light can travel in vacuum a distance of about

What is the speed of light?

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

graphic representing the speed of light showing lines of light of different colors; blue, green, yellow and white.

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 . 

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

Get the Space.com Newsletter

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

Vicky Stein

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. 

Rare 11th-century star chart reveals complex history of Islamic, Jewish and Christian astronomy

NASA's tiny CAPSTONE probe celebrates 450 days in orbit around the moon

Save 28% on these Celestron EclipSmart solar binoculars ahead of the April 8 solar eclipse

Most Popular

By Conor Feehly January 05, 2024

By Keith Cooper December 22, 2023

By Fran Ruiz December 20, 2023

By Fran Ruiz December 19, 2023

By Fran Ruiz December 18, 2023

By Tantse Walter December 18, 2023

By Robert Lea December 05, 2023

By Robert Lea December 04, 2023

By Robert Lea December 01, 2023

By Rebecca Sohn November 27, 2023

By Fran Ruiz November 21, 2023

  • 2 Stunning images from Very Large Telescope capture unique views of planet formation
  • 3 Sony FE 16-35mm f/2.8 GM II lens review
  • 4 Rare 11th-century star chart reveals complex history of Islamic, Jewish and Christian astronomy
  • 5 'Constellation' creators on ghostly voices and piecing together a satisfying sci-fi puzzle (exclusive)

Does Light Travel Forever?

Most recent answer: 01/23/2013

Hi Raja, Good question. First, let's think about why sound does not travel forever. Sound cannot travel through empty space; it is carried by vibrations in a material, or medium (like air, steel, water, wood, etc). As the particles in the medium vibrate, energy is lost to heat, viscous processes, and molecular motion. So, the sound wave gets smaller and smaller until it disappears. In contrast, light waves can travel through a vacuum, and do not require a medium. In empty space, the wave does not dissipate (grow smaller) no matter how far it travels, because the wave is not interacting with anything else. This is why light from distant stars can travel through space for billions of light-years and still reach us on earth. However, light can also travel within some materials, like glass and water. In this case, some light is absorbed and lost as heat, just like sound. So, underwater, or in our atmosphere, light will only travel some finite range (which is different depending on the properties of the material it travels through). There is one more aspect of wave travel to consider, which applies to both sound and light waves. As a wave travels from a source, it propagates outward in all directions. Therefore, it fills a space given approximately by the surface area of a sphere. This area increases by the square of the distance R from the source; since the wave fills up all this space, its intensity decreases by R squared. This effect just means that the light/sound source will appear dimmer if we are farther away from it, since we don't collect all the light it emits. For example, light from a distant star travels outward in a giant sphere. Only one tiny patch of this sphere of light actually hits our eyes, which is why stars don't blind us! David Schmid

(published on 01/23/2013)

Follow-Up #1: How far does light go?

Light just keeps going and going until it bumps into something.  Then it can either be reflected or absorbed.  Astronomers have detected some light that has been traveling for more that 12 billion years, close to the age of the universe.   

Light has some interesting properties.   It comes in lumps called photons.  These photons carry energy and momentum in specific amounts related to the color of the light.  There is much to learned about light.   I suggest you log in to our website and type  LIGHT into the search box.   Lots of interesting stuff there.

To answer your previous question "Can light go into a black hole?" ,  the answer is yes.

(published on 12/03/2015)

Follow-Up #2: less than one photon?

Certainly you can run the ouput of a single-photon source through a half-silvered mirror, and get a sort of half-ghost of the photon in two places. If you put ordinary photon detectors in those places, however, each will either detect zero or one. For each source photon, you'll get at most one of the detectors to find it. How does the half-ghost at the other one know whether it's detectably there or not? The name of that mystery is "quantum entanglement". At some level we don't really know the answer.

(published on 02/04/2016)

Follow-Up #3: stars too far away to see?

Most stars are too far for us to see them as individual stars even with our best telescopes. Still, we can get light from them, mixed with light from other stars. If our understanding of the universe is at all right, there are also stars that once were visible from here but now are outside our horizon so no light from them reaches us. It's probable that there are many more stars outside our horizon than inside, maybe infinitely more. It's hard to check, however, what's happening outside our horizon! It's even hard to define what we mean by "now" for things outside the horizon.

(published on 07/22/2016)

Follow-Up #4: light going out to space

Certainly ordinary light travels out to space. That's how spy cameras and such can take pictures of things here on the Earth's surface.

(published on 09/01/2016)

Follow-Up #5: end of the universe?

We don't think there's any "end" in the sense of some spatial boundary. Unless something changes drastically, there also won't be an end in time. The expansion looks like it will go on forever. So that wouldn't give a maximum range.

(published on 03/26/2017)

Follow-Up #6: seeing black holes

In principle a well-aimed beam would loop around the outside of the black hole and return to Earth. There aren't any black holes close enough to make this practical. Instead the bending of light by black holes is observed by their lensing effect on light coming from more distant objects.

The amazing gravitational wave signals observed from merging black holes provide even more direct and convincing proof that black holes exist and follow the laws of General Relativity.

(published on 01/29/2018)

Follow-up on this answer

Related Questions

  • Can you use light to attract or repel an item?
  • Absorption of short light pulses
  • light from Hiroshima
  • light dependent switches
  • Would a tin-can phone work in space?
  • refraction and reflection
  • light reflection from glass
  • light from old sources
  • Seeing reflected and emitted light
  • Speed of light in various directions

Still Curious?

Expore Q&As in related categories

  • Properties of Light
  • Properties of Sound

The Nature of Light

Introduction.

Light is a transverse, electromagnetic wave that can be seen by the typical human. The wave nature of light was first illustrated through experiments on diffraction and interference . Like all electromagnetic waves, light can travel through a vacuum. The transverse nature of light can be demonstrated through polarization .

  • In 1678, Christiaan Huygens (1629–1695) published Traité de la Lumiere , where he argued in favor of the wave nature of light. Huygens stated that an expanding sphere of light behaves as if each point on the wave front were a new source of radiation of the same frequency and phase.
  • Thomas Young (1773–1829) and Augustin-Jean Fresnel (1788–1827) disproved Newton's corpuscular theory.

Light is produced by one of two methods…

  • Incandescence is the emission of light from "hot" matter (T ≳ 800 K).
  • Luminescence is the emission of light when excited electrons fall to lower energy levels (in matter that may or may not be "hot").

Just notes so far. The speed of light in a vacuum is represented by the letter c from the Latin celeritas — swiftness. Measurements of the speed of light.

Veramente non l'ho sperimentata, salvo che in lontananza piccola, cioè manco d'un miglio, dal che non ho potuto assicurarmi se veramente la comparsa del lume opposto sia instantanea; ma ben, se non instantanea, velocissima….   In fact I have tried the experiment only at a short distance, less than a mile, from which I have not been able to ascertain with certainty whether the appearance of the opposite light was instantaneous or not; but if not instantaneous it is extraordinarily rapid ….       Galileo Galilei, 1638 Galileo Galilei, 1638

Ole Rømer (1644–1710) Denmark. "Démonstration touchant le mouvement de la lumière trouvé par M. Roemer de l'Académie des Sciences." Journal des Scavans . 7 December 1676. Rømer's idea was to use the transits of Jupiter's moon Io to determine the time. Not local time, which was already possible, but a "universal" time that would be the same for all observers on the Earth, Knowing the standard time would allow one to determine one's longitude on the Earth — a handy thing to know when navigating the featureless oceans.

Unfortunately, Io did not turn out to be a good clock. Rømer observed that times between eclipses got shorter as Earth approached Jupiter, and longer as Earth moved farther away. He hypothesized that this variation was due to the time it took for light to travel the lesser or greater distance, and estimated that the time for light to travel the diameter of the Earth's orbit, a distance of two astronomical units, was 22 minutes.

  • The speed of light in a vacuum is a universal constant in all reference frames.
  • The speed of light in a vacuum is fixed at 299,792,458 m/s by the current definition of the meter.
  • The speed of light in a medium is always slower the speed of light in a vacuum.
  • The speed of light depends upon the medium through which it travels.The speed of anything with mass is always less than the speed of light in a vacuum.

other characteristics

The amplitude of a light wave is related to its intensity.

  • Intensity is the absolute measure of a light wave's power density.
  • Brightness is the relative intensity as perceived by the average human eye.

The frequency of a light wave is related to its color.

  • Color is such a complex topic that it has its own section in this book.
  • Laser light is effectively monochromatic.
  • There are six simple, named colors in English (and many other languages) each associated with a band of monochromatic light. In order of increasing frequency they are red, orange, yellow, green, blue, and violet .
  • Light is sometimes also known as visible light to contrast it from "ultraviolet light" and "infrared light"
  • Other forms of electromagnetic radiation that are not visible to humans are sometimes also known informally as "light"
  • Nearly every light source is polychromatic.
  • White light is polychromatic.

A graph of relative intensity vs. frequency is called a spectrum (plural: spectra ). Although frequently associated with light, the term can be applied to any wave phenomena.

  • Blackbody radiators emit a continuous spectrum.
  • The excited electrons in a gas emit a discrete spectrum.

The wavelength of a light wave is inversely proportional to its frequency.

  • Light is often described by it's wavelength in a vacuum .
  • Light ranges in wavelength from 400 nm on the violet end to 700 nm on the red end of the visible spectrum.

Phase differences between light waves can produce visible interference effects. (There are several sections in this book on interference phenomena and light.)

Leftovers about animals.

  • Falcon can see a 10 cm. object from a distance of 1.5 km.
  • Fly's Eye has a flicker fusion rate of 300/s. Humans have a flicker fusion rate of only 60/s in bright light and 24/s in dim light. The flicker fusion rate is the frequency with which the "flicker" of an image cannot be distinguished as an individual event. Like the frame of a movie… if you slowed it down, you would see individual frames. Speed it up and you see a constantly moving image. Octopus' eye has a flicker fusion frequency of 70/s in bright light.
  • Penguin has a flat cornea that allows for clear vision underwater. Penguins can also see into the ultraviolet range of the electromagnetic spectrum.
  • Sparrow Retina has 400,000 photoreceptors per square. mm.
  • Reindeer can see ultraviolet wavelengths, which may help them view contrasts in their mostly white environment.

Sciencing_Icons_Science SCIENCE

Sciencing_icons_biology biology, sciencing_icons_cells cells, sciencing_icons_molecular molecular, sciencing_icons_microorganisms microorganisms, sciencing_icons_genetics genetics, sciencing_icons_human body human body, sciencing_icons_ecology ecology, sciencing_icons_chemistry chemistry, sciencing_icons_atomic & molecular structure atomic & molecular structure, sciencing_icons_bonds bonds, sciencing_icons_reactions reactions, sciencing_icons_stoichiometry stoichiometry, sciencing_icons_solutions solutions, sciencing_icons_acids & bases acids & bases, sciencing_icons_thermodynamics thermodynamics, sciencing_icons_organic chemistry organic chemistry, sciencing_icons_physics physics, sciencing_icons_fundamentals-physics fundamentals, sciencing_icons_electronics electronics, sciencing_icons_waves waves, sciencing_icons_energy energy, sciencing_icons_fluid fluid, sciencing_icons_astronomy astronomy, sciencing_icons_geology geology, sciencing_icons_fundamentals-geology fundamentals, sciencing_icons_minerals & rocks minerals & rocks, sciencing_icons_earth scructure earth structure, sciencing_icons_fossils fossils, sciencing_icons_natural disasters natural disasters, sciencing_icons_nature nature, sciencing_icons_ecosystems ecosystems, sciencing_icons_environment environment, sciencing_icons_insects insects, sciencing_icons_plants & mushrooms plants & mushrooms, sciencing_icons_animals animals, sciencing_icons_math math, sciencing_icons_arithmetic arithmetic, sciencing_icons_addition & subtraction addition & subtraction, sciencing_icons_multiplication & division multiplication & division, sciencing_icons_decimals decimals, sciencing_icons_fractions fractions, sciencing_icons_conversions conversions, sciencing_icons_algebra algebra, sciencing_icons_working with units working with units, sciencing_icons_equations & expressions equations & expressions, sciencing_icons_ratios & proportions ratios & proportions, sciencing_icons_inequalities inequalities, sciencing_icons_exponents & logarithms exponents & logarithms, sciencing_icons_factorization factorization, sciencing_icons_functions functions, sciencing_icons_linear equations linear equations, sciencing_icons_graphs graphs, sciencing_icons_quadratics quadratics, sciencing_icons_polynomials polynomials, sciencing_icons_geometry geometry, sciencing_icons_fundamentals-geometry fundamentals, sciencing_icons_cartesian cartesian, sciencing_icons_circles circles, sciencing_icons_solids solids, sciencing_icons_trigonometry trigonometry, sciencing_icons_probability-statistics probability & statistics, sciencing_icons_mean-median-mode mean/median/mode, sciencing_icons_independent-dependent variables independent/dependent variables, sciencing_icons_deviation deviation, sciencing_icons_correlation correlation, sciencing_icons_sampling sampling, sciencing_icons_distributions distributions, sciencing_icons_probability probability, sciencing_icons_calculus calculus, sciencing_icons_differentiation-integration differentiation/integration, sciencing_icons_application application, sciencing_icons_projects projects, sciencing_icons_news news.

  • Share Tweet Email Print
  • Home ⋅
  • Science ⋅
  • Physics ⋅
  • Sound & Light (Physics): How are They Different?

How Does Light Travel?

Light bends at the interface of two media.

Sound & Light (Physics): How are They Different?

The question of how light travels through space is one of the perennial mysteries of physics. In modern explanations, it is a wave phenomenon that doesn't need a medium through which to propagate. According to quantum theory, it also behaves as a collection of particles under certain circumstances. For most macroscopic purposes, though, its behavior can be described by treating it as a wave and applying the principles of wave mechanics to describe its motion.

Electromagnetic Vibrations

In the mid 1800s, Scottish physicist James Clerk Maxwell established that light is a form of electromagnetic energy that travels in waves. The question of how it manages to do so in the absence of a medium is explained by the nature of electromagnetic vibrations. When a charged particle vibrates, it produces an electrical vibration that automatically induces a magnetic one -- physicists often visualize these vibrations occurring in perpendicular planes. The paired oscillations propagate outward from the source; no medium, except for the electromagnetic field that permeates the universe, is required to conduct them.

A Ray of Light

When an electromagnetic source generates light, the light travels outward as a series of concentric spheres spaced in accordance with the vibration of the source. Light always takes the shortest path between a source and destination. A line drawn from the source to the destination, perpendicular to the wave-fronts, is called a ray. Far from the source, spherical wave fronts degenerate into a series of parallel lines moving in the direction of the ray. Their spacing defines the wavelength of the light, and the number of such lines that pass a given point in a given unit of time defines the frequency.

The Speed of Light

The frequency with which a light source vibrates determines the frequency -- and wavelength -- of the resultant radiation. This directly affects the energy of the wave packet -- or burst of waves moving as a unit -- according to a relationship established by physicist Max Planck in the early 1900s. If the light is visible, the frequency of vibration determines color. The speed of light is unaffected by vibrational frequency, however. In a vacuum, it is always 299,792 kilometers per second (186, 282 miles per second), a value denoted by the letter "c." According to Einstein's Theory of Relativity, nothing in the universe travels faster than this.

Refraction and Rainbows

Light travels slower in a medium than it does in a vacuum, and the speed is proportional to the density of the medium. This speed variation causes light to bend at the interface of two media -- a phenomenon called refraction. The angle at which it bends depends on the densities of the two media and the wavelength of the incident light. When light incident on a transparent medium is composed of wave fronts of different wavelengths, each wave front bends at a different angle, and the result is a rainbow.

