Imagine that you have a time machine to go to the end of 2019 and prevent the COVID-19 pandemic.
Your task is to meet the “zero patient” before they get infected and start spreading the coronavirus.
Sounds great, doesn’t it? The problem is a small detail that may prevent you from completing this mission.
Indeed, some interpretations of theoretical physics suggest that travel to the past is possible.
Einstein, for example, knew that his equations allowed for time travel in principle.
However, this hypothetical possibility runs into a so-called time paradox: a contradiction that makes it logically impossible to return to the past.
Among the several paradoxes associated with time travel, the most common example is one that even has a name: the Grandfather Paradox.
If a grandson kills his grandfather in the past before he starts a family, then neither the time traveler’s father nor, consequently, he himself, will be born. But then there would be no one to go back in time, and grandfather would still be alive. Accordingly, after some time, a malicious traveler will be born who will go back in time to kill his grandfather — this creates a paradox.
Let’s go back to the story of the pandemic.
If you do not allow the zero patient to be infected, the paradox immediately arises: there will be no pandemic in the present, so you will not have a motive to travel to the past, and you will not prevent a pandemic.
Such situations remain a favorite topic of science fiction writers.
In Ray Bradbury’s famous short story “A Sound of Thunder,” the hero, going to the past, accidentally steps on a butterfly. In the present, where he returns, it changes the result of the presidential election.
The closed cycle of logical contradictions seems to make the possibility of traveling to the past illusory.
However, a new study proves that the paradox can be circumvented.
Previously, we tried to achieve this by logical constructions. The paradox was resolved, for example, by the theory that each time the traveler changes the past, he creates an alternative branch of history in which he returns to the world changed by his actions, and not to the present from which he left (as in the Back To The Future Trilogy, for example, or Terminator). Another hypothesis suggests that once the traveler could go to the fatal meeting with his grandfather, he will not be able to kill him, despite all his efforts.
Now, two Australian scientists have proposed a mathematical solution to the problem.
University of Queensland physics student Germain Tobar and his research supervisor Professor Fabio Costa have theoretically calculated how a body moving through time and space will behave when entering the curve of travel to the past.
The mathematical model they created shows that an object traveling back and forth in the past can move in different ways, but it will always come to a certain point.
Thus, according to mathematical calculations, actions performed in the past do not affect the present.
“Events are constantly adapting to each other in such a way as to arrive at one unchanging result,” Germain Tobar told the BBC.
This means that if you had free will in the case of a pandemic, you could have done anything in the past, but you would not have changed the outcome in any way.
If you had managed to save the “zero patient” from the fatal step, someone else would have been infected, or even you yourself.
According to the Tobar model, events may vary individually. Still, in the aggregate, they will occur in such a way as to avoid a paradox and lead to the same result, in this case, a pandemic.
Of course, Tobar’s work is a mathematical abstraction that has no practical application yet.
“This is an interesting study,” Chris Fewster, a Professor of mathematics at York University who also studies the theoretical aspects of time travel, told the BBC.
However, he notes that it is necessary to see whether the abstract assumptions that the authors have based their model correspond to the physical theories that are currently known.
Tobar says that’s what he’s doing right now-testing the mathematical model from the point of view of physics.
He admits that his work is far from making travel to the past reality but sees it as a step towards a better understanding of the laws governing the Universe.