No grandfather paradox: Time travel would erase all memories leaving no trace of your journey

The dream of time travel has fueled stories, films, and scientific debates for generations. The idea that you could step into a machine and reappear in another era has captivated people for as long as we’ve looked at the stars. While physics doesn’t completely forbid the possibility, new research suggests that the reality of such a journey might look far stranger—and less adventurous—than you’d expect.

A recent study, published in the journal General Relativity and Quantum Cosmology, dives deep into what life would be like inside a spaceship moving along a “closed timelike curve,” or CTC. In plain language, this is a loop through spacetime where you return to the same moment you left. The study draws on standard quantum mechanics and thermodynamics rather than exotic new theories. The result is a picture of time travel that feels more like a cosmic reset button than a thrilling adventure.

The work begins with a simple setup: picture a spaceship following a circular path in a universe that allows these closed loops. The background is modeled after Gödel-type universes, which naturally include paths that circle back in time. The ship is assumed to be lightweight, so its presence doesn’t alter spacetime itself. Instead, the focus is on what happens to the physics inside.

Using Wigner’s theorem, which links spacetime symmetries to the laws of quantum evolution, the study finds that the spaceship’s internal physics must be self-consistent. After one full circuit, everything inside—coins, clocks, notebooks, even people—must return to its original state. The rule isn’t imposed from outside; it follows directly from the way quantum mechanics handles symmetry.

That one requirement reshapes everything we think about time travel. Classic paradoxes, like killing your grandfather before you were born, vanish because the laws themselves prevent contradictions. The evolution of the system makes sure the end always matches the beginning.

One of the most striking outcomes is that energy inside the looped ship doesn’t flow freely. Instead, energy levels must be spaced apart by exact multiples of a fundamental unit tied to the loop’s period. If a system’s cycles don’t “fit” neatly into the loop, they simply aren’t allowed.

That has big consequences for something as basic as keeping time. A clock must tick in exact harmony with the loop. If the loop period doesn’t match an even number of seconds, then your second-based clock would develop microscopic defects—tiny adjustments in its workings—to make sure it still ends up back at zero when the loop closes.

Matter itself follows the same logic. Oscillators, particles, and processes can only exist in states that repeat perfectly on schedule. It’s as if all of reality inside the ship has gears that must mesh exactly with the time loop.

The second law of thermodynamics tells us that entropy, or disorder, increases over time. This is why coffee cools down, eggs break, and memories form but don’t vanish. It gives time a forward direction.

But on a closed timelike curve, entropy can’t just rise without limit. Since the system must return to its starting state, there has to be both a point of lowest entropy and a point of highest entropy. From the low point, entropy increases in both directions, like two arrows pointing away from a center. When the maximum is reached, the arrow flips.

Lorenzo Gavassino, a mathematician at Vanderbilt University and author of the study, puts it plainly: “Beyond this point, all thermodynamic processes (including biological processes such as memory formation and aging) are reversed.” That means everything from your heartbeat to your brain’s storage of memories would start running backward.

The idea of reversed memory may be the most unsettling outcome. In Gavassino’s model, memory is seen as an interaction between an object and a “memory-keeper.” To stay consistent with the loop, any memories written during the trip must be erased by the time the loop ends.

In practice, this means that even if you lived through the entire journey, you wouldn’t remember it. From your point of view, it would feel like nothing happened. You’d step into the ship, complete the loop, and return to the same moment without any trace of the experience.

It’s not just people who lose their records. Computers, notebooks, and even atomic processes that act as clocks would also have their “memories” reset. The entire ship and everything inside would wipe clean as part of the loop’s demand for consistency.

The loops also create bizarre scenarios where cause and effect break down. Near the point of minimum entropy, complex structures can appear without a clear cause. Books could “fluctuate” into existence, or people might show up with memories that seem real but have no basis in past events.

This isn’t magic. It’s the result of Poincaré recurrence, a principle that says finite systems will eventually return to earlier states. On a CTC, the loop period makes those recurrences happen on a strict schedule rather than after unfathomable amounts of time.

Popular imagination often envisions meeting an older or younger version of yourself on a time-travel trip. The study carefully dismantles this idea. If only one traveler is present, then at the loop’s start there is just one version of you. The system’s self-consistency prevents multiples of “you” from occupying the same moment.

What if two people appear—say, a young traveler and someone claiming to be the older self from the future? The study suggests the “older” version’s memories may be illusions formed near the entropy minimum. In that case, the older person isn’t really a future self but more like a clone produced by the system’s fluctuation rules.

All of this paints a very different picture of time travel than the one you see in movies. Instead of swashbuckling through history or rewriting the future, life on a closed timelike curve would feel like pressing a reset button. Your ship’s energy, entropy, clocks, and memories would be locked into a rigid cycle that repeats endlessly.

Even more sobering is the fact that you wouldn’t even know it happened. “Any memory that is collected along the closed timelike curve will be erased before the end of the loop,” Gavassino explains. For the traveler, it’s like writing your life story in sand, only to have the tide wipe it away before anyone can read it.

The research doesn’t claim that CTCs exist in our universe. Stephen Hawking’s “chronology protection” idea, which suggests physics prevents such loops from forming, still hangs over the debate. The study instead asks a focused question: if CTCs were possible, what would happen inside them?

Within that thought experiment, the answer is clear. Quantum mechanics enforces self-consistency, energy quantization, entropy reversal, and memory erasure. Whether spacetime ever allows these loops is an entirely different matter.

But if nature does permit them, the trip would be nothing like the journeys dreamed up in science fiction. Instead of rewriting history, you’d reset it—and forget it.

Note: The article above provided above by The Brighter Side of News.

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