travel back in time speed of light

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

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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.

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No sense in nonsense —

Why the [expletive] can’t we travel back in time, if the inability to time travel were a fundamental part of our universe, you’d expect equally fundamental physics behind that rule..

Paul Sutter - Nov 30, 2021 12:30 pm UTC

Look, we’re not totally ignorant about time. We know that the dimension of time is woven together with the three dimensions of space, creating a four-dimensional fabric for the Universe. We know that the passage of time is relative; depending on your frame of reference, you can slip forward into the future as gently as you please. (You just need to either go close to the speed of light or get cozy with a black hole, but those are just minor problems of engineering, not physics.)

But as far as we can tell, we can’t reverse the flow of time. All evidence indicates that travel into the past is forbidden in our Universe. Every time we try to concoct a time machine, some random rule of the Universe comes in and slaps our hand away from the temporal cookie jar.

And yet, we have no idea why. The reasons really seem random; there is nothing fundamental we can point to, no law or equation or concept that definitively explains why thou shalt not travel into the past. And that’s pretty frustrating. It’s obvious that the Universe is telling us something important… we just don’t know what it’s saying.

Go ahead, kill your grandfather

There are all sorts of philosophical debates for and against the possibility of time travel. Take, for example, the famous “grandfather paradox.” Let’s say you build a time machine and travel back in time. You find your own grandfather and shoot him dead (I don’t know why, but roll with me here). But wait… if your grandfather is dead, it means he can’t father your father, which means you never exist. So how did you go back in time to do the awful deed?

Perhaps, however, time travel into the past is, indeed, allowed, but your actions are constrained. Maybe the past already exists and is completely set in stone. What has happened has simply happened. If you had the ability to travel back in time and monkey around with the past, then the past should already encode those acts—nothing is new, because it’s literally in the past. So you can’t kill your grandfather because you never have, but you could be the stranger that sets him up on a blind date with grandma.

Maybe, like, time doesn’t even exist, dude. Maybe it’s a construct of our human consciousness as a way to organize and synchronize our sensory inputs. Maybe we’re imposing some deep, fundamental preconceived notion on a Universe that doesn’t care, and so this whole discussion is moot.

This is all part of very legit discussions of philosophy. But let’s see if physics can take a crack at it. After all, if we could (even theoretically) build a time machine, then that would settle a lot of late-night bar bets.

Closed time-like curves

Physicists use a very particular language when trying to build time machines: the language of gravity, given to us by old Albert himself in the form of general relativity. That’s because the language of gravity as interpreted in GR is a story of the bending and warping of spacetime. GR is a theory of motion in our Universe and how that motion is tied to the underlying four-dimensional fabric of spacetime.

In GR, matter tells spacetime how to bend, and the bending of spacetime tells matter how to move.

To determine whether we can build a time machine, physicists want to know if it’s possible to construct a spacetime—to find a particular and peculiar arrangement of matter—that allows one to travel into the past.

The goal is to find “closed time-like curves,” or CTCs.

“Curve” means exactly what you think it does—a path through space and time. “Time like” means no cheating—at no point are you allowed to travel faster than light. “Closed” means that the curve meets up back with itself—imagine traveling in one direction, always moving forward, never exceeding light speed. Yet at the end of your journey, you find you’ve arrived in your own past.

That’s a time machine. That’s a CTC.

The weird thing is, CTCs exist! Over the decades we have managed to uncover many solutions of general relativity that allow for backward time travel:

• The (in)famous mathematician Kurt Gödel (yes, that Kurt Gödel) discovered if a universe is filled with uniform dust that was slowly rotating, you could find trajectories in that universe that wind up in their own past.
• You know wormholes, right? Those shortcuts through space? They can also act as time machines. The trick is to take one end of the wormhole and hold it still. Then take the other and accelerate it close to the speed of light. Keep it at that speed for however long you want. Now bring that end back to the original one. The two ends of the wormhole now no longer have synchronized clocks because of the time dilation effects of the near-lightspeed travel. Since one end is in the past of the other end, you can just hop on in and travel back in time.
• Let’s say you had an infinitely long cylinder (maybe you pick it up at your local home improvement store). Rotate that cylinder to nearly the speed of light. If you follow a careful, corkscrew path around the rotating cylinder, then, by golly, you’ll wind up in the past.
• The inside of a rotating black hole is a pretty interesting place, where the competing countercurrents of gravitational and centrifugal forces meet to open a throat in the center of a black hole, creating the possibility of CTCs.

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Is time travel possible? Why one scientist says we 'cannot ignore the possibility.'

A common theme in science-fiction media , time travel is captivating. It’s defined by the late philosopher David Lewis in his essay “The Paradoxes of Time Travel” as “[involving] a discrepancy between time and space time. Any traveler departs and then arrives at his destination; the time elapsed from departure to arrival … is the duration of the journey.”

Time travel is usually understood by most as going back to a bygone era or jumping forward to a point far in the future . But how much of the idea is based in reality? Is it possible to travel through time? 

Is time travel possible?

According to NASA, time travel is possible , just not in the way you might expect. Albert Einstein’s theory of relativity says time and motion are relative to each other, and nothing can go faster than the speed of light , which is 186,000 miles per second. Time travel happens through what’s called “time dilation.”

Time dilation , according to Live Science, is how one’s perception of time is different to another's, depending on their motion or where they are. Hence, time being relative. 

Learn more: Best travel insurance

Dr. Ana Alonso-Serrano, a postdoctoral researcher at the Max Planck Institute for Gravitational Physics in Germany, explained the possibility of time travel and how researchers test theories. 

Space and time are not absolute values, Alonso-Serrano said. And what makes this all more complex is that you are able to carve space-time .

“In the moment that you carve the space-time, you can play with that curvature to make the time come in a circle and make a time machine,” Alonso-Serrano told USA TODAY. 

She explained how, theoretically, time travel is possible. The mathematics behind creating curvature of space-time are solid, but trying to re-create the strict physical conditions needed to prove these theories can be challenging. 

“The tricky point of that is if you can find a physical, realistic, way to do it,” she said. 

Alonso-Serrano said wormholes and warp drives are tools that are used to create this curvature. The matter needed to achieve curving space-time via a wormhole is exotic matter , which hasn’t been done successfully. Researchers don’t even know if this type of matter exists, she said.

“It's something that we work on because it's theoretically possible, and because it's a very nice way to test our theory, to look for possible paradoxes,” Alonso-Serrano added.

“I could not say that nothing is possible, but I cannot ignore the possibility,” she said. 

She also mentioned the anecdote of  Stephen Hawking’s Champagne party for time travelers . Hawking had a GPS-specific location for the party. He didn’t send out invites until the party had already happened, so only people who could travel to the past would be able to attend. No one showed up, and Hawking referred to this event as "experimental evidence" that time travel wasn't possible.

What did Albert Einstein invent?: Discoveries that changed the world

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

Published: Nov 13, 2023

By: Magazine Editor

Written by Adi Foord , assistant professor of physics , UMBC

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

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

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

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

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

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

Time is relative

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

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

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

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

Paradoxes and failed dinner parties

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

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

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

Telescopes are time machines

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

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

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

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

Tags: CNMS , Physics , The Conversation

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Is There a Particle That Can Travel Back in Time?

A hypothetical particle could be the answer, but traveling in time would still be a complicated venture..

Yes, there is a hypothetical particle, called the tachyon , that could travel back in time. One catch: It almost certainly doesn’t exist.

