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Can information travel faster than light?

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One of the tenets of Einstein's Theory of Special Relativity is that nothing can travel faster than the speed of light in a vacuum. Light speed is considered the universal speed limit of everything, and this is widely accepted by the scientific community. But in science, if you make a hard-and-fast rule, someone will try to disprove it, or at least find a loophole. And the speed of light is no exception.

Light, in a vacuum, travels at approximately 299,792 kilometers per second (186,282 miles per second). In September 2011, physicists working on the Oscillation Project with Emulsion-tRacking Apparatus (OPERA) created a frenzy in the scientific community when they announced that their experiments resulted in subatomic particles called neutrinos traveling from the European Organization for Nuclear Research (CERN) near Geneva, Switzerland to the Gran Sasso National Laboratory near L'Aquila, Italy and arriving around 60 nanoseconds earlier than a beam of light. Ideas as to either how these neutrinos could have actually broken the speed of light, or as to what errors could have caused the impossible results, abounded. Finally, equipment issues, including a loose cable, were discovered as likely culprits, and the results were declared erroneous. So no rewriting of Einstein's theories turned out to be necessary.

Other researchers are trying to bend the rules rather than break them. In fact, bending space-time is one theory of how superluminal – faster-than-light -- speeds in space travel might be reached. The idea is that space time could be contracted in front of a spaceship and expanded behind it, while the ship would remain stationary in a warp bubble that itself was moving faster than the speed of light. This concept was originally modeled by Mexican theoretical physicist Miguel Alcubierre in 1994 as a theoretical possibility, but one that would require a universe-sized amount of negative energy to power the phenomenon. It was later refined to requiring a planet-sized amount and then again to needing an amount around the size of the Voyager 1 space probe. Unfortunately, the negative energy would have to come from exotic matter that is difficult to come by, and we're currently only at the level of miniature lab experiments on warp drives. The math behind these theories is based on the laws of relativity, so theoretically it wouldn't be breaking the rules. The technology, if it ever exists, could also be used for going slower than light, but much faster than we can go now, which might be more practical.

Space travel is just one of the possible applications of reaching or exceeding the speed of light. Some scientists are working on doing the same for the purposes of much faster data transfer. Read on to find out about current data speeds and the potential for faster-than-light information.

Can data even travel at the speed of light?

The possibility of superluminal data transfer.

Currently, most of our data travels through either copper wire or fiber optic cable. Even when we send data via our cell phones over radio waves, which also travel at light speed, it ends up traversing the wired networks of the Internet at some point. The two most common types of copper wire for long-distance information transfer are twisted pair (used first for telephony, and later for dial-up Internet and DSL ), and coaxial cable (used for cable TV initially, then Internet and phone). Coaxial cable is the faster of the two. But still faster is fiber optic cable. Rather than using copper to conduct data in the form of electrical signals, fiber optic cable moves data as pulses of light.

The "in a vacuum" reference on the previous page regarding the speed of light is important. Light through fiber optic is not as fast as light through a vacuum. Light, when moving through just about any medium, is slower than the universal constant we know as the speed of light. The difference is negligible through air, but light can be slowed down considerably through other media, including glass, which makes up the core of most fiber optic cabling. The refractive index of a medium is the speed of light in a vacuum divided by the speed of light in the medium. So if you know two of those numbers, you can calculate the other. The index of refraction of glass is around 1.5. If you divide the speed of light (approximately 300,000 kilometers, or 186,411 miles, per second) by this, you get around 200,000 kilometers (124,274 miles) per second, which is the approximate speed of light through glass. Some fiber optic cabling is made of plastic, which has an even higher refractive index, and therefore a lower speed.

Part of the reason for the decrease in speed is the dual nature of light. It has the attributes of both a particle and a wave. Light is actually made up of particles called photons , and they do not move in a straight line through the cabling. As the photons hit molecules of material, they bounce in various directions. Light refraction and absorption by the medium eventually lead to some energy and data loss. This is why a signal can't travel indefinitely and has to be boosted periodically to cover long distances. However, the slowing of light isn't all bad news. Some impurities are added to fiber optics to control the speed and aid in channeling the signal effectively.

Fiber optic cable is still far faster than copper wire, and isn't as susceptible to electromagnetic interference. Fiber can achieve speeds of hundreds of Gigabits per second, or even Terabits. Home Internet connections don't achieve those super high speeds, at least partially because wiring is being shared by many households over entire areas, and even networks that use fiber optics generally have copper running the last stretch into people's homes. But with fiber running all the way to your neighborhood or home, you can get something in the range of 50 to 100 Megabits per second of data transfer, compared to 1 to 6 Megabits per second from average DSL lines and 25 or so Megabits per second from cable. Actual data speeds vary greatly by location, provider and your chosen plan, of course.

There are also other things that cause signal latency (delay), such as the back and forth communication required when you access a Web page or download data (handshaking). Your computer and the server housing the data are communicating to make sure they are synchronized and data transfer is successful, causing a delay, albeit a brief and necessary one. The distance your data has to travel will also affect how long it takes to get there, and there could be additional bottlenecks at any hardware and cabling the data has to travel through to get to its destination. A system is only as fast as its slowest component, and every millisecond counts in the days of seemingly (but not really) instant communication.

There have been recent breakthroughs in transferring data over copper wiring at nearly fiber optic speeds via reducing interference and other techniques. And researchers are also working on transmitting data via light through the air, say using lightbulbs for WiFi, or transmitting laser beams from building to building. Again, light through the air does move at close to light speed, but nothing we have now is surpassing the speed limit. Can we achieve actual faster-than-light transfer?

The use of fiber optic cable wasn't the first attempt to harness light for data transfer. Alexander Graham Bell himself invented the photophone, which was essentially the first wireless telephone, but using light rather than the radio waves used by modern cell phones. It worked by projecting a voice toward a mirror, which caused the mirror to vibrate. Light from the sun was bounced off the vibrating mirror into a selenium receiver that converted it into an electrical current for transmission via telephone (his most famous invention). Its major flaw was that direct sunlight was necessary, so clouds or other objects could block the signal. Never mind making a call in the middle of the night. But it actually worked, and served as a predecessor to fiber optics.

Scientists at the National Institute of Standards and Technology (NIST) are claiming to have achieved faster-than-light transfer of quantum data using something called four-wave mixing, which incidentally is a phenomenon that's considered a form of interference in fiber optic lines. The experiment involves sending a short 200-nanosecond seed pulse through heated rubidium vapor and at the same time sending in a second pump beam at a different frequency to amplify the seed pulse. Photons from both beams interact with the vapor in a way that generates a third beam. Apparently, the peaks of both the amplified seed pulse and the newly generated pulse can exit faster than a reference beam traveling at the speed of light in a vacuum. The speed differences they reported were 50 to 90 nanoseconds faster than light through a vacuum. They even proclaimed being able to tune the speed of the pulses by altering the input seed detuning and power.

Another fast data transfer technology in the works is quantum teleportation , which relies on the existence of entangled pairs: two particles that are in tune with each other to the point that if you measure one, the other ends up with the same quality that you found in the first one, no matter their distance from one another. This also requires a third particle that contains the actual bits of data you are trying to transfer. A laser is used to teleport one of the entangled particles elsewhere, in a manner of speaking. It isn't really transporting a photon, but rather changing a new photon into a copy of the original. The photon in the entangled pair can be compared to the third photon to find their similarities or differences, and that information can be relayed to the other location and used for comparison with the twin particle to glean the data. This sounds like something that would result in instant transfer, but that's not the case. Laser beams only travel at the speed of light. But this has potential applications for sending encrypted data via satellite, and for networking quantum computers, should we ever invent them. And it's further along than any attempts at superluminal data transfer. It works over miles at this point, and researchers are trying to increase the teleportation distance.

The answer to whether meaningful information can travel faster than light is currently no. We're only at the level of moving a few quantum particles at speeds that may possibly be over the speed of light, if the data pans out on subsequent experiments. To have a practically applicable form of data transfer, you have to be able to send organized bits of data that mean something, uncorrupted, to another machine that can interpret it. The fastest transmission in the world will mean nothing otherwise. But you can be sure that if the speed of light is broken, we'll be applying it to our Internet transmissions far sooner than to interstellar travel. Our ability to watch the highest quality television and surf the net at the fastest speeds will be paramount. And perhaps for those purposes, even getting ourselves to truly as-fast-as-light transmission would do wonders.

Frequently Answered Questions

Is it possible for information to travel faster than light, lots more information, author's note.

Physics is a truly fascinating subject, as it attempts to find the answer to how everything in the universe works. Without the study of physics, we probably wouldn't have a lot of modern conveniences, for instance those that require electricity, or depend upon the behavior of waves of any sort (like just about every form of long distance communication). You certainly wouldn't be reading this right now. Without an understanding of physical laws, lifting a piano would be more difficult, video games wouldn't be as much fun (or exist), and cartoon animators wouldn't know what laws to break to make us laugh. And we certainly wouldn't have ventured into space, an ability we'll need if we discover, via astrophysics or a keen observer, that a planet-destroying asteroid is headed our way. Also, kudos to mathematics for making the study of physics possible. I will continue to sit back and reap the benefits made possible by all the hard-working mathematicians, physicists and engineers of the world.

