“The past is cruel,” Stephen King wrote in his book about a man going back in time to prevent the Kennedy assassination. “You don’t want to change.”
Turns out, King might have been onto something.
Countless science fiction tales have explored the paradox that would happen if you did something in the past that puts the future in danger. It is perhaps one of the most famous examples of pop culture Back to the futureWhen Marty McFly turns back in time and accidentally forbids his parents from meeting, endangering his existence.
But McFly might not have been in much danger after all. According to a new research paper from researchers at the University of Queensland, even if time travel is possible, the paradox really cannot exist.
The researchers ran over the numbers, and decided that even if you make a change in the past, the timeline will essentially self-correct, ensuring that everything that happened to get you back in time will continue.
University of Queensland scientist Fabio Costa told the university’s news service: “Let’s assume you traveled in time, trying to prevent a COVID-19 patient zero exposure to the virus.”
“But if you stop this person from getting infected – it will eliminate the motivation that pushes you back and stop the epidemic in the first place,” said Costa, who co-authored the research with university student Germain Tobar.
“This is a paradox – the inconsistency that often leads people to believe that time travel cannot happen in our universe.”
The difference is known as the “grandfather paradox” – a time traveler kills his grandfather, in the process of preventing the birth of a time traveler.
The logical paradox gave researchers a headache, in part because, according to Einstein’s theory of general relativity, “closed time-like curves” are possible, theoretically allowing the observer to travel back and interact with himself in the past – potentially putting himself at risk of his own existence.
But these researchers argue that such a contradiction will not necessarily be present, since events will adapt themselves.
Take the example of coronavirus patient zero. Tobar told the university news service, “You may try to prevent patient zero infection, but when you do that you will be infected with the virus and become patient zero, or someone else may do.”
In other words, a time traveler can make changes – but the original result will still find a way to happen. Maybe not in the same way it happened on the first timeline; But it’s close enough that the time traveler will still be around, and still be motivated to go back in time.
“No matter what you did,” Toubar said, “significant events will reevaluate them around you.”
The paper, “Inverse Dynamics of 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 time travel study published this summer in the peer-reviewed journal Physical review letters. That study found that changes made in the past will not radically alter the future.
Blake Crouch, a best-selling science fiction author who has written a lot about time travel, said the new study appears to support what some time travel models have assumed.
“The universe is inevitable and attempts to change the previous X event are destined to be the forces that create the past X event,” Crouch told NPR by email. “So the future can influence the past. Or maybe time is an illusion. But I think it’s great that the mathematics is realized.”