Time and Speed of Light

Before we start talking about time travel, we first must talk about the speed of light . All objects in our universe are constrained to go no faster than the speed of light. The only particles capable of achieving light speed are massless particles, like light itself. Anything with even a tiny amount of mass will find it impossible to achieve light speed. That’s because the faster you go the more massive you become, and at light speed your mass becomes infinite, which would take an infinite amount of energy to accelerate.

But the speed of light isn’t just an expression of how fast objects can travel. It’s an expression of how fast objects can influence each other. Every single interaction in the universe, whether it’s your sibling hitting you or a supernova ’s shock wave blasting through a gas cloud, is limited to the speed of light. The speed of light is actually the speed of causality – the fastest possible way that one cause can create an effect, and the fastest possible way that events can influence each other.

Read More: A Major Time Travel Perk May Be Technically Impossible

Going faster than light means that you could go faster than causality. Said another way, going faster than light means going faster than time itself , meaning that faster-than-light travel automatically allows for time travel into the past.

Tachyon and Time Travel

There is a hypothetical class of particles that always travel faster than light. Einstein himself played around with the idea, calling them “ meta-particles ,” but today we call them tachyons , a word coined in 1967 by physicist Gerald Feinberg from the Greek word meaning “swift.”

Tachyons would be strange. Just as we massive objects could never ever exceed the speed of light, tachyons could never dip below light speed – they would be equally constrained on the other side of that invisible boundary. For tachyons, slowing down means increasing mass, and slowing down all the way to light speed would require an infinite amount of energy. To make this work, the mass of the tachyon has to be imaginary, but in the mathematical sense: Its mass would be multiplied by a factor of the square root of negative one.

At first glance, tachyons wouldn’t cause much trouble. You could fly out in a rocket ship, and on Earth, I could beam tachyon messages to you. If you were looking back at me through a telescope, those tachyons would reach you before the photons carrying the image of me sending the message arrived in your telescope. That’s a little weird but doesn’t necessarily violate anything about physics.

Read More: Black Holes Are Accelerating The Expansion Of The Universe, Say Cosmologists

Time-Travel Paradox

The problem is that with tachyons, you could start to construct some truly weird scenarios. For example, you could move in a certain direction with a certain speed and send a tachyon signal back to me. If you construct things just right in the rocket ship, that signal can arrive back to me before I sent the original one out.

Suppose that signal back to me contained instructions to destroy my transmitter. The only way to destroy the transmitter is through the reception of your signal, but the only way to get your message is for me to first send mine. If I get my signal out, then my transmitter was destroyed in the past. But if the transmitter was destroyed, I can’t get the signal out.

This is just one of many common time-travel paradoxes brought about by traveling faster than light. This doesn’t rule out the existence of tachyons explicitly, but it does signal that they likely don’t exist. It seems impossible for us to travel backwards into the past or send signals into our own past: Everything in our universe not only travels no faster than the speed light, but also always in the direction of the future.

Impossible, or Not Proven?

Physicists have proposed the “causality protection conjecture,” which says that faster than light travel (and travel into the past) is outright impossible. As of now this conjecture is merely a, well, conjecture, and not proven. We do not currently understand why travel into the past is forbidden, but we hope that someday we can construct a law of physics that tells us why.

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September 1, 2015

12 min read

Traveling Backward in Time Is Kind of Hard

We already have the means to skip ahead in time, but going backward is a different wormhole

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

Time travel is not only possible, it has already happened, though not exactly as Wells imagined. The biggest time traveler to date is Sergei K. Krikalev, according to J. Richard Gott, an astrophysicist at Princeton University. Over the course of his long career, which began in 1985, the Russian cosmonaut spent a little over 803 days in space. As Einstein proved, time passes more slowly for objects in motion than for those at rest, so as Krikalev hurtled along at 17,000 miles an hour onboard the Mir space station, time did not flow at the same rate for him as it did on Earth. While Krikalev was in orbit, he aged 1/48 of a second less than his fellow earthlings. From another perspective, he traveled 1/48 of a second into the future.

The time-travel effect is much easier to see with longer distances and higher speeds. If Krikalev left Earth in 2015 and made a round-trip to Betelgeuse—a star that is about 520 light-years from Earth—at 99.995 percent the speed of light, by the time he returned to Earth he would be only 10 years older. Sadly, everyone he knew would be long dead because 1,000 years would have passed on Earth; it would be the year 3015. “Time travel to the future, we know we can do,” Gott says. “It's just a matter of money and engineering!”

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

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

A new way of looking at time

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

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

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

Gödel's strange universe

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

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

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

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

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

An annoying possibility

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

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

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

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

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

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

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

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

Did the universe create itself?

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

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

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

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

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

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

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

A cosmic chess game

For now, there is no way to test whether any of those theories might actually explain the origin of the universe. The famed physicist Richard Feynman compared the universe to a great chess game being played by the gods. Scientists, he said, are trying to understand the game without knowing the rules. We watch as the gods move a pawn one space forward, and we learn a rule: pawns always move one space forward. But what if we never saw the opening of a game, when a pawn can move two spaces forward? We might also assume, mistakenly, that pawns always remain pawns—that they never change their identity—until we see a pawn transformed into a queen. “You would say that's against the rules,” Gott says. “You can't change your pawn into a queen. Well, yes, you can! You just never saw a game that extreme before. Time-travel research is like that. We're testing the laws of physics by looking at extreme conditions. There's nothing logically impossible about time travel to the past; it's just not the universe we're used to.” Turning a pawn into a queen could be part of the rules of relativity.

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

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

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

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

Why does time change when traveling close to the speed of light? A physicist explains

Assistant Professor of Physics and Astronomy, Rochester Institute of Technology

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Why does time change when traveling close to the speed of light? – Timothy, age 11, Shoreview, Minnesota

Imagine you’re in a car driving across the country watching the landscape. A tree in the distance gets closer to your car, passes right by you, then moves off again in the distance behind you.

Of course, you know that tree isn’t actually getting up and walking toward or away from you. It’s you in the car who’s moving toward the tree. The tree is moving only in comparison, or relative, to you – that’s what we physicists call relativity . If you had a friend standing by the tree, they would see you moving toward them at the same speed that you see them moving toward you.

In his 1632 book “ Dialogue Concerning the Two Chief World Systems ,” the astronomer Galileo Galilei first described the principle of relativity – the idea that the universe should behave the same way at all times, even if two people experience an event differently because one is moving in respect to the other.

If you are in a car and toss a ball up in the air, the physical laws acting on it, such as the force of gravity, should be the same as the ones acting on an observer watching from the side of the road. However, while you see the ball as moving up and back down, someone on the side of the road will see it moving toward or away from them as well as up and down.

Special relativity and the speed of light

Albert Einstein much later proposed the idea of what’s now known as special relativity to explain some confusing observations that didn’t have an intuitive explanation at the time. Einstein used the work of many physicists and astronomers in the late 1800s to put together his theory in 1905, starting with two key ingredients: the principle of relativity and the strange observation that the speed of light is the same for every observer and nothing can move faster. Everyone measuring the speed of light will get the same result, no matter where they are or how fast they are moving.

Let’s say you’re in the car driving at 60 miles per hour and your friend is standing by the tree. When they throw a ball toward you at a speed of what they perceive to be 60 miles per hour, you might logically think that you would observe your friend and the tree moving toward you at 60 miles per hour and the ball moving toward you at 120 miles per hour. While that’s really close to the correct value, it’s actually slightly wrong.

This discrepancy between what you might expect by adding the two numbers and the true answer grows as one or both of you move closer to the speed of light. If you were traveling in a rocket moving at 75% of the speed of light and your friend throws the ball at the same speed, you would not see the ball moving toward you at 150% of the speed of light. This is because nothing can move faster than light – the ball would still appear to be moving toward you at less than the speed of light. While this all may seem very strange, there is lots of experimental evidence to back up these observations.