Related Articles

What is the formula for velocity of a wave, the famous physicist who discovered photons, how to convert hertz to nanometers, what happens to a white light when it passes through..., how does light travel from the sun to earth, why is the discovery of gravitational waves important, what is light measured in, what causes the dispersion of white light, how to convert photons to joules, how to calculate a wavenumber, how to calculate frequency in hertz, how to find resonant frequencies, what affects the angle of refraction of light, how to calculate oscillation frequency, what is the difference between radio waves & cell phone....

  • Boundless.com: Planck's Quantum Theory

About the Author

Chris Deziel holds a Bachelor's degree in physics and a Master's degree in Humanities, He has taught science, math and English at the university level, both in his native Canada and in Japan. He began writing online in 2010, offering information in scientific, cultural and practical topics. His writing covers science, math and home improvement and design, as well as religion and the oriental healing arts.

Photo Credits

Marcochow/iStock/Getty Images

Find Your Next Great Science Fair Project! GO

We Have More Great Sciencing Articles!

Wave-Particle Duality: An Overview

Physical optics vs. geometric optics: definition & differences.

It’s a wonderful world — and universe — out there.

Come explore with us!  

Science News Explores

Understanding light and other forms of energy on the move.

This radiation includes visible light, radio signals — even medical X-rays

a swirl of lights against darkness

Light is a form of energy created by the movement of electrons. Different wavelengths appear as different colors, although most wavelengths are not visible to the human eye.

Natasha Hartano/Flickr ( CC BY-NC 2.0 ); adapted by L. Steenblik Hwang

Share this:

  • Google Classroom

By Jennifer Look

July 16, 2020 at 6:30 am

Light is a form of energy that travels as waves. Their length — or wavelength — determines many of light’s properties. For instance, wavelength accounts for light’s color and how it will interact with matter. The range of wavelengths, from super short to very, very long, is known as the light spectrum. Whatever its wavelength, light will radiate out infinitely unless or until it is stopped. As such, light is known as radiation.

Light’s formal name is electromagnetic radiation. All light shares three properties. It can travel through a vacuum. It always moves at a constant speed, known as the speed of light, which is 300,000,000 meters (186,000 miles) per second in a vacuum. And the wavelength defines the type or color of light.

Just to make things interesting, light also can behave as photons , or particles. When looked at this way, quantities of light can be counted, like beads on a string.

Humans have evolved to sense a small part of the light spectrum. We know these wavelengths as “visible” light. Our eyes contain cells known as rods and cones. Pigments in those cells can interact with certain wavelengths (or photons) of light. When this happens, they create signals that travel to the brain. The brain interprets the signals from different wavelengths (or photons) as different colors.

The longest visible wavelengths are around 700 nanometers and appear red. The range of visible light ends around 400 nanometers. Those wavelengths appear violet. The whole rainbow of colors falls in between.

visible wavelengths of light

Most of the light spectrum, however, falls outside that range. Bees, dogs and even a few people can see ultraviolet (UV) light . These are wavelengths a bit shorter than violet ones. Even those of us without UV vision can still respond to UV light, however. Our skin will redden or even burn when it encounters too much.

Many things emit heat in the form of infrared light. As that name suggests, infrared wavelengths are somewhat longer than red’s. Mosquitoes and pythons can see in this range. Night-vision goggles work by detecting infrared light.

Light also comes in many other types. Light with really short, high-energy waves can be gamma rays and X-rays (used in medicine). Long, low-energy waves of light fall in the radio and microwave part of the spectrum.

electromagnetic spectrum

Desiré Whitmore is a physics educator at the Exploratorium in San Francisco, Calif. Teaching people about light as radiation can be difficult, she says. “People are afraid of the word ‘radiation.’ But all it means is that something is moving outward.”

The sun emits lots of radiation in wavelengths that span from X-rays to infrared. Sunlight provides almost all of the energy required for life on Earth. Small, cool objects release much less radiation. But every object emits some. That includes people. We give off small amounts of infrared light generally referred to as heat.

Whitmore points to her cell phone as a common source of many types of light. Smartphones use visible wavelengths to light up the screen display. Your phone talks to other phones via radio waves. And the camera has the ability to detect infrared light that human eyes cannot see. With the right app, the phone transforms this infrared light into visible light that we can see on the phone’s screen.

“This is fun to try out with your cell phone’s front-facing camera,” Whitmore says. Use a remote control for a television or other device. Its light is infrared, she notes, “so we cannot see it. But when you point the controller at your phone’s camera and press a button, “you can see a bright pink light appear on the screen!”   

“All these different types of radiation help improve our lives,” Whitmore says. They “have been shown to be safe when used in reasonable amounts,” she notes — but can be “dangerous when you use too much of it.”

More Stories from Science News Explores on Physics

an image that is filled with nothing but blueberries

Here’s why blueberries aren’t blue — but appear to be

a photo of STEVE and the green picket fence skyglows in a starry night sky. Still water refects the sky. On the far right is a typical green aurora.

The weird sky glow called STEVE is really confusing scientists

Jets of water extend out of an s-shaped sprinkler in a tank of liquid

Physics explains what happens when a lawn sprinkler sucks in water

Three images show water being poured from a teapot. The shape of the droplets is described by an effect known as Rayleigh-Plateau instability.

Physics explains why poured water burbles the way it does

light can travel in vacuum a distance of about

Scientists Say: 2-D Material

The produce section of a grocery store with lots of fruit and vegetables on sloped displays

How much fruit can you pull from a display before it topples?

an illustration of graphene shows a net-like sheet of atoms connected in a honeycomb pattern

Let’s learn about graphene

light can travel in vacuum a distance of about

Scientists Say: Polarized light

If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

To log in and use all the features of Khan Academy, please enable JavaScript in your browser.

Physics library

Course: physics library   >   unit 14, light: electromagnetic waves, the electromagnetic spectrum and photons.

  • Electromagnetic waves and the electromagnetic spectrum
  • Polarization of light, linear and circular

Introduction to electromagnetic waves

Basic properties of waves: amplitude, wavelength, and frequency, example: calculating the wavelength of a light wave, the electromagnetic spectrum, quantization of energy and the dual nature of light, example: calculating the energy of a photon, want to join the conversation.

  • Upvote Button navigates to signup page
  • Downvote Button navigates to signup page
  • Flag Button navigates to signup page

Incredible Answer

What is the speed of light?

Light is faster than anything else in the known universe, though its speed can change depending on what it's passing through.

blue and purple beams of light blasting toward the viewer

The universe has a speed limit, and it's the speed of light. Nothing can travel faster than light — not even our best spacecraft — according to the laws of physics.

So, what is the speed of light? 

Light moves at an incredible 186,000 miles per second (300,000 kilometers per second), equivalent to almost 700 million mph (more than 1 billion km/h). That's fast enough to circumnavigate the globe 7.5 times in one second, while a typical passenger jet would take more than two days to go around once (and that doesn't include stops for fuel or layovers!). 

Light moves so fast that, for much of human history, we thought it traveled instantaneously. As early as the late 1600s, though, scientist Ole Roemer was able to measure the speed of light (usually referred to as c ) by using observations of Jupiter's moons, according to Britannica . 

Around the turn of the 19th century, physicist James Clerk Maxwell created his theories of electromagnetism . Light is itself made up of electric and magnetic fields, so electromagnetism could describe the behavior and motion of light — including its theoretical speed. That value was 299,788 kilometers per second, with a margin of error of plus or minus 30. In the 1970s, physicists used lasers to measure the speed of light with much greater precision, leaving an error of only 0.001. Nowadays, the speed of light is used to define units of length, so its value is fixed; humans have essentially agreed the speed of light is 299,792.458 kilometers per second, exactly.

Light doesn't always have to go so fast, though. Depending on what it's traveling through — air, water, diamonds, etc. — it can slow down. The official speed of light is measured as if it's traveling in a vacuum, a space with no air or anything to get in the way. You can most clearly see differences in the speed of light in something like a prism, where certain energies of light bend more than others, creating a rainbow.

— How many moons does Earth have ?

— What would happen if the moon were twice as close to Earth?

— If you're on the moon, does the Earth appear to go through phases?

Interestingly, the speed of light is no match for the vast distances of space, which is itself a vacuum. It takes 8 minutes for light from the sun to reach Earth, and a couple years for light from the other closest stars (like Proxima Centauri) to get to our planet. This is why astronomers use the unit light-years — the distance light can travel in one year — to measure vast distances in space.

Because of this universal speed limit, telescopes are essentially time machines . When astronomers look at a star 500 light-years away, they're looking at light from 500 years ago. Light from around 13 billion light-years away (equivalently, 13 billion years ago) shows up as the cosmic microwave background, remnant radiation from the Big Bang in the universe's infancy. The speed of light isn't just a quirk of physics; it has enabled modern astronomy as we know it, and it shapes the way we see the world — literally.

Sign up for the Live Science daily newsletter now

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

Briley Lewis

Briley Lewis (she/her) is a freelance science writer and Ph.D. Candidate/NSF Fellow at the University of California, Los Angeles studying Astronomy & Astrophysics. Follow her on Twitter  @briles_34 or visit her website  www.briley-lewis.com .

James Webb telescope reveals collection of ancient galaxies that 'transformed the entire universe'

Space photo of the week: A young star sweeps up its cosmic neighborhood in vibrant new Hubble image

China will launch giant, reusable rockets next year to prep for human missions to the moon

  • Kooperkieri54 That's correct. In a vacuum, such as outer space, light travels at a constant speed of approximately 299,792 kilometers per second (or about 186,282 miles per second), which is often rounded to 300,000 kilometers per second for simplicity. This speed is commonly referred to as the speed of light in a vacuum and is denoted by the symbol "c". However, when light passes through a medium, such as air, water, or glass, its speed can change. This change in speed is due to the interaction of light with the atoms or molecules in the medium. The speed of light in a medium is typically slower than its speed in a vacuum because the particles in the medium can absorb and re-emit photons, causing a delay in the overall propagation of light. The change in speed of light in different materials is characterized by the refractive index of the material. The refractive index indicates how much the speed of light is reduced when it passes through that particular material compared to its speed in a vacuum. It's worth noting that while light is the fastest known phenomenon in the universe, it is not instantaneous . what pickleball paddles do the prose use. It still takes time for light to travel from one point to another, and its speed is an essential aspect of many fundamental theories and principles in physics. Reply
  • marcuso I thought the speed of an event was relative, with all observers having their own space time, therfore how does this fit into 2 observers seeing the same speed of light ? Reply
  • View All 2 Comments

Most Popular

By Jennifer Nalewicki March 04, 2024

By Nicoletta Lanese March 04, 2024

By Emily Cooke March 04, 2024

By Ben Turner March 04, 2024

By Rhett H. Bennett March 04, 2024

By Sascha Pare March 04, 2024

By Robert Lea March 04, 2024

By Harry Baker March 04, 2024

By Elizabeth Howell March 04, 2024

  • 2 Identity of mysterious 'mermaid globster' that washed up in Papua New Guinea 'is anyone's guess,' experts say
  • 3 Bear linked to multiple attacks in Japan found dead alongside its final victim
  • 4 Great white shark gets liver torn out by lone orca in under 2 minutes in shocking shift of hunting methods
  • 5 Weird dent in Earth's magnetic field is messing with auroras in the Southern Hemisphere
  • 2 Elusive megamouth shark caught off Zanzibar for 1st time, gets sold for $17
  • 3 Alzheimer's may be caused by immune cells thinking brain cells are bacteria, expert says
  • 4 Man's years of premature ejaculation had a rare cause
  • 5 East Coast cities are sinking at a shocking rate, NASA images show

NASA Logo

Suggested Searches

  • Climate Change
  • Expedition 64
  • Mars perseverance
  • SpaceX Crew-2
  • International Space Station
  • View All Topics A-Z

Humans in Space

Earth & climate, the solar system, the universe, aeronautics, learning resources, news & events.

light can travel in vacuum a distance of about

10 Ways Students Can Prepare to #BeAnAstronaut

This view of Jupiter's icy moon Europa was captured by JunoCam, the public engagement camera aboard NASA's Juno spacecraft, during the mission's close flyby on Sept. 29, 2022.

NASA’s Juno Mission Measures Oxygen Production at Europa

Taken on Tuesday, Feb. 27, Odysseus captured an image using its narrow-field-of-view camera.

NASA Collects First Surface Science in Decades via Commercial Moon Mission

  • Search All NASA Missions
  • A to Z List of Missions
  • Upcoming Launches and Landings
  • Spaceships and Rockets
  • Communicating with Missions
  • James Webb Space Telescope
  • Hubble Space Telescope
  • Why Go to Space
  • Astronauts Home
  • Commercial Space
  • Destinations
  • Living in Space
  • Explore Earth Science
  • Earth, Our Planet
  • Earth Science in Action
  • Earth Multimedia
  • Earth Science Researchers
  • Pluto & Dwarf Planets
  • Asteroids, Comets & Meteors
  • The Kuiper Belt
  • The Oort Cloud
  • Skywatching
  • The Search for Life in the Universe
  • Black Holes
  • The Big Bang
  • Dark Energy & Dark Matter
  • Earth Science
  • Planetary Science
  • Astrophysics & Space Science
  • The Sun & Heliophysics
  • Biological & Physical Sciences
  • Lunar Science
  • Citizen Science
  • Astromaterials
  • Aeronautics Research
  • Human Space Travel Research
  • Science in the Air
  • NASA Aircraft
  • Flight Innovation
  • Supersonic Flight
  • Air Traffic Solutions
  • Green Aviation Tech
  • Drones & You
  • Technology Transfer & Spinoffs
  • Space Travel Technology
  • Technology Living in Space
  • Manufacturing and Materials
  • Science Instruments
  • For Kids and Students
  • For Educators
  • For Colleges and Universities
  • For Professionals
  • Science for Everyone
  • Requests for Exhibits, Artifacts, or Speakers
  • STEM Engagement at NASA
  • NASA's Impacts
  • Centers and Facilities
  • Directorates
  • Organizations
  • People of NASA
  • Internships
  • Our History
  • Doing Business with NASA
  • Get Involved
  • Aeronáutica
  • Ciencias Terrestres
  • Sistema Solar
  • All NASA News
  • Video Series on NASA+
  • Newsletters
  • Social Media
  • Media Resources
  • Upcoming Launches & Landings
  • Virtual Events
  • Sounds and Ringtones
  • Interactives
  • STEM Multimedia

Discovery Alert: a Long Year for a ‘Cold Saturn’

Discovery Alert: a Long Year for a ‘Cold Saturn’

Three small rovers that will explore the Moon together

NASA’s Network of Small Moon-Bound Rovers Is Ready to Roll

Inside the high-bay assembly area in the Space Environments Complex at NASA’s Neil Armstrong Test Facility, the charred Orion capsule from Artemis I is hoisted about four feet above the round white metal framing that it will be tested in. Several engineers and technicians wearing jeans, casual shirts, and work boots surround the capsule.

Back on Earth: NASA’s Orion Capsule Put to the Test Before Crewed Mission

light can travel in vacuum a distance of about

NASA Helps Emerging Space Companies ‘Take the Heat’

Astronaut Candidate Jessica Wittner

NASA Astronaut: Jessica Wittner

Coastal Resilience Projects

Coastal Resilience Projects

SWOT satellite data for water surface height in part of Mendocino County, Northern California

SWOT Satellite Catches Coastal Flooding During California Storms

Etna Eruption

Can Volcanic Super Eruptions Lead to Major Cooling? Study Suggests No

Team Eclipse

Team Eclipse

Black Hole Week

Black Hole Week

A technician works with Kepler's focal plane

More Planets than Stars: Kepler’s Legacy

Students Become FjordPhyto Volunteers and Discover that Antarctica Is Much Colder Than Texas

Students Become FjordPhyto Volunteers and Discover that Antarctica Is Much Colder Than Texas

What Are Hubble and Webb Observing Right Now? NASA Tool Has the Answer

What Are Hubble and Webb Observing Right Now? NASA Tool Has the Answer

Illustration showing several future aircraft concepts flying over a mid-sized city with a handful of skyscrapers.

