how to time travel using light

• Newsletters

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

Please login to favourite this article.

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.

If you liked this, you may like:

A beginner's guide to time travel

Learn exactly how Einstein's theory of relativity works, and discover how there's nothing in science that says time travel is impossible.

Everyone can travel in time . You do it whether you want to or not, at a steady rate of one second per second. You may think there's no similarity to traveling in one of the three spatial dimensions at, say, one foot per second. But according to Einstein 's theory of relativity , we live in a four-dimensional continuum — space-time — in which space and time are interchangeable.

Einstein found that the faster you move through space, the slower you move through time — you age more slowly, in other words. One of the key ideas in relativity is that nothing can travel faster than the speed of light — about 186,000 miles per second (300,000 kilometers per second), or one light-year per year). But you can get very close to it. If a spaceship were to fly at 99% of the speed of light, you'd see it travel a light-year of distance in just over a year of time. 

That's obvious enough, but now comes the weird part. For astronauts onboard that spaceship, the journey would take a mere seven weeks. It's a consequence of relativity called time dilation , and in effect, it means the astronauts have jumped about 10 months into the future. 

Traveling at high speed isn't the only way to produce time dilation. Einstein showed that gravitational fields produce a similar effect — even the relatively weak field here on the surface of Earth . We don't notice it, because we spend all our lives here, but more than 12,400 miles (20,000 kilometers) higher up gravity is measurably weaker— and time passes more quickly, by about 45 microseconds per day. That's more significant than you might think, because it's the altitude at which GPS satellites orbit Earth, and their clocks need to be precisely synchronized with ground-based ones for the system to work properly. 

The satellites have to compensate for time dilation effects due both to their higher altitude and their faster speed. So whenever you use the GPS feature on your smartphone or your car's satnav, there's a tiny element of time travel involved. You and the satellites are traveling into the future at very slightly different rates.

But for more dramatic effects, we need to look at much stronger gravitational fields, such as those around black holes , which can distort space-time so much that it folds back on itself. The result is a so-called wormhole, a concept that's familiar from sci-fi movies, but actually originates in Einstein's theory of relativity. In effect, a wormhole is a shortcut from one point in space-time to another. You enter one black hole, and emerge from another one somewhere else. Unfortunately, it's not as practical a means of transport as Hollywood makes it look. That's because the black hole's gravity would tear you to pieces as you approached it, but it really is possible in theory. And because we're talking about space-time, not just space, the wormhole's exit could be at an earlier time than its entrance; that means you would end up in the past rather than the future.

Trajectories in space-time that loop back into the past are given the technical name "closed timelike curves." If you search through serious academic journals, you'll find plenty of references to them — far more than you'll find to "time travel." But in effect, that's exactly what closed timelike curves are all about — time travel

This article is brought to you by  How It Works .

How It Works is the action-packed magazine that's bursting with exciting information about the latest advances in science and technology, featuring everything you need to know about how the world around you — and the universe — works.

There's another way to produce a closed timelike curve that doesn't involve anything quite so exotic as a black hole or wormhole: You just need a simple rotating cylinder made of super-dense material. This so-called Tipler cylinder is the closest that real-world physics can get to an actual, genuine time machine. But it will likely never be built in the real world, so like a wormhole, it's more of an academic curiosity than a viable engineering design.

Yet as far-fetched as these things are in practical terms, there's no fundamental scientific reason — that we currently know of — that says they are impossible. That's a thought-provoking situation, because as the physicist Michio Kaku is fond of saying, "Everything not forbidden is compulsory" (borrowed from T.H. White's novel, "The Once And Future King"). He doesn't mean time travel has to happen everywhere all the time, but Kaku is suggesting that the universe is so vast it ought to happen somewhere at least occasionally. Maybe some super-advanced civilization in another galaxy knows how to build a working time machine, or perhaps closed timelike curves can even occur naturally under certain rare conditions.

This raises problems of a different kind — not in science or engineering, but in basic logic. If time travel is allowed by the laws of physics, then it's possible to envision a whole range of paradoxical scenarios . Some of these appear so illogical that it's difficult to imagine that they could ever occur. But if they can't, what's stopping them? 

Thoughts like these prompted Stephen Hawking , who was always skeptical about the idea of time travel into the past, to come up with his "chronology protection conjecture" — the notion that some as-yet-unknown law of physics prevents closed timelike curves from happening. But that conjecture is only an educated guess, and until it is supported by hard evidence, we can come to only one conclusion: Time travel is possible.

A party for time travelers 

Hawking was skeptical about the feasibility of time travel into the past, not because he had disproved it, but because he was bothered by the logical paradoxes it created. In his chronology protection conjecture, he surmised that physicists would eventually discover a flaw in the theory of closed timelike curves that made them impossible. 

In 2009, he came up with an amusing way to test this conjecture. Hawking held a champagne party (shown in his Discovery Channel program), but he only advertised it after it had happened. His reasoning was that, if time machines eventually become practical, someone in the future might read about the party and travel back to attend it. But no one did — Hawking sat through the whole evening on his own. This doesn't prove time travel is impossible, but it does suggest that it never becomes a commonplace occurrence here on Earth.

The arrow of time 

One of the distinctive things about time is that it has a direction — from past to future. A cup of hot coffee left at room temperature always cools down; it never heats up. Your cellphone loses battery charge when you use it; it never gains charge. These are examples of entropy , essentially a measure of the amount of "useless" as opposed to "useful" energy. The entropy of a closed system always increases, and it's the key factor determining the arrow of time.

It turns out that entropy is the only thing that makes a distinction between past and future. In other branches of physics, like relativity or quantum theory, time doesn't have a preferred direction. No one knows where time's arrow comes from. It may be that it only applies to large, complex systems, in which case subatomic particles may not experience the arrow of time.

Time travel paradox 

If it's possible to travel back into the past — even theoretically — it raises a number of brain-twisting paradoxes — such as the grandfather paradox — that even scientists and philosophers find extremely perplexing.

Killing Hitler

A time traveler might decide to go back and kill him in his infancy. If they succeeded, future history books wouldn't even mention Hitler — so what motivation would the time traveler have for going back in time and killing him?

Killing your grandfather

Instead of killing a young Hitler, you might, by accident, kill one of your own ancestors when they were very young. But then you would never be born, so you couldn't travel back in time to kill them, so you would be born after all, and so on … 

A closed loop

Suppose the plans for a time machine suddenly appear from thin air on your desk. You spend a few days building it, then use it to send the plans back to your earlier self. But where did those plans originate? Nowhere — they are just looping round and round in time.

Sign up for the Live Science daily newsletter now

Get the world’s most fascinating discoveries delivered straight to your inbox.

How It Works has a special formula for making learning fun by answering questions on science, space, history, technology, transport and the environment with engaging articles, in-depth special features, global science news, and topical interviews. With impressive cutaway illustrations that show how things function, and mindblowing photography of the planet’s most inspiring spectacles, How It Works represents the pinnacle of engaging, factual fun for a mainstream audience keen to keep up with the latest tech and the most impressive phenomena on the planet and beyond. Written and presented in a style that makes even the most complex subjects interesting and easy to understand, How It Works is enjoyed by readers of all ages.

Get fantastic offers by subscribing to the digital and/or print edition now. Subscribers get 13 issues per year!

How to safely record the April 8 eclipse with your phone

Single enormous object left 2 billion craters on Mars, scientists discover

Hair-straightening cream tied to woman's repeated kidney damage

Most Popular

By Anna Gora December 27, 2023

By Anna Gora December 26, 2023

By Anna Gora December 25, 2023

By Emily Cooke December 23, 2023

By Victoria Atkinson December 22, 2023

By Anna Gora December 16, 2023

By Anna Gora December 15, 2023

By Anna Gora November 09, 2023

By Donavyn Coffey November 06, 2023

By Anna Gora October 31, 2023

By Anna Gora October 26, 2023

• 2 Mass grave of plague victims may be largest ever found in Europe, archaeologists say
• 3 India's evolutionary past tied to huge migration 50,000 years ago and to now-extinct human relatives
• 4 1,900-year-old coins from Jewish revolt against the Romans discovered in the Judaen desert
• 5 Dying SpaceX rocket creates glowing, galaxy-like spiral in the middle of the Northern Lights
• 2 Speck of light spotted by Hubble is one of the most enormous galaxies in the early universe, James Webb telescope reveals
• 3 8-hour intermittent fasting tied to 90% higher risk of cardiovascular death, early data hint
• 4 James Webb telescope confirms there is something seriously wrong with our understanding of the universe
• 5 Beluga whales appear to change the shape of their melon heads to communicate, scientists discover

One Universe at a Time

Using Light To Simulate Time Travel

In Physics by Brian Koberlein 8 December 2015 2 Comments

While the idea of time travel gives rise to discussions of topics ranging from science fiction to ethics , understanding the possible effects of time travel gives us a better grasp of the foundations of general relativity and quantum theory. Most work in the area has focused on the theoretical aspects of time travel, but there are also attempts to simulate the effects of time travel experimentally.

In physics, a time machine is known as a closed timelike curve (CTC). Basically, an object makes a loop through spacetime to interact with its past self. In a recent work published in Nature , a team simulated the possible effect of a time machine using polarized light. Since they couldn’t actually make a beam of light travel back in time, they used two separate beams of light, with one beam mirroring an earlier state of the other. Their focus was to study how quantum computers might be affected by a CTC.

The DWave chip is promoted as a quantum computer. Credit: DWave

Quantum computers use the fuzzy aspects of quantum mechanics to perform calculations. Rather than discrete bits of 0s and 1s, a quantum computer uses quantum states or q-bits. The challenges of quantum computing are huge, but they have the potential to perform some incredibly difficult computations with relative ease. In the early 1990s, David Deutsch demonstrated that if a CTC is self-consistent on a quantum level, then quantum computers could solve computational problems known as PSPACE-complete. In other words, it would be the supercomputer of all supercomputers.