Time dilation and the twin paradox

Speed is not the only factor that changes relative to who is making the observation. Another consequence of relativity is the concept of time dilation , whereby people measure different amounts of time passing depending on how fast they move relative to one another.

Each person experiences time normally relative to themselves. But the person moving faster experiences less time passing for them than the person moving slower. It’s only when they reconnect and compare their watches that they realize that one watch says less time has passed while the other says more.

This leads to one of the strangest results of relativity – the twin paradox , which says that if one of a pair of twins makes a trip into space on a high-speed rocket, they will return to Earth to find their twin has aged faster than they have. It’s important to note that time behaves “normally” as perceived by each twin (exactly as you are experiencing time now), even if their measurements disagree.

You might be wondering: If each twin sees themselves as stationary and the other as moving toward them, wouldn’t they each measure the other as aging faster? The answer is no, because they can’t both be older relative to the other twin.

The twin on the spaceship is not only moving at a particular speed where the frame of references stay the same but also accelerating compared with the twin on Earth. Unlike speeds that are relative to the observer, accelerations are absolute. If you step on a scale, the weight you are measuring is actually your acceleration due to gravity. This measurement stays the same regardless of the speed at which the Earth is moving through the solar system, or the solar system is moving through the galaxy or the galaxy through the universe.

Neither twin experiences any strangeness with their watches as one moves closer to the speed of light – they both experience time as normally as you or I do. It’s only when they meet up and compare their observations that they will see a difference – one that is perfectly defined by the mathematics of relativity.

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What is the speed of light? Here’s the history, discovery of the cosmic speed limit

On one hand, the speed of light is just a number: 299,792,458 meters per second. And on the other, it’s one of the most important constants that appears in nature and defines the relationship of causality itself.

As far as we can measure, it is a constant. It is the same speed for every observer in the entire universe. This constancy was first established in the late 1800’s with the experiments of Albert Michelson and Edward Morley at Case Western Reserve University . They attempted to measure changes in the speed of light as the Earth orbited around the Sun. They found no such variation, and no experiment ever since then has either.

Observations of the cosmic microwave background, the light released when the universe was 380,000 years old, show that the speed of light hasn’t measurably changed in over 13.8 billion years.

In fact, we now define the speed of light to be a constant, with a precise speed of 299,792,458 meters per second. While it remains a remote possibility in deeply theoretical physics that light may not be a constant, for all known purposes it is a constant, so it’s better to just define it and move on with life.

How was the speed of light first measured?

In 1676 the Danish astronomer Ole Christensen Romer made the first quantitative measurement of how fast light travels. He carefully observed the orbit of Io, the innermost moon of Jupiter. As the Earth circles the Sun in its own orbit, sometimes it approaches Jupiter and sometimes it recedes away from it. When the Earth is approaching Jupiter, the path that light has to travel from Io is shorter than when the Earth is receding away from Jupiter. By carefully measuring the changes to Io’s orbital period, Romer calculated a speed of light of around 220,000 kilometers per second.

Observations continued to improve until by the 19 th century astronomers and physicists had developed the sophistication to get very close to the modern value. In 1865, James Clerk Maxwell made a remarkable discovery. He was investigating the properties of electricity and magnetism, which for decades had remained mysterious in unconnected laboratory experiments around the world. Maxwell found that electricity and magnetism were really two sides of the same coin, both manifestations of a single electromagnetic force.

As Maxwell explored the consequences of his new theory, he found that changing magnetic fields can lead to changing electric fields, which then lead to a new round of changing magnetic fields. The fields leapfrog over each other and can even travel through empty space. When Maxwell went to calculate the speed of these electromagnetic waves, he was surprised to see the speed of light pop out – the first theoretical calculation of this important number.

What is the most precise measurement of the speed of light?

Because it is defined to be a constant, there’s no need to measure it further. The number we’ve defined is it, with no uncertainty, no error bars. It’s done. But the speed of light is just that – a speed. The number we choose to represent it depends on the units we use: kilometers versus miles, seconds versus hours, and so on. In fact, physicists commonly just set the speed of light to be 1 to make their calculations easier. So instead of trying to measure the speed light travels, physicists turn to more precisely measuring other units, like the length of the meter or the duration of the second. In other words, the defined value of the speed of light is used to establish the length of other units like the meter.

How does light slow down?

Yes, the speed of light is always a constant. But it slows down whenever it travels through a medium like air or water. How does this work? There are a few different ways to present an answer to this question, depending on whether you prefer a particle-like picture or a wave-like picture.

In a particle-like picture, light is made of tiny little bullets called photons. All those photons always travel at the speed of light, but as light passes through a medium those photons get all tangled up, bouncing around among all the molecules of the medium. This slows down the overall propagation of light, because it takes more time for the group of photons to make it through.

In a wave-like picture, light is made of electromagnetic waves. When these waves pass through a medium, they get all the charged particles in motion, which in turn generate new electromagnetic waves of their own. These interfere with the original light, forcing it to slow down as it passes through.

Either way, light always travels at the same speed, but matter can interfere with its travel, making it slow down.

Why is the speed of light important?

The speed of light is important because it’s about way more than, well, the speed of light. In the early 1900’s Einstein realized just how special this speed is. The old physics, dominated by the work of Isaac Newton, said that the universe had a fixed reference frame from which we could measure all motion. This is why Michelson and Morley went looking for changes in the speed, because it should change depending on our point of view. But their experiments showed that the speed was always constant, so what gives?

Einstein decided to take this experiment at face value. He assumed that the speed of light is a true, fundamental constant. No matter where you are, no matter how fast you’re moving, you’ll always see the same speed.

This is wild to think about. If you’re traveling at 99% the speed of light and turn on a flashlight, the beam will race ahead of you at…exactly the speed of light, no more, no less. If you’re coming from the opposite direction, you’ll still also measure the exact same speed.

This constancy forms the basis of Einstein’s special theory of relativity, which tells us that while all motion is relative – different observers won’t always agree on the length of measurements or the duration of events – some things are truly universal, like the speed of light.

Can you go faster than light speed?

Nope. Nothing can. Any particle with zero mass must travel at light speed. But anything with mass (which is most of the universe) cannot. The problem is relativity. The faster you go, the more energy you have. But we know from Einstein’s relativity that energy and mass are the same thing. So the more energy you have, the more mass you have, which makes it harder for you to go even faster. You can get as close as you want to the speed of light, but to actually crack that barrier takes an infinite amount of energy. So don’t even try.

How is the speed at which light travels related to causality?

If you think you can find a cheat to get around the limitations of light speed, then I need to tell you about its role in special relativity. You see, it’s not just about light. It just so happens that light travels at this special speed, and it was the first thing we discovered to travel at this speed. So it could have had another name. Indeed, a better name for this speed might be “the speed of time.”

Related: Is time travel possible? An astrophysicist explains

We live in a universe of causes and effects. All effects are preceded by a cause, and all causes lead to effects. The speed of light limits how quickly causes can lead to effects. Because it’s a maximum speed limit for any motion or interaction, in a given amount of time there’s a limit to what I can influence. If I want to tap you on the shoulder and you’re right next to me, I can do it right away. But if you’re on the other side of the planet, I have to travel there first. The motion of me traveling to you is limited by the speed of light, so that sets how quickly I can tap you on the shoulder – the speed light travels dictates how quickly a single cause can create an effect.

