Physicist claims infamous time travel paradox might have an explanation

Whenever time travel is debated, the ‘grandfather paradox’ is usually given as a classic hypothetical situation that would render transporting someone to the past impossible.

The grandfather paradox asks what would happen if an individual travelled back in time and stopped their grandfather from having children. This action would erase the traveler’s parents and therefore their own existence.

If the time traveller is never born, they can’t whizz back through time to stop their grandfather from having children. This conundrum creates a contradiction known as the grandfather paradox.

However, a new study has suggested a solution to this issue. It combines general relativity, quantum mechanics, and thermodynamics.

According to Newtonian physics, events progress in a linear fashion from the past to the future. Einstein’s general theory of relativity challenges this, suggesting that space-time can behave in unexpected ways, such as the behaviour of black holes. One prediction from Einstein’s theory is the potential existence of closed curves that are paths through space-time that loop back on themselves. This would allow a time traveller to revisit the past.

“In general relativity, all forms of energy and momentum act as sources of gravity — not just mass," Lorenzo Gavassino, study author and a physicist at Vanderbilt University, told LiveScience. Gavassino’s research was published in December 2024 in the journal Classical and Quantum Gravity.

“This means that if matter is rotating, it can 'drag' spacetime along with it. While this effect is negligible on planets and stars, what if the entire universe was rotating?"

The theory does not involve a DeLorean DMC-12Universal Studios

Another matter of concern is entropy, a concept that originates from thermodynamics, described by LiveScience as the ‘laws that govern heat and energy’. It is unknown if these laws would function normally on a time loop.

“As far as we know, entropy is the sole reason we remember past events and cannot predict future ones,” Gavassino said. Entropy also governs how our bodies age. When we think about it in the context of biology and ageing, entropy relates to the gradual increase in disorder and the eventual decline in the body's ability to maintain homeostasis, the process by which our body maintains a stable internal environment.

Gavassino’s research provides a solution for this time travel paradox which draws inspiration from the work of physicist Carlo Rovelli. Per LiveScience, Gavassino, “demonstrated that the behaviour of thermodynamics fundamentally changes on a closed timelike curve. On such a loop, quantum fluctuations arise that can erase entropy — a process fundamentally different from what we experience in everyday life.”

One of the huge effects that could arise for a time traveller is as entropy decreases, their memories might vanish and ageing might reverse. “Entropy increase is the reason why we die. What happens when you invert death?" he said.

"Most physicists and philosophers in the past have argued that if time travel exists, nature will always find a way to prevent contradictory situations," he said. "A 'self-consistency principle' was introduced, suggesting that everything should align to create a logically coherent story.

“My work provides the first rigorous derivation of this self-consistency principle directly from established physics. Specifically, I applied the standard framework of quantum mechanics — without additional postulates or controversial assumptions — and demonstrated that the self-consistency of history naturally follows from quantum laws."

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