Is Time Travel Possible?

Source: Medium

Movies and TV make leaping to the past look straightforward. We explore whether a person can really travel through time and examine which movies and shows go back to the future best!

While the summer blockbusters are just getting started, 2019 is already shaping into the year of time travel in popular media. For example, television shows such as Star Trek: Discovery and The Orville both used time travel to drive their respective stories forward, with the former going where no Trek ship has gone before.

You don't need a machine to visit the future, but it might make things more comfortable. Source: The Time Machine, 2002
You don't need a machine to travel to the future, but it's nice to have one. Source: The Time Machine, 2002

At the same time, superheroes like The Flash are shown speeding back-and-forth through time, while the Avengers use the Quantum Realm to revisit some of their greatest hits and fight Thanos in Avengers: Endgame. Even fighting game Mortal Kombat 11 plays fast and loose with time by having past and present versions of characters battle against each other.

All of this fun leads us to one question: is time travel possible, or is it the stuff of science fiction? The easy answer is yes, time travel is possible. In fact, you’re doing it right now.

Traveling to the future is simple. If you want to stay young while the rest of the world gets older you either need to travel very fast – preferably around the speed of light – or hang out near a black hole and let its time dilation effects take care of the rest. Going backward in time is where things get weird.

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The Time Travel Paradox

Einstein believed time was a fourth dimension that could potentially be traveled in a similar fashion to points in 3D space. This concept is best explained in the 1895 novella The Time Machine by H.G. Wells, a recognizable cornerstone of time-bending sci-fi tales for decades. 

However, the whole idea of traveling to the past is a paradox that raises numerous questions. If this form of time travel were possible, why isn’t the past full of people trying to witness or change history?

Marty McFly begins to fade after negating his own existing. Source: Back to the Future, 1985
Marty McFly begins to fade after negating his own existing. Source: Back to the Future, 1985

Can one commit the grandparent paradox by killing their own ancestor or preventing their parents from meeting to negate their own existence? If so, they wouldn’t have been born to cause the paradox in the first place. Mind-twisting problems like these abound when you start messing with the one-way relationship between causality and effect.

Because of this, one must conclude that in a rational universe like the one we presumably live in, time travel to the past is impossible. Except it isn’t. As The Physics of Star Trek explains, Einstein’s equations of general relativity do not preclude the possibility of time travel, they outright encourage it. But don’t start planning your vacation aboard the TARDIS yet. Saying something is possible is different from saying that it’s achievable.

What is Time Travel?

In physics, time is a tricky concept. It can be regarded as a fourth dimension that’s inextricably woven into three-dimensional space to create a medium called space-time, though there literally can’t be one without the other.

You can’t be anywhere without time, and you can’t have existed anytime without space. The problem is, while objects may travel in any direction in space, time as we know it only flows in one direction. Additionally, traveling to the past isn’t just a matter of time, but of space.

The TARDIS from Doctor Who flying through the Time Vortex. Source: Doctor Who
The TARDIS from Doctor Who traveling through the Time Vortex. Source: Doctor Who

We’re on a spinning planet that’s orbiting a sun inside a spinning galaxy within an expanding universe. You may be in the same living room you were six months ago, but that room is now 200 million miles away from where it was in space. Navigating this requires complex mathematics along with technology and knowledge that we don’t have yet – and may never will, given the general lack of time tourists.

Sci-fi has found some ways around this conundrum. In movies like Avengers: Endgame, traveling back in time creates alternate timelines that splinter from the main one. In that scenario, time travel would consist of visiting other realities instead of what’s shown in Back to the Future.

Therefore, you can’t commit paradoxes like negating your own existence because the timeline you created is new. At the same time, you wouldn’t be able to change anything from your original timeline. So, go ahead and murder Hitler as a baby and stomp on as many butterflies in the Jurassic era as you want.

Nothing in this reality will change, but the one you live in moving forward will. And that’s ok, because you can create another branch if you screw things up too much in the hope that the whole thing won’t collapse in some horrifically catastrophic fashion.

Powering a Time Machine

USS Enterprise slingshots around the sun. Source: Star Trek,
USS Enterprise slingshots around the sun. Source: Star Trek, "Tomorrow is Yesterday"

Let’s get one thing out of the way by stating that flying quickly toward the sun and using its gravity to slingshot a ship into the past won’t work. As such, the approach taken by multiple Star Trek episodes and the movie Star Trek IV: The Voyage Home is out. Don’t try it.