The ability to go faster than light would allow effects to happen before their causes. In essence, time travel into the past would be possible with faster-than-light travel. Since we view time as the unbroken chain of causes and effects going from the past to the future, breaking the speed of light would break causality, which would seriously undermine our sense of the forward motion of time.

Why does light travel at this speed?

No clue. It appears to us as a fundamental constant of nature. We have no theory of physics that explains its existence or why it has the value that it does. We hope that a future understanding of nature will provide this explanation, but right now all investigations are purely theoretical. For now, we just have to take it as a given.

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The speed of light traveling through a vacuum is exactly 299,792,458 meters (983,571,056 feet) per second. That's about 186,282 miles per second — a universal constant known in equations as "c," or light speed. 

According to physicist Albert Einstein 's theory of special relativity , on which much of modern physics is based, nothing in the universe can travel faster than light. The theory states that as matter approaches the speed of light, the matter's mass becomes infinite. That means the speed of light functions as a speed limit on the whole universe . The speed of light is so immutable that, according to the U.S. National Institute of Standards and Technology , it is used to define international standard measurements like the meter (and by extension, the mile, the foot and the inch). Through some crafty equations, it also helps define the kilogram and the temperature unit Kelvin .

But despite the speed of light's reputation as a universal constant, scientists and science fiction writers alike spend time contemplating faster-than-light travel. So far no one's been able to demonstrate a real warp drive, but that hasn't slowed our collective hurtle toward new stories, new inventions and new realms of physics.

Related: Special relativity holds up to a high-energy test

A l ight-year is the distance that light can travel in one year — about 6 trillion miles (10 trillion kilometers). It's one way that astronomers and physicists measure immense distances across our universe.

Light travels from the moon to our eyes in about 1 second, which means the moon is about 1 light-second away. Sunlight takes about 8 minutes to reach our eyes, so the sun is about 8 light minutes away. Light from Alpha Centauri , which is the nearest star system to our own, requires roughly 4.3 years to get here, so Alpha Centauri is 4.3 light-years away.

"To obtain an idea of the size of a light-year, take the circumference of the Earth (24,900 miles), lay it out in a straight line, multiply the length of the line by 7.5 (the corresponding distance is one light-second), then place 31.6 million similar lines end to end," NASA's Glenn Research Center says on its website . "The resulting distance is almost 6 trillion (6,000,000,000,000) miles!"

Stars and other objects beyond our solar system lie anywhere from a few light-years to a few billion light-years away. And everything astronomers "see" in the distant universe is literally history. When astronomers study objects that are far away, they are seeing light that shows the objects as they existed at the time that light left them. 

This principle allows astronomers to see the universe as it looked after the Big Bang , which took place about 13.8 billion years ago. Objects that are 10 billion light-years away from us appear to astronomers as they looked 10 billion years ago — relatively soon after the beginning of the universe — rather than how they appear today.

Related: Why the universe is all history

Speed of light FAQs answered by an expert

We asked Rob Zellem, exoplanet-hunter and staff scientist at NASA's Jet Propulsion Lab, a few frequently asked questions about the speed of light. 

Dr. Rob Zellem is a staff scientist at NASA's Jet Propulsion Laboratory, a federally funded research and development center operated by the California Institute of Technology. Rob is the project lead for Exoplanet Watch, a citizen science project to observe exoplanets, planets outside of our own solar system, with small telescopes. He is also the Science Calibration lead for the Nancy Grace Roman Space Telescope's Coronagraph Instrument, which will directly image exoplanets. 

What is faster than the speed of light?

Nothing! Light is a "universal speed limit" and, according to Einstein's theory of relativity, is the fastest speed in the universe: 300,000 kilometers per second (186,000 miles per second). 

Is the speed of light constant?

The speed of light is a universal constant in a vacuum, like the vacuum of space. However, light *can* slow down slightly when it passes through an absorbing medium, like water (225,000 kilometers per second = 140,000 miles per second) or glass (200,000 kilometers per second = 124,000 miles per second). 

Who discovered the speed of light?

One of the first measurements of the speed of light was by Rømer in 1676 by observing the moons of Jupiter . The speed of light was first measured to high precision in 1879 by the Michelson-Morley Experiment. 

How do we know the speed of light?

Rømer was able to measure the speed of light by observing eclipses of Jupiter's moon Io. When Jupiter was closer to Earth, Rømer noted that eclipses of Io occurred slightly earlier than when Jupiter was farther away. Rømer attributed this effect due the time it takes for light to travel over the longer distance when Jupiter was farther from the Earth. 

How did we learn the speed of light?

As early as the 5th century BC, Greek philosophers like Empedocles and Aristotle disagreed on the nature of light speed. Empedocles proposed that light, whatever it was made of, must travel and therefore, must have a rate of travel. Aristotle wrote a rebuttal of Empedocles' view in his own treatise, On Sense and the Sensible , arguing that light, unlike sound and smell, must be instantaneous. Aristotle was wrong, of course, but it would take hundreds of years for anyone to prove it. 

In the mid 1600s, the Italian astronomer Galileo Galilei stood two people on hills less than a mile apart. Each person held a shielded lantern. One uncovered his lantern; when the other person saw the flash, he uncovered his too. But Galileo's experimental distance wasn't far enough for his participants to record the speed of light. He could only conclude that light traveled at least 10 times faster than sound.

In the 1670s, Danish astronomer Ole Rømer tried to create a reliable timetable for sailors at sea, and according to NASA , accidentally came up with a new best estimate for the speed of light. To create an astronomical clock, he recorded the precise timing of the eclipses of Jupiter's moon , Io, from Earth . Over time, Rømer observed that Io's eclipses often differed from his calculations. He noticed that the eclipses appeared to lag the most when Jupiter and Earth were moving away from one another, showed up ahead of time when the planets were approaching and occurred on schedule when the planets were at their closest or farthest points. This observation demonstrated what we today know as the Doppler effect, the change in frequency of light or sound emitted by a moving object that in the astronomical world manifests as the so-called redshift , the shift towards "redder", longer wavelengths in objects speeding away from us. In a leap of intuition, Rømer determined that light was taking measurable time to travel from Io to Earth. 

Rømer used his observations to estimate the speed of light. Since the size of the solar system and Earth's orbit wasn't yet accurately known, argued a 1998 paper in the American Journal of Physics , he was a bit off. But at last, scientists had a number to work with. Rømer's calculation put the speed of light at about 124,000 miles per second (200,000 km/s).

In 1728, English physicist James Bradley based a new set of calculations on the change in the apparent position of stars caused by Earth's travels around the sun. He estimated the speed of light at 185,000 miles per second (301,000 km/s) — accurate to within about 1% of the real value, according to the American Physical Society .

Two new attempts in the mid-1800s brought the problem back to Earth. French physicist Hippolyte Fizeau set a beam of light on a rapidly rotating toothed wheel, with a mirror set up 5 miles (8 km) away to reflect it back to its source. Varying the speed of the wheel allowed Fizeau to calculate how long it took for the light to travel out of the hole, to the adjacent mirror, and back through the gap. Another French physicist, Leon Foucault, used a rotating mirror rather than a wheel to perform essentially the same experiment. The two independent methods each came within about 1,000 miles per second (1,609 km/s) of the speed of light.

