Time travel has long been considered impossible, in part due to the grandfather paradox. This enigma poses the question of what would happen if someone traveled back in time and prevented their grandfather from having children. However, a new study, published in Classical and Quantum Gravity, may have solved this problem. The answer comes by combining general relativity, quantum mechanics and thermodynamics, but we go in parts. Our everyday understanding of time is based on Newtonian physics: Events progress linearly from the past to the future. But Einstein’s general theory of relativity challenges this assumption. According to relativity, the fabric of space-time can behave in ways that defy common sense, an example of this is black holes and their ability to slow down time. One of the predictions of general relativity is the possible existence of closed time curves: paths through space-time that loop back on themselveswhich theoretically allows a traveler to return to the past. “In general relativity, all forms of energy and momentum act as sources of gravity, not just mass – explains study author Lorenzo Gavassino -. This means that, If matter is rotating, it can drag spacetime with it. While this effect is negligible for planets and stars, what would happen if the entire universe was rotating?” In a universe where all matter rotates, space-time could warp so much that time would effectively fold back on itself, forming a loop. Thus, a spacecraft traveling along such a loop could, in theory, return to its starting point, not only in space but also in time. One of the biggest challenges to time travel lies in the paradoxes it creates. The grandfather paradox is just one example. These problems arise because We assumed that the laws of thermodynamics, the laws that govern heat and energy, would normally operate in a time loop. “In fact, the law of increase of entropy (a measure of disorder in a system) is the only law of physics that distinguishes between the past and the future – adds Gavassino -. As far as we know, entropy is the only reason we remember past events and cannot predict future ones.” Thus, fluctuations could have dramatic effects on a time traveler. For example, as entropy decreases, a person’s memories could disappear and aging would be reversed. “Increased entropy is the reason we die. What happens when death is reversed?” Gavassino asks. This phenomenon could even make irreversible events, like killing one’s grandfather, circumstantial in a time loop, nullifying the paradox entirely. While Gavassino’s findings offer a compelling theoretical framework for time travel, the question remains: do closed time-like curves really exist in the real universe? Most physicists are skeptical, Stephen Hawking, for example, famously proposed a conjecture. protection of chronology, suggesting that the laws of physics could prevent time loops from forming in the first place. This could involve spacetime becoming singular (or breaking apart) just before a loop can be established. span>Still, Gavassino’s work is valuable in expanding the limits of our understanding of the universe.
“What I find interesting about this topic is the way it forces us to think about the role of entropy in generating our experience of the universe, which is probably my favorite topic in all of physics,” Gavassino concludes. Even if time loops do not exist, understanding and modeling them could provide insights into real phenomena. For example, exploring how real entropy evolves and behaves at the subatomic scale could provide fascinating insights into the behavior of subatomic systems and their thermodynamics.