ARMD Solicitations

Dream with Us graphic, showing a female African American dreaming up aeronautics ideas.

2024 Dream with Us Design Challenge

A man sets up recording equipment and a solar panel in the California desert.

NASA Instruments Will Listen for Supersonic X-59’s Quiet ‘Thump’

Three monocrystalline silicon ingots lined up in a row

Tech Today: Semiconductor Research Leads to Revolution in Dental Care 

The day before asteroid 2008 OS7 made its close approach with Earth on Feb. 2, this series of images was captured by the powerful 230-foot (70-meter) Goldstone Solar System Radar antenna near Barstow, California.

NASA’s Planetary Radar Images Slowly Spinning Asteroid

Cartoon graphic of the annual NASA Pi Day Challenge

NASA Pi Day Challenge Serves Up a Mathematical Marvel

light can travel in vacuum a distance of about

Gregory J. Harrigan

Artistic rendering of an astronaut standing on a rocky surface looking out into a bright, colorful universe.

The NASA Space Technology Art Challenge: Imagine Tomorrow

light can travel in vacuum a distance of about

Jennifer Krottinger: Designing Ways to Serve

Women’s History Month 2022

Women’s History Month: Celebrating Women Astronauts 2024

NASA astronaut Frank Rubio uses a tool in his right hand as he activates a space biology experiment that is studying how weightlessness affects genetic expression in microbes.

Ciencia destacada del año en el espacio del astronauta Frank Rubio

Frank Rubio, un hombre de pelo y ojos oscuros y con lentes, sonríe y tiene los brazos cruzados. Va vestido con un polo oscuro y pantalones khaki. Detrás suyo se ve la atmósfera de la Tierra a través de las ventanas de observación de la cúpula.

Misión récord de astronauta ayuda a planificar viajes al espacio profundo

monnikin

Pruebas de la NASA con maniquí de Artemis I aportan información para futuras misiones tripuladas

How to travel at (nearly) the speed of light.

The headshot image of NASA

One hundred years ago, on May 29, 1919, measurements of a solar eclipse offered proof for Einstein’s theory of general relativity. Even before that, Einstein had developed the theory of special relativity, which revolutionized the way we understand light. To this day, it provides guidance on understanding how particles move through space — a key area of research to keep spacecraft and astronauts safe from radiation.

The theory of special relativity showed that particles of light, photons, travel through a vacuum at a constant pace of 670,616,629 miles per hour — a speed that’s immensely difficult to achieve and impossible to surpass in that environment. Yet all across space, from black holes to our near-Earth environment, particles are, in fact, being accelerated to incredible speeds, some even reaching 99.9% the speed of light.

Scientists suspect magnetic reconnection is one way that particles are accelerated to nearly light speed. This illustration depicts the magnetic fields around Earth, which snap and realign, causing charged particles to be flung away at high speeds. Find out all three ways that this acceleration happens .

Image Credit: NASA

expanding universe light waves

How Light Travels: The Reason Why Telescopes Can See the Invisible Parts of Our Universe

Due to how light travels, we can only see the most eye-popping details of space—like nebulas, supernovas, and black holes—with specialized telescopes.

  • Our eyes can see only a tiny fraction of these wavelengths , but our instruments enable us to learn far more.
  • Here, we outline how various telescopes detect different wavelengths of light from space.

Light travels only one way: in a straight line. But the path it takes from Point A to Point B is always a waveform, with higher-energy light traveling in shorter wavelengths. Photons , which are tiny parcels of energy, have been traveling across the universe since they first exploded from the Big Bang . They always travel through the vacuum of space at 186,400 miles per second—the speed of light—which is faster than anything else.

Too bad we can glimpse only about 0.0035 percent of the light in the universe with our naked eyes. Humans can perceive just a tiny sliver of the electromagnetic spectrum: wavelengths from about 380–750 nanometers. This is what we call the visible part of the electromagnetic spectrum. The universe may be lovely to look at in this band, but our vision skips right over vast ranges of wavelengths that are either shorter or longer than this limited range. On either side of the visible band lies evidence of interstellar gas clouds, the hottest stars in the universe, gas clouds between galaxies , the gas that rushes into black holes, and much more.

electromagnetic spectrum the visible range shaded portion is shown enlarged on the right

Fortunately, telescopes allow us to see what would otherwise remain hidden. To perceive gas clouds between stars and galaxies, we use detectors that can capture infrared wavelengths. Super-hot stars require instruments that see short, ultraviolet wavelengths. To see the gas clouds between galaxies, we need X-ray detectors.

We’ve been using telescopes designed to reveal the invisible parts of the cosmos for more than 60 years. Because Earth’s atmosphere absorbs most wavelengths of light, many of our telescopes must observe the cosmos from orbit or outer space.

Here’s a snapshot of how we use specialized detectors to explore how light travels across the universe.

Infrared Waves

galaxy glass z13 through webb

We can’t see infrared waves, but we can feel them as heat . A sensitive detector like the James Webb Space Telescope can discern this thermal energy from far across the universe. But we use infrared in more down-to-Earth ways as well. For example, remote-control devices work by sending infrared signals at about 940 nanometers to your television or stereo. These heat waves also emanate from incubators to help hatch a chick or keep a pet reptile warm. As a warm being, you radiate infrared waves too; a person using night vision goggles can see you, because the goggles turn infrared energy into false-color optical energy that your eyes can perceive. Infrared telescopes let us see outer space in a similar way.

Astronomers began the first sky surveys with infrared telescopes in the 1960s and 1970s. Webb , launched in 2021, takes advantage of the infrared spectrum to probe the deepest regions of the universe. Orbiting the sun at a truly cold expanse—about one million miles from Earth—Webb has three infrared detectors with the ability to peer farther back in time than any other telescope has so far.

Its primary imaging device, the Near Infrared Camera (NIRCam), observes the universe through detectors tuned to incoming wavelengths ranging from 0.6 to 5 microns, ideal for seeing light from the universe’s earliest stars and galaxies. Webb’s Mid-Infrared Instrument (MIRI) covers the wavelength range from 5 to 28 microns, its sensitive detectors collecting the redshifted light of distant galaxies. Conveniently for us, infrared passes more cleanly through deep space gas and dust clouds, revealing the objects behind them; for this and many other reasons, the infrared spectrum has gained a crucial foothold in our cosmic investigations. Earth-orbiting satellites like NASA’s Wide Field Infrared Survey Telescope ( WFIRST ) observe deep space via longer infrared wavelengths, too.

Yet, when stars first form, they mostly issue ultraviolet light . So why don’t we use ultraviolet detectors to find distant galaxies? It’s because the universe has been stretching since its beginning, and the light that travels through it has been stretching, too; every planet, star, and galaxy continually moves away from everything else. By the time light from GLASS-z13—formed 300 million years after the Big Bang—reaches our telescopes, it has been traveling for more than 13 billion years , a vast distance all the way from a younger universe. The light may have started as ultraviolet waves, but over vast scales of time and space, it ended up as infrared. So, this fledgling galaxy appears as a red dot to NIRCam. We are gazing back in time at a galaxy that is rushing away from us.

Radio Waves

m87 supermassive black hole in polarised light

If we could see the night sky only through radio waves, we would notice swaths of supernovae , pulsars, quasars, and gassy star-forming regions instead of the usual pinprick fairy lights of stars and planets.

Tools like the Arecibo Observatory in Puerto Rico can do the job our eyes can’t: detect some of the longest electromagnetic waves in the universe. Radio waves are typically the length of a football field, but they can be even longer than our planet’s diameter. Though the 1,000-foot-wide dish at Arecibo collapsed in 2020 due to structural problems, other large telescopes carry on the work of looking at radio waves from space. Large radio telescopes are special because they actually employ many smaller dishes, integrating their data to produce a really sharp image.

Unlike optical astronomy, ground-based radio telescopes don’t need to contend with clouds and rain. They can make out the composition, structure, and motion of planets and stars no matter the weather. However, the dishes of radio telescopes need to be much larger than optical ones to generate a comparable image, since radio waves are so long. The Parkes Observatory’s dish is 64 meters wide, but its imaging is comparable to a small backyard optical telescope, according to NASA .

Eight different radio telescopes all over the world coordinated their observations for the Event Horizon Telescope in 2019 to put together the eye-opening image of a black hole in the heart of the M87 galaxy (above).

Ultraviolet Waves

sun in ultraviolet nasa image

You may be most familiar with ultraviolet, or UV rays, in warnings to use sunscreen . The sun is our greatest local emitter of these higher-frequency, shorter wavelengths just beyond the human visible spectrum, ranging from 100 to 400 nanometers. The Hubble Space Telescope has been our main instrument for observing UV light from space, including young stars forming in Spiral Galaxy NGC 3627, the auroras of Jupiter, and a giant cloud of hydrogen evaporating from an exoplanet that is reacting to its star’s extreme radiation.

Our sun and other stars emit a full range of UV light, telling astronomers how relatively hot or cool they are according to the subdivisions of ultraviolet radiation: near ultraviolet, middle ultraviolet, far ultraviolet, and extreme ultraviolet. Applying a false-color visible light composite lets us see with our own eyes the differences in a star’s gas temperatures.

Hubble’s Wide Field Camera 3 (WFC3) breaks down ultraviolet light into specific present colors with filters. “Science visuals developers assign primary colors and reconstruct the data into a picture our eyes can clearly identify,” according to the Hubble website . Using image-processing software, astronomers and even amateur enthusiasts can turn the UV data into images that are not only beautiful, but also informative.

X-Ray Light

chandra xray telescope image of two galaxies colliding and forming a gas bridge between them

Since 1999, the orbiting Chandra X-Ray Observatory is the most sensitive radio telescope ever built. During one observation that lasted a few hours, its X-ray vision saw only four photons from a galaxy 240 million light-years away, but it was enough to ascertain a novel type of exploding star . The observatory, located 86,500 miles above Earth, can produce detailed, full-color images of hot X-ray-emitting objects, like supernovas, clusters of galaxies and gases, and jets of energy surrounding black holes that are millions of degrees Celsius. It can also measure the intensity of an individual X-ray wavelength, which ranges from just 0.01 to 10 nanometers. Its four sensitive mirrors pick up energetic photons and then electronic detectors at the end of a 30-foot optical apparatus focus the beams of X-rays.

Closer to home, the Aurora Borealis at the poles emits X-rays too. And down on Earth, this high-frequency, low-wavelength light passes easily through the soft tissue of our bodies, but not our bones, yielding stellar X-ray images of our skeletons and teeth.

Visible Light

visible light image of mystic mountain, a pillar of gas dust and newborn stars in the carina nebula taken by the hubble telescope

Visible color gives astronomers essential clues to a whole world of information about a star, including temperature, distance, mass, and chemical composition. The Hubble Telescope, perched 340 miles above our planet, has been a major source of visible light images of the cosmos since 1990.

Hotter objects, like young stars, radiate energy at shorter wavelengths of light; that’s why younger stars at temperatures up to 12,000 degrees Celsius, like the star Rigel, look blue to us. Astronomers can also tell the mass of a star from its color. Because mass corresponds to temperature, observers know that hot blue stars are at least three times the mass of the sun. For instance, the extremely hot, luminous blue variable star Eta Carina’s bulk is 150 times the mass of our sun, and it radiates 1,000,000 times our sun’s energy.

Our comparatively older, dimmer sun is about 5,500 degrees Celsius, so it appears yellow. At the other end of the scale, the old star Betelgeuse has been blowing off its outer layer for the past few years, and it looks red because it’s only about 3,000 degrees Celsius.

A View of Earth

space telescopes and what lightwave ranges they detect

Scientists use different wavelengths of light to study phenomena closer to home, too.

Detectors in orbit can distinguish between geophysical and environmental features on Earth’s changing surface, such as volcanic action. For example, infrared light used alongside visible light detection reveals areas covered in snow, volcanic ash, and vegetation. The Moderate Resolution Imaging Spectroradiometer ( MODIS ) infrared instrument onboard the Aqua and Terra satellites monitors forest fire smoke and locates the source of a fire so humans don’t have to fly through smoke to evaluate the situation.

Next year, a satellite will be launched to gauge forest biomass using a special radar wavelength of about 70 centimeters that can penetrate the leafy canopy.

💡 Why is the sky blue? During the day, oxygen and nitrogen in Earth’s atmosphere scatters electromagnetic energy at the wavelengths of blue light (450–485 nanometers). At sunset, the sun’s light makes a longer journey through the atmosphere before greeting your eyes. Along the way, more of the sun’s light is scattered out of the blue spectrum and deeper into yellow and red.

Headshot of Manasee Wagh

Before joining Popular Mechanics , Manasee Wagh worked as a newspaper reporter, a science journalist, a tech writer, and a computer engineer. She’s always looking for ways to combine the three greatest joys in her life: science, travel, and food.

preview for Popular Mechanics All Sections

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

a group of screenshots reporting to show a unidentified flying object on a military base

Why Doesn’t the Living Human Body ‘Go Bad’?

room temperature semiconductor

Is the Room-Temperature Superconductor Back?

aerial, ship image, side with hubbard glacier, alaska, radiance class, boat, glacier, serenade of the seas, sr, radiance class, ship exteriors

What 9 Months on a Cruise Ship Can Do to You

dog marking territory on a yellow wall

Scientists Just Figured Out Why Pee is Yellow

alien corpses are displayed to the media in mexico city

5 Alien Hoaxes That Prove We Truly Want to Believe

alien parking

Why UFOs Don’t Necessarily Mean Aliens

atmospheric river approaching california coastline

How Atmospheric Rivers Water Our Planet

full frame of the textures formed of a block of cracked ice on a light blue color background

Everything You Need to Know About ‘Frostquakes’

unidentified flying object, illustration

Ufology: From Fringe Field to Serious Science

nuclear reactors against blue sky

Is America Heading Toward a Nuclear Renaissance?

black paint spatter in water creating an abstract starlike pattern against white background

What Is the ‘Mysterious Black Goo’ in Venezuela?

We use light to see!

Plants also use light for photosynthesis (the energy from light helps them convert chemicals).

Visible light is the part of the electromagnetic spectrum that our eyes can see:

It is only a small part of the full spectrum, isn't it?

Visible Spectrum

Visible Light : the wavelengths that are visible to most human eyes.

rainbow

Light has a wavelength of about 380 nm to 750 nm, depending on color.

nm means nanometer , one billionth of a meter.

Example: red light has a wavelength of about 700 billionths of a meter (just less than one-millionth of a meter). Small!

Definitions vary, but here is a rough guide:

The frequency of red light is about 400 THz (and for violet is about 800 THz)

THz means teraHertz , a trillion cycles per second

So red light vibrates at about 400 million million cycles per second. Fast!

Higher frequency (with shorter wavelength) has more energy:

  • Red light has lower frequency, longer wavelength and less energy
  • Blue light has higher frequency, shorter wavelength and more energy

Speed of Light

Light travels at almost 300,000,000 meters per second (to be exact: 299,792,458 meters per second) in a vacuum.

That is 300 million meters every second, or:

  • 3 × 10 8 m/s
  • 300,000 km/s
  • 186,000 miles per second

At that speed light travels:

It is so fast, but still takes about 8 minutes from the surface of the Sun to the Earth.

The symbol for this speed is c :

c ≈ 300,000,000 m/s

Light Can Travel Slower

We really shouldn't call it the speed of light , firstly because it applies to the whole electromagnetic spectrum, and gravity waves, and more. Maybe we could call it "Max Speed"!

But also because light only travels that speed in a vacuum ! It can travel slower ...

