travelling faster than light time travel

Is Time Travel Possible?

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

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

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

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

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

How do we know that time travel is possible?

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

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

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

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

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

Credit: NASA/JPL-Caltech

Can we use time travel in everyday life?

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

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

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

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

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

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

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

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

In Summary:

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

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This Trick Flips Space and Time

By Meddling With Spacetime Dimensions, We Could Finally Reach Warp Speed

New research shows that the “superluminal observer” needs three separate time dimensions for a warp-speed math trick that would please even Galileo.

✅ Quick Facts:

• In new research, the lead scientist explains why just one space and one time aren’t enough for this scenario.
• Symmetry is a physics concept that goes all the way back to Galileo’s time.

The secret to faster-than-light physics could be to double down on the number of dimensions. Specifically, the solution may lie in three dimensions of time , with just one representing space. The math is deep and complicated, but the ideas may be within our grasp after all. And there’s one math trick at superspeeds that may just “flip” your lid.

The key idea at play is that of a “superluminal observer,” according to research published in December 2022 in the journal Classical and Quantum Gravity. “Superluminal” means faster than light, from super - meaning “more” or “most,” and - luminal like, well, Lumière from Beauty and the Beast, and the lumens that power your home movie projector. The superluminal observer is a hypothetical thing that is looking at the universe while traveling faster than light. It’s you in your Star Trek warp-speed shuttle.

Superluminal observers are cool because, in a way, they marry together two very different sides of physics: general relativity and quantum mechanics . General relativity is the work embodied by Albert Einstein, which governs how spacetime functions as bodies move around the universe at subluminal, or slower than light, speeds. Quantum mechanics explains how subatomic particles behave, or don’t behave, in very strange ways on the smallest of scales.

The research team—led by theoretical physicist Andrzej Dragan of the University of Warsaw and the National University of Singapore—has theorized that many parts of quantum physics, like indeterminism and superposition , can be explained if you take general relativity and apply its principles to the superluminal observer. In other words, how messy does spacetime get if we take our shuttle up to warp speed? Is everything suddenly in multiple places at once?

Dragan’s new work indicates that it’s at least a possibility. Perhaps more interestingly, the way general relativity becomes quantum phenomena at speeds greater than light doesn’t seem to introduce any causal paradoxes. In earlier work , published in the New Journal of Physics in March 2020, Dragan and his coauthor studied “just” one space dimension and one time dimension, known as 1+1. In the new paper, the researchers upped the ante to include one space dimension and three time dimensions, or 1+3.

When Time and Space Flip Math

Why do we need three time dimensions? To understand, we have to talk about some math. “[D]espite our common perception, time and space are strikingly similar according to relativity, and mathematically the only difference between them is the minus sign somewhere in the equations,” Dragan explains to Popular Mechanics in an email. That’s a small difference in complicated math, but think of the algebra example of the difference of two squares: x² - 16, for example, is the result of (x - 4)(x + 4). With one flipped sign, the middle term in the polynomial falls away.

But when the observer is going faster than the speed of light, the difference in signs also changes. That’s because time and space must flip in the math. “The time of the superluminal observer becomes space of the subluminal one, and their space becomes time,” Dragan says. In other words, the regular, non-light-speed observer’s space and time turn into the time and space, relatively, of the faster-than-light observer. “So their corresponding signs have to interchange.”

In a 1+1 scenario, that means the two dimensions are the same, making it redundant. If 50 = 50, does it matter which 50 is which? (In logic, we call this a tautology.) That means that if we want to truly study space and time as different things, we have to add a second “set” of two dimensions: space and time 1, together, represent space; while time 2 and time 3, together, represent time . It’s not quite the difference of two squares, but we have two balanced sets of dimensions.

The Symmetry in Physics

There’s another interesting aspect to this research, because Dragan’s team wants to show that even at superluminal speeds, physics shows symmetry.

“The idea of symmetry in physics can be traced back to Galileo,” Dragan says. “He noticed that no matter what velocity we move at, as long as that velocity is constant, our physics remains the same. A parrot flying in a moving ship experiences the same dynamical laws as at ‘rest’ on Earth.”

