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Every now and then an image appears online which people claim shows a time traveller somewhere they shouldn't be. But are they just cases of people letting their imaginations run wild?

We've rounded up some of the best and most interesting images of time travellers throughout history. Some turned out to be plain fakes or cases of mistaken identities, but others are certainly intriguing.

Which have you seen before?

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The time travelling hipster

This photo was snapped in 1941 at the re-opening ceremony for the South Fork Bridge in British Columbia.

If you look carefully, on the right-hand side you can see an unusually dressed man in what appears to be modern clothing, sporting sunglasses at a time when most were wearing hats and smart jackets.

Many argue this is a time traveller, while others have countered that he's simply a man with a fashion sense ahead of his time. Snopes has shown his clothing is relevant to the time and the area, but it's still great to imagine.

World Cup celebrations

This photo comes from the 1962 World Cup and shows the celebrations as the Brazilian team lifts the trophy.

If you look closely though, you'll see in the bottom centre of the image what looks like someone with a mobile phone snapping a photo of the event.

Could this be a time traveller as well? A bit odd to think someone in the future might have a flip phone , but then they have been making a comeback recently and we know folding phones are about to be big too .

The time travelling sun seeker

This image from 1943 apparently shows British factory workers escaping to the seaside for a break during the midst of wartime. The clothes and beachwear of most people certainly fit the era, but in the centre of a frame appears to be a man dressed like Mr Bean checking his mobile phone.

Or maybe it's a time travel device? Likely a bit of a stretch or a case of overactive internet imagination, but we still enjoy the thought. Maybe there are no public beaches in the future?

Mohawk time traveller

This image from 1905 appears to show the usual happenings of the time - including workers and a banana boat delivering its goods.

However, if you look near the edge of the boat you can spy a man in a white shirt with what appears to be a Mohawk-style haircut. A very unusual haircut for the time and possible proof of a time traveller? Who can say?

Film footage captured during the recording of Charlie Chaplin's 1928 silent film "The Circus" appears to show a lady dressed all in black, wearing a hat and walking around the set talking on her mobile phone.

The footage is a little iffy as is the idea that anyone could be talking on a mobile device in the 1920s, but it's certainly got some suggesting it might be proof time travellers are among us.

The ancient astronaut sculpture

In Salamanca, Spain, there's a cathedral with multiple sculptures carved into its sides. One such sculpture appears to show the likeness of a modern-day (or perhaps futuristic) astronaut.

Considering the cathedral's construction dates back to 1513, people have taken this as proof that time travellers made their way back to that time. However, the truth is the astronaut is merely a modern addition to the artwork carried out by Jerónimo García de Quiñones during renovations in 1992.

Time travelling celebrities

There's an interesting trend of people who closely resemble folks from a bygone era. This could just be a spooky coincidence, but maybe it's proof that time travel is possible.

Perhaps these celebrities are living a double life in another century. Here, Marxist-Leninist Revolutionary Leader Mahir Cayan who was born in 1946 and died in 1972 is shown to bear a striking resemblance to TV star Jimmy Fallon. Is Jimmy Fallon living a double life as a revolutionary communist? Seems hilariously unlikely.

A man and his mobile phone

Some claim that this oil painting by Pieter de Hooch, which was lovingly crafted in 1670 appears to show a young man holding his mobile phone. In an age where such a thing would probably have seen him burnt at the stake, this one is hard to believe.

A description of the image also suggests the young man is a messenger and that's a letter in his hand, not a phone, but it's still nice to let your imagination run wild once in a while. We've often wondered what it would be like to be able to travel back to simpler times to see what life was like for ourselves.

The Adidas trainers mummy

A couple of years ago, an ancient mummy was unearthed by archaeologists digging in Mongolia. At the time, it was suggested the funky-looking footwear she was wearing bore a striking resemblance to Adidas trainers. More evidence of a time traveller visiting ancient times? Investigation of the body dated it around 1,100 years old. That's one heck of a blast through the past.

However, further unearthing showed the woman was more likely to have been a Turkic seamstress which might explain the fresh kicks. She was found with an ancient clutch bag, a mirror, a comb, a knife and more. But no mobile phone.

The time surfer

Another image of an out-of-place individual that people have latched on to as proof that time travel is a reality.

This image dates back over 100 years and shows some smartly dressed Canadians sitting on the side of a hill.

On the left-hand side though, sits a young man in what appears to be a t-shirt and shorts with ruffled hair. He was quickly referred to as the surfing time traveller due to how unusual his attire is. Others have suggested people in the photo appear shocked by his appearance, even pointing out the woman on the right who seems to be gesturing in his direction. Again, this a bit of a stretch as would a time traveller really go through time dressed like that?

A visitor to wartime Reykjavík

This photograph apparently shows a scene from downtown Reykjavík in 1943.

In the heart of wartime, soldiers and sailors can be seen everywhere in the streets among civilians. The man circled though, appears to be on a mobile phone.

We've really got a theme going with these smartphone using time travellers. Who is he calling? And how? And if he is a time traveller, why is he not in Berlin trying to assassinate Hitler?

The dabbing WWII soldier

There's an apparent theme to these time traveller photos that not only includes smartphone users, but also people visiting the second world war.

In this image, a young soldier is seen dabbing, a dance move that became popular around 2014, but certainly wasn't known in wartime.

Of course, it turns out this photo isn't an image of a time traveller, but rather just an image of some actors from 2017's blockbuster Dunkirk . The fact that most of the soldiers are smiling should also be a bit of a giveaway with this one.

Greta Thunberg

In 2019, the internet discovered a photograph from 1898 which showed three children working at a gold mine in Canada's Yukon territory.

The image seemed to show a girl with an incredible likeness to the young climate activist Greta Thunberg. Does this make Thunberg a time traveller who's come through time to save the planet? Weird year for her to choose, but it's a nice idea.

A woman clutching a smartphone (1860)

The painting " The expected one " from 1860, by Ferdinand Georg Waldmüller appears to show a woman walking along a rough path, about to be accosted by an adoring young man clutching a pink flower.

A close look though and you'll see she appears to have her attention firmly glued to a modern smartphone. Is this woman actually a time traveller?

Vladimir Putin

A few years back, a number of images surfaced online that seemingly showed Russian President Vladimir Putin snapped over various decades without ageing. Either proof that he's a time traveller or perhaps just immortal?

If true, he's incredibly patriotic, with each image showing him serving his country in one way or another. Though it's more likely to just be a strong likeness.

The AI time traveller

Here's a time traveller with a difference. Stelfie the Time Traveller has been using AI to travel through time. Or at least to give the illusion of doing so.

This creative individual has been using Stable Diffusion to insert the likeness of a modern man into ancient civilisations including Egypt when the pyramids were being constructed, Rome with the centurions and the land of the dinosaurs . It's fun to imagine these as being real, though if you look closely they're clearly AI-generated. As this artificial intelligence improves we'll no doubt get even better images like this. Interestingly even the character taking the selfies isn't real here, but is also made using AI.

Do you believe in time travel? I’m a skeptic myself — but if these people’s stories about time travel are to be believed, then I am apparently wrong. Who knows? Maybe one day I’ll have to eat my words. In all honesty, that might not be so bad — because the tradeoff for being wrong in that case would be that time travel is real . That would be pretty rad if it were true.

Technically speaking time travel does exist right now — just not in the sci fi kind of way you’re probably thinking. According to a TED-Ed video by Colin Stuart, Russian cosmonaut Sergei Krikalev actually traveled 0.02 seconds into his own future due to time dilation during the time he spent on the International Space Station. For the curious, Krikalev has spent a total of 803 days, nine hours, and 39 minutes in space over the course of his career.

That said, though, many are convinced that time dilation isn’t the only kind of time travel that’s possible; some folks do also believe in time travel as depicted by everything from H. G. Wells’ The Time Machine to Back to the Future . It’s difficult to find stories online that are actual accounts from real people — many of them are either urban legends ( hi there, Philadelphia Experiment ) or stories that center around people that I’ve been unable to verify actually exist — but if you dig hard enough, sincere accounts can be found.

Are the stories true? Are they false? Are they examples of people who believe with all their heart that they’re true, even if they might not actually be? You be the judge. These seven tales are all excellent yarns, at any rate.

1 The Moberly–Jourdain Incident

In 1901, two Englishwomen, Anne Moberly and Eleanor Jourdain , took a vacation to France. While they were there, they visited the Palace of Versailles (because, y’know, that’s what one does when one visits France ). And while they were at Versailles, they visited what’s known as the Petit Trianon — a little chateau on the palace grounds that Louis XVI gave to Marie Antoinette as a private space for her to hang out and do whatever it was that a teenaged queen did when she was relaxing back then.

But while they were there, they claimed, they saw some… odd occurrences. They said they spotted people wearing anachronistic clothing, heard mysterious voices, and saw buildings and other structures that were no longer present — and, indeed, hadn’t existed since the late 1700s. Finally, they said, they caught sight of Marie Antoinette herself , drawing in a sketchbook.

They claimed to have fallen into a “time slip” and been briefly transported back more than 100 years before being jolted back to the present by a tour guide.

Did they really travel back in time? Probably not; various explanations include everything from a folie a deux (basically a joint delusion) to a simple misinterpretation of what they actually saw. But for what it’s worth, in 1911 — roughly 10 years after what they said they had experienced occurred — the two women published a book about the whole thing under the names Elizabeth Morison and Frances Lamont simply called An Adventure. These days, it’s available as The Ghosts of Trianon ; check it out, if you like.

2 The Mystery Of John Titor

John Titor is perhaps the most famous person who claims he’s time traveled; trouble is, no one has heard from him for almost 17 years. Also, he claimed he came from the future.

The story is long and involved, but the short version is this: In a thread begun in the fall of 2000 about time travel paradoxes on the online forum the Time Travel Institute — now known as Curious Cosmos — a user responded to a comment about how a time machine could theoretically be built with the following message:

“Wow! Paul is right on the money. I was just about to give up hope on anyone knowing who Tipler or Kerr was on this worldline.

“By the way, #2 is the correct answer and the basics for time travel start at CERN in about a year and end in 2034 with the first ‘time machine’ built by GE. Too bad we can’t post pictures or I’d show it to you.”

The implication, of course, was that the user, who was going by the name TimeTravel_0, came from a point in the future during which such a machine had already been invented.