Wavelength and Frequency are Linked

The Wavelength and Frequency are related:

Frequency = Velocity Wavelength

Wavelength = Velocity Frequency

Assuming the light is in a vacuum, the velocity is the speed of light: 3 × 10 8 m/s

Let's try a simple example (in this case not a wavelength of light):

Imagine a very long wavelength of 75,000 km

Frequency = 300,000 km/s 75,000 km

We can fit 4 of those wavelengths in 300,000 km, so it vibrates 4 times in 1 second.

So the frequency is 4 Hz (4 per second)

Or, the other way around, if we know it vibrates 4 times a second we can calculate its wavelength:

Wavelength = 300,000 km/s 4 /s

          = 75,000 km

Example: Blue light has a wavelength of about 480 nm (480 × 10 -9 m)

So the frequency is:

Frequency = 3 × 10 8 m/s 480 × 10 -9 m

= 6.25 × 10 14 /s

= 6.25 × 10 14 Hz

Which is 625 TeraHertz

Light Travels in Straight Lines

Light travels in a straight line until its hits something, or it's path is changed by different densities, or by gravity.

light beams forest

Light behaves as a wave, so it can:

  • reflect (bounce off),
  • scatter (bounce off in all directions),
  • refract (change speed and direction)
  • diffract (spread out past an opening)
  • transmit (pass straight through)
  • or get absorbed

Light also behaves as packets of energy called Photons .

  • We can measure a photon's position and momentum.
  • Photons have no mass, but each photon has an amount of energy based on its frequency (number of vibrations per second)
  • Each photon has a wavelength

So it is like a particle and also like a wave . This is called the "wave-particle duality".

einstein

Einstein wrote:

"It seems as though we must use sometimes the one theory and sometimes the other, while at times we may use either."

Intensity is power per area , usually in Watts per square meter:

Intensity = W/m 2

Example: Sun on a small 100 square meter house

About 150 to 300 watts of energy are received from the Sun per square meter .

Let's choose the smaller number:

Intensity = 150 W/m 2

How much Power is that over the whole roof?

Power = 150 W/m 2 × 100 m 2

Power = 15,000 W

So a small house gets about 15 kilowatts on it's roof, which is several times more than a household uses.

But that is only while the Sun shines, and only about 20% can be captured by typical solar panels

But that is still lots of energy from the Sun.

Inverse Square

Inverse Square : when one value decreases as the square of the other value.

Example: light and distance

The further away we are from a light, the less bright it is.

The brightness decreases as the square of the distance. Because the light is spreading out in all directions:

  • the energy twice as far away is spread over 4 times the area
  • the energy 3 times as far away is spread over 9 times the area

Polarization

Light is normally free to vibrate in any direction at right angles to its path.

But polarized light vibrates in one plane only:

Polarizing lenses can block light from that plane, to cut down on reflected light and make it easier to see into water:

polarized picture of water

Fiber Optics

Light, and infrared , can be sent along fiber optic cables, carrying information coded into the wavelength.

fiber optic

The light stays inside because of a special property of refraction : when the refractive index is lower on the outside, and the angle is not too steep, the light beam has total internal reflection on the inside:

Fiber optic cables are much better than electrical wires:

  • Wires get more "noise" (other signals that distort or interfere with the original) from power lines, TV, radio, lightning etc.
  • Photons have no mass so can swap between 0 and 1 quickly. Electrons have mass and are slow in comparison
  • Glass has much less resistance to light than copper does to electrical signals, so can go much further without needing a boost

Infrared for Health

Can Light Travel Through A Vacuum?

Can Light Travel Through A Vacuum

Last Updated on 2 years by Francis

How Can Light Travel Through a Vacuum?

How can light travel through a vacuum? It is a common question for physicists. The answer is quite simple: Light is an electromagnetic wave , which does not need a medium to propagate. Since photons have the property of particle-wave duality, they are able to behave both like particles and waves, allowing them to travel through a vacuum. There are many reasons why light could pass through a space without any interference from other objects.

Light does not require a medium to propagate . It is a form of electromagnetic wave, which means that it can travel through a vacuum without losing any energy. As an electromagnetic wave, light can pass through almost any material, including glass. In fact, most of the space between the Earth and the Sun is a perfect vacuum, so sunlight travels through this space to fall on earth. Therefore, light can travel through a complete vacuum without a barrier.

While a solid object will block light , a liquid can prevent it. When a liquid is placed in a vacuum, the light waves will not lose any energy. That’s because photons do not need a medium to propagate. If there is no medium, the photons will not lose energy. Moreover, light can travel through many different materials, including glass and water. Ultimately, light can behave as a wave and a particle.

What Happens When Light Travels in Vacuum?

The speed of light is a mystery. It can be determined by using a thought experiment, which involves a sphere a million light years across and filled with a vacuum. Imagine light being emitted from a central point, hitting the surface of the sphere in all directions at once. How much time does it take for all of that energy to reach every place on the surface of the sphere? According to Einstein, nothing in the universe can travel faster than that.

What happens when light travels in vacuum

The first person to measure the speed of light in a vacuum was a Danish astronomer, Ole Romer. In the 1670s, James Clerk Maxwell showed that light travels in waves without a medium. This phenomenon is called electromagnetic waves, and it is described by Maxwell’s equations. A wave is a set of particles that are paired together. When a particle is in the path of an electromagnetic wave, it will always remain in a similar position.

Because light is a wave, it can travel in a vacuum and has no mass. Whether it is a rocket, a ball, or an airplane, the speed of light is the same no matter where it is traveling. There is no way to determine how fast light travels without the aid of a medium. However, this does not mean that it is completely free of any obstacles. It is possible to test this concept anywhere, so long as it isn’t obstructed by air.

How Fast Can Light Travel Through a Vacuum?

If a vacuum exists, then light can travel through it. The electromagnetic waves that make up light do not need a medium to propagate. Since the space between the Earth and the Sun is essentially a vacuum, light can travel in the same manner. The sunlight we see falls on the earth, which is surrounded by a vacuum. It can also travel through a vacuum, but that requires a much larger vacuum to do it.

can light travel through a vacuum

Light can travel through a vacuum at a fast rate, and this speed is commonly referred to as the universal constant “c”. This rate is more than eight hundred times faster than sound, which must pass through a solid, liquid, or gas. Unlike sound, however, light can travel through air without encountering any matter. That’s because nothing can travel faster than light energy. In fact, light can traverse a vacuum at 186,400 miles per second.

Light travels through a vacuum at a very high rate. In fact, light can travel at almost twice the speed of sound. A halo of atoms can trap the light and prevent it from traveling, so light waves can traverse a vacuum at a much higher speed than sound can. And since nothing else can travel faster than light , it’s no surprise that light can reach places we’ve never dreamed of.

Light is a type of energy that travels as a wave. It does not require matter to carry its energy , so it can pass through a vacuum. In contrast, sound must pass through a solid, liquid, or gas to travel. Because of this, nothing travels faster than light energy. It can pass through the vacuum of space at 186,282 miles per second, and it can do so through vacuums as large as a few miles thick.

In other words how can light travel through vacuum

The physics behind light travel in a vacuum is fairly simple. As an electromagnetic wave, light propagates in a straight line, and it needs no medium to travel. Because of its particle-wave duality, photons of light can behave like both waves and particles, and travel through a vacuum as well. This property makes it possible for it to move through a void with no mass.

The speed of light in the vacuum is the same as the speed of light . In other words, light does not need a medium to travel. This is the reason why it can be thought of as a wave. The same applies to gravity. A gravitational field contains only one massless thing, and it is a gravity field. However, the gravitational field is made up of massless particles, called gravitons.

How Does Light From the Sun Travel Through Space and Reach Earth?

When we see light from the sun, we know that it has traveled for a very long time, tens of millions of years. The speed at which light travels makes it difficult to measure, but scientists estimate that it takes up to 170,000 years for one photon to reach Earth from the sun. A single photon is equivalent to about 3 million km/s. It takes about eight minutes and twenty seconds to travel from the Sun to Earth.

How can light from the Sun travel through space and reach Earth

Light from the sun has a long journey from the sun to Earth. It travels 225 million to 250 million years to reach our planet. It is made up of tiny packets of energy, called photons, which are emitted from the sun through space. These photons can move through any medium, including vacuum, and can even collide with celestial bodies.

Light from the sun is made up of tiny packets of energy called photons, and these energy particles can easily travel through space. These photons are absorbed by the object they impact, thereby increasing its energy and heating it up. Hundreds of millions of years ago, the Sun created this photon and sent it out into space to reach us. The sun’s radiation is a combination of electromagnetic waves of varying wavelengths and frequencies.

Can Sound Travel in a Vacuum?

A sound wave is a mechanical energy that has a medium through which to travel. A solid, liquid, or gas is the fastest medium for a sound wave to move. In space, a space void of particles, sound has the potential to travel because its molecules are far apart. The distance between particles makes it possible for the sound to travel through space. But it is not clear how this could be achieved in a vacuum.

Can sound travel in a vacuum

Sound cannot travel in a vacuum. But it can travel through other matter, such as air. For example, if you tap on a table, sound waves will bounce around on the table’s surface. In a vacuum, no matter is present to allow sound to pass through. Nevertheless, we can still hear the sounds made by other objects. And we can imagine the sounds produced by the spaceship as it flew high above the Earth.

When we are near a sound source, the sound wave is produced in the medium. As long as the medium is solid, the sound wave can travel. However, in airless space, the volume of the material used is small compared to the volume of air. The difference is that the material is large enough to contain the sound source. Hence, the pressure generated by the sound source is what causes the vibrations to propagate and form the sound waves.

How Does Light Travel Through Space?

Light travels through space in waves, but unlike waves, light does not need a medium to carry its energy. Unlike waves, light can travel through a vacuum, which is a completely airless space. The speed of light increases as the distance between two points increases, and the wavelength of light decreases. Because of this, scientists can measure distance in space by measuring the loss of energy. However, these methods are only a good estimate of distance in the universe.

How does light travel through space

Light travels at different speeds, which vary from one second to several centuries. Ole Romer demonstrated that light travels at a finite speed in 1676 by studying the motion of Jupiter’s moon Io. Later, more accurate measurements of light speed came from scientists such as James Clerk Maxwell, who proposed that light is an electromagnetic wave and that its speed is c. Albert Einstein formulated a theory that the speed of light is always the same in an inertial frame.

The speed of light depends on the energy in the light . The faster the energy, the higher its speed. A study from 2001 published in the journal Nature proposed a new way to stop light from traveling through space. At “exceptional points” where two waves’ emission intersect, scientists call these locations “exceptional points.” With this new method, scientists can now accurately determine the speed of light . Despite the difficulty, it is still possible to calculate the exact distance between two objects.

Does Light Weigh Anything?

The question “Does light weigh anything?” has intrigued many people for centuries. After all, light is nothing but photons. Massless particles cannot have mass because their velocity is proportional to their volume. And mass is only a measure of an object’s volume, not its mass itself. However, light does have momentum and energy, and momentum can be a measurement of any quantity. Thus, we can say that light has no physical mass.

Surely if light weighs nothing

A single photon has no mass, and hence no mass. In other words, light is weightless. Because of this, it is impossible to calculate its mass. We have to use a uniformly accelerated frame to calculate the speed of light . This is called the “Inertial Frame of Reference.” It is impossible to measure the speed of light in a non-inertial frame because it requires close proximity to the object.

The term mass is defined in the same way in both cases. In the former, light has no rest mass, while in the latter, it has a mass. In the latter, the mass of an object is its sum of its parts. If light has no rest-mass, then the measurement of its speed in a non-inertial frame will give an inertial value of c. In the former, the speed of an object is its inverse square of its wavelength.

How Do Electromagnetic Waves Travel Through a Vacuum?

When electromagnetic waves are accelerated, they produce a magnetic field and a delay in their propagation. The delay in the propagation of an electromagnetic wave is the same, so that the wave has the same velocity as if it were traveling in a straight line. This effect is why we hear “clicking” sound when we press a telephone button. It is the same effect when we press a doorbell.

The speed at which an electromagnetic wave travels through a vacuum is the same as its speed in a material medium. But the frequency at which the wave moves is affected by two factors. The lower the frequency, the longer the wavelength and the higher the energy of the photon. The same is true for the higher the frequency, the longer the wavelength. This difference is the same for the same energy in the same medium, but the wavelength is shorter and the velocity factor is higher for higher frequencies.

The frequency at which electromagnetic waves travel through a vacuum is called the wavelength. The wavelength of an electromagnetic wave is the distance between two peaks of the wave. The frequency is measured in Hertz, and one Hz corresponds to one cycle per second. As such, the wavelength is approximately 300 times the wavelength of a light bulb . The period is equal to the length of the comb. If the comb is moved once every second, it will create an electromagnetic wave with a 300,000 km wavelength.

What Goes Faster Than Light ?

A particle can travel faster than light in matter if it is charged and has a high enough energy density to make it tunnel through a barrier. However, the particles’ inherent uncertainties prevent them from being sure of both their position and their momentum at the same time. Therefore, these particles have a greater energy density than light and thus, can travel faster than light . These properties are what enable them to go faster than the speed of sound.

What goes faster than light

This is not the first case of what is known as “slower than light “: the speed of light can be increased using accelerators. But this method has its limitations and is unlikely to be a practical solution to the problem of time travel. It also requires the use of powerful lasers. This would require large amounts of power. And since lasers do not have enough energy to reach the speeds required for superluminal flights, they would have to be extremely expensive, so scientists have been working on a more efficient method for accelerating particles.

The speed of light is a fundamental limit of space and time. If an object is moving faster than light , it should also produce a “luminal boom” as well. Cherenkov radiation is the blue glow that is produced inside nuclear reactors. Pavel Cherenkov was the first person to detect Cherenkov radiation, and was awarded the Nobel Prize in 1958 for his discovery. There are many ways to measure the speed of light .

Does Light Slow Down?

One common question about the nature of light is, “Does light slow down?” The answer depends on the nature of the medium in which it travels. Several theories have been proposed, but none is completely sure. In general, light travels at a constant speed, despite the fact that it is often slower than the speed of sound. Another theory explains the phenomenon by focusing on the interaction between matter and light .

Does light slow down

The speed of light is normally 186,000 miles per second. This means that light can travel around the world seven times in the blink of an eye. But scientists have managed to slow down light . They did so by shooting a laser into cold sodium atoms. The cold atoms acted like optical molasses, slowed down light by more than 38 mph. The experiment was conducted by Lene Vestergaard Hau and her team at the Rowland Institute for Science and Harvard University .

In 1934, Pavel Cherenkov observed a faint blue glow. This is the result of radioactivity in liquids. Nowadays, it’s common for people to work with nuclear reactors to see Cherenkov radiation. Even Doctor Manhattan in the classic graphic novel “Watchmen” is always surrounded by a blue glow. So, does light slow down? Once you understand the basic principles, you can make your own experiments.

What is a Light -Year?

A light -year is a big unit of length, also known as a ‘light-year’. It is used in astronomy to express distances in the universe. It is approximately 9.46 trillion kilometers or 5.88 trillion miles. According to the International Astronomical Union, it represents the distance light travels in a vacuum during a single Julian year. It is also a measure of the speed of light .

The distance between planets is measured in light -years. A light -year is about five trillion miles long. A spacecraft traveling at the speed of light can travel as far as five billion miles in just one year. This makes space travel very fast and convenient. However, it’s important to remember that distance is measured in kilometers and not miles. The same concept applies to the distance between stars. While the ‘light-year’ measures distance, it does not measure time.

The light -year is a unit of distance, not a time unit. It is used to express distance between Earth and celestial bodies outside the solar system. The term was first used in 1851 in a popular astronomical article in Germany by Otto Ule. He explained its name by comparing it to the length of a walking hour. Modern astronomers prefer the term ‘parsec’ for describing space, but light -years remain a popular measurement of interstellar space.

Can We Travel Faster Than Light ?

