time travel using wormholes

December 1, 2015

12 min read

Can Time Travelers Reach the Past via Wormholes?

Astronauts already skip ahead in time, but the laws of physics seem to forbid going backward—or do they?

By Tim Folger

The famous writer H. G. Wells published his first novel, The Time Machine , in 1895, just a few years before Queen Victoria's six-decade reign over the U.K. ended. An even more durable dynasty was also drawing to a close: the 200-year-old Newtonian era of physics. In 1905 Albert Einstein published his special theory of relativity, which upset Isaac Newton's applecart and, presumably to Wells's delight, allowed something that had been impossible under Newton's laws: time travel into the future. In Newton's universe, time was steady everywhere and everywhen. It never sped up. It never slowed down. But for Einstein, time was relative.

Time travel is not merely possible—it has already happened, though not exactly as Wells imagined. The biggest journey through time so far, according to J. Richard Gott, an astrophysicist at Princeton University, was taken by Sergei K. Krikalev. Over the course of his long career, which began in 1985, the Russian cosmonaut spent 803 days in space. As Einstein proved, time passes more slowly for objects in motion than for those at rest, so as Krikalev hurtled along at 17,885 miles an hour onboard the Mir space station, time did not flow at the same rate for him as it did on Earth. While in orbit, Krikalev aged 1/48 of a second less than his fellow earthlings. Put another way, he traveled 1/48 of a second into the future.

The time-travel effect becomes easier to see as distances stretch longer and speeds creep higher. If Krikalev left Earth in 2015 and made a round-trip to Betelgeuse—a star that is about 650 light-years from Earth—at 99.995 percent the speed of light, then by the time he returned to Earth he would be only 10 years older. Sadly, everyone he knew would be long dead because 1,000 years would have passed on Earth; it would be the year 3015. “Time travel to the future, we know we can do,” Gott says. “It's just a matter of money and engineering!”

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Jumping a few nanoseconds—or even a few centuries—into the future is relatively straightforward, practical challenges aside. But going backward in time is harder. Einstein's special theory of relativity forbade it. After another decade of work, Einstein unveiled his general theory of relativity, which finally lifted that restriction. How someone would actually travel back in time, however, is a vexing problem because the equations of general relativity have many solutions. Different solutions assign different qualities to the universe—and only some of the solutions create conditions that permit time travel into the past.

Whether any of those solutions describes our own universe is an open question, which raises even more profound puzzles: Just how much tweaking of fundamental physics would it take to allow backward time travel? Does the universe itself somehow prevent such journeys even if Einstein's equations do not rule them out? Physicists continue to speculate, not because they imagine time travel to the past will ever be practical but because thinking about the possibility has led to some surprising insights about the nature of the universe we live in—including, perhaps, how it came to be in the first place.

A new way of looking at time With his special theory of relativity, Einstein made time malleable in a way that must have pleased Wells, who presciently believed that we inhabit a universe in which three-dimensional space and time are knit together into a four-dimensional whole. Einstein arrived at his revolutionary results by exploring the implications of two fundamental ideas. First, he argued that even though all motion is relative, the laws of physics must look the same for everyone anywhere in the universe. Second, he realized that the speed of light must be similarly unchanging from all perspectives: if everyone sees the same laws of physics operating, they must also arrive at the same result when measuring the speed of light.

To make light a universal speed limit, Einstein had to jettison two commonsense notions: that all observers would agree on the measurement of a given length and that they would also agree on the duration of time's passage. He showed that a clock in motion, whizzing past someone at rest, would tick more slowly than a stationary clock at the person's side. And the length of a ruler moving swiftly by would shorten. Yet for anyone who was traveling at the same speed as the clock and ruler, the passage of time and the length of the ruler would appear normal.

At ordinary speeds, the time-and-space-distorting effects of special relativity are negligible. But for anything moving at a hefty fraction of the speed of light (relative to the observer), they are very real. For example, many experiments have confirmed that the decay rate of unstable particles called muons slows by an order of magnitude when they are traveling at close to the speed of light. The speeding muons, in effect, are minuscule time travelers—subatomic Krikalevs—hopping a few nanoseconds into the future.

Gödel's strange universe Those speedy clocks and rulers and muons are all racing forward in time. Can they be thrown into reverse? The first person to use general relativity to describe a universe that permits time travel into the past was Kurt Gödel, the famed creator of the incompleteness theorems, which set limits on the scope of what mathematics can and cannot prove. He was one of the towering mathematicians of the 20th century—and one of the oddest. His many foibles included a diet of baby food and laxatives.

Gödel presented this model universe as a gift to Einstein on his 70th birthday. The universe Gödel described to his skeptical friend had two unique properties. It rotated, which provided centrifugal force that prevented gravity from crunching together all the matter in the cosmos, and thus created the stability Einstein demanded of any cosmic model. But it also allowed for time travel into the past, which made Einstein deeply uneasy. In Gödel's cosmos, space travelers could set out and eventually reach a point in their own past, as if the travelers had completed a circuit around the surface of a giant cylinder. Physicists call these trajectories in spacetime “closed timelike curves.”

A closed timelike curve is any path through spacetime that loops back on itself. In Gödel's rotating cosmos, such a curve would circle around the entire universe, like a latitude line on Earth's surface. Physicists have concocted a number of different types of closed timelike curves, all of which allow travel to the past, at least in theory. A journey along any of them would be disappointingly ordinary, however. Through the portholes of your spaceship, you would see stars and planets—all the usual sights of deep space. More important, time—as measured by your own clocks—would tick forward in the usual way; the hands of a clock would not start spinning backward even though you would be traveling to a location in spacetime that existed in your past.

“Einstein was already aware of the possibility of closed timelike curves back in 1914,” says Julian Barbour, an independent theoretical physicist who lives near Oxford, England. As Barbour recalls, Einstein said, “My intuition strives most vehemently against this.” The curves' existence would create all kinds of problems with causality—how can the past be changed if it has already happened? And then there is the hoary grandfather paradox: What happens to a time traveler who kills Granddad before Granddad meets Grandma? Would the demented, now parentless traveler ever be born?

Fortunately for fans of causality, astronomers have found no evidence that the universe is rotating. Gödel himself apparently pored over catalogs of galaxies, looking for clues that his theory might be true. Gödel might not have devised a realistic model of the universe, but he did prove that closed timelike curves are completely consistent with the equations of general relativity. The laws of physics do not rule out traveling to the past.

An annoying possibility Over the past few decades cosmologists have used Einstein's equations to construct a variety of closed timelike curves. Gödel conjured an entire universe that allowed them, but more recent enthusiasts have warped spacetime only within parts of our universe.

In general relativity, planets, stars, galaxies and other massive bodies warp spacetime. Warped spacetime, in turn, guides the motions of those massive bodies. As the late physicist John Wheeler put it, “Spacetime tells matter how to move; matter tells spacetime how to curve.” In extreme cases, spacetime might bend enough to create a path from the present back to the past.

Physicists have proposed some exotic mechanisms to create such paths. In a 1991 paper, Gott showed how cosmic strings—infinitely long structures thinner than an atom that may have formed in the early universe—would allow closed timelike curves where two strings intersected. In 1983 Kip S. Thorne, a physicist at the California Institute of Technology, began to explore the possibility that a type of closed timelike curve called a wormhole—a kind of tunnel joining two different locations in spacetime—might allow for time travel into the past. “In general relativity, if you connect two different regions of space, you're also connecting two different regions of time,” says Sean M. Carroll, a colleague of Thorne's at Caltech.

The entrance into a wormhole would be spherical—a three-dimensional entrance into a four-dimensional tunnel in spacetime. As is the case with all closed timelike curves, a trip through a wormhole would be “like any other journey,” Carroll says. “It's not that you disappear and are reassembled at some other moment of time. There is no respectable theory where that kind of science-fiction time travel is possible.” For all travelers, he adds, “no matter what they do, time flows forward at one second per second. It's just that your local version of ‘forward’ might be globally out of sync with the rest of the universe.”

Although physicists can write equations that describe wormholes and other closed timelike curves, all the models have serious problems. “Just to get a wormhole in the first place, you need negative energy,” Carroll says. Negative energy is when the energy in a volume of space spontaneously fluctuates to less than zero. Without negative energy, a wormhole's spherical entrance and four-dimensional tunnel would instantaneously implode. But a wormhole held open by negative energy “seems to be hard, probably impossible,” Carroll says. “Negative energies seem to be a bad thing in physics.”

