Courtesy of Unsplash. Photo by Bryan Goff.
With assassins (and time-lords) sauntering from past to future and back again all over our big – and small – screens, the subjects of parallel universes, reverse entropy and the grandfather paradox are popping up more than ever in conversations outside the quantum physics lab. But if you’re not exactly an innate science nerd and this is your first brush with the subject of time-travel – let’s take a closer look at a few of the theories drifting around in hyperspace. With this handy guide, you’ll soon be well-versed enough in the basics to debate with confidence – without developing a vitamin D deficiency.
Apart from making you seem super-smart to mere mortals, understanding special relativity is pretty much ground zero when it comes to understanding the concept of time-travel. Usually, we think of time as a ‘constant’, obeying a set of unbreakable rules. But physicist Albert Einstein showed unequivocally that time is, in fact, an illusion. Before you copy and paste this fact in an email to your boss, let’s explain what we mean. Time as we know it is relative. That means that it can vary from one observer to the next, depending on your speed through space. And by and large, humans move at the same speed through space. So for you and your boss, the same rules and regs of time-keeping still apply (sorry).
Courtesy of Unsplash. Photo by Laimannung
But Einstein revealed that time in the known universe is actually a ‘fourth dimension’. Think of space as a three-dimensional field, providing coordinates – i.e. length, width, and height – and giving the observer a particular location. Time then adds a fourth coordinate with which to locate someone, or something, known as direction – though conventionally that coordinate only ever moves forward. Einstein’s theory of special relativity says that time either slows down or speeds up depending on how fast you move, relative to something else. Take a hypothetical pair of twins: Twin Alice and Twin Bob. If, for example, Twin A were an astronaut travelling in a spaceship that was approaching the speed of light, she would age much more slowly than Twin B back on Earth. This is known as ‘time dilation’.
In a sense, it makes all astronauts time travellers, who return very slightly younger than their twins (if all astronauts had twins) at home. General relativity also shows that gravity can ‘bend’ time… and, with this revelation, that time travel to the future is, in fact, entirely possible. Let’s explore this weighty issue a little further…
Courtesy of Unsplash. Photo by Bryan Goff.
So now we’ve got a comfy hybrid-duvet of sorts called space-time. Think of it as a trippy piece of fabric, spread out in four dimensions. When anything that has mass sits on that piece of fabric, it causes a pocket, fold, or bend in space-time. This bending or warping of space-time causes things (biscuit crumbs, for example) to move along a curved path – and that curving of space is what we call gravity. And the faster you move, the more warping occurs – meaning that time moves more slowly. Or, alternatively, you could hang out in the vicinity of an object with massive amounts of gravity and you get a similar effect. This effect has already been proven on a small scale – a clock placed on an airplane and flown around the planet for several hours returned a fraction of a second behind a synchronised clock left on earth.
Take another example of the effect of mass on time: scientists have measured the ticking of atomic clocks at the top and bottom of a skyscraper. The clocks on the ground floor (that is, closer to the mass of the Earth) tick more slowly than those perched in the penthouse suite.
But why do all these ticking clocks mean that time travel is possible? The same principle applies when taken to great extremes… meaning that fraction of a second’s difference could expand to days, months, even decades of ‘travel’ into the future.
If you could hop on a spacecraft capable of travelling at 200 million metres a second (that’s 450 million mph to you racing enthusiasts), you’d experience a significant degree of time-slowing. On board, you wouldn’t notice – just as you would on board a plane, you could happily drink a scotch and soda, nibble peanuts and veg out in front of Paddington 2 without anyone judging. But after a jaunt to the edge of the galaxy and back, you’d notice you were significantly younger than your mates back on earth.
While this might seem like an expensive replacement for going to the gym and investing in a decent moisturiser, there are far-reaching implications for this possibility. But it’s not without significant obstacles. For one, building a spaceship that can travel at speeds close to that of light would involve levels and quantities of energy that are currently fantastical.
But what happens if you decide to return back in time to the place (and time) that you came from? This would require exceeding the universal ‘speed limit’, otherwise known as the speed of light. Many physicists say this is absolutely impossible. They include the legendary Stephen Hawking, so we’re inclined to respect this opinion. But some think there might be ‘shortcuts’ to the past. And these are known affectionately (depending on your feeling about worms) as ‘wormholes’.
Wormhole travel as envisioned by Les Bossinas for NASA. Digital art (Cortez III Service Corp.), 1998.
A wormhole is essentially a sort of connecting tunnel between two openings or ‘tears’ in the fabric of space-time. Remember that cosmic duvet? Now imagine someone or something has rudely ripped a hole in it, allowing many feathers to escape into outer space, and that through it you could reach another hole on the opposite side, which could restore back to you all the time you have lost trying to put duvets inside their covers. You’d be at least ten years younger, and significantly less stressed.
But seriously – for reasons that are possibly too complex to explain fully – quantum mechanics dictates that if such a wormhole existed, it would all-but-instantly collapse on itself and snap shut again, meaning it would be nearly impossible for a particle to get inside and pass through it in one piece, let alone a human. While wormholes have yet to be discovered, many still agree their existence is possible.
Black Holes and Infinite Cylinders
Another option involves flying a spaceship rapidly around a black hole, or to artificially create that condition with a huge, rotating structure. You could also send a spaceship in a spiral around an incredibly long, dense cylinder (which had a mass ten times that of the sun). This would set your spaceship along a time-like curve, though to do so it would have to very nearly reach the speed of light – a feat as yet unimaginable. But in theory, at least, this form of time travel would be possible.
As physicist Stephen Hawking says, “Around and around they’d go, experiencing just half the time of everyone far away from the black hole. The ship and its crew would be traveling through time.” In other words, for approximately five of their years, ten would have passed on Earth.
First image ever of a black hole, Messier 87, captured by The Event Horizon Telescope (EHT) in April 2019.
The Grandfather (or Grandmother) Paradox
This is the classic problem, often encountered in sci-fi time-travel movies. The hero is sent on a mission to the past (or future), with strict instructions not to interfere with certain events, catch sight of themselves, or murder their grandparents, for example. If a sequence of events is interfered with, i.e grandma dies before mother is born, it might mean that our hero is never even conceived (in which case, do they immediately cease to exist?) or that their life is forever altered.
Stephen Hawking has theorised that time would protect itself from such scenarios by preventing time travel to the past entirely. Others hypothesize that the time traveller would enter a parallel universe – one which evolves along its own separate route in space, an argument which aligns with the quantum ‘many worlds’ theory. Others say that light-particles or ‘photons’ tend toward consistency, which would in effect scupper any nefarious or suicidal schemes.
If all this temporal adventuring sounds a bit too much like hard work, or your brain is exhausted by the mere thought of it, why not time-travel the traditional way? Wrap up in your very own four-dimensional duvet (that’s the one on your bed, just to be clear, which does in fact exist in four dimensions)… and travel in space-time at the comfortable rate of one second per second?
If you’re feeling a little wild, refine your speed to one microsecond per microsecond – and just to be sure of your measurements, take reliable tools with you on your interstellar journey… like a TAG Heuer Chronograph, for example. Measure the minutes as they pass by at warp speed, and look good trying.
But joking aside, the amazing fact of the matter is that a TAG Heuer chronograph is perfectly capable of measuring everyday time travel. Whether you’re breaking the human land speed record on the racetrack, or crossing the Atlantic on a red-eye from New York to London, your speed does in fact cause time to slow by measurable fractions of a second. Perhaps that’s the reason you look so much younger than your years…
We fuel your drive to challenge the limits: TAG Heuer watches and chronographs designed for performance, perfect for a competitive wrist.