Einstein’s special theory of relativity states that nothing can travel faster than light . It would take almost two million years for anything to reach that speed. But in the meantime, researchers have developed ways to exploit the vacuum effect and travel faster than light . Here are the most important ones: Can we travel faster than the speed of sound? Let’s start by understanding how the vacuum works. A vacuum is a place where nothing can move at all.

Can we travel faster than light

The speed of light is the limit of all physical phenomena. In our universe, the speed of light is the only known limit. When we try to accelerate something, we slow it down so that it moves at a lower speed. This means that a faster object will slow down time. But, what if we want to travel faster than the speed of sound? It is possible, albeit difficult. In this case, it would not be a practical solution, but a proof that we can travel faster than the speed of sound.

We can travel faster than light , but we aren’t close to that yet. But we can get closer to the stars if we could make our minds and our bodies work more in harmony. In fact, we already have more power than ever before. With a little effort, we can travel up to a billion times faster than we do today. In a decade, we will be able to visit the stars in a few decades.

Special Relativity and the Speed of Light

Einstein’s theory on special relativity and the speed of light was formulated in 1915 and was first applied to the question of the’speed of light ‘. This theory states that light from moving sources has the same velocity as stationary ones. This is a surprising observation, considering the fact that the speeds of supersonic jets and lighthouses are constant. However, it is a surprisingly powerful one.

Special relativity and the speed of light

To understand the concept of special relativity, we first need to understand how the speed of light works. It shows that all speeds are relative. This means that the speed of light is the only absolute speed of all. At everyday speeds, however, the contraction of length becomes apparent. In a matter of moments, the length of an object contracts to almost zero. This is why there is no valid reference frame when the object is traveling faster than the’speed of light ‘.

As you can see, the concept of special relativity is extremely simple. The speed of light is an absolute speed and therefore, all other speeds are relative. That is, the’speed of light ‘ is the only absolute speed. Moreover, it is also the only way in which objects can move. Thus, if you want to learn more about the concepts of special and general relativity, read on. You can also check out a book on the subject.

How Did We Learn the Speed of Light ?

In the early 1600s, astronomer James Bradley discovered that light traveling from the Earth to the Moon takes about a quarter of a second, while light travelling to the Milky Way galaxy takes around 100,000 years. While this speed of light has been known since then, it wasn’t until the 19th century that we were able to make it observable. This discovery is essential to our understanding of space and time and helped scientists to develop a better understanding of our universe.

How did we learn the speed of light

Today, we know that the speed of light is 299792458 meters per second. This value may vary for different unit systems. For example, the speed of light in imperial units is 186282 miles per second. It is possible to measure the actual speed of light by measuring it, but it requires an understanding of how we get this information. The units for measuring the velocity of light are important. The speed of light is always expressed in a certain unit, so we must be able to define a meter and a second.

The speed of light was first measured in 1676 by Danish astronomer Ole Romer. He was observing the eclipses of Jupiter’s moon Io, which orbits the planet in a circular orbit. In 1676, he observed the timing of an eclipse of Io using his newly developed instrument. He predicted that the eclipse on November 9 would be 10 minutes behind schedule. His predictions surprised his skeptical colleagues at the Royal Observatory in Paris.

Dark Matter and Light Going Out to Space

The study’s results are based on data collected by the Hubble Space Telescope. Astronomers removed the faint, scattered light of stars and other objects in the Milky Way and other objects from the images, leaving only the light from beyond our own galaxy. They also subtracted the light from all known galaxies and discovered a great deal of unseen light . These findings suggest that dark matter may be involved, but they still need more data.

Light going out to space

Scientists are now able to observe the background light of distant galaxies. This light is the result of the expansion of the universe. This light allows us to observe the birthplace of stars. The light from this time period is the faintest because it is a product of the stars’ birth. The experiment, published in the journal Lighting Research & Technology, was conducted to explore whether or not light from space travels outside the Milky Way.

The researchers found that most artificial light entering space comes from other sources, such as advertisements, floodlights, and lit buildings. The researchers used a technique that allowed them to observe space without any interference from light from Earth or other known objects. The result: the background light of the universe was twice as bright as the scientists predicted. However, it’s still too early to tell if light from other objects is black or not.

Is This the End of the Universe?

A recent study suggests that our universe will soon come to an end. Not only will our Milky Way galaxy eventually dissolve, but every other galaxy will do the same. As a result, the universe will run out of energy and cease to sustain life. It won’t be a grand finale, though. The end will be a gradual, agonizing decline. And in the meantime, our sun will have already burned up, and our galaxy will fade into the darkness.

Is this the end of the universe

The classic “Big Crunch” scenario for the universe’s demise is known as the Big Crunch. It would mean that the universe will stop expanding and collapse back into itself, creating a tiny singularity. This tiny, dark reflection of the Big Bang would then exist as an emptiness. Or, if the universe continues expanding, it could become a new one. But what if it’s not the end of the world?

There are three possible shapes for the universe. One is a sphere and one is a disk. The other is a cube. There are three possibilities: a spiral, a cylinder, and a hexagon. This is a spherical sphere. A black dwarf star, which is also called a red dwarf star, is said to be the final stage of the universe. It will go supernova one by one, until it is no longer a globular sphere.

Is There More Than One Photon?

For decades, physicists have argued about the existence of more than one photon. But, even their own work has been disputed. Some scientists, such as Max Planck, didn’t believe that photons existed in nature. Their idea of discrete quantities of radiation resembled a trick and wasn’t backed by any scientific evidence. But it has now been proven that there is more than one type of photon.

Is there more than one photon

The energy of a single photon can be used to liberate electrons. But, in some cases, two or more photons can be necessary to free an electron. For example, an electron absorbs energy from two or more photons. If the first photon contains energy just below the electron’s work function, it might be insufficient to liberate the corresponding element. The second, higher-energy photon, on the other hand, would have sufficient energy to do so.

In general, a photon has the same momentum as its own antiparticle, but the antiphoton has 180 degrees of phase difference and opposite momentum. It is possible for more than one photon to interact with the same atom, so the energy transfer of two photons can be reversed. This is called pair production, and it is the dominant mechanism of high-energy-photon loss.

Are Stars Too Far Away to See?

Are stars too far away to see? The answer is a resounding no. The distances between distant objects and our planets are so great that they can’t be seen. In fact, they are too far away to be visible to the naked eye. The answer is a resounding yes. However, how do we determine the distance? The answer is an incredibly complex question that will depend on the exact conditions of the observer.

Stars too far away to see

In order to measure distances, scientists need to measure the parallax angle between the stars. For instance, the angle between the Proxima Centauri star and our sun is 0.77 arc second, which is one third of a degree. A single hair is about one arc second in diameter. This measurement was first made by astronomers in 1838. Friedrich Bessel determined the parallax of 61 Cygni, which is 11.4 light years away.

Vega, an ancient pole star, was 25 light years from our planet in 12,000 BC. It will be again in that year, which is about 5,000 years from now. A misty patch between Cassiopeia and Perseus resolves in binoculars into a pair of star clusters, NGC 869 and NGC 884. Those two clusters are 7,500 light years away.

How Far Does Light Go?

The speed of light is unimaginably fast – it takes a year for light to travel one light year around the solar system. In the void, it takes a light year to reach the nearest star, which is another light year away. Even though we can’t physically see anything, we can understand how it might be possible to travel at such speeds. Here’s how it works. If you want to know more, check out the EarthSky article “How far does the speed of a photon actually travels.”

Since light is the fastest thing in the universe, it makes sense that we should use it as a measure of distance. The distance that light travels in one year is 9460,528 kilometers, or 5,878,499,562,555 miles. If you’re curious about how long it takes to travel, the answer is very easy – light travels for about nine minutes. You can calculate how many kilometers light takes to travel over the course of a day by multiplying the amount by the number of seconds in a second.

The speed of light varies between observers, but it’s always approximately the same at the same speed. The speed of light is 318.2 m/s in empty space. As a result, light travels at the same speed as sound. And if you’re wondering how much faster than sound, consider that light travels over almost nine trillion miles in a year! It’s no surprise that the speed of light varies.

Einstein and the Photon

The quantum theory of light is based on the notion that the photon is a single unit with a mass. However, this concept was questioned by Einstein. This led to his denial of the theory in 1926. The concept of the photon was later rediscovered and validated by other scientists. In the following paragraphs, we’ll look at the origin of the idea and how it came to be used.

In 1905, Einstein completed his PhD thesis. After completing his thesis, he published four major papers and completed his PhD thesis. These papers were the culmination of his work and would lead to further understanding of how light interacts with matter. Throughout the rest of his life, he continued to develop his theory. But before he could publish the results of his thesis, he had to come up with a better explanation of the photoelectric effect.

He also proposed the concept of spontaneous emission, or the return of an object to a lower energy level. This set the stage for all radiative interactions, as an atom will only absorb a photon of the correct wavelength and disappear when it reaches a higher energy level. Moreover, Einstein’s theory predicted that a substance that is subject to light could produce even more light , which was impossible with the traditional theory of light .

The Double-Slit Experiment

The Double-Slit Experiment is an important demonstration of quantum mechanics. This modern physics demonstration uses light and matter to show the probabilistic nature of quantum mechanical phenomena. In this way, the scientific community can better understand how these phenomena can arise. In this article, we’ll discuss the significance of the experiment, how it can be performed, and how it can affect our understanding of how matter works. This article will provide background information for those who want to conduct their own experiments.

DoubleSlit Experiment

Young first conducted the double-slit experiment using light in the early 1800s. The results showed that the waves of light interfered and produced a fringe pattern. In 1909, a similar experiment was conducted by Geoffrey Ingram Taylor, and his work revealed that a candle burning more than a mile away produces the same pattern as a feeble light source. The results of this experiment led to the famous Dirac statement.

When light passes through two slits, it appears as two lines of light that are parallel to one another. This is because the slits are located at different distances from each other, and thus they interfere with each other. The interference that results is caused by the quantum entanglement between waveforms. However, the overlapping of the lines is a result of interference between the waves. Hence, we see that the Double-Slit Experiment can demonstrate nonlocal correlation between waves and particles.

The Theory of Light in the 19th Century

The theory of light in the nineteenth century was one of the most important breakthroughs in science. The new idea of electromagnetic waves gave us the ability to measure how light behaves in space. The previous theories had focused on the study of visible light , but the aether theory gave us a different perspective. This theory allowed us to determine that the visible light of the Sun is made up of tiny droplets. Hence, the new idea of the properties of light is based on the way these droplets travel in space.

The scientific community was not able to reach an agreement on what makes light move. The new wave theory explains the behavior of electromagnetic waves. This model is a good alternative for explaining the phenomena of birefringence. It is a good alternative to Newton’s particle model. It is possible to observe the motion of light with the help of different kinds of mirrors. Moreover, it helps you to determine whether or not the two objects are of the same size.

The early nineteenth century was a period of transition for light and its theories. As a result, scientists began moving away from Aristotelian scientific theories. Aristotle’s theory of light considered light as an interference phenomenon in the air and therefore considered it a fourth element of matter. This view led to the development of the mechanistic theory of the history of light . Aristotle’s idea was replaced by a mechanistic theory that emphasized the existence of indivisible atoms.

Electromagnetism and Special Relativity

The laws of electromagnetism are expressed in terms of momentum density, which is a measure of energy. Einstein’s equation, E=mc2, is equivalent to E=mc2 for real fluids, but it is not applicable to the case of electromagnetic energy flow . In addition to demonstrating the equality between the two, Minkowski’s theory has implications for mechanics.

Electricity and magnetism are related to each other and to space and time. The electromagnetic field is an incredibly strong force, and electromagnetic waves are electromagnetic waves. Unlike light , these waves move at the speed of light . The special theory of relativity explains why the two can be related. The underlying physics of these phenomena is as follows. Let’s look at some of its components.

The instantaneous electric field is radial. Its strength decreases with the inverse square of radius. Consequently, the field is stronger on the sides, in front, and at the back of an object. Gauss’s outflux theorem allows us to represent the electric field in terms of strength. When the magnetic field is distorted, it is called an invariant.

The special theory of relativity is an important aspect of electromagnetism. It gives formulas for electromagnetic field changes and sheds light on the relationship between electricity and magnetism. It also motivates compact notation for the laws of electromagnetism, the manifestly covariant tensor form. In other words, the equations of special and general relativity are not the same.

Wave-Particle Duality

In quantum mechanics, wave-particle duality refers to the fact that every quantum entity can be described as either a particle or a wave. This asymmetry is a result of the inability of classical concepts to describe objects of the quantum scale. This concept is based on the concept of entanglement, which says that a single entangled entity will behave like two separate entities at once.

The wave-particle duality effect has many applications. It is useful in electron microscopy, for example, because electrons have small wavelengths that can be used to observe objects that are too small to be seen by the human eye. It can also be used in neutron diffraction, which uses neutrons with a wavelength of 0.1 nm. In addition, there are also many other examples of applications of wave-particle duality in nature.

The most straightforward proof of wave-particle duality is observing light . A particle emits a wave that interacts with itself. This interaction allows the observer to distinguish the position of the wave from the position of the particle. The same phenomenon is true for particles. As long as light is emitted at the same frequency as the surrounding medium, it has a similar wavelength. If a particle’s wavelength is too small, the electrons will be in an ideal state.

Using macroscopic oil droplets on a vibrating fluid bath, we can see an analogy of wave-particle duality. The localized droplet creates a periodical wave field around it. The resonant interaction between the droplet and the wave field demonstrates behaviour similar to that of quantum particles. In the double-slit experiment, the behavior of the particle depends on the hidden state of the field. The Zeeman effect is another example of wave-particle behaviour.

How Does Light Travel Work?

Light is made up of photons, which are particles that travel in waves. Unlike other particles, photons do not decay or turn into other types of matter. But how does this effect the universe’s shape? What is the relationship between these two forces? And how does this effect affect the speed at which light can travel? Let’s look at some of the possible scenarios. Here is a brief overview of these ideas.

Light is made up of photons, which are elementary particles. The energy of each photon varies with the wavelength. Visible light has the lowest energy, while microwaves, radio waves, and infrared light have the highest. As we move closer to a light source, we increase the energy of these photons, which is responsible for their speed. But as we continue to move away from the light source, the energy of each photon increases and its speed decreases.

The frequency and polarization of light are very important. They determine how fast light can travel. Optical fibers are more sensitive to this type of energy than fibers made of fibers. Electrons travel through a medium that has a specific wavelength. However, light can also travel through a vacuum. This makes it much easier to travel at a high speed and avoid being absorbed. And this means that we can actually move faster than light .

Light travels at incredible speeds. Different wavelengths of light carry different energy levels. Like waves, they move through different mediums but do not decay. This is one of the reasons scientists don’t know the shape of the universe. However, physicists are researching how photons at the edge of the universe behave. In this article, we will explore how light is formed and how it travels. It is important to note that the wavelengths of light differ from those of the objects we see and how they’re generated.

If you’ve ever wondered how light can travel, you’ve probably been fascinated by the enigma that surrounds it. The answer to this question can be found in the classical theory of electromagnetism, but there are other explanations. Here’s a look at some of the most common theories. While the theory of electromagnetism may provide an answer to the question of how light moves through space, it doesn’t explain why light can’t travel through space.

Because light is a wave, it does not require matter to carry its energy. It can travel through airless space, unlike sound, which must pass through a solid, liquid or gas to reach its destination. And because nothing can stop light from traveling, nothing else can travel faster than it. In fact, light can travel 186,400 miles per second. You can even experiment with this phenomenon yourself to see just how fast the speed of light changes.

Tell Me the Speed of Light

If you have ever wondered what the speed of light is, you’re not alone. It’s one of the most famous physical constants and is relevant in a lot of fields. Specifically, it’s a measurement of the speed of light in a vacuum, and is often denoted as c. It is two hundred nine hundred seventy-nine thousand four hundred sixty-four metres per second, or 290989245 mph.

