
	Where results make sense

Topic: The speed of light in vacuum

Related Topics

light year

light rail

speed of light

light cruiser

Docklands Light Railway

Electric Light Orchestra

light bulb

The Guiding Light

light emitting diode

visible light

faster than light

traffic light

In the News (Wed 30 Dec 09)

Northern Trust

Marvin Harrison

Peter Chernin

Gary Locke

Match Play

Penelope Cruz

Mickey Rourke

AR Rahman

Danny Boyle

Hugh Jackman

	Speed of light - Wikipedia, the free encyclopedia
		Note that this speed is a definition, not a measurement; in fact, the fundamental SI unit of distance, the metre, is defined in terms of the speed of light (it is the distance light travels in a vacuum in 1/299,792,458 of a second).
		The speed of light through a transparent medium (that is, not in vacuum) is less than c; the ratio of c to this speed is called the refractive index of the medium.
		However, these jets are not actually moving at speeds in excess of the speed of light: the apparent superluminal motion is a projection effect caused by objects moving near the speed of light and at a small angle to the line of sight.
	en.wikipedia.org /wiki/Speed_of_light (4300 words)

	Light - Encyclopedia.WorldSearch (Site not responding. Last check: 2007-10-09)
		Light is electromagnetic radiation with a wavelength that is visible to the eye, or in a more general sense, any electromagnetic radiation in the range from infrared to ultraviolet.
		Light excites the rod cells and cone cells in the retina of the human eye, creating electrical nerve impulses that travel up the optic nerve to the brain, producing vision.
		The constant speed of light predicted by Maxwell's equations contradicted the mechanical laws of motion that had been unchallenged since the time of Galileo, which stated that all speeds were relative to the speed of the observer.
	encyclopedia.worldsearch.com /light.htm (2504 words)

	Speed of light -- Facts, Info, and Encyclopedia article (Site not responding. Last check: 2007-10-09)
		This exact speed is a definition, not a measurement, as the ((prosody) the accent in a metrical foot of verse) metre itself is defined in terms of the speed of light and the (1/60 of a minute; the basic unit of time adopted under the Systeme International d'Unites) second.
		The speed of light through a medium (that is, not in vacuum) is less than c (defining the (The ratio of the velocity of light in a vacuum to that in a medium) refractive index of the medium).
		In passing through materials, light is slowed to less than c by the ratio called the (The ratio of the velocity of light in a vacuum to that in a medium) refractive index of the material.
	www.absoluteastronomy.com /encyclopedia/s/sp/speed_of_light.htm (4105 words)

	Speed of light
		At present, the speed of light is a definition, not a measurement, as the metre is defined in terms of the speed of light and not vice versa.
		Given that the speed of light is slower in an Optical fiber and that straight lines rarely occur in communications situations, a typical time as of 2004 for an Australia or Japan to US computer-to-computer ping is 0.250 seconds.
		The finite speed of light was not conclusively established by these observations, as it could be argued the differences in the times of eclipses were due to perturbations of the orbits of the satellites.
	www.brainyencyclopedia.com /encyclopedia/s/sp/speed_of_light.html (2181 words)

	Theory (Site not responding. Last check: 2007-10-09)
		The speed of light in a vacuum is 3.0108 m/sec (c), but in any other medium the speed* of light is c/n where n is refractive of that medium.
		The index of refraction is defined as the ratio of the speed of light in a vacuum to the speed of light in the medium.
		It is the group velocity of a wave (the speed at which a bundle of light moves) which must be less than or equal to the speed of light in a vacuum.
	www.bergen.org /EST/Backup/Year2/Projects/Optics/Theory.html (672 words)

	Topic 16. Refraction and Snell's Law
		The ratio of the speed of light in vacuum to the speed of light in any material is called the index of refraction of that material.
		Conversely, when light crosses a boundary into a medium where its velocity is greater, the angle of the refracted ray with respect to the normal is larger than the angle of incidence.
		The light that finally strikes the road is almost perfectly reflected, since the angle of incidence is close to 90 degrees, and these reflected rays will appear to come from a virtual object that is below the surface of the roadway.
	www.colorado.edu /physics/phys1230/phys1230_fa01/topic16.html (703 words)

	Speed of Light Surprise!
		This is not the speed of light inside matter (example: speed of light in glass is 199,861.638 km/s; that is around 100,000 km/s slower than in vacuum).
		Since we are comparing the velocity of the moon relative to the speed of light, therefore we have to compare them inside the same medium, that is either both compared inside the same gravitational field or both outside.
		Since 299,792.458 km/s is the speed of light outside gravitational fields, then for any meaningful comparison, we have to calculate the velocity of the moon outside all gravitational fields as well before comparing them (we have to calculate Vo without any external forces at all; zero acceleration velocity).
	www.speed-light.info (543 words)

