train time travel theory

Einstein’s Relativity Explained in 4 Simple Steps

The revolutionary physicist used his imagination rather than fancy math to come up with his most famous and elegant equation.

Albert Einstein’s theory of relativity is famous for predicting some really weird but true phenomena, like astronauts aging slower than people on Earth and solid objects changing their shapes at high speeds.

But the thing is, if you pick up a copy of Einstein’s original paper on relativity from 1905, it’s a straightforward read. His text is plain and clear, and his equations are mostly just algebra—nothing that would bother a typical high-schooler.

That’s because fancy math was never the point for Einstein. He liked to think visually, coming up with experiments in his mind’s eye and working them around in his head until he could see the ideas and physical principles with crystalline clarity. (Read “ 10 Things You (Probably) Didn’t Know About Einstein. ”)

To bring his process to life, National Geographic created an interactive version of one of Einstein’s most famous thought experiments : a parable about lightning strikes as seen from a moving train that shows how two observers can understand space and time in very different ways.

Here’s how Einstein got started on his thought experiments when he was just 16, and how it eventually led him to the most revolutionary equation in modern physics.

1895: Running Beside a Light Beam

By this point, Einstein’s ill-disguised contempt for his native Germany’s rigid, authoritarian educational methods had already gotten him kicked out of the equivalent of high school, so he moved to Zurich in hopes of attending the Swiss Federal Institute of Technology (ETH). (Also see “ Why the FBI Kept a 1,400-Page File on Einstein .”)

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First, though, Einstein decided to put in a year of preparation at a school in the nearby town of Aarau—a place that stressed avant garde methods like independent thought and visualization of concepts. In that happy environment, he soon he found himself wondering what it would be like to run alongside a light beam.

Einstein had already learned in physics class what a light beam was: a set of oscillating electric and magnetic fields rippling along at 186,000 miles a second, the measured speed of light. If he were to run alongside it at just that speed, Einstein reasoned, he ought to be able to look over and see a set of oscillating electric and magnetic fields hanging right next to him, seemingly stationary in space.

Yet that was impossible. For starters, such stationary fields would violate Maxwell’s equations, the mathematical laws that codified everything physicists at the time knew about electricity, magnetism, and light. The laws were (and are) quite strict: Any ripples in the fields have to move at the speed of light and cannot stand still—no exceptions.

Worse, stationary fields wouldn’t jibe with the principle of relativity, a notion that physicists had embraced since the time of Galileo and Newton in the 17th century. Basically, relativity said that the laws of physics couldn’t depend on how fast you were moving; all you could measure was the velocity of one object relative to another.

But when Einstein applied this principle to his thought experiment, it produced a contradiction: Relativity dictated that anything he could see while running beside a light beam, including the stationary fields, should also be something Earthbound physicists could create in the lab. But nothing like that had ever been observed.

This problem would bug Einstein for another 10 years, all the way through his university work at ETH and his move to the Swiss capital city of Bern, where he became an examiner in the Swiss patent office. That’s where he resolved to crack the paradox once and for all.

1904: Measuring Light From a Moving Train

It wasn’t easy. Einstein tried every solution he could think of, and nothing worked. Almost out of desperation, he began to consider a notion that was simple but radical. Maybe Maxwell’s equations worked for everybody, he thought, but the speed of light was always constant.

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When you saw a light beam zip past, in other words, it wouldn’t matter whether its source was moving toward you, away from you, or off to the side, nor would it matter how fast the source was going. You would always measure that beam’s velocity to be 186,000 miles a second. Among other things, that meant Einstein would never see the stationary, oscillating fields, because he could never catch the light beam.

This was the only way Einstein could see to reconcile Maxwell’s equations with the principle of relativity. At first, though, this solution seemed to have its own fatal flaw. Einstein later explained the problem with another thought experiment: Imagine firing a light beam along a railroad embankment just as a train roars by in the same direction at, say, 2,000 miles a second.

Someone standing on the embankment would measure the light beam’s speed to be the standard number, 186,000 miles a second. But someone on the train would see it moving past at only 184,000 miles a second. If the speed of light was not constant, Maxwell’s equations would somehow have to look different inside the railway carriage, Einstein concluded, and the principle of relativity would be violated.

This apparent contradiction left Einstein spinning his wheels for almost a year. But then, on a beautiful morning in May 1905, he was walking to work with his best friend Michele Besso, an engineer he had known since their student days in Zurich. The two men were talking with about Einstein’s dilemma, as they often did. And suddenly, Einstein saw the solution. He worked on it overnight, and when they met the next morning, Einstein told Besso, “Thank you. I’ve completely solved the problem.”

May 1905: Lightning Strikes a Moving Train

Einstein’s revelation was that observers in relative motion experience time differently: it’s perfectly possible for two events to happen simultaneously from the perspective of one observer, yet happen at different times from the perspective of the other. And both observers would be right.

Einstein later illustrated this point with another thought experiment. Imagine that you once again have an observer standing on a railway embankment as a train goes roaring by. But this time, each end of the train is struck by a bolt of lightning just as the train’s midpoint is passing. Because the lightning strikes are the same distance from the observer, their light reaches his eye at the same instant. So he correctly says that they happened simultaneously.

Meanwhile, another observer on the train is sitting at its exact midpoint. From her perspective, the light from the two strikes also has to travel equal distances, and she will likewise measure the speed of light to be the same in either direction. But because the train is moving, the light coming from the lightning in the rear has to travel farther to catch up, so it reaches her a few instants later than the light coming from the front. Since the light pulses arrived at different times, she can only conclude the strikes were not simultaneous—that the one in front actually happened first.

In short, Einstein realized, simultaneity is what’s relative. Once you accept that, all the strange effects we now associate with relativity are a matter of simple algebra.

Einstein dashed off his ideas in a fever pitch and sent his paper in for publication just a few weeks later. He gave it a title—“ On the Electrodynamics of Moving Bodies ”—that spoke to his struggle to reconcile Maxwell’s equations with the principle of relativity. And he concluded it with a thank you to Besso (“I am indebted to him for several valuable suggestions”) that guaranteed his friend a touch of immortality.

September 1905: Mass and Energy

That first paper wasn’t the end of it, though. Einstein kept obsessing on relativity all through the summer of 1905, and in September he sent in a second paper as a kind of afterthought.

It was based on yet another thought experiment. Imagine an object that’s sitting at rest, he said. And now imagine that it spontaneously emits two identical pulses of light in opposite directions. The object will stay put, but because each pulse carries off a certain amount of energy, the object’s energy content will decrease.

Now, said Einstein, what would this process look like to a moving observer? From her perspective, the object would just keep moving in a straight line while the two pulses flew off. But even though the two pulses’ speed would still be the same—the speed of light—their energies would be different: The pulse moving forward along the direction of motion would now have a higher energy than the one moving backward.

With a little more algebra, Einstein showed that for all this to be consistent, the object not only had to lose energy when the light pulses departed, it had to lose a bit of mass, as well. Or, to put it another way, mass and energy are interchangeable.

Einstein wrote down an equation that relates the two. Using today’s notation, which abbreviates the speed of light using the letter c , he produced easily the most famous equation ever written: E = mc 2 .

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Is Time Travel Possible?

We all travel in time! We travel one year in time between birthdays, for example. And we are all traveling in time at approximately the same speed: 1 second per second.

We typically experience time at one second per second. Credit: NASA/JPL-Caltech

NASA's space telescopes also give us a way to look back in time. Telescopes help us see stars and galaxies that are very far away . It takes a long time for the light from faraway galaxies to reach us. So, when we look into the sky with a telescope, we are seeing what those stars and galaxies looked like a very long time ago.

However, when we think of the phrase "time travel," we are usually thinking of traveling faster than 1 second per second. That kind of time travel sounds like something you'd only see in movies or science fiction books. Could it be real? Science says yes!