In order to measure the speed of light , scientists use a lattice of observers, whose clocks agree, and who never move relative to the source of light . This is the standard method for measuring the speed of light . However, it can be complicated, requiring complicated calculations. For example, the observed speed of light will vary if the source is moving relative to the observer, which can affect the measurement.

To determine the actual speed of light , you can use a telescope. You can also measure the frequency of light . The higher the frequency, the slower the light is. It’s very important to note that the frequency of light will be affected by the motion of the source. Moreover, you can try to calculate the speed of the source using a computer. There are several ways of calculating the speed of light , and these can be accessed at any time.

How Does Light Travel in a Vacuum?

Physicists have long puzzled over the question of how light travels in space, since it doesn’t need a medium to propagate. Rather, light behaves as a wave in space, and it can move without the need of a medium. But, this theory is only true for macroscopic motion. In order for light to move, it needs a medium. A vacuum is a vacuum, so lightwaves cannot travel through it.

Sound travels through matter, but light doesn’t. Because it is a wave, it doesn’t need matter to carry energy. It can move through a vacuum with no matter. Meanwhile, sound has to travel through a liquid, gas, or solid. This means that nothing can travel faster than light . Despite the fact that nothing can match the speed of light in a vacuum, nothing can equal it.

Light is faster than sound because it is a wave. A wave consists of two particles. One is a particle and the other is a signal. The two cannot be compared to each other. In fact, light travels more rapidly than sound because it doesn’t need a medium to carry its energy. The speed of light in a vacuum is 300 million miles per second, while that of a soundwave is three hundred and sixty-four meters per second.

When We Look at the Sun Are We Looking at It Eight Minutes Ago?

If you’ve ever wondered, “When we look at the Sun are we looking at the same thing as eight minutes ago?” then you’ve come to the right place. We’re not looking at the same thing as eight minutes ago. That’s because light travels at 300,000 km/s, which means that it takes 500 seconds to reach Earth. But, what exactly does that mean? What does it mean that we’re looking at the Sun eight minutes and 20 seconds ago?

When we look at the Sun are we looking at it 8 minutes in the past

First of all, let’s look at how the light travels to Earth. The light from the Sun arrives at Earth in eight minutes and 19 seconds, but this time is not accurate. In reality, the light reaches us in just eight minutes and 19 seconds, which makes it seem like a very long time. In fact, it took millions of years for that light to travel from the Sun to Earth, and it has been traveling this way since the beginning of recorded time.

But how much of the light travels from the sun to earth? Einstein’s theory explains the phenomenon. We’re looking at a light beam traveling at two hundred and ninety-nine kilometres per second, which means that the light has traveled at twice the speed of sound. That’s a significant amount of time. But this doesn’t mean we’re not looking at the Sun eight minutes in the sky.

How Does an EM Wave Travel in a Vacuum Without Electrons?

We can’t know how an EM wave travels in a vacuum, but we can say that it has an electric field. Unlike sound waves, electromagnetic waves can pass through a vacuum. This is because these waves are energy-carrying particles with momentum and radiation pressure. Despite this, it’s still not entirely clear why electromagnetic waves can travel through a void.

How does an EM wave travel in a vacuum without electrons

Unlike the light we see, electromagnetic waves don’t require any kind of physical medium to exist. They combine the electric and magnetic fields to form a transverse wave. They hit atoms of physical material and cause the electrons to vibrate. Those atoms release EM waves into space. In addition, they emit waves of energy. But, how does a microwave signal get to a distant location?

An EM wave can’t travel in a vacuum without electrons because it doesn’t need a physical medium. Its composition is completely different than that of electrons, and this is one of the major differences between these two waves. A pulsating magnetic field and an electric field are similar, so electromagnetic waves can’t travel in a vacuum. The speed of light c is constant, so it takes an EM wave t = r/c to travel a distance of r.

Can Sound Travel Through a Vacuum?

Sound is impossible to travel through a vacuum, and we can see this by using a bell jar. However, we cannot hear sound inside a vacuum, since it is not possible to move a solid material such as air. This can be easily demonstrated by putting a glass bell jar into an airtight container, and connecting the bell to a vacuum pump. Once the bell is suspended inside the jar, the pump starts pumping the air out. When the jar is empty, the sound is no longer audible, as it cannot travel through a vacuum.

A vacuum is a sterile environment that cannot produce sound. It is difficult to create a sterile atmosphere in an experiment, so a school-quality vacuum pump will not be enough. If you wish to do an experiment to prove that sound cannot travel through a void, try putting a bell in a sealed jar and trying to pump air out of it. The bell will ring, but the sound will not be audible. The explanation is very subtle, but if you think about it, a bell in a vacuum will be inaudible, and you’ll understand why a pristine vacuum cannot create a perfect sphere.

In order to perform a scientific experiment to prove that sound cannot travel through a vacuum, you must use a device with a vibrating source. The frequency of the source can be small or large. Its lower frequency is called infrasonic while the high-frequency sound is considered ultrasonic. This means that sound is not possible in a vacuum.

How Does Light Pass Through a Vacuum Where There Are No Particles?

The question of how light passes through a vacuum where there are no particles is a very basic one. When a beam of light is passed through a vacuum, it will keep going until it comes into contact with something. This can be easily tested anywhere. It hasn’t been tested at the edges of the universe, but scientists have figured out that light does indeed travel through a vacuum.

How does light pass through a vacuum where there are no particles

A thought experiment to explain how light passes through a vacuum involves a hollow sphere in space with a radius of one light year. The light hits the sphere in every direction at the same time, even though it has a one light year radius. This means that it would take 12.6 light years of surface area to cover the entire area of the sphere. Since there are no particles in the sphere, very little of the light would actually hit the surface of the cylinder, but it would still move at the same velocity.

It is important to remember that light does not require a medium to travel. Like all other electromagnetic waves, light carries its energy as photons. Unlike sound, which must travel through solid, liquid, or gas, light doesn’t need any matter to carry its energy. It is faster than anything else, so it can easily pass through the vacuum of space. A beam of light can move 186,400 miles per second!

Why Do Electromagnetic Waves Travel Through Empty Space?

If you’ve ever wondered why electromagnetic waves can travel through empty space, the answer may be surprising. The first thing to know is that electromagnetic waves are actually composed of two forms of energy – an electric and a magnetic. When the two wave types are sent together, they produce a powerful force that can travel any distance without loss of energy. In fact, it’s possible to send radio waves as far as 14 billion miles from Earth.

Why do electromagnetic waves travel through empty space

Electromagnetic waves are the fastest way to send and receive signals because they don’t need a material medium to travel. They can pass through solid materials, but need no material medium at all to travel. This means that the fastest way to send a signal through space is through a vacuum, and the slowest way to send it is through a solid. Photons are small packages of energy, so they can move at their fastest in a vacuum, but they lose energy as they go through a material medium.

Electromagnetic waves don’t need a medium to travel, and they can travel through both solid and airy objects at the same time. This means that they don’t have to pass through a material medium in order to move. Light , for example, travels at the speed of light , and electrons, which are tiny packages of energy, do not need a material medium to move. Unlike other particles, photons do not decay or spontaneously change into other types of particles, so the speed of light doesn’t matter.

What Happens If You Travel Faster Than the Speed of Light ?

What happens if you travel faster than the rate of light ? The question of how to achieve such speeds is a common one among science fiction lovers, but few people really understand how the concept works. In simple terms, the speed of light is the speed of an object travelling in a vacuum, and when we move faster than this, we shrink the spatial dimension and slow down the time. The problem with this is that our perception of time and space is not fixed in the first place.

What happens if you travel faster than the speed of light

The first attempts to answer this question were unsuccessful. There were no experiments to confirm the theory, and scientists were not sure whether or not the concept was real. Many believed that it was impossible, but a few years later, physicists flew super-accurate caesium atomic clocks on commercial aircraft. The resulting measurements showed that the moving clocks ran slower than the reference clock in a laboratory. Einstein predicted that time would slow down at higher speeds because photons would be impeded by particles and other media. In fact, light only moves at 75% of the speed of the force of gravity through water.

If you travel faster than the speed of light , time will slow down. The more you move, the more time you will slow down. When you get closer to the speed of light , the faster your speed will be. Eventually, it will stop. However, it will return to normal at a slower pace. But how will you know if you’re traveling faster than the frequency of light ?

Is Light Visible in a Vacuum?

The question of “Is light visible in a vacuum?” can be a complex one. While we observe objects, such as stars in the night sky, they are millions of light years away. Hence, it’s unlikely that the distant stars would be seen by us if we don’t see them. In addition, light must travel across vast stretches of space, which is composed of a large amount of vacuum. However, light can be detected in a vacuum, and this is the main reason for its visible presence in space.

Is light visible in a vacuum

Light is electromagnetic radiation. It can be a wave or a particle. The wavelength of a given light varies with its frequency. In a vacuum, the speed of light is 300 million kilometers per second. This same speed of light can’t be measured. Its wavelength defines its wavelength. The quantity of visible light , called a photon, is measurable. And, unlike other forms of energy, light is not a single substance – it’s made up of photons.

While the frequency of light in a vacuum is the same as the speed of light in a solid, transparent medium, the velocity of light in a vacuum is much slower than in a solid. It also takes longer to travel in a vacuum than in a solid or a liquid. This means that the wavelength of light is a different number for each wavelength. A simple example of this is a fluorescent light .

What Happens to the Matter in Outer Space?

We don’t feel comfortable in space. But this might not be true for long. As the universe expands, the void in outer space shrinks as well. As a result, the space around us is empty. Until the universe expands again, it won’t be filled with any matter. Therefore, if outer spaces are actually empty, it should be completely empty! A question arises: “What happens to the matter in outer space?”

If outer space is a vacuum

The concept of a vacuum has its roots in physics. A vacuum is a region of space and time that is completely devoid of matter. The space surrounding the Solar System has five atoms per cubic centimeter. Interstellar space has one atom per cubic centimetre. In contrast, intergalactic space has a hundred times less atomic density. This difference in density is because quantum theory states that energy fluctuations and virtual particles pop into empty space .

The concept of a vacuum is very controversial. The strictest definition of a ‘vacuum’ is a region of space and time where all stress-energy tensor components are zero. This means that the area is devoid of particles and physical fields. This state is unattainable in our present-day universe, so a ‘vacuum’ is not an ideal place to live.

What Kind of Waves Can Travel Through a Void?

What kind of waves can travel through a void? A vacuum can only carry certain kinds of energy, such as electromagnetic waves. This is because they don’t require a medium for propagation. Among these, sound and light waves. These can be sent from one point to another. A vacuum cannot contain these two types of energy. So which is more likely to occur in the absence of a medium?

There are three kinds of waves that can travel through a void: electromagnetic waves, transverse waves, and longitudinal ones. While electromagnetic waves can travel through a void without any medium, they can’t. They all need a material medium to move through. While these types of waves can move through a vacuum, only light can be sent through a void. However, light is considered a transverse wave.

Electromagnetic waves and mechanical waves can travel through a void. These are the types of waves that can move through a vacuum without any medium. These are the electromagnetic waves that we commonly think of when we think about light or sound. While they can move through a void, they require a material medium in order to be transmitted. This is not the case with gamma rays, which have a higher frequency.

are infrared waves electromagnetic or mechanical

Leave a Comment Cancel reply

Hello and welcome to my infrared for health site ! I’m very excited to show you that the infrared technology will be able to recover your health in no matter what the current condition your body’s state. I will try my best to make this site very comprehensive and articles will be helpful and informative why you need infrared products to make your life fruitful.

Latest Blogs

hooga health

Boost Well-Being with Hooga Health Essentials

February 9, 2024

how to turn on a treadmill

How to Turn On a Treadmill: Quick Start Guide

employment in qatar for foreigners

Work in Qatar: Guide for Foreign Job Seekers

February 8, 2024

© Infraredforhealth.com

Library homepage

  • school Campus Bookshelves
  • menu_book Bookshelves
  • perm_media Learning Objects
  • login Login
  • how_to_reg Request Instructor Account
  • hub Instructor Commons
  • Download Page (PDF)
  • Download Full Book (PDF)
  • Periodic Table
  • Physics Constants
  • Scientific Calculator
  • Reference & Cite
  • Tools expand_more
  • Readability

selected template will load here

This action is not available.

Physics LibreTexts

3.1: Light as a Wave

  • Last updated
  • Save as PDF
  • Page ID 18452

  • Tom Weideman
  • University of California, Davis

What is "Waving"?

The jump from mechanical waves to sound was a difficult one, mainly because the "displacement" of the wave changed from matter that oscillates back-and-forth, to (in the case of sound in a gas) oscillations in pressure or density. This difficulty gets greatly magnified for the case of light. We know that light is a wave based on how it behaves – it exhibits the same properties of other waves we have examined – it interferes with itself, it follows an inverse-square law for intensity (brightness), and so on. But we also know that we can see light from the sun, moon, and stars, which means that light waves can travel through the vacuum of space. Unlike every other wave we have seen, it doesn't require any medium at all! So what do we use as the "displacement" for our wave function?

Back in the 19th century, physicists studied extensively the subjects of electricity (lightning, shocking your finger on a doorknob, balloons sticking to your hair, etc.) and magnetism (compasses, sticking things to your refrigerator, etc.). It started becoming clear that the two forces, while different, had some links. Electric currents were found to affect compass needles, and magnets moving near wires were found to create electric currents. It all came together with an amazing (for the time) effort in mathematics by a man named James Clerk Maxwell. He showed that changing electric fields could induce magnetic fields, while changing magnetic fields could in turn induce electric fields. This is a recipe for propagation of these fields, and the equation he derived for this propagation was exactly the wave equation! So he predicted, from results taken from experiments in electricity and magnetism, that an electromagnetic wave could be produced. The wave equation included physical constants from both electricity and magnetism, and extracting the wave speed from this equation resulted in a number Maxwell was already familiar with – the speed of light. It is traditional to denote this speed with a lower-case 'c':

\[c = 3.0\times10^8\frac{m}{s}\]

So the "displacement" of such a wave is actually the electric and magnetic field vectors (both types of fields are waving simultaneously, with each inducing the other) in the space through which the light wave is traveling. Don't worry that this doesn't make much sense right now – it should be a bit clearer when you get to Physics 9C and study electricity & magnetism.

Okay, so for light we now have the wave speed and the "displacement." Let's address a couple other elements of light as a wave. First, a medium is not needed, as electric and magnetic field can exist in a vacuum. The presence of a medium (such as air or water) does effect the electric and magnetic fields, because media are made up of atoms, which are composed of positive and negative electric charges. Because of this, the speed of light within a medium is different (slower) than its speed in a vacuum. Mathematics and experiments show that light is a transverse wave – the electric and magnetic field vectors point in directions that are perpendicular to the direction of motion of the light wave (and as it turns out, they also rare always perpendicular to each other).

Figure 3.1.1 – Electromagnetic Wave

The red arrows in the figure above represent electric field vectors, and blue arrows magnetic field vectors. Specifically, this is a plane-polarized EM wave, which means the field vectors of a given type remain in a single plane. We will discuss plane polarization soon, but it should be noted that EM waves do not have to behave this way, so long as the electric and magnetic field vectors remain perpendicular to each other and to the direction of motion. For example, a circularly polarized EM wave features electric and magnetic field vectors that circulate their directions (while remaining perpendicular to each other and the direction of motion) as the wave propagates, like the hands of an analog clock, and can do so in a clockwise or counterclockwise manner.

Finally, we need to say two things about light perception. For sound, intensity (proportional to amplitude-squared) is perceived as loudness, and for light it is brightness. For sound, frequency is perceived as pitch, and for visible light it is perceived as color. The qualification "visible" must be appended because we can only see a very limits spectrum of light frequencies, the rainbow of colors often described with the acronym ROYGBIV (Red, Orange, Yellow, Green, Blue, Indigo, Violet). The red end of the visible spectrum exhibit the lowest frequencies, and the violet the highest. But of course light waves can come in frequencies much lower and much higher, and at various arbitrary cutoffs, they are given names you have probably heard before. In order of increasing frequency below the red end of the visible spectrum we have: radio waves , microwaves , and infrared ; and above the violet end of the spectrum: ultraviolet , x-rays , and gamma rays .