✅ Galileo Galilei was an influential Italian scientist who lived during the 16th and 17th centuries. As an elderly man, he received a life sentence for going public with his belief that Earth orbited the sun!

But our conceptions of physics are limited by the long-running (and reasonable!) belief that nothing can travel faster than light, Dragan explains. That means the superluminal observer, by definition, exists as a kind of exception into which we must work to extend the idea of symmetry. Does it make sense that a superluminal observer would still be subject to symmetry? Is the parrot traveling faster than light still the same as the parrot in the ship or on Earth?

“We argued that this additional limiting assumption isn’t necessary,” Dragan says. He believes symmetry may extend into faster-than-light speeds, and our parrot friend would be just as affected by the same laws of physics while traveling in the warp-speed shuttle.

Toward a Grand Unified Theory

So, this paper isn’t about traveling at warp speed, but instead an analysis of physics to show how we can bring two very different physics branches together. Why is that, itself, so important?

“The idea of more than one time dimension has been considered by others over the years, so that particular premise is not novel,” Harold “Sonny” White, a onetime NASA physicist and the founder of the Limitless Space Institute (LSI), a group that funds and promotes far-out space travel and physics research, tells Popular Mechanics . “But the mathematical framework developed by the authors in this published paper is unique. It would seem the authors’ perceived benefit from the effort is that it establishes a mathematical basis for why we need a field theoretical framework.”

What is a field theoretical framework? It’s the big picture of physics that can bring everything together. “[I]f we envision the standard models of physics as a Venn diagram, there would be two circles side-by-side that touch at a single tangent point,” White explains. “The idea of a grand unified field theory might be envisioned as a larger circle that encircles both the smaller circles.”

By showing their work, these researchers have pointed out a really specific way in which one big basket of physics—rather than two baskets that we aren’t sure how to carry at the same time—would make more sense in practical and mathematical terms.

Okay, sure, you may be thinking: all this superluminal jabberwocky is interesting. But warp speed itself is science fiction, right? (At least for now: White’s LSI funds education that may eventually lead us elsewhere.) The superluminal observer is just a thought exercise ... right?

Dragan isn’t so sure. “The last remaining question is whether superluminal objects are only a mathematical possibility, or they actually exist in reality,” he concludes. “We believe the latter to be that case, and that is the purpose of our further research.”

That means our warp-speed shuttle, once the most far-out thing science fiction writers could even imagine, could embody an elegant theory that brings together two very different kinds of physics. Indeed, objects in the superluminal mirror may be closer than they appear.

Caroline Delbert is a writer, avid reader, and contributing editor at Pop Mech. She's also an enthusiast of just about everything. Her favorite topics include nuclear energy, cosmology, math of everyday things, and the philosophy of it all. 

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Warp drives: Physicists investigate faster-than-light space travel

The closest star to Earth is Proxima Centauri. It is about 4.25 light-years away, or about 25 trillion miles (40 trillion kilometers). The fastest ever spacecraft, the now- in-space Parker Solar Probe will reach a top speed of 450,000 mph. It would take just 20 seconds to go from Los Angeles to New York City at that speed, but it would take the solar probe about 6,633 years to reach Earth’s nearest neighboring solar system.

If humanity ever wants to travel easily between stars, people will need to go faster than light. But so far, faster-than-light travel is possible only in science fiction.

In Issac Asimov’s Foundation series , humanity can travel from planet to planet, star to star or across the universe using jump drives. As a kid, I read as many of those stories as I could get my hands on. I am now a theoretical physicist and study nanotechnology, but I am still fascinated by the ways humanity could one day travel in space.

Some characters – like the astronauts in the movies “Interstellar” and “Thor” – use wormholes to travel between solar systems in seconds. Another approach – familiar to “Star Trek” fans – is warp drive technology. Warp drives are theoretically possible if still far-fetched technology. Two recent papers made headlines in March when researchers claimed to have overcome one of the many challenges that stand between the theory of warp drives and reality.

But how do these theoretical warp drives really work? And will humans be making the jump to warp speed anytime soon?