Another scientist who tackled the speed of light mystery was Poland-born Albert A. Michelson, who grew up in California during the state's gold rush period, and honed his interest in physics while attending the U.S. Naval Academy, according to the University of Virginia . In 1879, he attempted to replicate Foucault's method of determining the speed of light, but Michelson increased the distance between mirrors and used extremely high-quality mirrors and lenses. Michelson's result of 186,355 miles per second (299,910 km/s) was accepted as the most accurate measurement of the speed of light for 40 years, until Michelson re-measured it himself. In his second round of experiments, Michelson flashed lights between two mountain tops with carefully measured distances to get a more precise estimate. And in his third attempt just before his death in 1931, according to the Smithsonian's Air and Space magazine, he built a mile-long depressurized tube of corrugated steel pipe. The pipe simulated a near-vacuum that would remove any effect of air on light speed for an even finer measurement, which in the end was just slightly lower than the accepted value of the speed of light today. 

Michelson also studied the nature of light itself, wrote astrophysicist Ethan Siegal in the Forbes science blog, Starts With a Bang . The best minds in physics at the time of Michelson's experiments were divided: Was light a wave or a particle? 

Michelson, along with his colleague Edward Morley, worked under the assumption that light moved as a wave, just like sound. And just as sound needs particles to move, Michelson and Morley and other physicists of the time reasoned, light must have some kind of medium to move through. This invisible, undetectable stuff was called the "luminiferous aether" (also known as "ether"). 

Though Michelson and Morley built a sophisticated interferometer (a very basic version of the instrument used today in LIGO facilities), Michelson could not find evidence of any kind of luminiferous aether whatsoever. Light, he determined, can and does travel through a vacuum.

"The experiment — and Michelson's body of work — was so revolutionary that he became the only person in history to have won a Nobel Prize for a very precise non-discovery of anything," Siegal wrote. "The experiment itself may have been a complete failure, but what we learned from it was a greater boon to humanity and our understanding of the universe than any success would have been!"

Special relativity and the speed of light

Einstein's theory of special relativity unified energy, matter and the speed of light in a famous equation: E = mc^2. The equation describes the relationship between mass and energy — small amounts of mass (m) contain, or are made up of, an inherently enormous amount of energy (E). (That's what makes nuclear bombs so powerful: They're converting mass into blasts of energy.) Because energy is equal to mass times the speed of light squared, the speed of light serves as a conversion factor, explaining exactly how much energy must be within matter. And because the speed of light is such a huge number, even small amounts of mass must equate to vast quantities of energy.

In order to accurately describe the universe, Einstein's elegant equation requires the speed of light to be an immutable constant. Einstein asserted that light moved through a vacuum, not any kind of luminiferous aether, and in such a way that it moved at the same speed no matter the speed of the observer. 

Think of it like this: Observers sitting on a train could look at a train moving along a parallel track and think of its relative movement to themselves as zero. But observers moving nearly the speed of light would still perceive light as moving away from them at more than 670 million mph. (That's because moving really, really fast is one of the only confirmed methods of time travel — time actually slows down for those observers, who will age slower and perceive fewer moments than an observer moving slowly.)

In other words, Einstein proposed that the speed of light doesn't vary with the time or place that you measure it, or how fast you yourself are moving. 

Therefore, objects with mass cannot ever reach the speed of light. If an object ever did reach the speed of light, its mass would become infinite. And as a result, the energy required to move the object would also become infinite: an impossibility.

That means if we base our understanding of physics on special relativity (which most modern physicists do), the speed of light is the immutable speed limit of our universe — the fastest that anything can travel. 

What goes faster than the speed of light?

Although the speed of light is often referred to as the universe's speed limit, the universe actually expands even faster. The universe expands at a little more than 42 miles (68 kilometers) per second for each megaparsec of distance from the observer, wrote astrophysicist Paul Sutter in a previous article for Space.com . (A megaparsec is 3.26 million light-years — a really long way.) 

In other words, a galaxy 1 megaparsec away appears to be traveling away from the Milky Way at a speed of 42 miles per second (68 km/s), while a galaxy two megaparsecs away recedes at nearly 86 miles per second (136 km/s), and so on. 

"At some point, at some obscene distance, the speed tips over the scales and exceeds the speed of light, all from the natural, regular expansion of space," Sutter explained. "It seems like it should be illegal, doesn't it?"

Special relativity provides an absolute speed limit within the universe, according to Sutter, but Einstein's 1915 theory regarding general relativity allows different behavior when the physics you're examining are no longer "local."

"A galaxy on the far side of the universe? That's the domain of general relativity, and general relativity says: Who cares! That galaxy can have any speed it wants, as long as it stays way far away, and not up next to your face," Sutter wrote. "Special relativity doesn't care about the speed — superluminal or otherwise — of a distant galaxy. And neither should you."

Does light ever slow down?

Light in a vacuum is generally held to travel at an absolute speed, but light traveling through any material can be slowed down. The amount that a material slows down light is called its refractive index. Light bends when coming into contact with particles, which results in a decrease in speed.

For example, light traveling through Earth's atmosphere moves almost as fast as light in a vacuum, slowing down by just three ten-thousandths of the speed of light. But light passing through a diamond slows to less than half its typical speed, PBS NOVA reported. Even so, it travels through the gem at over 277 million mph (almost 124,000 km/s) — enough to make a difference, but still incredibly fast.

Light can be trapped — and even stopped — inside ultra-cold clouds of atoms, according to a 2001 study published in the journal Nature . More recently, a 2018 study published in the journal Physical Review Letters proposed a new way to stop light in its tracks at "exceptional points," or places where two separate light emissions intersect and merge into one.

Researchers have also tried to slow down light even when it's traveling through a vacuum. A team of Scottish scientists successfully slowed down a single photon, or particle of light, even as it moved through a vacuum, as described in their 2015 study published in the journal Science . In their measurements, the difference between the slowed photon and a "regular" photon was just a few millionths of a meter, but it demonstrated that light in a vacuum can be slower than the official speed of light. 

Can we travel faster than light?

— Spaceship could fly faster than light

— Here's what the speed of light looks like in slow motion

— Why is the speed of light the way it is?

Science fiction loves the idea of "warp speed." Faster-than-light travel makes countless sci-fi franchises possible, condensing the vast expanses of space and letting characters pop back and forth between star systems with ease. 

But while faster-than-light travel isn't guaranteed impossible, we'd need to harness some pretty exotic physics to make it work. Luckily for sci-fi enthusiasts and theoretical physicists alike, there are lots of avenues to explore.

All we have to do is figure out how to not move ourselves — since special relativity would ensure we'd be long destroyed before we reached high enough speed — but instead, move the space around us. Easy, right? 

One proposed idea involves a spaceship that could fold a space-time bubble around itself. Sounds great, both in theory and in fiction.

"If Captain Kirk were constrained to move at the speed of our fastest rockets, it would take him a hundred thousand years just to get to the next star system," said Seth Shostak, an astronomer at the Search for Extraterrestrial Intelligence (SETI) Institute in Mountain View, California, in a 2010 interview with Space.com's sister site LiveScience . "So science fiction has long postulated a way to beat the speed of light barrier so the story can move a little more quickly."

Without faster-than-light travel, any "Star Trek" (or "Star War," for that matter) would be impossible. If humanity is ever to reach the farthest — and constantly expanding — corners of our universe, it will be up to future physicists to boldly go where no one has gone before.

Additional resources

For more on the speed of light, check out this fun tool from Academo that lets you visualize how fast light can travel from any place on Earth to any other. If you’re more interested in other important numbers, get familiar with the universal constants that define standard systems of measurement around the world with the National Institute of Standards and Technology . And if you’d like more on the history of the speed of light, check out the book " Lightspeed: The Ghostly Aether and the Race to Measure the Speed of Light " (Oxford, 2019) by John C. H. Spence.

