TIME TRAVEL
We’ve seen the future, and it’s you enjoying our feature on the appliance of science in classic time-skip flicks.
Time travel in movies always throws up big questions. Could you interfere with your own history? Do parallel universes exist? Is a DeLorean really the best car to build a time machine out of? Frankly, they are mysteries that could blow the average human mind, so Total Film has tracked down someone who really knows what he’s talking about to find out which movies get the science right – and wrong.
Professor Jim Al-Khalili is a top theoretical physicist, as well as being the host of BBC Radio 4’s The Life Scientific, and many a science documentary on BBC Four. He’s also watched plenty of time-travel films.
“I’m not one of these people who storms out of a cinema if the science is wrong,” he tells Total Film. “I appreciate it when they take some notice of the science, and you can always tell when movies have talked to a science consultant and listened to them. But there are other sciencefiction films where it’s just fun and not meant to be taken seriously. If it’s a good story, I can enjoy it. But if it’s an awful story as well as being a bad science premise like, I dunno, Hot Tub Time Machine, that’s just a waste of my life!”
PLANET OF THE APES 1968
TIME-TRAVEL JOURNEY Cigar-chewing astronaut George Taylor and his brave crew leave Earth on the Icarus, a spaceship travelling close to the speed of light. By the time they land, 2,000 years have passed on Earth – and the planet is ruled by damn dirty apes.
JIM’S VERDICT “There’s nothing violating the laws of physics there. Einstein has two theories of relativity and the Planet Of The Apes scenario is special relativity. That’s your E=mc2, where time is the fourth dimension, nothing travels faster than light, and time slows down if you travel close to the speed of light – it’s called time dilation. Less time elapses for you, more time elapses on Earth, and when you come back to Earth, a lot more time has gone by. Travelling close to the speed of light and slowing time down is no big deal, we do that all the time in particle accelerators – it’s just that we haven’t built any spacecraft that can travel at a significant fraction of the speed of light. Essentially [in Planet Of The Apes] they’ve travelled into the future, though whether you can call it actual time travel is debatable – some people say that if you want to travel into the future, the future has to already be there waiting for you.”
Wormholes, parallel universes, the spacetime continuum… Could any of the timetravel scenarios we see in film actually happen? Top physicist Professor Jim AlKhalili does the maths on some classic movies to tell Total Film what might be possible – and what’s definitely not… WORDS RICHARD EDWARDS
INTERSTELLAR 2014
TIME-TRAVEL JOURNEY The crew of the Endurance visit a planet orbiting a black hole, where time slows down so much that minutes are like years on Earth. Pilot Cooper (Matthew McConaughey) encounters a race who live across five dimensions, experiencing past, present and future simultaneously.
JIM’S VERDICT “All the science in the movie may be highly theoretical and speculative, but it’s not wrong. With Interstellar we’re [dealing with] the effects on time predicted by general relativity. That’s Einstein’s theory of gravity, which says time slows down not because you’re travelling very fast, but because you’re sitting in a very strong gravitational field. When McConaughey and his crew land on this planet orbiting a black hole – which has very strong gravity – their time is being slowed down all the time they’re in close proximity to it. You can do the sums about how much gravity will slow time down – that every hour that goes by is years on Earth – and I think it’s all correct because one of the producers of Interstellar was Kip Thorne, a physicist who won a Nobel Prize for his work on gravitational waves.
“Could there be a race of beings who experience time as fifth dimension? When you bring in gravity, four-dimensional spacetime gets curved. If it’s curved, you can think of it as being embedded in the fifth dimension – it’s like if you want to imagine the curvature of a two-dimensional piece of paper, you’ve got to bend it within three dimensions to appreciate what it’s curving into. For us, [living] within spacetime, we just experience it moment by moment. But if you could sit outside spacetime and look at it, you would see all times frozen and co-existing.
“At this point in the film things start to get a bit weird and wacky and they’re not textbook physics as we would teach students. They’re not wrong in the sense that they don’t violate general relativity, but it’s in the realm of speculation.”
CONTACT 1997
TIME-TRAVEL JOURNEY Using instructions sent by a mysterious alien species, Dr. Ellie Arroway travels through a series of wormholes to arrive at another world. The movie’s not strictly about time travel, but space and time are so intertwined with the story that similar laws of physics apply.