This image from the Hubble Space Telescope shows galaxies that are very far away as they existed a very long time ago. Credit: NASA, ESA and R. Thompson (Univ. Arizona)

How do we know that time travel is possible?

More than 100 years ago, a famous scientist named Albert Einstein came up with an idea about how time works. He called it relativity. This theory says that time and space are linked together. Einstein also said our universe has a speed limit: nothing can travel faster than the speed of light (186,000 miles per second).

Einstein's theory of relativity says that space and time are linked together. Credit: NASA/JPL-Caltech

What does this mean for time travel? Well, according to this theory, the faster you travel, the slower you experience time. Scientists have done some experiments to show that this is true.

For example, there was an experiment that used two clocks set to the exact same time. One clock stayed on Earth, while the other flew in an airplane (going in the same direction Earth rotates).

After the airplane flew around the world, scientists compared the two clocks. The clock on the fast-moving airplane was slightly behind the clock on the ground. So, the clock on the airplane was traveling slightly slower in time than 1 second per second.

Credit: NASA/JPL-Caltech

Can we use time travel in everyday life?

We can't use a time machine to travel hundreds of years into the past or future. That kind of time travel only happens in books and movies. But the math of time travel does affect the things we use every day.

For example, we use GPS satellites to help us figure out how to get to new places. (Check out our video about how GPS satellites work .) NASA scientists also use a high-accuracy version of GPS to keep track of where satellites are in space. But did you know that GPS relies on time-travel calculations to help you get around town?

GPS satellites orbit around Earth very quickly at about 8,700 miles (14,000 kilometers) per hour. This slows down GPS satellite clocks by a small fraction of a second (similar to the airplane example above).

GPS satellites orbit around Earth at about 8,700 miles (14,000 kilometers) per hour. Credit: GPS.gov

However, the satellites are also orbiting Earth about 12,550 miles (20,200 km) above the surface. This actually speeds up GPS satellite clocks by a slighter larger fraction of a second.

Here's how: Einstein's theory also says that gravity curves space and time, causing the passage of time to slow down. High up where the satellites orbit, Earth's gravity is much weaker. This causes the clocks on GPS satellites to run faster than clocks on the ground.

The combined result is that the clocks on GPS satellites experience time at a rate slightly faster than 1 second per second. Luckily, scientists can use math to correct these differences in time.

If scientists didn't correct the GPS clocks, there would be big problems. GPS satellites wouldn't be able to correctly calculate their position or yours. The errors would add up to a few miles each day, which is a big deal. GPS maps might think your home is nowhere near where it actually is!

In Summary:

Yes, time travel is indeed a real thing. But it's not quite what you've probably seen in the movies. Under certain conditions, it is possible to experience time passing at a different rate than 1 second per second. And there are important reasons why we need to understand this real-world form of time travel.

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Stephen Hawking's time machine

In an article in the Daily Mail this week, British cosmologist Stephen Hawking outlined not one, but three, theoretically realistic ideas for traveling through time, one of which he says is even practical.

The fourth dimension First, though, you have to get your head around the notion that time is a dimension, just like width, height and length.

Hawking uses the example of driving in your car: You go forward. That's one direction. You turn left or right, that's a second. You journey up a mountain road, that's a third. The fourth dimension is time.

"Time travel movies often feature a vast, energy-hungry machine. The machine creates a path through the fourth dimension , a tunnel through time. A time traveler, a brave, perhaps foolhardy individual, prepared for who knows what, steps into the time tunnel and emerges who knows when. The concept may be far-fetched, and the reality may be very different from this, but the idea itself is not so crazy," Hawking writes.

The laws of physics actually accommodate the notion of time travel, through portals known as wormholes.

"The truth is wormholes are all around us, only they're too small to see. They occur in nooks and crannies in space and time," Hawking writes. "Nothing is flat or solid. If you look closely enough at anything you'll find holes and wrinkles in it. It's a basic physical principle, and it even applies to time. Even something as smooth as a pool ball has tiny crevices, wrinkles and voids.

Quantum foam and tiny wormholes "Down at the smallest of scales, smaller even than molecules, smaller than atoms, we get to a place called the quantum foam. This is where wormholes exist. Tiny tunnels or shortcuts through space and time constantly form, disappear, and reform within this quantum world. And they actually link two separate places and two different times."

The tunnels, unfortunately, are far too small for people to pass through — just a billion-trillion-trillionths of a centimeter -- but physicists believe it may be possible to catch a wormhole and make it big enough for people, or spaceships, to enter, Hawking writes.

"Theoretically, a time tunnel or wormhole could do even more than take us to other planets. If both ends were in the same place, and separated by time instead of distance, a ship could fly in and come out still near Earth, but in the distant past. Maybe dinosaurs would witness the ship coming in for a landing," Hawking writes.

Ultimately, scientists may find that only travel into the future is possible, as the laws of nature may make travel to the past impossible so the relationship between cause and effect is maintained. For example, if you could travel in the past and do something that prevents yourself from being born, how could you exist in the future to travel back in time?

Time as a flowing river Hawking suspects radiation feedback would collapse any wormholes scientists managed to expand to useable sizes, rendering them useless for actual travel. But there's another way — navigating the variable rivers of time.

"Time flows like a river and it seems as if each of us is carried relentlessly along by time's current. But time is like a river in another way. It flows at different speeds in different places, and that is the key to traveling into the future," Hawking writes.

Albert Einstein first proposed this idea 100 years ago that there should be places where time slows down, and others where time speeds up, notes Hawking. "He was absolutely right."

The proof, says Hawking, lies in the Global Positioning System satellite network, which in addition to helping us navigate on Earth, reveals that time runs faster in space.

"Inside each spacecraft is a very precise clock. But despite being so accurate, they all gain around a third of a billionth of a second every day. The system has to correct for the drift, otherwise that tiny difference would upset the whole system, causing every GPS device on Earth to go out by about six miles a day," Hawking writes.

The clocks aren't faulty — it's the pull of Earth that's to blame.

"Einstein realized that matter drags on time and slows it down like the slow part of a river. The heavier the object, the more it drags on time," Hawking writes. "And this startling reality is what opens the door to the possibility of time travel to the future."

Black holes and flying at the speed of light The keys to time travel are black holes, objects so dense that not even light can escape their gravitational grip.

"A black hole ... has a dramatic effect on time, slowing it down far more than anything else in the galaxy. That makes it a natural time machine," Hawking writes.

Here's how it might work:

Imagine a spaceship orbiting the super-massive black hole at the center of the Milky Way galaxy, 26,000 light years away. From Earth, it would look like the ship is making one orbit every 16 minutes, Hawking writes.

"But for the brave people on board, close to this massive object, time would be slowed down," Hawking writes. "For every 16-minute orbit, they'd only experience eight minutes of time."

If they circled for five years, local time, 10 years would have passed back on Earth.

This scenario doesn't produce the paradoxes inherent in wormhole travel, but it's still pretty impractical, Hawking acknowledges.

But there's one more possibility: traveling super fast.

"This is due to another strange fact about the universe," writes Hawking — the cosmic speed limit: 186,000 miles per second, or the speed of light.

"Nothing can exceed that speed. It's one of the best established principles in science," writes Hawking, but "believe it or not, traveling at near the speed of light transports you to the future."

"Imagine a track that goes right around Earth, a track for a super-fast train. Onboard are passengers with a one-way ticket to the future. The train begins to accelerate, faster and faster. Soon it's circling the Earth over and over again.

"To approach the speed of light means circling the Earth seven times a second. But no matter how much power the train has, it can never quite reach the speed of light, since the laws of physics forbid it.

"Instead, let's say it gets close," writes Hawking. "Something extraordinary happens: Time starts flowing slowly on board relative to the rest of the world, just like near the black hole, only more so. Everything on the train is in slow motion."