Over the course of many messages spanning from that first thread all the way through the early spring of 2001, the user, who became known as John Titor, told his story. He said that he had been sent back to 1975 in order to bring an IBM 5100 computer to his own time; he was just stopping in 2000 for a brief rest on his way back home. The computer, he said, was needed to debug “various legacy computer programs in 2036” in order to combat a known problem similar to Y2K called the Year 2038 Problem . (John didn’t refer to it as such, but he said that UNIX was going to have an issue in 2038 — which is what we thought was going to happen back when the calendar ticked over from 1999 to 2000.)

Opinions are divided on whether John Titor was real ; some folks think he was the only real example of time travel we’ve ever seen, while others think it’s one of the most enduring hoaxes we’ve ever seen. I fall on the side of hoax, but that’s just me.

3 Project Pegasus And The Chrononauts

In 2011, Andrew D. Basiago and William Stillings stepped forward, claiming that they were former “chrononauts” who had worked with an alleged DARPA program called Project Pegasus. Project Pegasus, they said, had been developed in the 1970s; in 1980, they were taking a “Mars training class” at a community college in California (the college presumably functioning as a cover for the alleged program) when they were picked to go to Mars. The mode of transport? Teleportation.

It gets better, too. Basiago and Stillings also said that the then- 19-year-old Barack Obama , whom they claimed was going by the name “Barry Soetero” at the time, was also one of the students chosen to go to Mars. They said the teleportation occurred via something called a “jump room.”

The White House has denied that Obama has ever been to Mars . “Only if you count watching Marvin the Martian,” Tommy Vietor, then the spokesman for the National Security Council, told Wired’s Danger Room in 2012.

4 Victor Goddard’s Airfield Time Slip

Like Anne Moberly and Eleanor Jourdain, senior Royal Air Force commander Sir Robert Victor Goddard — widely known as Victor Goddard — claimed to have experienced a time slip.

In 1935, Goddard flew over what had been the RAF station Drem in Scotland on his way from Edinburgh to Andover, England. The Drem station was no longer in use; after demobilization efforts following WWI, it had mostly been left to its own devices. And, indeed, that’s what Goddard said he saw as he flew over it: A largely abandoned airfield.

On his return trip, though, things got… weird. He followed the same route he had on the way there, but during the flight, he got waylaid by a storm. As he struggled to regain control of his plane, however, he spotted the Drem airfield through a break in the clouds — and when he got closer to it, the bad weather suddenly dissipated. But the airfield… wasn’t abandoned this time. It was busy, with several planes on the runway and mechanics scurrying about.

Within seconds, though, the storm reappeared, and Goddard had to fight to keep his plane aloft again. He made it home just fine, and went on to live another 50 years — but the incident stuck with him; indeed, in 1975, he wrote a book called Flight Towards Reality which included discussion of the whole thing.

Here’s the really weird bit: In 1939, the Drem airfield was brought back to life. Did Goddard see a peek into the airfield's future via a time slip back in 1935? Who knows.

5 Space Barbie

I’ll be honest: I’m not totally sure what to do with thisone — but I’ll present it to you here, and then you can decide for yourself what you think about it. Here it is:

Valeria Lukyanova has made a name for herself as a “human Barbie doll” (who also has kind of scary opinions about some things ) — but a 2012 short documentary for Vice’s My Life Online series also posits that she believes she’s a time traveling space alien whose purpose on Earth is to aid us in moving “from the role of the ‘human consumer’ to the role of ‘human demi-god.’”

What I can’t quite figure out is whether this whole time traveling space alien thing is, like a piece of performance art created specifically for this Vice doc, or whether it’s what she actually thinks. I don’t believe she’s referenced it in many (or maybe even any) other interviews she’s given; the items I’ve found discussing Lukyanova and time travel specifically all point back to this video.

But, well… do with it all as you will. That’s the documentary up there; give it a watch and see what you think.

6 The Hipster Time Traveler

In the early 2010s, a photograph depicting the 1941 reopening of the South Fork Bridge in Gold Bridge, British Columbia in Canada went viral for seemingly depicting a man that looked… just a bit too modern to have been photographed in 1941. He looks, in fact, like a time traveling hipster : Graphic t-shirt, textured sweater, sunglasses, the works. The photo hadn’t been manipulated; the original can be seen here . So what the heck was going on?

Well, Snopes has plenty of reasonable explanations for the man’s appearance; each item he’s wearing, for example, could very easily have been acquired in 1941. Others have also backed up those facts. But the bottom line is that it’s never been definitively debunked, so the idea that this photograph could depict a man from our time who had traveled back to 1941 persists. What do you think?

7 Father Ernetti’s Chronovisor

According to two at least two books — Catholic priest Father Francois Brune’s 2002 book Le nouveau mystère du Vatican (in English, The Vatican’s New Mystery ) and Peter Krassa’s 2000 book Father Ernetti's Chronovisor : The Creation and Disappearance of the World's First Time Machine — Father Pellegrino Ernetti, who was a Catholic priest like Brune, invented a machine called a “chronovisor” that allowed him to view the past. Ernetti was real; however, the existence of the machine, or even whether he actually claimed to have invented it, has never been proven. Alas, he died in 1994, so we can’t ask him, either. I mean, if we were ever able to find his chronovisor, maybe we could… but at that point, wouldn’t we already have the information we need?

(I’m extremely skeptical of this story, by the way, but both Brune’s and Krassa’s books swear up, down, left, and right that it’s true, so…you be the judge.)

Although I'm fairly certain that these accounts and stories are either misinterpreted information or straight-up falsehoods, they're still entertaining to read about; after all, if you had access to a time machine, wouldn't you at least want to take it for a spin? Here's hoping that one day, science takes the idea from theory to reality. It's a big ol' universe out there.

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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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.

Can we time travel? A theoretical physicist provides some answers

Emeritus professor, Physics, Carleton University

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Peter Watson received funding from NSERC. He is affiliated with Carleton University and a member of the Canadian Association of Physicists.

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• Bahasa Indonesia

Time travel makes regular appearances in popular culture, with innumerable time travel storylines in movies, television and literature. But it is a surprisingly old idea: one can argue that the Greek tragedy Oedipus Rex , written by Sophocles over 2,500 years ago, is the first time travel story .

But is time travel in fact possible? Given the popularity of the concept, this is a legitimate question. As a theoretical physicist, I find that there are several possible answers to this question, not all of which are contradictory.

The simplest answer is that time travel cannot be possible because if it was, we would already be doing it. One can argue that it is forbidden by the laws of physics, like the second law of thermodynamics or relativity . There are also technical challenges: it might be possible but would involve vast amounts of energy.

There is also the matter of time-travel paradoxes; we can — hypothetically — resolve these if free will is an illusion, if many worlds exist or if the past can only be witnessed but not experienced. Perhaps time travel is impossible simply because time must flow in a linear manner and we have no control over it, or perhaps time is an illusion and time travel is irrelevant.

Laws of physics

Since Albert Einstein’s theory of relativity — which describes the nature of time, space and gravity — is our most profound theory of time, we would like to think that time travel is forbidden by relativity. Unfortunately, one of his colleagues from the Institute for Advanced Study, Kurt Gödel, invented a universe in which time travel was not just possible, but the past and future were inextricably tangled.

We can actually design time machines , but most of these (in principle) successful proposals require negative energy , or negative mass, which does not seem to exist in our universe. If you drop a tennis ball of negative mass, it will fall upwards. This argument is rather unsatisfactory, since it explains why we cannot time travel in practice only by involving another idea — that of negative energy or mass — that we do not really understand.

Mathematical physicist Frank Tipler conceptualized a time machine that does not involve negative mass, but requires more energy than exists in the universe .

Time travel also violates the second law of thermodynamics , which states that entropy or randomness must always increase. Time can only move in one direction — in other words, you cannot unscramble an egg. More specifically, by travelling into the past we are going from now (a high entropy state) into the past, which must have lower entropy.

This argument originated with the English cosmologist Arthur Eddington , and is at best incomplete. Perhaps it stops you travelling into the past, but it says nothing about time travel into the future. In practice, it is just as hard for me to travel to next Thursday as it is to travel to last Thursday.

Resolving paradoxes

There is no doubt that if we could time travel freely, we run into the paradoxes. The best known is the “ grandfather paradox ”: one could hypothetically use a time machine to travel to the past and murder their grandfather before their father’s conception, thereby eliminating the possibility of their own birth. Logically, you cannot both exist and not exist.

Read more: Time travel could be possible, but only with parallel timelines

Kurt Vonnegut’s anti-war novel Slaughterhouse-Five , published in 1969, describes how to evade the grandfather paradox. If free will simply does not exist, it is not possible to kill one’s grandfather in the past, since he was not killed in the past. The novel’s protagonist, Billy Pilgrim, can only travel to other points on his world line (the timeline he exists in), but not to any other point in space-time, so he could not even contemplate killing his grandfather.

The universe in Slaughterhouse-Five is consistent with everything we know. The second law of thermodynamics works perfectly well within it and there is no conflict with relativity. But it is inconsistent with some things we believe in, like free will — you can observe the past, like watching a movie, but you cannot interfere with the actions of people in it.

Could we allow for actual modifications of the past, so that we could go back and murder our grandfather — or Hitler ? There are several multiverse theories that suppose that there are many timelines for different universes. This is also an old idea: in Charles Dickens’ A Christmas Carol , Ebeneezer Scrooge experiences two alternative timelines, one of which leads to a shameful death and the other to happiness.

Time is a river

Roman emperor Marcus Aurelius wrote that:

“ Time is like a river made up of the events which happen , and a violent stream; for as soon as a thing has been seen, it is carried away, and another comes in its place, and this will be carried away too.”

We can imagine that time does flow past every point in the universe, like a river around a rock. But it is difficult to make the idea precise. A flow is a rate of change — the flow of a river is the amount of water that passes a specific length in a given time. Hence if time is a flow, it is at the rate of one second per second, which is not a very useful insight.

Theoretical physicist Stephen Hawking suggested that a “ chronology protection conjecture ” must exist, an as-yet-unknown physical principle that forbids time travel. Hawking’s concept originates from the idea that we cannot know what goes on inside a black hole, because we cannot get information out of it. But this argument is redundant: we cannot time travel because we cannot time travel!

Researchers are investigating a more fundamental theory, where time and space “emerge” from something else. This is referred to as quantum gravity , but unfortunately it does not exist yet.

So is time travel possible? Probably not, but we don’t know for sure!

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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. 

Join our Space Forums to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at: [email protected].

