Time travel stories are one of the most polarizing things for film fans. They either love them, or they turn their noses up at them. Still, that doesn’t stop writers from coming up with them, and it’s not even for the science fiction fields. Time travel stories have an unexpectedly strong placement in romance fiction as well, such as The Time Traveler’s Wife or the upcoming Starz series Outlander, based on Diana Gabaldon’s best-selling historical romance series.
While many of these romance-driven stories — like Somewhere in Time and more recently Richard Curtis’s About Time — are not concerned with the greater implications of meddling with the space-time continuum, the science fiction movies are. Traveling through time has been a central figure in stories for years, often presenting the viewer with a crash course in theoretical physics and opening themselves up to plot holes almost impossible to close.
As a personal fan of the time-traveling story, I love to see what the writers will come up with next. But these movies always get me wondering… is it possible to travel through time the way people do in the movies?
The Answer: Theoretically, but probably not in a phone booth or a DeLorean.
Before diving into the question of time travel, let’s make sure we all have an understanding of the nature of time. We think of our world as a three-dimensional one, in which we can move forwards or backward, left or right, and up or down. Time is actually another dimension through which we move.
Back in 1988, celebrated physicist Stephen Hawking wrote the best-seller “A Brief History of Time,” which broke down a lot of high-concept science for the average person to understand. Here, he explains modern science’s understanding of the nature of time:
“Before 1915, space and time were thought of as a fixed arena in which events took place, but which was not affected by what happened in it… Space and time are now dynamic quantities: when a body moves, or a force acts, it affects the curvature of space and time – and in turn the structure of space-time affects the way in which bodies move and forces act.” (p. 33)
In other words, space and time are intrinsically linked and inseparable. Like the character of Hiro Nakamura (Masi Oka) in NBC’s Heroes, the ability to travel through time is also the ability to travel through space. The difference between time and the three dimensions of space we normally recognize is that – unlike the character of Hiro – we have no control of our direction or speed in time.
In George Pal’s classic film The Time Machine, we see the character of George (Rod Taylor) speed ahead through the time stream in a stationary machine. In reality, he wouldn’t disappear from the present. Instead, the mechanisms of his invention would simply let him move faster through time. Of course, this is a forgivable inaccuracy considering the original book was written by H.G. Wells in 1895, decades before the nature of space-time as a whole were understood.
Still, the moving ahead into the future faster than we normally experience isn’t an impossibility, according to Einstein’s theory of relativity, Hawking explains:
“In the theory of relativity there is no unique absolute time, but instead each individual has his own personal measure of time that depends on where he is and how he is moving.” (p. 33)
This means that if someone could travel close to the speed of light, his or her personal timeline would become dilated, or slow down, making the one he or she left back on Earth to appear to speed ahead. As Hawking explains in his Discovery Channel series Into the Universe with Stephen Hawking, this could allow people to speed up their own personal timeline and return to Earth many thousands of years in the future.
That’s all fine and dandy, but what if you want to make a jump rather than just speed things up?
Find a Shortcut
In Star Trek IV: The Voyage Home, the crew of the Enterprise travels back to 1986 San Francisco to find a pair of humpback whales. They reach the speed to break the time barrier by sling-shotting around the sun. However, dilithium crystals or not, the problem with accelerating a spaceship close to the speed of light is that it would take an infinite amount of energy, according to Albert Einstein’s famous equation in his theory of relativity: E=mc^2, which equates energy (E), mass (m), and the speed of light (c), which is constant and cannot be overcome. In A Brief History of Time, Hawking explains:
“Because of the equivalence of energy and mass, the energy which and object has due to its motion will add to its mass. In other words, it will make it harder to increase its speed. The effect is only really significant for objects moving at speeds close to the speed of light… As an object approaches the speed of light, its mass rises ever more quickly so it takes more and more energy to speed it up further. It can in fact never reach the speed of light, because by then its mass would have become infinite, and by the equivalence of mass and energy, it would have taken an infinite amount of energy to get there.” (pp. 20–21)
There is a theoretical way to get around the speed of light, or rather, a way through. A wormhole is a theoretical phenomenon that links two points in space-time. According to Hawking, subatomic wormholes exist throughout the universe in what is known as the quantum foam, the space between subatomic particles. In Into the Universe with Stephen Hawking, he suggests that scientists could one day expand one of these wormholes to human size.