Speed of light protection This happens to protect the cosmic speed limit, Hawking said. Here's why:

Say there's a child running forward up the train. "Her forward speed is added to the speed of the train, so couldn't she break the speed limit simply by accident? The answer is no," writes Hawking. "The laws of nature prevent the possibility by slowing down time onboard. Now she can't run fast enough to break the limit. Time will always slow down just enough to protect the speed limit."

This is the essence of why time travel into the future is possible.

"Imagine that the train left the station on January 1, 2050. It circles Earth over and over again for 100 years before finally coming to a halt on New Year's Day, 2150. The passengers will have only lived one week because time is slowed down that much inside the train. When they got out they'd find a very different world from the one they'd left. In one week they'd have travelled 100 years into the future," Hawking writes.

Right now, the fastest motion on Earth is taking place in the circular tunnels of the world's largest particle accelerator at CERN, in Geneva.

"When the power is turned on (particles) accelerate from zero to 60,000 mph in a fraction of a second. Increase the power and the particles go faster and faster, until they're whizzing around the tunnel 11,000 times a second, which is almost the speed of light. But just like the train, they never quite reach that ultimate speed. They can only get to 99.99 per cent of the limit. When that happens, they too start to travel in time. We know this because of some extremely short-lived particles, called pimesons. Ordinarily, they disintegrate after just 25 billionths of a second. But when they are accelerated to near-light speed they last 30 times longer."

To accelerate humans to that speed, we'll need to be in space, concludes Hawking, noting that so far, the fastest that people have traveled is 25,000 mph aboard Apollo 10.

"To travel in time we'll have to go more than 2,000 times faster (than Apollo 10).  And to do that we'd need a much bigger ship, a truly enormous machinebig enough to carry a huge amount of fuel, enough to accelerate it to nearly the speed of light. Getting to just beneath the cosmic speed limit would require six whole years at full power.

"We could, in theory, travel extraordinary distances within one lifetime," Hawking writes. "A trip to the edge of the galaxy would take just 80 years."

April 26, 2023

Is Time Travel Possible?

The laws of physics allow time travel. So why haven’t people become chronological hoppers?

By Sarah Scoles

yuanyuan yan/Getty Images

In the movies, time travelers typically step inside a machine and—poof—disappear. They then reappear instantaneously among cowboys, knights or dinosaurs. What these films show is basically time teleportation .

Scientists don’t think this conception is likely in the real world, but they also don’t relegate time travel to the crackpot realm. In fact, the laws of physics might allow chronological hopping, but the devil is in the details.

Time traveling to the near future is easy: you’re doing it right now at a rate of one second per second, and physicists say that rate can change. According to Einstein’s special theory of relativity, time’s flow depends on how fast you’re moving. The quicker you travel, the slower seconds pass. And according to Einstein’s general theory of relativity , gravity also affects clocks: the more forceful the gravity nearby, the slower time goes.

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“Near massive bodies—near the surface of neutron stars or even at the surface of the Earth, although it’s a tiny effect—time runs slower than it does far away,” says Dave Goldberg, a cosmologist at Drexel University.

If a person were to hang out near the edge of a black hole , where gravity is prodigious, Goldberg says, only a few hours might pass for them while 1,000 years went by for someone on Earth. If the person who was near the black hole returned to this planet, they would have effectively traveled to the future. “That is a real effect,” he says. “That is completely uncontroversial.”

Going backward in time gets thorny, though (thornier than getting ripped to shreds inside a black hole). Scientists have come up with a few ways it might be possible, and they have been aware of time travel paradoxes in general relativity for decades. Fabio Costa, a physicist at the Nordic Institute for Theoretical Physics, notes that an early solution with time travel began with a scenario written in the 1920s. That idea involved massive long cylinder that spun fast in the manner of straw rolled between your palms and that twisted spacetime along with it. The understanding that this object could act as a time machine allowing one to travel to the past only happened in the 1970s, a few decades after scientists had discovered a phenomenon called “closed timelike curves.”

“A closed timelike curve describes the trajectory of a hypothetical observer that, while always traveling forward in time from their own perspective, at some point finds themselves at the same place and time where they started, creating a loop,” Costa says. “This is possible in a region of spacetime that, warped by gravity, loops into itself.”

“Einstein read [about closed timelike curves] and was very disturbed by this idea,” he adds. The phenomenon nevertheless spurred later research.

Science began to take time travel seriously in the 1980s. In 1990, for instance, Russian physicist Igor Novikov and American physicist Kip Thorne collaborated on a research paper about closed time-like curves. “They started to study not only how one could try to build a time machine but also how it would work,” Costa says.

Just as importantly, though, they investigated the problems with time travel. What if, for instance, you tossed a billiard ball into a time machine, and it traveled to the past and then collided with its past self in a way that meant its present self could never enter the time machine? “That looks like a paradox,” Costa says.

Since the 1990s, he says, there’s been on-and-off interest in the topic yet no big breakthrough. The field isn’t very active today, in part because every proposed model of a time machine has problems. “It has some attractive features, possibly some potential, but then when one starts to sort of unravel the details, there ends up being some kind of a roadblock,” says Gaurav Khanna of the University of Rhode Island.

For instance, most time travel models require negative mass —and hence negative energy because, as Albert Einstein revealed when he discovered E = mc 2 , mass and energy are one and the same. In theory, at least, just as an electric charge can be positive or negative, so can mass—though no one’s ever found an example of negative mass. Why does time travel depend on such exotic matter? In many cases, it is needed to hold open a wormhole—a tunnel in spacetime predicted by general relativity that connects one point in the cosmos to another.

Without negative mass, gravity would cause this tunnel to collapse. “You can think of it as counteracting the positive mass or energy that wants to traverse the wormhole,” Goldberg says.

Khanna and Goldberg concur that it’s unlikely matter with negative mass even exists, although Khanna notes that some quantum phenomena show promise, for instance, for negative energy on very small scales. But that would be “nowhere close to the scale that would be needed” for a realistic time machine, he says.

These challenges explain why Khanna initially discouraged Caroline Mallary, then his graduate student at the University of Massachusetts Dartmouth, from doing a time travel project. Mallary and Khanna went forward anyway and came up with a theoretical time machine that didn’t require negative mass. In its simplistic form, Mallary’s idea involves two parallel cars, each made of regular matter. If you leave one parked and zoom the other with extreme acceleration, a closed timelike curve will form between them.

Easy, right? But while Mallary’s model gets rid of the need for negative matter, it adds another hurdle: it requires infinite density inside the cars for them to affect spacetime in a way that would be useful for time travel. Infinite density can be found inside a black hole, where gravity is so intense that it squishes matter into a mind-bogglingly small space called a singularity. In the model, each of the cars needs to contain such a singularity. “One of the reasons that there's not a lot of active research on this sort of thing is because of these constraints,” Mallary says.

Other researchers have created models of time travel that involve a wormhole, or a tunnel in spacetime from one point in the cosmos to another. “It's sort of a shortcut through the universe,” Goldberg says. Imagine accelerating one end of the wormhole to near the speed of light and then sending it back to where it came from. “Those two sides are no longer synced,” he says. “One is in the past; one is in the future.” Walk between them, and you’re time traveling.

You could accomplish something similar by moving one end of the wormhole near a big gravitational field—such as a black hole—while keeping the other end near a smaller gravitational force. In that way, time would slow down on the big gravity side, essentially allowing a particle or some other chunk of mass to reside in the past relative to the other side of the wormhole.

Making a wormhole requires pesky negative mass and energy, however. A wormhole created from normal mass would collapse because of gravity. “Most designs tend to have some similar sorts of issues,” Goldberg says. They’re theoretically possible, but there’s currently no feasible way to make them, kind of like a good-tasting pizza with no calories.

