NounPlural uncountable speed of light (uncountable) (abbreviated as c)
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From Wiktionary under the GNU Free Documentation License. The speed of light, usually denoted by c, is a physical constant, so named because it is the speed at which light and all other electromagnetic radiation travels in vacuum. Its value is exactly 299,792,458 metres per second, often approximated as 300,000 kilometres per second or 186,000 miles per second. In the theory of relativity, c connects space and time in spacetime, and appears in the famous equation of mass–energy equivalence E = mc. The speed of light is the speed of all massless particles and associated fields in vacuum, and it is believed to be the speed of gravity and of gravitational waves and an upper bound on the speed at which energy, matter, and information can travel. The speed at which light propagates through transparent materials, such as glass or air, is less than c. The ratio between c and the speed v at which light travels in a material is called the refractive index n of the material (n = c / v). For example, for visible light the refractive index of glass is typically around 1.5, meaning that light in glass travels at c / 1.5 ≈ 200,000 km/s; the refractive index of air for visible light is about 1.0003, so the speed of light in air is very close to c. For much of human history, it was debated whether light was transmitted instantaneously or merely very quickly. Ole Rømer first demonstrated that it travelled at a finite speed by studying the apparent motion of Jupiter's moon Io. After centuries of increasingly precise measurements, in 1975 the speed of light was known to be 299,792,458 m/s with a relative measurement uncertainty of 4 parts per billion. In 1983, the metre was redefined in the International System of Units (SI) as the distance travelled by light in vacuum in ⁄299,792,458 of a second. As a result, the numerical value of c in metres per second is now fixed exactly by the definition of the metre. From Wikipedia under the
GNU Free Documentation License Why is it impossible for an object to reach the speed of light? Q. I've always wondered about what exactly's stopping an object from going up to or even past that light speed. Asked by Erehwon - Sun Jul 5 17:12:50 2009 - - 5 Answers - 0 Comments A. An object's mass increases the faster it goes. An object which had mass to start with (so photons don't count) would have infinite mass as light speed. F=m*a so to make an object go at light speed you would need an infinite amount of force (because m = infinite). It's physically impossible. Answered by Philip - Sun Jul 5 17:17:59 2009 I have a theory concerning travelling at the speed of light? Q. According to Einstein's theory of relativity, it is impossible to travel at light speed, but let's say it is. If you are inside a train, say, then due to the theory of relativity would you see everything INSIDE the train normally (you are going a constant speed ) like how if you drop something it falls directly downwards unless you are a) accelerating/decceleratin g or b) going round a corner, OR would Einstein's theory that light travels at the same speed for all observers kick into action and some weird space-time warping thing would happen and you wouldn't see anything? Also, if you wouldn't see inside the train normally and things behind you were black, what would you see in front of you as you would reach where they had been before… [cont.] Asked by eggz - Tue Aug 21 11:18:20 2007 - - 15 Answers - 0 Comments A. Einsteins's special theory of relativity only states two things: Law 1 - The laws of physics are the same for all observers in uniform motion (same direction and speed). Law 2 - The speed of light in a vacuum is constant to all observers. Under law one, therefore, the laws of physics will change for an observer at or above the speed of light! Weird space-time warping would happen. Since we cannot observe what happens above the speed of light your opinion is just as good as Einstein's. Neither can be tested by observation. Under law 2 - If Einstein is correct, then anyone measuring the speed of light in a vacuum when travelling at or above the speed of light would find that light is travelling at the speed of light relative to them.… [cont.] Answered by The Red Fool - Tue Aug 21 18:25:46 2007 Is there something similar to the sound barrier at the speed of light?
Q. Were it possible to go faster than light-speed would you ride the crest of some kind of wave similar to that experienced at the sound barrier? Asked by Hva Faen - Sun Jan 17 18:04:11 2010 - - 2 Answers - 0 Comments A. Well, the universe is expanding in which the velocity of 2 objects is proportional to Hubble's Constant and the distance between the 2 objects. That means that things a certain distance from us are receding from us faster than light and their light will never reach us. Therefore, since light travels in all directions we can say that there is a light barrier in our universe. We call this Hubble's radius or the visible universe. Answered by Will Click - Sun Jan 17 18:10:33 2010 From Yahoo Answer Search: "speed of light"  news.google.com UPI.com ... light to illuminate a sample, STEM views samples using a carefully controlled beam of electrons accelerated to nearly the speed of light , Klie said. ... New Electron Microscope Promises Sharper Nano-Viewing Article Ant (press release) all 11 news articles » news.google.com Wall Street Journal Because of that, "traffic in our little town can fly around at the speed of light ," but viewing a YouTube video isn't any faster than in other parts of the ... and more » news.google.com Tampa Tribune "What you put out there, It boomerangs back to you at the speed of light ." WHAT: A sampling of Ybor City's tapas, hors d'oeurves and treats; ... and more » From Google News Search: "speed of light"  speed-light.info 552px x 560px | 82.30kB [source page] put we cannot see Dark Matter nor collide with it but we can detect its gravity In this image two huge clusters of invisible Dark Matter in blue clashed with each other With each cluster having a mass of 10 000 galaxies each cluster a quadrillion times the mass of the Sun 1015 See Universe Today However upon impact instead of  physics.unlv.edu 717px x 947px | 13.50kB [source page] properly The vacuum speed of light is the ultimate physical speed It is much faster than the speed of sound sound speed in air at sea level at 20 degrees C is about 343 m s The speed of light We emphasize that the vacuum speed of light is the ultimate physical speed By this we mean that no physical information or effect can propagate faster than  lloydgodman.net 687px x 900px | 26.90kB [source page] the speed of light an interactive installation of self developing photograms Lloyd Godman 2002 From Yahoo Image Search: "speed of light"  autoblog.com Jonathon Ramsey hu, 08 Jul 2010 21:20:00 GM Now it might be that you do things differently in the US but I was always taught (in Australia) that the yellow . light. is to tell you that there's a red . light. coming and to make a intelligent judgement based on your . speed. , distance from ...  blogs.discovermagazine.com Phil Plait Wed, 07 Jul 2010 13:20:44 GM You can't beam a picture from a satellite in close orbit around the sun because the beam itself is composed of photons or microwaves or radio waves and those also travel at the . speed of light. . You'd get the image from the satellite at ...  gizmag.com unknown hu, 11 Mar 2010 05:21:21 GM IBM researchers have developed their latest building block in their effort to achieve photon-based communication and computing. From Google Blog Search: "speed of light" |