Even if negative energy kept a wormhole open, just when you would be on the verge of turning that into a time machine, “particles would be moving through the wormhole, and every particle would loop back around an infinite number of times,” Carroll says. “That leads to an infinite amount of energy.” Because energy deforms spacetime, the entire thing would collapse into a black hole—an infinitely dense point in spacetime. “We're not 100 percent sure that that happens,” Carroll says. “But it seems to be a reasonable possibility that the universe is actually preventing you from making a time machine by making a black hole instead.”

Unlike black holes, which are a natural consequence of general relativity, wormholes and closed timelike curves in general are completely artificial constructs—a way of testing the bounds of the theory. “Black holes are hard to avoid,” Carroll says. “Closed timelike curves are very hard to make.”

Even if wormholes are physically implausible, it is significant that they fit in with the general theory of relativity. “It's very curious that we can come so close to ruling out the possibility of time travel, yet we just can't do it. I also think that it's annoying,” Carroll says, exasperated that Einstein's beautiful theory might allow for something so seemingly implausible. But by contemplating that annoying possibility, physicists may gain a better understanding of the kind of universe we live in. And it may be that if the universe did not permit backward time travel, it never would have come into existence.

Did the universe create itself? General relativity describes the universe on the largest scales. But quantum mechanics provides the operating manual for the atomic scale, and it offers another possible venue for closed timelike curves—one that gets at the origin of the universe.

“On a very small scale (10−30 centimeter) you might expect the topology of spacetime to fluctuate, and random fluctuations might give you closed timelike curves if nothing fundamental prevents them,” says John Friedman, a physicist at the University of Wisconsin–Milwaukee. Could those quantum fluctuations somehow be magnified and harnessed as time machines? “There's certainly no formal proof that you can't have macroscopic closed timelike curves,” Friedman says. “But the community of people who have looked at these general questions would bet pretty heavily against it.”

There is no doubt that the creation of a loop in spacetime on either a quantum scale or a cosmic one would require some very extreme physics. And the most likely place to expect extreme physics, Gott says, is at the very beginning of the universe.

In 1998 Gott and Li-Xin Li, an astrophysicist now at Peking University in China, published a paper in which they argued that closed timelike curves were not merely possible but essential to explain the origin of the universe. “We investigated the possibility of whether the universe could be its own mother—whether a time loop at the beginning of the universe would allow the universe to create itself,” Gott says.

Just as in standard big bang cosmology, Gott and Li's universe “starts” with a bout of inflation, where an all-pervasive energy field drove the universe's initial expansion. Many cosmologists now believe that inflation gave rise to countless other universes besides our own. “Inflation is very hard to stop once it gets started,” Gott says. “It makes an infinitely branching tree. We're one of the branches. But you have to ask yourself, Where did the trunk come from? Li-Xin Li and I said it could be that one of the branches just loops around and grows up to be the trunk.”

A simple two-dimensional sketch of Gott and Li's self-starting universe looks like the number “6,” with the spacetime loop at the bottom and our present-era universe as the top stem. A burst of inflation, Gott and Li theorized, allowed the universe to escape from the time loop and expand into the cosmos we inhabit today.

It is difficult to contemplate the model, but its main appeal, Gott says, is that it eliminates the need for creating a universe out of nothing. Yet Alexander Vilenkin of Tufts University, Stephen Hawking of the University of Cambridge and James Hartle of the University of California, Santa Barbara, have proposed models in which the universe does indeed arise out of nothing. According to the laws of quantum mechanics, empty space is not really empty but is filled with “virtual” particles that spontaneously pop into and out of existence. Hawking and his colleagues theorized that the universe burst into being from the same quantum-vacuum stew. But in Gott's view, the universe is not made out of nothing; it is made out of something—itself.

A cosmic chess game For now, there is no way to test whether any of those theories might actually explain the origin of the universe. The famed physicist Richard Feynman compared the universe to a great chess game being played by the gods. Scientists, he said, are trying to understand the game without knowing the rules. We watch as the gods move a pawn one space forward, and we learn a rule: pawns always move one space forward. But what if we never saw the opening of a game, when a pawn can move two spaces forward? We might also assume, mistakenly, that pawns always remain pawns—that they never change their identity—until we see a pawn transformed into a queen.

“You would say that's against the rules,” Gott says. “You can't change your pawn into a queen. Well, yes, you can! You just never saw a game that extreme before. Time-travel research is like that. We're testing the laws of physics by looking at extreme conditions. There's nothing logically impossible about time travel to the past; it's just not the universe we're used to.” Turning a pawn into a queen could be part of the rules of relativity.

Such wildly speculative ideas may be closer to philosophy than to physics. But for now, quantum mechanics and general relativity—powerful, counterintuitive theories—are all we have to figure out the universe. “As soon as people start trying to bring quantum theory and general relativity into this, the first thing to say is that they really have no idea what they're doing,” says Tim Maudlin, a philosopher of science at New York University. “It's not really rigorous mathematics. It's one piece of mathematics that sort of looks like general relativity and another little piece of mathematics that sort of looks like quantum theory, mixed together in some not entirely coherent way. But this is what people have to do because they honestly don't know how to go forward in a way that makes sense.”

Will some future theory eliminate the possibility of time travel into the past? Or will the universe again turn out to be far stranger than we imagine? Physics has advanced tremendously since Einstein redefined our understanding of time. Time travel, which existed only in the realm of fiction for Wells, is now a proved reality, at least in one direction. Is it too hard to believe that some kind of symmetry exists in the universe, allowing us to travel backward in time? When I put the question to Gott, he replies with an anecdote:

“There's a story where Einstein was talking to a guy. The guy pulled a notebook out and scribbled something down. Einstein says, ‘What's that?’ The guy says, ‘A notebook. Whenever I have a good idea, I write it down.’ Einstein says, ‘I've never had any need for a notebook; I've only had three good ideas.’”

Gott concludes: “I think we're waiting for a new good idea.”

Tim Folger is a freelance journalist who writes for National Geographic , Discover , and other national publications.

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Bizarre portal-like ‘ring wormholes’ could let you time travel

A ring wormhole is one that you could simply step through, like a portal through space – but new, more detailed models have shown that they could be a portal through time as well

By Leah Crane

14 July 2023

A ring wormhole might be a time portal

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Wormholes are often thought of as tunnels through space-time with black holes for entrances, but they could theoretically be flat instead, like a door into another location or even another universe. These are known as “ring wormholes”, and in some cases they could also become time machines.

Ring wormholes, first proposed in 2016, are made up of a string of exotic matter with negative energy – a property that is possible due to quantum effects, but only, as far as we know,…

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Scientists Have Determined How to Travel Back in Time With a Ring Wormhole

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• A recent study claims to have calculated a potential method of time travel.
• It involves a highly theoretical object called a “ring wormhole,” which is a type of wormhole that connects two regions of space, like a portal.
• Ring wormholes had previously been theorized to be portals to other universes, and researchers now propose they could act as time machines as well.

But that hasn’t stopped scientists from trying to figure out how we maybe could, someday, jump around out of order in the time stream. And recently, a team of theoretical physicists published a paper on exactly what laws of physics could be stretched just far enough to make it happen.

The key to the whole idea is wormholes —specifically, a type of wormhole called a ring wormhole. Now, wormholes are already entirely theoretical, so this discussion is going to get weird. And ring wormholes get even weirder than “normal” wormholes.

Your average, run-of-the-mill wormholes, as we tend to think of them, are basically holes punched in the fabric of spacetime by the immense gravity of black holes. The gravity well at the center of these objects is so intense that scientists have often theorized they could act as tunnels to another universe , or another time.

But ring wormholes aren’t black-hole dependent. Instead, the (again, highly theoretical) objects are caused by circles of mass that have negative energy, something only made possible by the strange effects of the quantum realm . This circle of negative energy would basically create a portal to another universe without the need to go through a black hole tunnel.

“You could go through and not even notice that you went to another universe,” Andrei Zelnikov, one of the authors on the recent paper, told New Scientist .

The paper —published in the journal Physical Review D by Zelnikov and his team—puts forth calculations that claim a ring wormhole could not only act as a universe-to-universe teleport, but as a time machine .