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• ABC Science. "Ask an Expert - Why is fibre optic technology 'faster' than copper?" (Nov. 24, 2012) http://www.abc.net.au/science/articles/2010/10/21/3044463.htm
• Alwayn, Vivek. "Optical Network Design and Implementation. Chapter: Fiber-Optic Technologies." Apr. 23, 2004. (Nov. 26, 2012) http://www.ciscopress.com/articles/article.asp?p=170740
• America's Library. "Alexander Graham Bell Invented the Photophone - June 3, 1880." (Dec. 2, 2012) http://www.americaslibrary.gov/jb/gilded/jb_gilded_bell_1.html
• Anderson, Nate. "Copper wire as fast as fiber?" Ars Technica. Oct. 10, 2006. (Nov. 24, 2012) http://arstechnica.com/gadgets/2006/10/7952/
• Anderson, Nate. "New life for twisted-pair? 500Mbps over copper wiring." Ars Technica. Mar. 16, 2009. (Nov. 25, 2012) http://arstechnica.com/tech-policy/2009/03/ericsson-500mbps-over-copper-wiring/
• Boyle, Rebecca. "Fed Up With Sluggish Neutrinos, Scientists Force Light To Move Faster Than Its Own Speed Limit." PopSci. May 3, 2012. (Nov. 26, 2012) http://www.popsci.com/science/article/2012-05/fed-sluggish-neutrinos-scientists-force-light-move-faster-its-own-speed-limit
• CBC News. "'Faster-than-light' data in doubt after new results." Mar. 19, 2012. (Nov. 15, 2012) http://www.cbc.ca/news/technology/story/2012/03/19/technology-faster-than-light-neutrinos-icarus.html
• CBC News. "'Faster-than-light' particles may have been even speedier." Feb. 23, 2012. (Nov. 15, 2012) http://www.cbc.ca/news/story/2012/02/23/technology-faster-than-light-neutrinos-opera.html
• Ceurstemont, Sandrine. "One-Minute Physics: Why light slows down in glass." New Scientist TV. Oct. 24, 2011. (Nov. 30, 2012) http://www.newscientist.com/blogs/nstv/2011/10/one-minute-physics-why-light-slows-down-in-glass.html
• Collins, Nick. "Speed of light 'broken' at CERN, scientists claim." The Telegraph. Sept. 22, 2011. (Nov. 30, 2012) http://www.telegraph.co.uk/science/science-news/8783011/Speed-of-light-broken-at-CERN-scientists-claim.html
• Condliffe, Jamie. "Did Scientists Really Just Break the Speed of Light?" Gizmodo. May 7, 2012. (Nov. 15, 2012) http://gizmodo.com/5908206/did-scientists-really-just-break-the-speed-of-light
• Das, Saswato R. "Was Einstein Wrong?" New York Times. Sept. 29, 2011. (Dec. 2, 2012) http://www.nytimes.com/2011/09/30/opinion/30iht-eddas30.html
• Diaz, Jesus. "Ridiculous: A Loose Cable Caused Those 'Faster-Than-Light' Particles." Gizmodo. Feb. 22, 2012. (Nov. 15, 2012) http://gizmodo.com/5887398/a-loose-cable-caused-the-faster+than+light-particles-test
• Dillow, Clay. "Physicists Say Speed-of-Light Breaking Neutrinos Would've Lost Their Energy Along the Way." PopSci. Oct. 3, 2011. (Nov. 30, 2012) http://www.popsci.com/science/article/2011-10/physicists-say-speed-light-breaking-neutrinos-wouldve-lost-their-energy-along-way
• Dodson, Brian. "Warp drive looks more promising than ever in recent NASA studies." Gizmag. Oct. 3, 2012. (Nov. 27, 2012) http://www.gizmag.com/warp-drive-bubble-nasa-interstellar/24392/
• FCC. "Measuring Broadband America - July 2012." July 2012. (Dec. 2, 2012) http://www.fcc.gov/measuring-broadband-america/2012/july
• Fettweis, Alfred. "Can signals truly be faster than light?" Signal Processing. August 2003, Volume 83, Issue 8, Pages 1583-1596. (Nov. 20, 2012)
• Finnie, Matthew. "How clouds cheat the speed of light." The Guardian. Sept. 6, 2012. (Nov. 24, 2012) http://www.guardian.co.uk/media-network/media-network-blog/2012/sep/06/cloud-computing-speed-light-network
• Glasser, Ryan T, Ulrich Vogl, and Paul D. Lett. "Stimulated generation of superluminal light pulses via four-wave mixing." Apr. 3, 2012. (Nov. 20, 2012) http://arxiv.org/pdf/1204.0810v1.pdf
• Hartley, Darleen. "Data Faster Than the Speed of Light." BSN. June 27, 2012. (Nov. 30, 2012) http://www.brightsideofnews.com/news/2012/6/27/data-faster-than-the-speed-of-light.aspx
• Higginbotham, Stacey. "Kotura: A startup betting on the speed of light in the data center." GigaOM. Nov. 23, 2012. (Nov. 25, 2012) http://gigaom.com/cloud/kotura-a-startup-betting-on-the-speed-of-light-in-the-data-center/
• Hsu, Jeremy. "Spaceship Could Fly Faster Than Light." Space.com. Aug. 13, 2008. (Dec. 1, 2012) http://www.space.com/5725-spaceship-fly-faster-light.html
• Iannone, P. "Optical Communications." IEEE Photonics Society. (Nov. 24, 2012) http://www.photonicssociety.org/content/optical-communications
• Johnston, James H. "Internet With the Speed of Light." Legal Times. Volume XXV, Issue 45, Nov. 18, 2002. (Nov. 30, 2012) http://www.ieeeusa.org/communications/Massmedia/files/Internet%20With%20the%20Speed....pdf
• Kawalec, Tomasz. "Should we bother with the speed of light in everyday life? A closer look at GSM technology." Physics Education. Volume 47, Issue 5, Pages 579-583. September 2012. (Nov. 15, 2012)
• Knapp, Alex. "Chinese Researchers Quantum Teleport Photons Over 60 Miles." Forbes. May 11, 2012. (Nov.25, 2012) http://www.forbes.com/sites/alexknapp/2012/05/11/chinese-researchers-quantum-teleport-photons-over-60-miles/
• Lentine, A. "Optical Interconnects & Processing Systems." IEEE Photonics Society. (Nov. 24, 2012) http://www.photonicssociety.org/content/optical-interconnects-processing-systems
• Mann, Adam. "The Race to Bring Quantum Teleportation to Your World." Wired. Oct. 3, 2012. (Dec. 2, 2012) http://www.wired.com/wiredscience/2012/10/quantum-satellite-teleportation/all/
• Mims, Christopher. "Achieving Fiber Optic Speeds over Copper Lines." MIT Technology Review. Apr. 22, 2012. (Nov. 25, 2012) http://www.technologyreview.com/news/418646/achieving-fiber-optic-speeds-over-copper-lines/
• Moskowitz, Clara. "Einstein's math may also describe faster-than-light velocities." Christian Science Monitor. Oct. 10, 2012. (Dec. 1, 2012) http://www.csmonitor.com/Science/2012/1010/Einstein-s-math-may-also-describe-faster-than-light-velocities
• Page, Lewis. "US gov boffins achieve speeds FASTER THAN LIGHT - 'Loophole' found in Special Theory of Relativity." The Register. May 7, 2012. (November 15, 2012) http://www.theregister.co.uk/2012/05/07/faster_than_light_quantum/
• Pennsylvania State University. "Researchers push transmission rate of copper cables." Nov. 14, 2007. (Nov. 24, 2012) http://live.psu.edu/story/27265
• Plumb, Marisa. "Copper at the Speed of Fiber?" IEEE Spectrum. October 2011. (Nov. 25, 2012) http://spectrum.ieee.org/telecom/internet/copper-at-the-speed-of-fiber
• Quigley, Brian. "Speed of Light in Fiber - The First Building Block of a Low-Latency Trading Infrastructure." Technically Speaking. Apr. 7, 2011. (Nov. 30, 2012) http://blog.advaoptical.com/speed-light-fiber-first-building-block-low-latency-trading-infrastructure/
• Reich, Eugenie Samuel. "Neutrino experiment replicates faster-than-light finding." Nature. Nov. 18, 2011. (Nov. 15, 2012) http://www.nature.com/news/neutrino-experiment-replicates-faster-than-light-finding-1.9393
• Schneider, David. "Financial Trading at the Speed of Light." IEEE Spectrum. Oct. 2011. (Nov. 25, 2012) http://spectrum.ieee.org/computing/it/financial-trading-at-the-speed-of-light
• Wrenn, Eddie. "Can we finally break the speed of light? Nasa breakthrough suggested Star Trek's 'warp drives' may not only be possible - but practical." Daily Mail. Sept. 18, 2012. (Dec. 1, 2012) http://www.dailymail.co.uk/sciencetech/article-2204913/Nasa-breakthrough-suggests-Star-Treks-warp-drives-possible--practical.html
• Wright, Robert. "Richard Feynman on the Weirdness of Physical Reality." Video of lecture at Cornell University: The Character of Physical Law: Probability and Uncertainty - The Quantum Mechanical View of Nature - November 18, 1964. The Atlantic. July 11, 2012. (Nov. 30, 2012) http://www.theatlantic.com/technology/archive/2012/07/richard-feynman-on-the-weirdness-of-physical-reality/259718/

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Hidden in Einstein's Math: Faster-than-Light Travel?

Although Einstein's theories suggest nothing can move faster than the speed of light, two scientists have extended his equations to show what would happen if faster-than-light travel were possible.

Despite an apparent prohibition on such travel by Einstein’s theory of special relativity , the scientists said the theory actually lends itself easily to a description of velocities that exceed the speed of light.

"We started thinking about it, and we think this is a very natural extension of Einstein's equations," said applied mathematician James Hill, who co-authored the new paper with his University of Adelaide, Australia, colleague Barry Cox. The paper was published Oct. 3 in the journal Proceedings of the Royal Society A: Mathematical and Physical Sciences.

Special relativity, proposed by Albert Einstein in 1905, showed how concepts like speed are all relative: A moving observer will measure the speed of an object to be different than a stationary observer will. Furthermore, relativity revealed the concept of time dilation , which says that the faster you go, the more time seems to slow down. Thus, the crew of a speeding spaceship might perceive their trip to another planet to take two weeks, while people left behind on Earth would observe their passage taking 20 years.

Yet special relativity breaks down if two people's relative velocity, the difference between their respective speeds, approaches the speed of light. Now, Hill and Cox have extended the theory to accommodate an infinite relative velocity. [ Top 10 Implications of Faster-Than-Light Neutrinos ]

Interestingly, neither the original Einstein equations, nor the new, extended theory can describe massive objects moving at the speed of light itself. Here, both sets of equations break down into mathematical singularities, where physical properties can't be defined.

"The actual business of going through the speed of light is not defined," Hill told LiveScience. "The theory we've come up with is simply for velocities greater than the speed of light."

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In effect, the singularity divides the universe into two: a world where everything moves slower than the speed of light, and a world where everything moves faster. The laws of physics in these two realms could turn out to be quite different.

In some ways, the hidden world beyond the speed of light looks to be a strange one indeed. Hill and Cox's equations suggest, for example, that as a spaceship traveling at super-light speeds accelerated faster and faster, it would lose more and more mass, until at infinite velocity, its mass became zero.

"It's very suggestive that the whole game is different once you go faster than light," Hill said.

Despite the singularity, Hill is not ready to accept that the speed of light is an insurmountable wall. He compared it to crossing the sound barrier. Before Chuck Yeager became the first person to travel faster than the speed of sound in 1947, many experts questioned whether it could be done. Scientists worried that the plane would disintegrate, or the human body wouldn't survive. Neither turned out to be true.

Fears of crossing the light barrier may be similarly unfounded, Hill said.

"I think it's only a matter of time," he said. "Human ingenuity being what it is, it's going to happen, but maybe it will involve a transportation mechanism entirely different from anything presently envisaged."

Follow Clara Moskowitz on Twitter  @ClaraMoskowitz  or LiveScience  @livescience . We're also on Facebook  &  Google+ .

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Warp drives: Physicists give chances of faster-than -light space travel a boost

Associate Professor of Physics, Oklahoma State University

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

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The closest star to Earth is Proxima Centauri. It is about 4.25 light-years away, or about 25 trillion miles (40 trillion km). 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 10 meters (33 feet). 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.

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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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• Speed of light
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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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March 9, 2021

Breaking the warp barrier for faster-than-light travel

by University of Göttingen

If travel to distant stars within an individual's lifetime is going to be possible, a means of faster-than-light propulsion will have to be found. To date, even recent research about superluminal (faster-than-light) transport based on Einstein's theory of general relativity would require vast amounts of hypothetical particles and states of matter that have 'exotic' physical properties such as negative energy density. This type of matter either cannot currently be found or cannot be manufactured in viable quantities. In contrast, new research carried out at the University of Göttingen gets around this problem by constructing a new class of hyper-fast 'solitons' using sources with only positive energies that can enable travel at any speed. This reignites debate about the possibility of faster-than-light travel based on conventional physics. The research is published in the journal Classical and Quantum Gravity .

The author of the paper, Dr. Erik Lentz, analyzed existing research and discovered gaps in previous 'warp drive' studies. Lentz noticed that there existed yet-to-be explored configurations of space-time curvature organized into 'solitons' that have the potential to solve the puzzle while being physically viable. A soliton—in this context also informally referred to as a 'warp bubble'—is a compact wave that maintains its shape and moves at constant velocity. Lentz derived the Einstein equations for unexplored soliton configurations (where the space-time metric's shift vector components obey a hyperbolic relation), finding that the altered space-time geometries could be formed in a way that worked even with conventional energy sources. In essence, the new method uses the very structure of space and time arranged in a soliton to provide a solution to faster-than-light travel , which—unlike other research—would only need sources with positive energy densities. No exotic negative energy densities needed.

If sufficient energy could be generated, the equations used in this research would allow space travel to Proxima Centauri, our nearest star, and back to Earth in years instead of decades or millennia. That means an individual could travel there and back within their lifetime. In comparison, the current rocket technology would take more than 50,000 years for a one-way journey. In addition, the solitons (warp bubbles) were configured to contain a region with minimal tidal forces such that the passing of time inside the soliton matches the time outside: an ideal environment for a spacecraft. This means there would not be the complications of the so-called 'twin paradox' whereby one twin traveling near the speed of light would age much more slowly than the other twin who stayed on Earth: in fact, according to the recent equations both twins would be the same age when reunited.

"This work has moved the problem of faster-than-light travel one step away from theoretical research in fundamental physics and closer to engineering. The next step is to figure out how to bring down the astronomical amount of energy needed to within the range of today's technologies, such as a large modern nuclear fission power plant. Then we can talk about building the first prototypes," says Lentz.

