Physicists have constructed a mathematical model designed to prevent backward time travel, though the framework introduces an instability that could allow tiny disturbances in spacetime to grow exponentially, ScienceAlert reported.
Stephen Hawking proposed his chronology protection conjecture in 1992 to explore whether backward time travel was possible, stating that the laws of physics do not allow the appearance of closed timelike curves.
Einstein’s general theory of relativity allows for closed timelike curves, which are paths through spacetime that can lead a traveler back to their own past. Physicist Brandon Carter showed in 1968 that such loops exist inside spinning black holes, according to Euronews Next.
However, researchers Moustafa Ismail and David Mattingly of the University of New Hampshire investigated whether gravity itself might hold the answer to preventing these time loops. They utilized an alternative framework for gravity called metric-affine gravity, which loosens the relationship between the metric and the mathematical connection of spacetime.
Ismail and Mattingly constructed a model named Metric-Affine Gravity Imposing Chronology, or MAGIC, in which spacetime could have a built-in direction of time. Under these conditions, time always moves forward along any path a traveler could take, making it impossible to loop back into the past. Euronews Next noted that physicist Zhang identified topological loops as the loophole to watch for such travel.
“The loophole that could matter is topology, and that is exactly the one that looks least likely to arise without deliberate engineering,” Zhang told Euronews Next.
Despite successfully preventing local time loops in their model, MAGIC introduces a third way for gravity to fluctuate known as the scalar mode.
The research has been published in Physical Review D, building upon foundations related to the chronology protection conjecture and Zhang’s research.