According to the heavy-duty number-crunching, the ring wormholes could generate something called a “closed timelike curve” if one “mouth” of the wormhole near a bunch of mass and the other “mouth” was far away from any significant amount of mass . If the conditions are right around the mouths of the wormhole, the closed timelike curves generated are then able to turn a portal into a time machine.

“The time machine is a natural consequence of the wormhole existing,” Toby Wiseman, a professor of theoretical physics at the Imperial College London who was not a part of the study, told New Scientist . “Apart from the crazy matter that makes up the wormhole, there’s nothing too wild being postulated here, and then the consequence is something even more crazy.”

You can decide for yourself if proposing a method for time travel is “too wild.” But wild or not, scientists remain dedicated to truly understanding all of the laws of time and space —and exactly how we can bend them to make the coolest things possible.

Jackie is a writer and editor from Pennsylvania. She's especially fond of writing about space and physics, and loves sharing the weird wonders of the universe with anyone who wants to listen. She is supervised in her home office by her two cats.

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What Are Wormholes, and Could They Be the Answer to Time Travel?

Wormholes, cosmic tunnels also known as einstein-rosen bridges, are a staple of science fiction. could they allow real-world humans to travel back in time.

The sci-fi landscape is littered with wormholes. From Douglas Adam's Hitchhiker's Guide to the Galaxy and Rick and Morty to the Marvel Cinematic Universe, these theoretical constructs allow characters to zip between distant points in the universe as easy as stepping through a doorway.

An Einstein-Rosen bridge is the simplest kind of wormhole. And while it can, in theory, allow you to meet a new friend from a distant part of the universe, there are some important reasons why it won’t let you travel back in time.

Black Holes, White Holes and Wormholes

Let’s start with everybody’s favorite astronomical mystery: a black hole . Despite their fearsome reputation, they’re actually rather simple creature. They have a point of infinite density, known as the singularity, in their centers. They are surrounded by a boundary called the event horizon.

The event horizon doesn’t exist in the same way that the surface of a planet exists. Instead it’s just a mathematical line in the sand that tells you one thing: if you cross within that special distance, you’re trapped forever, because you’ll have to travel faster than the speed of light to escape.

Read More: 'Fuzzballs' Might Be the Answer to a Decades-Old Paradox About Black Holes

And that’s it. That’s a black hole. A singularity and an event horizon. All things that cross the event horizon will never escape back into the universe – things go in and never come out.

Mathematically we can also define the polar opposite of a black hole, which is conveniently called a white hole. White holes also have a singularity, but their event horizons act differently. Anything already on the outside of a white hole (like, the entire universe) can never, ever cross within it, no matter how hard it tries. And anything already inside the white hole will find itself ejected from it faster than the speed of light.

Now when we take a black hole and a white hole and connect their singularities together, we get an entirely new kind of object: an Einstein-Rosen bridge , better known as a wormhole.

Read More: Astronomers Found a Baffling Black Hole That Existed 13 Billion Years Ago

What Is a Wormhole?

Wormholes are essentially hollow tubes through space and time that can connect very distant regions of the universe. A star may be thousands of light-years away, but a wormhole can connect that star to us with a tunnel only a few steps long.

Wormholes also have the somewhat mystical ability to allow backwards time travel. If you take one end of the wormhole and accelerate it to a speed close to that of light, it will experience time dilation — its internal “clock” will run slower than the rest of the universe.

That will cause the two ends of the wormhole to no longer be synchronized in time. Then you could walk in one end and end up in your own past. Voilà: time travel.

Read More: Is There a Particle That Can Travel Back in Time?

Can Humans Travel Through Wormholes?

There's just one, tiny, teensy problem with this setup: Einstein-Rosen bridges are indeed wormholes, but the entrance to the wormhole sits behind the black hole event horizon. And the number one rule of black hole event horizons is that once you cross them, you’re never allowed to escape. Ever.

Once you pass through a black hole event horizon, you are forced towards the singularity, where you are guaranteed to meet your gruesome end. In other words, once you enter an Einstein-Rosen bridge, you will never escape.

So, the unfortunate truth with Einstein-Rosen bridges is that while they appear to be magical doorways to distant reaches of the universe, they are just as deadly as black holes. When you enter you can meet other travelers who have fallen in from the other side, and you could even carry on a conversation…briefly, before you both struck the singularity.

There have been attempts to stabilize Einstein-Rosen bridges and make them traversable by somehow getting their entrances to sit outside the event horizon. So far the only way we know how to do this is with exotic matter. If you threaded the wormhole tunnel with matter that had negative mass, then in principle you could have a not-deadly-at-all wormhole.

Alas, negative matter does not appear to exist in the universe, and so our wormhole — and time travel — dreams will have to remain as mere mathematical fantasies.

Read More: What Did Einstein's Theories Say About the Illusion of Time?

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Wormhole Is Best Bet for Time Machine, Astrophysicist Says

The concept of a time machine typically conjures up images of an implausible plot device used in a few too many science-fiction storylines. But according to Albert Einstein's general theory of relativity, which explains how gravity operates in the universe, real-life time travel isn't just a vague fantasy.

Traveling forward in time is an uncontroversial possibility, according to Einstein's theory. In fact, physicists have been able to send tiny particles called muons , which are similar to electrons, forward in time by manipulating the gravity around them. That's not to say the technology for sending humans 100 years into the future will be available anytime soon, though.

Time travel to the past, however, is even less understood. Still, astrophysicist Eric W. Davis, of the EarthTech International Institute for Advanced Studies at Austin, argues that it's possible. All you need, he says, is a wormhole , which is a theoretical passageway through space-time that is predicted by relativity. [ Wacky Physics: The Coolest Little Particles in Nature ]

"You can go into the future or into the past using traversable wormholes," Davis told LiveScience.

Where's my wormhole?

Wormholes have never been proven to exist, and if they are ever found, they are likely to be so tiny that a person couldn't fit inside, never mind a spaceship.

Even so, Davis' paper, published in July in the American Institute of Aeronautics and Astronautics' journal, addresses time machines and the possibility that a wormhole could become, or be used as, a means for traveling backward in time.

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Both general-relativity theory and quantum theory appear to offer several possibilities for traveling along what physicists call a "closed, timelike curve," or a path that cuts through time and space — essentially, a time machine.

In fact, Davis said, scientists' current understanding of the laws of physics "are infested with time machines whereby there are numerous space-time geometry solutions that exhibit time travel and/or have the properties of time machines."

A wormhole would allow a ship, for instance, to travel from one point to another faster than the speed of light — sort of. That's because the ship would arrive at its destination sooner than a beam of light would, by taking a shortcut through space-time via the wormhole. That way, the vehicle doesn't actually break the rule of the so-called universal speed limit — the speed of light — because the ship never actually travels at a speed faster than light. [ Warped Physics: 10 Effects of Traveling Faster Than Light ]

Theoretically, a wormhole could be used to cut not just through space, but through time as well. 

" Time machines are unavoidable in our physical dimensional space-time," David wrote in his paper. "Traversable wormholes imply time machines, and [the prediction of wormholes] spawned a number of follow-on research efforts on time machines."

However, Davis added, turning a wormhole into a time machine won't be easy. "It would take a Herculean effort to turn a wormhole into a time machine. It's going to be tough enough to pull off a wormhole," he told LiveScience.

That's because once a wormhole is created, one or both ends of it would need to be accelerated through time to the desired position, according to general relativity theory.

Challenges ahead

There are several theories for how the laws of physics might work to prevent time travel through wormholes .

"Not only do we assume [time travel into the past] will not be possible in our lifetime, but we assume that the laws of physics, when fully understood, will rule it out entirely," said Robert Owen, an astrophysicist at Oberlin College in Ohio who specializes in black holes and gravitation theory.

According to scientists' current understanding, keeping a wormhole stable enough to traverse requires large amounts of exotic matter, a substance that is still very poorly understood.  

General relativity can't account for exotic matter — according to general relativity, exotic matter can't exist. But exotic matter does exist . That's where quantum theory comes in. Like general relativity, quantum theory is a system for explaining the universe, kind of like a lens through which scientists observe the universe. [ Video – How to Time Travel ]

However, exotic matter has only been observed in very small amounts — not nearly enough to hold open a wormhole. Physicists would have to find a way to generate and harness large amounts of exotic matter if they hope to achieve this quasi-faster-than-light travel and, by extension, time travel.