Wormholes tend to be popular means of time travel throughout film and television. Star Trek: Deep Space Nine and the Stargate series all use wormholes to travel through extended points in space. Other films like The Terminator series, Timecop, Looper, and even more whimsical pieces like Bill and Ted’s Excellent Adventure and Mr. Peabody & Sherman all use portal which could be described as wormholes.
Even the flux capacitor in the DeLorean from Back to the Future appears to use some form of wormhole technology because it essentially teleports the car from one point in space-time to another.
So if it’s theoretically possible, where is the problem with these movies?
One of the biggest problems with time travel stories, and why so many people seem to get annoyed with them, is they often violate the rules of the game. They either create internal paradoxes, or they simply break their own rules to make things work out right in the end.
The sticky nature of time travel is that the time traveler could create a paradox. No, not the Timecop paradox in which Max Walker (Jean-Claude Van Damme) dispenses the evil Senator Aaron McComb (Ron Silver) by throwing his older version into him, saying, “The same matter cannot occupy the same space.”
The good news is, if you met another version of yourself, you wouldn’t devolve into a screaming pile of goo and teeth.
Rather, the classic time travel paradox example is the grandfather paradox, in which the time traveler goes back in time and kills his own grandfather. The paradox emerges because if the grandfather died, the time traveler would never exist, and thus he’d never be able to travel back in time and kill his grandfather.
Many films fall apart when the paradoxes are considered. For example, in the original Planet of the Apes series, where did the super-intelligent ape bloodline come from? The first ape of its kind born on earth was Caesar, who was the son of Cornelius from the Earth’s future. However, Cornelius is a direct descendant of Caesar.
In another example, at the end of Looper, Young Joe (Joseph Gordon-Levitt) kills himself to ensure his older self (Bruce Willis) never comes back. However, it is the exact actions of Old Joe (who ceases to exist after Young Joe kills himself) that cause Young Joe to kill himself. This is simply a reworking of the classic grandfather paradox.
The Terminator series is even more twisted. In the first film, Kyle Reese (Michael Biehn) goes back in time and ends up fathering John Conner, who is the person who sends him back in time to begin with. That’s a relatively tightly-written story that suggests the time stream is fixed. Then you get to Terminator 2: Judgement Day, which allows the characters to change the future. Things switch up again in Terminator 3: Rise of the Machines and later Terminator: Salvation, which let the computers take over the world after all. Plot holes and paradoxes abound.
Even more problematic is the element of Chaos Theory known as the butterfly effect. (No, not that awful movie with Ashton Kutcher and Amy Smart, which has very little to do with the actual butterfly effect). In short, the butterfly effect suggests that a time change in something considered insignificant can multiply to massive changes in other parts of the world. Bill Nighy’s character from About Time sums this up rather nicely to explain why his son’s child is different after he changes the past: “The exact sperm at the exact moment got you this particular baby, so if you do anything the tiniest bit different, you’ll have a different child.”
Some television shows that use time travel a lot manage to plug this hole. Star Trek has occasionally employed the parallel universe theory (most notably in the series finale of Star Trek: The Next Generation), suggesting that changes in one timeline can cause an offshoot of an alternate universe in another. This convention can avoid most of the holes of time travel, including the paradoxes, but it’s far more confusing to the audience than a single time stream.
Doctor Who explains that there are fixed moments in time and the flow of time will correct itself if things change. This works for the most part, but considering the Doctor has broken practically every rule of time travel in the past 50 years (including the fixed-point-in-time theory in “The Wedding of River Song”), he’s not winning many points with this explanation.
In the end, time travel is far more complex and offers far too many problems than most movies care to spend time explaining. If, as Stephen Hawking believes, we might one day learn to achieve a certain form of time travel, it will likely be nothing like anything we’ve seen.