Deutsch’s model is controversial because it relies on an interpretation of quantum mechanics that invokes “parallel universes.” And without a real time machine, his ideas are impossible to prove. For this simulated time machine, the team tweaked the states of their light beams to see what results they could get. They found that the results were self-consistent as Deutsch proposed, and they also completely agreed with relativity. This doesn’t mean that Deutsch is right, but rather if Deutsch is right the effects would work as he claims. There are other quantum models that would also prevent time-traveling paradoxes, but wouldn’t allow for the construction of a super-duper supercomputer.

The results of this work aren’t particularly surprising, but it’s an excellent demonstration of just how subtle and sophisticated optical experiments can be. And until someone is able to make a real time machine, simulated time machines like this one are the only way we can study time travel experimentally.

Paper: Martin Ringbauer, et al. Experimental simulation of closed timelike curves . Nature Communications 5, Article number: 4145 (2014)

Related Posts

Hi Brian, could you explain a bit more about the experiment setup, particularly how the mirroring of the earliet stage of the beam works? Is there a “past” and “present” beam so as to speak?

Leave a Reply Cancel reply

• Amazon Big Spring Sale Deals
• Best Mint alternative
• Apple wants to bring Gemini AI to iPhone
• Best MacBook for 2024

Scientists simulate time travel using light particles

We may never see practical time travel in our lifetimes, if it's possible at all . However, a team at the University of Queensland has given the Doc Browns of the world a faint glimmer of hope by simulating time travel on a very, very small scale. Their study used individual photons to replicate a quantum particle traveling through a space-time loop (like the one you see above) to arrive where and when it began. Since these particles are inherently uncertain, there wasn't room for the paradoxes that normally thwart this sort of research. The particle couldn't destroy itself before it went on its journey, for example.

As you might have gathered from the "simulation" term, sci-fi isn't about to become reality just yet. The scientists haven't actually warped through time -- they've only shown how it can work. It could take a long time before there's proof that whole atoms and objects can make the leap, let alone a real-world demonstration. Should you ever step into a time machine, though, you'll know where it all started... and ended.

Latest Stories

Anti-trans hate is ‘widespread’ on facebook, instagram and threads, report warns.

Meta is failing to enforce its own rules against anti-trans hate speech on its platform, a new report from GLAAD warns.

Israel’s military reportedly used Google Photos to identify civilians in Gaza

The New York Times reports that Israel’s military intelligence has been using an experimental facial recognition program in Gaza that’s misidentified civilians as having ties to Hamas.

Apple's M3 and M2 MacBook Airs have never been cheaper

The Apple MacBook Air with an M3 chip is on sale for an all-time low of $999 at Amazon and B&H. Several other configurations of the laptop are also discounted.

Samsung Galaxy S24 phones are on sale for record-low prices at Amazon

Samsung's latest Galaxy S24 smartphones have dropped to record low prices. The S24 Ultra and S24+ are both $150 off.

Sega of America workers have ratified their union contract

Workers at Sega of America, a division of Sega Sammy Holdings Inc., have officially ratified their union contract. This makes it one of the first major North American video-game companies to take this step.

Immortals of Aveum headlines April’s PS Plus monthly games

Sony unveiled April’s PlayStation Plus monthly games on Wednesday. The batch includes Immortals of Aveum, Minecraft Legends, Skul: The Hero Slayer and an Overwatch 2 skins-and-skips bundle.

Google's Circle to Search feature will soon handle language translation

Google just announced that it's expanding the Circle to Search feature to include translating from one language to another. The search giant also revealed an AI-centric update to Maps.

Hulu on Disney+ officially launches, bringing together Mickey Mouse and The Handmaid's Tale

Hulu on Disney+ is officially coming out of beta, making it easy for subscribers to access content for both services.

Some of our favorite portable JBL Bluetooth speakers are up to 34 percent off

Several portable JBL Bluetooth speakers are currently on sale. The JBL Charge 5 has dropped by $50, while the Xtreme 3 is 34 percent off.

Marvel Rivals is a new Overwatch-like team shooter

Marvel Rivals is a new Overwatch-like team shooter from Marvel Games and NetEase. The multiplayer title will let people play as characters like Black Panther and Spider-Man.

Eight years after launch, No Man's Sky gets computer-generated space stations that are different each time

No Man’s Sky is still getting major updates. Developer Hello Games’ “Orbital” update, due Wednesday, adds procedurally generated space stations, a ship editor and a Guild system to the nearly eight-year-old space sim.

The Google Pixel 8 is $230 off and down to a new record-low price

The new Google Pixel 8 is on sale for $470 at Woot.

Apple refutes every claim made in DOJ's antitrust lawsuit

Apple refuted the DOJ's claims in its lawsuit via statements shared with Apple Insider.

The Morning After: Apple’s WWDC 2024 kicks off June 10

The biggest news stories this morning: Meta limits ‘political’ content recommendations on Instagram and Threads, Microsoft is finally adding keyboard and mouse support to Xbox Cloud Gaming titles, My quest for the perfect productivity mouse.

My quest for the perfect productivity mouse

The humble PC mouse is underestimated. We tested some of the best on the market to see which can serve as a reliable daily driver.

The Grok chatbot will soon be enabled for X Premium users, Elon Musk says

xAI's Grok chatbot, the Elon Musk-helmed company's answer to OpenAI's ChatGPT, will be available to X's Premium subscribers later this week.

The FTC might sue TikTok over its handling of users’ privacy and security

TikTok, already fighting a proposed law that could lead to a ban of the app in the United States, may soon also find itself in the crosshairs of the Federal Trade Commission.

Apple’s WWDC 2024 keynote is scheduled for June 10

Apple has scheduled the WWDC keynote for June 10, which should provide updates on various software updates. The 35th annual Worldwide Developers Conference goes until June 14.

Microsoft is finally bringing keyboard and mouse support to Xbox Cloud Gaming titles

Microsoft is finally enabling keyboard and mouse support on some Xbox Cloud Gaming titles. Testers can now use the option for the likes of Fortnite, Halo Infinite and Sea of Thieves.

This camera captures 156.3 trillion frames per second

Scientists have created a blazing-fast scientific camera that shoots images at an encoding rate of 156.3 terahertz (THz) to individual pixels — equivalent to 156.3 trillion frames per second.

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

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

Disclosure statement

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

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

View all partners

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

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

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

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

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

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

Time is relative

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

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

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

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

Paradoxes and failed dinner parties

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

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

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

Telescopes are time machines

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

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

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

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

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

• Time travel
• Special Relativity
• Thermodynamics
• Stephen Hawking
• Curious Kids
• Curious Kids US
• Time travel paradox

Research Fellow in Tropical Climate Variability

Director, Defence and Security

Opportunities with the new CIEHF

School of Social Sciences – Public Policy and International Relations opportunities

Deputy Editor - Technology

Scientists Discovered How to Speed Up Time. Seriously.

We can reverse it, too.

• In the physical world, time marches in one direction, but things aren’t so straight forward in the quantum realm.
• This isn’t exactly time travel , but is instead implementing or reverting to different quantum states from different points in time.

In the subatomic universe of quantum physics, you can achieve things considered impossible in our flesh-and-blood physical world. Things like superposition , entanglement , and even teleportation all seem possible when things go quantum. Now, scientists from the Austrian Academy of Sciences (ÖAW) and University of Vienna are adding a kind of time travel to the list.

In a series of papers published throughout the past few years on preprint servers and in various online journals (including Optica , arXiv , and Quantum ), researchers including ÖAW’s Miguel Navascués and University of Vienna’s Philip Walther explain the possibility of speeding up, slowing down, and even reversing the flow of time within a quantum system.

Navascués compares the phenomenon to different movie-watching experiences. “In a theater [classical physics], a movie is projected from beginning to end, regardless of what the audience wants,” he explains to the Spanish-language newspaper El País . “But at home [the quantum world], we have a remote control to manipulate the movie. We can rewind to a previous scene or skip several scenes ahead.”

The researchers achieved this by “evolving” a single photon as it passes through a crystal . Using an experimental device called a “quantum switch,” the single photon of light returns to its previous state before it ever makes the journey. In a way, this is less Doc Brown-style time travel and more about reverting or otherwise altering the states of quantum particles, or “time translation” as Navascués described in 2020 .

However, this isn’t exactly like a rewind button on your TV because usually, viewers can see how things got from plot point A to B—just sped up and in reverse. In quantum mechanics, however, simply observing a system causes it to change, which makes it impossible to track a system’s progress through time. Crucially, these rewinding protocols still work because they can be performed without knowing what the changes were or its “internal dynamics,” according to the scientists.

And this quantum time machine doesn’t just go one direction—Navascués says they’ve also hit upon a method for going forward in evolutionary time as well. He tells El País :

“To make a system age 10 years in one year, you must get the other nine years from somewhere. In a year-long experiment with 10 systems, you can steal one year from each of the first nine systems and give them all to the tenth. At the end of the year, the tenth system will have aged 10 years; the other nine will remain the same as when the experiment began.”

Sadly, these sci-fi findings in the quantum world can’t be sized up to send humans backward and forward in time, because a single human represents a mind-boggling amount of information to “rejuvenate”—in fact, the scientists estimate it would take millions of years to pull it off for just one second.

But for the teams at ÖAW and the University of Vienna, the point isn’t jetting off to the distant future of 2015 , but the ability to increase the capability of quantum processors by arming them with the possibility of reversing errors in a system. After all, if life had a rewind button, wouldn’t you use it?

Darren lives in Portland, has a cat, and writes/edits about sci-fi and how our world works. You can find his previous stuff at Gizmodo and Paste if you look hard enough. 