Currently, the amount of energy required for this new type of space propulsion drive is still immense. Lentz explains, "The energy required for this drive traveling at light speed encompassing a spacecraft of 100 meters in radius is on the order of hundreds of times of the mass of the planet Jupiter. The energy savings would need to be drastic, of approximately 30 orders of magnitude to be in range of modern nuclear fission reactors." He goes on to say: "Fortunately, several energy-saving mechanisms have been proposed in earlier research that can potentially lower the energy required by nearly 60 orders of magnitude." Lentz is currently in the early-stages of determining if these methods can be modified, or if new mechanisms are needed to bring the energy required down to what is currently possible.

Provided by University of Göttingen

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[Physics FAQ] - [Copyright]

By Philip Gibbs, 1997, 1998.

It might be thought that special relativity provides a short negative answer to this question.  In actual fact, there are many trivial ways in which things can be going faster than light (FTL) in a sense, and there may be other more genuine possibilities.  On the other hand, there are also good reasons to believe that real FTL travel and communication will always be unachievable.  This article is not a full answer to the question (which no doubt will continue to be discussed in the newsgroups for the foreseeable future), but it does cover some of the more common points that are repeatedly made.

It is sometimes objected that "they said no-one would ever go faster than sound and they were wrong.  Now they say no-one will ever go faster than light..."   Actually it is probably not true that anybody said it was impossible to go faster than sound.  It was known that rifle bullets go faster than sound long before an aircraft did.  The truth is that some engineers once said that controlled flight faster than sound might be impossible, and they were wrong about that.  FTL travel is a very different matter.  It was inevitable that someone would one day succeed in flying faster than sound, once technology got around the problems.  It is not inevitable that one day technology will enable us to go faster than light.  Relativity has a lot to say about this.  If FTL travel or FTL communication were possible, then causality would probably be violated and some very strange situations would arise.

First we will cover the trivial ways in which things can go FTL.  These points are mentioned not because they are interesting, but because they come up time and time again when FTL is being discussed, and so they are necessary to deal with.  Then we will think about what we mean by non-trivial FTL travel/communication and examine some of the arguments against it.  Finally, we will look at some of the more serious proposals for real FTL.  Many of these things are discussed in more detail elsewhere in the FAQ and hyper-links are provided.  The sections are numbered so that they can be referred to individually.

Trivial FTL Travel

1. cherenkov effect.

One way to go faster than light is to make the light slow down!  Light in vacuum travels at a speed c which is a universal constant (see the FAQ entry Is the speed of light constant? ), but in a dense medium such as water or glass, light slows down to c/n where n is the refractive index of the medium (1.0003 for air, 1.4 for water).  It is certainly possible for particles to travel through air or water faster than light travels in that medium, and Cherenkov radiation is produced as a result.  See the FAQ entry Is there an equivalent of the sonic boom for light? .

When we discuss moving faster than light, we are really talking about exceeding the speed of light in vacuum c (299,792,458 m/s).  The Cherenkov effect is thus not considered to be a real example of FTL travel.

2. Third-Party Observers

If a rocket A is travelling away from me at 0.6c in a westerly direction, and another B is travelling away from me at 0.6c in an easterly direction, then the total distance between A and B as seen in my frame of reference is increasing at 1.2c .  An apparent relative speed greater than c can be observed by a third person in this way.

But this is not what is normally meant by relative speeds.  The true speed of rocket A relative to rocket B is the speed at which an observer in rocket B observes his distance from A to be increasing.  The two speeds must be added using the relativistic formula for addition of velocities.  (See the FAQ entry How do You Add Velocities in Special Relativity? )  In this case the relative speed is actually about 0.88c , so this is not an example of FTL travel.

3. Shadows and Light Spots

Think about how fast a shadow can move.  If you project the shadow of your finger using a nearby lamp onto a distant wall and then wag your finger, the shadow will move much faster than your finger.  If your finger moves parallel to the wall, the shadow's speed will be multiplied by a factor D/d where d is the distance from the lamp to your finger, and D is the distance from the lamp to the wall.  The speed can even be much faster than this if the wall is at an angle to your finger's motion.  If the wall is very far away, the movement of the shadow will be delayed because of the time it takes light to get there, but the shadow's speed is still increased by the same ratio.  The speed of a shadow is therefore not restricted to be less than the speed of light.

This behaviour of a shadow is all about the arrival of successive "pieces of light" (photons, if you will) at a screen.  It is really no different to the faster-than-light speed of a spot on the Moon's surface caused by a laser that has been aimed at that surface and is being waved around on Earth.  Given that the distance to the Moon is 385,000 km, try working out the speed of that spot if you wave the laser at a gentle speed.  You might also like to think about a water wave arriving obliquely at a long straight beach.  How fast can the point at which the wave is breaking travel along the beach?

This sort of thing turns up in Nature; for example, the beam of light from a pulsar can sweep across a dust cloud.  A bright explosion emits an expanding spherical shell of light or other radiation.  When this shell intersects a surface, it creates a circle of light which expands faster than light.  A natural example of this has been observed when an electromagnetic pulse from a lightning flash hits an upper layer of the atmosphere.

These are all examples of "things" that seem to be moving faster than light.  In reality, no object or signal is moving faster that light here.  For a more prosaic example, imagine squirting water from a garden hose at a fence, and moving your aim from one end of the fence to the other.  The intersection point of water stream and fence moves quickly, but of course no thing or signal is really moving along the fence.  A succession of water molecules strikes the fence, but their speed of travel has nothing to do with how quickly you move the hose.  It is a kind of optical illusion for us to think that the wet spot advancing along the fence is a moving object or signal.  The ban in relativity against faster-than-light travel actually concerns the speed of signals (which includes material objects and waves): in a vacuum, no signal is allowed to move faster than light moves in its vicinity.  Neither a moving shadow, nor a laser spot, nor a wet spot on a fence, constitute a signal that is being sent from the initial position of those spots to the final position.  Since these moving spots don't constitute a signal, they are all allowed to move faster than light.  This is not really what we mean by faster-than-light travel, although it shows how difficult it is to define what we really do mean by faster-than-light travel.  See also the FAQ The Superluminal Scissors .

4. Rigid Bodies

If you have a long rigid stick and you hit one end, wouldn't the other end have to move immediately?  Would this not provide a means of FTL communication?

Well, it would if there were such things as perfectly rigid bodies.  In practice the effect of hitting one end of the stick propagates along it at the speed of sound in the material; this speed depends on the stick's elasticity and density.  Relativity places an absolute limit on material rigidity in such a way that the speed of sound in the material will not be greater than c .

The same principle applies if you hold a long string or rod vertically in a gravitational field and let go of the top end.  The point at which you let go will start to move immediately, but the lower end cannot move until the effect has propagated down the length.  That speed of propagation depends on the nature of the material and the strength of the gravitational field.

It is difficult to formulate a general theory of elastic materials in relativity, but the general principle can be illustrated with newtonian mechanics.  The equation for longitudinal motion in an ideal elastic body can be derived from Hooke's law.  In terms of the mass per unit length p and Young's modulus of elasticity Y , the longitudinal displacement X satisfies a wave equation (see for example Goldstein's "Classical Mechanics"):

Plane wave solutions travel at the speed of sound s where s 2 = Y/p .  This wave equation does not allow any causal effect to propagate faster than s .  Relativity therefore imposes a limit on elasticity: Y < pc 2 .  In practice, no known material comes anywhere near this limit.  Note that even if the speed of sound is near c , the matter does not necessarily move at relativistic speeds.  But how can we know that no material can possibly exceed this limit?  The answer is that all materials are made of particles whose interaction are governed by the standard model of particle physics, and no influence faster than light can propagate in that model (see the section on Quantum Field Theory below).

So although there is no such thing as a rigid body, there is such a thing as rigid body motion; but this is another example in the same category as the shadows and light spots described above which do not give FTL communication.  (See also the FAQ articles The Superluminal Scissors and The Rigid Rotating Disk in Relativity ).

5. Phase, Group, and Signal Velocities

Look at this wave equation:

This has solutions of the form:

These solutions are sine waves propagating with a speed

But this is faster than light, so is this the equation for a tachyon field?  (See the paragraph on tachyons below ).  No, it is the usual relativistic equation for an ordinary particle with mass!

Superluminal speeds such as this present no problem once we recognise three types of speed associated with wave motion: phase velocity , group velocity , and signal velocity .  Phase velocity is the velocity of waves that have well-defined wavelengths, and it often varies as a function of this wavelength.  We can combine ("superpose") waves of different wavelengths to build a wave packet , a blob of some specified extent over which the wave disturbance is not small.  This packet does not have a well-defined wavelength, and because it usually spreads out as it travels, it doesn't have a well-defined velocity either; but it does have representative velocity, and this is called its group velocity, which will usually be less than c .  Each of the packet's constituent wave trains travels with its own individual phase velocity, which in some instances will be greater than c .  But it is only possible to send information with such a wave packet at the group velocity (the velocity of the blob), so the phase velocity is yet another example of a speed faster than light that cannot carry a message.

In some situations, we can build a fairly exotic wave packet whose group velocity is greater than c .  Does this then constitute an example of information being sent at a speed faster than light?  It turns out that for these packets, information does not travel at the group velocity; instead, it travels at the signal velocity , which has to do with the time of arrival of the initial rise of the wave front as it reaches its destination.  You might not now be surprised to learn that the signal velocity turns out always to be less than c .

6. Superluminal Galaxies

If something is coming towards you at nearly the speed of light and you measure its apparent speed without taking into account the diminishing time it takes light to reach you from the object, you can get an answer that is faster than light.  This is an optical illusion, and is not due to the object's moving at FTL.  See the FAQ Apparent Superluminal Velocity of Galaxies .

7. Relativistic Rocket

A controller based on Earth is monitoring a space ship moving away at a speed 0.8c .  According to the theory of relativity, he will observe a time dilation that slows the ship's clocks by a factor of 5/3, even after he has taken into account the Doppler shift of signals coming from the space ship.  If he works out the distance moved by the ship divided by the time elapsed as measured by the onboard clocks, he will get an answer of 4/3 c .  He infers from this that the ship's occupants determine themselves to be traversing the distances between stars at speeds greater than the speed of light when measured with their clocks.  From the point of view of the occupants their clocks undergo no slowing; rather, they maintain that it is the distance between the stars which has contracted by a factor of 5/3.  So they also agree that they are covering the known distances between stars at 4/3 c .

This is a real effect which in principle could be used by space travellers to cover very large distances in their lifetimes.  If they accelerate at a constant acceleration equal to the acceleration due to gravity on Earth, they would not only have a perfect artificial gravity on their ship, but would also be able to cross the galaxy in only about 12 years of their own "proper time": that is, they would age 12 years during the journey.  See the FAQ What are the Equations for the Relativistic Rocket?

Nevertheless, this is not true FTL travel.  The effective speed calculated used the distance in one reference frame and the time in another.  This is no way to calculate a speed.  Only the occupants of the ship benefit from this effective speed.  The controller will not measure them to be travelling large distances in his own lifetime.

8. Speed of Gravity

Some people have argued that the speed of gravity in a gravitationally bound system is much greater than c or even infinite.  In fact, gravitational effects and gravitational waves travel at the speed of light c .  See the articles Does Gravity Travel at the Speed of Light? and What is Gravitational Radiation? for the explanation.

9. EPR Paradox

In 1935 Einstein, Podolsky, and Rosen published a thought experiment that seemed to produce a paradox in quantum mechanics, as well as demonstrating that it was incomplete.  Their argument used the fact that there can be an apparent instantaneous interaction in the measurement of two separated particles that have been prepared in a certain "entangled" manner.  Einstein called it "spooky action at a distance".  It has been shown by Eberhard that no information can be passed using this effect; so there is no FTL communication, but the paradox is still very controversial.  See the FAQ article The EPR Paradox and Bell's Inequality for more details.

10. Virtual Photons

In quantum field theory forces are mediated by "virtual particles".  The Heisenberg Uncertainty Principle allows these virtual particles to move faster than light.  But virtual particles are not called "virtual" for nothing.  They are only part of a convenient mathematical notation, and once again, no real FTL travel or communication is possible.  See the FAQ Virtual Particles .