Aristotle. “On Sense and the Sensible.” The Internet Classics Archive, 350AD. http://classics.mit.edu/Aristotle/sense.2.2.html .

D’Alto, Nick. “The Pipeline That Measured the Speed of Light.” Smithsonian Magazine, January 2017. https://www.smithsonianmag.com/air-space-magazine/18_fm2017-oo-180961669/ .

Fowler, Michael. “Speed of Light.” Modern Physics. University of Virginia. Accessed January 13, 2022. https://galileo.phys.virginia.edu/classes/252/spedlite.html#Albert%20Abraham%20Michelson .

Giovannini, Daniel, Jacquiline Romero, Václav Potoček, Gergely Ferenczi, Fiona Speirits, Stephen M. Barnett, Daniele Faccio, and Miles J. Padgett. “Spatially Structured Photons That Travel in Free Space Slower than the Speed of Light.” Science, February 20, 2015. https://www.science.org/doi/abs/10.1126/science.aaa3035 .

Goldzak, Tamar, Alexei A. Mailybaev, and Nimrod Moiseyev. “Light Stops at Exceptional Points.” Physical Review Letters 120, no. 1 (January 3, 2018): 013901. https://doi.org/10.1103/PhysRevLett.120.013901 . 

Hazen, Robert. “What Makes Diamond Sparkle?” PBS NOVA, January 31, 2000. https://www.pbs.org/wgbh/nova/article/diamond-science/ . 

“How Long Is a Light-Year?” Glenn Learning Technologies Project, May 13, 2021. https://www.grc.nasa.gov/www/k-12/Numbers/Math/Mathematical_Thinking/how_long_is_a_light_year.htm . 

American Physical Society News. “July 1849: Fizeau Publishes Results of Speed of Light Experiment,” July 2010. http://www.aps.org/publications/apsnews/201007/physicshistory.cfm . 

Liu, Chien, Zachary Dutton, Cyrus H. Behroozi, and Lene Vestergaard Hau. “Observation of Coherent Optical Information Storage in an Atomic Medium Using Halted Light Pulses.” Nature 409, no. 6819 (January 2001): 490–93. https://doi.org/10.1038/35054017 . 

NIST. “Meet the Constants.” October 12, 2018. https://www.nist.gov/si-redefinition/meet-constants . 

Ouellette, Jennifer. “A Brief History of the Speed of Light.” PBS NOVA, February 27, 2015. https://www.pbs.org/wgbh/nova/article/brief-history-speed-light/ . 

Shea, James H. “Ole Ro/Mer, the Speed of Light, the Apparent Period of Io, the Doppler Effect, and the Dynamics of Earth and Jupiter.” American Journal of Physics 66, no. 7 (July 1, 1998): 561–69. https://doi.org/10.1119/1.19020 . 

Siegel, Ethan. “The Failed Experiment That Changed The World.” Forbes, April 21, 2017. https://www.forbes.com/sites/startswithabang/2017/04/21/the-failed-experiment-that-changed-the-world/ . 

Stern, David. “Rømer and the Speed of Light,” October 17, 2016. https://pwg.gsfc.nasa.gov/stargaze/Sun4Adop1.htm . 

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

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Fastest Things in the Universe: Top 5 Cosmic Phenomena With Immensely High Speed

As we gaze at the night sky, imagining the universe as a calm and unhurried place is easy. In reality, however, the cosmos is home to things that move fast. Here are five of the fastest things and events humans have observed in the universe.

1. Cosmic Expansion (Faster than Light)

Scientists agree that the universe is expanding. However, the universe's expansion is not in a way that fills up 'empty space.' Instead, it is 'space' itself that is expanding.

The laws of physics suggest that two objects cannot move faster than the speed of light relative to each other. Still, there is no restriction on expanding the actual space they move in.

In principle, the furthest we can observe in the universe is known as the ' cosmological horizon ,' beyond which light cannot yet reach us during the universe's lifetime. Although we can never see it, the cosmos still exists beyond this limit, and the invisible parts of the universe recede from us at a rate more significant than the speed of light. Unfortunately, we can never see those parts of the universe, so we cannot be sure just exactly how fast they are receding.

2. Light ( 299,792.458 km/s )

Light, or the entire electromagnetic spectrum, is the fastest 'physical' thing in the universe. According to scientists, the speed of light is also the universe's self-imposed speed limit.

Nothing can move faster than the speed of light. This is because objects with mass need energy to accelerate them, and the laws of physics suggest that infinite energy is required to accelerate a mass up to light speed. What is even more confusing is that objects traveling faster than light would have to be traveling backward in time.

READ ALSO: Faster Than Speed of Light: Can Tachyon Really Travel Back in Time?

3. Gravitational Waves ( 299,792.458 km/s )

All particles without mass travel at the speed of light, as do the force fields like the weak and strong nuclear forces and the gravitational force. The same goes for gravitational waves, or the ripples in the fabric of space-time created by moving mass.

The first direct detection  of gravitational waves was announced in 2016. Since then, the study of these cosmic ripples has helped astronomers increase their understanding of the universe.

4. Cosmic Rays ( 299,792.4579999 km/s )

Cosmic rays hold the record for ordinary matter traveling at high speed. However, they are not rays but subatomic particles generated in the most powerful events in the universe, such as galaxy mergers and hypernovae , the explosive deaths of extremely big stars.

The fastest cosmic ray yet detected traveled so close to the speed of light that it had the same amount of energy as a medium-paced cricket ball, even though it was a fraction of the size of a single atom.

5. Blazer Jets ( 299,492.666 km/s )

The speed record for large chunks of matter, as opposed to subatomic particles, is held by the 'jets' observed in ' blazars .' A blazar  is a galaxy with an intensely bright central nucleus that contains a supermassive black hole, much like a quasar.

Black holes at the centers of these active galaxies emit vast amounts of energy, which is funneled into jets by a dense, highly magnetic  accretion disk. Jets observed so far move at about 99.99 % of the speed of light.

RELATED ARTICLE: What Is the Speed of Gravity? Do Gravitational Waves Travel Exactly at the Speed of Light?

Check out more news and information on Speed of Light  in Science Times.

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Storm chance Wednesday, cooling & clearing later

WEDNESDAY SHOWERS

A cold front is on the way, there will be a few showers ahead of this front this morning, but it won’t be a big impact and won’t amount to much. You’ll still want the rain gear with you at any point through the early afternoon, isolated showers and the potential for some thunder are things to watch. Ahead of this front, it will be cloudy and warmer with highs in the low 60s. We will dry things out before sunset this evening, and will even see some breaks of sunshine too!

COLDER MORNINGS

That same cold front will usher in colder temperatures overnight. We will wake up in the upper 20s to low 30s, brr! A freeze watch has been issued across parts of the south coast and south shore where the growing season has begun, but all of us will be feeling that chill early Thursday. Expect sunshine and mid 50s for Thursday, we are back to another colder night with temperatures in the low 30s early Friday.

WEEKEND IN VIEW

The chill won’t last long, a nice warm-up is on the way for the weekend. Highs will reach the 60s Saturday and Sunday with 70s heading into next week! Enjoy the warm weather, but keep an eye on our forecast as we track a chance for rain on Sunday.

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April 22, 2024

Making history: brightline west breaks ground on america’s first high-speed rail project connecting las vegas to southern california  , officials hammer the first spike commemorating the groundbreaking for brightline west.