.css-cuqpxl:before{padding-right:0.3125rem;content:'//';display:inline;} Science .css-xtujxj:before{padding-left:0.3125rem;content:'//';display:inline;}

Scientists Spotted ‘Massless’ Electrons

Diamond Is About to Be Dethroned

Could the Chair You Sit on Have a Soul?

A Transgenic Cow Produces Milk With Human Insulin

We Gave the Wrong Guy Credit for the Decimal Point

3 Ancient Tombs Reveal New Jin Dynasty Secrets

49 Killer Whales Are Reshaping the Ocean

Here’s How We Could Live in Trees

Scientists Create the Most Powerful 'Sound Laser'

The Engine Driving Our Oceans Could Die by 2100

A Natural Superconductor Has Rocked the World

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].

Get the Space.com Newsletter

Breaking space news, the latest updates on rocket launches, skywatching events and more!

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

NASA gets $25.4 billion in White House's 2025 budget request

'Interstellar meteor' vibrations actually caused by a truck, study suggests

How fast will April's total solar eclipse travel?

Most Popular

By Fran Ruiz January 29, 2024

By Fran Ruiz January 26, 2024

By Conor Feehly January 05, 2024

By Keith Cooper December 22, 2023

By Fran Ruiz December 20, 2023

By Fran Ruiz December 19, 2023

By Fran Ruiz December 18, 2023

By Tantse Walter December 18, 2023

By Robert Lea December 05, 2023

By Robert Lea December 04, 2023

By Robert Lea December 01, 2023

• 2 Total solar eclipse 2024: Live updates
• 3 Drilling for water ice on Mars: How close are we to making it happen?
• 4 Astronauts' mementos packed on Boeing Starliner for crew flight test
• 5 'Spaceman' director Johan Renck on making a romantic sci-fi fable (exclusive)

Light Year Calculator

What is light year, how to calculate light years.

With this light year calculator, we aim to help you calculate the distance that light can travel in a certain amount of time . You can also check out our speed of light calculator to understand more about this topic.

We have written this article to help you understand what a light year is and how to calculate a light year using the light year formula . We will also demonstrate some examples to help you understand the light year calculation.

A light year is a unit of measurement used in astronomy to describe the distance that light travels in one year . Since light travels at a speed of approximately 186,282 miles per second (299,792,458 meters per second), a light year is a significant distance — about 5.88 trillion miles (9.46 trillion km) . Please check out our distance calculator to understand more about this topic.

The concept of a light year is important for understanding the distances involved in space exploration. Since the universe is so vast, it's often difficult to conceptualize the distances involved in astronomical measurements. However, by using a light year as a unit of measurement, scientists and astronomers can more easily compare distances between objects in space.

As the light year is a unit of measure for the distance light can travel in a year , this concept can help us to calculate the distance that light can travel in a certain time period. Hence, let's have a look at the following example:

• Source: Light
• Speed of light: 299,792,458 m/s
• Time traveled: 2 years

You can perform the calculation in three steps:

Determine the speed of light.

The speed of light is the fastest speed in the universe, and it is always a constant in a vacuum. Hence, the speed of light is 299,792,458 m/s , which is 9.46×10¹² km/year .

Compute the time that the light has traveled.

The subsequent stage involves determining the duration of time taken by the light to travel. Since we are interested in light years, we will be measuring the time in years.

To facilitate this calculation, you may use our time lapse calculator . In this specific scenario, the light has traveled for a duration of 2 years.

Calculate the distance that the light has traveled.

The final step is to calculate the total distance that the light has traveled within the time . You can calculate this answer using the speed of light formula:

distance = speed of light × time

Thus, the distance that the light can travel in 100 seconds is 9.46×10¹² km/year × 2 years = 1.892×10¹³ km

How do I calculate the distance that light travels?

You can calculate the distance light travels in three steps:

Determine the light speed .

Determine the time the light has traveled.

Apply the light year formula :

distance = light speed × time

How far light can travel in 1 second?

The light can travel 186,282 miles, or 299,792,458 meters, in 1 second . That means light can go around the Earth just over 7 times in 1 second.

Why is the concept of a light year important in astronomy?

The concept of a light year is important in astronomy because it helps scientists and astronomers more easily compare distances between objects in space and understand the vastness of the universe .

Can light years be used to measure time?

No , despite the name, you cannot use light years to measure time. They only measure distance .

Normal force

Polar moment of inertia, steps to calories.

• Biology (99)
• Chemistry (98)
• Construction (144)
• Conversion (292)
• Ecology (30)
• Everyday life (261)
• Finance (569)
• Health (440)
• Physics (508)
• Sports (104)
• Statistics (182)
• Other (181)
• Discover Omni (40)

March 18, 2024

The Great Debate: Could We Ever Travel through Time?

Our space and physics editors go head-to-head over a classic mind-bending question.

By Clara Moskowitz & Lee Billings

cemagraphics/Getty Images

Clara Moskowitz: Hi, I’m Clara Moskowitz, a space editor here at Scientific American. We’re taking a break this week to look back at some of our favorite podcast episodes. I chose this one about the physics of time travel, because I’m a big sci-fi geek, so I’m fascinated by the topic. But also, it was such a fun debate to have with my colleague and friend, Lee Billings, another space editor here. We each picked a side – I was pro time travel, he was con—and dug our heels in. Check it out!

[Clip: Show theme music]

Moskowitz: We’re here today to talk about time travel. A perennial – dare I say, timeless–topic of science fiction, but is it possible? Is there any chance at all that it could actually happen?

On supporting science journalism

If you're enjoying this article, consider supporting our award-winning journalism by subscribing . By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.

Lee Billings: No. No, no no no no. (laughs). Well, kinda. Not really. ARGH. I’m Lee Billings.

Moskowitz: I’m Clara Moskowitz, and this is Cosmos, Quickly , the biweekly space podcast from Scientific American . 

Moskowitz: We’re going to have a little friendly debate.

Billings: Really? I came for a throwdown.

Moskowitz: Well, a wrangle. A parley. A confab. Lee, what do you have against time travel?

Billings: So I love the idea of time travel! And in fact I do it all the time—like most everyone else I’m traveling into the future at one second per second. I’m less of a fan, though, of more speculative time travel, which is good fodder for goofy sci-fi stories, but in the real world it’s an implausible distraction.

Moskowitz: But really, we can stay within plausible physics and still see how more extreme versions of time travel are possible. See, Einstein’s special theory of relativity shows that the rate time flows at depends on how fast you’re moving. 

Billings: Einstein strikes again, what a rascal.

Moskowitz: If you’re traveling in a starship at close to the speed of light, you’ll still experience the familiar one-second-per-second ticking of a clock– but an observer back on Earth would see your clock moving glacially slow. To them, you’d be moving through time at a snail’s pace. That means that when you finally got back,  maybe only a year would have passed for you, but a century could have gone by for your friends on Earth. Ergo, you just traveled to the future! 

Billings: Right, right, no one’s disputing any of that! We can even measure this sort of “time dilation” right now on Earth, not with starships, but with subatomic particles. Some of those particles have very short lifetimes, decaying almost instantaneously. But if we drastically speed them up, like in a particle accelerator, we find they endure longer in proportion to how fast they’re going. So riddle me this, though, Clara: How can we travel into the past? That’s something so hard to do–effectively impossible, almost–that it’s scarcely worth thinking about.

[Clip: Back to the Future : “This is what makes time travel possible. The flux capacitor!”]

Moskowitz: I get it—no one has yet conceived of a way to journey to the past. But the crazy thing is it’s not impossible. Time is one of the four dimensions in the universe, along with three dimensions of space. And we move through space in all directions just fine, and according to physics, travel through time should be just as possible.

One way that people have looked into is via a wormhole—a shortcut bridge through spacetime that was predicted by general relativity. Wormholes can connect distant points in spacetime, meaning you could conceivably use one to bridge not just the gap between here and a distant galaxy, but the span between 2023 and 1923. 

[CLIP: Interstellar : “That’s the wormhole.”]

Billings : Ah yes, wormholes—the last refuge of scoundrels and desperate physicists. The trouble with wormholes Clara, is that, unlike a DeLorean, we have no evidence they actually exist—and, even if they did, it seems the only ways to make them traversable and stable involves using negative energy or negative mass  to prop them open. And, guess what, just like wormholes themselves, we have no evidence these weird forms of matter and energy actually exist, either. And let’s just beat this dead horse one more time—even if wormholes exist, as well as the means to make them traversable, to go back in time seems to require anchoring one end in a region of very warped spacetime, like around a black hole, or accelerating it to nearly lightspeed. Are you sensing a theme here, Clara?

Moskowitz: Yeah, yeah. All I can say is that just because there’s no evidence any of these things exist, there’s also no evidence they don’t or can’t exist. Wormholes are real solutions to the equations of general relativity, and even negative energy and mass are concepts that come up in the math and aren’t prohibited.

Billings: Well how about some more practical arguments, then? If time travel were possible, wouldn’t we have met some time travelers by now? Wouldn’t someone have gone back and killed Hitler—or at least prevented me from wearing that ridiculous outfit to my high school prom? You know there’s a famous story about physicist Stephen Hawking, who invited time travelers to come to a party he was holding. The trick was the the party happened in 2009, but the invitation came out in a miniseries that was broadcast in 2010—thus, only time travelers would have been able to attend. 

[CLIP: Stephen Hawking Time Travel Party: “Here is the invitation, giving the exact coordinates in time and space. I am hoping in one form or another it will survive for many thousands of years.”]

Billings: Sadly, the hors d'oeuvres went uneaten and the champagne sat unopened, because, clearly, time travel to the past is impossible! 

Moskowitz: I admit a party with Stephen Hawking should have been pretty alluring to time travelers, if they were out there. But you’re forgetting about the International Clause of Secrecy that all time travelers probably have to swear to, making sure to hide their identities and abilities from those in earlier eras.  