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Vicky Stein is a science writer based in California. She has a bachelor's degree in ecology and evolutionary biology from Dartmouth College and a graduate certificate in science writing from the University of California, Santa Cruz (2018). Afterwards, she worked as a news assistant for PBS NewsHour, and now works as a freelancer covering anything from asteroids to zebras. Follow her most recent work (and most recent pictures of nudibranchs) on Twitter. 

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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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Time Travel Probably Isn't Possible—Why Do We Wish It Were?

Time travel exerts an irresistible pull on our scientific and storytelling imagination.

Since H.G. Wells imagined that time was a fourth dimension —and Einstein confirmed it—the idea of time travel has captivated us. More than 50 scientific papers are published on time travel each year, and storytellers continually explore it—from Stephen King’s JFK assassination novel 11/22/63 to the steamy Outlander television series to Woody Allen’s comedy Midnight in Paris . What if we could travel back in time, we wonder, and change history? Assassinate Hitler or marry that high school sweetheart who dumped us? What if we could see what the future has in store?

These are some of the ideas that bestselling author James Gleick explores in his thought-provoking new book, Time Travel: A History. Speaking from his home in New York City, he recalls how Stephen Hawking once sent out invitations to a party that had already taken place ; why the Chinese government has branded time travel as “incorrect” and “frivolous” ; and how the idea of time travel is, ultimately, about our desire to defeat death.

Let’s cut right to the chase: What is time?

Oh, no, you didn’t! [ Laughs. ] In A.D. 400, St. Augustine said—and many people have said the same thing since, either quoting him consciously or unconsciously—“What, then, is time? If no one asks me, I know. If I wish to explain it to one that asks, I know not.” I think that is actually not a quip, but quite profound.

The best way to understand time is to recognize that we actually are very sophisticated about it. Over the past century-plus, we’ve learned a great deal. The physicist John Archibald Wheeler said, “Time is nature’s way to keep everything from happening all at once.” If you look it up in a dictionary, you get stuff like, “The general term for the experience of duration.” But that’s just completely punting because what is duration ?

I try to steer away from aphorisms and dictionary definitions, just to say two things. First, that we have a lot of contradictory ways of talking about time. We think of time as something we waste, spend, or save, as if it’s a quantity. We also think of time as a medium we are passing through every day, a river carrying us along. All of these notions are aspects of a complicated subject that has no bumper sticker answer.

When does the idea of time travel first appear in the West? And how did it impact popular culture?

I assumed, as a person who always read sci-fi a lot when I was a kid, that time travel is an obvious idea we’re born knowing and fantasizing about. And that it must always have been part of human culture, that there must be time travel Greek myths and Chinese legends. But there aren’t! Time travel turns out to be a very new idea that essentially starts with H.G. Wells’s 1895 novel, The Time Machine . Before that nobody thought of putting the words time and travel together. The closest you can come before that is people falling asleep, like Rip Van Winkle, or fantasies like Charles Dickens’s A Christmas Carol .

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The beginning of my book is an attempt to answer the question, “Why? Why not before? Why suddenly at the end of the 19 th century was it possible— necessary— for people to dream up this crazy fantasy?” Even though it’s H.G. Wells who does it, people pick up his ball very quickly and run with it. You find it in American science fiction that started appearing in pulp magazines in the 1920s and 1930s, or in the great new modernist literature of Marcel Proust’s In Search of Lost Time , James Joyce, and Virginia Woolf.

All these writers were suddenly making time their explicit subject, twisting time in new ways, inventing new narrative techniques to deal with time, to explore the vagaries of memory or the way our consciousness changes over time.

In 1991, Stephen Hawking wrote a paper called “Chronology Protection Conjecture , ” in which he asked: If time travel is possible, why are we not inundated with tourists from the future? He has a point, doesn’t he?

Yes! He even scheduled a party and sent out an invitation inviting time travelers to come to a party that had taken place in the past. Then he observed that none of them had shown up. [Laughs.] Hawking is one of these physicists who love playing with the idea of time travel. It’s irresistible because it’s so much fun! When he talks about the paradoxes of time travel it’s because he’s reading the same science fiction stories as the rest of us.

The paradoxes started appearing in magazines aimed mostly at young people in the 1920s. Somebody wrote in and said, “Time travel is a weird idea, because what if you go back in time and you kill your grandfather? Then your grandfather never meets your grandmother and you’re never born.” It’s an impossible loop.

Hawking, like other physicists, decided, “Time is my business. What if we take this seriously? Can we express this in physical terms?” I don’t think he succeeded but what he proposed was that the reason these paradoxes can’t happen is because the universe takes care of itself. It can’t happen because it didn’t happen. That’s the simple way of saying what the chronology protection conjecture is.

How have the Internet and other new technologies changed our perception and experience of time?

We are just beginning to see what the Internet is doing to our perception of time. We are living more and more in this networked world in which everything travels at light speed. We are multitasking and experiencing new forms of simultaneity, so the Internet appears to us as a kind of hall of mirrors. It feels as though we’re embedded in an ever expanding present.

Our sense of the past changes because in some ways the past becomes more vivid than ever. We’re looking at the past on our video screens and it’s just as vivid if the movie is about something that happened 20 years ago, as if it is a live stream. We can’t always tell the difference. On the other hand, the past that’s more distant—and isn’t available in video form—starts to seem more remote and fuzzier. Maybe we are forgetting how to visualize the past from reading histories. We’re entering a new period of time confusion, in which we suddenly find ourselves in what looks like an unending present.

In 2011, the Chinese government issued an extraordinary denunciation of the idea of time travel. What was their beef?

They thought it was corrupting and decadent. It’s a reminder that time travel is neither a simple nor innocent idea. It’s very powerful. It enables us to imagine alternative universes, and this is another line that science fiction writers have explored. What if someone was able to go back in time and kill Hitler?

Time travel is also a powerful way of allowing us to imagine what the future might bring. A lot of futurists nowadays tend to be dystopian. Time travel gives us ways of exploring how the worst tendencies of our current societies could grow even worse. That’s what George Orwell did in 1984 . I imagine the Chinese government doesn’t particularly want the equivalent of 1984 to be published in Beijing. [ Laughs. ]

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More than 50 scientific papers a year are now published on the idea of time travel. why are scientists drawn to the subject.

Scientists live in the same science fictional universe as all the rest of us. Time travel is a sexy and romantic idea that appeals to the physicist as much as it appeals to every teenager. I don’t think scientists are ever going to solve the problem of time travel for us but they still love to talk about wormholes and dark matter.

There’s a fascinating coincidence in the early history that when H.G. Wells needed to set the stage for his time machine hurtling into the future, he decided not to just jump right into his story but set the scene with a framing device—his time traveler lecturing a group of friends on the science of time—in order to justify the possibility of a time machine. His lecture introduces the idea that time is nothing more than a fourth dimension, that traveling through time is analogous to traveling through space. Since we have machines that can take us into any of the three special dimensions, including balloons and elevators, why shouldn’t we have a machine able to travel through the fourth dimension?

A decade later, Einstein burst onto the scene with his theory of relativity in which time is a fourth dimension , just like space. Soon after that, Hermann Minkowski pronounced that, henceforth, we were not going to talk about space and time as separate quantities but as a union of the two, spacetime , a four-dimensional continuum in which the future already exists and the past still exists.

I’m not claiming that Einstein read H.G. Wells 10 years before. But there was something in the air that both scientists and imaginative writers were empowered to visualize time in a new way. Today, that’s the way we visualize it. We’re comfortable talking about time as a fourth dimension.

You quote Ursula K. Le Guin , who writes, “Story is our only boat for sailing on the river of time.” Talk about storytelling and its relationship to time.

One of the things that has happened, along with our heightened awareness of time and its possibilities, is that people who invent narratives have learned very clever new techniques. Literal time travel is only one of them. You don’t actually need to send your hero into the future or into the past to write a story that plays with time in clever new ways. Narrative is also how everybody, not just writers, constructs a vision of our own relationship with time. We imagine the future. We remember the past. When we do that, we’re making up stories.

Psychologists are learning something that great storytellers have known for some time, which is that memory is not like computer retrieval. It’s an active process. Every time we remember something we are remembering it a little bit differently. We’re retelling the story to ourselves.

If time travel is impossible, why do we continue to be so fascinated with the idea?

One of the reasons is we want to go back and undo our mistakes. When you ask yourself, “If I had a time machine, what would I do?” sometimes the answer is, “I would go back to this particular day and do that thing over.” I think one of the great time travel movies is Groundhog Day , the Bill Murray movie where he wakes up every morning and has to live the same day over and over again. He gradually realizes that perhaps fate is telling him he needs to do it over, right. Regret is the time traveler’s energy bar. But that’s not the only motivation for time travel. We also have curiosity about the future and interest in our parents and our children. A lot of time travel fiction is a way of asking questions about what our parents were like, or what our children will be like.

At some point during the four years I worked on this book, I also realized that, in one way or another, every time travel story is about death. Death is either explicitly there in the foreground or lurking in the background because time is a bastard, right? Time is brutal. What does time do to us? It kills us. Time travel is our way of flirting with immortality. It’s the closest we’re going to come to it.

This interview was edited for length and clarity.

Simon Worrall curates Book Talk . Follow him on Twitter or at simonworrallauthor.com .

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Paradox-Free Time Travel Is Theoretically Possible, Researchers Say

Matthew S. Schwartz

A dog dressed as Marty McFly from Back to the Future attends the Tompkins Square Halloween Dog Parade in 2015. New research says time travel might be possible without the problems McFly encountered. Timothy A. Clary/AFP via Getty Images hide caption

A dog dressed as Marty McFly from Back to the Future attends the Tompkins Square Halloween Dog Parade in 2015. New research says time travel might be possible without the problems McFly encountered.

"The past is obdurate," Stephen King wrote in his book about a man who goes back in time to prevent the Kennedy assassination. "It doesn't want to be changed."

Turns out, King might have been on to something.

Countless science fiction tales have explored the paradox of what would happen if you went back in time and did something in the past that endangered the future. Perhaps one of the most famous pop culture examples is in Back to the Future , when Marty McFly goes back in time and accidentally stops his parents from meeting, putting his own existence in jeopardy.

But maybe McFly wasn't in much danger after all. According a new paper from researchers at the University of Queensland, even if time travel were possible, the paradox couldn't actually exist.

Researchers ran the numbers and determined that even if you made a change in the past, the timeline would essentially self-correct, ensuring that whatever happened to send you back in time would still happen.

"Say you traveled in time in an attempt to stop COVID-19's patient zero from being exposed to the virus," University of Queensland scientist Fabio Costa told the university's news service .