Furthermore, other physicists have used quantum mechanics to posit that trying to travel through a wormhole would create something called a quantum back reaction.

In a quantum back reaction, the act of turning a wormhole into a time machine would cause a massive buildup of energy, ultimately destroying the wormhole just before it could be used as a time machine.

However, the mathematical model used to calculate quantum back reaction only takes into account one dimension of space-time.

"I am confident that, since [general relativity] theory has not failed yet, that its predictions for time machines, warp drives and wormholes remain valid and testable, regardless of what quantum theory has to say about those subjects," Davis added.

This illustrates one of the key problems in theories of time travel: physicists have to ground their arguments in either general relativity or quantum theory, both of which are incomplete and unable to encompass the entirety of our complex, mysterious universe.

Before they can figure out time travel, physicists need to find a way to reconcile general relativity and quantum theory into a quantum theory of gravity. That theory will then serve as the basis for further study of time travel.

Therefore, Owen argues that it's impossible to be certain of whether time travel is possible yet. "The wormhole-based time-machine idea takes into account general relativity, but it leaves out quantum mechanics," Owen added. "But including quantum mechanics in the calculations seems to show us that the time machine couldn't actually work the way we hope."

Davis, however, believes scientists have discovered all they can about time machines from theory alone, and calls on physicists to focus first on faster-than-light travel. 

"Until someone makes a wormhole or a warp drive , there's no use getting hyped up about a time machine," Davis told LiveScience.

Accomplishing this will require a universally accepted quantum gravity theory — an immense challenge — so don't go booking those time-travel plans just yet.

Email  [email protected] or follow her @JillScharr . Follow LiveScience @livescience , Facebook  & Google+ . Original article on  LiveScience .

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How to time travel with wormholes

Brian Greene ,   professor of physics and mathematics at Columbia University and co-founder of the World Science Festival , explains what we know about time travel so far. Following is a transcript of the video.

Brian Greene: I’m Brian Greene, professor of physics and mathematics at Columbia University and co-founder of the World Science Festival.

It's critical that you realize that there are two types of time travel , and they are radically different. Time travel to the future? Definitely possible.

We know how to do it because Einstein showed us the way over a hundred years ago. It’s surprising how few people actually really know about this in their bones. He showed that if you go out into space and travel near the speed of light, and you turn around, and you come back, your clock will be ticking off time more slowly. So, when you step off it's going to be the future on planet Earth. You will have time traveled into the future.

He also showed that if you hang out near a nice strong source of gravity — a neutron star, a black hole — and you kind of get right near the edge of that object, time also for you would slow down real slow relative to everybody else. And therefore, when you come back to Earth, for instance, it'll again be far into the future.

This is not controversial stuff. Any physicist who knows what they're talking about agrees with this. But the other kind of time travel — to the past is where the arguments start to happen because many of us don't think that time travel to the past is possible.

The main proposal that people at least consider worthy of attention for traveling to the past does make use of a weird concept called wormholes . A wormhole is something that really … Albert Einstein again discovered. The guy has like got his name written over everything in this field.

It's a bridge, if you will, from one location space to another. It's kind of a tunnel that gives you a shortcut to go from here to here. Now he discovered this in 1935 but it was subsequently realized that if you manipulate the openings of a wormhole — put one near a black hole or take one on a high-speed journey — then time of the two openings of this wormhole tunnel will not take off at the same rate, so that you will no longer just go from one location in space to another, if you go through this tunnel — through this wormhole — you'll go from one moment in time to a different moment in time. Go one way, you'll travel to the past, the other way, travel to the future.

Now again, we don't know if wormholes are real. We don't know if they are real whether you'll be able to go through them. So, there are all sorts of uncertainties here. Most of us think that you're not going to actually go on a whirlwind journey through a wormhole to the past. But it's still not ruled out.

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The Missing Piece: Are Wormholes the Key to Time Travel?

Time travel -- it's a concept we're all too familiar with. From Hollywood Movies (shout out to Back to the Future) to theoretical physics, many theories have circulated regarding the bewildering topic of time travel. However, recently students at the California Institute of Technology1 have shed new light on a relatively dated theory: that wormholes may be the missing piece in the seemingly unsolvable puzzle behind time travel. So, step aside Doc Brown, because we're going to explore how a unique and mysterious part of our universe- the wormhole- connects to traveling through time!

Just like many principles in Physics, this concept finds its base in Einstein's Theory of General Relativity (for some background on this topic, view our previous blog post, "What happens to Matter inside a Black Hole?"). Basically, the theory attributes the characteristics of a wormhole to its incredibly high velocity. Similar to a black hole, a wormhole would compress an entering object to the size of a singularity and accelerate it to immeasurable speeds through the "throat" of the wormhole to the other side of the funnel. So, for now, think of a wormhole as a black hole that has a start and end point.2

Now, this is where the physics becomes complex. We know that a wormhole can basically "teleport" compressed objects at super speeds from one end to another, but how does that explain the time travel aspect? Well, the concept of time dilation can explain that. Time dilation is the relative difference in the passage of time between two entities due to a stark difference in either gravity or relative velocity. In the case of the wormhole, both are in play, which only compounds the effects. For a tangible example to grasp, let's look to the astronauts aboard the International Space Station. After 6 months aboard the ISS (where there is less gravity, but greater velocity of movement), these astronauts have actually aged .007 seconds less than the crew stationed on Earth.3 While this seems insignificant, we have to remember that because the velocity is increased but the gravity is decreased, each is actually mitigating the effects of the other. However, in a wormhole, where the effects of both gravity and velocity are exponentially amplified AND working in tandem, their relativistic effects are enormous.4

This graphic portrays an accurate depiction of velocities' effect on time dilation: http://upload.wikimedia.org/wikipedia/commons/7/72/Nonsymmetric_velocity_time_dilation.gif

Now that we have an understanding of time dilation, we want to leave you with this example. Imagine two test subjects at each side of a wormhole in the year 1995. One mouth of the wormhole has been accelerated to a point where relativistic effects (i.e. time dilation) apply significantly and the other mouth is stationary. When the two subjects pass through their respective mouths, they end up at where their counterpart stood... but at different times! The accelerated mouth would land its test subject in, let's say, 2000. However, the stationary mouth would place its test subject in a later year - we'll call it 2005- since the accelerated mouth exists in a different time caused by time dilation. The time travel becomes evident when we consider the following: what if the test subject who landed in 2005 stepped back into the mouth? They would end up in the year 2000, or 5 years in the past! A bit of manipulation, therefore, could technically transport this subject to any point in time between 2000 and 2005.5

Unfortunately, scientists have been unable to totally grasp how we could adapt the power of a wormhole into time machine-esq technology. We have yet to even theorize how we could accelerate a wormhole to relativistic speeds. Given that this is another theoretical aspect of our known universe, testing is extremely limited and all postulates have very little opportunity for tangible proof. What is certain, though, is that the advances we've made thus far in the field have brought us several pieces closer to solving the time traveler's puzzle!

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• January 23, 2014 The Search for the God Particle
• January 21, 2014 Can We Make the Jump?
• September 07, 2013 An Enlightening View of Solar Eclipses
• September 02, 2013 Sunny Side Down: The Future Destruction of the Sun
• August 28, 2013 The Missing Piece: Are Wormholes the Key to Tim...
• July 30, 2013 What Happens to Matter Inside a Black Hole?

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Is time travel even possible? An astrophysicist explains the science behind the science fiction

Published: Nov 13, 2023

By: Magazine Editor

Written by Adi Foord , assistant professor of physics , UMBC

Curious Kids is a series for children of all ages. If you have a question you’d like an expert to answer, send it to [email protected] .

Will it ever be possible for time travel to occur? – Alana C., age 12, Queens, New York

Have you ever dreamed of traveling through time, like characters do in science fiction movies? For centuries, the concept of time travel has captivated people’s imaginations. Time travel is the concept of moving between different points in time, just like you move between different places. In movies, you might have seen characters using special machines, magical devices or even hopping into a futuristic car to travel backward or forward in time.

But is this just a fun idea for movies, or could it really happen?

