Wormhole Time Travel 'Possible' (If You're a Photon)
Image credit: Sara Hayward/Getty Images
Top 5 Time Travel Methods from the Movies
Oh, how we often long to travel back in time and change our pasts, to stop some horrible event, to rewrite history. Movies often indulge and inspire us with their time travel adventures, but how many of these have any basis in real science? Let's, for this purpose, ignore how much the movies tug at the heartstrings, entertain us, or tickle our funny bone. We can never forget great ones like "Back to the Future," "Bill and Ted's Excellent Adventure," "Time Cop" and many others. But this is a focus on how the heck we are going to get these movies to come true. Ron Mallett, professor of physics at the University of Connecticut and author of Time Traveler: A Scientist's Personal Mission to Make Time Travel a Reality, has spent his whole career studying the possibilities of time travel and he weighed in on what aspects of the movies are on the edge of possibility and which ones are not. Derived from the expertise of Mallett, here are the top five time travel movies ranked on their basis in science and their true feasibility. Sorry "Hot Tub Time Machine", you didn't make the cut.
Image: Frank (Dennis Quaid) communicates with
Frank Sullivan, played by Dennis Quaid, communicates with his son John (Jim Caviezel) 30 years into the future through a radio. They work together to save Frank's life and to find John's mother's would-be-killer. Frequency's time travel is largely based around an unusual environmental phenomenon in the aurora borealis. This solar disturbance causes Frank's radio to send its signal to the same radio in the future, where John now has it in the same home. The idea that the energy from a solar disturbance could alter spacetime in some way that sends radio waves through time is very much outside the realms of possibility. The aurora borealis could never produce that much energy and if it were to do so, there would likely be some disastrous side effects. But being outside the realms of possibility isn't a problem when it comes to sci-fi time travel. However, Brian Greene, physicist and author of several books including The Elegant Universe, was a consultant for the film, so his input certainly gave the movie some extra weight as far as feasibility goes.
Image: An artist's rendition of a wormhole. C
Déjà Vu (2006)
After a ferry bombing, Agent Doug Carlin (Denzel Washington) joins forces with a special team that has technology to see four days into the past. This technology turns out to be a "time window" which Carlin convinces them to use as a time machine and send him into the past. He ends up saving the ferry from the bomber, played by Jim Caviezel. This is a stretch and would involve technology and an understanding of wormholes that we just don't have right now. The "Snow White" project, as it's called in Déjà Vu, somehow controls wormholes or what they call a "time window" to travel through time and space. Wormholes, also called Einstein-Rosen bridges, are a valid theoretical method for time travel, but solely theoretical. Their existence has never been proven and requires something called "exotic matter" to keep them stable. Yet, Mallett says that any movie involving theories of Einstein for time travel is more feasible than those that do not. The movie takes the theory to the extreme in a way that is very entertaining and smart. Brian Greene, who consulted in "Frequency," was also a consultant for "Déjà Vu". You definitely need a theoretical physicist to keep all the timelines straight in this one.
Image: H. George Wells (Rod Taylor) fires up
The Time Machine (1960)
H.G. Wells wrote the original book and the movie's lead character is named H. George Wells (Rod Taylor) after him. He uses his machine to travel from the year 1900 through the future seeing two world wars and accidentally ending up in the year 802,701, where he finds a future people who he tries to help. Mallett has this high on his list (of course he says the book is even better) because it's the only movie that accurately states time as a fourth dimension. Although in modern relativistic physics, space and time are combined into one metric called "spacetime." The machine itself; not so feasible. A chair with spinning parts and a lever that controls time travel is something today's scientists have yet to find viable. It's quite miraculous that the fictional H. George Wells was able to invent it in the early 1900s. Another positive note for this version: it does not have him traveling to the past beyond the invention of his machine. The movie doesn't explain this rule, but it does follow the true physics of time travel. Mallett says, "Since it is the device that creates the effect, then is not possible to go back before the device was created."
Image: The bridge of the Enterprise in Star T
Star Trek (2009)
Time travel is featured in the "Star Trek" series many times, but the way the most recent movie dealt with time travel makes it very easy to understand without having to be a physics expert. "They actually brought in a number of current ideas," says Mallett. The movie's use of parallel universes is done very well and explained very well. There is a valid scientific theory in quantum mechanics that says there are many parallel universes. Plus, when you go back into the past you actually arrive in the past of a parallel universe, where you can change the future of that universe, but in your time those things have already happened. It's also important to know that once you are in this alternate reality you cannot, as another time travel movie suggests, go back to the future. Black holes are a very popular method for sci-fi time travel and one that could actually be possible. Einstein's general theory of relativity basically says that gravity effects time and since black holes have gravity so strong that light can't even escape, they create the possibility for time travel. If you were able to get close to a black hole, time would slow down. When you escaped, time outside would have passed a lot more quickly. Making things more complicated, when the black hole is rotating, it can cause time to be twisted into a loop that allows you to go into the past. That still leaves some scientific flaws in the movie, but nobody's perfect. It was still one of the most (if not the most) entertaining "Star Trek" movies.