Billings: Hmm, yes the clause of secrecy here. Feels like we’re really veering into science fiction territory special pleading here. And don’t forget all the paradoxes that we have to worry about too. There are lots of good reasons to think time travel might introduce insurmountable paradoxes in physics. The most famous being the grandfather—or grandmother—paradox. If time travel were possible into the past, so the thinking goes, then a person could go back in time and kill their own grandparents, thus making it impossible for them to be born and impossible for them to travel back in time to ever commit the murder, and so on and so on.

Moskowitz: I wonder if it could be like a many-worlds scenario, where each change a time traveler makes to the past spawns a whole new universe that carries on from that point. So if I went back in time and killed one of my forebears, then a new branch universe would begin where that whole line of descendents, including me, never existed. I mean, it sounds crazy, but then again, physics is pretty enamored with multiverses, and they seem to pop up for lots of reasons already. Maybe it’s not impossible? 

Billings: If not impossible, then I’d say, implausible.

Moskowitz: Well, I’m forever an optimist, Lee! Thanks for listening to the Cosmos, Quickly .

Billings: Our show is produced by Jeff DelViscio, Tulika Bose and Kelso Harper.  Our music was composed by Dominic Smith.

Moskowtiz: If you like the show, please consider rating or leaving a review. You can also email feedback, questions, and tips to [email protected] . 

Billings: For more spacetime hijinks and all your science news, head to SciAm.com. This has been Cosmos, Quickly . I’m Lee Billings. 

Moskowitz: I’m Clara Moskowitz. 

Billings: And we’ll see you next time, in the future!

• Utility Menu

Harvard Natural Sciences Lecture Demonstrations

1 Oxford St Cambridge MA 02138 Science Center B-08A (617) 495-5824

• Key to Catalog

enter search criteria into the search box

Relativity train, what it shows:.

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

How it works:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Setting it up:

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

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

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

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

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

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

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

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

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

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

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

Demo Subjects

Newtonian Mechanics Fluid Mechanics Oscillations and Waves Electricity and Magnetism Light and Optics Quantum Physics and Relativity Thermal Physics Condensed Matter Astronomy and Astrophysics Geophysics Chemical Behavior of Matter Mathematical Topics

Key to Catalog Listings

Size : from small [S] (benchtop) to extra large [XL] (most of the hall)  Setup Time : <10 min [t], 10-15 min [t+], >15 min [t++] /span> Rating : from good [★] to wow! [★★★★] or not rated [—] 

Complete key to listings

Time Travel: The Science of Time Zones

Does time travel make one younger? Actually yes! A fun fact about the topic is that you get older slower than those who do not fly. This process is explained by natural science based on spectral relativity.

• Share on Twitter
• Share on Facebook
• Share on LinkedIn
• Share on Pinterest
• Share via Email

As a scientist, I frequently happen to have digital worldwide research collaborations or be invited to global conferences and events. Recently, I traveled to San Francisco (CA, USA) because I had the opportunity to present my research work at the Annual Meeting of the Cognitive Neuroscience Society . It is my third time in the USA, for the same reason, and if you think it is a long trip from Germany, where I currently work. Therefore, I had enough time to think about what would have been an excellent topic to discuss and write about on the flight. By looking at the display located right in front of my face. The display indicated the local time of the departure city and the current time of the arrival city. San Francisco is 9 hours backward compared to Germany. Therefore, I started questioning how time zones work across the world, why this event happens, and what the effects are on human life and habits.

Furthermore, based on my regular experience having Zoom meetings with the USA, I was thinking, “do people in the USA age later than people in the EU?” and “When I text or call a USA colleague, am I doing it in the future?” “Are they living in the present or still in the past?”

These were curious questions about time that I needed to answer. And while doing so, the best way was to write an article about it. So, if you are a curious explorer like I am, hang on and read this.

What are time zones?

Why do we have different time zones?

A good way to understand time zones is to start with the question, “How long does it take the Earth to make one full rotation on its axis?

Our planet Earth has the shape of a sphere that spins on an imaginary pole (axis), and every 24 hours, it makes a complete rotation around it. Thus, a complete rotation equals a day. However, during this rotation, some parts of the Earth will be exposed to light while others to darkness. During this movement, day and night are defined. For example, as your location on Earth rotates into the sunlight, you see the sunrise, whereas, in a rotation out of sunlight, you would see the sunset . Therefore, time zones are needed to enter and exit daylight at different times. Otherwise, a specific time (e.g., noon) would be in the middle of the day in some locations, but it might also be early morning or night in others.

Living in time zones is certainly not a new topic, but compared to centuries ago, today, in a fully connected world, this fact becomes more complicated and needs organization. Indeed, when people started to travel across North America by train , train stations had to match 75 time zones! Thus, to solve this problem, in the late 1800s, scientists proposed the “standard time,” and by studying the movement of the Earth, they created a zone map of the world. While rotating around its axis, every 60 minutes, the Earth moves about 15 degrees. Thus, after 24 hours (one day), it completes a full rotation of 360 degrees. Based on this concept, the Earth was divided into 24 time zones, and each would be 15 degrees of longitude wide. Moreover, at the equator level, the distance between zones is the greatest, which gets shorter at the pole locations due to the planet's curvature. In addition, the equator is 24,902 miles long, and the distance between zones at the equator is 1,038 miles (approximately).

How does time work?

What is Greenwich ? The imaginary lines dividing these zones begin at Greenwich (a suburb of London). The primary line is called the prime meridian , and this longitude dividing line is the angular distance between the prime meridian at Greenwich and any other meridian points. Hence, this reference time at Greenwich is called Greenwich Mean Time (GMT). For example, moving 15 degrees to the west from Greenwich would shift into one hour earlier, whereas moving to the east an hour later. However, some countries (e.g., China) did not accept the standard time, and instead, they preferred to set their own time. Other countries also adopted different systems that modify the time zones by smaller increments (e.g., 15 or 30 minutes). Therefore, today we experience more zones than the standard 24 .

So how do time zones work across the world? For example, if you live in San Francisco (GMT - 7) and I live in Germany (GMT + 2), we have 9 hours difference. When you wake up at 7 am, I would be in the middle of my afternoon (4 pm).  However, in the continental United States, there are four time zones (Eastern, Central, Mountain, and Pacific), and each of these locations also has different time zones. Thus, if you live in New York (GMT - 4), we have a 6 hours difference.

GMT or UTC? What is the reference?

I previously described what GMT is and how time zones are defined based on it. However, the Coordinated Universal Time (UTC) is often used now. Thus, what is their difference ?

GMT refers to mean solar time at the Royal Observatory, and it is a system initially developed in 1850 to track time according to the Earth’s rotation. UTC is not a time zone but an atomic time scale that approximates GMT developed in 1970. The UTC system is the International Atomic time (TAI), with leap seconds added at irregular intervals to compensate for the Earth’s slowing rotation . Nevertheless, it refers to the mean solar time at Greenwich. This video explains the history of time zones worldwide and how GMT and UTC were used.

One hour backward and forward

Lastly, if time zones look complicated, there is something more that may exacerbate things even more. However, this is the daily light saving time (DST), which is considered just in some countries. DST is not a time zone, but it requires some countries and states to set the clock one hour forward or backward from the standard time . In short, DST would allow better use of daily light. Hence, setting the clock one hour earlier in autumn would shift that hour from the evening to the morning. Viceversa, placing one hour later in spring would guarantee one more hour of light in the evening. However, not being used to DST might affect the circadian rhythm by altering the body clock and therefore causing sleep disturbances . So, those countries that apply DST should adopt a healthy lifestyle that recommends attention to sleeping enough.

To know more about time zones and their science, read here .

You can find a list of time zones by country here .

Do time zones influence our health and aging process?

“Traveling allows you to become so many different versions of yourself” (Unknown)

UTC, CEST, PST, EAST… Different countries, different times. Hence my question was, “traveling from country A to country B, where the difference is 9 hours, would affect my age?” Let’s suppose I turn 30 on day X in country A, but traveling to country B, is still day Y. Am I 30 also in country B?

Legally it might make a difference. Thus, I can be of full age in one country but fly to another not being full age yet. So, does time travel make one younger? Actually yes! A fun fact about the topic is that you get older slower than people who do not fly. This process is explained by natural science based on spectral relativity. In this article , the twin paradox is presented to further clarify this event from physics, time dilation , and the principles of relativity .

What about sleep?

Recent research published in the Journal of Health Economics [1] found that living on the wrong side of a time zone can negatively influence health and a person’s wallet. The problem might be related to the prolonged natural light in the evening hours. Indeed, the sunset is a powerful biological trigger because it allows the body to release melatonin (i.e., a hormone that initiates drowsiness). Therefore, those who live on the eastern side of the time zone, where the sun sets earlier than on the western side, tend to go to sleep earlier. Changes in bedtimes would affect a person’s physical and economic well-being . The study suggests that those who live in locations with a later sunset went to sleep, on average, 19 minutes later than people with earlier sunsets. However, going to bed later does not change the time you wake up (e.g., going to work or school) [2], which translates to 115 hours of sleep deprivation a year. “Individuals on the late sunset side of a time zone boundary are more likely to be sleep-deprived, more likely to sleep less than 6 hours, and less likely to sleep at least 8 hours,” commented the authors . “The effects are larger among individuals with early working schedules and individuals with children of school age.” [2]

Furthermore, individuals who live on the late side of the sunset across the USA time zones were more likely to be overweight and obese. In addition, diabetes was also more prevalent. Likewise higher risk for heart attack and breast cancer was shown. Sleep deprivation would also affect productivity and, thus, the general economy [2]. The bright side of late sunset? People may enjoy more daily light where an extra hour of sunlight for recreation may compensate for the lack of sleep. Hence, “As long work hours, work schedules, school start times, and the timing of TV shows can create conflicts between our biological rhythms and social timing, our findings suggest that reshaping social schedules in ways that promote sleeping may have non-trivial effects on health and economic performance,” said Giuntella and Mazzonna, authors of this research study. [2]

The planet Earth with its rotation is an incredible phenomenon, and thanks to scientists, we understand how to track the time across countries and be fully connected. In addition, knowing how time zones might affect health might enhance awareness of establishing new habits and lifestyles.

