Paradox-free time travel is theoretically possible, say researchers


“The past is stubborn,” Stephen King wrote in his book about a man who goes back in time to prevent the Kennedy assassination. “It doesn’t want to be changed. “Turns out King might have been onto something.

Countless sci-fi tales have explored the paradox of what would happen if you did something in the past that endangers the future. Perhaps one of the most famous examples of pop culture is Back to the future, when Marty McFly went back in time and accidentally prevented his parents from meeting, putting his own existence in danger.

But maybe McFly wasn’t in great danger after all. According to a new article by researchers at the University of Queensland, even though time travel was possible, the paradox could not actually exist.

The researchers ran the numbers and determined that even if you make a change in the past, the calendar will essentially correct itself on its own, ensuring that whatever happens to send you back on time will still happen.

“Suppose you have traveled through time, to try to prevent COVID-19 patient zero from being exposed to the virus,” Fabio Costa, a scientist from the University of Queensland, told the press service. university.

“However, if you were to prevent that person from getting infected, it would take away the motivation for you to go back and stop the pandemic in the first place,” said Costa, who co-authored the article with student honors. undergraduate Germain Tobar.

“It’s a paradox – an inconsistency that often leads people to believe that time travel cannot happen in our universe. ”

One variation is known as the ‘grandfather paradox’ – in which a time traveler kills his own grandfather, thereby preventing the birth of the time traveler.

The logical paradox has given researchers a headache, in part because according to Einstein’s general theory of relativity, “closed time-like curves” are possible, theoretically allowing an observer to time travel and d ‘interacting with their past self – and potentially endangering their own existence.

But these researchers say such a paradox wouldn’t necessarily exist, as events would adjust on their own.

Take the example of the zero coronavirus patient. “You could try to prevent patient zero from becoming infected, but in doing so you would catch the virus and become patient zero, or someone else would,” Tobar told the university’s press service.

In other words, a time traveler could make changes – but the initial result would always find a way to happen. Maybe not the same way it happened in the first timeline; but close enough that the time traveler still exists, and is always motivated to go back in time.

“No matter what you did, the big events would just recalibrate around you,” Tobar said.

The article, “Reversible dynamics with closed time curves and freedom of choice,” was published last week in the peer-reviewed journal Classical and quantum gravity. The results appear consistent with another study on time travel published this summer in the peer-reviewed journal Physical examination letters. This study found that changes made in the past will not drastically change the future.

Best-selling sci-fi author Blake Crouch, who has written extensively on time travel, said the new study appears to support what some time travel tropes have always argued.

“The universe is deterministic, and attempts to modify past event X are meant to be the forces that give birth to past event X,” Crouch told NPR via email. “So the future can affect the past. Or maybe time is just an illusion. But I guess it’s cool that the math checks. “

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