Compression and expansion

Physicists’ current understanding of spacetime comes from Albert Einstein’s theory of general relativity . General relativity states that space and time are fused and that nothing can travel faster than the speed of light. General relativity also describes how mass and energy warp spacetime – hefty objects like stars and black holes curve spacetime around them. This curvature is what you feel as gravity and why many spacefaring heroes worry about “getting stuck in” or “falling into” a gravity well. Early science fiction writers John Campbell and Asimov saw this warping as a way to skirt the speed limit.

What if a starship could compress space in front of it while expanding spacetime behind it? “Star Trek” took this idea and named it the warp drive.

In 1994, Miguel Alcubierre, a Mexican theoretical physicist, showed that compressing spacetime in front of the spaceship while expanding it behind was mathematically possible within the laws of General Relativity . So, what does that mean? Imagine the distance between two points is 33 feet (10 meters). If you are standing at point A and can travel one meter per second, it would take 10 seconds to get to point B. However, let’s say you could somehow compress the space between you and point B so that the interval is now just one meter. Then, moving through spacetime at your maximum speed of one meter per second, you would be able to reach point B in about one second. In theory, this approach does not contradict the laws of relativity since you are not moving faster than light in the space around you. Alcubierre showed that the warp drive from “Star Trek” was in fact theoretically possible.

Proxima Centauri here we come, right? Unfortunately, Alcubierre’s method of compressing spacetime had one problem: it requires negative energy or negative mass.

A negative energy problem

Alcubierre’s warp drive would work by creating a bubble of flat spacetime around the spaceship and curving spacetime around that bubble to reduce distances. The warp drive would require either negative mass – a theorized type of matter – or a ring of negative energy density to work. Physicists have never observed negative mass, so that leaves negative energy as the only option.

To create negative energy, a warp drive would use a huge amount of mass to create an imbalance between particles and antiparticles. For example, if an electron and an antielectron appear near the warp drive, one of the particles would get trapped by the mass and this results in an imbalance. This imbalance results in negative energy density. Alcubierre’s warp drive would use this negative energy to create the spacetime bubble.

But for a warp drive to generate enough negative energy, you would need a lot of matter. Alcubierre estimated that a warp drive with a 100-meter bubble would require the mass of the entire visible universe .

In 1999, physicist Chris Van Den Broeck showed that expanding the volume inside the bubble but keeping the surface area constant would reduce the energy requirements significantly , to just about the mass of the Sun. A significant improvement, but still far beyond all practical possibilities.

A sci-fi future?

Two recent papers – one by Alexey Bobrick and Gianni Martire and another by Erik Lentz – provide solutions that seem to bring warp drives closer to reality.

Bobrick and Martire realized that by modifying spacetime within the bubble in a certain way, they could remove the need to use negative energy. This solution, though, does not produce a warp drive that can go faster than light.

Independently, Lentz also proposed a solution that does not require negative energy. He used a different geometric approach to solve the equations of general relativity, and by doing so, he found that a warp drive wouldn’t need to use negative energy. Lentz’s solution would allow the bubble to travel faster than the speed of light.

It is essential to point out that these exciting developments are mathematical models. As a physicist, I won’t fully trust models until we have experimental proof. Yet, the science of warp drives is coming into view. As a science fiction fan, I welcome all this innovative thinking. In the words of Captain Picard , things are only impossible until they are not.

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Faster-Than-Light Discovery Raises Prospect of Time Travel

If a report of particles traveling faster than the speed of light turns out to be true, it will rock the foundations of modern physics — and perhaps even change the way scientists think about time travel.

But don't fire up the DeLorean just yet. Physicists are skeptical that the tiny subatomic particles , called neutrinos, really are breaking the cosmic rule that nothing goes faster than light. And even if they are, neutrinos don't make the best vessel for sending signals to the past because they pass through ordinary matter almost unaffected, interacting only weakly with the wider world. [ Countdown of Bizarre Subatomic Particles ]

So you may be able to send neutrinos back in time, but would anyone notice? "If you're trying to get people's attention by bouncing neutrinos off their head, you could wait for quite awhile," Seth Lloyd, a physicist at the Massachusetts Institute of Technology, told LiveScience.