On which side of the world are you? And which is your time zone?

“There’s a sunrise and a sunset every single day, and they’re absolutely free. Don’t miss so many of them” ( Jo Walton)

References:

• Osea Giuntella, Fabrizio Mazzonna, Sunset time and the economic effects of social jetlag: evidence from US time zone borders, Journal of Health Economics, Volume 65,2019, Pages 210-226, ISSN 0167-6296, https://doi.org/10.1016/j.jhealeco.2019.03.007 .
• Ingrham, C. (2019). How living on the wrong side of a time zone can be hazardous to your health. The Washington Post. Available at: https://www.washingtonpost.com/business/2019/04/19/how-living-wrong-side-time-zone-can-be-hazardous-your-health/ [Accessed on April 29]

Beatrice Barbazzeni

Beatrice is a Ph.D. student in Neuroscience aimed to achieve her MTP with discipline, perseverance and grit:“empower inner potential leading to the growth of exponential winners".

ExO Insight Newsletter

Join the newsletter to receive the latest updates in your inbox.

You might also like

The digital twin concept — healthcares transition towards homecare — the making of an exponential health metaverse paid members public.

Next Generation Healthcare systems will need to focus on prevention / early detection and pro-active therapy, and they will employ exponential technologies. This likely will lead to significant changes in the way we experience, think about, and deliver healthcare.

Welcome to the Amplified Future: A Musical Wonderland For Technology, Health, And Human Potential Paid Members Public

You are entering a world in which millions of people will benefit from precision and personalized medicine; new populations will have affordable access to quality health resources, and health science research will move from the lab to the wild—using real-time biometric tracking on the individual.

Featured Posts

Transforming corporate sustainability: the future of decarbonization.

From Idea to Platform: Inside the Pro Foundations Course

Disruptive Potential: How Exponential Attributes Are Transforming Education #2

Contribute towards amplifying the voices of the community.

Pedro LOPEZ SELA

Pedro helps individuals & organisations thrive. He simplifies complexity, identifies inefficiencies, connects dots & imagines ideas that drive meaningful outcomes.

Chander Nagpal

With more than 25 years of experience in driving transformation initiatives, Chander is pronounced with a passion for delivering sustainable 10X impact through inspiring, engaging & enabling people.

The One Simple Secret to Traveling Light. And It’s Easier Than You Think

There is a secret to traveling light, but it’s actually not much of a secret. In fact, you may already know it—you probably just choose to ignore it.

Learning how to travel light or even  traveling carry-on only  is easier than most people think.

It’s made out to be a complicated secret. A method that’s utilized by pro travelers. Only the most experienced travelers can pull this kind of thing off, right?

There’s a secret to traveling light, and you may already know it.

Have you ever heard of  Parkinson’s Law ? It posits the idea that “work expands so as to fill the time available for its completion.”

If you have four hours to complete a report, it’s going to take you four hours to finish it. But if you have eight hours to complete it, it’s going to take you eight hours.

See where I’m going with this?

How to Travel Light

Traveling light is simple, really. You don’t have to fight with your suitcase every time you go on a trip.

The amount of stuff you have will expand so as to fill the space available.

In other words: Buy a  carry-on backpack  that’s the size you want to carry, and you’ll end up taking only enough stuff that will actually fit.

That 120L suitcase in your closet? Throw it out. OK, well, maybe don’t throw it out—you might need it sometime. But let’s work on downsizing.

How big do you want your bag to be? In fact, let’s reframe that question. How small do you want your bag to be? A carry-on backpack? A much smaller suitcase? A weekender bag?

I’m a huge fan of the following  carry-on luggage  options:

• Osprey Farpoint 40L
• Tortuga Setout 45L
• Arc’teryx Khamski 38L
• Pacsafe Toursafe AT21  (42L wheeled luggage)

Buy that bag, then commit to carrying only that bag. If something doesn’t fit, or if something takes up a disproportionate amount of space, get rid of it. You won’t be taking it with you on this trip!

How to Save Space in Your Bag

Fitting everything you want/need (they’re not the same thing!) into a smaller bag isn’t always easy. There are a few simple tricks you can use to keep yourself both organized and traveling light.

1. Use Packing Cubes

Packing cubes are a popular choice. They’re easy to use and they keep everything bunched together in nice little pouches. They’re perfect for organizing your bag and keeping your stuff compartmentalized. Organization is of paramount importance if you want to pack light.

Mise en place . It’s a famous French saying for, “a place for everything.”

When you don’t have random pairs of socks and underwear floating around your bags, it’s much easier to maintain an organized, tightly, expertly packed bag.

2. Use Compression Sacs

The less popular choice—and I’m still at a loss for why—are compression sacs. They’re vacuum-sealed “packing cubes” for your clothes.

Especially if you need to carry bulkier items—and especially heavier jackets or mid layers—throw them into the right sized compression sac, squeeze all the air out, and you’ve likely just reduced the amount of space that item takes up by somewhere around 50 percent.

Seriously, they’re that good.

3. Don’t Stuff in What You Don’t Need

On top of getting rid of the extra clothing you probably won’t wear more than a couple times, get rid of the heavier and space-consuming items like bulky jeans or large toiletries.

You should also ditch all the shoe options since shoes take up the largest amount of awkward space in your bags. Bring only the essentials—one pair of sneakers if you’ll need them (wear them), one pair of hiking shoes and a pair of sandals.

Make sure whatever shoes you pack can go with all of the clothes you pack, too. Leave the extra Jordans, Nikes, and Converse at home this time.

But What if You Forget Things?

If you want to learn how to travel light, you have to go into it with the right mindset. You have to overcome the fear that you might be forgetting something, or that you might leave something behind that you’re going to need at your destination.

The fact is: You probably will.

But part of traveling is overcoming fear. And overcoming the fear of packing light has to be your first step. Assuming you don’t want to lug 70 pounds of luggage around with you from place to place, of course.

Forgot your sandals? Pick up a new pair when you arrive. Didn’t realize it was going to be so cold? Buy a new jacket or sweatshirt when you touch down.

Whatever it is that you need, it’s guaranteed you’ll be able to find one wherever you’re traveling.

And lastly, when you’re on the road, for the love of everything that’s holy, don’t buy things you don’t need. Small souvenirs? Sure—go for it. But just remember that you’re going to have to carry with you anything you buy along the way.

No matter how much you want it, resist. If you need it, go for it. Just remember, you might have to throw something else out to free up some space.

So pack only the essentials —the bare minimum of what you’ll definitely need. The rest you can pick up along the way.

Pretty simple, isn’t it?

• The 65 Best Travel Tips I’ve Learned After 10 Years of Traveling
• The Best Travel Insurance Companies
• 12 Smart Ways Keep Your Stuff Safe When You Travel

Traveling Light FAQs

What's the secret to traveling light.

The secret to traveling light is to use a smaller bag and not bring anything that doesn’t fit. Simple.

What is the 1-2-3-4-5-6 packing rule?

The 1-2-3-4-5-6 packing rule is to pack 1 hat, 2 pairs of shoes/sandals, 3 bottoms, 4 tops, 5 pairs of socks, and 6 pairs of underwear.

How to travel light for 3 weeks?

The best way to travel light for 3 weeks or longer is to only bring enough clothes for a week or so, and then do laundry during your trip.

What is the golden rule of packing?

The golden rule of packing is to bring less stuff. The less you bring, the more you can focus on the experiences and not the stuff.

How do you pack successfully?

The best way to pack successfully if you want to travel light is to use a smaller bag. Anything that doesn’t fit gets left behind.

Jeremy Scott Foster

I have to travel light Jeremy, due to a bad spine and agree with what you say, except for the packing cubes, I find they actually take up more room (because of the sides) than bags with a draw strings. All the soft stuff goes at the bottom to cushion my travel writing kit.

My pack is a small 35L one.

I carry one change of clothes (wear one, wash one). My travel writing kit: – Tablet and smartphone or small Leica/Lumix camera for short trips. – 12.6 inch Laptop and the small camera. – A small linen towel (they dry faster) – The usual paperwork. – First Aid kit and a few other little bits. – Empty cool bag for food (often as padding under it all).

Often I’m left with room for stuff I might pick up on the road.

Total weight between 9-13 lbs depending on the travel writing kit I take.

What I don’t carry Toothpaste (buy it there) flip-flops I buy when there from the cheapest shop I can find.

Works for me….

I admire how little you travel with, Ted! It’s exactly that kind of packing that makes all the difference.

As for packing cubes, some are definitely better (rather, smaller) than others. Mine are really thin so barely take up any space. Some are quite a bit more bulky though. Regardless, I do think organization–especially if using a small suitcase–is a big part of packing light.

Keep doing that thing you do! Thanks for the comment.

Oh yea, I’ve always struggled with this.. But you’re right that the size of the bag is of paramount importance. I like to travel on long weekend trips with my CabinZero. For longer trips, I’ve at least managed to do away with a smaller suitcase.

Nice one! I’ll have to check them out.

“Mise en place” a famous french saying… I’m French and I’ve never heard it said in that sense. =D

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed .

Search our latest articles, reviews and gear guides

• TravelFreak on Instagram
• TravelFreak on Facebook
• TravelFreak on Twitter
• TravelFreak on Pinterest

Sign up now and get the best gear, travel tips, deals and destinations, straight to your inbox.