Huygens's Principle

When we discussed the case of a wave on a string, we said that the wave causes each particle on the string to vibrate up-and-down in harmonic motion. It should therefore not be surprising that if we grab the string at a single point and force it to vibrate in harmonic motion, that a wave will propagate away from that point. In fact, this gives us a way of describing how the wave propagates: The wave causes a single point to oscillate, which in turn causes a wave to be generated, which then vibrates another point, and so on. In the 17th century a Dutch scientist named Christian Huygens generalized this idea to three dimensions. The principle which now bears his name can be stated this way:

Every (3-dimensional) wave propagates by having every point on a wavefront being an independent generator of a new spherical wave, and the interference of all of those individual spherical waves results in the overall wave observed.

When we look at a single point light source, the farther away it is, the flatter the light wavefronts will be when they reach us. When the source is very far away (e.g. the sun), then the wavefronts are essentially flat. We call waves with such flat wavefronts plane waves , for obvious reasons. But now the question arises, “If Huygens’s principle is valid, how can plane waves occur?” After all, each point on the plane wave behaves as a point source of a spherical wave. Let's look at the spherical wave contributions of many point sources on a plane. We'll do this gradually, starting with just a few points on a plane, and filling in the spaces between them little-by-little:

Figure 3.1.2 – Plane Wave from Huygens's Principle

Huygens_plane_waves.png

One might ask why a plane wave only propagates in a single direction. Suppose a plane wave propagating to the right. If each new wavefront becomes a source for a new wave, why don't waves come out of it in both directions? It is difficult to express in a simple diagram like the one above the effects of superposition, but the short answer is that there is destructive interference between all of the previous wavefronts and the new one, which results in zero wave energy traveling "backwards."

It should also be noted that a plane wave is a one-dimensional wave, which means that its intensity does not drop off with distance. But the intensities of the spherical wavelets do follow an inverse-square law. So if they get weaker with distance, why don't plane waves? The reason is that the farther a wavelet travels, the more other wavelets it encounters. These encounters result in constructive interference, bolstering the amplitude (and therefore the intensity) The rate at which the wavelets encounter other wavelets and constructively interfere is exactly enough to compensate for each wavelet losing its own individual intensity, maintaining the plane wave's intensity.

Where Huygens's principle becomes particularly useful is in explaining what happens when a plane wave encounters a barrier. A plane wave moves straight ahead because there is destructive interference of the wavelets in other directions. But a barrier removes a number of wavelets by either absorbing or reflecting the part of the wavefront from which those wavelets were going to spawn. The result is that the wave "bends around corners," a phenomenon known as diffraction .

Figure 3.1.3 – Diffraction from Huygens's Principle

diffraction.png

Like other wave phenomena, this is not unique to light. Ocean waves diffract around barriers like reefs, peninsulas, and docks. It's certainly possible to hear a sound made from around a corner. Of course reflections of waves are also responsible for their ability to change direction in the presence of barriers, but the phenomenon of diffraction in conjunction with interference leads to other important observable properties that we will deal with next.

You should be aware that diffraction is so intimately tied up with the interference effects that it causes (the subjects of the next few sections) that many physicists use the word "diffraction" to indicate the interference phenomena themselves, rather than the "going around corners" definition.

  • 17.1 Understanding Diffraction and Interference
  • Introduction
  • 1.1 Physics: Definitions and Applications
  • 1.2 The Scientific Methods
  • 1.3 The Language of Physics: Physical Quantities and Units
  • Section Summary
  • Key Equations
  • Concept Items
  • Critical Thinking Items
  • Performance Task
  • Multiple Choice
  • Short Answer
  • Extended Response
  • 2.1 Relative Motion, Distance, and Displacement
  • 2.2 Speed and Velocity
  • 2.3 Position vs. Time Graphs
  • 2.4 Velocity vs. Time Graphs
  • 3.1 Acceleration
  • 3.2 Representing Acceleration with Equations and Graphs
  • 4.2 Newton's First Law of Motion: Inertia
  • 4.3 Newton's Second Law of Motion
  • 4.4 Newton's Third Law of Motion
  • 5.1 Vector Addition and Subtraction: Graphical Methods
  • 5.2 Vector Addition and Subtraction: Analytical Methods
  • 5.3 Projectile Motion
  • 5.4 Inclined Planes
  • 5.5 Simple Harmonic Motion
  • 6.1 Angle of Rotation and Angular Velocity
  • 6.2 Uniform Circular Motion
  • 6.3 Rotational Motion
  • 7.1 Kepler's Laws of Planetary Motion
  • 7.2 Newton's Law of Universal Gravitation and Einstein's Theory of General Relativity
  • 8.1 Linear Momentum, Force, and Impulse
  • 8.2 Conservation of Momentum
  • 8.3 Elastic and Inelastic Collisions
  • 9.1 Work, Power, and the Work–Energy Theorem
  • 9.2 Mechanical Energy and Conservation of Energy
  • 9.3 Simple Machines
  • 10.1 Postulates of Special Relativity
  • 10.2 Consequences of Special Relativity
  • 11.1 Temperature and Thermal Energy
  • 11.2 Heat, Specific Heat, and Heat Transfer
  • 11.3 Phase Change and Latent Heat
  • 12.1 Zeroth Law of Thermodynamics: Thermal Equilibrium
  • 12.2 First law of Thermodynamics: Thermal Energy and Work
  • 12.3 Second Law of Thermodynamics: Entropy
  • 12.4 Applications of Thermodynamics: Heat Engines, Heat Pumps, and Refrigerators
  • 13.1 Types of Waves
  • 13.2 Wave Properties: Speed, Amplitude, Frequency, and Period
  • 13.3 Wave Interaction: Superposition and Interference
  • 14.1 Speed of Sound, Frequency, and Wavelength
  • 14.2 Sound Intensity and Sound Level
  • 14.3 Doppler Effect and Sonic Booms
  • 14.4 Sound Interference and Resonance
  • 15.1 The Electromagnetic Spectrum
  • 15.2 The Behavior of Electromagnetic Radiation
  • 16.1 Reflection
  • 16.2 Refraction
  • 16.3 Lenses
  • 17.2 Applications of Diffraction, Interference, and Coherence
  • 18.1 Electrical Charges, Conservation of Charge, and Transfer of Charge
  • 18.2 Coulomb's law
  • 18.3 Electric Field
  • 18.4 Electric Potential
  • 18.5 Capacitors and Dielectrics
  • 19.1 Ohm's law
  • 19.2 Series Circuits
  • 19.3 Parallel Circuits
  • 19.4 Electric Power
  • 20.1 Magnetic Fields, Field Lines, and Force
  • 20.2 Motors, Generators, and Transformers
  • 20.3 Electromagnetic Induction
  • 21.1 Planck and Quantum Nature of Light
  • 21.2 Einstein and the Photoelectric Effect
  • 21.3 The Dual Nature of Light
  • 22.1 The Structure of the Atom
  • 22.2 Nuclear Forces and Radioactivity
  • 22.3 Half Life and Radiometric Dating
  • 22.4 Nuclear Fission and Fusion
  • 22.5 Medical Applications of Radioactivity: Diagnostic Imaging and Radiation
  • 23.1 The Four Fundamental Forces
  • 23.2 Quarks
  • 23.3 The Unification of Forces
  • A | Reference Tables

Section Learning Objectives

By the end of this section, you will be able to do the following:

  • Explain wave behavior of light, including diffraction and interference, including the role of constructive and destructive interference in Young’s single-slit and double-slit experiments
  • Perform calculations involving diffraction and interference, in particular the wavelength of light using data from a two-slit interference pattern

Teacher Support

The learning objectives in this section will help your students master the following standards:

  • (D) investigate behaviors of waves, including reflection, refraction, diffraction, interference, resonance, and the Doppler effect

Section Key Terms

Diffraction and interference.

[BL] Explain constructive and destructive interference graphically on the board.

[OL] Ask students to look closely at a shadow. Ask why the edges are not sharp lines. Explain that this is caused by diffraction, one of the wave properties of electromagnetic radiation. Define the nanometer in relation to other metric length measurements.

[AL] Ask students which, among speed, frequency, and wavelength, stay the same, and which change, when a ray of light travels from one medium to another. Discuss those quantities in terms of colors (wavelengths) of visible light.

We know that visible light is the type of electromagnetic wave to which our eyes responds. As we have seen previously, light obeys the equation

where c = 3.00 × 10 8 c = 3.00 × 10 8 m/s is the speed of light in vacuum, f is the frequency of the electromagnetic wave in Hz (or s –1 ), and λ λ is its wavelength in m. The range of visible wavelengths is approximately 380 to 750 nm. As is true for all waves, light travels in straight lines and acts like a ray when it interacts with objects several times as large as its wavelength. However, when it interacts with smaller objects, it displays its wave characteristics prominently. Interference is the identifying behavior of a wave.

In Figure 17.2 , both the ray and wave characteristics of light can be seen. The laser beam emitted by the observatory represents ray behavior, as it travels in a straight line. Passing a pure, one-wavelength beam through vertical slits with a width close to the wavelength of the beam reveals the wave character of light. Here we see the beam spreading out horizontally into a pattern of bright and dark regions that are caused by systematic constructive and destructive interference. As it is characteristic of wave behavior, interference is observed for water waves, sound waves, and light waves.

That interference is a characteristic of energy propagation by waves is demonstrated more convincingly by water waves. Figure 17.3 shows water waves passing through gaps between some rocks. You can easily see that the gaps are similar in width to the wavelength of the waves and that this causes an interference pattern as the waves pass beyond the gaps. A cross-section across the waves in the foreground would show the crests and troughs characteristic of an interference pattern.

Light has wave characteristics in various media as well as in a vacuum. When light goes from a vacuum to some medium, such as water, its speed and wavelength change, but its frequency, f , remains the same. The speed of light in a medium is v = c / n v = c / n , where n is its index of refraction. If you divide both sides of the equation c = f λ c = f λ by n , you get c / n = v = f λ / n c / n = v = f λ / n . Therefore, v = f λ n v = f λ n , where λ n λ n is the wavelength in a medium, and

where λ λ is the wavelength in vacuum and n is the medium’s index of refraction. It follows that the wavelength of light is smaller in any medium than it is in vacuum. In water, for example, which has n = 1.333, the range of visible wavelengths is (380 nm)/1.333 to (760 nm)/1.333, or λ n = λ n = 285–570 nm. Although wavelengths change while traveling from one medium to another, colors do not, since colors are associated with frequency.

The Dutch scientist Christiaan Huygens (1629–1695) developed a useful technique for determining in detail how and where waves propagate. He used wavefronts , which are the points on a wave’s surface that share the same, constant phase (such as all the points that make up the crest of a water wave). Huygens’s principle states, “Every point on a wavefront is a source of wavelets that spread out in the forward direction at the same speed as the wave itself. The new wavefront is a line tangent to all of the wavelets.”

Figure 17.4 shows how Huygens’s principle is applied. A wavefront is the long edge that moves; for example, the crest or the trough. Each point on the wavefront emits a semicircular wave that moves at the propagation speed v . These are drawn later at a time, t , so that they have moved a distance s = v t s = v t . The new wavefront is a line tangent to the wavelets and is where the wave is located at time t . Huygens’s principle works for all types of waves, including water waves, sound waves, and light waves. It will be useful not only in describing how light waves propagate, but also in how they interfere.

What happens when a wave passes through an opening, such as light shining through an open door into a dark room? For light, you expect to see a sharp shadow of the doorway on the floor of the room, and you expect no light to bend around corners into other parts of the room. When sound passes through a door, you hear it everywhere in the room and, thus, you understand that sound spreads out when passing through such an opening. What is the difference between the behavior of sound waves and light waves in this case? The answer is that the wavelengths that make up the light are very short, so that the light acts like a ray. Sound has wavelengths on the order of the size of the door, and so it bends around corners.

[OL] Discuss the fact that, for a diffraction pattern to be visible, the width of a slit must be roughly the wavelength of the light. Try to give students an idea of the size of visible light wavelengths by noting that a human hair is roughly 100 times wider.

If light passes through smaller openings, often called slits, you can use Huygens’s principle to show that light bends as sound does (see Figure 17.5 ). The bending of a wave around the edges of an opening or an obstacle is called diffraction . Diffraction is a wave characteristic that occurs for all types of waves. If diffraction is observed for a phenomenon, it is evidence that the phenomenon is produced by waves. Thus, the horizontal diffraction of the laser beam after it passes through slits in Figure 17.2 is evidence that light has the properties of a wave.

Once again, water waves present a familiar example of a wave phenomenon that is easy to observe and understand, as shown in Figure 17.6 .

Watch Physics

Single-slit interference.

This video works through the math needed to predict diffraction patterns that are caused by single-slit interference.

Which values of m denote the location of destructive interference in a single-slit diffraction pattern?

  • whole integers, excluding zero
  • whole integers
  • real numbers excluding zero
  • real numbers

The fact that Huygens’s principle worked was not considered enough evidence to prove that light is a wave. People were also reluctant to accept light’s wave nature because it contradicted the ideas of Isaac Newton, who was still held in high esteem. The acceptance of the wave character of light came after 1801, when the English physicist and physician Thomas Young (1773–1829) did his now-classic double-slit experiment (see Figure 17.7 ).

When light passes through narrow slits, it is diffracted into semicircular waves, as shown in Figure 17.8 (a). Pure constructive interference occurs where the waves line up crest to crest or trough to trough. Pure destructive interference occurs where they line up crest to trough. The light must fall on a screen and be scattered into our eyes for the pattern to be visible. An analogous pattern for water waves is shown in Figure 17.8 (b). Note that regions of constructive and destructive interference move out from the slits at well-defined angles to the original beam. Those angles depend on wavelength and the distance between the slits, as you will see below.

Virtual Physics

Wave interference.

This simulation demonstrates most of the wave phenomena discussed in this section. First, observe interference between two sources of electromagnetic radiation without adding slits. See how water waves, sound, and light all show interference patterns. Stay with light waves and use only one source. Create diffraction patterns with one slit and then with two. You may have to adjust slit width to see the pattern.

Visually compare the slit width to the wavelength. When do you get the best-defined diffraction pattern?

  • when the slit width is larger than the wavelength
  • when the slit width is smaller than the wavelength
  • when the slit width is comparable to the wavelength
  • when the slit width is infinite

Calculations Involving Diffraction and Interference

[BL] The Greek letter θ θ is spelled theta . The Greek letter λ λ is spelled lamda . Both are pronounced the way you would expect from the spelling. The plurals of maximum and minimum are maxima and minima , respectively.

[OL] Explain that monochromatic means one color. Monochromatic also means one frequency . The sine of an angle is the opposite side of a right triangle divided by the hypotenuse. Opposite means opposite the given acute angle. Note that the sign of an angle is always ≥ 1.

The fact that the wavelength of light of one color, or monochromatic light, can be calculated from its two-slit diffraction pattern in Young’s experiments supports the conclusion that light has wave properties. To understand the basis of such calculations, consider how two waves travel from the slits to the screen. Each slit is a different distance from a given point on the screen. Thus different numbers of wavelengths fit into each path. Waves start out from the slits in phase (crest to crest), but they will end up out of phase (crest to trough) at the screen if the paths differ in length by half a wavelength, interfering destructively. If the paths differ by a whole wavelength, then the waves arrive in phase (crest to crest) at the screen, interfering constructively. More generally, if the paths taken by the two waves differ by any half-integral number of wavelengths ( 1 2 λ ,   3 2 λ ,   5 2 λ ,  etc .) ( 1 2 λ ,   3 2 λ ,   5 2 λ ,  etc .) , then destructive interference occurs. Similarly, if the paths taken by the two waves differ by any integral number of wavelengths ( λ ,   2 λ ,   3 λ ,  etc .) ( λ ,   2 λ ,   3 λ ,  etc .) , then constructive interference occurs.