"However, if you stopped that individual from becoming infected, that would eliminate the motivation for you to go back and stop the pandemic in the first place," said Costa, who co-authored the paper with honors undergraduate student Germain Tobar.

"This is a paradox — an inconsistency that often leads people to think that time travel cannot occur in our universe."

A variation is known as the "grandfather paradox" — in which a time traveler kills their own grandfather, in the process preventing the time traveler's birth.

The logical paradox has given researchers a headache, in part because according to Einstein's theory of general relativity, "closed timelike curves" are possible, theoretically allowing an observer to travel back in time and interact with their past self — potentially endangering their own existence.

But these researchers say that such a paradox wouldn't necessarily exist, because events would adjust themselves.

Take the coronavirus patient zero example. "You might try and stop patient zero from becoming infected, but in doing so, you would catch the virus and become patient zero, or someone else would," Tobar told the university's news service.

In other words, a time traveler could make changes, but the original outcome would still find a way to happen — maybe not the same way it happened in the first timeline but close enough so that the time traveler would still exist and would still be motivated to go back in time.

"No matter what you did, the salient events would just recalibrate around you," Tobar said.

The paper, "Reversible dynamics with closed time-like curves and freedom of choice," was published last week in the peer-reviewed journal Classical and Quantum Gravity . The findings seem consistent with another time travel study published this summer in the peer-reviewed journal Physical Review Letters. That study found that changes made in the past won't drastically alter the future.

Bestselling science fiction author Blake Crouch, who has written extensively about time travel, said the new study seems to support what certain time travel tropes have posited all along.

"The universe is deterministic and attempts to alter Past Event X are destined to be the forces which bring Past Event X into being," Crouch told NPR via email. "So the future can affect the past. Or maybe time is just an illusion. But I guess it's cool that the math checks out."

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A history of time travel: the how, the why and the when of turning back the clock

Pop on Aqua's 'Turn Back Time' and settle in

For most of human history, the world didn’t change very quickly. Until the 1700s, kids could largely expect their lives to be similar to their parents, and that their children would have an experience very similar to their own, too. There were obviously changes in how humans lived over longer stretches of time, but nothing that even different generations could easily observe.

My first introduction to science fiction was Valérian and Laureline. I was ten years old. Every Wednesday there was a magazine called Pilote in France, and there was two pages of Valerian every week. It was the first time I’d seen a girl and a guy in space, agents travelling in time and space. That was amazing.

The past is written. The present? We have to deal with it. But the future is a white page. So I don’t understand why people on this white page are putting all this darkness.

God! Let’s have some color! Let’s have some fun! Let’s at least imagine a better world. Maybe we won’t be able to do it, but we have to try.

The industrial revolution changed all of this. For the first time in human history, the pace of technological change was visible within a human lifespan. 

It is not a coincidence that it was only after science and technological change became a normal part of the human experience, that time travel became something we dreamed of.

Time travel is actually somewhat unique in science fiction. Many core concepts have their origins earlier in history. 

The historical roots of the concept of a 'robot' can be seen in Jewish folklore for example: Golems were anthropomorphic beings sculpted from clay. In Greek mythology, characters would travel to other worlds, and it's no coincidence that The Matrix features a character called Persephone. But time travel is different.

The first real work to envisage travelling in time was The Time Machine by HG Wells, which was published in 1895. 

The book tells the story of a scientist who builds a machine that will take him to the year 802,701 - a world in which ape-like Morlocks are evolutionary descendants of humanity, and have regressed to a primitive lifestyle. 

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The book was a product of its time - both in terms of the science played upon (Charles Darwin had only published Origin of the Species 35 years earlier), and the racist attitudes: it is speculated that the Morlocks were inspired by the Morlachs, a real ethnic group in the Balkans who were often characterised as “primitive”.

Real science

But of course, this was science fiction - what about science fact? The two have always been closely linked, and during the early days it was no different. In 1907, the physicist Hermann Minkowski first argued that Einstein’s Special Relativity could be expressed in geometric terms as a fourth dimension (to add to our known three) - which is exactly how Wells visualised time travel in his work of fiction.

The development of Special and then General Relativity was significant as it provided the theoretical backbone for how time travel could be conceived in scientific terms. In 1949 Kurt Gödel took Einstein’s work and came up with a solution which as a mathematical necessity included what he called “closed timelike curves” - the idea that if you travel far enough, time will loop back around (like how if you keep flying East, you’ll eventually end up back where you started).

In other words, using what became known as the Gödel Metric, it is theoretically possible to travel between any one point in time and space and any other. 

There was just one problem: for Gödel’s theory to be right, the universe would have to be spinning - and scientists don’t believe that it is. So while the maths might make sense, Gödel’s universe does not appear to be the one we’re actually living in. Though he never gave up hope that he might be right: Apparently even on this deathbed, he would ask if anyone has found evidence of a spinning universe. And if he does ever turn out to be right, it means that time travel can happen, and is actually fairly straightforward (well, as far as physics goes anyway).

Since Gödel, scientists have continued to hypothesise about time travel, with perhaps the best known example being tachyons - or particles that move faster than the speed of light (therefore, effectively travelling in time). So far, despite one false alarm at CERN in 2011, there is no evidence that they actually exist.

Chancers and hoaxes

Of course, the lack of real science when it comes to time travel has not stopped some people from claiming to have done it. With the likes of Marty McFly and Doctor Who on the brain, chancers and hoaxers have realised that time travel is immediately a compelling prospect. Here’s a couple of amusing examples.

At the turn of the millennium, when the internet was still in its infancy, forums were captivated by the story of John Titor. Titor claimed he was from the year 2036, and had been sent back in time by the government to obtain an IBM 5100 computer. The thinking appeared to be that by obtaining the computer, the government could find a solution to the UNIX 2038 bug - in which clocks could be reset, Millennium Bug-style, leading to chaos everywhere.

Posting on the 'Time Travel Institute' forums, Titor went into details on how his time machine worked:  It was powered by “two top-spin, dual positive singularities”, and used an X-ray venting system. He also gave a potted history of what humanity could expect: A new American civil war in 2004, and World War III in 2015. He also claimed the “many worlds” interpretation of quantum physics was true, hence why he wasn’t violating the so-called “grandfather paradox”.

Titor claimed he was from the year 2036, and had been sent back in time by the government to obtain an IBM 5100 computer.

Okay, so he probably wasn’t a real time traveller, but in the early days of the internet, when anonymity was more commonplace, he truly captured the imaginations of nerdy early adopters who perhaps, just a little bit, hoped that he might be the real thing.

More recently, in 2013, an Iranian scientist named Ali Razeghi claimed to have invented a time machine of sorts. It was supposedly capable of predicting the next 5-8 years for an individual, with up to 98% accuracy. According to The Telegraph , Razeghi said the invention fits into the size of a standard PC case and “It will not take you into the future, it will bring the future to you”. The idea is that the Iranian government could use it to predict future security threats and military confrontations. So perhaps it is time to check in and see if he managed to predict Donald Trump?

So is this the best we can do? Will we ever manage to crack time travel? Some scientists are still sceptical that it could ever be possible. This includes Stephen Hawking, who proposed the 'Chronology Protection Conjecture' – which is what it sounds like. Essentially, he argues that the laws of physics are as they are to specifically make time travel impossible – on all but “submicroscopic” scales. Essentially, this is to protect how causality works, as if we are suddenly allowed to travel back and kill our grandfathers, it would create massive time paradoxes.

Hawking revealed to Ars Technica in 2012 how he had held a party for time travellers, but only sent out invitations after the date it was held. So did the party support his argument that time travel is impossible? Or did he end up spending the evening in the company of John Titor and Doctor Who?

“I sat there a long time, but no one came”, he said, much to our disappointment.

Huge thanks to Stephen Jorgenson-Murray for walking us through some of the more brain-mangling science for this article.

To celebrate the release of Valerian and the City of a Thousand Planets , Luc Besson is today behind the lens at TechRadar. Here’s what we’ve got in store for you:

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Valerian and the City of a Thousand Planets is released in UK cinemas August 2nd, and is out now in the US.

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My Singing Monsters: Travelers of Time (MSM Quibble Fan)

MSM ToT (for short) is a MSM Fan Project made by MSM Quibble Fan and sophiestrawberry (aka the person who voiced siresula). They later added another ToT series called Into the Future.

• 3.1 Single Elementals
• 3.2 Double Elementals
• 3.3 Triple Elementals
• 3.4 Quad Elementals
• 4.2 Glyphic
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https://drive.google.com/drive/folders/1IM4o52mVPknYx-NPVT8jhbRfLfERJS89

Monsters by Scratch [ ]

Single elementals [ ], double elementals [ ], triple elementals [ ], quad elementals [ ], elements [ ].

An element representing Prehistory and represented by Tuskus

Glyphic [ ]

An element representing Antiquity and represented by Gliffon

An element representing Medieval Times and represented by Dragoonder

An element representing Victorian Times and represented by Galendær

Digital [ ]

An element representing Modernity and represented by Plugaris

An element representing The Future/Space and represented by Cursis

Islands [ ]

• Plant: Minac, with plants on its head.
• Cold: Mosquge, being covered in snow.
• Air: Soblor, currently the only Dark quad to fly (Glittorms is suspended by a rope), and also having wind turbines.
• Water: Krakinos, being an octopus (an aquatic creature).
• Earth: Cavein, whose body comprises of rocks.
• Fire: Steeruptor, as it has a literal mini-volcano.
• Light: Glittorms, with their LED/spotlight eyes/heads.
• Psychic: Auromaura, as they are stated to have an average IQ of 2000 and are able to communicate telepathically.
• Faerie: Stramato, being an insect (an animal associated with fairies), and being stated to have magical powers.
• Bone: Eyard, being literal bones.
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Universe Today

Space and astronomy news

Cosmonaut Sergei Krikalev, the World’s Most Prolific Time Traveler

Is time travel a fact or is it just science fiction? Thanks to time dilation and Einstein’s theory of relativity, we know that time travel can and actually does happen, albeit only in extremely tiny increments at the speeds and distances we can travel in space. If you add up the accumulated speed cosmonaut Sergei Krivalev has traveled in space – the most of any human with a total time spent in orbit of 803 days 9 hours and 39 minutes – he has actually time-traveled into his own future by 0.02 seconds. Time dilation is caused by differences in either gravity or relative velocity — each of which affects time in different ways. When astronauts and satellites orbit the Earth, they are slightly further away from the center of the planet –compared to people on the ground – and so they actually experience less gravitational time dilation. This means the astronauts’ time would run slightly faster, and when they return to Earth, they’d have to “come back” to the past compared to when they were in space.