That hasn't stopped physicists from imagining the possibilities in a world where faster-than-light travel is possible. If the neutrino experiment is confirmed, it opens the door to at least sending messages through time using those neutrinos, physicists say. You might even be able to send messages to "past you" with neutrinos, one physicist suggests. Experiencing time backwards, once thought impossible, might be outside the realm of sci-fi, another imagines. Of course, this is all predicated on the finding being true — and it raises thorny questions of how the universe would work if people were able to go back in time and, say, erase their own existence.

Physics shocker

The news that European researchers had detected neutrinos traveling faster than light broke yesterday (Sept. 22), triggering both typical scientific skepticism and pure amazement in the physics world. In an experiment that zaps neutrinos from CERN in Geneva to the INFN Gran Sass Laboratory in Italy, scientists clocked the particles outrunning light by 60 nanoseconds over 453.6 miles (730 kilometers) — a neck-and-neck race to be sure. [ Infographic: See How Neutrino Experiment Works ]

According to Einstein's Theory of Special Relativity, neutrinos shouldn't even be able to match light speed, much less break it. Neutrinos have (very small) mass, and as Einstein posited in his famous E=mc squared equation, mass is equal to energy. As something speeds up, its energy increases, too. Because energy is equivalent to mass, its mass increases. Now you've got a heavier object, so you've got to add even more energy to get it going faster. Before you know it, you need "completely unreasonable" amounts of energy to keep inching your object toward light speed, said Harvard University physicist Gary Feldman.

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"You keep accelerating but you just incrementally approach [light speed], so you have to add more and more energy to go faster and faster, but it becomes less and less effective," Feldman told LiveScience. 

Some particles have been shown to exceed the speed of light when traveling in a medium rather than a vacuum, but neutrinos pass through the Earth as if it were a vacuum, so they shouldn't ever be able to zip past light speed . The buzz in the physics community is that they probably haven’t.

"Even though the experimenters have done a very careful job and it's a very impressive paper … it was a very complicated analysis and there's always a possibility that there's just an error in what they did," Feldman said.

One possible error could be in the calculations the scientists used to correct for the effect of the atmosphere in their experiment, Lloyd said. Light actually gets a bit bogged down when it isn't in a vacuum, while neutrinos zip through the atmosphere without any effect. It's possible that the CERN researchers miscalculated in correcting for the atmospheric effect and that neutrinos aren't actually going faster, but the light is just going a smidge slower than they realize.

If it's true ...

But if the results do hold, "it's major, it's humongous, it's the biggest thing in 100 years," said Michio Kaku, a theoretical physicist at the City University of New York.

"You're talking about a tidal wave hitting physics if it's true," Kaku told LiveScience. "There are two rocks upon which modern physics is based. One is quantum theory and one is relativity. If one of the pillars falls, we're in deep trouble."

What does that mean for time travel ? In theory, it might be more possible than scientists had thought. Einstein pointed out that time is relative: As you approach light speed, your experience of time is not the same as it is for the folks chugging along at their usual speed. What feels like a second to you will feel like much longer to them. This idea, called "time dilation," spawned such sci-fi classics as 1968's "Planet of the Apes," in which what feels like 18 months to Charleton Heston and his crew is enough time for gorillas, chimps and orangutans to evolve language and complex societies back on Earth. [ Top 10 Scary Sci-Fi Series ]

There are a lot of barriers to approaching light speed, much less breaking it, but if you could, you could theoretically experience time running backward, Kaku said. Here's how it would work: As you approach light speed, you might time goes slower in the outside world than it does for you. When you hit light speed, the outside world goes so slow in relation to you that it stops (again, in relation to you; people in the outside world feel as if time is the same as always). So if you could push past that speed limit, the outside world would be so slow as to be moving backward in relation to you.

So far, this seems pretty much impossible, not least because some other side effects of faster-than-light travel should include reducing your weight and width to less than nothing, Kaku said. [Watch: Can You Time Travel? ]

If the neutrinos are actually going faster than light, though, it might be possible to use them to communicate with the past, Lloyd said. You could send off a faster-than-light message to someone moving at a rapid velocity with respect to you. They could then bounce the faster-than-light message back, and it would arrive before the signal you sent to them.