11. Quantum Tunnelling

Quantum Tunnelling is the quantum mechanical effect that permits a particle to pass through a barrier when it does not have enough energy to do so classically.  You can do a calculation of the time it takes a particle to tunnel through such a barrier.  The answer you get can come out less than the time it takes light to cover the distance at speed c .  Does this provide a means of FTL communication? Ref: T. E. Hartman, J. Appl. Phys. 33 , 3427 (1962).

The answer must surely be "No!"—otherwise our understanding of QED is very suspect.  Yet a group of physicists have performed experiments that seem to suggest that FTL communication by quantum tunneling is possible.  They claim to have transmitted Mozart's 40th Symphony through a barrier 11.4cm wide at a speed of 4.7 c .  Their interpretation is, of course, very controversial.  Most physicists say this is a quantum effect where no information can actually be passed at FTL speeds.  If the effect is real it is difficult to see why it should not be possible to transmit signals into the past by placing the apparatus in a fast-moving frame of reference. Refs: W. Heitmann and G. Nimtz, Phys. Lett. A196 , 154 (1994); A. Enders and G. Nimtz, Phys. Rev. E48 , 632 (1993).

Terence Tao has pointed out that apparent FTL transmission of an audio signal over such a short distance is not very impressive.  The signal takes less than 0.4 ns to travel the 11.4 cm at light speed, but it is quite easy to anticipate an audio signal ahead of time by up to 1000 ns simply by extrapolating the signal waveform.  Although this is not what is being done in the above experiments, it does illustrate that the experimenters will need to use a much higher frequency random signal, or transmit over much larger distances, if they are to demonstrate FTL information transfer convincingly.

The likely conclusion is that there is no real FTL communication taking place, and that the effect is another manifestation of the Heisenberg Uncertainty Principle.

12. Casimir Effect

The Casimir Effect describes the fact that a very small but measurable force exists between two uncharged conducting plates when they are very close together.  It is due to the existence of vacuum energy (see the FAQ article on the Casimir Effect ).  A surprising calculation by Scharnhorst suggests that photons travelling across the gap between the plates in the Casimir Effect must go faster than c by a very very small amount (at best 1 part in 10 24 for a 1 nanometre gap.) It has been suggested that in certain cosmological situations, such as in the vicinity of cosmic strings if they exist, the effect could be much more pronounced.  Even so, further theoretical investigations have shown that, once again, there is no possibility of FTL communication using this effect. Refs: K. Scharnhorst, Physics Letters B236 , 354 (1990) S. Ben-Menahem, Physics Letters B250 , 133 (1990) Andrew Gould (Princeton, Inst. Advanced Study). IASSNS-AST-90-25 Barton & Scharnhorst, J. Phys. A26 , 2037 (1993).

13. Expansion of the Universe

According to Hubble's Law, two galaxies that are a distance D apart are moving away from each other at a speed HD , where H is Hubble's constant.  So this interpretation of Hubble's Law implies that two galaxies separated by a distance greater than c/H must be moving away from each other faster than light.  Actually, the modern viewpoint describes this situation differently: general relativity takes the galaxies as being at rest relative to one another, while the space between them is expanding.  In that sense, the galaxies are not moving away from each other faster than light; they are not moving away from each other at all!  This change of viewpoint is not arbitrary; rather, it's in accord with the different but very fruitful view of the universe that general relativity provides.  So the distance between two objects can be increasing faster than light because of the expansion of the universe, but this does not mean, in fact, that their relative speed is faster than light.

As was mentioned above, in special relativity it is possible for two objects to be moving apart by speeds up to twice the speed of light as measured by an observer in a third frame of reference.  In general relativity even this limit can be surpassed, but it will not then be possible to observe both objects at the same time.  Again, this is not real faster-than-light travel; it will not help anyone to travel across the galaxy faster than light.  All that is happening is that the distance between two objects is increasing faster when taken in some cosmological reference frame.

14. The Moon revolves round my head faster than light!

Stand up in a clear space and spin round.  It is not too difficult to turn at one revolution each two seconds.  Suppose the Moon is on the horizon.  How fast is it spinning round your head?  It is about 385,000 km away, so the answer is 1.21 million km/s, which is more than four times the speed of light!  It might sound ridiculous to say that the Moon is going round your head when really it is you who is turning, but according to general relativity all co-ordinate systems are equally valid, including rotating ones.  So isn't the Moon going faster than light?

What it comes down to is the fact that velocities in different places cannot be compared directly in general relativity.  Notice that the Moon is not overtaking any light in its own locality.  The speed of the Moon can only be compared to the speeds of other objects in its own locality.  Indeed, the concept of speed is not a very useful one in general relativity, and this makes it difficult to define what "faster than light" means.  Even the statement that "the speed of light is constant" is open to interpretation in general relativity.  Einstein himself, on page 76 of his book "Relativity: the Special and the General Theory", wrote that the statement cannot claim unlimited validity.  When there is no absolute definition of time and distance it is not so clear how speeds should be determined.

Nevertheless, the modern interpretation is that the speed of light is constant in general relativity and this statement is a tautology given that standard units of distance and time are tied together using the speed of light.  The Moon is given to be moving slower than light because it remains within the "future light cone" propagating from its position at any instant.

Relativity Arguments Against FTL Travel

15. what does "faster than light" mean.

The cases given so far only demonstrate how difficult it is to pin down exactly what we mean by FTL travel or communication.  If we do not include things such as moving shadows, then what exactly do we mean by FTL?

In relativity there is no such thing as absolute velocity, only relative velocity; but there is a clear distinction between "world lines" that are "timelike", "lightlike", and "spacelike".  By "world line" we mean a curve traced out in the four dimensions of space-time.  Such a curve is the set of all events that make up the history of a particle.  If a world line is spacelike then it describes something moving faster than light.  So there is a clear meaning of what is meant by a "faster-than-light" speed which does not depend on the existence of third-party observers.

But what do we mean by an "object" if we don't want to include shadows?  We could define an object to be anything that carries energy, charge, spin, or information; or perhaps just that it must be made of atoms, but there are technical problems in each case.  In general relativity energy cannot be localised, so we had better avoid using energy in our definition.  Charge and spin can be localised, but not every object need have charge or spin.  Using the concept of information is better but tricky to define, and sending information faster than light is really just FTL communication—not FTL travel.  Another difficulty is knowing whether an object seen at A is the same as the one that was earlier seen at B when we claim that it has travelled across the gap faster than light.  Could it not be a duplicate?  It could even be argued that FTL communication makes FTL travel possible, because you can send the blueprint for an object FTL as advance information, and then reconstruct the object—although not everyone would accept such teleportation as FTL travel.

The problems of specifying just what we mean by FTL are more difficult in general relativity.  A valid form of FTL travel may mean distorting space-time (e.g. making a worm hole) to get from A to B without going on a spacelike curve locally.  There is a distinction between going faster than light locally and getting from A to B faster than light globally .  When a gravitational lens bends the light coming from a distant galaxy asymmetrically, the light coming round the galaxy on one side reaches us later than light that left at the same time and went round the other side.  We must avoid a definition of FTL travel that says a particle going from A to B gets there before light that has made the same journey along a lightlike geodesic.  This makes it very difficult, perhaps impossible, to define global FTL travel unambiguously.

If you were expecting me to finish this section with a precise definition of what is meant by FTL travel and FTL communication, I am afraid I must disappoint you!  The above difficulties are insurmountable.  Nonetheless, you will probably recognise the real thing when confronted with it now that I have given some examples of what would not be FTL travel.

16. The Infinite-Energy Argument

When Einstein wrote down his postulates for special relativity, he did not include the statement that you cannot travel faster than light.  There is a misconception that it is possible to derive it as a consequence of the postulates he did give.  Incidentally, it was Henri Poincare who said "Perhaps we must construct a new mechanics [...] in which the speed of light would become an impassable limit."  That was in an address to the International Congress of Arts and Science in 1904—before Einstein announced special relativity in 1905.

It is a consequence of relativity that the energy of a particle of rest mass m moving with speed v is given by

As the speed approaches the speed of light, the particle's energy approaches infinity.  Hence it should be impossible to accelerate an object with rest mass to the speed of light; also, particles with zero rest mass must always move at exactly the speed of light, since otherwise they would have no energy.  This is sometimes called the "light speed barrier", but it is very different from the "sound speed barrier".  As an aircraft approaches the speed of sound it starts to feel pressure waves which indicate that it is moving close to the speed of sound, and before the existence and effects of these waves were well understood, they destroyed several aircraft in the mid 20th century; hence the old name of sound "barrier".  In fact, with more thrust and the right aerodynamics, an aircraft can certainly pass through the sound barrier.

The situation is different for light.  As the light speed barrier is approached (in a perfect vacuum) there are no such waves according to relativity (destructive or otherwise).  Moving at 0.999 c is just like standing still with everything rushing past you at −0.999 c .  Particles are routinely pushed to these speeds and beyond in accelerators, so the theory is well established.  Trying to attain the speed of light in this way is a matter of chasing something that is forever just out of your reach.

This explains why it is not possible to exceed the speed of light by ordinary mechanical means.  But it does not in itself rule out FTL travel.  It is really just one way in which things cannot be made to go faster than light, rather than a proof that there is no way to do so.  Particles are known to decay instantly into other particles which fly off at high speed.  It is not necessary to think in terms of the particles' having been accelerated, so how could we say that they could not go faster than light?  What about the possibility of particles that might always have been moving faster than light, and which might be used to send information if they can be detected without ever slowing down to less than the speed of light?  Even if such "tachyons" don't exist (and we don't believe that they do exist), there may be ways of moving matter from A to B faster than light is able to travel from A to B by the usual route, but without anything having to go at a FTL speed locally.  See the paragraph on tachyons below .

17. Quantum Field Theory

Except for gravity, all physical phenomena are observed to comply with the "Standard Model" of particle physics.  The Standard Model is a relativistic quantum field theory which incorporates the nuclear and electromagnetic forces as well as all the observed particles.  In this theory, any pair of operators corresponding to physical observables at space-time events separated by a spacelike interval "commute" (i.e. their order can be reversed).  In principle, this implies that effects cannot propagate faster than light in the standard model, and it can be regarded as the quantum field theory equivalent of the infinite energy argument.

But no completely rigorous proofs of anything exist in the quantum field theory of the Standard Model, since no one has yet succeeded in showing that the theory is completely self consistent; and in fact, most likely it is not!  In any case, there is no guarantee that there are not other undiscovered particles and forces that disobey the no-FTL rule.  Nor is there any generalisation that takes gravity and general relativity into account.  Many physicists working on quantum gravity doubt that such simplistic expressions of causality and locality will be generalised.  All told, there is no guarantee that light speed will be meaningful as a speed limit in a more complete theory that might arise in the future.

18. Grandfather Paradox

A better argument against FTL travel is the Grandfather Paradox.  In special relativity, a particle moving FTL in one frame of reference will be travelling back in time in another.  FTL travel or communication should therefore also give the possibility of travelling back in time or sending messages into the past.  If such time travel is possible, you would be able to go back in time and change the course of history by killing your own grandfather.  This is a very strong argument against FTL travel, but it leaves open the perhaps-unlikely possibility that we may be able to make limited journeys at FTL speed that did not allow us to come back.  Or it may be that time travel is possible and causality breaks down in some consistent fashion when FTL travel is achieved.  That is not very likely either, but if we are discussing FTL then we had better keep an open mind.

Conversely, if we could travel back in time we might also claim the ability to travel FTL, because we can go back in time and then travel at a slow speed to arrive somewhere before light got there by the usual route.  See the FAQ article on Time Travel for more on this subject.

Open Possibilities for FTL Travel

In this last section I give a few of the speculative but serious suggestions for possible faster-than-light travel.  These are not the kinds of thing usually included in the FAQ because they raise more questions than answers.  They are included merely to make the point that serious research is being done in this direction.  Only a brief introduction to each topic is given; more information can be found all over the Internet (and should, like almost everything on the Internet, be taken with a huge grain of salt!).

19. Tachyons

Tachyons are hypothetical particles that travel faster than light locally.  Their mass must take on imaginary values (i.e. to do with the square root of −1) to be able to do so, but they have real-valued energy and momentum.  Sometimes people imagine that such FTL particles would be impossible to detect, but there is no reason to think so.  Shadows and spotlights suffice to show that there is no logic in this suggestion, because they can certainly go FTL and still be seen.