The question of whether time is reversible remains one of the biggest unresolved questions in science. If the universe follows the laws of thermodynamics , it may not be possible. The second law of thermodynamics states that things in the universe can either remain the same or become more disordered over time.

It’s a bit like saying you can’t unscramble eggs once they’ve been cooked. According to this law, the universe can never go back exactly to how it was before. Time can only go forward, like a one-way street.

Time is relative

However, physicist Albert Einstein’s theory of special relativity suggests that time passes at different rates for different people. Someone speeding along on a spaceship moving close to the speed of light – 671 million miles per hour! – will experience time slower than a person on Earth.

People have yet to build spaceships that can move at speeds anywhere near as fast as light, but astronauts who visit the International Space Station orbit around the Earth at speeds close to 17,500 mph. Astronaut Scott Kelly has spent 520 days at the International Space Station, and as a result has aged a little more slowly than his twin brother – and fellow astronaut – Mark Kelly. Scott used to be 6 minutes younger than his twin brother. Now, because Scott was traveling so much faster than Mark and for so many days, he is 6 minutes and 5 milliseconds younger .

Some scientists are exploring other ideas that could theoretically allow time travel. One concept involves wormholes , or hypothetical tunnels in space that could create shortcuts for journeys across the universe. If someone could build a wormhole and then figure out a way to move one end at close to the speed of light – like the hypothetical spaceship mentioned above – the moving end would age more slowly than the stationary end. Someone who entered the moving end and exited the wormhole through the stationary end would come out in their past.

However, wormholes remain theoretical: Scientists have yet to spot one. It also looks like it would be incredibly challenging to send humans through a wormhole space tunnel.

Paradoxes and failed dinner parties

There are also paradoxes associated with time travel. The famous “ grandfather paradox ” is a hypothetical problem that could arise if someone traveled back in time and accidentally prevented their grandparents from meeting. This would create a paradox where you were never born, which raises the question: How could you have traveled back in time in the first place? It’s a mind-boggling puzzle that adds to the mystery of time travel.

Famously, physicist Stephen Hawking tested the possibility of time travel by throwing a dinner party where invitations noting the date, time and coordinates were not sent out until after it had happened. His hope was that his invitation would be read by someone living in the future, who had capabilities to travel back in time. But no one showed up.

As he pointed out : “The best evidence we have that time travel is not possible, and never will be, is that we have not been invaded by hordes of tourists from the future.”

Telescopes are time machines

Interestingly, astrophysicists armed with powerful telescopes possess a unique form of time travel. As they peer into the vast expanse of the cosmos, they gaze into the past universe. Light from all galaxies and stars takes time to travel, and these beams of light carry information from the distant past. When astrophysicists observe a star or a galaxy through a telescope, they are not seeing it as it is in the present, but as it existed when the light began its journey to Earth millions to billions of years ago. https://www.youtube.com/embed/QeRtcJi3V38?wmode=transparent&start=0 Telescopes are a kind of time machine – they let you peer into the past.

NASA’s newest space telescope, the James Webb Space Telescope , is peering at galaxies that were formed at the very beginning of the Big Bang, about 13.7 billion years ago.

While we aren’t likely to have time machines like the ones in movies anytime soon, scientists are actively researching and exploring new ideas. But for now, we’ll have to enjoy the idea of time travel in our favorite books, movies and dreams.

This article is republished from The Conversation under a Creative Commons license. Read the original article and see more than 250 UMBC articles available in The Conversation.

Tags: CNMS , Physics , The Conversation

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April 15, 2019

Travel through wormholes is possible, but slow

by American Institute of Physics

A Harvard physicist has shown that wormholes can exist: tunnels in curved space-time, connecting two distant places, through which travel is possible.

But don't pack your bags for a trip to other side of the galaxy yet; although it's theoretically possible, it's not useful for humans to travel through, said the author of the study, Daniel Jafferis, from Harvard University, written in collaboration with Ping Gao, also from Harvard and Aron Wall from Stanford University.

"It takes longer to get through these wormholes than to go directly, so they are not very useful for space travel ," Jafferis said. He will present his findings at the 2019 American Physical Society April Meeting in Denver.

Despite his pessimism for pan-galactic travel, he said that finding a way to construct a wormhole through which light could travel was a boost in the quest to develop a theory of quantum gravity.

"The real import of this work is in its relation to the black hole information problem and the connections between gravity and quantum mechanics ," Jafferis said.

The new theory was inspired when Jafferis began thinking about two black holes that were entangled on a quantum level, as formulated in the ER=EPR correspondence by Juan Maldacena from the Institute for Advanced Study and Lenny Susskind from Stanford. Although this means the direct connection between the black holes is shorter than the wormhole connection—and therefore the wormhole travel is not a shortcut—the theory gives new insights into quantum mechanics.

"From the outside perspective, travel through the wormhole is equivalent to quantum teleportation using entangled black holes," Jafferis said.

Jafferis based his theory on a setup first devised by Einstein and Rosen in 1935, consisting of a connection between two black holes (the term wormhole was coined in 1957). Because the wormhole is traversable, Jafferis said, it was a special case in which information could be extracted from a black hole.

"It gives a causal probe of regions that would otherwise have been behind a horizon, a window to the experience of an observer inside a spacetime, that is accessible from the outside," said Jafferis.

To date, a major stumbling block in formulating traversable wormholes has been the need for negative energy, which seemed to be inconsistent with quantum gravity. However, Jafferis has overcome this using quantum field theory tools, calculating quantum effects similar to the Casimir effect.

"I think it will teach us deep things about the gauge/gravity correspondence, quantum gravity, and even perhaps a new way to formulate quantum mechanics," Jafferis said.

Provided by American Institute of Physics

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Is time travel even possible? An astrophysicist explains the science behind the science fiction

Assistant Professor of Astronomy and Astrophysics, University of Maryland, Baltimore County

Disclosure statement

Adi Foord does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

University of Maryland, Baltimore County provides funding as a member of The Conversation US.

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Curious Kids is a series for children of all ages. If you have a question you’d like an expert to answer, send it to [email protected] .

Will it ever be possible for time travel to occur? – Alana C., age 12, Queens, New York

Have you ever dreamed of traveling through time, like characters do in science fiction movies? For centuries, the concept of time travel has captivated people’s imaginations. Time travel is the concept of moving between different points in time, just like you move between different places. In movies, you might have seen characters using special machines, magical devices or even hopping into a futuristic car to travel backward or forward in time.

But is this just a fun idea for movies, or could it really happen?

The question of whether time is reversible remains one of the biggest unresolved questions in science. If the universe follows the laws of thermodynamics , it may not be possible. The second law of thermodynamics states that things in the universe can either remain the same or become more disordered over time.

It’s a bit like saying you can’t unscramble eggs once they’ve been cooked. According to this law, the universe can never go back exactly to how it was before. Time can only go forward, like a one-way street.

Time is relative

However, physicist Albert Einstein’s theory of special relativity suggests that time passes at different rates for different people. Someone speeding along on a spaceship moving close to the speed of light – 671 million miles per hour! – will experience time slower than a person on Earth.

People have yet to build spaceships that can move at speeds anywhere near as fast as light, but astronauts who visit the International Space Station orbit around the Earth at speeds close to 17,500 mph. Astronaut Scott Kelly has spent 520 days at the International Space Station, and as a result has aged a little more slowly than his twin brother – and fellow astronaut – Mark Kelly. Scott used to be 6 minutes younger than his twin brother. Now, because Scott was traveling so much faster than Mark and for so many days, he is 6 minutes and 5 milliseconds younger .

Some scientists are exploring other ideas that could theoretically allow time travel. One concept involves wormholes , or hypothetical tunnels in space that could create shortcuts for journeys across the universe. If someone could build a wormhole and then figure out a way to move one end at close to the speed of light – like the hypothetical spaceship mentioned above – the moving end would age more slowly than the stationary end. Someone who entered the moving end and exited the wormhole through the stationary end would come out in their past.

However, wormholes remain theoretical: Scientists have yet to spot one. It also looks like it would be incredibly challenging to send humans through a wormhole space tunnel.

Paradoxes and failed dinner parties

There are also paradoxes associated with time travel. The famous “ grandfather paradox ” is a hypothetical problem that could arise if someone traveled back in time and accidentally prevented their grandparents from meeting. This would create a paradox where you were never born, which raises the question: How could you have traveled back in time in the first place? It’s a mind-boggling puzzle that adds to the mystery of time travel.