LAS VEGAS (April 22, 2024)  – Today, Brightline West officially broke ground on the nation's first true high-speed rail system which will connect Las Vegas to Southern California. The 218-mile system will be constructed in the middle of the I-15 and is based on Brightline’s vision to connect city pairs that are too short to fly and too far to drive. Hailed as the greenest form of transportation in the world, Brightline West will run zero emission, fully electric trains capable of speeds of 200 miles per hour. Brightline West is a watershed project for high-speed rail in America and will establish the foundation for the creation of a new industry and supply chain. The project was recently awarded $3 billion in funding from President Biden’s Bipartisan Infrastructure Bill. The rest of the project will be privately funded and has received a total allocation of $3.5 billion in private activity bonds from USDOT.

The groundbreaking included remarks from U.S. Transportation Secretary Pete Buttigieg, Brightline Founder Wes Edens, Nevada Gov. Joe Lombardo, Sen. Catherine Cortez Masto, Sen. Jacky Rosen, Senior Advisor to President Biden Steve Benjamin and Vince Saavedra of the Southern Nevada Building Trades. In addition, Nevada Reps. Dina Titus, Susie Lee and Steve Horsford and California Reps. Pete Aguilar and Norma Torres made remarks and joined the celebration. More than 600 people, including union representatives, project supporters and other state and local officials from California and Nevada, attended the event.

“People have been dreaming of high-speed rail in America for decades – and now, with billions of dollars of support made possible by President Biden’s historic infrastructure law, it’s finally happening,” said Secretary Buttigieg. “Partnering with state leaders and Brightline West, we’re writing a new chapter in our country’s transportation story that includes thousands of union jobs, new connections to better economic opportunity, less congestion on the roads, and less pollution in the air.”

“This is a historic project and a proud moment where we break ground on America’s first high-speed rail system and lay the foundation for a new industry,” said Wes Edens, Brightline founder. “Today is long overdue, but the blueprint we’ve created with Brightline will allow us to repeat this model in other city pairs around the country.”

CONSTRUCTION OF BRIGHTLINE WEST

Brightline West's rail system will span 218 miles and reach speeds of 200 mph. The route, which has full environmental clearance, will run within the median of the I-15 highway with zero grade crossings. The system will have stops in Las Vegas, Nev., as well as Victor Valley, Hesperia and Rancho Cucamonga, Calif.

The privately led infrastructure project is one of the largest in the nation and will be constructed and operated by union labor. It will use 700,000 concrete rail ties, 2.2 million tons of ballast, and 63,000 tons of 100% American steel rail during construction. Upon completion, it will include 322 miles of overhead lines to power the trains and will include 3.4 million square feet of retaining walls. The project covers more than 160 structures including viaducts and bridges. Brightline West will be fully Buy America Compliant.

STATIONS AND FACILITIES

Brightline West will connect Southern California and Las Vegas in two hours or almost half the time as driving. The Las Vegas Station will be located near the iconic Las Vegas Strip, on a 110-acre property north of Blue Diamond Road between I-15 and Las Vegas Boulevard. The site provides convenient access to the Harry Reid International Airport, the Las Vegas Convention Center and the Raiders’ Allegiant Stadium. The station is approximately 80,000 square feet plus parking.

The Victor Valley Station in Apple Valley will be located on a 300-acre parcel southeast of Dale Evans Parkway and the I-15 interchange. The station is intended to offer a future connection to the High Desert Corridor and California High Speed Rail. The Victor Valley Station is approximately 20,000 square feet plus parking.

The Rancho Cucamonga Station will be located on a 5-acre property at the northwest corner of Milliken Avenue and Azusa Court near Ontario International Airport. The station will be co-located with existing multi-modal transportation options including California Metrolink, for seamless connectivity to Downtown Los Angeles and other locations in Los Angeles, Orange, San Bernardino and Riverside Counties. The Rancho Cucamonga Station is approximately 80,000 square feet plus parking.

The Hesperia Station will be located within the I-15 median at the I-15/Joshua Street interchange and will function primarily as a local rail service for residents in the High Desert on select southbound morning and northbound evening weekday trains.

The Vehicle Maintenance Facility (VMF) is a 200,000-square-foot building located on 238 acres in Sloan, Nev., and will be the base for daily maintenance and staging of trains. This site will also serve as one of two hubs for the maintenance of way operations and the operations control center. More than 100 permanent employees will report on a daily basis once operations begin and will serve as train crews, corridor maintenance crews, or operations control center teammates. A second maintenance of way facility will be located adjacent to the Apple Valley station.

The Las Vegas and Southern California travel market is one of the nation’s most attractive corridors with over 50 million trips between the region each year. Additionally, Las Vegas continues to attract visitors from around the world, with 4.7 million international travelers flying into the destination. The city dubs itself on being the world’s No. 1 meeting destination, welcoming nearly 6 million people to the Las Vegas Convention Center last year.

In California, approximately 17 million Southern California residents are within 25 miles of the Brightline West station sites. Studies show that one out of every three visits to Las Vegas come from Southern California.

ECONOMIC & ENVIRONMENTAL BENEFITS

Brightline West's $12 billion infrastructure investment will create over $10 billion in economic impact for Nevada and California and will generate more than 35,000 jobs, including 10,000 direct union construction roles and 1,000 permanent operations and maintenance positions. The investment also includes over $800 million in improvements to the I-15 corridor and involves agreements with several unions for skilled labor. The project supports Nevada and California's climate goals by offering a no-emission mobility option that reduces greenhouse gasses by over 400,000 tons of CO2 annually – reducing vehicle miles traveled by more than 700 million each year and the equivalent of 16,000 short-haul flights. The company will also construct three wildlife overpasses, in partnership with the California Department of Fish and Wildlife and Caltrans for the safe passage of native species, primarily the bighorn sheep.

BRIGHTLINE FLORIDA

Brightline’s first rail system in Florida connecting Miami to Orlando began initial service between its South Florida stations in 2018. In September 2023, Brightline’s Orlando station opened at Orlando International Airport, connecting South Florida to Central Florida. The company has plans to expand its system with future stops in Tampa, Florida’s Space Coast in Cocoa and the Treasure Coast in Stuart.

BRIGHTLINE WEST

ABOUT BRIGHTLINE WEST

Brightline is the only private provider of modern, eco-friendly, intercity passenger rail service in America – offering a guest-first experience designed to reinvent train travel and take cars off the road by connecting city pairs and congested corridors that are too short to fly and too long to drive. Brightline West will connect Las Vegas and Southern California with the first true high-speed passenger rail system in the nation. The 218-mile, all-electric rail service will include a flagship station in Las Vegas, with additional stations in Victor Valley and Rancho Cucamonga. At speeds up to 200 miles per hour, trains will take passengers from Las Vegas to Rancho Cucamonga in about two hours, twice as fast as the normal drive time.

Brightline is currently operating its first passenger rail system connecting Central and South Florida with stations in Miami, Aventura, Fort Lauderdale, Boca Raton, West Palm Beach, and Orlando, with future stations coming to Stuart and Cocoa. For more information, visit  www.brightlinewest.com  and follow on  LinkedIn ,  X ,  Instagram  and  Facebook .

