least as far as we know – but the question of whether such a feat is theoretically possible or not continues to fascinate scientists.
Like movies like The Terminator, Donnie Darko, Back to the Future and many others show, moving in time creates a lot of problems with the fundamental 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 monumental headache known as the “grandfather paradox,” but now physics student Germain Tobar of the University of Queensland in Australia says he has come up with how to “balance the numbers”
“Classical dynamics say that if you know the state of a system at a particular time, it can tell us the whole history of the system,” says Tobar.
“However, Einstein’s theory of general relativity predicts the existence of time cycles or time travel – where an event can be both in the past and in the future of itself – theoretically overturning the study of dynamics.”
What the calculations show is that spacetime can potentially adapt to avoid paradoxes.
To use a topical example, imagine a time traveler traveling into the past to stop the spread of a disease: if the mission was successful, the time traveler would have no disease to go back in time to defeat it.
Tobar’s work suggests that the disease would have escaped in some other way anyway, through a different path or a different method, removing the paradox. Whatever the time traveler did, the disease would not be stopped.
Tobar’s work is not easy for non-mathematicians to delve into, but it examines the influence of deterministic processes (without any randomness) on an arbitrary number of regions in the space-time continuum and demonstrates how both closed time-type curves (such as predicted by Einstein) can fit the rules of free will and classical physics.
“The math goes well – and the results are science fiction stuff,” says physicist Fabio Costa of the University of Queensland, who oversaw the research.
The new research smooths out the problem with another hypothesis, that time travel is possible but that time travelers would be limited in what they have done, to prevent them from creating a paradox. In this model, time travelers have the freedom to do what they want, but paradoxes are not possible.
While the numbers might work, actually bending space and time to enter the past remains elusive: the time machines scientists have devised so far are so high that they currently only exist as calculations on a page.
We may get there someday – Stephen Hawking surely thought it was possible – and if we did, this new research suggests we would be free to do whatever we wanted in the world in the past: it would readjust accordingly.
“However much you try to create a paradox, events will always adapt by themselves, to avoid any inconsistencies,” says Costa. “The range of mathematical processes 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.