Famously, physicist Stephen Hawking tested the possibility of time travel by throwing a dinner party where invitations noting the date, time and coordinates were not sent out until after it had happened. His hope was that his invitation would be read by someone living in the future, who had capabilities to travel back in time. But no one showed up.

As he pointed out : “The best evidence we have that time travel is not possible, and never will be, is that we have not been invaded by hordes of tourists from the future.”

Telescopes are time machines

Interestingly, astrophysicists armed with powerful telescopes possess a unique form of time travel. As they peer into the vast expanse of the cosmos, they gaze into the past universe. Light from all galaxies and stars takes time to travel, and these beams of light carry information from the distant past. When astrophysicists observe a star or a galaxy through a telescope, they are not seeing it as it is in the present, but as it existed when the light began its journey to Earth millions to billions of years ago.

NASA’s newest space telescope, the James Webb Space Telescope , is peering at galaxies that were formed at the very beginning of the Big Bang, about 13.7 billion years ago.

While we aren’t likely to have time machines like the ones in movies anytime soon, scientists are actively researching and exploring new ideas. But for now, we’ll have to enjoy the idea of time travel in our favorite books, movies and dreams.

Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to [email protected] . Please tell us your name, age and the city where you live.

And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.

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Time travel: Is it possible?

Science says time travel is possible, but probably not in the way you're thinking.

Albert Einstein's theory

• General relativity and GPS
• Wormhole travel
• Alternate theories

Science fiction

Is time travel possible? Short answer: Yes, and you're doing it right now — hurtling into the future at the impressive rate of one second per second. 

You're pretty much always moving through time at the same speed, whether you're watching paint dry or wishing you had more hours to visit with a friend from out of town. 

But this isn't the kind of time travel that's captivated countless science fiction writers, or spurred a genre so extensive that Wikipedia lists over 400 titles in the category "Movies about Time Travel." In franchises like " Doctor Who ," " Star Trek ," and "Back to the Future" characters climb into some wild vehicle to blast into the past or spin into the future. Once the characters have traveled through time, they grapple with what happens if you change the past or present based on information from the future (which is where time travel stories intersect with the idea of parallel universes or alternate timelines). 

Related: The best sci-fi time machines ever

Although many people are fascinated by the idea of changing the past or seeing the future before it's due, no person has ever demonstrated the kind of back-and-forth time travel seen in science fiction or proposed a method of sending a person through significant periods of time that wouldn't destroy them on the way. And, as physicist Stephen Hawking pointed out in his book " Black Holes and Baby Universes" (Bantam, 1994), "The best evidence we have that time travel is not possible, and never will be, is that we have not been invaded by hordes of tourists from the future."

Science does support some amount of time-bending, though. For example, physicist Albert Einstein 's theory of special relativity proposes that time is an illusion that moves relative to an observer. An observer traveling near the speed of light will experience time, with all its aftereffects (boredom, aging, etc.) much more slowly than an observer at rest. That's why astronaut Scott Kelly aged ever so slightly less over the course of a year in orbit than his twin brother who stayed here on Earth. 

Related: Controversially, physicist argues that time is real

There are other scientific theories about time travel, including some weird physics that arise around wormholes , black holes and string theory . For the most part, though, time travel remains the domain of an ever-growing array of science fiction books, movies, television shows, comics, video games and more. 

Einstein developed his theory of special relativity in 1905. Along with his later expansion, the theory of general relativity , it has become one of the foundational tenets of modern physics. Special relativity describes the relationship between space and time for objects moving at constant speeds in a straight line. 

The short version of the theory is deceptively simple. First, all things are measured in relation to something else — that is to say, there is no "absolute" frame of reference. Second, the speed of light is constant. It stays the same no matter what, and no matter where it's measured from. And third, nothing can go faster than the speed of light.

From those simple tenets unfolds actual, real-life time travel. An observer traveling at high velocity will experience time at a slower rate than an observer who isn't speeding through space. 

While we don't accelerate humans to near-light-speed, we do send them swinging around the planet at 17,500 mph (28,160 km/h) aboard the International Space Station . Astronaut Scott Kelly was born after his twin brother, and fellow astronaut, Mark Kelly . Scott Kelly spent 520 days in orbit, while Mark logged 54 days in space. The difference in the speed at which they experienced time over the course of their lifetimes has actually widened the age gap between the two men.

"So, where[as] I used to be just 6 minutes older, now I am 6 minutes and 5 milliseconds older," Mark Kelly said in a panel discussion on July 12, 2020, Space.com previously reported . "Now I've got that over his head."

General relativity and GPS time travel

The difference that low earth orbit makes in an astronaut's life span may be negligible — better suited for jokes among siblings than actual life extension or visiting the distant future — but the dilation in time between people on Earth and GPS satellites flying through space does make a difference. 

Read more: Can we stop time?

The Global Positioning System , or GPS, helps us know exactly where we are by communicating with a network of a few dozen satellites positioned in a high Earth orbit. The satellites circle the planet from 12,500 miles (20,100 kilometers) away, moving at 8,700 mph (14,000 km/h). 

According to special relativity, the faster an object moves relative to another object, the slower that first object experiences time. For GPS satellites with atomic clocks, this effect cuts 7 microseconds, or 7 millionths of a second, off each day, according to the American Physical Society publication Physics Central .  

Read more: Could Star Trek's faster-than-light warp drive actually work?

Then, according to general relativity, clocks closer to the center of a large gravitational mass like Earth tick more slowly than those farther away. So, because the GPS satellites are much farther from the center of Earth compared to clocks on the surface, Physics Central added, that adds another 45 microseconds onto the GPS satellite clocks each day. Combined with the negative 7 microseconds from the special relativity calculation, the net result is an added 38 microseconds. 

This means that in order to maintain the accuracy needed to pinpoint your car or phone — or, since the system is run by the U.S. Department of Defense, a military drone — engineers must account for an extra 38 microseconds in each satellite's day. The atomic clocks onboard don’t tick over to the next day until they have run 38 microseconds longer than comparable clocks on Earth.

Given those numbers, it would take more than seven years for the atomic clock in a GPS satellite to un-sync itself from an Earth clock by more than a blink of an eye. (We did the math: If you estimate a blink to last at least 100,000 microseconds, as the Harvard Database of Useful Biological Numbers does, it would take thousands of days for those 38 microsecond shifts to add up.) 

This kind of time travel may seem as negligible as the Kelly brothers' age gap, but given the hyper-accuracy of modern GPS technology, it actually does matter. If it can communicate with the satellites whizzing overhead, your phone can nail down your location in space and time with incredible accuracy. 

Can wormholes take us back in time?

General relativity might also provide scenarios that could allow travelers to go back in time, according to NASA . But the physical reality of those time-travel methods is no piece of cake. 

Wormholes are theoretical "tunnels" through the fabric of space-time that could connect different moments or locations in reality to others. Also known as Einstein-Rosen bridges or white holes, as opposed to black holes, speculation about wormholes abounds. But despite taking up a lot of space (or space-time) in science fiction, no wormholes of any kind have been identified in real life. 

Related: Best time travel movies

"The whole thing is very hypothetical at this point," Stephen Hsu, a professor of theoretical physics at the University of Oregon, told Space.com sister site Live Science . "No one thinks we're going to find a wormhole anytime soon."

Primordial wormholes are predicted to be just 10^-34 inches (10^-33 centimeters) at the tunnel's "mouth". Previously, they were expected to be too unstable for anything to be able to travel through them. However, a study claims that this is not the case, Live Science reported . 

The theory, which suggests that wormholes could work as viable space-time shortcuts, was described by physicist Pascal Koiran. As part of the study, Koiran used the Eddington-Finkelstein metric, as opposed to the Schwarzschild metric which has been used in the majority of previous analyses.

In the past, the path of a particle could not be traced through a hypothetical wormhole. However, using the Eddington-Finkelstein metric, the physicist was able to achieve just that.

Koiran's paper was described in October 2021, in the preprint database arXiv , before being published in the Journal of Modern Physics D.

Alternate time travel theories

While Einstein's theories appear to make time travel difficult, some researchers have proposed other solutions that could allow jumps back and forth in time. These alternate theories share one major flaw: As far as scientists can tell, there's no way a person could survive the kind of gravitational pulling and pushing that each solution requires.