And maybe the problem is not just that we don’t know how to make time travel machines but also that it’s not possible to do so except on microscopic scales—a belief held by the late physicist Stephen Hawking. He proposed the chronology protection conjecture: The universe doesn’t allow time travel because it doesn’t allow alterations to the past. “It seems there is a chronology protection agency, which prevents the appearance of closed timelike curves and so makes the universe safe for historians,” Hawking wrote in a 1992 paper in Physical Review D .

Part of his reasoning involved the paradoxes time travel would create such as the aforementioned situation with a billiard ball and its more famous counterpart, the grandfather paradox : If you go back in time and kill your grandfather before he has children, you can’t be born, and therefore you can’t time travel, and therefore you couldn’t have killed your grandfather. And yet there you are.

Those complications are what interests Massachusetts Institute of Technology philosopher Agustin Rayo, however, because the paradoxes don’t just call causality and chronology into question. They also make free will seem suspect. If physics says you can go back in time, then why can’t you kill your grandfather? “What stops you?” he says. Are you not free?

Rayo suspects that time travel is consistent with free will, though. “What’s past is past,” he says. “So if, in fact, my grandfather survived long enough to have children, traveling back in time isn’t going to change that. Why will I fail if I try? I don’t know because I don’t have enough information about the past. What I do know is that I’ll fail somehow.”

If you went to kill your grandfather, in other words, you’d perhaps slip on a banana en route or miss the bus. “It's not like you would find some special force compelling you not to do it,” Costa says. “You would fail to do it for perfectly mundane reasons.”

In 2020 Costa worked with Germain Tobar, then his undergraduate student at the University of Queensland in Australia, on the math that would underlie a similar idea: that time travel is possible without paradoxes and with freedom of choice.

Goldberg agrees with them in a way. “I definitely fall into the category of [thinking that] if there is time travel, it will be constructed in such a way that it produces one self-consistent view of history,” he says. “Because that seems to be the way that all the rest of our physical laws are constructed.”

No one knows what the future of time travel to the past will hold. And so far, no time travelers have come to tell us about it.

Where Does the Concept of Time Travel Come From?

Time; he's waiting in the wings.

The dream of traveling through time is both ancient and universal. But where did humanity's fascination with time travel begin, and why is the idea so appealing?

The concept of time travel — moving through time the way we move through three-dimensional space — may in fact be hardwired into our perception of time . Linguists have recognized that we are essentially incapable of talking about temporal matters without referencing spatial ones. "In language — any language — no two domains are more intimately linked than space and time," wrote Israeli linguist Guy Deutscher in his 2005 book "The Unfolding of Language." "Even if we are not always aware of it, we invariably speak of time in terms of space, and this reflects the fact that we think of time in terms of space."

Deutscher reminds us that when we plan to meet a friend "around" lunchtime, we are using a metaphor, since lunchtime doesn't have any physical sides. He similarly points out that time can not literally be "long" or "short" like a stick, nor "pass" like a train, or even go "forward" or "backward" any more than it goes sideways, diagonal or down.

Related: Why Does Time Fly When You're Having Fun?

Perhaps because of this connection between space and time, the possibility that time can be experienced in different ways and traveled through has surprisingly early roots. One of the first known examples of time travel appears in the Mahabharata, an ancient Sanskrit epic poem compiled around 400 B.C., Lisa Yaszek, a professor of science fiction studies at the Georgia Institute of Technology in Atlanta, told Live Science 

In the Mahabharata is a story about King Kakudmi, who lived millions of years ago and sought a suitable husband for his beautiful and accomplished daughter, Revati. The two travel to the home of the creator god Brahma to ask for advice. But while in Brahma's plane of existence, they must wait as the god listens to a 20-minute song, after which Brahma explains that time moves differently in the heavens than on Earth. It turned out that "27 chatur-yugas" had passed, or more than 116 million years, according to an online summary , and so everyone Kakudmi and Revati had ever known, including family members and potential suitors, was dead. After this shock, the story closes on a somewhat happy ending in that Revati is betrothed to Balarama, twin brother of the deity Krishna. 

Time is fleeting

To Yaszek, the tale provides an example of what we now call time dilation , in which different observers measure different lengths of time based on their relative frames of reference, a part of Einstein's theory of relativity.

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Such time-slip stories are widespread throughout the world, Yaszek said, citing a Middle Eastern tale from the first century BCE about a Jewish miracle worker who sleeps beneath a newly-planted carob tree and wakes up 70 years later to find it has now matured and borne fruit (carob trees are notorious for how long they take to produce their first harvest). Another instance can be found in an eighth-century Japanese fable about a fisherman named Urashima Tarō who travels to an undersea palace and falls in love with a princess. Tarō finds that, when he returns home, 100 years have passed, according to a translation of the tale published online by the University of South Florida . 

In the early-modern era of the 1700 and 1800s, the sleep-story version of time travel grew more popular, Yaszek said. Examples include the classic tale of Rip Van Winkle, as well as books like Edward Belamy's utopian 1888 novel "Looking Backwards," in which a man wakes up in the year 2000, and the H.G. Wells 1899 novel "The Sleeper Awakes," about a man who slumbers for centuries and wakes to a completely transformed London. 

Related: Science Fiction or Fact: Is Time Travel Possible ?

In other stories from this period, people also start to be able to move backward in time. In Mark Twain’s 1889 satire "A Connecticut Yankee in King Arthur's Court," a blow to the head propels an engineer back to the reign of the legendary British monarch. Objects that can send someone through time begin to appear as well, mainly clocks, such as in Edward Page Mitchell's 1881 story "The Clock that Went Backwards" or Lewis Carrol's 1889 children's fantasy "Sylvie and Bruno," where the characters possess a watch that is a type of time machine . 

The explosion of such stories during this era might come from the fact that people were "beginning to standardize time, and orient themselves to clocks more frequently," Yaszek said. 

Time after time

Wells provided one of the most enduring time-travel plots in his 1895 novella "The Time Machine," which included the innovation of a craft that can move forward and backward through long spans of time. "This is when we’re getting steam engines and trains and the first automobiles," Yaszek said. "I think it’s no surprise that Wells suddenly thinks: 'Hey, maybe we can use a vehicle to travel through time.'"

Because it is such a rich visual icon, many beloved time-travel stories written after this have included a striking time machine, Yaszek said, referencing The Doctor's blue police box — the TARDIS — in the long-running BBC series "Doctor Who," and "Back to the Future"'s silver luxury speedster, the DeLorean . 

More recently, time travel has been used to examine our relationship with the past, Yaszek said, in particular in pieces written by women and people of color. Octavia Butler's 1979 novel "Kindred" about a modern woman who visits her pre-Civil-War ancestors is "a marvelous story that really asks us to rethink black and white relations through history," she said. And a contemporary web series called " Send Me " involves an African-American psychic who can guide people back to antebellum times and witness slavery. 

"I'm really excited about stories like that," Yaszek said. "They help us re-see history from new perspectives."

Time travel has found a home in a wide variety of genres and media, including comedies such as "Groundhog Day" and "Bill and Ted's Excellent Adventure" as well as video games like Nintendo's "The Legend of Zelda: Majora's Mask" and the indie game "Braid." 

Yaszek suggested that this malleability and ubiquity speaks to time travel tales' ability to offer an escape from our normal reality. "They let us imagine that we can break free from the grip of linear time," she said. "And somehow get a new perspective on the human experience, either our own or humanity as a whole, and I think that feels so exciting to us." 

That modern people are often drawn to time-machine stories in particular might reflect the fact that we live in a technological world, she added. Yet time travel's appeal certainly has deeper roots, interwoven into the very fabric of our language and appearing in some of our earliest imaginings. 

