We see time travel in popular culture all the time. Sometimes it’s done well, and sometimes it’s used to explain away plot holes, but it’s almost always left in the realm of fiction. Is time travel possible, though? What time travel theory is most plausible? Let’s take a look at current theories, according to modern physics, and some of the best and worst examples of the science in popular culture.
Einstein’s Special Relativity
Einstein’s theories of relativity have impacted the way we look at everything from space travel to gravity, but what does that have to do with time travel? To understand that, we need to look at his theory of special relativity.
Essentially, special relativity means space and time are part of the same thing — spacetime — and if you’re traveling through it, there’s a speed limit. Everything, including light, moves at or below this speed limit of 300,000 km/s. If you could reach something close to that speed limit — say 99.5 percent of the speed of light— in a spacecraft, time would slow down for you but continue to move at the same pace for the rest of the universe. You could spend five years traveling while 50 could pass here on Earth.
While this is a kind of time travel, and could potentially help us reach the ends of the universe in our limited human lifetime, you’re still only moving forward in a linear stream.
This sort of distortion doesn’t just happen at high speeds — it also occurs near strong gravitational forces. This was beautifully demonstrated in the 2014 film “Interstellar.” When the crew of the Endurance descends to the surface of a water planet in orbit around a supermassive black hole, time passes much more quickly for them than it does for the crew member they left behind on the ship. Three hours on the planet equated to more than 23 years in orbit. While the actual time dilation might not be that dramatic, it’s a fantastic example of Einstein’s special relativity of time travel theory.
Wormholes show up in movies and television shows all the time. If there’s space involved, at some point, characters will likely encounter a wormhole. “Stargate” used them to travel to distant planets and even other galaxies. “Star Trek: Deep Space 9” built a space station near a stable wormhole. They’re all over the fictional universe, but we have yet to encounter one in reality. That hasn’t stopped scientists from theorizing potential time travel through these tears in spacetime.
Einstein and fellow physicist Nathan Rosen theorized the existence of bridges or wormholes that connect two points in spacetime. Dubbed Einstein-Rosen bridges, they could theoretically connect two different locations in the universe — or in two separate timelines.
Right now, wormholes aren’t a viable way to travel back or forward in time. Even if we can find a wormhole large enough to send a ship though, the chances are high that it will only carry us to another point in spacetime, instead of through time itself. Even in popular culture, wormholes don’t generally equate to time travel unless acted upon by an outside force. In “Stargate SG-1,” for example, the wormhole that lets the team travel to other planets took them back and forward in time after coming into contact with a solar flare.
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Cosmic String Theory
The Big Bang is the origin of the universe as we know it. This massive explosion flung matter and energy out in all directions, creating everything we’ve currently studied and everything that is still beyond our reach. According to cosmic string theory, the fabric of the universe isn’t solid. Instead, it’s peppered with one-dimensional cracks known as cosmic strings.
These strings are still theoretical, but if proven right, they could provide a viable option for time travel. Theoretically, they contain so much energy, left over from the birth of the universe, they could warp the spacetime around them. If we could figure out a way to travel through them, we might find they are either infinite, giving us a path to travel through time as well as space, or loops with no end, allowing us to move through the cosmos and back to our point of origin.
These cosmic strings were theorized back in 1991, but as of yet, we haven’t figured out how to find them.
Imagine if you could build a cylinder out of material 10 times the mass of our sun. If you could set up this cylinder to spin on a longitudinal axis, you could theoretically use it to travel through time. According to Tipler’s time travel theory, a ship traveling in a tight spiral around the cylinder could potentially move billions of years into the future.
Of course, to make this work, we’d need the capability to make a cylinder that’s mostly a black hole in a bottle. According to Stephen Hawking, it wouldn’t be possible to travel through time unless there was negative energy, so you would need an infinitely long cylinder to achieve actual time travel.
It’s a neat time travel theory, but it’s not a viable method.
According to numerous theories, our universe isn’t the only one out there. Instead, there are a nearly infinite number of parallel universes that exist close to our own. It’s possible that if we started trying to travel through time, we could end up in a parallel universe instead.
This theory would preclude time travel and open up an entirely different can of worms. Instead of traveling into our past or future, we might end up moving to the past or future of an altogether different universe. It might be similar to our own, or entirely different. Here, we know and understand the laws of physics. Somewhere else in the multiverse, our ships might not work because the laws of physics as we know them are entirely different.
Time Travel in Popular Culture
As promised, let’s take a closer look at some of the best and worst examples of time travel in popular culture.
- Best — “Bill and Ted’s Excellent Adventure” This movie is incredibly silly, but it handles time travel surprisingly well, from the fact that time continues to move forward while they’re going back, to the fact that if they make any significant changes, they carry over into the present. It makes fun of itself, but it’s very entertaining.
- Worst — “Lost in Space” While it isn’t the worst movie overall, “Lost In Space’s” idea of time travel — using nuclear power to rip open a portal in time that can only take one person one way — ignores most of the fundamental laws of physics. It even bypasses the theories we’ve detailed in this piece.
- Best — “12 Monkeys” Traveling back in time to save the world from destruction is one thing, but the “12 Monkeys” television show pays careful attention to the laws of physics and time travel. “You can’t travel back in time to change something because you haven’t,” is one of the lines from the show, explaining how they avoid paradox while tampering with the time stream.
- Worst — “Superman” Come on. Flying super fast to reverse the Earth’s rotation wouldn’t turn back time. Time travel doesn’t work that way. All Superman would manage to do is cause the Earth to break apart.
The Future of Time Travel
We’re a long way off from being able to successfully travel through time. Even if we can manage it, there’s no guarantee we’d be able to come back from such a trip. If you’re outside your timeline, it will continue to move forward without you, and you may not be able to get back. That being said, it’s a fun thing to speculate about and makes for great TV and movies.