Infinite cylinder theory

Astronomer Frank Tipler proposed a mechanism (sometimes known as a Tipler Cylinder ) where one could take matter that is 10 times the sun's mass, then roll it into a very long, but very dense cylinder. The Anderson Institute , a time travel research organization, described the cylinder as "a black hole that has passed through a spaghetti factory."

After spinning this black hole spaghetti a few billion revolutions per minute, a spaceship nearby — following a very precise spiral around the cylinder — could travel backward in time on a "closed, time-like curve," according to the Anderson Institute. 

The major problem is that in order for the Tipler Cylinder to become reality, the cylinder would need to be infinitely long or be made of some unknown kind of matter. At least for the foreseeable future, endless interstellar pasta is beyond our reach.

Time donuts

Theoretical physicist Amos Ori at the Technion-Israel Institute of Technology in Haifa, Israel, proposed a model for a time machine made out of curved space-time — a donut-shaped vacuum surrounded by a sphere of normal matter.

"The machine is space-time itself," Ori told Live Science . "If we were to create an area with a warp like this in space that would enable time lines to close on themselves, it might enable future generations to return to visit our time."

Amos Ori is a theoretical physicist at the Technion-Israel Institute of Technology in Haifa, Israel. His research interests and publications span the fields of general relativity, black holes, gravitational waves and closed time lines.

There are a few caveats to Ori's time machine. First, visitors to the past wouldn't be able to travel to times earlier than the invention and construction of the time donut. Second, and more importantly, the invention and construction of this machine would depend on our ability to manipulate gravitational fields at will — a feat that may be theoretically possible but is certainly beyond our immediate reach.

Time travel has long occupied a significant place in fiction. Since as early as the "Mahabharata," an ancient Sanskrit epic poem compiled around 400 B.C., humans have dreamed of warping time, Lisa Yaszek, a professor of science fiction studies at the Georgia Institute of Technology in Atlanta, told Live Science .  

Every work of time-travel fiction creates its own version of space-time, glossing over one or more scientific hurdles and paradoxes to achieve its plot requirements. 

Some make a nod to research and physics, like " Interstellar ," a 2014 film directed by Christopher Nolan. In the movie, a character played by Matthew McConaughey spends a few hours on a planet orbiting a supermassive black hole, but because of time dilation, observers on Earth experience those hours as a matter of decades. 

Others take a more whimsical approach, like the "Doctor Who" television series. The series features the Doctor, an extraterrestrial "Time Lord" who travels in a spaceship resembling a blue British police box. "People assume," the Doctor explained in the show, "that time is a strict progression from cause to effect, but actually from a non-linear, non-subjective viewpoint, it's more like a big ball of wibbly-wobbly, timey-wimey stuff." 

Long-standing franchises like the "Star Trek" movies and television series, as well as comic universes like DC and Marvel Comics, revisit the idea of time travel over and over. 

Related: Marvel movies in order: chronological & release order

Here is an incomplete (and deeply subjective) list of some influential or notable works of time travel fiction:

Books about time travel:

• Rip Van Winkle (Cornelius S. Van Winkle, 1819) by Washington Irving
• A Christmas Carol (Chapman & Hall, 1843) by Charles Dickens
• The Time Machine (William Heinemann, 1895) by H. G. Wells
• A Connecticut Yankee in King Arthur's Court (Charles L. Webster and Co., 1889) by Mark Twain
• The Restaurant at the End of the Universe (Pan Books, 1980) by Douglas Adams
• A Tale of Time City (Methuen, 1987) by Diana Wynn Jones
• The Outlander series (Delacorte Press, 1991-present) by Diana Gabaldon
• Harry Potter and the Prisoner of Azkaban (Bloomsbury/Scholastic, 1999) by J. K. Rowling
• Thief of Time (Doubleday, 2001) by Terry Pratchett
• The Time Traveler's Wife (MacAdam/Cage, 2003) by Audrey Niffenegger
• All You Need is Kill (Shueisha, 2004) by Hiroshi Sakurazaka

Movies about time travel:

• Planet of the Apes (1968)
• Superman (1978)
• Time Bandits (1981)
• The Terminator (1984)
• Back to the Future series (1985, 1989, 1990)
• Star Trek IV: The Voyage Home (1986)
• Bill & Ted's Excellent Adventure (1989)
• Groundhog Day (1993)
• Galaxy Quest (1999)
• The Butterfly Effect (2004)
• 13 Going on 30 (2004)
• The Lake House (2006)
• Meet the Robinsons (2007)
• Hot Tub Time Machine (2010)
• Midnight in Paris (2011)
• Looper (2012)
• X-Men: Days of Future Past (2014)
• Edge of Tomorrow (2014)
• Interstellar (2014)
• Doctor Strange (2016)
• A Wrinkle in Time (2018)
• The Last Sharknado: It's About Time (2018)
• Avengers: Endgame (2019)
• Tenet (2020)
• Palm Springs (2020)
• Zach Snyder's Justice League (2021)
• The Tomorrow War (2021)

Television about time travel:

• Doctor Who (1963-present)
• The Twilight Zone (1959-1964) (multiple episodes)
• Star Trek (multiple series, multiple episodes)
• Samurai Jack (2001-2004)
• Lost (2004-2010)
• Phil of the Future (2004-2006)
• Steins;Gate (2011)
• Outlander (2014-2023)
• Loki (2021-present)

Games about time travel:

• Chrono Trigger (1995)
• TimeSplitters (2000-2005)
• Kingdom Hearts (2002-2019)
• Prince of Persia: Sands of Time (2003)
• God of War II (2007)
• Ratchet and Clank Future: A Crack In Time (2009)
• Sly Cooper: Thieves in Time (2013)
• Dishonored 2 (2016)
• Titanfall 2 (2016)
• Outer Wilds (2019)

Additional resources

Explore physicist Peter Millington's thoughts about Stephen Hawking's time travel theories at The Conversation . Check out a kid-friendly explanation of real-world time travel from NASA's Space Place . For an overview of time travel in fiction and the collective consciousness, read " Time Travel: A History " (Pantheon, 2016) by James Gleik. 

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Ailsa is a staff writer for How It Works magazine, where she writes science, technology, space, history and environment features. Based in the U.K., she graduated from the University of Stirling with a BA (Hons) journalism degree. Previously, Ailsa has written for Cardiff Times magazine, Psychology Now and numerous science bookazines. 

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Scientists say time travel via wormholes might actually be possible

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• Scientists have found a way to send humans through wormholes and keep them alive for the journey.
• The theory assumes a lot about various physics models that remain unproven.
• If you were to travel through one, time would pass by thousands of years for everyone else except for you.

If you’re trying to come up with the holy grail of scientific achievement it’s pretty much a tossup between discovering the secret to immortality and developing time travel. We’re certainly not nearing an age where humans can live as long as they choose, but with regards to time travel, a rather tantalizing discovery has just been made.

As you might expect, the research paper gets into some pretty intense math and theoretical setups that might not actually be possible. It relies heavily on the Randall-Sundrum model of physics, primarily because the Standard Model only allows for microscopic wormholes to exist, and if we want to travel through time, we’re going to need a wormhole large enough that a person could pass through it and come out the other end in one piece.

“Better wormholes are possible by using a Randall Sundrum II model with a U(1) gauge field,” the researchers explain. “This model allows for large enough wormholes that could be traversed humanely, i.e. surviving the tidal forces. Using them, one could travel in less than a second between distant points in our galaxy. A second for the observer that goes through the wormhole. It would be tens of thousands of years for somebody looking from the outside.”

Again, this is all theoretical,  but based on the conditions of the wormhole, you could pass through it, and, from an outsider’s point of view, by the time you appeared on the other side you might possibly be the last human alive in the entire universe.

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Understanding Wormholes: A Path To Time Travel?

Have you ever dreamed of traveling through time? It may seem like an impossible feat, but scientists have been exploring the concept of time travel for decades. One theory that has gained momentum in recent years is the idea of using wormholes as a path to time travel.

Wormholes are tunnels in space-time that connect two distant points in the universe. They were first proposed by physicist Albert Einstein's theory of general relativity, and although they have yet to be discovered, they continue to capture our imagination. In this article, we'll explore the science behind wormholes, how they could potentially be used for time travel, and what implications this might have on our understanding of the universe. So buckle up and get ready for a journey through space-time!