	UFO Evidence : Speed of Light Limit (Site not responding. Last check: 2007-10-09)
		Physicists have been concocting light pulses that do travel faster than c (the speed of light in a vacuum) for almost two decades, although none of the experiments could be used to send information that fast, according to most physicists.
		Physicists have been concocting light pulses that travel faster than c (the speed of light in a vacuum) for almost two decades, although none of the experiments could be used to send information that fast, according to most physicists.
		The speed of light and other fixed numbers (called constants) that scientists rely on to explain the universe and its formation mathematically may not be so constant, according to a new study conducted by an international team of researchers.
	www.ufoevidence.org /topics/speedoflight.htm (1467 words)

	Curious About Astronomy: Is the speed of light constant?
		My concern is about the constancy of c (the speed of light); as light goes into a denser medium than the medium it was previously travelling in, the light slows down and it bends as a cause of this.
		However, the speed of light is not constant as it moves from medium to medium.
		(The speed of light in a medium with index n is c/n.) The index of refraction is determined by the electric and magnetic properties of the medium.
	curious.astro.cornell.edu /question.php?number=630 (525 words)

	Faster-than-Light Laser Pulses? - UFO Evidence (Site not responding. Last check: 2007-10-09)
		The frequency of the entering light pulse was arranged to be between two optical resonances in the cesium gas, where there existed a region of "anomalous dispersion" in which the usual dependence of frequency on inverse wavelength was reversed.
		Since light in vacuum travels at a speed of about a nanosecond per foot, the peak of the exiting pulse was therefore about 62 feet beyond the apparatus at the time when the peak of the input pulse was just entering the cesium gas.
		The light pulse has been reshaped by the cesium gas so that its centroid is advanced, but the front of the laser pulse, the first few photons, are not advanced and do not emerge from the cesium gas before they arrive.
	www.ufoevidence.org /documents/doc1096.htm (2236 words)

	Speed of light
		are the speeds of the spaceships relative to the observer, and
		Francis Bacon argued that the speed of light is not necessarily infinite, since something can travel too fast to be perceived, such as a musket ball.
		Since such misalignment had not be observed, Descartes concluded the speed of light is infinite.
	www.sciencedaily.com /encyclopedia/speed_of_light (2136 words)

	Relativity in Quran (Islam)
		Speed of Light a constant at 299792.5 km/s
		Unlike the speed of light, the velocity of the moon is not constant.
		Consequently, the average orbital speed increases, the length of the lunar orbit increases, and the orbital radius increases.
	islam.speed-light.info /relativity_quran.htm (7247 words)

	Color wavelength
		The speed of light is the velocity of electromagnetic wave in vacuum, which is 300,000 km/sec.
		Light travels slower in other media, and different wavelengths travel at different speeds in the same media.
		When light passes from one media to another, it changes speed, which causes a deflection of light called refraction.
	www.usbyte.com /common/approximate_wavelength.htm (128 words)

	Is The Speed of Light Constant?
		It is a basic postulate of the theory of relativity that the speed of light is constant.
		The speed of light is independent of the motion of the observer.
		The Earth moves around the sun at a speed of about 30 km/sec so if velocities added vectorially as Newtonian mechanics requires, the last 5 digits in the value of the speed of light now used in the SI definition of the metre would be meaningless.
	www2.corepower.com:8080 /~relfaq/speed_of_light.html (2071 words)

	Speed of Light - Bad Astronomy and Universe Today Forum (Site not responding. Last check: 2007-10-09)
		Of course, if by 'speed of light' you allow 'speed of light in medium X' and not 'speed of light in a vacuum', then 'man' has already travelled at many, many times the speed of light! After all, some clever scientists have managed to create a medium in which light moves slower than treacle.
		c is the speed of light in a vacuum.
		It is infact the speed of light in a vacuum.
	www.bautforum.com /showthread.php?t=27252 (3263 words)

	Faster than the Speed of Light? How do we know? (Site not responding. Last check: 2007-10-09)
		However, particles can move faster than the speed of light in a material, which is less than the speed of light in a vacuum.
		When a particle goes faster than the speed of light through a material, it gives off a shockwave of energy, and that is Cerenkov radiation.
		Light can be slowed down in materials because light (photons) interacts with particles of the material.
	van.hep.uiuc.edu /van/qa/section/New_and_Exciting_Physics/Relativity/20020211082231.htm (175 words)