No tachyons have definitely been found and most physicists doubt their existence.  There has been a claim that experiments to measure neutrino mass in tritium beta decay indicated that the neutrinos were tachyonic. ; while this is very doubtful, it is not entirely ruled out.  Tachyon theories have problems because, apart from the possibility of causality violations, they destabilise the vacuum.  It may be possible to get around such difficulties—but then we would not be able to use tachyons for the kind of FTL communication that we would like.

The truth is that most physicists consider tachyons to be a sign of pathological behaviour in field theories, and the interest in them among the wider public stems mostly from the fact that they are used so often in science fiction.  See the FAQ article on Tachyons .

20. Worm Holes

A famous proposition for global FTL travel is to use "worm holes".  Worm holes are shortcuts through space-time from one place in the universe to another which would permit you to go from one end to the other in a shorter time than it would take light passing by the usual route.  Worm holes are a feature of classical general relativity, but to create them you have to change the topology of space-time.  That might be possible within a theory of quantum gravity.

To keep a worm hole open, regions of negative energy would be needed.  Misner and Thorne have suggested using the Casimir Effect on a grand scale to generate the negative energy, while Visser has proposed a solution involving cosmic strings.  These are very speculative ideas which may simply not be possible.  Exotic matter with negative energy may not exist in the form required.

Thorne has found that if worm holes can be created, then they can be used to construct closed timelike loops in space-time which would imply the possibility of time travel.  It has been suggested that the "multiverse" interpretation of quantum mechanics (many universes co-existing) gets you out of trouble by allowing time to evolve differently if you succeed in going back to a previous time.  But multiverses are entirely out of keeping with the Ockham's Razor approach to doing science, and constitute more of a popular interpretation of quantum mechanics than a serious physical theory.  Hawking says that worm holes would simply be unstable and therefore unusable.  The subject remains a fertile area for thought experiments that help clarify what is and what is not possible according to known and suggested laws of physics. Refs: W. G. Morris and K. S. Thorne, American Journal of Physics 56 , 395–412 (1988) W. G. Morris, K. S. Thorne, and U. Yurtsever, Phys. Rev. Letters 61 , 1446–9 (1988) Matt Visser, Physical Review D39 , 3182–4 (1989) See also "Black Holes and Time Warps", Kip Thorne, Norton & co. (1994) For an explanation of the multiverse see "The Fabric of Reality" David Deutsch, Penguin Press.

21. Warp Drives

A "warp drive" such as used in the Star Trek science fiction series would be a mechanism for warping space-time in such a way that an object could move faster than light.  Miguel Alcubierre made himself famous by working out a space-time geometry which describes such a warp drive.  The warp in space-time makes it possible for an object to go FTL while remaining on a timelike curve.  The main catch is the same one that may stop us making large worm holes.  To make such a warp, you would need exotic matter with negative energy density.  Even if such exotic matter can exist, it is not clear how it could be deployed to make the warp drive work. Ref.   M. Alcubierre, Classical and Quantum Gravity, 11 , L73–L77, (1994). Ref.   S. Finazzi, S. Liberati, C. Barcel�, Semiclassical instability of dynamical warp drives at arxiv.org.

• To begin with, it is rather difficult to define exactly what is really meant by FTL travel and FTL communication.  Many things such as shadows can go FTL, but not in a useful way that can carry information.
• There are several serious possibilities for real FTL which have been proposed in the scientific literature, but these always come with technical difficulties.
• The Heisenberg Uncertainty Principle tends to stop the use of apparent FTL quantum effects for sending information or matter.
• In general relativity there are potential means of FTL travel, but they may be impossible to make work.  It is thought highly unlikely that engineers will be building space ships with FTL drives in the foreseeable future, if ever, but it is curious that theoretical physics as we presently understand it seems to leave the door open to the possibility.
• FTL travel of the sort science fiction writers would like is almost certainly impossible.  For physicists the interesting question is "why is it impossible and what can we learn from that?"

The idea that characters can fly from planet to planet, or star to star, defying current science and technology, is central to science fiction. Although some of these ideas predated the space age, after the 1950s, fictional depictions of space travel needed to suggest conceivable ways to cross interstellar distances to seem plausible. Some authors suggested faster-than-light drives, hyper drives, jump drives, worm holes, and black holes.

Scientific understanding of light speed as an absolute natural limit derives from Albert Einstein’s publications on special relativity in 1905, confirmed by his work on general relativity in 1916. In classical physics, speed has no limits. But relativistic theory shows that mass increases with acceleration until mass becomes infinite at light speed. Yet author E. E. “Doc” Smith imagined spaceships traveling faster than the speed of light in his “Skylark of Space” stories. Smith’s cover story appeared in the same issue of Amazing Stories in 1928 that included Philip Francis Nowlan’s first short story about Anthony (later “Buck”) Rogers.

Within a couple of decades, the fictional idea of faster-than-light travel made intuitive sense to a public familiar with recent supersonic flights. In 1947, Chuck Yeager broke the speed of sound aboard the Bell X-1 Glamorous Glennis . Writers extrapolated supersonic speeds into the idea of spacecraft traveling at multiples of the speed of light. Frank Hampson’s British comic Dan Dare offered one of the earliest uses of faster-than-light travel. In 1955, he introduced interstellar travel in “The Man from Nowhere” trilogy. The technology was inherently alien, however, and faster-than-light travel was not featured regularly afterward. Forbidden Planet (1956) was the first film to depict a fictional faster-than-light spaceship created by humans. From the exterior, the C-57D ship was an undifferentiated flying saucer. After a loudspeaker announcement, however, the crew stood in “DC stations” that held them immobile while the ship slowed. By the mid-1960s, however, as both the United States and the Soviet Union made regular human spaceflights, science fiction audiences became more intuitively aware of the time that it took to travel in space.

The U.S.S. Enterprise created for Star Trek (NBC, 1966-69) represented a major leap forward. Walters “Matt” Jefferies, a WWII flight engineer and private pilot, used “aircraft logic” to design a vehicle with components that visually communicated their purpose. With the two engine nacelles, Jefferies effectively invented warp drives, fictional engines that could propel the ship at multiples of the speed of light. As seen in Star Trek: First Contact (1996), the first flight of Zephram Cochran’s warp-capable Phoenix demonstrated the mark of a culture that was ready to participate in interstellar civilization. Jefferies’ design raised the bar for imagined vehicles. After Star Trek, undifferentiated flying saucers and flame-spewing pointed rockets largely disappeared from fictional depictions. Instead, imagined propulsion that bent space-time or traversed alternate dimensions become more prevalent.

Rather than just having the vehicles fly faster, some science fiction suggested traveling through or outside of normal four-dimensional space (including time), either by jumping within ordinary space, utilizing hyperspace, or exploiting natural or artificial shortcuts through space. Beginning in the 1940s, Isaac Asimov included jump drives in the short stories that later became his Foundation (1951) series of novels. Because fictional jump drives turn long flights into direct hops, allowing ships to disappear from one place and reappear in another, they facilitate storytelling without interrupting it. The reimagined Battlestar Galactica (2003) uses the same kind of travel but calls the mechanisms “FTL drives.”

A production model of the Millennium Falcon was on display at the Museum in 1998-99 as a part of the "Star Wars: The Magic of Myth".

The Star Wars universe postulates a hyperdrive, a computer-guided system that allows spacecraft to enter hyperspace at faster-than-light speeds and navigate to a successful exit at a distant destination. Solo: A Star Wars Story (2018) reveals that the extensive navigational maps and rapid calculating ability of the Millennium Falcon ’s hyperdrive computer are actually the downloaded memories of L3-37, a spirited and female-identified droid pilot.

The two-season program Buck Rogers in the 25th Century (NBC, 1979-1981) showed interstellar travel being accomplished using stargates. Four lights arranged in a diamond in space showed that the stargate had opened, offering access to hyperspace. A similar concept had a more physical presence in J. Michael Straczynski’s Babylon 5 (Syndicated & TNT, 1993-1998). In that show, external “jumpgates” shown using computer-generated imaging provided a physical infrastructure for generating stable vortices to hyperspace.

The idea of artificial space-time vortices as conduits drew power from speculation published in technical and popular literature. Speculation about wormholes must be distinguished, however, from black holes, which are real astronomical phenomena. Stories involving black holes often include time dilation. Einstein’s theories—including special and general relativity—explain that a person travelling near a massive gravitational field experiences time more slowly. The plot of director Christopher Nolan’s Interstellar (2014) employed time differences for dramatic purposes and also represented a giant leap in visual effects. To create the effect of the rapidly spinning black hole, theoretical astrophysicist Kip Thorne assisted the Interstellar production team. The resulting black hole appeared as a three-dimensional, spherical, hole in spacetime, drawing in all of the light around it. When the Event Horizon Telescope project imaged a real black hole in 2019, that image demonstrated how close to reality Interstellar ’s fictional imagination had come.

This explanation of the various aspects of a black hole shows the recent three-dimensional visualization.

Although writers have been imagining travel to space-based destinations for hundreds of years, the use of faster-than-light travel as a narrative device remains relatively young. As the sound barrier disappeared and the space age dawned, writers began imagining ways for interstellar travelers to cross the immensity of space. More important, audiences came to expect plausible explanations of faster-than-light travel to consider the stories credible.

Dr. Margaret A. Weitekamp is the Chair of the Museum’s Space History Department and author of “Ahead, Warp Factor Three, Mr. Sulu”: Imagining Interstellar Faster-Than-Light Travel in Space Science Fiction.” The Journal of Popular Culture 52 (2019), 1036-57.

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Quantum Physics

Title: apparent violation of causality in relativistic quantum mechanics.

Abstract: In relativistic theories the principle of microscopic causality states that ``information cannot travel faster than the speed of light'' \cite{kaku}. In the present work we show that the time evolution of relativistic wave functions violates this principle. We consider here the wave functions of massless and massive particles. In the case of massless particles the wave functions which violate the microscopic causality have an analytic form while in the case of massive particles we have to rely on numerical calculations. In both cases the wave functions which are strictly localized at $t=0$, at later times do not vanish {\it outside} the future light cone. \end{abstract}

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The Impossible Physics of Faster-Than-Light Travel

Traveling faster than light is impossible. But if it weren't, what would it look like?

Traveling faster than the speed of light is a staple of science fiction. Whether it's jumping to hyperspace, engaging the warp drive, or opening the stargate, most stories about interstellar travel have some hack to get from point A to point B faster than light.

But here in the real world, we have to obey the laws of physics. And physics is very strict about nothing moving faster than the speed of light. Or is it? While the laws of relativity forbid you and I from moving faster than light, the mathematics of relativity still work even at faster-than-light speeds. This means we can find out what it would look like if we could break the universe's speed limit.

Picture two spaceships headed from Earth to a distant star 100 light-years away. The first ship leaves at 50 percent of the speed of light, so it would take 200 years to arrive. The second ship has some kind of warp drive and leaves at twice the speed of light, 100 years after the first. What does that look like?

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In relativity, the answer depends greatly on perspective. From the Earth, it looks like one ship leaves and travels a good distance before another ship moving four times as fast overtakes it. From the perspective of the slower ship, things look a little different.

The faster-than-light ship is moving so fast that it can outrun any light that it emits. This creates a kind of 'sonic boom' made of light, which produces some interesting effects. As the warp-capable ship overtakes the slower one, and after the two ships pass each other, the light the faster ship emits is still traveling to the slower one.

The result is that the first time the slower ship can see the faster one is when they're right on top of each other. From the perspective of the slower ship, the warp ship will simply appear out of nowhere. Then, the light from two directions will reach the slower ship all at once, and it will perceive two versions of the ship moving away in both directions.

From the perspective of the slower ship, the warp ship will simply appear out of nowhere.

There are all sorts of other strange results that happen when traveling faster than light, which might be why the universe forbids it. Unfortunately, it seems likely that warp drives and hyperspace shall forever exist only in the realm of science fiction.

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What is the speed of light?

The speed of light is the speed limit of the universe. Or is it?

What is a light-year?