But time dilation due to velocity means that clocks for astronauts in space run slightly slower relative to people who are on the ground. When you come back to Earth, you’d be have to go into the future slightly to catch up with clocks on the ground.

The effect of time dilation due to gravity, however, “is quite small because Earth’s gravity is quite weak,” says educator Colin Stuart in this great instructional video from TedEd, “and so the time dilation due to their speed wins out and astronauts really do travel a tiny amount into their futures.”

But, as stated earlier, with our current technology limiting the velocities of astronauts, these differences are minuscule: after 6 months on the ISS, an astronaut has aged less than those on Earth, but only by about 0.007 seconds. The effects would be greater if we could get the ISS to orbit Earth at near the speed of light (approximately 300,000 km/s), instead of the actual speed of about 7.7 km/s.

This effect has been proven by GPS satellites, which orbit Earth at about 14,000 km/h (9,000 mph) which cuts several microseconds off their clocks daily, relative to clocks on Earth.

Watch the video for more information and see associated material from TedEd , or read these interesting articles from Huffington Post and DailyMail. Here are some calculations about time and the “Twin Paradox.”

And if you really want to know what time it is, check out the website for the primary atomic clock.

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Time travel: five ways that we could do it

Cathal O’Connell

Cathal O'Connell is a science writer based in Melbourne.

In 2009 the British physicist Stephen Hawking held a party for time travellers – the twist was he sent out the invites a year later (No guests showed up). Time travel is probably impossible. Even if it were possible, Hawking and others have argued that you could never travel back before the moment your time machine was built.

But travel to the future? That’s a different story.

Of course, we are all time travellers as we are swept along in the current of time, from past to future, at a rate of one hour per hour.

But, as with a river, the current flows at different speeds in different places. Science as we know it allows for several methods to take the fast-track into the future. Here’s a rundown.

1. Time travel via speed

This is the easiest and most practical way to time travel into the far future – go really fast.

According to Einstein’s theory of special relativity, when you travel at speeds approaching the speed of light, time slows down for you relative to the outside world.

This is not a just a conjecture or thought experiment – it’s been measured. Using twin atomic clocks (one flown in a jet aircraft, the other stationary on Earth) physicists have shown that a flying clock ticks slower, because of its speed.

In the case of the aircraft, the effect is minuscule. But If you were in a spaceship travelling at 90% of the speed of light, you’d experience time passing about 2.6 times slower than it was back on Earth.

And the closer you get to the speed of light, the more extreme the time-travel.

Computer solves a major time travel problem

The highest speeds achieved through any human technology are probably the protons whizzing around the Large Hadron Collider at 99.9999991% of the speed of light. Using special relativity we can calculate one second for the proton is equivalent to 27,777,778 seconds, or about 11 months , for us.

Amazingly, particle physicists have to take this time dilation into account when they are dealing with particles that decay. In the lab, muon particles typically decay in 2.2 microseconds. But fast moving muons, such as those created when cosmic rays strike the upper atmosphere, take 10 times longer to disintegrate.

2. Time travel via gravity

The next method of time travel is also inspired by Einstein. According to his theory of general relativity, the stronger the gravity you feel, the slower time moves.

As you get closer to the centre of the Earth, for example, the strength of gravity increases. Time runs slower for your feet than your head.

Again, this effect has been measured. In 2010, physicists at the US National Institute of Standards and Technology (NIST) placed two atomic clocks on shelves, one 33 centimetres above the other, and measured the difference in their rate of ticking. The lower one ticked slower because it feels a slightly stronger gravity.

To travel to the far future, all we need is a region of extremely strong gravity, such as a black hole. The closer you get to the event horizon, the slower time moves – but it’s risky business, cross the boundary and you can never escape.

And anyway, the effect is not that strong so it’s probably not worth the trip.

Assuming you had the technology to travel the vast distances to reach a black hole (the nearest is about 3,000 light years away), the time dilation through travelling would be far greater than any time dilation through orbiting the black hole itself.

(The situation described in the movie Interstellar , where one hour on a planet near a black hole is the equivalent of seven years back on Earth, is so extreme as to be impossible in our Universe, according to Kip Thorne, the movie’s scientific advisor.)

The most mindblowing thing, perhaps, is that GPS systems have to account for time dilation effects (due to both the speed of the satellites and gravity they feel) in order to work. Without these corrections, your phones GPS capability wouldn’t be able to pinpoint your location on Earth to within even a few kilometres.

3. Time travel via suspended animation

Another way to time travel to the future may be to slow your perception of time by slowing down, or stopping, your bodily processes and then restarting them later.

Bacterial spores can live for millions of years in a state of suspended animation, until the right conditions of temperature, moisture, food kick start their metabolisms again. Some mammals, such as bears and squirrels, can slow down their metabolism during hibernation, dramatically reducing their cells’ requirement for food and oxygen.

Could humans ever do the same?

Though completely stopping your metabolism is probably far beyond our current technology, some scientists are working towards achieving inducing a short-term hibernation state lasting at least a few hours. This might be just enough time to get a person through a medical emergency, such as a cardiac arrest, before they can reach the hospital.

In 2005, American scientists demonstrated a way to slow the metabolism of mice (which do not hibernate) by exposing them to minute doses of hydrogen sulphide, which binds to the same cell receptors as oxygen. The core body temperature of the mice dropped to 13 °C and metabolism decreased 10-fold. After six hours the mice could be reanimated without ill effects.

Unfortunately, similar experiments on sheep and pigs were not successful, suggesting the method might not work for larger animals.

Another method, which induces a hypothermic hibernation by replacing the blood with a cold saline solution, has worked on pigs and is currently undergoing human clinical trials in Pittsburgh.

4. Time travel via wormholes

General relativity also allows for the possibility for shortcuts through spacetime, known as wormholes, which might be able to bridge distances of a billion light years or more, or different points in time.

Many physicists, including Stephen Hawking, believe wormholes are constantly popping in and out of existence at the quantum scale, far smaller than atoms. The trick would be to capture one, and inflate it to human scales – a feat that would require a huge amount of energy, but which might just be possible, in theory.

Attempts to prove this either way have failed, ultimately because of the incompatibility between general relativity and quantum mechanics.

5. Time travel using light

Another time travel idea, put forward by the American physicist Ron Mallet, is to use a rotating cylinder of light to twist spacetime. Anything dropped inside the swirling cylinder could theoretically be dragged around in space and in time, in a similar way to how a bubble runs around on top your coffee after you swirl it with a spoon.

According to Mallet, the right geometry could lead to time travel into either the past and the future.

Since publishing his theory in 2000, Mallet has been trying to raise the funds to pay for a proof of concept experiment, which involves dropping neutrons through a circular arrangement of spinning lasers.

His ideas have not grabbed the rest of the physics community however, with others arguing that one of the assumptions of his basic model is plagued by a singularity, which is physics-speak for “it’s impossible”.

The Royal Institution of Australia has an Education resource based on this article. You can access it here .

Related Reading: Computer solves a major time travel problem

Originally published by Cosmos as Time travel: five ways that we could do it

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Snuggling up on the couch for a late night binge session of your favorite Korean drama is only the best feeling ever. And when those dramas involve an unique time travel premise combined with adventure, heartfelt romance, or mysteries spanning eras, it makes for the perfect escape.

Korean dramas are no longer a novel experience for the global audience. The medium's capacity to engage a wider audience with its compelling storytelling and gripping character drama is enormous, and the more genres it dives into, the more it stands out.

Among the many exciting tales told over decades, those surrounding time travel are particularly exhilarating thanks to how the subject seamlessly blends science fiction, history, and romance , and generates high re-watch value. Imagining what it might be like to travel back in time or see the future is endlessly entertaining, and the possibilities are endless.

While it's impossible for humans to time travel ( sort of ), you can live vicariously through these incredible stories. We've brought together an intriguing list of 20 Korean dramas that incorporate time travel into their alluring stories about star-crossed lovers and brave protagonists willing to right historical wrongs — or just puzzled individuals displaced through time. Whatever time travel tale you're in the mood for, this list has it.

20 Queen and I (2012)

When a time-traveling scholar named Kim Boong Do finds a magic talisman and travels from Joseon dynasty to modern-day Seoul, 300 years into the future, he has one goal — to find Queen In Hyun.

Apparently, when she was being deposed by the council, Boong Do was her only supporter. But upon arriving in the future, he realizes that she’s a mere character being played in a drama by up-and-coming actress Choi Hee Jin.

A Time-Traveling Scholar’s Accidental Love Story

Queen and I perfectly blends history, comedy and romance through the fish-out-of-water scenario where Boong Do has to not only adapt to the traditions of the modern world, but also find a way to travel back to the Joseon era.

Starring Ji Hyun Woo and Yoo In Na, the drama features an unconventional partnership and blossoming romance against the backdrop of royal intrigue. Yoo In Na also won massive acclaim for her performance, making Queen and I a huge hit.

19 Splash Splash Love (2015)

The main protagonist of Splash Splash Love is Dan Bi, a high school student who hates math. On the day of her KSAT exam, she decides to run away and ends up on a playground in the middle of a freak rain which transports her to the Joseon kingdom.

She arrives hundreds of years in the past, in the middle of a drought. Dan Bi then meets King Lee Do, a man who yearns to be intellectual. Since Dan Bi’s high school level mathematics is still way ahead of Joseon’s teachings, she schools Lee Do and inspires him to bring change to the kingdom.

A Charming Tale of Transformation

The K-drama won hearts for its charming take on time travel and feel-good romance . For the most part, the episodes are heavy with emotion, balancing the more serious tone of the era with subtle glances and earnest dialogue. The leads, Kim Seul-gi and Yoon Doo-joon are extremely likable. Paired with the beautiful songs, the two-episode miniseries seems as breezy as it is breathtaking.

Stream Splash Splash Love on Kocowa

18 Rooftop Prince (2012)

In Rooftop Prince , Crown Prince Lee Gak finds himself mysteriously transported to modern-day Seoul along with his three retainers. There, he meets Hong Se Na, who is the spitting image of his beloved wife, who was found dead under mysterious circumstances.

It does not help that Lee Gak bears a striking resemblance to the grandson of the CEO of Se Na’s company. He tries to get close to her with the hopes that he’ll learn clues about the murder of the Crown Princess.