One way to think of this is like a mirror, Lloyd said. You send a message to the mirror, and it reflects it back, but so quickly that "past you" is the one who receives it.

Stuck in time

But all of this is moot if it's only neutrinos that can be coaxed past the speed of light, Lloyd said. Because they don't interact with much, your messages would likely go unnoticed by past generations. An April 13, 1865, warning to Abraham Lincoln not to go into Ford's Theater the next day would pass through the president like a ghost. [Read: 'Time Traveler' Spotted? ]

Doing away with Einstein's theory would also complicate causality, the idea that things influence each other in chronological order. When you allow the past, present and future to interact, "that gets all messed up," Lloyd said, and you start to get paradoxes . A classic is the Grandfather Paradox : What if you went back in time and shot your grandfather, preventing your own birth and thus preventing yourself from ever shooting your grandfather?

It's a headache, to say the least. And not all researchers are convinced that the finding, even if true, would ultimately overturn the well-tested, century-old Special Theory of Relativity that keeps things from getting so messy.

"This effect is very small, it's two parts in 100,000," Feldman said. "If this is true, what it means is that there is some aspect of the Special Theory of Relativity that's been overlooked or not understood well, but I can't imagine that it really overtakes the Special Theory of Relativity."

You can follow LiveScience   senior writer Stephanie Pappas on Twitter @sipappas . Follow LiveScience for the latest in science news and discoveries on Twitter @livescience   and on Facebook .

Stephanie Pappas is a contributing writer for Live Science, covering topics ranging from geoscience to archaeology to the human brain and behavior. She was previously a senior writer for Live Science but is now a freelancer based in Denver, Colorado, and regularly contributes to Scientific American and The Monitor, the monthly magazine of the American Psychological Association. Stephanie received a bachelor's degree in psychology from the University of South Carolina and a graduate certificate in science communication from the University of California, Santa Cruz. 

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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 22, 2011

Particles Found to Travel Faster Than Speed of Light

Neutrino results challenge a cornerstone of Albert Einstein's special theory of relativity, which itself forms the foundation of modern physics

By Geoff Brumfiel & Nature magazine

An Italian experiment has unveiled evidence that fundamental particles known as neutrinos can travel faster than light. Other researchers are cautious about the result, but if it stands further scrutiny, the finding would overturn the most fundamental rule of modern physics—that nothing travels faster than 299,792,458 meters per second.

The experiment is called OPERA (Oscillation Project with Emulsion-tRacking Apparatus), and lies 1,400 meters underground in the Gran Sasso National Laboratory in Italy. It is designed to study a beam of neutrinos coming from CERN, Europe's premier high-energy physics laboratory located 730 kilometers away near Geneva, Switzerland. Neutrinos are fundamental particles that are electrically neutral, rarely interact with other matter, and have a vanishingly small mass. But they are all around us—the sun produces so many neutrinos as a by-product of nuclear reactions that many billions pass through your eye every second. [ Click here to read more about CERN's Large Hadron Collider ]

The 1,800-tonne OPERA detector is a complex array of electronics and photographic emulsion plates, but the new result is simple—the neutrinos are arriving 60 nanoseconds faster than the speed of light allows. "We are shocked," says Antonio Ereditato, a physicist at the University of Bern in Switzerland and OPERA's spokesman.

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Breaking the law

The idea that nothing can travel faster than light in a vacuum is the cornerstone of Albert Einstein's special theory of relativity, which itself forms the foundation of modern physics. If neutrinos are traveling faster than light speed , then one of the most fundamental assumptions of science—that the rules of physics are the same for all observers—would be invalidated. "If it's true, then it's truly extraordinary," says John Ellis, a theoretical physicist at CERN.

Ereditato says that he is confident enough in the new result to make it public. The researchers claim to have measured the 730-kilometer trip between CERN and its detector to within 20 centimeters. They can measure the time of the trip to within 10 nanoseconds, and they have seen the effect in more than 16,000 events measured over the past two years. Given all this, they believe the result has a significance of six-sigma—the physicists' way of saying it is certainly correct. The group will present their results September 23 at CERN, and a preprint of their results will be posted on the physics website ArXiv.org .