"I think it's a way to make sense of the otherwise intangible and inexplicable, because it's hard to grasp time," Yaszek said. "But this is one of the final frontiers, the frontier of time, of life and death. And we're all moving forward, we're all traveling through time."

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Originally published on Live Science .

Adam Mann is a freelance journalist with over a decade of experience, specializing in astronomy and physics stories. He has a bachelor's degree in astrophysics from UC Berkeley. His work has appeared in the New Yorker, New York Times, National Geographic, Wall Street Journal, Wired, Nature, Science, and many other places. He lives in Oakland, California, where he enjoys riding his bike. 

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3 Popular Time Travel Theory Concepts Explained

Time travel theory. It’s one of the most popular themes in fiction. But every plotline falls into one of these three Time Travel Theories.

Time travel is one of the most popular themes in cinema . Although most time travel movies are in the sci-fi genre, every genre, even comedy, horror, and drama, have tackled complicated storylines involving time travel theory. Chances are, you’ve seen at least a few of the movies listed below:

But what about…

The possibility of time travel, time travel theory.

• Bill & Ted’s Excellent Adventure (1989)
• The Time Machine  (2002)
• Timeline (2003)
• Time Cop (2004)
• Back to the Future  (1985)
• 12 Monkeys  (1995)
• Terminator Series (1984)
• Star Trek (2009)
• Harry Potter and the Prisoner of Azkaban (2004)
• Freejack (1992)
• Looper (2012)

But one thing you might not have realized, even if you’ve seen hundreds of time travel-related films, is that there are only  3 different theories of time travel. That’s it. Every time travel movie or book that you’ve ever enjoyed falls into one of these time travel theories.

Fixed Timeline: Time Travel Theory

Want to change the future on Earth by modifying the past or present? Don’t even bother according to this time travel theory. In a fixed timeline, there’s a single history that is unchangeable. Whatever you are attempting to change by time-traveling is what created the problems in the present that you’re trying to fix ( 12 Monkeys ). Or you’re just wasting your time because the events you are trying to prevent will happen anyway ( Donnie Darko ).

Dynamic Timeline: Time Travel Theory

History is fragile and even the smallest changes can have a huge impact. After traveling back in time, your actions may impact your own timeline. The result is a paradox. Your changes to the past might result in you never being born, like in Back to the Future (1985), or never traveling in time in the first place. In The Time Machine (2002), Hartdegen goes back in time to save his sweetheart Emma but can’t. Doing so would have resulted in his never developing the time machine that he used to try and save her.

One common way to explore this paradox theory is by killing your own grandfather. The grandfather paradox is when a time traveler attempts to kill their grandfather before the grandfather meets their grandmother. This prevents the time travel’s parents from being born and thus the time traveler himself from being born. But if the time traveler was never born, then the traveler would never have traveled back in time, therefore erasing his or her actions involving the death of their grandfather.

Multiverse: Time Travel Theory

Travel all over time and do whatever you want. It doesn’t matter because there are multiple universes and your actions only create new timelines. This is a common theory used by the science fiction TV series, Doctor Who . Using the multiverse theory of time travel, it’s assumed that there are multiple coexisting alternate timelines.

Therefore, when the traveler goes back in time, they end up in a new timeline where historical events can differ from the timeline they came from, but their original timeline does not cease to exist. This means the grandfather paradox can be avoided. Even if the time traveler’s grandparent is killed at a young age in the new timeline, he/she still survived to have children in the original timeline, so there is still a causal explanation for the traveler’s existence.

Time travel may actually create a new timeline that diverges from the original timeline at the moment the time traveler appears in the past, or the traveler may arrive in an already existing parallel universe. There’s just one problem… you can’t go back ( The One , 2002).

Some may argue that people who are “trapped” in time are time travelers as well. This happens in countless time travel movies including Robin Williams ‘ character in the 1995 film Jumanji who gets trapped inside a board game. The list of “people who are cryogenically frozen and then successfully thawed out in the future” is even longer and includes Austin Powers: The Spy Who Shagged Me  (1999), Planet of the Apes (1968) and so on.

Although these characters are “moving” through time, they are doing so by pausing and then rejoining the current timeline. The lack of a time machine device disqualifies them from technically being “time travelers” and included in this list of theories on time travel.

So will time travel ever be possible? All we know for sure is that the experts don’t agree. According to the Albert Einstein theory of relativity, time is relative, not constant and the bending of spacetime could be possible. But according to  Stephen Hawking , time travel is not possible. The Stephen Hawking time travel theory suggests that the absence of present-day time travelers from the future is an argument against the existence of time travel — a variant of the Fermi paradox (aka where the hell is everybody?). But it’s fun to think about.

NERD NOTE:  What happens to time in a black hole? We don’t know for sure, but according to both Stephen Hawking and Albert Einstein’s theory, time near a black hole slows down. This is because a black hole’s gravitational pull is so strong that even light can’t escape. Since gravity also affects light, time would also slow down.

If you could successfully travel into the future, or back in time, what would you do? Warn people about natural disasters? Buy a winning lottery ticket ? Try to prevent your own death? What do you think about these time travel theory ideas or the time travel movies that we included in this article? Please tell us in the comments below.

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Frank Wilson is a retired teacher with over 30 years of combined experience in the education, small business technology, and real estate business. He now blogs as a hobby and spends most days tinkering with old computers. Wilson is passionate about tech, enjoys fishing, and loves drinking beer.

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Mar 24, 2015 at 11:24 PM

are there really only 3 theories? i feel like there are more but i cant think of any besides the movies listed here. hummmmmmmmm

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Relativity train, what it shows:.

The Relativity Train is a realization of the famous Einstein gedanken experiments involving traveling trains carrying clocks and meter sticks. The demonstration is used to show how the preservation of the postulated constancy of physical laws and the speed of light in all inertial frames requires length contraction and time dilation in the train frame relative to the lab frame of reference. The demonstration is, of course, not a real experiment but rather a visual means of showing (without using any equations) how length contraction and time dilation are necessary consequences of Einstein's two assumptions.

How it works:

The Relativity Train is a large model train 1 on a 4.8 m long track (a schematic picture is shown below). Three large clocks 2 are mounted on it (one on top of the engine, the middle, and the last car) and move with the train. Two similar "station" clocks sit in front of the train track and represent the clocks in the laboratory frame, or rest frame. Two photons, 3 moving in opposite directions and parallel with the train, represent light emitted from an imaginary firecracker or lightning flash. The train moves at 3/5 the speed of light as defined by the speed of the two photons. Special "meter sticks" and arrow markers complete the props for the experiment. The obvious should be stated at the outset: the apparatus does not provide a real display of relativistic effects but rather mimics those effects in slow motion.

The normal procedure in the presentation is to (1) go through the exercise of synchronizing first the station clocks and then the moving train clocks, (2) perform some simple measurements in both the moving and stationary reference frames, (3) discover that the measurements in the two reference frames do not agree and hence violate one or both of Einstein's postulates, (4) invoke length contraction and/or time dilation on the moving train reference frame and, (5) repeat the measurements in (2) and discover that symmetry has been restored in agreement with Einstein's postulates, i.e. the measurements in the two reference frames agree. The details in these five steps will be discussed presently, but it is important to appreciate the logic and flow of the presentation. To summarize, one starts off assuming nothing except Einstein's two postulates: (a) the speed of light is constant (the same in all inertial frames, independent of the motion of the source and the same in all directions) and (b) physical laws are the same in all inertial frames. In other words, it is impossible to tell by any experiment whether you are "truly" at rest or moving with a uniform velocity. Step (3) provides a loop-hole or contradicts this last statement and thus we "fix things up" by invoking length contraction and/or time dilation on the moving frame. This is a qualitative exercise to show, without any mathematics, that length contraction and time dilation are necessary consequences of Einstein's postulates. The general scheme of the demonstration has been outlined and now we will enumerate the details:

In general, it is best to go slowly. The complete use of the demonstration can take two full class hours. Everyone must understand and accept each step as inevitably required by the two postulates initially agreed upon.