Figure 17.9 shows how to determine the path-length difference for waves traveling from two slits to a common point on a screen. If the screen is a large distance away compared with the distance between the slits, then the angle θ θ between the path and a line from the slits perpendicular to the screen (see the figure) is nearly the same for each path. That approximation and simple trigonometry show the length difference, Δ L Δ L , to be d sin θ d sin θ , where d is the distance between the slits,

To obtain constructive interference for a double slit, the path-length difference must be an integral multiple of the wavelength, or

Similarly, to obtain destructive interference for a double slit, the path-length difference must be a half-integral multiple of the wavelength, or

The number m is the order of the interference. For example, m = 4 is fourth-order interference.

Figure 17.10 shows how the intensity of the bands of constructive interference decreases with increasing angle.

Light passing through a single slit forms a diffraction pattern somewhat different from that formed by double slits. Figure 17.11 shows a single-slit diffraction pattern. Note that the central maximum is larger than those on either side, and that the intensity decreases rapidly on either side.

The analysis of single-slit diffraction is illustrated in Figure 17.12 . Assuming the screen is very far away compared with the size of the slit, rays heading toward a common destination are nearly parallel. That approximation allows a series of trigonometric operations that result in the equations for the minima produced by destructive interference.

When rays travel straight ahead, they remain in phase and a central maximum is obtained. However, when rays travel at an angle θ θ relative to the original direction of the beam, each ray travels a different distance to the screen, and they can arrive in or out of phase. Thus, a ray from the center travels a distance λ / 2 λ / 2 farther than the ray from the top edge of the slit, they arrive out of phase, and they interfere destructively. Similarly, for every ray between the top and the center of the slit, there is a ray between the center and the bottom of the slit that travels a distance λ / 2 λ / 2 farther to the common point on the screen, and so interferes destructively. Symmetrically, there will be another minimum at the same angle below the direct ray.

Below we summarize the equations needed for the calculations to follow.

The speed of light in a vacuum, c , the wavelength of the light, λ λ , and its frequency, f , are related as follows.

The wavelength of light in a medium, λ n λ n , compared to its wavelength in a vacuum, λ λ , is given by

To calculate the positions of constructive interference for a double slit, the path-length difference must be an integral multiple, m , of the wavelength. λ λ

where d is the distance between the slits and θ θ is the angle between a line from the slits to the maximum and a line perpendicular to the barrier in which the slits are located. To calculate the positions of destructive interference for a double slit, the path-length difference must be a half-integral multiple of the wavelength:

For a single-slit diffraction pattern, the width of the slit, D , the distance of the first ( m = 1) destructive interference minimum, y , the distance from the slit to the screen, L , and the wavelength, λ λ , are given by

Also, for single-slit diffraction,

where θ θ is the angle between a line from the slit to the minimum and a line perpendicular to the screen, and m is the order of the minimum.

Worked Example

Two-slit interference.

Suppose you pass light from a He-Ne laser through two slits separated by 0.0100 mm, and you find that the third bright line on a screen is formed at an angle of 10.95º relative to the incident beam. What is the wavelength of the light?

The third bright line is due to third-order constructive interference, which means that m = 3. You are given d = 0.0100 mm and θ θ = 10.95º. The wavelength can thus be found using the equation d sin θ = m λ d sin θ = m λ for constructive interference.

The equation is d sin θ = m λ d sin θ = m λ . Solving for the wavelength, λ λ , gives

Substituting known values yields

To three digits, 633 nm is the wavelength of light emitted by the common He-Ne laser. Not by coincidence, this red color is similar to that emitted by neon lights. More important, however, is the fact that interference patterns can be used to measure wavelength. Young did that for visible wavelengths. His analytical technique is still widely used to measure electromagnetic spectra. For a given order, the angle for constructive interference increases with λ λ , so spectra (measurements of intensity versus wavelength) can be obtained.

Single-Slit Diffraction

Visible light of wavelength 550 nm falls on a single slit and produces its second diffraction minimum at an angle of 45.0° relative to the incident direction of the light. What is the width of the slit?

From the given information, and assuming the screen is far away from the slit, you can use the equation D sin θ = m λ D sin θ = m λ to find D .

Quantities given are λ λ = 550 nm, m = 2, and θ 2 θ 2 = 45.0°. Solving the equation D sin θ = m λ D sin θ = m λ for D and substituting known values gives

You see that the slit is narrow (it is only a few times greater than the wavelength of light). That is consistent with the fact that light must interact with an object comparable in size to its wavelength in order to exhibit significant wave effects, such as this single-slit diffraction pattern.

Practice Problems

What is the width of a single slit through which 610-nm orange light passes to form a first diffraction minimum at an angle of 30.0°?

Check Your Understanding

Use these problems to assess student achievement of the section’s learning objectives. If students are struggling with a specific objective, these problems will help identify which and direct students to the relevant topics.

  • The wavelength first decreases and then increases.
  • The wavelength first increases and then decreases.
  • The wavelength increases.
  • The wavelength decreases.
  • This is a diffraction effect. Your whole body acts as the origin for a new wavefront.
  • This is a diffraction effect. Every point on the edge of your shadow acts as the origin for a new wavefront.
  • This is a refraction effect. Your whole body acts as the origin for a new wavefront.
  • This is a refraction effect. Every point on the edge of your shadow acts as the origin for a new wavefront.

As an Amazon Associate we earn from qualifying purchases.

This book may not be used in the training of large language models or otherwise be ingested into large language models or generative AI offerings without OpenStax's permission.

Want to cite, share, or modify this book? This book uses the Creative Commons Attribution License and you must attribute Texas Education Agency (TEA). The original material is available at: https://www.texasgateway.org/book/tea-physics . Changes were made to the original material, including updates to art, structure, and other content updates.

Access for free at https://openstax.org/books/physics/pages/1-introduction
  • Authors: Paul Peter Urone, Roger Hinrichs
  • Publisher/website: OpenStax
  • Book title: Physics
  • Publication date: Mar 26, 2020
  • Location: Houston, Texas
  • Book URL: https://openstax.org/books/physics/pages/1-introduction
  • Section URL: https://openstax.org/books/physics/pages/17-1-understanding-diffraction-and-interference

© Jan 19, 2024 Texas Education Agency (TEA). The OpenStax name, OpenStax logo, OpenStax book covers, OpenStax CNX name, and OpenStax CNX logo are not subject to the Creative Commons license and may not be reproduced without the prior and express written consent of Rice University.

Light Year Calculator

What is light year, how to calculate light years.

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

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

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

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

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

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

You can perform the calculation in three steps:

Determine the speed of light.

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

Compute the time that the light has traveled.

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

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

Calculate the distance that the light has traveled.

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

distance = speed of light × time

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

How do I calculate the distance that light travels?

You can calculate the distance light travels in three steps:

Determine the light speed .

Determine the time the light has traveled.

Apply the light year formula :

distance = light speed × time

How far light can travel in 1 second?

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

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

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

Can light years be used to measure time?

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

Chilled drink

Curie's law, humans vs vampires, thermal diffusivity.

  • Biology ( 98 )
  • Chemistry ( 98 )
  • Construction ( 144 )
  • Conversion ( 292 )
  • Ecology ( 30 )
  • Everyday life ( 261 )
  • Finance ( 565 )
  • Food ( 66 )
  • Health ( 439 )
  • Math ( 660 )
  • Physics ( 508 )
  • Sports ( 104 )
  • Statistics ( 182 )
  • Other ( 180 )
  • Discover Omni ( 40 )

IMAGES

  1. SOLVED:Determine the distance in feet that light can travel in vacuum during 1.00 ns

    light can travel in vacuum a distance of about

  2. The Speed Of Light Can Vary In A Vacuum

    light can travel in vacuum a distance of about

  3. Can Light Travel in a Vacuum? Exploring the Physics and Properties of Light

    light can travel in vacuum a distance of about

  4. Why can light travel in vacuum

    light can travel in vacuum a distance of about

  5. [Solved] In a vacuum, can you see light which is not

    light can travel in vacuum a distance of about

  6. Physics: Sound And Vacuum: Level 1 activity for kids

    light can travel in vacuum a distance of about

VIDEO

  1. Is There anything that Travels at the Speed of Light⁉️ Neil deGrasse Tyson #physics #universe

  2. It is said that light can travel a hundred times faster than light. Do you#funny

  3. REFRACTION OF LIGHT: LESSON 3

  4. Let me tell you, the speed of light is mind-blowingly incredible!

  5. How to use vacuum bags to pack for travel (also an unboxing)

  6. This is how light travels in the universe !

COMMENTS

  1. What is light, and how can it travel in a vacuum forever in all

    How can light (or electromagnetic radiation) travel through a vacuum when there is nothing there to act as a medium, and do so forever in all directions? For example the light coming from a star millions of light years away. Light is observed as traveling at velocity v=c, according to the second postulate of special relativity. But according to ...

  2. How do we know that light can travel through a vacuum?

    The reason you can see each object is that light has traveled a great distance through a vacuum to your eyeball. There have also been experiments on earth that require light to pass through a man made vacuum. Scientist actually use the speed and properties of light traveling through a vacuum as a standard. Click Here to return to the search form.

  3. How fast does light travel?

    The speed of light in a vacuum is 186,282 miles per second (299,792 kilometers per second), and in theory nothing can travel faster than light.

  4. Does Light Travel Forever?

    In contrast, light waves can travel through a vacuum, and do not require a medium. In empty space, the wave does not dissipate (grow smaller) no matter how far it travels, because the wave is not interacting with anything else. This is why light from distant stars can travel through space for billions of light-years and still reach us on earth.

  5. Speed of light

    The speed of light in vacuum, commonly denoted c, is a universal physical constant that is exactly equal to 299,792,458 metres per second (approximately 300,000 kilometres per second; 186,000 miles per second; 671 million miles per hour). According to the special theory of relativity, c is the upper limit for the speed at which conventional matter or energy (and thus any signal carrying ...

  6. Speed of Light Calculator

    The final step is to calculate the total distance that the light has traveled within the time. You can calculate this answer using the speed of light formula: distance = speed of light × time. Thus, the distance that the light can travel in 100 seconds is 299,792,458 m/s × 100 seconds = 29,979,245,800 m. FAQs.

  7. The Nature of Light

    Like all electromagnetic waves, light can travel through a vacuum. The transverse nature of light can be demonstrated through polarization. In 1678, Christiaan Huygens ... Falcon can see a 10 cm. object from a distance of 1.5 km. Fly's Eye has a flicker fusion rate of 300/s. Humans have a flicker fusion rate of only 60/s in bright light and 24 ...

  8. How Does Light Travel?

    If the light is visible, the frequency of vibration determines color. The speed of light is unaffected by vibrational frequency, however. In a vacuum, it is always 299,792 kilometers per second (186, 282 miles per second), a value denoted by the letter "c." According to Einstein's Theory of Relativity, nothing in the universe travels faster ...

  9. Physics Explained: Here's Why The Speed of Light Is The ...

    Today the speed of light, or c as it's commonly known, is considered the cornerstone of special relativity - unlike space and time, the speed of light is constant, independent of the observer. What's more, this constant underpins much of what we understand about the Universe. It matches the speed of a gravitational wave, and yes, it's the ...

  10. Understanding light and other forms of energy on the move

    All light shares three properties. It can travel through a vacuum. It always moves at a constant speed, known as the speed of light, which is 300,000,000 meters (186,000 miles) per second in a vacuum. And the wavelength defines the type or color of light. Just to make things interesting, light also can behave as photons, or particles. When ...

  11. 16.1 Traveling Waves

    Electromagnetic waves can travel through a vacuum at the speed of light, v = c = 2.99792458 × 10 8 m/s. v = c = 2.99792458 × 10 8 m/s. For example, light from distant stars travels through the vacuum of space and reaches Earth. ... the velocity of the wave can be found by dividing the distance traveled by the wave by the time it took the wave ...

  12. 1.1 The Propagation of Light

    The speed of light in a vacuum c is one of the fundamental constants of physics. ... and the distance to the mirror, Fizeau determined the speed of light to be 3.15 ... There are three ways in which light can travel from a source to another location . It can come directly from the source through empty space, such as from the Sun to Earth.

  13. Light: Electromagnetic waves, the electromagnetic spectrum and photons

    We can start with our equation that relates frequency, wavelength, and the speed of light. c = λ ν. Next, we rearrange the equation to solve for wavelength. λ = c ν. Lastly, we plug in our given values and solve. λ = 3.00 × 10 8 m s 1.5 × 10 14 1 s = 2.00 × 10 − 6 m.

  14. What is the speed of light?

    This is why astronomers use the unit light-years — the distance light can travel in one year — to measure ... In a vacuum, such as outer space, light travels at a constant speed of ...

  15. How to Travel at (Nearly) the Speed of Light

    The theory of special relativity showed that particles of light, photons, travel through a vacuum at a constant pace of 670,616,629 miles per hour — a speed that's immensely difficult to achieve and impossible to surpass in that environment. Yet all across space, from black holes to our near-Earth environment, particles are, in fact, being ...

  16. 16.2: Traveling Waves

    Electromagnetic waves can travel through a vacuum at the speed of light, v = c = 2.99792458 x 10 8 m/s. For example, light from distant stars travels through the vacuum of space and reaches Earth. ... the velocity of the wave can be found by dividing the distance traveled by the wave by the time it took the wave to travel the distance.

  17. How Light Travels: Telescopes Can Show Us the Invisible Universe

    They always travel through the vacuum of space at 186,400 miles per second—the speed of light—which is faster than anything else. Too bad we can glimpse only about 0.0035 percent of the light ...

  18. Light

    Light Can Travel Slower. ... Maybe we could call it "Max Speed"! But also because light only travels that speed in a vacuum! It can travel slower ... Medium Speed million m/s; Vacuum: 299.8: Air: 299.7: Ice: 228: Water: 225: Ethanol: 220: Glass: 205: ... The brightness decreases as the square of the distance. Because the light is spreading out ...

  19. Light Waves

    That means in one second light travels a distance of 300 000 000 m - which is about seven and half times around the world, in one second. ... Can they travel through a vacuum? Yes: No: How are ...

  20. Can Light Travel Through A Vacuum?

    In fact, light can traverse a vacuum at 186,400 miles per second. Light travels through a vacuum at a very high rate. In fact, light can travel at almost twice the speed of sound. A halo of atoms can trap the light and prevent it from traveling, so light waves can traverse a vacuum at a much higher speed than sound can.

  21. 3.1: Light as a Wave

    The wave equation included physical constants from both electricity and magnetism, and extracting the wave speed from this equation resulted in a number Maxwell was already familiar with - the speed of light. It is traditional to denote this speed with a lower-case 'c': c = 3.0 ×108m s (3.1.1) (3.1.1) c = 3.0 × 10 8 m s.

  22. 17.1 Understanding Diffraction and Interference

    Diffraction and Interference. We know that visible light is the type of electromagnetic wave to which our eyes responds. As we have seen previously, light obeys the equation. c = f λ, where c = 3.00 × 10 8 m/s is the speed of light in vacuum, f is the frequency of the electromagnetic wave in Hz (or s -1 ), and λ is its wavelength in m.

  23. Light Year Calculator

    The speed of light is the fastest speed in the universe, and it is always a constant in a vacuum. Hence, the speed of light is 299,792,458 m/s, which is 9.46×10¹² km/year. ... Thus, the distance that the light can travel in 100 seconds is 9.46×10¹² km/year × 2 years = 1.892×10¹³ km. FAQ