At least one other experiment has seen a similar effect before, albeit with a much lower confidence level. In 2007, the Main Injector Neutrino Oscillation Search (MINOS) experiment in Minnesota saw neutrinos from the particle-physics facility Fermilab in Illinois arriving slightly ahead of schedule. At the time, the MINOS team downplayed the result, in part because there was too much uncertainty in the detector's exact position to be sure of its significance, says Jenny Thomas, a spokeswoman for the experiment. Thomas says that MINOS was already planning more accurate follow-up experiments before the latest OPERA result. "I'm hoping that we could get that going and make a measurement in a year or two," she says.

Reasonable doubt

If MINOS were to confirm OPERA's find, the consequences would be enormous. "If you give up the speed of light, then the construction of special relativity falls down," says Antonino Zichichi, a theoretical physicist and emeritus professor at the University of Bologna, Italy. Zichichi speculates that the "superluminal" neutrinos detected by OPERA could be slipping through extra dimensions in space, as predicted by theories such as string theory.

Ellis, however, remains skeptical. Many experiments have looked for particles traveling faster than light speed in the past and have come up empty-handed, he says. Most troubling for OPERA is a separate analysis of a pulse of neutrinos from a nearby supernova known as 1987a. If the speeds seen by OPERA were achievable by all neutrinos, then the pulse from the supernova would have shown up years earlier than the exploding star's flash of light; instead, they arrived within hours of each other. "It's difficult to reconcile with what OPERA is seeing," Ellis says.

Ereditato says that he welcomes skepticism from outsiders, but adds that the researchers have been unable to find any other explanation for their remarkable result. "Whenever you are in these conditions, then you have to go to the community," he says.

This article is reproduced with permission from the magazine Nature . The article was first published on September 22, 2011.

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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Breaking the speed limit: is faster-than-light travel possible.

Traveling faster than light – or as scientists call it, FTL – has long been a staple of science fiction; but according to Einstein’s theory of relativity, it’s an impossible task. However, new research proposes several methods through which FTL travel might be possible . While these ideas are exciting, there are significant hurdles to overcome. Let’s delve deeper into this fascinating concept and explore the challenges that lie ahead in making FTL travel a reality!

What is Faster-Than-Light Travel?

Imagine stretching a rubber sheet flat. That sheet represents the fabric of spacetime, according to Einstein’s theory of relativity. Everything in the universe, from tiny particles to massive stars, are like marbles sitting on this sheet, some much larger than others. Each marble causes the sheet of spacetime to curve and bend (Skruse, 2). Most propositions for FTL travel propose a way to manipulate this spacetime fabric itself, creating a kind of warp or shortcut that would allow a spacecraft to travel faster than the speed of light, which is currently considered the cosmic speed limit. In essence, FTL wouldn’t be about the spacecraft pushing itself to faster speeds than light, which is considered impossible, but rather about warping spacetime around it to create a faster path or a shortcut.

The Warp Drive Theory

So how could one actually do this? One theory involves folding and unfolding the rubber sheet in a specific way. (Figure 1) The marble on the sheet, representing a spaceship, wouldn’t move very quickly on its own, but by riding the folds and unfolds of the sheet, (Baron, 1) it could travel vast distances very quickly. However, at the moment, we have no method to actually bend spacetime, so this idea still remains a theory.

This concept is a simplified version of “warp drive” but there also exist other contenders for FTL travel. Other theories explore ideas like utilizing negative energy or manipulating phenomena like wormholes, which are shortcuts through spacetime that could connect distant points in the universe. (Lewis, 3)

Visualization of Warp Drive

Source: Omspace Rocket and Exploration

Negative Energy: Fuel for FTL Dreams or Nightmares?

Another intriguing idea involves negative energy, a hypothetical form of energy with properties opposite to our regular understanding. This is a scenario where energy isn’t just used up, but can somehow be formed – that’s the basic principle behind negative energy.

