A bit of fun - Why is backwards time travel impossible?

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Updated 3 weeks ago

Ah, the grand mystery of time travel! There’s a lot of allure around the idea of zipping backward in time, meeting our younger selves, buying Bitcoin in 2011, and correcting those questionable hairstyle choices. But let’s talk about why, at least as far as we know today, backward time travel is likely impossible (or at the very least, a really, really bad idea).

The Physics Gets Complicated – Fast

To get to the heart of the matter, let’s start with the core idea of time travel in physics. Einstein’s theory of relativity threw open the doors on a new way of thinking about time, showing that it’s not this unbending force ticking away in the background but something flexible, tied up with space itself in this “fabric” we call spacetime. In this view, if you can manipulate spacetime in just the right way, theoretically, you could mess with time.

But there’s a catch: Einstein’s relativity allows for some mind-bending stuff like wormholes, which might be able to connect different points in space and time.

But even if wormholes exist (which is far from certain), making them big enough for a human and keeping them stable would be an engineering nightmare, and one that we don’t yet have a solution for.

The Grandfather Paradox: Just One of Many Issues

Suppose you manage to crack this engineering nut and step back in time. What’s to stop you from doing something drastic, like, I don’t know, stopping your grandfather from meeting your grandmother?

This is what’s called the Grandfather Paradox. If you stop them from meeting, you’d never be born, and if you’re never born, who went back to prevent the meeting?

Time travel theorists have spun themselves in knots over this one. Some suggest that time would “self-correct,” somehow stopping you from altering events in a way that would lead to such a paradox.

Others propose “many worlds” interpretations where each choice branches off into a new universe, meaning your actions just create a new timeline.

But so far, it’s all theoretical, and these theories don’t offer an easy way to jump between timelines or resolve paradoxes in our existing one.

Causality Says “No Way”

Physics doesn’t just have laws; it has some fundamental rules it really doesn’t want broken. One of these is causality: the principle that a cause must precede an effect. If you could go back in time, you could mess with that order, creating effects before their causes. It’s like dropping a plate and seeing it shatter before it leaves your hands.

Causality is fundamental to our understanding of physics, and breaking it would unravel the structure of everything we know.

Entropy is the Killjoy of Time Travel

Entropy is another big hurdle. In simple terms, entropy is the idea that the universe tends to go from order to disorder. It’s why a dropped vase shatters, but you never see broken pieces spontaneously jumping back into a vase.

This “arrow of time” points one way—forward. Moving backward in time would mean reversing entropy, which isn’t just hard; it’s thought to be impossible on a large scale. Think of entropy like trying to unscramble an egg or unmix cream from your coffee. Good luck with that!

The Energy Problem – It’s Astronomical

For argument’s sake, let’s say we somehow bypass all those physics obstacles and hop into our time machine. There’s still the issue of energy. Bending spacetime enough to allow backward time travel would require staggering amounts of energy—more than our current technology could even dream of producing.

If we somehow managed to build a time machine, we’d probably need the power output of an entire galaxy or a black hole. So unless we discover some new physics or an energy source beyond what we understand today, we’re not likely to get there.

The Quantum Mechanics Angle

Quantum mechanics, the physics of the very small, sometimes seems to bend the rules. Particles can “tunnel” through barriers, exist in multiple states at once, and even communicate over vast distances. Some physicists speculate that at the quantum level, tiny bits of “backward” time travel could theoretically occur.

But even if true, these events are isolated to subatomic particles and don’t scale up to larger objects—like humans.

So, Is There Any Hope?

Well, physicists like Stephen Hawking were pretty firm on their “no” to backward time travel. In fact, he suggested a “chronology protection conjecture,” which basically argues that the laws of physics protect themselves from paradoxes, making backward time travel a no-go.

And while that’s frustrating for anyone hoping for a chance to relive the 80s, it’s a neat way for physics to ensure a stable universe.

There are other ideas, though. Theoretical physicist Kip Thorne proposed something called “closed timelike curves,” which could potentially allow time travel without paradoxes in certain circumstances.

But even these ideas don’t give us an easy way to move through time—and they certainly don’t solve the problems of paradoxes and causality on a scale that would let us zip back in time to 1955.

Where Does This Leave Us?

The short answer is, backward time travel probably isn’t possible. The universe seems to have a pretty tight handle on keeping things moving forward. But who knows?

Physics keeps surprising us, and maybe someday, we’ll find a way to cheat entropy, dodge causality, or tap into the colossal energy needed to bend time itself.

So, what would you do if you could go back in time for just one day?

And don’t say “buy more crypto”—we’ve all thought of that one!

Let me know in the comments—I love hearing all the different ways people would use a backward jaunt through time.