Thank you for signing up!

Giant Freakin Robot

Time Travel Equation Solved By Astrophysicist

Posted: March 25, 2024 | Last updated: March 25, 2024

After a lifetime of pursuing the idea, Physics Professor Ronald Mallett at the University of Connecticut has potentially figured out the theoretical aspects of time travel. Professor Mallett believes that black holes, rotating light, and gravitational pulls may hold the key to exploring time, but it’s all theoretical for now. There are still a lot of hurdles and limitations to handle before time travel can have real, practical applications.

A Life Spent Thinking About Time Travel

Love and loss pushed Professor Mallett into an obsession with time and space. When he was 10 years old, his father passed away from a heart attack. It was his father who nourished his love of science, but H.G. Wells’ book The Time Machine pushed him towards a focus on time travel.

He was hooked from the very first paragraph of the book, “Scientific people know very well that Time is only a kind of Space. And why cannot we move in Time as we move about in the other dimensions of Space?”

That paragraph never left him, and the professor let that time travel question guide him through school and into the Professor Emeritus of Physics position at the University of Connecticut.

Einstein And Black Holes

As he grew up, Professor Mallett spent much of his time on Albert Einstein’s theories about black holes. While his interest in time travel only continued to grow, a potential solution never showed itself. At least, not until the professor ended up in a hospital with a heart condition.

There, lying in the hospital bed, inspiration hit him. Black holes and the gravitational fields they created were the answer to time travel. These gravitational fields had the potential to lead to time loops, which then theoretically could allow people and objects to travel back in time.

Black Holes Manipulating Gravity

While this idea offered an ability to manipulate time, the other problem was how to use these time loops for time travel.

Professor Mallett found this time travel solution much easier than the first problem. Strong and continuous beams of light, like a ring of lasers, with a particular rotation could be used to manipulate gravity and mimic the distorting effects of a black hole.

Though the details are rather complicated, the big time travel picture is a lot simpler to grasp. The professor offers a comparison to help people understand. “Let’s say you have a cup of coffee in front of you. Start stirring the coffee with the spoon. It started to spin, right? That’s what a spinning black hole does. In Einstein’s theory, space and time are related to each other. That’s why it’s called space-time. So when the black hole spins, it will actually cause time to shift.”

Much To Figure Out

Professor Mallett may now have a theory on time travel and a machine to use to make it possible, but that doesn’t mean it will be here in the next few decades.

There’s still a lot to figure out to make such travel practical, such as where the insane amount of energy such a machine would require could come from, and how big the machine would need to be.

There’s also a major constraint on the machine. According to his theories, time travel would only be possible to the very beginning of when the machine was first built. In this way, it’s more like a one-way message service. You can potentially go forward quite a distance, but going back in time is limited by the machine’s creation.

Theoretical Aspects Of Time Travel

The professor has made a huge leap in figuring out the theoretical aspects of time travel, but there’s a lot more to discover and quite a few hurdles and paradoxes to figure out before scientists practically start messing around in time.

Still, the theory is a step in the right direction and does suggest that people can push past what science currently considers possible.

Source: Earth.com

More for You

25 facts you may not know about the Civil War

15 Things That Are Total Rip-Offs

Inside ‘the world’s least-visited country’ – where dirty cars are illegal and social media is banned

4 great movies to watch before they leave Netflix in April

Some Legal Scholars Push For Justice Sonia Sotomayor To Retire

America’s 10 Largest Zoos

Family Finds 22 Stolen WWII Artifacts From the Battle of Okinawa in Their Father's Attic

16 Compliments You Didn’t Realize Are Actually Pretty Insulting

UK general admits military 'couldn't fight Russia for more than a couple of months'

An astrophysicist claims he finally figured out time travel

What Democrats' vote against women reveals about the future of sports

Billionaire Says His Long-Delayed ‘Titanic II' Ship Will Be an Antidote to ‘Woke' Politics

The 10 most popular TV shows on Netflix right now

Here Are 6 Things White People Say That Highlight Their Privilege And OMG I Hear These Allllll The Time

The 5 Safest Islands To Visit For a Peaceful and Worry-free Vacation

Chapter 11 bankruptcy on table for nationwide restaurant chain

US and Ally Move To Block North Korea's Nuclear Weapons Program

If You Did These 17 Things in the ’60s & ’70s, You Were a Hippie

What is 'flextirement' and how common could it become?

Spring 2024 TV shows: Here's when new shows premiere, favorites return

Using 'time travel' to think about technology from the perspective of future generations

The world approaches an environmental tipping point, and our decisions now regarding energy, resources, and the environment will have profound consequences for the future. Despite this, most sustainable thought tends to be limited to the viewpoint of current generations.

In a study published in Technological Forecasting and Social Change , researchers from Osaka University have revealed that adopting the perspective of "imaginary future generations" (IFGs) can yield fascinating insights into long-term social and technological trends.

The researchers organized a series of four workshops at Osaka University, with participants drawn from the faculty and student body of the Graduate School of Engineering. The workshops discussed the state of future society and manufacturing in general, and also looked at one technology in particular: hydrothermally produced porous glass. During the workshops, the participants were asked to think about this technology from the perspective of IFGs, to imagine how this technology might be adopted in the future and to assess its future potentiality.

"We chose hydrothermally produced porous glass for the case study because of the generational trade-offs involved," says lead author of the study Keishiro Hara. "Porous glass is incredibly useful as either a filter for removing impurities or an insulator for buildings. Also, it can be recycled into new porous glass more or less indefinitely. The problem is that making it takes a lot of energy -- both to pulverize waste glass and to heat water to very high temperatures. There's a striking trade-off between costs now and gains in the future."

In the workshops, the participants first looked at issues involving society and manufacturing from the perspective of the present and were then asked to imagine themselves in the shoes of their counterparts in 2040.

"The future the participants imagined was quite different from the future as seen from the perspective of the current generation," explains Toshihiro Tanaka, senior author. "Most groups described a future in which sustainability has become a central concern for society. Meanwhile, advances in renewal energy mean that energy is abundant, as are resources, as frontiers such as the moon and deep ocean are opened to exploration. In this context, hydrothermally produced porous glass comes into its own as a sustainable way to recycle glass, and the energy needed to produce it is readily available."

The participants were surveyed between workshops and asked to rank indicators related to the future potentiality of the technology. Interestingly, these rankings looked quite different after the workshops in which the participants were asked to take on the perspective of "imaginary future generations."

"We noticed that when the "imaginary future generations" method, which has been proven to be effective in facilitating long-term thinking, was adopted, participants perceived the feasibility of this technology differently, and their adoption scenarios changed accordingly," says Hara.

The study suggests that the simple act of putting ourselves in the position of future generations may provide new perspectives on issues of sustainability and technology, helping us to rethink our priorities and set new directions for research and development.

• Energy Technology
• Energy and Resources
• Engineering and Construction
• Educational Technology
• Information Technology
• Computer Science
• Environmental Policies
• STEM Education
• Energy Issues
• Emerging technologies
• Engineering
• Nanomedicine
• Scientific method
• Liquid nitrogen economy
• Earth science

Story Source:

Materials provided by Osaka University . Note: Content may be edited for style and length.

Journal Reference :

• Keishiro Hara, Iori Miura, Masanori Suzuki, Toshihiro Tanaka. Assessing future potentiality of technologies from the perspective of “imaginary future generations” – A case study of hydrothermal technology . Technological Forecasting and Social Change , 2024; 202: 123289 DOI: 10.1016/j.techfore.2024.123289

Cite This Page :

Explore More

• Robot, Can You Say 'Cheese'?
• Researchers Turn Back the Clock On Cancer Cells
• Making Long-Term Memories: Nerve-Cell Damage
• A Solar Cell You Can Bend and Soak in Water
• Risk Factors for Faster Brain Aging
• Deep Space Objects Can Become 'Ice Bombs'
• Want to Feel Young? Protect Your Sleep
• Century-Old Powdered Milk in Antarctica
• New Artificial Reef Stands Up to Storms
• Persistent Hiccups in a Far-Off Galaxy

Trending Topics

Strange & offbeat.

Routine is key to healthy sleep habits, but shift work, holidays and overseas travel can turn that upside down

Are you one of those people who wakes up automatically — just before your alarm goes off?

Many humans like routine, and if you are a person who works regular hours, you might find you open your eyes in time to stop the alarm off just before it rudely wakes you.

How does the brain know it's time to wake up? It's all about the body clock.

Sleep and respiratory physiologist Peter Catcheside from Flinders University said when an individual's 24-hour body clock (otherwise known as the circadian clock) lines up with their sleep system, it has a good sense of what time it is.

"By the end of the night, close to our normal waking time, it’s already run through the sleep processes that it needs to run through during the night, so it's naturally coming towards waking up," he said.

"So it's really that body clock sensation of time of day which is helping us to wake up at the right time of day." 

The body clock likes routine

Health experts say getting a good night's sleep is important for our health and wellbeing, and sticking to routines for going to sleep and waking up at about the same time is the best way to maintain that.

But if you are among the increasing numbers of shift workers starting at different hours of the day or night, a new parent, travelling overseas or on holiday hoping to catch up on lost sleep, routine is likely to be out the window.

People with changing sleep patterns are likely to have irregular light exposure and disrupted exercise and meal routines, all of which affect their body clock and have negative health effects, according to the Sleep Health Foundation .

A disrupted body clock can lead to jet-lag, insomnia or shift work disorder, and play a role in chronic diseases and mental health problems, Professor Catcheside said.

"When we don't get enough good quality sleep and when our body clocks are out of phase with our normal daily schedules our brains don't function and the rest of our body is on the wrong time to function at its optimal," he said.

