The Science Behind Why We Can’t Change the Past
I haven’t made a lot of mistakes in life, just a few, but nothing that keeps me awake at night. Well, maybe one, but nothing driven by guilt.
Yet, more often than I can imagine, I wish I could go back in time and fix those mistakes. I wish I hadn’t tried to be a hero once, or I hadn’t treated a particular patient who broke me for a while, or I hadn’t said something to my mom and left the house in anger, or had a better interaction with my dad before he passed away, or spent more time with my dog before I lost him. Lately, I’ve been reminiscing about everything that could’ve been done in my life to make it perfect.
But I also heard someone say, “We’re made of our mistakes, not our wins.” This reminds me that our mistakes shape us, teaching us lessons and making us who we are today.
I call myself a man of science because science almost has explanations for most of the things we know today. And why irrespective of how hard I want to go back in time and fix my mistakes, I just can’t.
The Scientific Explanation of why going back in the past is extremely hard. (Or nearly impossible)
Thermodynamics
Entropy = measure of disorder or randomness in a system
The second law of thermodynamics states that the state of entropy of the entire universe, as an isolated system, will always increase over time
This creates an “arrow of time,” pointing from the past to the future. Reversing time would require reversing entropy, which contradicts this fundamental law. Once a system evolves to a higher entropy state, it can’t naturally return to a lower entropy state.
Quantum Mechanics and Uncertainty
Quantum mechanics, which governs the behavior of particles at the smallest scales, introduces uncertainty through the Heisenberg Uncertainty Principle.
This principle states that certain pairs of properties (like position and momentum) cannot both be precisely known at the same time. Reversing time would require precise control over all particle states, which is fundamentally impossible due to this inherent uncertainty.
Quantum Decoherence
In quantum mechanics, decoherence describes the loss of quantum coherence, where a system transitions from a quantum superposition to classical states. This process is time-irreversible due to environmental interactions, making it impossible to return to a previous quantum state once decoherence has occurred.
No-Hair Theorem and Information Loss
In the context of black holes, the no-hair theorem suggests that all information about matter falling into a black hole is lost from the observable universe. If time reversal were possible, it would imply recovering this lost information, conflicting with the current understanding of information theory and black hole physics. (I say current because we still know very little to nothing about a black hole)
Einstein’s theory of relativity (Causality and Relativity)
Einstein’s theory of relativity links space and time into a single entity called spacetime. Within this framework, causality is crucial: causes precede effects. One would have to break this cause-and-effect relationship to go back in time, leading to paradoxes (e.g., the “grandfather paradox” where altering the past could prevent one’s existence).
Closed Timelike Curves (CTCs)
Some solutions to Einstein’s field equations allow for closed timelike curves (paths in spacetime that loop back on themselves). However, these scenarios often require exotic matter with negative energy density, which has not been observed. Even if CTCs existed, they would introduce severe causality issues and paradoxes, making consistent history nearly impossible.
The increase of entropy, the preservation of causality, quantum uncertainty, and the nature of information loss all contribute to the one-way flow of time and the impossibility of altering past events.
In a hypothetical universe, a universe where advanced civilizations have discovered how to manipulate entropy, allowing for reversible time and the creation of stable closed timelike curves. In this realm, the multiverse theory is a reality, enabling changes to the past without causing paradoxes, as new timelines branch off from the original. Deterministic quantum mechanics and information recovery ensure that every particle returns to its precise state, maintaining coherence. With these modifications, time travel and altering the past become feasible, showcasing the potential of scientific advancement and imagination.
