By David K. Johnson, Ph.D., King’s College
Many sci-fi ideas have experimented with the idea of time travel, and all of them have variations of how the feat is actually possible. The original Planet of the Apes movie and the Star Trek series are famous examples. But the long-running Doctor Who series uses the idea of time travel consistently and in virtually every episode. So, is Doctor Who’s time-traveling device a real possibility?
The Space-Time Whirlpool
There are many methods of time travel explored in the Star Trek series. One fan favorite is the slingshot maneuver in Star Trek IV: The Voyage Home, where Mr. Spock uses the Sun’s gravity to accelerate the ship and then whip around the Sun, appearing on the other side in the past.
This idea is loosely based on Einstein’s relativity. Relativity entails that space-time, the fabric of the universe, is a substance that is affected by the mass and rotation of large objects. If an object is massive enough and rotates enough, it collects space-time around it, like a whirlpool. If a spaceship was going near the speed of light, was pulled in by the rotation, orbited for a certain time, and then exited the orbit at a certain angle, the crew would find themselves at a moment in the past.
The problem with the scientific accuracy of the Star Trek stories is that the Sun simply doesn’t have enough mass to produce the required effect. Indeed, the only thing massive enough is a giant rotating cylinder of infinite length. So it doesn’t seem that this method of time travel is possible.
Learn more about the possibility of time travel.
Planet of the Apes
A kind of time travel that could actually happen, however, is depicted in the original Planet of the Apes. It had astronauts traveling away from the Earth and back again at a very high speed. While they traveled in their spaceship only a few years, the Earth aged so much that, once they returned, it was unrecognizable.
Traveling away from and then returning to the Earth at high speeds would have this effect because, according to the theory of relativity, time passes more slowly in reference frames that are traveling faster.
The basic idea is that when someone returns, they will find that more time has passed for the inhabitants of Earth than has passed for them.
The problem is that the effect of such time dilation is not that pronounced. A 62-year round-trip at nearly the speed of light would put someone only 10 years in the future: 72 years would have passed on Earth.
Needless to say, unless travelers can survive hundreds of years of hibernation, they’re going to be dead before completing a journey long enough to enable Earth to become the ‘Planet of the Apes’. But at least this one is a possible method.
This is a transcript from the video series Sci-Phi: Science Fiction as Philosophy. Watch it now, on Wondrium.
The Time Vortex and the TARDIS
Another series that uses time travel regularly is Doctor Who—which expounds on the adventures of the Doctor, a Time Lord from Gallifrey, who travels through time and space in his TARDIS (‘Time And Relative Dimension In Space’). The TARDIS travels in time by traversing what is called the time vortex. To facilitate this, the Time Lords of Gallifrey created an infinite series of wormholes, spanning all of time and space—a time vortex—and then built machines, called TARDISes, that are able to navigate this vortex.
Interestingly, time travel via what might be called a time vortex could theoretically be possible. A wormhole is like a portal between two places; it’s created when two distant points in space are joined by space-time itself being bent in a higher dimension. By passing through the wormhole, long distances can be traveled instantaneously.
The Wormhole Hypothesis
So, say there is a wormhole, but its two ends are fairly close together. Suppose whatever is keeping the wormhole open is taken in a spaceship, and then that and its wormhole are made to travel away at near the speed of light and then return again. Just like in Planet of the Apes, upon its return, one end of the wormhole would be older than the other. Side A may be 60 years old while side B is, say, 70. This would be a ‘time-dilated’ wormhole.
If a person were to step into Side B of the time-dilated wormhole while it is 70 years old, they would emerge from side A when it is 70 years old. But that side wouldn’t be 70 until 10 years after the moment they stepped into Side B. So, they will have traveled 10 years into the future. But, of course, in 10 years, side B will be 80 years old—so they could step in it and travel 10 more years into the future. This process can be repeated ad infinitum. As long as the wormhole stays open and the person doesn’t want to travel to a time before its creation, they could travel where they wanted.
Learn more about time travel paradoxes.
Is this really possible? Well, wormholes actually happen all the time. That’s good for the possibility of time travel. Unfortunately, these wormholes are smaller than quantum particles and they blink in and out of existence so quickly not even light can travel through them.
If they could be enlarged and kept open, a time machine could be built. Unfortunately, according to physicist Kip Thorne, this would require the use of something called negative energy, and negative energy is not known to be real.
Interestingly, Benjamin Tippett and David Tsang have written a paper on whether time travel via TARDIS is actually possible. Their conclusion is encouraging: it seems that such a device is physically possible in our universe. Closed time-like curves, which wormholes can create, are possible in our universe, and they could theoretically allow one to travel in time. Of course, they observe “limitations which may prevent us from ever constructing a TARDIS”. But, then again, the universe is so large and old—maybe, eventually, someone will overcome those limits.
Common Questions about Wormholes, the Time Vortex, and the TARDIS
In the Star Trek series, many methods of time travel are explored. One favorite is the slingshot maneuver in Star Trek IV: The Voyage Home, where Mr. Spock uses the Sun’s gravity to accelerate the ship and then whip around the Sun, appearing on the other side in the past.
In Planet of the Apes, the astronauts traveled away from the Earth and back again at a very high speed. They were away for only a few years, but the Earth aged so much that, once they returned, it was unrecognizable. According to the theory of relativity, time passes more slowly in reference frames that are traveling faster.
Doctor Who uses a device called the TARDIS (‘Time And Relative Dimension In Space’) to navigate through time via the time vortex.