'Holiday mode' changes routines

Sleep experts say despite the obvious benefits of holidays, a change in habits can create ongoing problems including insomnia.

Director of the centre for sleep science at the University of Western Australia, Jennifer Walsh, said many people started holidays in "sleep debt", so their bodies try to make up for lost sleep.

But going into "holiday mode" where you sleep in or go to bed earlier than usual can change regular patterns.

"It can cause problems with our sleep down the track, so some people will go into a pattern where they don't sleep well and that might perpetuate and turn into insomnia, that's the biggest risk," she said.

More alcohol, caffeine and food while catching up with family and friends during festive or cultural holidays can also exacerbate things, Dr Walsh said.

Shift work sleep routine

About 10 to 15 per cent of shift workers may suffer from "shift work sleep disorder" characterised by insomnia-like symptoms, excessive sleepiness and fatigue.

That is a significant proportion of people working outside nine to five, which in Australia equals about 16 to 20 per cent or about 1.6 million employees, associate professor in the department of health sciences at Macquarie University, Christopher Gordon, said.

People with sleep disorders and shift workers can benefit from what's called a "shift work sleep routine" to maximise their potential for shut eye, Dr Gordon said.

"[It involves] going to bed at the same time, trying to wake at the same time, reducing things like caffeine and alcohol before you try to go to sleep [as well as] heavy meals, and really trying to get that routine established," he said.

"There's other things you can do with your environment such as making the room very dark and if you can't do that, possibly wearing an eye mask and using ear plugs can also help."

'Nudging' the body clock

In the hope of addressing some of these body clock problems, Professor Catcheside and a team of researchers at Flinders University are investigating personalised sleep regimes.

"We want to solve one of the biggest ongoing problems in sleep medicine, by devising a practical way to reliably track and treat people with a body-clock timing problem," Professor Catcheside said.

Doctors and psychologists are largely using guesswork unless they have data based on the individual's body clock, Professor Catcheside said.

The team is developing technology for a personalised tracker which would measure the daily core body temperature, a key marker of when the body clock is most sensitive to being influenced by light.

"That would be new technology that could automate the process of tracking when the body is timed each day, giving information back to users about when is a good time to try and go to sleep and when to get up, and also when is the best time to get blue light exposure," Professor Catcheside said. 

The good news is that initial results show that light exposure at the right time should help "nudge" a person's body clock in the right direction.

"The timing of therapy is critical because the body clock is most sensitive to blue-enriched light for only a few hours a day and can be advanced or delayed depending on light exposure timing," he said.

• X (formerly Twitter)

Related Stories

Significant number of young australians not getting enough sleep, study finds.

'A trap you want to avoid': The common sleep misconceptions getting in the way of a good night's rest

7 things you've heard about sleep that aren't true

Avoid the daylight saving blues. Here's how to get a good night's sleep when the change kicks in

• Academic Research
• Lifestyle and Leisure
• Medical Research
• Science and Technology
• Sleep Disorders

The 14 Best Acne Light Therapy Devices to Zap Stubborn Breakouts

Add one of these expert picks to your skin routine

Every product on this page was chosen by a Harper's BAZAAR editor. We may earn commission on some of the items you choose to buy.

Think of acne devices as the supporting cast in your treatment plan next to topicals. While the best acne light therapy devices are powerful enough to clear up breakouts, board-certified dermatologist Mamina Turegano tells Bazaar that in the derm world, LED devices are considered to be lower on the treatment scale, but can still be effective when paired with an expert-approved acne skincare routine. " Topical and prescription treatments are first recommended. A good foundational skincare regimen is important, followed by evidence-based tried and true medications, whether over-the-counter or prescription." Turegano notes that light tools can also serve as an alternative treatment for those who cannot tolerate or don’t respond well to conventional therapy like prescription topicals.

Shop the Best Acne Light Therapy Devices

Best for Travel

Skin gym zitlit led acne fighting stick.

Editor's Pick

Solawave bye acne spot treatment.

Best for Light Therapy Patch

Facegym acne light shot.

Best for Recurring Acne

Foreo espada 2 plus.

Best Multitasking Tool

Therabody theraface pro.

Most Viral Device

Dr. dennis gross skincare drx spectralite faceware pro.

Best for Beginners

Riki miracle.

Best for Mild to Moderate Acne

Lightstim lightstim lightstim for acne.

Best Value Device

Light activated beauty acne light therapy patch.

Best for Large Surface Areas

Spa sciences claro acne treatment light therapy system.

So how exactly does a light work clear skin? "LED blue light, targets the acne-causing bacteria cutibacterium acnes. The bacterium C. acnes produces porphyrins. These proteins absorb light energy in the spectrum of blue light. This leads to a chemical reaction that essentially destroys the bacteria," she explains. It's always best to chat with a dermatologist before starting a new skincare treatment. The efficacy of an acne light therapy device depends heavily on the type of acne you're looking to treat. "With mild acne, LED skincare can even be superior to many topical regimens, especially for those with sensitive skin who get easily irritated by standard medicines," Ellen Marmur , board-certified dermatologist, and founder of MMSkincare says. "For severe acne, LED tools and devices are additive to the skincare routine rather than a replacement," she adds. Once you're ready to try one of the best acne light therapy devices, look to one of the following expert-recommended options below.

This handy LED light nicely fits in your bag and combines red and blue lights for a zit-zapping effect that works in three minutes. And did we mention it's completely painless?

One satisfied customer writes: "Awesome product!! I love how slim and portable this is. Works great for the deep acne. This kills the bacteria growing inside and allows your body to heal it without it having to erupt! Easy to use and doesn't dry my skin out." — Gloria

The small but mighty SolaWave Bye Acne Spot packs enough power to treat a pimple in three minutes flat— we've tested it first-hand . It combines red and blue light treatments to clear pores while calming skin at the same time.

One satisfied customer writes: "I love how compact this product is it makes it really easy for me to travel with it and use it on the go. The packaging is great quality is amazing and I’ve noticed that it helps minimize blemishes after just a few uses." — Jess

For breakouts that cover more than just a spot but not your entire face, try this Acne Light Shot from Face Gym. It comes with 60 medical-grade adhesive strips that'll stay put while treating and goggles to protect your eyes from any light sensitivity.

One satisfied customer writes: "This has been the only thing that has helped clear up my cheek acne. I also use retinol and low percentage benzoyl peroxide, but adding this has made a huge difference. " — Christiebelle

Foreo's handy Espada 2 Plus tool is perfect made for more targeted treatments. The tapered tip directs the light right to a specific blemish or spot where recurring pimples pop up to kill bacteria beneath the skin's surface. The device also features ultrasonic vibration to stimulate cell turnover and get rid of scarring.

One satisfied customer writes: "The precise light guide itself is quite small (you get exactly what you see in the pictures), hence making it a perfect device to treat small, curved, and hard-to-reach areas like around the nose, or right below the eyebrow." — Emily E.

Turegano recommends this eight-in-one device—one that Bazaar editors also love —which has detachable treatment heads to clear away pimples. It also helps bring down inflammation, firm less than taut skin with its built-in microcurrent , and provides a nice facial massage at the same time.

This pick from Dr. Dennis Gross may look intense, but it's probably the closest to a professional facial that you'll get at home. The mask features 62 blue LED lights to treat and prevent acne-causing bacteria and 100 red LED lights to help minimize acne scarring and boost collagen production. You can treat skin with each light shade individually or at the same time.

One satisfied customer writes: "Not only is this device user-friendly with its hands-free design and adjustable strap, but the impact on my skin has been remarkable. The combination of red and blue lights proved to be a dynamic duo in combating both wrinkles and acne. Surprisingly, within days, I noticed a visible reduction in new acne development, and over the course of two weeks, my mild hyperpigmentation from previous breakouts is beginning to fade." —Victoria B.

Consider this the LED version of your favorite hydrocolloid pimple patch . The device comes with sticky patches that help it adhere to skin. Each treatment is six minutes long and emits blue and red light to kill bacteria and bring down inflammation. Plus, it has a rechargeable battery and a storage case to keep it clean.

One satisfied customer writes: "The results are noticeable immediately after one use. I have hormonal acne and this product has been my saver! It’s very easy to use, and you don’t have to stop what you’re doing because it’s hands-free. Love it!" — Malena

Designed with a combo of 36 blue and red LEDs, Lightstim for Acne is best used to treat mild to moderate breakouts. The tool is also ideal for keeping your skin in the clear to prevent new acne from forming.

One satisfied customer writes: "Since the start of the pandemic, I've been getting really bad hormonal breakouts along my chin. I'm in my late 20's and never suffered acne like this before. It's been deep cystic pimples that would leave behind bad scarring. I've tried a few different products, and the LightStim has so far been the best." — LAinLALA

Lab's single blemish LED works similarly to other options on this list, except this one is under $20 and works for 30 treatments before needing to be replaced.

One satisfied customer writes: "It's pretty great, and a single box lasts a long time. Used this on Friday, and woke up Saturday with clearer skin. I was skeptical, but the results were real!" —Alex

While several other tools on this list integrate both blue and red LEDs into one head, this option from Spa Sciences has separate treatment heads, each with a larger surface area than most devices for a more concentrated treatment of either acne or the post-acne scarring that can come with it.

One satisfied customer writes: "I have been using this for a little over 2 months and my favorite part is the reduction of inflammation from the breakouts I have had. It definitely seems to reduce the redness and speed healing time!" —Sandra

MM Skincare MMSphere 2Go

Marmur created this multi-purpose device to treat a range of skin concerns, including acne. The device features a full range of light wavelengths with different colors (blue, red, green, purple, and amber) to improve acne, prevent breakouts, and reduce redness and acne scars. It's also portable so you can treat skin even while traveling.