• Speed of light FAQs
• Special relativity
• Faster than light
• Slowing down light
• Faster-than-light travel

Bibliography

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, 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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• 06 May 2018

Electrons travel faster than light in glass

Using ultrashort laser pulses, physicists have been able to generate hot electrons that travel faster than the speed of light in a piece of glass 1 .

This opens a new avenue for understanding several areas of high-energy science ranging from laser-driven fusion to developing advanced radiation sources that have potential applications in the industrial and medical fields.

Ultrashort laser pulses, each one lasting a millionth of a billionth of a second (a femtosecond), can accelerate electrons on a solid surface to near light speeds. However, little is known about the fate of such short-lived electrons inside the solid.

An international research team, including physicists from the Tata Institute of Fundamental Science in Mumbai, India, shone ultrashort laser pulses on a glass target in a vacuum chamber placed on top of a table. The laser ejected electrons inside the glass and instantly kicked them to speeds approaching that of light.

After travelling small distances at speeds faster than that of light, the electrons dissipate energy in the glass medium. They emit Cherenkov radiation, light produced by charged particles when they pass through an optically transparent medium at speeds greater than the speed of light. They emit such radiation throughout the length of the target.

The fast electrons last 2000 times longer than the laser pulses. Theoretically speaking, this is much longer than the time they should take to traverse the target. This research is a significant step towards developing a method that will help understand hot-electron transport through solids, the researchers say.

doi: https://doi.org/10.1038/nindia.2018.58

Shaikh, M. et al . Mapping the damping dynamics of mega-ampere electron pulses inside a solid. Phys. Rev. Lett. 120 , 065001 (2018)

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Breaking the Warp Barrier for Faster-Than-Light Travel: New Theoretical Hyper-Fast Solitons Discovered

By University of Göttingen March 11, 2021

Artistic impression of different spacecraft designs considering theoretical shapes of different kinds of “warp bubbles.” Credit: E Lentz

Astrophysicist at Göttingen University discovers new theoretical hyper-fast soliton solutions.

If travel to distant stars within an individual’s lifetime is going to be possible, a means of faster-than-light propulsion will have to be found. To date, even recent research about superluminal (faster-than-light) transport based on Einstein’s theory of general relativity would require vast amounts of hypothetical particles and states of matter that have “exotic” physical properties such as negative energy density. This type of matter either cannot currently be found or cannot be manufactured in viable quantities. In contrast, new research carried out at the University of Göttingen gets around this problem by constructing a new class of hyper-fast ‘solitons’ using sources with only positive energies that can enable travel at any speed. This reignites debate about the possibility of faster-than-light travel based on conventional physics. The research is published in the journal Classical and Quantum Gravity.

The author of the paper, Dr. Erik Lentz, analyzed existing research and discovered gaps in previous ‘warp drive’ studies. Lentz noticed that there existed yet-to-be explored configurations of space-time curvature organized into ‘solitons’ that have the potential to solve the puzzle while being physically viable. A soliton – in this context also informally referred to as a ‘warp bubble’ – is a compact wave that maintains its shape and moves at constant velocity. Lentz derived the Einstein equations for unexplored soliton configurations (where the space-time metric’s shift vector components obey a hyperbolic relation), finding that the altered space-time geometries could be formed in a way that worked even with conventional energy sources. In essence, the new method uses the very structure of space and time arranged in a soliton to provide a solution to faster-than-light travel, which – unlike other research – would only need sources with positive energy densities. No “exotic” negative energy densities needed.

Image to show how long it would take different types of spacecraft to travel from our solar system to Proxima Centauri (the nearest known star). Currently, the only option would be to use a chemical rocket meaning a journey time of over 50,000 years. Credit: E Lentz

If sufficient energy could be generated, the equations used in this research would allow space travel to Proxima Centauri, our nearest star, and back to Earth in years instead of decades or millennia. That means an individual could travel there and back within their lifetime. In comparison, the current rocket technology would take more than 50,000 years for a one-way journey. In addition, the solitons (warp bubbles) were configured to contain a region with minimal tidal forces such that the passing of time inside the soliton matches the time outside: an ideal environment for a spacecraft. This means there would not be the complications of the so-called “twin paradox” whereby one twin traveling near the speed of light would age much more slowly than the other twin who stayed on Earth: in fact, according to the recent equations both twins would be the same age when reunited.

“This work has moved the problem of faster-than-light travel one step away from theoretical research in fundamental physics and closer to engineering. The next step is to figure out how to bring down the astronomical amount of energy needed to within the range of today’s technologies, such as a large modern nuclear fission power plant. Then we can talk about building the first prototypes,” says Lentz.

Currently, the amount of energy required for this new type of space propulsion drive is still immense. Lentz explains, “The energy required for this drive traveling at light speed encompassing a spacecraft of 100 meters in radius is on the order of hundreds of times of the mass of the planet Jupiter . The energy savings would need to be drastic, of approximately 30 orders of magnitude to be in range of modern nuclear fission reactors.” He goes on to say: “Fortunately, several energy-saving mechanisms have been proposed in earlier research that can potentially lower the energy required by nearly 60 orders of magnitude.” Lentz is currently in the early-stages of determining if these methods can be modified, or if new mechanisms are needed to bring the energy required down to what is currently possible.

Reference: “Breaking the warp barrier: hyper-fast solitons in Einstein–Maxwell- plasma theory” by Erik W Lentz, 9 March 2021, Classical and Quantum Gravity . DOI: 10.1088/1361-6382/abe692

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22 comments on "breaking the warp barrier for faster-than-light travel: new theoretical hyper-fast solitons discovered".

“Sufficient Energy” This already exist in the form of Element 115. If the Unauthorized Black Projects are ever revealed, word on the grapevine says its actually instantaneous. Lets go to Alpha Centaur i.

If we had that kind of energy on earth, everyone would know.

If only because that much energy in one place would have as much gravity as Jupiter.

Proposed mechanism is a propagation of a distortion of spacetime of a particular form. Thus it is ultimately very much like propagation of gravitational waves. However gravitational waves propagate with speed of light. Therefore I don’t see how it may be possible.

“Take us Out… Chekov”

The biggest form of untapped energy is at rest and stable energy. We only think of energy in it’s transitions. If we would convert the energy of stable space it is limitless.

Useful work of any kind has always, not only by man but by nature as well, only been accomplishable by exploiting an energy gradient (i.e. harnessing the movement of energy from where it is plentiful to where it is scarce). That’s what entropy is.

Find a way around that and we won’t *need* warp drives, we can simply create anything and everything we could ever want from nothing, forever.

You mean element 151…

IDK. I think it is about TIME… to find a horse of a different color. The protocols heron defined have “designed” a wonderful “horseshoe” (RELATIVELY speaking) and are busy trying to fit it to an elephant just because it’s in the ROOM: where time and space are limited… TIME to leave the womb… er… ROOM. Which is to say: Star Trekking is a fantasy, a phantasm and a FICTION devised inside a “boxy” Universe, whose PHYSICS seem to conform to the BIAS of Mortality (TIME is the limiting factor). It engenders HASTE in seeking a solution: We are “on the run”, desperately looking for a way to boldly go where no HUMAN has gone before. Good LUCK with that. Back to the Horseshoe, in want of a “NAIL”. As DANTE writ above the GATES of Hell: “Abandon ye all HOPE who enter here:” Where strayeth the MIND the FEET will follow. But it’s not about Feet, or Miles or Light Years. SINGULARITIES ALL: Infinite acceleration = Infinite ENTROPY. One is effectively DEAD in the water, while the proverbial WORM in the HOLE has a feast. It’s about standing still in the STREAM of Time, while SPACE flows on around ONE: A STREAM where the banks are in motion as well. It’s about being IN the FIELD and NOT UNDER IT. No need for flesh-liquifying SPEED. Think about it… In the meantime, ring up ACME Fireworks Inc. Ask for the “Wile E Coyote” Package. Next stop: Alpha CENTAURI… now passing URANUS on the way out of here. WARP NINE MISTER WARF. MAKE IT SO. Walk the World Round and wind up where you started from. FEET again. It is the ultimate Circular Argument of Intent in a two-dimensional UNIVERSE, OUTSIDE of TIME. The FABRIC of a DREAM…

A very small craft might be fitted with a very high power drive. A craft of 100m radius is mentioned. Eventually we will miniaturize the craft.

I totally agree with you because no way would time ever change no matter how much energy is used in traveling. The most important aspect of this research as I’m working on is understanding hot and cold. Gravity and acceleration of planet and stars to then making a mechanism that can trick the universe into believing the mechanism behavior is indeed faster heavier or lighter then what would be expected for such a device on Earth. Artificial takes new meaning with my studies and I wish you all the best likewise.

Warp drive or not we are not ready until we are one we will never understand we will never be welcomed to intelligent beyond earth I believe ther are watching.

At the present time nothing is faster than light, but there is! It’s always been here watch! The Sun’s light takes about 8 minutes to arrive to earth. If I (THINK) about the sun to earth I have beat the light travel. Human thought is faster than light. Just for thought. Now let’s get down to business. WARP DRIVE can be achieved. Anti-gravity is negative energy. Loaded in darkness of space. What u need in space is large amounts of gravity to pull or accelerate. Warp Drive is a push pull in a sense. A laser SCOPE can achieve this. Space/time bends light as u know, riding on a laser beam moving to a point of reference (sun) gives u the positive gravity neccessary inside the bubble to move. In theory the light is behind you. Still within einstein’s theory.more to say later see ya

The illustration atop this page is an excellent example of WHY artists impressions are NOT useful is the discussion of science.

Put most simply : there is no data, yet there IS an illustration… of SOMETHING, that means nothing. What is there to learn from this?

We Warp Drive manufacturing, our fission-annihilation antigravity propulsion accelerate to lightspeed, but by nuclear annihilation reaction generate high-density time-space, so from outside observation, we traveling on higher speed. The best is to travel outside of the galactic disk for maximum speed. To understand advanced physic is necessary to first understand the Theory of Relativity. Sped of light is constant only in the frame, outside dependant on the speed of time.

Chris m exactly..rest energy would be the best for getting us out of this area..it’s the ink pen vs pencil problem.spend tons of cash on writing with a pen or use a pencil for $.05.we already have the oxygen thing worked out..I say we just jump on in and figure it out as we go haha

Why not look into the idea like the Enterprise u already have this ISS up there why not try to buid a space hanger to build the ship like the Enterprise in it we have the technology to do it and while ship was getting built u cold work on the warp drive engines to power it this is the 21st century we should be thinking on lines like that im not saying theres vulcans or klingonns out there but with a ship like that we might get to see if we are alone in this galaxy or not

This would also allow for sub-light speed as well with I am assuming lesser energy requirements. Works be with losing for just to get around the solar system faster

How do we stop this spaceship?

by “breaking” the warp bubble in advance by a few nano seconds. lowering the space ship to sub light speeds temporarily.

Just traveling at light speed would be an accomplishment, yet no one talks about sailing on waves of gravity which would take much less energy. Even though warp speed is faster, we should probably walk before we run.

faster than light propulsion and anti-gravity

https://pronewsreport.com/2021/05/31/antigravity-flying-saucer-for-solar-system-exploration/

Antimatter for Antigravity and Faster than Light Propulsion

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How to destroy a black hole

A black hole would be tough to destroy, but in the season two premiere of Dead Planets Society our hosts are willing to go to extremes, from faster-than-light bombs to time travel

By Leah Crane

16 April 2024

Dead Planets Society is a podcast that takes outlandish ideas about how to tinker with the cosmos – from snapping the moon in half to causing a gravitational wave apocalypse – and subjects them to the laws of physics to see how they fare. Listen on Apple , Spotify or on our podcast page .

Dead Planets Society is back for season two, and our intrepid hosts Chelsea Whyte and Leah Crane are going after the toughest adversaries in the universe: black holes. These cosmic behemoths are so big and so sturdy that they can devour pretty much anything that is thrown at them without so much as flinching – so is it even possible to destroy one?

Black holes are expected to evaporate on their own thanks to Hawking radiation , a process by which they emit a slow leak of particles, but this would take much longer than the age of the universe to happen naturally. Just waiting isn’t really an option, so our hosts are joined by black hole astronomer Allison Kirkpatrick at the University of Kansas in an attempt to find a faster way.