QUOTE SHEET

“Through this visionary partnership, we are going to create thousands of jobs, bring critical transportation infrastructure to the West, and create an innovative, fast, and sustainable transportation solution. Nevada looks forward to partnering with Brightline on this historic project.”  - Governor Joe Lombardo, Nevada

“Today, not only are we breaking ground on a historic high-speed rail project here in Nevada, we are breaking ground on thousands of good paying American jobs, union jobs.”  - Steve Benjamin, Senior Advisor to the President and Director of the White House Office of Public Engagement

“For decades, Nevadans heard about the promise of high-speed rail in our state, and I’m proud to have led the charge to secure the funding to make it a reality. Today’s groundbreaking is the beginning of a new era for southern Nevada -- creating thousands of good-paying union jobs, bringing in billions of dollars of economic development, enhancing tourism to the state, reducing traffic, and creating a more efficient and cleaner way to travel. This is a monumental step, and I’m glad to have worked across the aisle to make this project come true.”  - Senator Jacky Rosen (D-NV)

“Having high-speed rail in Las Vegas will electrify our economy in Southern Nevada, and I’m thrilled to celebrate this milestone today. This project is on track to create tens of thousands of good-paying union jobs while cutting down traffic on I-15, and I’ll keep working with the Biden Administration to get this done as quickly as possible and continue delivering easier and cleaner transportation options for everyone in Nevada.”  - Senator Catherine Cortez Masto (D-NV)

“Today’s groundbreaking is a historic step in modernizing rail service in the United States. Californians driving between the Los Angeles region and Las Vegas often face heavy traffic, causing emissions that pollute the air in surrounding communities. The Brightline West Project will provide travelers with more options—helping Californians and visitors alike get to their final destination without facing gridlock on the road.”  - Senator Alex Padilla (D-Calif.)

"High-speed rail in the Southwest has been a dream as far back as the nineties when Governor Bob Miller appointed me to the California-Nevada Super Speed Train Commission. As a senior Member of the House Transportation & Infrastructure Committee, I am honored to have helped write the Bipartisan Infrastructure Law and secure $3 billion to turn that dream into a reality which will generate millions of dollars in tax revenue, reduce carbon emissions by easing traffic on Interstate 15, and create thousands of good-paying union jobs. I am proud to stand with advocates and transportation leaders as we break ground on the Brightline West project and look forward to welcoming high-speed passenger rail to Southern Nevada."  - Congresswoman Dina Titus (NV-1)

“For decades, high-speed rail was just a dream in southern Nevada – but now, I’m beyond proud that we finally made it a reality. I worked across the aisle to help negotiate, craft, and ultimately pass the Bipartisan Infrastructure Law because I knew it would kickstart transformative projects like Brightline West that will stand the test of time. Together, we’re cutting down on traffic, boosting our tourism economy, and creating thousands of good-paying union jobs.”  - Congresswoman Susie Lee (NV-3)

“I am proud to join Brightline West for the groundbreaking of this monumental project for Southern Nevada and the southwestern United States. By connecting Las Vegas to Southern California via high-speed rail, we will boost tourism, reduce congestion on the I-15 corridor, and create jobs. The impact on our local economy and the people of the Silver State will be tremendous. In my conversations with Secretary Buttigieg, Brightline West, and our Nevada labor leaders, I know that local workers and our Nevada small businesses will benefit from this transformational investment. This will be the nation's first true high-speed rail system, blazing a new path forward for our nation’s rail infrastructure, and we hope it will serve as a blueprint for fostering greater regional connections for many other cities across the country.  - Congressman Steven Horsford (NV-4)

“Brightline West’s groundbreaking today marks the construction of a dynamic high-speed rail system that will link Las Vegas, Hesperia, and Apple Valley to Rancho Cucamonga’s Metrolink Station, creating new jobs and fostering economic growth in California’s 23rd Congressional District. This convenient alternative to driving will reduce the number of cars on the road, decreasing emissions and reducing congestion in our High Desert communities. This is an exciting step and I look forward to the completion of this project.”  - Congressman Jay Obernolte (CA-23)

"Today's groundbreaking on the Brightline West high-speed rail project marks an incredible milestone in the Biden-Harris Administration's commitment to fulfilling the promise of high-speed rail and emissions-free transportation across the country. As a longtime supporter of this project, I helped pass the Bipartisan Infrastructure Law, which has already invested over $3 billion to support the completion of this project. By increasing transportation options, spurring job creation and new economic opportunities, and improving our environment through cutting over 400,000 tons of carbon pollution each year, this project will be transformative to my district and all of Southern California for generations—particularly in and around the last stop in Rancho Cucamonga. With the goal of being operational in time for Los Angeles to host the Summer Olympic Games in 2028, I look forward to Brightline West facilitating travel for the millions visiting our region and elevating our 21st-century connectivity on the global stage."  - Congresswoman Judy Chu (CA-28)

"As the Member of Congress that represents the City of Rancho Cucamonga and a member of the House Appropriations Subcommittee on Transportation, Housing, and Urban Development, it is my honor to participate in breaking ground on one of the most highly anticipated high-speed rail projects in the country. We gathered today thanks to the Biden Administration's leadership, which enacted the Bipartisan Infrastructure Law and the Inflation Reduction Act to fund vital projects like this and transform our economy. The Brightline project is a stellar illustration of the power of successful public-private partnerships. Thanks to all the labor unions, Tribes, and wildlife advocates for their hard work, which brought this project to life. The bright line is fully electric and has zero emissions, which is excellent for our environment. I am eagerly anticipating the completion of this project in my district and look forward to seeing everyone there."  - Congresswoman Norma J. Torres (CA-35)

Media Contact

Vanessa Alfonso [email protected]

Green Energy

• Electric train
• Los Angeles

The Las Vegas–LA electric high-speed rail line just broke ground

Brightline West, a future electric high-speed rail line between Las Vegas and Los Angeles, broke ground today in Nevada.

On December 6, 2023, Electrek reported that the Biden administration awarded Brightline West $3 billion in funding. The money was part of $6 billion previously earmarked for high-speed rail, and came from the Biden administration’s Bipartisan Infrastructure Law as part of its Federal-State Partnership Program. (The other $3 billion will go to the public high-speed Los Angeles to San Francisco rail project, which has more than 100 miles of a high-speed line under construction.)

Brightline West will be a privately owned, 218-mile, all-electric high-speed rail service that will include a flagship station in Las Vegas (pictured above), with additional stations in Apple Valley, Hesperia, and Rancho Cucamonga. At speeds of more than 186 miles per hour, trains will take passengers from Las Vegas to Rancho Cucamonga, which is 37 miles east of downtown Los Angeles, in just 2 hours and 10 minutes – twice as fast as the normal drive time. 

Florida-based Brightline Holdings is expected to model the Las Vegas-LA rail line on its high-speed route between Miami and Orlando – the US’s only privately owned and operated intercity passenger railroad.

Brightline West estimates it will remove 3 million cars from I-15 annually, reducing over 400,000 tons of carbon emissions annually. It also anticipates creating an astounding 35,000 union jobs. The federal funding will enable the project, which is aiming to open by 2028, to begin construction.

Rick Harnish, executive director of the national nonprofit High Speed Rail Alliance , said today:

This is a transformational investment in American trains. Getting a high-speed line in operation this decade will show Americans this terrific way to travel. If you have ever felt frustrated by traffic gridlock or airport hassles, a better future just got closer.

Top comment by Al

I'm very excited to see this project completed. I never go to Vegas personally, but I think the more Americans that are introduced to the beauty of high speed rail, the less resistance there will be for future projects.

And why do people profess that the money spent has simply disappeared? That money went to jobs in the area and across the nation, both directly and indirectly. I've read that the economic multiplier is about 1.8, I don't understand how you have an issue with that.

Read more: The US’s busiest rail corridor just got a $16.4B boost – why that’s huge

Photos: Brightline West

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Michelle Lewis is a writer and editor on Electrek and an editor on DroneDJ, 9to5Mac, and 9to5Google. She lives in White River Junction, Vermont. She has previously worked for Fast Company, the Guardian, News Deeply, Time, and others. Message Michelle on Twitter or at [email protected]. Check out her personal blog.

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