Related: 20 K-Dramas With No Boring Episodes

Crown Prince Finds Himself Out Of Place And Time

With Park Yoo-chun and Han Ji-min taking up the lead roles, it’s impossible for the drama to go wrong. What’s better is that Rooftop Prince has a multi-layered storyline that intertwines to reveal a greater plot, making the series more engaging episode after episode.

Seeing historical royals experience 21st century culture shock provides comic relief, and the time slip romance between Lee Gak and Se Na is simply marvelous.

Stream Rooftop Prince on Kocowa

17 Times (2021)

Times has a premise Hollywood has played with a number of times. Lee Jin Woo is an exceptionally talented reporter who will stop at nothing to uncover the truth about a case. When a mysterious phone call connects him to another hard-as-nails reporter named Seo Jung In, he’s shocked to discover that she’s speaking to him from five years in the future.

Jung In warns Jin Woo about the threat against her father, South Korea’s President, and together they work to find the culprit and break free of the strange time warp.

A Reporter’s Race Against Time

The drama is both a political thriller and a mind-bending time travel mystery. What makes it stand out is the intense performances from the lead actors, Lee Seo-jin and Lee Joo-young. Their chemistry with one another, especially when developed just over the phone, makes the show more endearing, and the suspenseful plot adds a gripping urgency to each episode.

Moreover, by charting away from a traditional time travel storyline, which often turns to be about romance, this innovative crime-solving drama subverts expectations.

Stream Times on Rakuten Viki

16 Hit the Top (2017)

As a member of a popular K-pop idol group, Yoo Hyun-Jae is nothing short of a star. Especially if you consider the ‘90s, when the group was at the height of its fame. However, when Hyun-Jae travels from 1993 to 2017, he finds out that he goes missing in the year 1994 and is presumed dead shortly after.

Determined to uncover the truth about his disappearance, he befriends Lee Ji Hoon and Choi Woo Seung, two aspiring young musicians.

Lighthearted, Feel-Good, But Complicated

We’re currently witnessing an evolution in the K-pop industry, with new talents emerging from the ground to become massive superstars. But it all started a bunch of years ago, and Hit the Top brings back the nostalgia and humor of the time.

Moreover, its predictable storyline never feels dull because of the upbeat soundtrack and dazzling performances. Definitely an underrated gem, Hit the Top is a must-watch in the genre.

15 Tomorrow, with You (2017)

Instead of going back centuries or traveling to the present day, Tomorrow, with You takes an innovative approach towards time travel and introduces us to Yoo So Joon, the CEO of a real estate company, who holds the power to decide when he wants to travel back in time.

Once, on a subway, he sees a future in which he’s unhappy and dissatisfied with life. To avoid facing it, he marries Song Ma Rin, a free-spirited photographer, unaware of her personal struggles.

A Bittersweet Romance

Taking the road less traveled, this brilliant Korean drama explores the complexities and sorrows of a loveless marriage through a time-travel premise.

Helped by outstanding performances from lead actors Shin Min-a (who you may know from Hometown Cha-Cha-Cha ) and Lee Je-hoon, this poignant melodrama tugs at the heartstrings with its slow-burn romance. Overall, the touching story reminds us to cherish the present and appreciate the little things in life.

14 Signal (2016)

Much like Times , Signal features a mysterious time-travel phenomenon involving walkie-talkies and an unidentified serial killer. Park Hae Yeong, a criminal profiler and police officer, stumbles upon a walkie-talkie and connects with a detective from the past, Lee Jae Han.

He reminds Hae Yeong of a crime he witnessed as a child and encourages him to solve cold cases with him. Together, they work on several investigations and solve decades-old crimes.

A Detective Duo Communicating Across Time

What’s interesting about the drama is that it is inspired by real-life crime stories and a murder case. The way it blends procedural thrills and heartfelt character drama is immensely terrific.

Concept-wise, Signal is truly unique and consistently full of suspense, making it hard not to binge. The pacing is beautiful, the actors, including Cho Jin-woong and Lee Je-hoon, as well as the young cast, are phenomenal in their roles.

Stream Signal on Paramount+

13 Familiar Wife (2018)

Going back in time and changing certain regretful events always has consequences. Playing with the same idea, Familiar Wife introduces us to Cha Joo Hyuk, who has been married to his college sweetheart Seo Woo Jin. But he is dissatisfied with the decisions he’s made and the life he’s living.

When a car accident sends him into the past, he experiences a drastic shift in his destiny by doing tiny things differently. Joo Hyuk ends up causing more trouble than before, including with his first love, Lee Hee Won.

Related: Movies Where Time Travel Actually Made Sense

Underrated and Unforgettable

Familiar Wife probably has one of the most unique executions on time travel ever seen in Korean dramas. Even though the premise seems unoriginal, it is the series’ ability to reflect on relationships, provide meaningful lessons on self-growth, and deliver a truckload of emotions that makes it stand out from the rest. Not heavy on drama but still pretty intense on chemistry, the series leaves an indelible mark on viewers.

12 Go Back Couple (2017)

Adapted from the webtoon Do it One More Time , Go Back Couple is a fun, 12-episode drama that follows an unhappily married couple. Choi Ban Do and Ma Jin Joo were adorable sweethearts when they married, but growing up together took a toll on them and how they simply cannot stand each other.

When they find themselves traveling back to their college days, away from career responsibilities and their young son, the two vow to make different choices and rekindle the lost romance.

Second Chances and First Loves

Instead of throwing one person back in time, Go Back Couple sends two people back to when they weren’t dating. It also combines moving insights on relationships, the complications and pitfalls of marrying young, and the beauty of being in love, with an enormous amount of humor and top-notch writing. Son Ho Jun and Jang Na Ra are truly exceptional as a couple, sharing swoon-worthy moments with an effortless and natural dynamic.

Stream Go Back Couple on Rakuten Viki

11 The Light in Your Eyes (2019)

With a melancholic start and an all-consuming end, The Light in Your Eyes is a beautiful, albeit heartbreaking drama. It follows 25-year-old Kim Hye Ja, who is in possession of a mysterious watch that can turn back time. In a desperate attempt to save her father, Hye Ja turns the watch several times and ends up aging herself to seventy years old.

Grappling with her situation, and realizing everybody she knew no longer recognizes her, she finds solace in the company of Lee Joon Ha, the man she once loved.

A Tragic Time-Travel Romance

The 2019 drama soars high because of its heartbreaking portrayal of romance between two souls torn apart by tragedy. Starring One Spring Night’s Han Ji Min and Start-Up’s Nam Joo Hyuk , The Light in Your Eyes is filled with stunning cinematography and emotionally moving storytelling.

The contrast between decades as well as the parting lessons towards the finale leave few dry eyes. That said, the series has remained among the more underappreciated gems.

Stream The Light in Your Eyes on Netflix

10 My Perfect Stranger (2023)

Among the few recent time travel Korean dramas on this list is My Perfect Stranger . Just as the title promises, the series follows two strangers who end up traveling back to the same year, 1987, and discover the poignant bond they share.

On one hand, there is Yoon Hae Joon, a kindhearted journalist who wants to get to the bottom of a serial murder case. And on the other hand, Baek Yoon Young wants to stop her parents from marrying because her mother dies in the future.

Keeps You Guessing Till The Very End

Featuring a smooth genre blend, this compelling time travel story finds a spot among the best K-dramas because of its ability to absorb the viewers’ attention. The series explores heavy themes like grief, hope, and trauma, as well as the extraordinary lengths one is willing to go for the truth. Kim Dong-wook and Jin Ki-joo are absolutely stunning as two souls grappling with their realities.

Stream My Perfect Stranger on Rakuten Viki

9 Moon Lovers: Scarlet Heart Ryeo (2016)

Despite being a flop in South Korea, Moon Lovers: Scarlet Heart Ryeo has found a devoted fan base in the West for its storyline, which sees IU as an unassuming young girl named Go Ha Jin.

On the day of a total eclipse, she travels back to Goryeo-era Korea, where she wakes up in the body of the 16-year-old Hae Soo. Now entangled in kingdom politics, tragic losses, and power struggles, Ha Jin must rise above being a mere pawn and take control of the throne.

Sweeping Romance Set In An Ancient Land

With its epic production values and breathtaking costume design , Moon Lovers: Scarlet Heart Ryeo captured the hearts of many viewers. Beyond the visual appeal, however, the drama also has a brilliant pacing and an intense aesthetic that keeps you hooked from start to finish. By moonlighting as a passionate romance, the series shocks you with its emotional depth and un-fairytale-like ending. However, the characters played by IU and Lee Joon-Gi resonate the most.

8 Tunnel (2017)

First set in 1986, Tunnel introduces us to a highly skilled and enthusiastic crime detective named Park Gwang Ho. Hot on the tail of a serial killer, he chases him through a tunnel which turns out to be a time portal. Gwang Ho is transported to present day, the year 2016, where the same serial killer is on a murder spree. Enter another elite detective, Kim Sun Jae. The two detectives form a partnership like no other, navigating uncharted territory of the criminal underground.

Related: 10 K-Dramas with the Best Plot Twists, Ranked

An Epic Crime-Solving Korean Fantasy Drama

Featuring a healthy dose of heart-pounding action and a gripping mystery, Tunnel is one of the most engaging thriller series out there. It breaks boundaries with the innovative plotlines and stunning cinematography. Addictive from start to finish, it also lets you revel in the feel-good bromance between Choi Jin-hyuk and Yoon Hyun-min.

Stream Tunnel on The Roku Channel

7 Chicago Typewriter (2017)

More of a fantasy than a drama, Chicago Typewriter is about three resistance fighters across two timelines, with one being set in the 1930s, the time of the Japanese occupation of Korea, and the second in the 21st century. As they work undercover, disguised as a book enthusiast, a ghostwriter, and a bestselling author respectively, dark secrets from their past continue to haunt them.

Reincarnated Friendships Haunted By A Past

At its core, Chicago Typewriter is a story about three people’s friendships across time. From failing to protect those they loved dearly to cherishing what’s left in a liberated, dreamlike modern world, their journey endures as a memorable work of art. Yoo Ah-in, Im Soo-jung, and Go Kyung-pyo are phenomenal as star-crossed souls anchoring the poignant and multi-layered drama.

6 A Time Called You (2023)

Adapted from the Taiwanese television series Someday or One Day , this recent Korean drama deserves a spot on the list for its charming leads and refreshing premise. It’s been a year, and Han Jun Hee is still devastated about losing her boyfriend.