Theorists propose that negative energy could be used to create a repulsive force, counteracting the attractive nature of gravity. This, in turn, could potentially be harnessed to manipulate spacetime and create a warp bubble (Landis, 2) for FTL travel. However, there are significant challenges associated with negative energy. First and foremost, negative energy remains purely theoretical. No experiment or observation has ever confirmed its existence. Although we can theorize about its properties, there’s no concrete evidence to work with. Also, even if we could somehow generate negative energy, theories suggest it might be incredibly unstable. Negative energy might have a natural tendency to cancel out positive energy, making it difficult to control and potentially leading to catastrophic consequences if let out of control.

Despite these challenges, the allure of negative energy as a key to FTL travel persists. Scientists continue to explore theoretical models and search for any hints of its existence in the universe. For now, though, it remains a fascinating but highly speculative concept.

Wormholes: Cosmic Tunnels or Celestial Traps?

While manipulating spacetime with exotic energy sources is mind-bending, another theoretical pathway to FTL travel involves cosmic shortcuts known as wormholes. Going back to the metaphor of the universe as a vast sheet of fabric, a wormhole would be represented as a hidden tunnel piercing through it. These hypothetical tunnels wouldn’t require immense energy manipulation, but rather make use of the natural curvature of spacetime to connect two distant points. (Figure 2) Through wormholes, galaxies millions of light-years away could be within reach. However, there are several significant hurdles to consider.

First of all, theorists suggest wormholes might be inherently unstable. Like a tunnel made of wet sand, it would likely collapse on itself before anything could travel through. Similarly, a naturally occurring wormhole might be too short-lived or constantly fluctuating in size, making it incredibly dangerous to navigate. (Bambi, 5) Secondly, even if a stable wormhole existed, some theories suggest it might require a form of exotic matter with negative energy properties to keep it from collapsing. As discussed earlier, negative energy is purely hypothetical and incredibly difficult to control, making the creation or stabilization of a wormhole highly improbable with our current understanding of physics. And finally, other theories propose that wormholes might only be traversable in one direction. (Stojkovic, 1) Imagine a cosmic drain, allowing travel into another region of space but not back out. This one-way trip scenario would be a major drawback for interstellar exploration.

Despite these challenges, the possibility of wormholes continues to intrigue scientists and science fiction writers alike. Future discoveries about the nature of gravity and exotic forms of matter might shed light on the existence and stability of wormholes. For now, they remain a fascinating but still theoretical concept on the roadmap to FTL travel.

Bending Spacetime to Form a Wormhole

Source: Physics Stack Exchange

Chasing the Stars: Can We Ever Achieve FTL?

FTL travel, once relegated to the realm of science fiction, is now a concept being seriously explored by physicists. While immense challenges lie ahead, the potential rewards are equally immense. Traveling beyond the constraints of light speed would open up the vast expanse of the cosmos, allowing us to explore distant galaxies, potentially encounter new forms of life, and revolutionize our understanding of the universe.

The road to FTL travel will undoubtedly be long and arduous. It will require breakthroughs in our understanding of physics, the development of new technologies, and perhaps even the discovery of entirely new physical phenomena. However, the human spirit of exploration thrives on challenges. By continuing to push the boundaries of knowledge and explore these fascinating concepts, we inch closer to the day when humanity can truly touch the stars. The journey itself, filled with discovery and innovation, may be just as rewarding as the ultimate destination.

References and Sources

Skuse, Benjamin. (2021, March 24). Spacecraft in a “warp bubble” could travel faster than light, claims physicist. Physics World. 

Finazzi, S., Liberati, S., & Barceló, C. (2009, July 14). Semiclassical instability of dynamical warp drives. arXiv.org.

McMonigal, B., Lewis, G. F., & O’Byrne, P. (2012, February 26). The Alcubierre Warp Drive: On the matter of matter. arXiv.org.

Alcubierre, M. (2000, September 5). The Warp Drive: Hyper-fast travel within general relativity. arXiv.org.

Landis, Geoffrey. (2012, November 12). Negative Mass in Contemporary Physics, and its Application to Propulsion. National Aeronautics and Space Administration.

Bambi, Cosimo. (2021, May 8). Astrophysical Wormholes. arXiv.org.

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What If You Traveled Faster Than the Speed of Light?