One satisfied customer writes: "I had a friend today tell me my skin looked the best he'd seen it in ten years. After 6 weeks of using the Sphere, I'm never going to stop. Combined with the MMRepose serum I've found my scarring reduced, my skin consistently clearer and feeling more taut and bouncy. " — Duncan M.

Revive Light Therapy Glō Portable LED Light Therapy Device

In addition to bacteria-killing blue light, Revive's Glō device also featured infrared shades of deep red, red, and amber lights for more thorough inflammation reduction. Plus, the size of the tools makes for easy treatments while traveling.

One satisfied customer writes: "This is my new favorite skincare tool! I have used it every day for the past few weeks and I have noticed less acne and a reduction in my fine lines. I love that I can easily use this while I am working at my computer, and take this with me when I travel." —Deborah P.

PMD Clean Acne

PMD's Clean Acne device not only checks the cute box, but it fills the space of two tools in one. The silicone brush side uses sonic vibration to clear away grime and bacteria, and when flipped, the blue LED does the deep pore purging.

One satisfied customer writes: "I use it every night to clean my face and then use the blue light on my problem areas. Finally, I’m getting my healthy, clear, glowing skin back!" —Alina

Clear LED Mask

This device from Omnilux features a flexible silicone design that treats the entire face in one fell swoop. It contains 132 professional-grade LED lights to clear up acne and soften the appearance of post-breakout scars. The mask even has built-in eye shields to protect your eyes as you treat your skin.

One satisfied customer writes: "Omnilux is clearly doing its magic. I’m so excited to finally be acne-free for the first time in my entire life. This is coming from someone who tried everything on the planet since middle school." —Zack

.css-1jvcbpx{font-family:NewParisTextBook,NewParisTextBook-roboto,NewParisTextBook-local,Georgia,Times,Serif;font-weight:normal;letter-spacing:-0.015rem;margin-bottom:0.625rem;margin-top:0.625rem;}@media(max-width: 48rem){.css-1jvcbpx{font-size:2.25rem;line-height:1.1;}}@media(min-width: 48rem){.css-1jvcbpx{font-size:2rem;line-height:1.1;}}@media(min-width: 64rem){.css-1jvcbpx{font-size:2.625rem;line-height:1.1;}}.css-1jvcbpx b,.css-1jvcbpx strong{font-family:inherit;font-weight:bold;}.css-1jvcbpx em,.css-1jvcbpx i{font-style:italic;font-family:inherit;} Meet the Experts

• Mamina Turegano, M.D., F.A.A.D, is a triple board-certified dermatologist based in Metairie, Louisiana.
• Ellen Marmur, M.D., is a board-certified dermatologist and founder of Marmur Medical and MMSkincare, based in New York City.

When in my routine should I use one of the best acne light devices?

Marmur notes that best time to use an acne light device is after cleansing your face as "debris and dry skin cells can block the light energy." Acne light therapy devices work on most types of acne, but won't do much for blackheads , whiteheads, or deep cystic pimples, Turegano cautions—so stick to topical treatments and oral medication for those. And before your session, the derm says to avoid using products that exfoliate or cause increased skin cell turnover, like exfoliating acids or retinoids , as they may make your skin more sensitive.

Why trust Harper’s Bazaar ?

For more than 150 years, Harper’s Bazaar has been the preeminent fashion and beauty resource for women at every age. We cover what’s new and what’s next in beauty by working with the world’s leading authorities in dermatology, plastic surgery, cosmetics, skincare, hair care, and fragrance. Every story we publish has been thoroughly researched and vetted by our team of beauty editors and industry experts.

The Edit: Beauty

The 15 Best Tinted Sunscreens

These 8 Spa-Level Showerheads Feel Like Luxury

Beautycounter Now Has a Suite of Clean Fragrances

How to Hydrate Skin Like a Pro

12 Teeth Whitening Kits Experts Swear By

The 22 Body Washes Experts Love

Here’s Exactly How to Get Rid of Under-Eye Bags

The 21 Best Eye Creams for Dark Circles

These Essential Tanners Won't Leave You Orange

Want a Brighter Smile? Try These 11 Toothpastes

The Best Sol de Janeiro Scents Our Editors Love

Advertisement

How the Key Bridge Collapsed in Baltimore: Maps and Photos

By Weiyi Cai ,  Agnes Chang ,  Lauren Leatherby ,  Lazaro Gamio ,  Leanne Abraham and Scott Reinhard

On Tuesday, a major bridge in Baltimore collapsed into the water seconds after it was struck by a cargo ship, sending vehicles on the bridge into the river below. The ship lost power and issued a mayday call shortly before it hit the bridge.

The ship, a 948-foot-long cargo vessel called Dali, was about a half hour into its journey toward Colombo, Sri Lanka, when it hit a main pillar of the bridge. All crew members are safe, according to the ship’s owners.

Follow our live coverage .

A mayday call from the ship gave officials enough time to stop traffic at both ends of the bridge. The waters where the bridge collapsed are about 50 feet deep. By Tuesday morning, six construction workers who had been fixing potholes on the bridge remained missing as divers and other emergency workers on boats and helicopters continued to search for them. Two others had been rescued, and one was in the hospital.

Francis Scott

Patapsco River

The ship left the Port

of Baltimore around

1 a.m. on Tuesday.

Where impact occurred

Direction of the ship

The ship hit the

bridge at 1:28 a.m.

The ship hit the bridge at 1:28 a.m.

Where impact

Source: Spire Global

The New York Times; satellite image by Google Earth

The lights of the ship flickered on and off as it lost power in the minutes before the ship changed bearing and hit the bridge.

Ship approached from

the Port of Baltimore

Road repair crews

Ship changed heading

as it neared pillar

Ship hit pillar

Southern and central spans

of bridge began to collapse within

seconds of impact

Northern span began to

collapse seconds later

Within 30 seconds of impact,

the central part of bridge had

entirely collapsed.

Source: StreamTime Live via YouTube

Timestamps are from StreamTime Live video.

The New York Times

The Francis Scott Key Bridge was opened in 1977 and carried more than 12.4 million vehicles last year. The bridge was one of the three major ways to cross the Patapsco River and formed part of Baltimore’s beltway.

The Port of Baltimore is a major trade hub that handled a record amount of foreign cargo last year. It is an especially important destination — the nation’s largest by volume last year — for deliveries of cars and light trucks.

Ship impact

To Chesapeake Bay

Sources: Maryland Port Administration, OpenStreetMap, MarineTraffic

Note: Ship positions are as of 2:46 p.m. Eastern time.

Overall, Baltimore was the 17th biggest port in the United States in 2021, ranked by total tons, according to the Bureau of Transportation Statistics. The bridge collapse brought marine traffic there to a standstill, with seven cargo or tanker ships stranded in the harbor as of Tuesday afternoon.

Gov. Wes Moore declared a state of emergency for Maryland and said that his office was in close communication with Pete Buttigieg, the U.S. transportation secretary. The White House issued a statement saying that President Biden had been briefed on the collapse.

Erin Schaff/The New York Times

• Share full article

Where is the Francis Scott Key Bridge? What to know about collapsed Baltimore bridge

The collapse of the Francis Scott Key Bridge , a major transportation link in the Baltimore area, sparked a massive search and rescue effort early Tuesday morning.

The bridge has been a critical transportation passageway along the East Coast for decades. Video captured the collapse , after Singapore-flagged container ship, the Dali, collided with one of the bridge's pillars.

The ship had caught fire, and several vehicles fell into the river below.

Here's what to know about the Francis Scott Key Bridge.

Follow here for live updates → Baltimore's Key Bridge collapses after ship collision; rescue effort underway

Where is the Francis Scott Key Bridge located?

The bridge crosses over the Patapsco River on I-695 and is the final link on the Baltimore Beltway, according to the Maryland Transportation Authority .

It is the outermost of the three tollways that cross Baltimore's Harbor.

How long is the Francis Scott Key Bridge?

The 4-lane bridge structure alone is 1.6 miles long. The facility also includes the Curtis Creek Drawbridge. Including approach roadways, the entire stretch is around 10.9 miles long, MDTA said.

Why did a ship hit the Francis Scott Key Bridge?

The ship, a container vessel chartered by Maersk, apparently lost power a few minutes before striking the bridge, a senior U.S. official told USA TODAY .

No Maersk crew or personnel were onboard the vessel when it struck the bridge, according to a statement from the company. It was operated by a charter company, Synergy Group, and owned by Grace Ocean Pte., based in Singapore, and ultimately bound for Sri Lanka.

Accidents like this, called Marine casualties, are not uncommon, the official told USA TODAY, with an allision (an immobile object being struck by a ship) occurring about every 10 years or so. Investigators will likely look into the cause of the power outage and whether there was a mechanical failure on the ship.

How old is the Key Bridge in Baltimore?

The Francis Scott Key Bridge opened in March 1977, according to the Maryland Transportation Authority .

What type of bridge is the Francis Scott Key?

The steel-arched bridge was the second-longest continuous-truss bridge span in the world when it was built and remains the second longest in the United States and third in the world,  according to the American Civil Engineering Society .

When was the Francis Scott Key Bridge built?

Construction of the Francis Scott Key Bridge began in 1972.

Francis Scott Key Bridge has a deep history

According to the MDTA, the bridge crosses over the Patapsco River, near where Francis Scott Key, the bridge's namesake, was inspired to write the lyrics of the Star Spangled Banner.

Key is believed to have witnessed the bombardment of Fort McHenry on the night of Sept. 12, 1814, within 100 yards of the modern-day bridge. That battle is what inspired him to the national anthem.

How vital is the Francis Scott Key Bridge?

The bridge is critical to East Coast shipping. The port’s private and public terminals handled 847,158 autos and light trucks in 2023, the most of any U.S. port. The port also handles farm and construction machinery, sugar, gypsum and coal, according to a Maryland government website.