	Is The Speed of Light Constant?
		Then, the metre was defined as 1,650,763.73 wavelengths of the reddish-orange light from a krypton-86 source, and the second was defined (then as now) as 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of caesium-133.
		The Earth moves around the sun at a speed of about 30 km/s, so if velocities added vectorially as Newtonian mechanics requires, the last 5 digits in the value of the speed of light now used in the SI definition of the metre would be meaningless.
		The use of c as a conversion between units of metres and seconds, as in the SI definition of the metre, is fully justified on theoretical grounds as well as practical terms, because c is not merely the speed of light, it is a fundamental feature of the geometry of spacetime.
	math.ucr.edu /home/baez/physics/Relativity/SpeedOfLight/speed_of_light.html (2232 words)

	Laser smashes light-speed record (July 2000) - News - PhysicsWeb
		Special relativity prevents any object with mass travelling at the speed of light, and the principle of causality - the notion that the cause comes before the effect - is used to rule out the possibility of superluminal (faster-than-light) travel by light itself.
		Their experimental set-up is remarkably similar to that used to slow light to a speed of just 17 metres per second last year.
		One definition is that it is the speed at which the point of half the maximum intensity on the leading edge of the pulse travels, but this velocity is superluminal in the Princeton experiment.
	physicsweb.org /article/news/4/7/8/1 (594 words)

	Light Speed
		People talk about the speed of light in a material being less than the speed of light in vacuum, and this view does describe an overall effect in conveniently measurable terms, but it doesn't say anything essential about light.
		The point is this: while the constancy of the speed of light in a vacuum is required by the theory of relativity, that requirement pre-dates Einstein and relativity.
		So the short answer is that the speed of light has never been observed to exceed its speed in a vacuum, and if it were observed to do so, all of the laws of both classical theory and modern theory of light would have to be scrapped.
	www.newton.dep.anl.gov /askasci/phy00/phy00230.htm (1035 words)

	The Speed of Light and the Index of Refraction
		The Speed of Light and the Index of Refraction
		Whenever light is in a vacuum, its speed has that exact value, no matter who measures it.
		Even if the vacuum is inside a box in a rocket traveling away from earth, both an astronaut in the rocket and a hypothetical observer on earth will measure the speed of light moving through that box to be exactly c.
	www.rpi.edu /dept/phys/Dept2/APPhys1/optics/optics/node4.html (641 words)

	Constancy of the Velocity of Light
		The Vacuum, Light Speed and the Redshift, by Barry Setterfield
		Vacuum permittivity, the measure of strength of electric fields in a vacuum, is a function of the spacetime geometry of Einstein's general relativity.
		Astrophysical Probes of the Constancy of the Velocity of Light, Ellis, Farakis, Mavromatos, Mitsuo, and Nanopoulos, (7/24/99).
	www.ldolphin.org /constc.shtml (3895 words)

	Lorentz Transformation
		Therefore the above speed of light has been adopted as a standard value and the length of the meter is redefined to be consistent with this value.
		The speed of light c is said to be the speed limit of the universe because nothing can be accelerated to the speed of light with respect to you.
		A common resistance to the speed limit is to suggest that you just accelerate two different objects to more than half of the speed of light and point them toward each other, giving a relative speed greater than c.
	hyperphysics.phy-astr.gsu.edu /hbase/relativ/ltrans.html (415 words)

	SPACE.com -- Scientists Claim To Break Speed-of-Light Barrier
		Whats more, the light pulse appears to have left the confines of the chamber before it even entered a seemingly impossible occurrence according to theories of causality, which predict that causes must always precede their effects.
		Chiao, one of a group of researchers who have been working to break the speed-of-light limit, explained that although a common object such as a baseball could never be flung faster than the speed of light, pulses of energy with certain complex properties have been known to bend the rules.
		A light beam traveling through such a medium has two different velocities a velocity for the individual light waves in the beam and a group velocity for the entire beam.
	www.space.com /scienceastronomy/generalscience/faster_than_c_000719.html (729 words)

	Signals Exceed Light's Speed - July, 2000 (Site not responding. Last check: 2007-10-09)
		Various teams have transmitted superluminal light pulses, but experiments at the Italian Council for Scientific Research have achieved such feats in a less complex system and over a greater distance.
		Its group velocity can be higher than the speed of light, at least in a zone relatively near the source.
		The result is consistent with the theory of Bessel beams: The signal seems to propagate 5.3 percent faster than the light in the region where the correct field distribution typical of Bessel beams can be expected.
	www.photonics.com /spectra/tech/XQ/ASP/techid.879/QX/read.htm (414 words)

Try your search on: Qwika (all wikis)