Image: Charlton Heston finds himself in front
Planet of the Apes (1968)
Put briefly, astronaut Taylor (Charlton Heston) unknowingly goes on a journey to a future Earth where apes have guns, don't believe in the possibility of flight, and rule the planet. Humans are still around in this future, but are mute and quite unintelligent. The best thing about this movie is that they talk about real scientific theories in explaining how they traveled through time. "According to Dr. Hasslein's theory of a vehicle traveling near the speed of light, the earth has aged nearly 700 years since we left it, while we've aged hardly at all," says Taylor in the opening scene of the movie. Actually, it's based more on theories of a man named Albert Einstein. His special theory of relativity says that time for a moving clock slows down. In 1971, the Hafele-Keating experiment proved this with very accurate atomic clocks. One was on Earth and another was flown around the world on a passenger jet. When the jet landed, the clock on the jet was about 50 nanoseconds behind the one on Earth, just like Einstein predicted in 1905. "This means, for a space traveler traveling close to the speed of light, that this effect will happen dramatically. A few years will pass for those on board, but when the rocket lands, decades will have passed on Earth," explains Mallett. So as Heston and his crew travel near the speed of light, they would in fact be traveling through time relative to those of us on Earth. Getting a ship close to the speed of light is the practical challenge in this case, but very plausible in theory. The portion of the movie in which apes control the planet is a little more questionable.
The idea of traversable wormholes has been science fiction fodder since Einstein first theorized their existence with the formulation of his general theory of relativity, but do wormholes even exist in nature? Actually, we have no idea if they exist or not, but if they do, theoretical physicists have proposed that they could act as portals into the future and the past or connect two distant regions of space.
But before you grab your Grays Sports Almanac and get ready for some temporal mischief, there’s one huge caveat to this idea — only photons may travel… and even photons may be too much of a stretch for the hypothetical shortcut through spacetime.
In a paper published to the arXiv preprint service (and submitted to the journal Physical Review D), theoretical physicist Luke Butcher of the University of Cambridge has revisited wormhole theory and potentially found a way to bridge these notoriously unstable entities.
In the late 1980s, physicist Kip Thorne, of the California Institute of Technology (Caltech), theorized that to make a wormhole ‘traversable’ — as in to actually make these spacetime shortcuts stable enough to travel through — some form of negative energy would be required. In the quantum world, this negative energy could come in the form of Casimir energy.
It is well known that if two perfectly smooth plates are held very close together in a vacuum, quantum effects between the plates will have a net repulsive (or attractive, depending on the plate configuration) effect between the two. This is caused by waves of energy being too large to fit between the plates, causing a net negative energy between the plates when compared with the surrounding “normal” space.
As realized by Thorne and his Caltech team, this Casimir energy could be applied to the neck of a wormhole, potentially holding it open long enough for something to pass through.
Alas, we are talking about quantum-sized wormhole throats, meaning Marty McFly’s speeding DeLorean will be left revving in the 1985 parking lot, unable to squeeze through. But even if some quantum-sized traveler could pass through the wormhole’s neck, the wormhole would still likely collapse very quickly.
On reevaluating this scenario, Butcher has identified some more stable wormhole configurations and, in certain situations, the wormhole collapse could be prevented for an “arbitrarily long time.” But for this to happen, the wormhole needs to be very long and have a very narrow throat. In this case it seems possible that photons could traverse the wormhole.
“(T)he negative Casimir energy does allow the wormhole to collapse extremely slowly, its lifetime growing without bound as the throat-length is increased,” writes Butcher. “We find that the throat closes slowly enough that its central region can be safely traversed by a pulse of light.”
Butcher admits that although it’s not clear from his calculations whether the light pulse will be able to complete its journey from one end to the other, there is a tantalizing possibility for sending signals faster than the speed of light or even back in time.
“These results tentatively suggest that a macroscopic traversable wormhole might be sustained by its own Casimir energy, providing a mechanism for faster-than-light communication and closed causal curves.”
For the moment, this work is highly theoretical, but, as pointed out by Matt Visser of Victoria University of Wellington, New Zealand, in New Scientist on Tuesday, this research could renew interest in the study of wormholes and their potential spacetime-bridging capabilities.
So if we were to look for physical evidence of wormholes, could this research help us? Could we perhaps look out for be some kind of unique polarization of light that has traveled from another part of the Universe or some other time, appearing randomly in our local volume of spacetime? For answers to these questions, and as to whether this may spawn some kind of faster-then-light communications technology, we’ll likely have to wait until the theoretical physicists have crunched more numbers.