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When we were kids, we were amazed that Superman could travel "faster than a speeding bullet." We could even picture him, chasing down a projectile fired from a weapon, his right arm outstretched, his cape rippling behind him. If he traveled at half the bullet 's speed, the rate at which the bullet moved away from him would halve. If he did indeed travel faster than the bullet, he would overtake it and lead the way. Go, Superman!

In other words, Superman's aerial antics obeyed Newton's views of space and time : that the positions and motions of objects in space should all be measurable relative to an absolute, nonmoving frame of reference [source: Rynasiewicz ].

In the early 1900s, scientists held firm to the Newtonian view of the world. Then a German-born mathematician and physicist by the name of Albert Einstein came along and changed everything. In 1905, Einstein published his theory of special relativity , which put forth a startling idea: There is no preferred frame of reference. Everything, even time, is relative.

Two important principles underpinned his theory. The first stated that the same laws of physics apply equally in all constantly moving frames of reference. The second said that the speed of light — about 186,000 miles per second (300,000 kilometers per second) — is constant and independent of the observer's motion or the source of light. According to Einstein, if Superman were to chase a light beam at half the speed of light, the beam would continue to move away from him at exactly the same speed [source: Stein , AMNH.org ].

These concepts seem deceptively simple, but they have some mind-bending implications. One of the biggest is represented by Einstein's famous equation, E = mc², where E is energy, m is mass and c is the speed of light.

According to this equation, mass and energy are the same physical entity and can be changed into each other. Because of this equivalence, the energy an object has due to its motion will increase its mass. In other words, the faster an object moves, the greater its mass. This only becomes noticeable when an object moves really quickly. If it moves at 10 percent the speed of light, for example, its mass will only be 0.5 percent more than normal. But if it moves at 90 percent the speed of light, its mass will double [source: LBL.gov ].

As an object approaches the speed of light, its mass rises precipitously. If an object tries to travel 186,000 miles per second, its mass becomes infinite, and so does the energy required to move it. For this reason, no normal object can travel as fast or faster than the speed of light.

That answers our question, but let's have a little fun and modify the question slightly.

Almost As Fast As the Speed of Light?

We covered the original question, but what if we tweaked it to say, "What if you traveled almost as fast as the speed of light?" In that case, you would experience some interesting effects. One famous result is something physicists call time dilation , which describes how time runs more slowly for objects moving very rapidly. If you flew on a rocket traveling 90 percent of light-speed, the passage of time for you would be halved. Your watch would advance only 10 minutes, while more than 20 minutes would pass for an Earthbound observer [source: May ]

You would also experience some strange visual consequences. One such consequence is called aberration , and it refers to how your entire field of view would shrink down to a tiny, tunnel-shaped "window" out in front of your spacecraft. This happens because photons (those exceedingly tiny packets of light) — even photons behind you — appear to come in from the forward direction.

In addition, you would notice an extreme Doppler effect , which would cause light waves from stars in front of you to crowd together, making the objects appear blue. Light waves from stars behind you would spread apart and appear red. The faster you go, the more extreme this phenomenon becomes until all visible light from stars in front of the spacecraft and stars to the rear become completely shifted out of the known visible spectrum (the colors humans can see). When these stars move out of your perceptible wavelength, they simply appear to fade to black or vanish against the background.

Of course, if you want to travel faster than a speeding photon, you'll need more than the same rocket technology we've been using for decades.

In a March 2021 paper published in the journal Classical and Quantum Gravity , astrophysicist Erik Lentz of the University of Göttingen in Germany proposed the idea of rearranging space-time to create a warp bubble, inside which a spacecraft might be able to travel at faster-than-light speeds.

Speed of Light FAQ

Is there anything faster than the speed of light, how fast is the speed of light in miles, why is "c" the speed of light, what is the speed of light on earth, lots more information, related articles.

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• Rynasiewicz, Robert, "Newton's Views on Space, Time, and Motion."Stanford Encyclopedia of Philosophy. Summer 2014. (Feb. 16, 2022) https://plato.stanford.edu/cgi-bin/encyclopedia/archinfo.cgi?entry=newton-stm
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• Van Zyl, Miezam (project editor)."Universe: The Definitive Visual Guide." Dorling Kindersley Limited. 2020. (Feb. 16, 2022) https://bit.ly/33q5Mpm.

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