According to astrophysicist Neil deGrasse Tyson, our sun simply doesn’t have enough gravity to provide the energy needed for time travel, even if it’s used in combination with a warp drive. With that being the case, we can also rule out the flux capacitor, powered by a single canister of plutonium or a Mr. Fusion, affixed to a DeLorean moving at 88 mph.

It should also go without saying that changing the Earth’s rotation by flying in orbit at raging Superman speeds wouldn’t work either. Not even the TARDIS in Doctor Who, which harnesses the immense power of a huge star called the Eye of Harmony the moment it started to collapse into a black hole, is enough to jump through time each week.

The Red Angel is revealed to be a time traveler. Source: Star Trek: Discovery
The Red Angel is revealed. Source: Star Trek: Discovery

We’re guessing a supernova might not be enough to power something as small as the time suit from Star Trek: Discovery either. Another approach uses a device like a warp drive to fold space, pulling two points of space-time together with the destination being in the past –– but that also requires immense amounts of energy, as would a wormhole or Stargate.

Tyson said that creating an artificial wormhole to slip through time and space would probably require all the energy generated by an entire galaxy for starters. That’s pretty reasonable, given how we are talking about the ultimate mastery over the universe. However, there are alternatives that might be a little less energy intensive and would allow you to travel back in time without necessarily creating a branching reality.

Going Back to the Future

Gravity slows time down, so it’s possible there are layers of the past trapped inside black holes, similar to the rings inside a tree. As part of a theoretical trajectory, one could journey through a black hole that may shoot you out at a point in time before you arrived. You just need a ship that can go through a black hole without being destroyed.

But there’s no guarantee that using a black hole for time travel will account for the time dilation effects. In his book Startalk, Tyson explains, “If you travel to the black hole Cygnus X-1 in a year, stay a year, and then come back in a year, you will have aged only three years, but traveled 1,201 years into the future.”

Strangely, no one thinks to use the Time Stone to time travel. Source: Avengers: Infinity War, 2018
Strangely, no one thinks to use the Time Stone to time travel. Source: Avengers: Infinity War, 2018

A different theory states that we can visit the past by going to the future. In the Futurama episode “The Late Philip J. Fry,” the gang uses a forward-only time machine to watch the universe come to its eventual end. After the last proton decays, a big bang occurs, starting a new universe that plays out identically to the previous one. Then all they had to do was travel forward to the point where they left, accidentally kill their alternate selves, and “Pow! We took care of the time travel paradox.

Although this is played up for humor, some findings in quantum mechanics suggest that the universe could be collapsed and restarted after it ends. We could be part of an endless loop of entropic destruction and restarts, which is both depressing and awe-inspiring at the same time. Still, traveling to the end of the universe and witnessing its beginnings just to revisit some point in Earth’s relatively short history seems like taking the extremely long way.

It would be like flying around several galaxies just to reach a restaurant down the block, not knowing whether there really is a restaurant at the end of the universe. It’s equally likely that continued travel will be impossible once the universe stretches to the point where time comes to a complete standstill. There might be no time left to travel.

This Big Ball of Wibbly Wobbly, Timey Wimey Stuff

There is hope for doing things Back to the Future style. Tyson mentions tachyons, which are theoretical particles that move faster than the speed of light. If they exist, then they may hold the key to time travel.

For example, if you sent a message to yourself using tachyons, you could receive it before you wrote it. You could also theoretically revisit your childhood by entering a higher dimension, where all of time may be laid out and traversed the way space is. So, it looks like A Wrinkle in Time, Interstellar, and Avengers: Endgame may not be too far off the mark when it comes to time travel.

Cooper enters a tesseract, where he can see his daughter in the past. Source: Interstellar, 2014
Cooper enters a tesseract, where he can see his daughter in the throughout the past. Source: Interstellar, 2014

However, there’s no way to know if we can change anything when traveling through time via the fifth dimension. We’d have to build a tesseract to find out, and it would probably be full of tachyons, driven by the power of a dying star, and require the user to enter the event horizon of a supermassive black hole to work.

Editor

Steven is a pop culture junkie who regularly binges on sci-fi TV shows, movies, books, and video games before completely overthinking them.