(1) synchronization of clocks : Begin with all clocks set to arbitrary times. (i) First measure the length of a meter stick in the station frame (no clocks are required for this) by simply placing arrow markers at the ends of the stick (at arbitrary times) and stating that the length of the stationary meter stick is equal to the distance between the two arrow markers. (ii) Repeat this "experiment" by measuring the length of a moving meter stick (the stick is on the train) from the station frame. This is done by dropping arrow markers (at arbitrary times) in the station frame at the place where the moving stick happened to be. The students will immediately recognize the "error" in this measurement and will tell you that the positions must be indicated at the same time . Repeat the experiment again, dropping the arrow markers at the same time as indicated by the station clocks. The class will scream at you when you do this, pointing out that the clocks are not synchronized . This leads very nicely into the reasons why clocks must be synchronized when you want to compare lengths . (iii) Now you go through the process of synchronizing the fixed station clocks. An imaginary firecracker is set off midway between the clocks resulting in two photons traveling (at the speed of light) in opposite directions. The clocks are then adjusted so they read the same time when the photons arrive. This will be defined as the way to do all synchronizing of clocks during all future experiments. As a check, measure the speed of light by measuring the time for a photon to go from one clock to the other. Do this in both directions to check postulate (a). This seems so simple to the point of being boring, but wait! It's time to (iv) synchronize the moving train clocks; with the train moving , go through the same procedure as in (iii) in adjusting the train clocks. There is obviously a need to fiddle with the clocks - the one at the front must be set back in order for the photons to reach each clock at the same reading. Suddenly the class wakes up again. They claim that the clocks are not synchronized. But you remind them that you are just repeating the same procedure for synchronizing that you used before and, by the principle of relativity, you can't tell if you're moving or not. With the clocks synchronized thusly, measure the photon's speed each way to show the same time for light to travel forwards or backwards. Now that we know how to synchronize clocks, we can return to length measurements.

(2) Length measurements in stationary and moving reference frames . Put the long (100 cm) meter stick on the train and measure its length in the station frame of reference by placing arrow markers simultaneously (simultaneously in the station frame, i.e. everyday simultaneity). There are only two station clocks and the audience is asked to picture an ensemble of station clocks, spread out in the station frame, all appropriately synchronized (this is easy to do in the station frame). The number of cm's between the arrow markers is the station's measurement of the train's meter stick. Now measure the station's meter stick from the train in similar manner. Again, it should be emphasized to the audience that they are to imagine a continuum of synchronized clocks on the train (even though only three are used) and that, to carry out this measurement, the people on the train have been instructed to place an arrow marker as follows: at some specified, predetermined time, whichever person is closest to either end of the meter stick will record a mark at that position. In actuality, the lecturer "simultaneously" (as defined by the train's clocks - here it becomes obvious that simultaneity is not absolute) places the arrow markers on the moving train at this predetermined time at the position where either end of the meter stick is relative to the train. This measurement is a bit tricky and the way it's easiest to accomplish is to place a marker on the train next to one end of the station's meter stick when it is at the last clock on the train, note the time on that clock, and then place a marker "simultaneously" at the other end of the meter stick (i.e., the other end is marked when the nearest train clock reads the time that was previously noted). The number of cm's between the arrow markers is the train's measurement of the station's meter stick.

(3) Violation of Postulates! A comparison of the two measurements in part (2) shows a discrepancy; in the station frame the train's meter stick is the same length as the station's meter but in the moving train frame, the station's meter stick is measured to be shorter than the train's. This asymmetry allows us to tell who is really moving, in violation of the second postulate.

(4) Length Contraction is invoked : We substitute a shorter meter stick for the train (4/5 of the length of the station's).

(5) Symmetry is restored : With the short meter stick on the train (length contraction), the measurements in section (2) above are repeated, the results of which are now symmetric; i.e. both measurements indicate that the meter stick in the other frame is shorter than the meter stick in the frame in which the measurement is made. The train will find the station's meter to be only 4/5 as long as its own and the station measures the train's meter to be 4/5 as long as its meter.

The above discussion is summarized in this video from January 1981 featuring Prof. Costas Papaliolios.

There are three different ways we can introduce time dilation at this point: (a) show that c (the speed of light) is different in different frames, (b) show asymmetry in measuring the rate of a moving clock or, (c) show that relative velocity is different when measured by different frames. For brevity, only (a) and (b) will be described in detail.

Having agreed on a consistent set of length standards, we are now equipped to measure the speed of light in each frame. All clocks (moving and stationary) are running at the same rate.

(1) Speed of Light Measurement : Using the station meter stick and the station clock, measure the speed of light (try both directions). Record the value. Note that you would really need two station clocks to do this. Repeat this measurement using the train meter stick and the train clocks (again, try both directions). The answers are different! This clearly violates the postulates, and since the units of length are already set consistently, the problem has to lie in the units of time.

(2) Time Dilation is Invoked : Since the station's value of time for light to travel one station meter is smaller than the train's value, we must slow down the train's clocks or speed up the station clocks (either would do equally well, but for purely electromechanical reasons we have chosen to speed up the station clocks rather than slow down the moving train clocks - the audience need not be bothered with this bit of information). In any case, the flick of a switch accomplishes the deed and the clock rates can be compared - the train's clocks run at 4/5 the rate of the station clocks, as measured from the station.

(3) Symmetry is restored : Now measure the rate at which the station clocks run as seen by the train's synchronized clocks. Measure on the station clock the time the (train's) length standard takes to pass by. Measure the same interval in the train frame by taking the difference between the first train clock at the start of the interval and the trailing train clock at the end of the interval (as each clock passes the station clock in turn). In the train frame the station clocks run at 4/5 the proper rate! (note this is the same factor as that for length contraction) We can now repeat the speed of light measurements in step (1) above and find that that result too is consistent with the relativity postulates. Thus, having introduced time dilation (and length contraction) one can now demonstrate that (a) the velocity of light is the same in both frames, (b) each frame measures the other's clock as running slow and, (c) relative velocities are the same in both frames.

Setting it up:

The apparatus occupies the whole space in the front of the lecture hall. A hand-held remote control allows the lecturer to operate the train without having to constantly walk back to the main control box. Once in the hall, put it through its paces before lecture time. The apparatus has its idiosyncrasies and what can go wrong, will. It is advised to practice extensively before using this demo. Because of its size, the apparatus can not be wheeled into Lecture Hall A and advance notice is necessary to make appropriate arrangements for its use.

The relativity train allows the student to see changes in train position, clock positions, and wave (photon) position proceeding simultaneously. This all happens sufficiently slowly that one has time to notice all the important aspects unfolding and can at any instant halt the development of the physical process to examine in detail the prevailing situation. The size and visual clarity of this demonstration makes it especially useful for large audiences with little mathematical background as well as students more sophisticated in mathematics and/or physics and any variety of audiences. The original design was conceived by Prof. Costas Papaliolios (Harvard University) in 1971 and is predated by a more complex device by J. Streib. 4 It has been very popular through the years and is highly recommended if the lecturer is willing to invest the time (both in class and preparation).