The Science Behind Wormholes

Wormholes as shortcuts in space, could wormholes be used for time travel, the implications of time travel, the future of wormhole research, frequently asked questions, what is the history of the concept of wormholes in science fiction, how would the discovery of a stable wormhole affect global politics and economics, what ethical considerations should be taken into account when considering the use of time travel, could wormholes be used for intergalactic travel, what technological advancements would be necessary for practical use of wormholes.

You're about to discover the mind-bending science that could revolutionize our understanding of the universe. To begin with, let's talk about wormhole mechanics. A wormhole is a theoretical concept in physics that suggests the existence of a shortcut between two points in space-time. According to Einstein's theory of relativity, space and time are intertwined, and any massive object warps spacetime around it. Therefore, a wormhole would be formed by connecting two points in spacetime through a tunnel-like structure.

Theoretical physicists have been studying the possibility of wormholes for decades, but it wasn't until recently that they started to understand how they could work. The key lies in the idea of negative energy, which is required to keep a wormhole stable enough for travel. This negative energy would create an anti-gravitational force that could counterbalance the gravitational pull of matter and prevent the collapse of the wormhole. With this knowledge in hand, we can begin to explore how wormholes might serve as shortcuts in space without having to bend or warp time itself.

Imagine taking a cosmic detour that cuts through the fabric of space and shaves off light-years from your journey - wormholes essentially act as galactic bypasses. These shortcuts in space are fascinating phenomena that have intrigued scientists and science fiction enthusiasts alike. As we delve deeper into understanding the science behind wormholes, one important aspect to consider is their stability. While theoretical physicists have proposed the existence of these tunnels connecting two points in space-time, it is still unclear whether they could actually exist or if they would collapse before anything could pass through.

Despite the unknowns surrounding wormhole stability, there are potential practical applications for these cosmic shortcuts. For instance, a stable wormhole could be used to transport cargo or people across vast distances without expending too much energy or time. The concept of using wormholes as portals has also been explored in popular culture, where characters travel between different worlds by hopping through a hole in space-time. However, until we can confirm the existence and stability of wormholes, their use remains purely speculative.

As we explore further into the possibilities that come with understanding wormholes, one question arises: Could these tunnels be used for time travel?

If you're a fan of science fiction, the idea of using shortcuts in space to journey through time may seem like an exciting possibility. But is it really possible? According to some theories in physics, wormholes could be used for time travel. However, this concept raises many questions about paradoxes and limitations.

One major concern with the use of wormholes for time travel is the potential for paradoxes. For example, if someone were to go back in time and prevent their own birth from occurring, how would they have been able to travel back in time in the first place? This creates a loop that seems impossible to resolve. Additionally, there are limitations on the use of wormholes for time travel due to their instability and high energy requirements. It's unclear whether we will ever be able to create or sustain a stable wormhole long enough for human transportation.

These philosophical implications raise important questions about our understanding of time and its relationship with space. What does it mean to truly “travel” through time? Is it possible or simply a fantasy? The implications of time travel extend far beyond scientific theory – they challenge our very perception of reality itself.

The consequences of potentially traveling through temporal dimensions pose a significant challenge to our comprehension of the nature of existence. The concept of time travel is not only fascinating, but it also raises ethical concerns and societal impacts that must be considered. If time travel were possible, one could potentially change the course of history, leading to unforeseen consequences in the present day. This could have severe implications for society as a whole, altering the trajectory of human development and progress.

Moreover, there are also philosophical implications to consider. If we could go back in time or travel to the future, then what does that say about free will? Are we really making choices if we can go back and change them? These are complex questions that require careful consideration before any exploration into time travel is made. Nevertheless, understanding the possibilities offered by wormholes allows us to better comprehend our place in space-time and how it shapes our reality.

As we continue to explore these fascinating scientific concepts, it's important to think critically about their potential impacts on society. The future of wormhole research promises exciting advancements in physics and technology, but it's crucial that we approach these developments with caution and foresight. We must remain mindful of not just what is scientifically possible but also what is ethically responsible.

Scientists are delving deeper into the mysteries of space-time, unlocking new possibilities for interstellar travel and exploration. The future of wormhole research is promising as interdisciplinary collaborations between physicists, mathematicians, and engineers continue to push the boundaries of our understanding. With technological advancements in fields such as quantum mechanics and astrophysics, we may soon be able to harness the power of wormholes for practical applications.

One potential application is time travel. While still a theoretical concept, wormholes could potentially allow us to travel through time by creating a shortcut through space-time. However, there are many challenges that must be overcome before this becomes a reality. For example, we would need to find stable wormholes that can remain open long enough for us to pass through them safely. Nonetheless, with continued research and development in this field, it's exciting to think about what the future holds for interstellar travel and exploration using wormholes.

When it comes to the exploration of wormholes in popular culture, science fiction has played a significant role. The concept of wormholes as shortcuts through space and time has been used in various forms of media, from books to movies. However, the scientific accuracy of wormholes in fiction is often debated. While some authors and filmmakers strive to depict them as realistically as possible based on current theories, others take artistic liberties for the sake of storytelling. Regardless, the idea of traversing through a wormhole remains an intriguing one that continues to capture our imaginations.

As the possibility of discovering a stable wormhole becomes more feasible, the impact on society cannot be understated. The geopolitical implications alone are staggering. With the potential to transport people and goods across vast distances in an instant, entire industries could be disrupted, governments could rise or fall based on access to this technology, and global power dynamics could shift overnight. As the adage goes, "with great power comes great responsibility," and it will be up to those who control this technology to ensure that its benefits are shared equitably among all nations and peoples. The discovery of a stable wormhole would undoubtedly change the course of human history forever, for better or for worse.

When we consider the use of time travel, there are a multitude of moral implications and societal consequences that must be taken into account. The ability to travel through time would undoubtedly have an enormous impact on our world as we know it, both in terms of how we view the past, present, and future but also how we interact with each other. It's important to consider questions such as: Who gets access to this technology? What happens if someone alters the timeline? How do we ensure that people don't use time travel for personal gain or harm others? These are complex ethical considerations that require careful thought and planning before any sort of time travel technology is developed or implemented.

Interstellar transportation is an exciting prospect that could revolutionize the way we explore the universe. While it may seem like science fiction, recent advancements in technology have made intergalactic travel a scientific feasibility. One proposed method for achieving this type of transportation is through the use of wormholes, which are tunnels through space-time that connect distant points in the universe. Although still largely theoretical, scientists believe that harnessing this phenomenon could allow us to travel vast distances and explore new worlds beyond our solar system. However, there are many challenges and risks associated with such a venture, including the potential dangers of navigating unknown territories and ensuring the safety of astronauts over long periods of time. Despite these challenges, interstellar transportation remains an exciting area of research with the potential to unlock some of the greatest mysteries of our universe.

To fully harness the power of wormholes for intergalactic travel, we would need to make significant advancements in quantum mechanics and our understanding of black holes. The ability to manipulate quantum particles and understand their behavior is crucial in creating a stable wormhole that can withstand the immense gravitational forces present near black holes. Furthermore, we must have a deeper understanding of how black holes function and interact with space-time. Only then can we hope to create a practical method of utilizing these cosmic shortcuts for efficient space travel. These technological advancements are not just important for intergalactic travel but also have implications for our fundamental understanding of the universe around us.

So, can wormholes really be a path to time travel? While the science behind wormholes is fascinating and holds promise for space exploration, the idea of using them for time travel remains purely theoretical. The implications of such technology are mind-boggling, but also raise important ethical questions about altering the course of history or creating paradoxes.

Despite these uncertainties, the research into wormholes continues to push the boundaries of our understanding of space-time. Like a diver exploring uncharted depths, scientists are diving deeper into this mysterious phenomenon in hopes of uncovering more secrets and unlocking new possibilities. Wormholes may not lead us to time travel just yet, but they have opened up a whole new realm of possibility that is sure to captivate both scientists and science fiction enthusiasts alike. As we continue to unravel the mysteries of our universe, who knows what other hidden treasures await us?

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An Overview and Comparison by Dr. David Lewis Anderson

Traversability

Faster-than-light travel, time travel.

• Wormhole Engineering