Throwing anything at the black hole won’t really help either, whether it is a planet made of TNT or clumps of antimatter – the black hole will just swallow it up and get even more massive.

That doesn’t mean it is impossible to dream up something that would destroy a black hole by falling in . The escape velocity of a black hole – the speed at which one would have to fly away from its centre to escape its gravitational influence – is faster than the speed of light, so a ship that could travel beyond that physical limitation might be able to escape, or a bomb that could explode faster than the speed of light might be able to make a dent.

That is only the beginning of the outlandish ways to potentially wreck a black hole. Theoretical objects called white holes might work, but that could mean sending the black holes back in time, which wouldn’t be great for the past or the future.

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A black hole could perhaps be stretched out, but whether that works depends on the question of how quantum mechanics and general relativity mesh together, which may be the biggest unsolved question in physics. Our hosts find that giant magnets could help, with potentially horrifying results.

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+3.8% excluding

food and energy

+3.5% in March

Jeanna Smialek

What to know about the surprisingly strong inflation report.

A closely watched measure of inflation remained stronger than expected in March, worrying news for Federal Reserve officials who have become increasingly concerned that their progress on lowering price increases might be stalling.

The surprisingly stubborn inflation reading raised doubts among economists about when — and even whether — the Fed will be able to start cutting interest rates this year.

The Consumer Price Index climbed 3.8 percent on an annual basis after stripping out food and fuel prices, which economists do in order to get a better sense of the underlying inflation trend. That “core” index was stronger than the 3.7 percent increase economists had expected, and unchanged from 3.8 percent in February. The monthly reading was also stronger than what economists had forecast.

Counting in food and fuel, the inflation measure climbed 3.5 percent in March from a year earlier, up from 3.2 percent in February and faster than what economists have anticipated. A rise in gas prices contributed to that inflation number.

This week’s inflation figures come at a critical juncture for the Fed. Central bankers have been hoping to confirm that warmer-than-expected inflation figures at the start of the year were just a seasonal quirk, not evidence that inflation is getting stuck well above the 2 percent inflation target. Wednesday’s report offers little comfort that the quick early 2024 readings have not lasted.

“It is what it is: It’s a stronger than expected number, and it’s showing that those price pressures are strong across goods and services,” said Blerina Uruci, chief U.S. economist at T. Rowe Price. “It’s problematic for the Fed. I don’t see how they can justify a June cut with this strong data.”

Policymakers have made it clear in recent months that they want to see further evidence that inflation is cooling before they cut interest rates. Fed officials raised borrowing costs to 5.3 percent in 2022 and mid-2023, which they think is high enough to meaningfully weigh on the economy. Central bankers forecast in March that they will cut interest rates three times this year.

But Fed officials do not want to cut rates before they are confident inflation is on track to return to normal. Lowering borrowing costs too early or too much would risk allowing price increases to pick back up. And if households and businesses come to expect inflation to remain slightly higher, officials worry that could make it even harder to stamp out down the road.

That threat of lingering inflation has become a more serious concern for policymakers since the start of the year. Inflation flatlined in January and February after months of steady declines, raising some alarm at the Fed and among forecasters. Going into the year, investors expected the Fed to cut rates sharply in 2024 — to about 4 percent — but have steadily dialed back those expectations . Investors have recently begun to expect just two or three rate cuts.

Stocks futures dropped sharply following the inflation release as investors further pared back their expectations for lower rates.

Investors would like to see lower interest rates, which tend to bolster prices for assets like stocks. But the Fed might struggle to explain why it is cutting rates at the current moment: Not only is inflation showing signs of getting stuck well above the central bank’s target, but the economy is growing at a fairly rapid pace and employers are hiring at a robust clip.

In short, the Fed’s policies do not appear to have pushed America to the brink of a recession — and in fact, there are signs that they may not be having as much of an effect as policymakers had expected when it comes to growth.

While the Fed officially targets Personal Consumption Expenditures inflation , a separate measure, the Consumer Price Index report released on Wednesday comes out earlier and includes data that feeds into the other metric. That makes it a closely watched signal of how price pressures are shaping up.

The inflation report’s details offered little reason to dismiss the gauge’s continued stubbornness as a fluke. They showed that housing inflation remains firm, auto insurance costs picked up at a rapid pace and apparel prices climbed.

In a development that is likely to be especially notable for Fed officials, a measure of services inflation contributed to the pickup in annual inflation. Policymakers watch those prices closely, because they can reflect the strength of the underlying economy and because they tend to persist over time.

The question, increasingly, is whether Fed officials can cut interest rates at all this year in a world where inflation appears to be flatlining.

Ms. Uruci said that with every month inflation stays stubborn, the Fed may need to see more convincing evidence — and a more sustained return to deceleration — to feel confident that price increases are genuinely coming under control.

If the Fed does not cut rates soon, the election could make the start of reductions more politically fraught. Central bankers are independent of the White House and typically insist that they do not make policy with an eye on the political calendar.

Still, cutting in the months just before the election could put policymakers under a partisan spotlight : former President Donald J. Trump, the presumptive Republican nominee, has already painted possible rate cuts as a political ploy to help Democrats.

But given inflation’s unexpected staying power, the Fed is likely to want to take its time in adjusting policy. Kathy Bostjancic, Nationwide’s chief economist, said that rate cuts could now be delayed to this autumn — if they happen in 2024 at all.

“We now think September, if they start to cut rates, is more likely than July,” Ms. Bostjancic said. “It shakes the confidence that inflation is on this downward trend.”

Joe Rennison

Wall Street shudders on signs of unexpectedly strong inflation.

Signs of stubborn inflation rattled Wall Street on Wednesday, with stock prices sliding and government bond yields, which underpin interest rates throughout the economy, jolting higher.

The S&P 500 fell almost 1 percent. Other major indexes, including the tech-heavy Nasdaq Composite and the Russell 2000 index of smaller companies, also fell.

The moves followed a consumer inflation report that came in hotter than expected, with prices rising 3.5 percent in March from a year earlier, marking another month of stubbornly high inflation. That made it harder for investors to dismiss earlier signs that the progress in cooling inflation was patchy.

“The stalled disinflationary narrative can no longer be called a blip,” said Seema Shah, chief global strategist at Principal Asset Management.

That means the Federal Reserve could keep interest rates — the central bank’s primary tool for fighting inflation — elevated for longer.

Bets on a rate cut in June have dwindled since the data was released, pushing the first expected cut back later in the year. In January, investors had thought the Fed could cut rates as early as March.

So far this year, the fading prospects for rate cuts, which would be seen as supportive for the stock market, have yet to derail a tremendous rally that has taken hold in recent months. But some analysts question how long that can continue, with higher rates eventually squeezing consumers and crimping corporate earnings in a more significant way.

The two-year Treasury yield, which is sensitive to changes in interest rate expectations, lurched toward 5 percent on Wednesday, a threshold it hasn’t breached since November. The dollar gained about 1 percent against a basket of other major currencies — a major move in that market — as the prospect of U.S. rates remaining high made the dollar more attractive to global investors.

“The Fed is not done fighting inflation and rates will stay higher for longer,” said Torsten Slok, chief economist at the investment giant Apollo, adding that he does not expect any cuts to interest rates this year.

Even as many investors noted that the economy remained resilient, the fresh inflation numbers appeared to dim the outlook just as Fed officials had started gaining confidence in their ability to wrangle inflation nearer to their 2 percent target.

Lindsay Rosner, head of multi-sector investing at Goldman Sachs Asset Management, said the data did not “eclipse” the Fed’s confidence.

“It did, however, cast a shadow on it,” she said.

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The economists I’ve talked to this morning are pushing back their rate-cut expectations based on today’s report. And for some, it’s not just a matter of expecting a July or September move instead of a June one: A few think it’s increasingly likely that the Fed won’t lower rates at all this year.

The logic here is that if officials don’t cut rates this summer, it might be optically tricky to begin doing so just before the election. “If they don’t go in July, are they going to really go in September? It’s like: If not June, then July. And if not July, then December,” Neil Dutta at Renaissance Macro told me.

J. Edward Moreno

Energy prices rose in March.

The price of energy continued to rise in March, driven in part by geopolitical risks that have pushed up the price of oil, contributing to a stronger-than-expected pace of inflation.

Wars in Ukraine and the Middle East have caused the price of Brent crude oil, the international benchmark, to rise more than 20 percent since mid-December. That rise may have been reflected in the inflation data: Energy prices rose 1.1 percent month over month and 2.1 percent year over year.

The price of gasoline rose 1.7 percent in March and 1.3 percent over the past year. Gas prices rose at a sharper rate in February, at 3.8 percent, but had declined for four months prior.

The Federal Reserve tends to ignore moves in gas prices in the short term, because fuel is volatile and responds more to global developments than to domestic economic policy. Even so, higher gas costs are felt acutely by consumers and can eventually bleed into other types of inflation — pushing up transportation costs like airline fares, for instance.

The price of utilities rose 0.7 percent in March and 3.1 percent year over year.

Electricity prices rose nearly 1 percent in March and have gone up 5 percent in the past year. Gas utility prices were flat in March and have fallen 3.2 percent in the past year.

Jim Tankersley

A hot inflation report is a blow to President Biden.

President Biden said on Wednesday that he still expected the Federal Reserve would cut interest rates this year despite a re-acceleration in price growth across the economy, though he said new data suggested that cut might be pushed to later in the year.

“I do stand by my prediction that before the year is out, there will be a rate cut,” Mr. Biden said at a news conference alongside Prime Minister Kishida Fumio of Japan, after the two of them met at the White House.

“This may delay it a month or so — I’m not sure of that,” Mr. Biden said. “We don’t know what the Fed is going to do for certain. But look, we have dramatically reduced inflation.”

Mr. Biden’s comments dipped a toe into what has historically — with notable exceptions — been a taboo subject for presidents: weighing in on Fed policy. Many of Mr. Biden’s predecessors have refrained from even speculating about interest-rate decisions, citing the Fed’s independence. The president’s immediate predecessor and now re-election opponent, Donald J. Trump, broke from that history, by frequently and loudly criticizing the Fed when he was president and demanding the central bank to reduce interest rates.

Mr. Biden’s aides talk frequently about the need for the central bank to remain independent. His comments, even though they were more in the vein of punditry than directive, risked, albeit slightly, blurring that line.

Mr. Biden has been banking on cooling inflation — and ensuing rate cuts — to lift his re-election prospects.

The president and his aides have publicly cheered the retreat of annual inflation rates over the past year, after watching the fastest price growth in 40 years dent the president’s approval ratings earlier in his tenure.

They have been anxious for inflation to fall even further, in order give relief to consumers and to potentially spur the Federal Reserve to cut interest rates — a move that would help to drive down borrowing costs for mortgages, car loans and other consumer credit. Mr. Biden has been particularly focused on home buyers, including young voters who are key to his electoral coalition, and who are struggling to afford high housing prices as mortgage rates remain around 7 percent.

Wall Street analysts saw Wednesday's surprise pickup in the inflation rate as a sign that the Fed could leave rates on hold for months longer than expected. That could mean no cuts before the November election, a campaign where Mr. Biden’s Republican opponent, former President Donald J. Trump, has slammed Mr. Biden for both rapid price increases and high borrowing costs.

The news comes as polls have begun to show Americans’ views of the economy slowly improving over recent months. Democratic pollsters have also pointed to recent surveys as a road map for how Mr. Biden should talk about inflation in the months to come: They suggest American voters blame corporate greed, more than government spending, for price increases. Mr. Biden has leaned into that message, including calling out companies in his State of the Union address for keeping prices high.

He struck a similar tone on Wednesday in a statement that emphasized consumer frustration with inflation.

“Prices are still too high for housing and groceries, even as prices for key household items, like milk and eggs, are lower than a year ago,” Mr. Biden said. “I have a plan to lower costs for housing — by building and renovating more than two million homes — and I’m calling on corporations, including grocery retailers, to use record profits to reduce prices.”

Madeleine Ngo

After the report’s release, President Biden said his administration was making progress on fighting inflation, but there was still work to be done.