When she’s mysteriously transported to the year 1998 and takes on the identity of a high school student named Kwon Min Joo, things begin falling into place. She meets Nam Si Heon, who bears a striking resemblance to her late boyfriend.

Absolute Delight For Ahn Hyo-Seop Fans

Released on Netflix in September 2023, A Time Called You charmed viewers with its fresh take on a time-crossed love story. For those who have already watched the original, the portrayal of timelines as well as character drama is equally soulful and moving. Along with its beautiful soundtrack and fantastic performances from Ahn Hyo-seop, Jeon Yeo-been, and Kang Hoon, the series sends you on a rollercoaster of emotions.

Stream A Time Called You on Netflix

5 Mr. Queen (2020)

Mr. Queen is an extremely intriguing and twisted historical Korean drama based on the Chinese web series Go Princess Go . In it, ambitious chef Jang Bong Hwan serves South Korea’s most elite residents and politicians.

When he gets into a freak accident, he finds himself waking up in the body of Kim So Yong in the Joseon dynasty . As he navigates the treacherous court politics, he uncovers dark secrets about the supposedly meek King Cheol Jong.

Fascinating Body-Swap Romance In A Monarchy

Offering endless emotions as the story explores a commoner experiencing a sudden royal life, Mr. Queen was nothing short of a masterpiece. With their career-best performances, Shin Hye-sun and Kim Jung-hyun became overnight stars and one of the major reasons for the show’s success. The sharp writing, jarring plot twists, comedic timing, and satisfying ending make the drama capture the essence of an era long gone.

Stream Mr. Queen on Netflix

4 The King: Eternal Monarch (2020)

In his quest to create a balance between two worlds and escape the wound inflicted upon him as a child, the Emperor of the Kingdom of Corea, Lee Gun, accidentally gets propelled into another universe. He's surprised to learn that the strange new world — modern day Seoul — operates under the Republic of Korea, and not a Kingdom. Lee Gon teams up with Jeong Tae Eul, a detective, and together they work to stop an evil that plagues both worlds.

An Epic Combination of Fantasy and Romance

Back in 2020, The King: Eternal Monarch became the most popular Korean drama across the globe. It featured lavish production values, sweeping action, and spectacular performances from stars like Lee Min-ho and Kim Go-eun. But beyond the obvious reasons for its success, it was the series’ ambitious parallel universe premise and the epic combination of fantasy and romance that had an astonishing effect on the audience.

Stream The King: Eternal Monarch on Netflix

3 Live Up to Your Name (2017)

When a Joseon era doctor named Heo Im finds himself in modern-day Korea, almost 400 years into the future, he is stunned by the medical practices being followed currently. His unmatched traditional knowledge is suddenly dated.

Soon, he clashes with modern doctor Yeon Gyung and she mocks his invaluable medical know-how. Despite their differences, Yeon Gyung travels back with him to the Joseon era and realizes just how challenging ancient techniques can be.

Related: 10 Medical Drama TV Shows That Are Absolute Tearjerkers

Medical Drama Meets Time Travel

Finding its charm in the delicate examination of traditional Eastern medicine and Western practices, Live Up to Your Name is a humorous period drama. The development of clashes and eventual admiration between both protagonists makes the heart of the show, with the entertaining cast consisting of Kim Nam-gil and Kim Ah-joong. Every episode feels rich in Korean history and character development — no wonder it became such a fan favorite.

2 Life on Mars (2018)

Known to be the best in his profession, with the reputation of having solved the hardest of cases, detective Han Tae Joo is very close to rising up the ranks. However, while chasing a serial killer, he gets into an accident and finds himself transported back to 1988. Appointed as a rookie detective in a small city, Tae Joo must navigate the retro world of payphones and tape recorders. He soon realizes that he must solve a case of the past to get back to the future.

One Detective's Surreal Journey To The Past

Life on Mars drew a lot of praise and applause for its creative blend of crime thriller, mystery, and comedy. The drama is based on the 2006 British series of the same name , and suffice it to say, it does not disappoint. Whether it is the nostalgia of its late-80s setting or the impressive production design, there are elements that keep you engaged and guessing till the very end. Plus, Jung Kyung-ho, who you may know from Netflix's Crash Course in Romance , delivers a charming performance.

1 Marry My Husband (2024)

Despite only having four episodes premiered so far, Marry My Husband has shown great potential for becoming one of the best K-dramas of the year. The series starts off strong, with Kang Ji Won experiencing a troubled married life with her neglectful husband and abusive mother-in-law.

Things only get worse when she's diagnosed with cancer. And then on a fateful afternoon, Ji Won witnesses her husband Park Min Hwan in bed with her best friend Jung Soo Min. The two end up murdering her, and Ji Won surprisingly wakes up 10 years into the past, determined to exact revenge on them.

Modern Woman's Chaotic Attempts At Redoing The Past

Marry My Husband is based on the web novel of the same name written by Sung So-jak, and much like the source material, the series does a fantastic job at setting up the intrigue and tone by making us root for the protagonist.

Starring Park Min-young in an unabashedly endearing role, the series puts a more poignant spin on time travel tropes. Watching the protagonist moving past manipulation for genuine love and self-realized narrative has audiences eagerly waiting for another episode.

Stream Marry My Husband on Prime Video

• The Leadership Brief

Intuitive Machines CEO Steve Altemus on Making Moon Landing History and the Future of Private Space Travel

N obody would want to get famous the way Steve Altemus got famous. It was in 2003 that Altemus’s name first became widely known, back when he was working for NASA in the human spaceflight division. On Feb. 1 of that year, the space agency was shaken to its roots, after the space shuttle Columbia disintegrated on reentry, claiming the lives of its seven-person crew. Altemus was put in charge of the forensic examination following the tragedy, assembling the 85,000 pieces of Columbia debris to help determine the cause of the accident. He did his job well—so well that the surviving three shuttles were able to fly without incident for eight and a half more years before their retirement in the summer of 2011.

Two years after the last shuttle flew, Altemus left NASA and co-founded Intuitive Machines , a pocket-sized aerospace company of fewer than 400 people, headquartered in Houston, Texas. The small outfit, which is one of TIME’s 100 Most Influential Companies of 2024, has big dreams, however—nothing short of working to establish a new lunar economy. The job involves building and flying scientific and communications spacecraft on and around the moon, most notably in cooperation with NASA’s Artemis program, which aims to have astronauts back on the lunar surface before the end of the decade.

On Feb. 22 of this year, Intuitive Machines scored a huge win—becoming the first private company to soft-land a spacecraft on the moon, a feat previously achieved only by the space agencies of the U.S., the former Soviet Union, China, India, and Japan. The spacecraft, named Odysseus , touched down near the south lunar pole, a region rich in deposits of water ice, which could be used by future crews for breathable oxygen, rocket fuel, and drinking water. Odysseus lived for just under a month before its power systems winked out. But Intuitive Machines has plenty of other missions pending, working not just with NASA, but with the private sector to build communications satellites, enable resource harvesting, provide surface transportation, and deploy scientific research instruments.

In a conversation with TIME in April, condensed and edited for clarity, Altemus talked about the literally otherworldly future of his company—and of humanity writ large.

You made history with the Odysseus landing. Tell us a little bit about the mission and where you think it stands in the arc of space exploration.

We launched on February 15, spent about a week in transit, landed on the 22nd and executed our full mission as planned. What's amazing about that is to be able to do this on the first try and be successful. It’s unprecedented. We didn't do that in Apollo. The Russians didn't do that. Nobody's done that. What's even more impactful and what I think the legacy of the company will be is more than landing on the moon, but creating that economy around the moon.

Part of Intuitive Machines’ remit is to provide lunar transportation services for the private sector, but your biggest customer currently is NASA. How did you and the space agency initially connect?

For the first five years of the company, we were bouncing around in the single digit millions in revenue. ​​Our original mission was to use human spaceflight engineering skills and methodologies to solve problems in the industries here in Houston, which are oil and gas, healthcare, and aerospace. It wasn't until 2018 that the National Security Council said the moon is in our strategic interests, because of the geopolitical tensions with China. We then pivoted the entire company, to going back to the moon. That same year, we got an anchor contract with NASA for $2.6 billion over ten years.

What missions will you be flying under that arrangement?

In addition to Odysseus, we have two other spacecraft coming up that are replicas of Odysseus, but carry a different complement of deployable payloads. We also expect the award of a bigger contract at the end of May to put a constellation of six satellites around the moon to provide communications and navigation for the Artemis program. Those satellites will also allow us to sell navigation and communication services to and from the moon for any user globally.

Communications infrastructure around the moon requires similar infrastructure on Earth to connect with the satellites and process data. How does that part of the system function?

We’ve established the only lunar distance communications network around the world, in over 12 countries. We use underutilized radio astronomy dishes in the United Kingdom, Australia, South Africa, the United States—in both Kentucky and California—and elsewhere.

You also secured a major deal recently when you won another NASA contract to build the 21st century version of the Apollo era’s lunar rover, which astronauts used to travel extended distances on the missions of Apollo 15, 16, and 17. That could be an impressive piece of hardware.

Yes, our rover is about 1.5 metric tons, which is about the size of an F-150 pickup truck. It will be able to provide extreme mobility to astronauts. It's also self-driving so that when the astronauts are not there, we can use it commercially to do scientific and discovery work. We can search for water ice or for rare minerals or metals. Put those pieces together and we not only can fly to the moon, but communicate, navigate, and actually move out from location. We're the only company in the world that is doing these pieces like this in this way.

And yet you’re a small company competing with legacy operations like Boeing, or with giant upstarts like SpaceX. How do you stay in that game?

Our goal is to be a tier-one aerospace company, but do things differently. Most of the tier one aerospace companies came up during World War II and went through the consolidation in the 1970s and ’80s. They made their money on inventions on a wartime footing. Intuitive Machines is relatively small, but is still bidding on missions and being successful. Taking an intractably difficult mission like landing on the moon and doing it at a fixed price for about $100 million is just unheard of in the era of cost plus award fee contracting. About 75% to 80% of our business is with the U.S. government; the remainder is currently commercial and international. But since we landed on the moon we're seeing more requests from commercial companies and international governments to fly on our missions without NASA's involvement. Some interest has come directly to us from the Saudi space agency, the Australian space agency, Germany, Hungary, and JAXA—the Japanese space agency. 

You’ve been publicly traded since 2023. How is that phase of your growth going?