Some technical details for those wishing to reproduce a similar demonstration: Obviously this demonstration can be scaled down to suit your particular needs and constraints. We present here some of the design features which may be generally useful, regardless of size.

motor drive : It was discovered early on that the train's own engine motor is not sufficiently powerful to drive the train, clocks, and photons without serious slippage problems. We pull the train by a loop of Posi-Drive™ chain using a Bodine (series 200) motor whose power supply is in the main control box mounted on the tressel. It is remotely controlled by a hand-held master switch on a 20-ft cable and has three positions: brake and forward positions (both with a positive lock) and a spring-loaded reverse position. A safety switch, tripped by the engine cowling, is mounted on the trestle at the far forward end and will halt forward, but not reverse, motion. This is important as the lecturer will undoubtedly be so absorbed in the demonstration as to let the train crash into the bumper track. The train travels the two meter length in about 27.5 seconds.

photons : At the rear end of the track, mounted on the same shaft as the Posi-Drive idler pulley, are two pulleys (2.75 cm and 4.53 cm dia.) which serve to drive the photons. The photon drive pulley (1.30 cm dia.) is mounted on a post meant to look like a utility pole and is coupled to the track pulley via a rubber band. The front end of the track has a similar post with an idler pulley on top. A fishing line (5-lb test monofilament) tightly loops around the photon pulleys and the photons themselves are loosely suspended from this line. The top/bottom pulley diameter ratios determine the speed of the photons to be 5/3 the speed of the train.

clocks : We found that controlling the speed of simple DC motors by merely changing the DC supply voltage was not reproducible enough for our clocks. AC synchronous motors are cheap and very reliable, but a switching power supply must be used to slow down (or speed up) the motor. All the clock motors (train and station) are Cramer™ 110 VAC, 2 RPM motors. The station clocks are set up so that they may be run either (1) at the same speed as the train clocks or, (2) 25% faster than the train clocks. To provide option (2), a special circuit is used to supply 110 VAC at 75 Hz. This is accomplished by using a 12 VAC, center-tap, step-down transformer in reverse: the 12 V winding is used as the primary and the 110 V winding feeds the clock motors. A 12 VDC power supply feeds the center-tap of the primary. The DC voltage is switched in a push-pull mode by power transistors (2N3055) which are gated at 75 Hz by a 555 oscillator. A Darlington pair of transistors (2N2213) act as a buffer between the oscillator and the power transistors.

trestle : Rather than assembling and setting up the train on the lecture benches, a dedicated 4.8 m long cart was constructed on which the train and all accessories are stored. It was designed to look like a trestle (in keeping with the train theme) and the Dexion™-type angle iron used in the construction looks very much like steel girders. Model railroading "grass" and "gravel" on the trackbed add the finishing touches.

1 G-gauge, LGB train and track, manufactured by Lehmann, Gross and Bahn of Germany (available through toy or model stores such as F.A.O Schwartz or Eric Fuchs Inc., Boston).

2 30 cm square smoked plexiglass clock faces with bright yellow circles in place of numbers on each face. The clocks have a single hand whose position can be changed by the lecturer and are driven by Cramer type 117, AC, 2 RPM motors.

3 The photons are yellow cardboard disks, 4.5 cm in diameter, suspended from 5-lb test monofilament. The photons hang without slipping as they are moved along by the monofilament until they reach the end of their travel, at which time they do slip.

4 John F. Streib, Am J Phys 31 , 802 (1963).

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Einstein and Time Travel – His Theories

Cristina Boros April 17, 2016 16 Comments

Einstein and time travel , Einstein theories , theory of relativity

Welcome, and I am very happy to have you here again today 🙂 and talk to you about Albert Einstein and time travel.

Let’s have a look at the scientific part of this subject of time travel. Do you think time travel is just fiction found in movies, books, and games, or could it be a future reality?

We have had some great minds of the century some offered theories, one of them being by the physicist Albert Einstein. So, talking about Einstein and time travel let’s try to understand his theories.

I know it is not a very simple subject but I also think many of you would like to know his ideas, so I will try to explain them as clearly and as simple as I can.

I am not a physicist myself so let’s see in simple terms what Einstein proved with his theories.

The Theory of Special Relativity

First of all, Einstein proved that time is relative; a very different opinion from Newton who claimed that time is absolute. But which one was right? How did Einstein sustain his theory?

His theory says that when you move through space-time at the speed of light, time goes slower for you than for the others.

For example

Travelling with a very fast spaceship, one person would get older by only a few days whereas another who is on the earth, by month or years.

It is said that the faster we travel, the slower time passes.

In 1905, Einstein explained in this theory time-space as a fourth dimension.

  To prove this theory, in 1975 Carol Allie made an experiment at the University of Maryland.

Two clocks were synchronized and one was placed on an airplane and another in the laboratory.

When the clock that was placed on the aircraft returned after a few hours of flight, it was seen to be a fraction of a second faster than the clock that remained in the laboratory.

Ok, this is an experiment on a small scale, but what if the clock was placed on a spaceship that flew at the speed of light?

Einstein claims that for a time travel journey to be successful, you would need to be able to travel at the speed of light.

So according to his theory, Einstein claims that traveling at a speed close to the speed of light will slow the time, reaching the speed of light will stop time and if it will be ever possible to pass the speed of light, time will reverse.

General Relativity – Einstein’s Theory

  Another theory of this great physicist was that time passes slower for objects in a gravitational field than for an object which is far from such a field.

So here we have black holes, where the gravity is intense.

Kip Thorne (University of California) claimed that wormholes do exist in space and that they are shortcuts to the past. If two wormholes are connected, it could make a passageway to the past or future.

His theory was confirmed in 1919 when during a solar eclipse, astronomers measured the curving of starlight around the Sun.

One more time in 1922, during another sun eclipse confirmed Einstein was right and he became famous worldwide.

Even today flights are based on his theory.

Researchers today say that they have detected gravitational waves coming from two wormholes that crashed together, located at a distance 1.3 billion light years away.

Physicists say that it is difficult to succeed in time travel because, in our world, the laws of physics are not pushed to the limit, but if we could break these rules, time travel would be possible.

Breaking the Rules

Many physicists have tried to violate Einstein’s theories or to ‘break the rules’.

Marian Scully, Lijun Wang, Gunter Nimtz, and Alfons Stalhofen are some of those names who claimed that they have succeeded in violating these theories.

The last two, at the University of Koblenz, transmitted photons at a speed faster than the speed of light, so the photons traveled into the past.

I will not write about each one because it is pure science, physics, and calculus. It would take a mind such as Einstein to understand it.

Based on Einstein theories, the novelist H.G. Wells wrote the novel ‘The time machine’ and physicists think that he was really onto something.

Einstein’s equation E=mc2 proves that time travel into the past is possible theoretically and scientists say that if it is still impossible for us to put this into practice, it doesn’t mean that time travel is impossible.

Stephen Hawkins says about Einstein’s theories, that to travel with a speed faster than light is almost impossible, at least in our world, and if time travel will ever be possible the past will make you stop.

The laws of physics are made not to allow us to change the past.

Now, what to think?

Reading so many different opinions I can understand just one thing. Time travel is possible but we need a more advanced technology to break the laws of physics, to use gravity and travel at the speed of light.

Does the past want to be changed?

I understand that it would be really fascinating if we could do this, but maybe this is too much?

David Lewis gives a good example of this talking about compossibility and the ability to change the past.

It is true that changing past events would have many implications, and practically it is impossible.

Lewis gives as an example

Tim, a man that hates his grandfather wants to travel into the past and kill him.

Would it be possible?

If the grandfather is killed when he is young, this would mean Tim’s parents would not exist, so Tim would also not exist to kill him.

If for example the grandfather normally dies in 1993 and Tim goes back to 1955 to kill him, would he?

Considering the present and that the grandfather should live for Tim to exist, (I will not confuse you more), Tim will be stopped from the past to succeed in killing him.

Lewis’s conclusion and exact quote is:

‘Tim doesn’t but can because he has what it takes ‘(clear shot, daylight) and also he believes that if Tim finally tries to do it, everything will stop him, a bird will fly in front of him, the gun will jam or he will just fall every time he will want to shot his grandfather.

This paradox can also be seen in many films.

So what is your conclusion?

Reading all these theories and ideas, what do you really think?

