Peter Capaldi and Jenna Coleman time travel in the TARDIS.

Time Travel Ban: Exploring Time In Science And Science Fiction – Sorry, Doctor

Time travel has been the dream of science fiction writers – and some scientists – for generations. But while time travel in novels, movies, and television shows seems so easy that you could virtually do it by accident, the reality of time travel is very different from a scientific standpoint.

Albert Einstein said future time travel was fine
Albert Einstein said future time travel was fine. [Image by Central Press/Getty Images]

Time Travel in Science Fiction

H.G. Wells’ The Time Machine and Mark Twain’s A Connecticut Yankee in King Arthur’s Court are early examples of time travel stories. Even Rip van Winkle can be viewed as a story about a man who time travels into the future by taking a nap.

Most of the earliest time travel stories provided little or no science – or even Star Trek-style technobabble – to explain just how the time traveler managed to get from now to then – or from now to later. For the purposes of the plot, technical details were glossed over.

More recent science fiction writers try to incorporate the latest theories about the nature of the universe to give their stories greater realism. This is why black holes, wormholes, and other outer space phenomena have been enlisted as time travel plot devices.

Time travel with style in a DeLorean.
Time travel with style in a DeLorean. [Image by Theo Wargo/Getty Images]

For decades, movies and television have also taken advantage of the possibilities time travel offers for storytelling. In the classic 1985 film Back to the Future, Marty McFly careens through time in Doc Brown’s pimped-out DeLorean. But other than learning that the flux capacitor requires a major-league power source, there’s nothing in this movie to explain how time travel actually works.

Television has also tried its hand at time travel. Way back in the 1960s, Captain Kirk and the Enterprise were constantly being thrown back in time by spatial distortions, black holes, and alien devices. In attempting to associate known physical aspects of the universe, such as the four-dimensional nature of space and the gravitational effects of black holes, at least Star Trek writers on the various incarnations of the show offered a pseudoscience excuse for time travel.

Enterprise D also did some time travel episodes.
Enterprise D also did some time travel episodes. [Image by Mario Tama/Getty Images]

Other shows like Doctor Who and Legends of Tomorrow have actually moved away from attempting to provide viewers with clear – even if scientifically inaccurate – explanations for how their respective time machines actually operate. When Doctor Who‘s Martha Jones at one point asks how the TARDIS travels through time, David Tennant’s version of the Doctor replied, “It just does.” And that was that.

The Doctor Who TARDIS makes time travel look easy.
The Doctor Who TARDIS makes time travel look easy. [Image by Adam Gasson/Getty Images]

Time Travel Theory 101

While virtually all physicists acknowledged that it would – at least in theory – be possible to travel into the distant future, most of them feel that travel into the past is a physical and logical impossibility for a variety of reasons. This backward time travel ban is extremely annoying for anyone wanting to shake hands with Abraham Lincoln or watch Julius Caesar cross the Rubicon.

Since Einstein, scientists have known that light speed time dilation can get you to the future – if you can afford it and if it doesn’t kill you. As pointed out by NASA, time dilation is an effect in which objects with mass – including people – accelerated close to the speed of light experience time more slowly than the surrounding universe.

This means that – again in theory – if you had an antimatter rocket capable of propelling you close to light speed and it took you on a flight hundreds of light years away and then returned you to the Earth, you would arrive in the far distant future. Don’t forget to invest in tax-free municipal bonds before you leave.

There are three major problems with this approach to time travel. The first difficulty is – and it’s a big one – we have only the vaguest ideas about how to build a spacecraft capable of achieving near-light-speed velocities.

Another problem is that – even if we could accelerate a ship close to light speed – the crew might die from lethal radiation caused by particles striking the front of the ship as it plowed its way toward Alpha Centauri. Hardly worth the trip really.

And as noted by the University of Michigan, this approach also doesn’t allow you to travel into the past, which means you couldn’t go home to brag about your time traveling exploits to friends and family.

In order to time travel into the past using any kind of accelerating spacecraft, the ship would have to actually exceed the speed of light. But according to Einstein and every reputable physicist, it’s absolutely impossible for any object that has mass to accelerate itself – or to be accelerated by an external force – beyond the speed of light. So, faster-than-light time travel is out too.

There are highly theoretical particles with mass that supposedly always travel faster than light. Known as tachyons, these particles are the flip side of the time travel coin in that they can’t decelerate themselves below the speed of light. But no one has any idea how to interact with such hyper fast particles, let alone how they could be used to help us travel faster than light.

Warp drive lets the Enterprise break the light speed barrier without time travel.
Warp drive lets the Enterprise break the light speed barrier without time travel. [Image by Haynes Publishing/Getty Images]

As noted by Big Think, in 1963 a New Zealand mathematician named Roy Kerr offered up a somewhat contrived situation for time travel. In this scenario, a black hole could theoretically form itself into a doughnut shape from a spinning neutron star, creating what was appropriately named a Kerr Black Hole.

Since this doughnut black hole would have no atom crushing singularity at its center, Kerr theorized that a ship could travel through the ring and come out through a purely hypothetical “white hole” at some point in the past. It has even been suggested that quasars – which actually do exist – might be these theoretical white holes, although most physicists reject this idea.

Stephen Hawking thinks time travel to the past is impossible.
Stephen Hawking thinks time travel to the past is impossible. [Image by Bryan Bedder/Getty Images for Breakthrough Prize Foundation]

But even assuming you could somehow time travel to the past, physicists like Stephen Hawking feel that the result would be paradoxes that would make no logical sense. You have probably heard of the thought experiment in which you could travel back in time and kill your grandfather – perhaps he yelled at you a lot.

The problem in this scenario is, if you actually did time travel and managed to off your grumpy grandfather, you would then no longer exist yourself and would be unable to go back in time and kill him. Thus, you have created a brain twisting paradox – quite apart from any legal problems resulting from killing your annoying relative.

In short, because of the interrelated, domino-like nature of the world around us, it’s hard to see how any action you might take when you time travel to kill bad grandpa wouldn’t change the future. Even occupying the space previously taken up by old timey air molecules would most likely create a new timeline you might not exist in. Unless you want to talk about the multi-verse – and we do.

The Multi-Verse and Time Travel

One alternative theory about the nature of the universe is that it exists as a “multi-verse” containing an infinite number of possible versions of our reality. This idea was first jokingly suggested by Edwin Schrodinger in 1952. It is also known by the term “many worlds theory” – as proposed by Hugh Everett in 1957.

Instead of the current idea underlying quantum mechanics in which the reality of any situation collapses into a single timeline when it is “observed” – Schrodinger’s cliche semi-dead cat – in the many worlds approach, every possible outcome and potential version of reality actually exists. So despite the recent election, this theory implies there is a reality where Hillary Clinton is president.

Continuing with the cat analogy, the hapless feline isn’t both dead and alive until observed – as Schrodinger would have put it. It’s dead in one timeline, alive in another timeline, breakdancing in a third timeline, and so on. But when we open the box, we merely find out which timeline we ourselves happen to be in. Alternate versions of us in the other timelines would have seen something else. Perhaps the breakdancing.

But again, while this theory hasn’t necessarily been disproved and may even turn out to be true, there are still problems. Scientists have no idea how one could go about traveling into the past, interact with that past so as to follow one of the separate timelines, and then still return to your own timeline to report the result. So even with the many worlds of the multi-verse, the ban on time travel into the past may still stand.

[Featured Image by Stuart C. Wilson/Getty Images]