“Prices are still too high for housing and groceries, even as prices for key household items like milk and eggs are lower than a year ago,” Mr. Biden said. “I have a plan to lower costs for housing — by building and renovating more than 2 million homes — and I’m calling on corporations including grocery retailers to use record profits to reduce prices.”

Lydia DePillis

Julia Pollak, chief economist for the job search website ZipRecruiter, noted that inflation’s remedy — high interest rates — actually props up one of the largest drivers of price increases. “Rapidly rising housing costs continue to be the economy’s Achilles heel — and the inventory crunch brought about by mortgage rate hikes isn’t exactly helping,” she wrote.

One way of looking at goods inflation is to divide it into durables, like cars and furniture, and nondurables, like food and clothing. Durables have been coming down in price gradually, but nondurables are still near their peak, and are up 1.7 percent over the year.

Driven in part by rapid population growth, price increases have been swiftest in the South, at 3.8 percent over the past year versus 2.8 percent in the Midwest. Across cities, the Labor Department highlighted inflation in Dallas at 4.9 percent since last March, and Minneapolis at only 2.7 percent.

Talmon Joseph Smith

The core inflation rate “surprised to the upside" because of some auto-related categories, like insurance, repair and leased cars, said Omair Sharif of the firm Inflation Insights, adding that “auto insurance doesn’t show any signs of slowing down.”

There has been a lot of talk about how the data on shelter costs was “lagged,” mostly reflecting rent increases from 2022. But, for now, those expected lags are not unfurling. According to the latest data, the rise in the index of shelter costs was the largest factor in the monthly increase in the "core" inflation measure.

Good news for parents: The price of toys, which had been dropping through the late 2010s and flattened out during the pandemic, has resumed its downward slide and is now 8.2 percent lower over the year.

Ben Casselman

Housing costs continued to rise faster than before the pandemic.

Inflation’s most stubborn category remained stubborn last month.

Housing costs rose 0.4 percent in March and were up 5.7 percent from a year earlier, both unchanged from the month before. Shelter inflation has cooled since last year, when it peaked at more than 8 percent, but lately that progress has slowed.

Housing is by far the largest monthly expense for most families, which means it also weighs heavily in inflation calculations. Shelter accounts for more than a third of the Consumer Price Index, meaning it will be difficult for the Federal Reserve to tame inflation fully as long as housing costs continue to rise at their recent rate. Before the pandemic, shelter costs rose at a rate of about 3.5 percent per year.

Housing costs in the Consumer Price Index are based on rents. Economists have been expecting housing inflation to cool because of data from companies like Zillow and Apartment List showing rents rising more slowly or even falling outright in some markets.

The government’s rent index tends to move more slowly than the private-sector measures because of methodological differences, but economists have been surprised by how long the gap has persisted.

Most forecasters still believe the rent slowdown will show up in the government’s official measures eventually. But a few have begun to wonder if changes in the housing market, alongside demographics and other forces, could cause housing costs to continue to rise at a faster pace than before the pandemic. That would be bad news for the Fed because it would mean that prices in other parts of the economy would have to rise more slowly in order for overall inflation to return to its long-run target.

“This strength in shelter inflation, it’s concerning and somewhat puzzling,” said Blerina Uruci, chief U.S. economist at T. Rowe Price.

Capital Economics’ Chief North America economist Paul Ashworth wrote in a note that the report “pretty much kills off hopes of a June rate cut from the Fed,” noting that expected drops in rental costs haven’t manifested.

Food inflation remained relatively unchanged in March. Overall, food prices climbed 0.1 percent from the prior month, a slight increase from February, when prices were flat. Grocery prices were also flat for the second straight month.

Egg prices, however, continued to climb at a relatively rapid rate. In March, egg prices rose 4.6 percent over the month. That was still down from the previous month, though, when egg prices rose 5.8 percent.

Medical care services, which include hospitals and health insurance, are another factor propping up the index. After sagging in 2022 and 2023, they turned around over the past six months and are now up 2.1 percent over the year.

Food inflation remained relatively unchanged in March.

Food price gains remained relatively unchanged in March, providing little relief for consumers struggling to deal with higher food costs.

Overall, food prices climbed 0.1 percent from the prior month. That is a slightly faster rate than February, when prices were flat.

Grocery prices were flat for the second straight month. The cost of dining out climbed 0.3 percent, an increase from 0.1 percent in February.

Compared to a year earlier, food inflation rose at the same rate it did in February. Although the annual rate had been moderating for several months, food prices were up 2.2 percent for the second straight month.

Prices for fruits and vegetables increased 0.1 percent over the month after they fell 0.2 percent in February. Meats, poultry and fish prices rose 0.6 percent, up from February, when prices declined 0.3 percent. Costs for dairy and related products declined 0.1 percent in March.

Egg prices continued their ascent, although they increased at slower rate than February. In March, egg prices rose 4.6 percent from the month before, down from February, when egg prices climbed 5.8 percent. Economists have largely attributed the recent uptick in egg prices to avian influenza outbreaks . Although bird flu outbreaks also contributed to a big surge in egg prices early last year, prices have not risen as much as they did then. Egg prices are still down 6.8 percent over the past year.

Food inflation has cooled over the past several months as transportation and raw material costs have moderated. The cost of eating at restaurants, however, has been slower to ease because higher labor costs continue to put pressure on business owners.

Economists said they expected to see overall food inflation continue to ease in the coming months. Still, many consumers continue to struggle with higher food prices, and some surveys have found that consumer estimates of food inflation were significantly higher than actual figures.

“Americans are overestimating food price inflation, not just by a little, but by a lot,” said Joseph Balagtas, a professor of agricultural economics at Purdue University.

Some economists have said that consumers might not be feeling much relief because food prices are much higher than they were several years ago. Although overall food prices have been increasing at a slower rate in recent months, they are still up about 25 percent compared to four years ago.

The dollar is up about 0.6 percent against a basked other currencies, as investors expect higher interest rates to stick around for longer. Higher rates make the dollar more attractive for foreign investors trying to profit from the higher costs of borrowing, pushing up the value of the dollar.

“It is what it is: It’s a stronger than expected number, and it’s showing that those price pressures are high across goods and services. So I think it’s problematic for the Fed,” said Blerina Uruci, chief U.S. economist at T. Rowe Price.

The story is more encouraging for motor vehicles. Prices for new cars and trucks have been essentially flat for the past year, while used vehicles continued their bumpy decline, dropping 1.1 percent over the month.

In some evidence that the goods disinflation that we’ve been seeing might be stalling out, apparel prices rose a surprising amount, at 0.7 percent over the month. The increase was driven by girls’ clothing, which had been decreasing in price, while boys’ clothing had never dropped much.

Investors had appeared to shift their focus recently to the strength of the economy rather than on inflation’s stubbornness. These numbers will test their resolve, prompting a re-evaluation of how long interest rates will stay high and, as a result, how long the screws will be turned on the economy.

One of the strongest categories in March was transportation services, which rose 1.5 percent over the month. It was driven primarily by motor vehicle repair and insurance costs, which my colleague Talmon wrote in February were surging as insurers took big rate increases.

Investors reacted swiftly to the new numbers, with futures on the S&P 500 sliding by as much as 1 percent. Investors also appear to expect interest rates to stay higher to tame stubborn inflation, with the two-year Treasury yield, which is sensitive to changes in interest rate expectations, rising sharply to 4.9 percent.

“This number did not eclipse the Fed’s confidence, it did, however, cast a shadow on it,” said Lindsay Rosner, head of multi-sector investing at Goldman Sachs Asset Management.

Consumer prices rose 0.4 percent in March and were up 3.5 percent from a year earlier. “Core” prices, which exclude the volatile food and fuel categories, were up 0.4 percent from February and 3.8 percent from a year earlier.

These numbers are hotter than what forecasters expected, and definitely not what the Fed was looking for.

One thing not to worry too much about? Inflation is expected to pick up on an overall annual basis, to 3.4 percent from 3.2 percent previously. That’s largely because of gas prices, which matter a lot for customers but which bounce around so much that economists mostly ignore them in the short run.

Stanley Reed

What’s behind the recent rise in oil prices.

Oil prices have climbed in recent weeks, spurred by concerns over supplies and geopolitical risks, including wars in Ukraine and the Middle East. Analysts say the momentum could carry prices higher.

The price of a barrel of Brent crude oil, the international benchmark, has risen more than 20 percent since mid-December. It has jumped more than 10 percent over the past month alone, to around $90 per barrel. “The sentiment is really bullish,” said Viktor Katona, an analyst at Kpler, a commodities research firm.

Rising oil prices could make efforts by central banks to reduce inflation more challenging. In the United States, higher gasoline prices during the summer driving season would also be unwelcome for the Biden administration, which faces a difficult election in November. The average price at the pump has risen about 50 cents per gallon since early January, to around $3.70, according to the Energy Information Administration.

The price of gold, seen as a hedge against inflation, has hit new highs.

Wall Street is puzzled.

Gold, typically seen as a haven in periods of economic turmoil, especially as a hedge against inflation, has risen sharply in price over the past month, even as the outlook for the economy has improved and inflation, although still elevated, is well below recent highs.

The precious metal has set a series of record highs as it surged roughly $300, to $2,350 per troy ounce, since the start of March.

The move has been attributed, at least in part, to a burst of gold buying from central banks around the world, including China. But investors said that central bank purchases did not fully explain such a sudden price increase.

“It’s perplexing to anybody in the gold market,” said Chris Mancini, a gold portfolio manager at Gabelli Funds.

He noted that exchange-traded funds, a type of investment vehicle that trades publicly like a stock, had been suffering withdrawals from investors, which is usually a warning sign for gold watchers. And in futures markets, which are derivatives linked to the price of gold, demand had remained muted until the start of this month when some money managers began buying, official data showed.

And that still does not explain how the rally got started, with some speculation that tumultuous geopolitics are driving public and private investments in gold.

“All we can point to is that it is physical demand from somewhere that is not being picked up in the data we see,” Mr. Mancini said.

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Travel could be a good deal this summer. Here's when plane ticket prices will peak.

Spring is springing, and according to Hopper, it’s time to start thinking about your summer vacation plans.

New data from the online booking site shows some favorable trends for travelers in the next few months, including slightly lower airfares compared with 2023 and hotel and car rental prices that are more or less flat year-over-year.

Here’s what you need to know as you prepare to book, whether you’re looking for a domestic getaway or go on an overseas adventure. It’s also not too late to take advantage of deals on some last-minute trips.

How much are spring and summer plane tickets?

According to Hopper, the best deals right now are on domestic airline tickets. Round-trip flights within the U.S. are averaging $290 in April, but prices are expected to rise in the months ahead.

Hopper’s data shows prices for domestic flights will peak between May and June at $315 on average, then will gradually fall through the summer, reaching a low of $264 on average in September.

On a call with investors discussing first-quarter earnings Wednesday, Delta Air Lines CEO Ed Bastian said summer travel demand has been pushed forward in recent years in part because schools, especially in the South, are finishing their summer breaks earlier in the year.

Is airport Wi-Fi safe to use? How to keep your information safe while traveling.

Short vs. long cruises: Which one is right for you? Here's how they compare.

This summer also will be a good time to travel internationally; Hopper data shows fares to most destinations abroad are down compared with last year. 

“Airfare to international destinations continues to improve following two years of bloated prices due to quickly recovering demand, high fuel prices and supply constraints. Airfare to most major regions of the world has dropped compared to last year with the exception of trips to Canada,” Hayley Berg, Hopper’s chief economist, said in the report. “International fares remain higher than pre-pandemic levels to most regions, as higher fuel prices persist and airlines continue to rebuild capacity to many regions.”

How much will a hotel room for the spring and summer cost?

Hotel prices remain mostly flat compared with the same time last year. Rooms in the U.S. are averaging $206 a night; better deals are available in some trending international destinations like Osaka, Japan, and Istanbul, Turkey.

According to Hopper, Las Vegas, New York and Chicago remain popular destinations in the U.S.

Will car rental prices rise this summer?

Car rental prices also haven’t increased much since last year and average $42 a day, according to Hopper.

The report shows most travelers rent a car for about four days, and warm-weather destinations like Orlando and Los Angeles remain popular pickup points.

Zach Wichter is a travel reporter for USA TODAY based in New York. You can reach him at [email protected].