Is time travel possible only theoretically, or if we push a little bit harder on the laws of nature, can we do

I would like to know your opinion and if you have any questions just ask.

I look forward to hearing from you all and thanks for reading.

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16 Comments

Hi Cristina,

I just bumped into your site. That is a very informative and quite interesting article on time travelling.

So many historical personalities delved into the matter, many of them you mention in your post.

Humans are extrordinary creatures when and if they want to so I wouldn’t be surprised if that became a reality in the future.

I hope I am alive to experience it.

thanks for reading and i hope too, one time will see it real. i am the first to try :))i fell we are close

Hello Cristina, appreciate your post and very exited to read about Travel travel theories. There is nothing impossible and if the scientist put full focus on law of nature theories, we can achieve the time travel goal. However this technology should be limitedly used for example to see our earth some 5000, 10000 etc years back and future as well like year 5050. Awesome to imagine this. However all the best! Thanks

thank you for your reading and of course, if will ever be possible time travel should be used for very good reasons:)Thanks again and soon, more articles will bring the news:)

Hi, I loved all the science. I took time to view your video. It was interesting and I learned some information I didn’t know before.

Traveling in time is an intriguing idea. On the one hand I would like to see time travel become a reality. On the other hand changing time could be a problem.

One of my favorite books is The End of Eternity by Isaac Asimov. Thanks, Dave

thank you for reading. yes I think you are absolutely right if it will ever be possible time travel, i don’t think is a good idea for everyone to be able to do it .about the book i will read it and i will tell you my opinion:) thanks again

I just watched 12 monkeys and time travel is one of my favorite genres when watching TV shows and movies. I also watched a documentary of Einsten’s life and I got a gist of his theory of time-space, but still I cannot get the bending and the solar eclipse experiment. But I did enjoy the documentary. Honestly, if I could change the past, I would but my senses are telling that it is very far from reality, and may not happen in this lifetime. That is why I enjoy entertainment about it, so at least I feel contentment. How about you? How do you feel about time travel?

to be honest, I think is possible but not for everyone. It is still researched and i think that if we don’t know yet the way to do it , the ancient civilization sure did. and there are proves that there are time travelers but coming from the future . thanks for reading and I am glad that you enjoy it 🙂

Hi Cristina,I myself believe in time travel and think Einsteins theory is right on.I enjoyed your article very much, thought it was very interesting.Nice job

me too, to be honest, I believe. This is the reason i write about it and I search so many things, I am glad that you enjoyed it and stay around, 🙂 i will write more articles and I hope you will like them:)

I am seriously mind blown right now. The experiment you mentioned back in 1975 is awesome! I would like to know if they have done anymore like this recently with faster planes. I agree that we are bound by the laws of physics, but i really think that we can get over it with technology advancing more and more everyday!. I enjoyed reading this article!

i am happy that you enjoyed reading my article . i think experiments are done every year and the technology advances day by day but as soon as i know about something new… i will write about :)) i am sure in a few year you will have big surprises about faster planes . thanks 🙂

This is the most interesting article I have ever read in my life! Ok so in my opinion, I believe that time travel is possible, maybe not in our lifetime but it’s definitely possible. I mean just look at how far we’ve come over the past 15 years. Now I know that in order to travel to the past or to the future you have to travel faster than the speed of light, which is time in space.

I believe in time that we will eventually be able to live on multiple planets as technology and our resources get more and more advanced. Great article!

I also think in the future we will leave on other planets 🙂 It is also planned to colonize Mars so..it is not too far:)

Do you think not in out life time? Maybe, who knows:) 

Thanks for reading and if you want to know more there are plenty of articles on my site so..have a nice time and if I can help , ask me anything:)

Interesting read! I was never 100% sure if I believed in time travel being real, but, I generally do enjoy hearing other stories and theories about that!

As far as Albert Einstein goes, I probably should learn more about him, as he seems to be one of the smartest men to live.

One thing I was not aware of was that the speed at which we travel impacts the speed at which time progresses!

His theory on going at the speed of light has me wondering, would this send one towards the future or the past? And would there be a deciding factor in terms of how far beyond or backwards in time?

I am also somewhat curious to know how he came up with this theory. Do you have an opinion on this?

Hello there:) Arie

In Einstein’s opinion based on his theories time travel can be done in the future is we travel with a speed faster than the speed of light. Not in the past.How he came up with it? He came up with this idea in 1905 , 200 years after Newton wrote about the law of motion.he publishes his theory in 1915, after ten years of studies. So hew exactly came up is a long story and I will write a post very soon stay close:)

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Train Travel as Embodied Space-Time in Narrative Theory

• © 2023
• Atsuko Sakaki 0

University of Toronto, Toronto, Canada

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• Argues that the train is a loaded trope for reconfiguring narrative theories past their “spatial turn”
• Exploits literary and cinematic narratives and interdisciplinary perspectives to draw connections to narrative
• Pays attention to the formation of affordances in terms of passenger experience of the train carriage

Part of the book series: Geocriticism and Spatial Literary Studies (GSLS)

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About this book

Train Travel as  Embodied  Space-Time in Narrative Theory argues that the train is a loaded trope for reconfiguring narrative theories past their “spatial turn.” Atsuko Sakaki ’ s method exploits intensive and rigorous close reading of literary and cinematic narratives on one hand, and on the other hand interdisciplinary perspectives that draw out larger connections to narrative theory. The book utilizes not only narratological frameworks but also concepts of space-focused humanity oriented social sciences, such as human geography, mobility studies, tourism studies, and qualitative/experience-based ethnography, in their post “narrative turn.” On this interface of narrative studies and spatial studies, this book pays concerted attention to the formation of affordances, or relations in which the human subject uses a space-time and things in it, in terms of passenger experience of the train carriage and its extension. Affiliation: Atsuko Sakaki, University of Toronto, Toronto, Canada.

• narrative turn
• spatial turn
• mobilities studies
• narrative theory
• human geography
• Literature and Space
• spatial literary studies

Table of contents (7 chapters)

Front matter, introduction: the train as embodied space-time, with case studies of the lady vanishes , the narrow margin , and night train.

Atsuko Sakaki

Traveling Alone on the Rails into the Future: Sanshirō , My Most Secret Council , Night Train to Lisbon , and Zone

Juncture 1: wendy and lucy, best friends for a while: fugitives on the train in “night of the milky way railway,” night passage , and the naked eye, juncture 2: clouds of sils maria, it’s not “i,” it’s “you”: a second-person protagonist on the train in la modification , blue journey , and suspects on the night train, conclusion: stations as an extension of the train space-time in the romantic narrative “north station”, back matter, authors and affiliations, about the author.

Atsuko Sakaki is Professor of East Asian studies and Comparative Literature at University of Toronto, Canada. She is the author of many articles and three books, including Recontextualizing Texts: Narrative Performance in Modern Japanese Fiction (Harvard, 1999)  and The Rhetoric of Photography in Modern Japanese Literature (Brill 2015).

Bibliographic Information

Book Title : Train Travel as Embodied Space-Time in Narrative Theory

Authors : Atsuko Sakaki

Series Title : Geocriticism and Spatial Literary Studies

DOI : https://doi.org/10.1007/978-3-031-40548-8

Publisher : Palgrave Macmillan Cham

eBook Packages : Literature, Cultural and Media Studies , Literature, Cultural and Media Studies (R0)

Copyright Information : The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2023

Hardcover ISBN : 978-3-031-40547-1 Published: 02 November 2023

Softcover ISBN : 978-3-031-40550-1 Due: 15 November 2024

eBook ISBN : 978-3-031-40548-8 Published: 01 November 2023

Series ISSN : 2578-9694

Series E-ISSN : 2634-5188

Edition Number : 1

Number of Pages : XVI, 286

Topics : Contemporary Literature , Literary Theory , Literature, general , Cultural Studies

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