JIM’S VERDICT “When Carl Sagan was writing the book of Contact and he wanted an idea for making a shortcut through space, he sent the manuscript to Kip Thorne and asked if there was a way of doing so without violating laws of physics. Thorne said there was this idea of wormholes that join two different points in space. Sagan used the idea in his book, and that sparked the idea with Thorne and his collaborators that, if relativity says time and space are connected, a shortcut between two points in space would also be a shortcut between two points in time. You travel one way you get into the future, you travel the other way you get back into the past. In serious physics research it’s still seen as a trick of the maths – it’s fun and it’s not wrong, but we think there are too many paradoxes involved with it.”
STAR TREK IV: THE VOYAGE HOME 1986
TIME TRAVEL JOURNEY Admiral James T. Kirk and his veteran crew pilot their hijacked Klingon Bird-of-Prey around the Sun at faster-than-light warp speed. The slingshot effect throws the ship back to 1986, where Kirk and co track down the humpback whales that’ll save the Earth…
JIM’S VERDICT “Relativity theory says nothing can go faster than light. The algebra’s quite simple to show that anything that could go faster than light would also necessarily be going backwards in time, but it’s a ridiculous notion. The idea of tachyons – hypothetical particles which are supposed to be able to go faster than light – is allowed by the maths, but it’s a nonsensical idea in the real world. It’s a bit like saying I’ve got a square carpet that’s nine square metres and it’s three metres each side – but that it’s also minus-three metres each side, because minus-three times minusthree is also nine. You can’t have something minus-three metres in length, so you ignore that solution, even though the maths tells you it’s right. In Star Trek, though, they sometimes come up with an idea and then retrospectively try to argue the science to justify it!”
BACK TO THE FUTURE 1985
TIME TRAVEL JOURNEY Dr. Emmett L. Brown builds a time machine – out of a DeLorean – that can take you to any point in history or the future. Which proves problematic for Marty McFly when he inadvertently starts messing around with his parents’ timelines.
JIM’S VERDICT “Relativity would say a fixed point in time exists. In the idea of fourdimensional spacetime, we are experiencing the present moment, the past is lost and the future is yet to unfold. But if you think about a wormhole linking two points in time, even as you go into the future you still have access to that other end of the wormhole stuck at a particular point in the past. Of course, people will ask, if you build a time machine, can we go back to the age of the dinosaurs or the Wild West? But the logic is that a time machine would only be able to take you back to the moment you first switched it on, and anything before that is lost to you. Thus building a time machine to travel back in time at will should not be possible. Primer picked up on that subtlety.
“But there’s no reason why you couldn’t interact with your past self – you wouldn’t be like a ghost – and no reason why you shouldn’t be able to mess with the course of events. But you should only be able to do things to cause them to turn out the way they have [previously] turned out. For example, could a time traveller go back 66 million years and fire a missile to destroy the meteor that killed off the dinosaurs? Well, no, because the dinosaurs did go extinct. But what could have happened is that the missile managed to break up a meteor that would have destroyed all life on Earth, a smaller fragment hit the Earth, and only wiped out the dinosaurs. The time traveller’s intervention would cause things to turn out the way they always turned out.
“But this all depends on a very important condition, which is whether our universe is the only reality – if Marty McFly travelled back into a parallel universe, he could change the course of the future in that universe in the sense that it wouldn’t interfere with the way his own universe ended up evolving.”
STAR TREK 2009
TIME-TRAVEL JOURNEY When a Romulan ship travels back in time from the post-Next Generation era and destroys the USS Kelvin, a new Star Trek timeline is created – one where the experiences of Kirk, Spock and the rest of the Enterprise crew are subtly different.
JIM’S VERDICT “The many-worlds interpretation is one of the ways of explaining away the weirdness of quantum mechanics. The idea is that every time we make a measurement the universe splits in two. For example, every time an electron decides to go left or right there are two universes created – one where it went left, one where it went right. Everything in those two universes would be identical apart from what that particle did. That change may then be amplified as time goes by – a butterfly effect – but by and large, the universe is splitting and bifurcating all the time.
“There wouldn’t be much difference between the universes, but because we’re stuck in one timeline we don’t know what the others are like – the maths tells us they should be very similar and just as real as ours. It’s all a bit metaphysical because we can never actually make contact with them.”