We went public on February 15, 2023, one year to the day before we launched to the moon. Our call sign is lunar—LUNR—on the NASDAQ. We have about 120 million shares. [ The company’s market value was more than $500 million as of Aug. 16 . ] But there is a larger mission for us. If we're going to maintain global competitiveness, we have to find a way to break the back of the paradigm that it takes a decade or two to build a space system. The moon is here to stay and it is worth going all in to do this on behalf of the United States, for the United States.

More Must-Reads from TIME

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• Heman Bekele Is TIME’s 2024 Kid of the Year
• The Reintroduction of Kamala Harris
• What a $129 Frying Pan Says About America’s Eating Habits
• A Battle Over Fertility Law in China
• The 1 Heart-Health Habit You Should Start When You’re Young
• Cuddling Might Help You Get Better Sleep
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Write to Jeffrey Kluger at [email protected]

When should you leave? The best and worst times for traffic over Labor Day Weekend 2024

• Travel during the final long weekend of summer will be busy within the U.S., with domestic travel up by 9% from last year.
• This year, international travel is down 4% from 2023, likely due to rising costs.
• The roads will be most congested during the afternoons of Thursday, Aug. 29, and Friday, Aug. 30, and early evening and morning of Saturday, Aug. 31.

As Labor Day weekend approaches, travelers are gearing up for one last summer getaway .

This year, Labor Day falls on Sept. 2, marking the end of a record-breaking travel season. Travel during the final long weekend of summer will be busy within the U.S., with domestic travel up by 9% from last year, according to AAA.

Those driving to their destination can expect heavy traffic, especially during peak travel hours. But they can at least enjoy lower gas prices: The national average is about 20 cents a gallon less than last year's holiday weekend.

This year, international travel is down 4% from 2023, likely because of rising costs. According to AAA booking numbers, international travel for Labor Day weekend 2024 costs 11% more than last year.

Here's what travelers can expect for Labor Day weekend 2024.

Learn more: Best travel insurance

What are the most popular domestic destinations for Labor Day weekend 2024?

This year, many U.S. travelers are heading toward Seattle with bookings for the Emerald City up nearly 30% from last year, according to AAA's booking data. Some will be continuing to Alaska, with Anchorage and Juneau also topping the list for the most popular U.S. end-of-summer destinations.

"This is the time of year to go on an Alaska cruises ,” said Paula Twidale, senior vice president of AAA Travel, said in a news release. "There are fewer crowds compared to earlier in the summer, and if you’re lucky, you might even catch a glimpse of fall colors! It’s no surprise Alaska cruises are sold out this Labor Day weekend."

What are the most popular international destinations for Labor Day weekend 2024?

Just north of the Canadian-U.S. border, Vancouver tops the list for the most popular international destination, according to AAA. Following closely behind are beloved European destinations including Rome, London, Paris, Dublin and Amsterdam.

Learn more:   Best travel insurance

What are the worst times to drive for Labor Day weekend 2024?

The roads will be most congested during the afternoons of Thursday, Aug. 29, and Friday, and early evening and morning of Saturday. Returning home from the long weekend, drivers can expect the worst traffic during the afternoon of Sunday, Sept. 1, from 11 a.m. to 8 p.m., Monday and the morning of Tuesday.

"Drivers should expect the most severe traffic jams before the holiday weekend as commuters mix with travelers,” Bob Pishue, transportation analyst at INRIX, said in a statement. "Monitoring traffic apps, local news stations, and 511 traveler information services may help drivers navigate around congestion and reduce driver frustration this Labor Day."

What are the best times to drive for Labor Day weekend 2024?

If you're hoping to avoid traffic jams, plan to hit the road at night or the early morning. The best times to drive for Labor Day weekend are before 11 a.m. on Thursday, Aug. 29, before noon or after 7 p.m. on Friday, and after noon on Saturday.

For returning home, depart before noon on Sunday, Sept. 1, before 10 a.m. on Monday, or after 1 p.m. on Tuesday.

The Key Points at the top of this article were created with the assistance of Artificial Intelligence (AI) and reviewed by a journalist before publication. No other parts of the article were generated using AI. Learn more .

How to avoid the worst of jet lag and maximize your travel time

Jet lag is a problem for many travelers but there are some easy ways to adjust your body clock

LONDON -- It's the bane of many travelers: jet lag. Nobody wants to lose out because they're too tired to enjoy the delights of their vacation spot.

Here are some tips on how to handle jet lag, wherever you might end up.

Scientists define jet lag as the effect on the human body of traveling across different time zones. Our bodies have biological clocks programmed into almost every cell in the body, according to Sofia Axelrod, who studies circadian rhythms at Rockefeller University in New York.

“The clock is set by the 24-hour light and dark pattern,” Axelrod said. “Every morning when we wake up, specialized (light) receptor cells in our retina receive a daylight signal, which is transmitted to the brain and from there, the whole body.”

When we travel to another time zone, our eyes receive the daylight signal at a different time than usual, causing our internal clocks to reset. But that process can take awhile — and it’s during that adjustment period that we feel the effects of jet lag.

Yes, but that can come at a cost. Malcolm von Schantz, a professor who specializes in circadian rhythms at Northumbria University in Newcastle, said that flying in premium cabins where travelers can stretch out and properly rest, can ward off sleep deprivation, but he acknowledges that isn't an option for most people. Still, he said that timing your flights can help. For example, he suggests flying from Europe to North America during the day, so that it’s evening when passengers land and they can get a proper night’s sleep.

“If you take the evening flight instead, you’ll be woken up at midnight to be served breakfast and land an hour or two later, when both jet lag and sleep deprivation will hit you hard and simultaneously,” he said.

Von Schantz also said flying in newer models with a lighter frame, like the Airbus A350 or Boeing 787 Dreamliner, would help. That’s because those planes can maintain a more comfortable cabin atmosphere, which should help travelers feel less worn out by the end of their flights.

Experts say getting exposure to sunlight is critical to resetting your internal body clock. That can mean either avoiding morning sun or deliberately seeking it out, depending on where you’ve travelled from. Getting light in the morning will advance your body clock, while light exposure in the early evening will delay it. Naps are OK, but scientists warn against taking long siestas later in the day, as that might compromise your ability to sleep through the night.

Melatonin, a hormone that the brain naturally produces when the body thinks it’s night, can be helpful. But it’s not available everywhere and in some countries like the U.K. and France, a prescription is required. Von Schantz of Northumbria University said that one of the advantages of melatonin is that you can start taking it before your journey, to reset your internal clock quicker.

“If you’re in a part of the world where melatonin is available over the counter, you can combine the effects of light and melatonin to achieve the advance or delay (in your body clock) that you need,” he said.

Business travelers might want to consider arriving a day or two ahead of any important meetings or events, said Russell Foster of Oxford University, who has authored a book on circadian rhythms.

“You should just be aware that if you’re jet-lagged, you’re more likely to make unwise decisions, be less empathetic and unable to multitask,” he said.

Tourists might not need to be as alert as business travelers, but they should still be careful, he said. He advises tourists to get caught up on their sleep before doing anything potentially risky or that requires concentration, like driving.

Foster said he tries to maximize his light exposure when he arrives at a new destination to offset jet lag. But he also has a fallback strategy: coffee.

“I’m not suggesting it’s an ideal thing to do, but caffeine will help override the sleepiness and cognitive impairment you might be feeling as a result of jet lag,” he said.

The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Science and Educational Media Group. The AP is solely responsible for all content.

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New Redding to Chico bus line starts this week

Travelers will be able to take Redding Area Bus Authority transportation from downtown Redding to Chico starting Thursday under a new agreement with the San Joaquin Joint Powers Authority.

It's the first RABA bus service to operate outside of Shasta County, said Transit General Manager John Andoh.

"We're hoping that it'll get more riders, especially people going between Shasta and Butte counties," he said.

"I figure, like, maybe we can get folks that live in Redding that would want to go to classes at California State University, Chico, for instance," said Andoh.

He said the agency is hoping the expansion means ridership will increase from the current 10 to 15 passengers per trip to 25 to 30 riders, or "half a full bus. So that would be ideal for us."

How Amtrak's 'bus bridge' operates

Currently, the bus out of Redding carries passengers from Redding to Sacramento via Amtrak's Thruway bus service that is open only to Amtrak passengers heading for the train station in Sacramento.

The Buzz: 'The Hound' is back. Greyhound returns to downtown Redding

California law hadn't allowed people to buy Amtrak tickets just to ride the bus. But lawmakers in 2022 changed the law so public transit agencies like RABA that operate an Amtrak route now can sell bus tickets without requiring people to also ride the train.

That translates to new travel destinations for RABA bus riders, since passengers can ultimately buy an Amtrak bus ticket between Redding, Red Bluff and Chico and connect to buses going to Sacramento or Stockton, all stops along the Route 3 corridor. "And they don't have to ride the train," said Andoh.

Once in Chico, passengers wanting to continue to other cities can transfer to another Amtrak bus, he said.

Is there a bus that goes to the Sacramento airport?

The new service does not go to Sacramento International Airport. To get there, bus passengers would need to go to Sacramento and then transfer to the public Yolobus or Sacramento Regional Transit District systems, which are located near Sacramento's Amtrak station, Andoh said.

All aboard: The Buzz: Greyhound returns to Redding

FlixBus — the German bus services company and current owner of the Greyhound bus line — now operates only two trips a day between Redding and Chico, he said.

People can see the bus-only schedule on the RABA website and buy Amtrak tickets for bus travel on Amtrak.com .

Amtrak's operator in the region, the San Joaquin Joint Powers Authority, was hearing that the public wanted a bus-only service along the Interstate 5 corridor that did not also require the purchase of a train ticket.

The authority is paying RABA $392,000 annually to operate the Redding-to-Chico bus service 365 days a year, said Andoh.

Whatever happened to the Salmon Runner bus?

Andoh said the new bus travel additions from Redding are not meant to replace a proposed Redding to Sacramento airport bus service called the Salmon Runner.

"This is an interim step towards the Salmon Runner should Shasta Regional Transportation Agency wish to continue to implement it," said Andoh, adding that "the pandemic changed a lot of things."

SRTA is now evaluating the inter-city needs for Shasta County and whether the demand for the Salmon Runner still exists, he said. Officials are seeking opinions from the public here: https://ca-srta.civicplus.com/373/North-State-Intercity-Bus-to-Rail-Plan.

Redding Record Searchlight Local Managing Editor Michele Chandler can be reached at [email protected] or 530-338-7753. To support and sustain our local news coverage, please  subscribe  today.