‘Grandfather Paradox’: What would happen if you caused your grandfather’s death by traveling in time?

The big question that arises when we think about time travel and that always fuels philosophical and scientific debates on this subject is the so-called “grandfather paradox”, which is considered one of the greatest theoretical obstacles to imagined temporal displacements. Although theoretical, this question continues to attract the attention of scientists.

Let’s say you managed to travel back in time and find your grandfather before he had children. If you somehow knowingly or unknowingly prevent him from meeting his grandmother or accidentally kill him, he will never have a child, meaning his father and mother will not be born. So how can you exist to travel to the past?

Now, in a study recently published in the journal Classical and Quantum Gravity, mathematician Lorenzo Gavassino of Vanderbilt University in Nashville, US, has used general relativity, quantum mechanics and thermodynamics to show how time travel might be possible without creating such contradictions.

Time travel and the physics of cycles

According to Gavassino, such a paradox arises because our common understanding of time is based on Newtonian physics, where events follow a linear progression from past to future. But starting in 1915, Einstein’s theory of general relativity introduced a more complex perspective, suggesting that space-time could move in surprising ways.

This has been demonstrated in events such as black holes, where deformation is so intense that it creates an “extreme curvature” in space-time, potentially closed temporal curves. These paths in space-time could take a hypothetical spacecraft back to its starting pointsays the research.

“In general relativity, all forms of energy and momentum act as sources of not only mass but also gravity,” the study’s author told LiveScience. In other words, if matter rotates, it has the ability to drag space-time with it. Although this is imperceptible on planets and stars, Gavassino thinks: “What if the entire universe is rotating?”

The effect of entropy on time travel

But unless the laws of physics somehow prohibit time travel, it leads to some strange consequences, the worst of which, according to the author, is this: No human being who makes this journey can remember this. According to the laws of physics, this space traveler’s memory would be erased as soon as he returned to the present.

And this happens due to the well-known second law of thermodynamics: entropy, which indicates increasing disorder in any system over time. Unlike other laws of physics, this law makes a clear distinction between time going forward and backward. In other words, eggs “do not break”, milk “do not break”, etc.

Entropy affects nearly every aspect of our lives, from aging to the most basic activities like walking. According to Gavassino, this ubiquity of entropy underlies our ability to form memories and our inability to predict the future.

quantum solution

New research offers an innovative solution inspired by the work of Italian physicist Carlo Rovelli. He showed that the behavior of thermodynamics can change fundamentally in a closed time curve. In such a cycle, Quantum fluctuations emerge that can erase entropy.

These anomalies could have profound effects on the possibility of becoming a time traveler. As entropy decreases, aging as well as memory loss can reverse itself. “The reason we die is increased entropy. What happens when you reverse death?” asks Gavassino. In other words, can death be reversed within a time loop?

The “self-consistency principle”, proposed by Russian physicist Igor Novikov in the 1980s to solve the famous grandfather paradox, suggested that nature would always avoid temporal paradoxes. Gavassino not only provides the first definitive deduction of this principle, but he does so by applying the standard framework of quantum mechanics without any additional propositions or any discussion.

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