X-MEN: DAYS OF FUTURE PAST 2014
TIME-TRAVEL JOURNEY With the Earth an apocalyptic wasteland and mutant-kind all-but wiped out, Professor X and Magneto send Wolverine’s consciousness back to the 1970s on a mission to prevent the mutant-killing Sentinels being created – and fix the present.
JIM’S VERDICT “Using an idea like a wormhole, a connection between two different times, theoretically it should be possible to get back to a moment before some cataclysmic event and pick a different path. If parallel universes exist, then there are lots of timelines in which different things have happened. That means you’re not stopping the events that you don’t like from ever happening in your universe; you’re abandoning your timeline and jumping ship into another timeline where it doesn’t happen.
“I’ve always found that rather selfish. We could jump into a timeline where Adolf Hitler was never born, live happily and say thank goodness, it’s a much happier world. But there was still another universe where five million people were killed in gas chambers, that still happens. All possible things happen in some universe, but that’s metaphysically not very satisfying, because there’s nothing special about your own timeline.” AVENGERS: ENDGAME 2019
TIME TRAVEL JOURNEY Using Pym Particles to shrink themselves down to subatomic size, the Avengers use the tricksy time properties of the Quantum Realm to travel back into the past. As they keep reminding us, it’s not like Back To The Future…
JIM’S VERDICT “One of the major problems we have in theoretical physics today is that, compared to relativity, quantum mechanics [the physics of the very small] gives us a very different picture of what time is. Relativity says time is the fourth dimension, but quantum mechanics doesn’t talk about time in that way – it says that everything’s reversible, that things can move forward and backward without any concerns, but time isn’t a direction in itself. Quantum mechanics doesn’t really tell us how you could move forward or backward through time. Unifying quantum mechanics with relativity is one of the big challenges in physics.”
THE TERMINATOR 1984
TIME-TRAVEL JOURNEY On a mission to save humanity’s saviour, John Connor, future soldier Kyle Reese travels back to 1984 to protect Connor’s mother, Sarah, from a cyborg assassin – and, thanks to a complex time loop, winds up being John’s dad.
JIM’S VERDICT “Logically this could work, provided you’re careful. Essentially the future goes back and fixes the past, creating a past that causes that future. Without these time loops something else would have happened, so the future isn’t changing the past, it’s creating the past that caused that future. That means that inevitably you have to travel back into the past to create that future. With these time loops, the logic is there, but the problem is it means the future is fixed in the same way the past is. That messes with the idea of free will.
“But I think a lot of physicists – and I’m inclined to be one of them – believe that our universe is deterministic, which means the future is fixed and decided. Of course, this has philosophical implications. Does it mean that we have no control over what happens? Well, we have the illusion of free will and we do what we do. If you could see spacetime from outside, you’d see everything is fixed and set in place. In hindsight we can look back and say it was always going to be thus but at the time we feel we’re making free choices.”
BACK TO THE FUTURE: PART II 1989
TIME-TRAVEL JOURNEY Marty McFly buys a sports almanac containing information about future sporting events. When Biff Tannen gets hold of the book, his winning streak at the bookies radically alters history.
JIM’S VERDICT “This leads to all sorts of paradoxes. The simplest one is that you find a blueprint for a time machine, you build it and then you take that blueprint with you back in time and place it where you found it – you’ve created information out of nothing. Logically it’s not inconsistent, providing your loops are all sorted out carefully, but it can lead to paradoxes. What if you decide not to put the blueprint where you found it? Does that mean that you didn’t find the blueprint and you didn’t build the time machine? The only way to get out of these paradoxes is to have parallel universes – then the person who designs the time machine could come from a parallel universe and leave it in my universe to find.”
BILL & TED’S EXCELLENT ADVENTURE 1989
TIME-TRAVEL JOURNEY As they round up famous figures from history they’ve lost around San Dimas, Bill S. Preston Esq and Ted ‘Theodore’ Logan are helped by objects and notes their future selves will later put in place for them to find.
JIM’S VERDICT “I think Bill & Ted is very underrated and the film was cleverly done. They had to remember to do that, to remember to do this, and leave notes for themselves… I think someone sat down with a flow chart, and said if this happens then this happens, as well as having things looping back on themselves in order for them to know that this other thing had to be in place. Again, it’s logically consistent, provided you don’t push too hard and break it with a paradox – which is something you always can do with time travel!”