Speed of light
hideThe term speed of light generally refers to a fundamental physical constant of spacetime that limits the rate of transfer of matter or information. The speed of light is the speed of not just visible light, but of all electromagnetic radiation in vacuum (also called free space), and usually is denoted by the symbol c. Speeds faster than that of light are encountered in physics but, in all such cases, no matter or information is transmitted faster than c. The speed of light also plays a role in general relativity, and is believed to be the speed of gravitational waves.
In SI units, the magnitude of the speed of light in vacuum is exactly 299,792,458 metres per second (m/s) because of the way the metre is defined. More about this topic is found below in Speed of light set by definition.
For many practical purposes, the speed of light is so great that it can be regarded to travel instantaneously. An exception is where long distances or precise time measurements are involved. For example, in the Global Positioning System (GPS), a GPS receiver measures its distance to satellites based on how long it takes for a radio signal to arrive from the satellite. In astronomy, distances are often measured in light-years, the distance light travels in a year.
The speed of light when it passes through a transparent or translucent material medium, like glass or air, is less than its speed in vacuum. The speed is inversely proportional to the refractive index of the medium. In specially-prepared media, the speed can be tiny, or even zero.
For many years the speed of light was the subject of speculation, some believing it to be infinite. The first effective measurements of the speed of light were made in the seventeenth century, and these were progressively refined until, in 1983, the speed of light in vacuum was fixed by definition.
For more information about Speed of light, read the full article at
Wikipedia.
This text uses material from Wikipedia and is available under the GNU Free Documentation License.
News tagged with speed of light
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A team of physicists has directly observed a reverse shock wave of light in a specially tailored structure known as a left-handed metamaterial. Although it was first predicted over forty years ago, this is ...
Gamma-ray photon race ends in dead heat; Einstein wins this round
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Racing across the universe for the last 7.3 billion years, two gamma-ray photons arrived at NASA's orbiting Fermi Gamma-ray Space Telescope within nine-tenths of a second of one another. The dead-heat finish ...
LHC now colder than deep space
Oct 20, 2009 |
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(PhysOrg.com) -- The LHC (Large Hadron Collider) is once again colder than deep space as it is prepared for experiments to resume in late November.
Scientists discover, visualize exotic electrons on surfaces of unique insulators
Aug 10, 2009 |
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(PhysOrg.com) -- In two separate studies, Princeton-led teams of scientists have found a new type of “light-like” electron and visualized for the first time another type that doesn’t bounce back when material imperfections ...
Particle collider: Black hole or crucial machine?
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(AP) -- When launched to great fanfare nearly a year ago, some feared the Large Hadron Collider would create a black hole that would suck in the world. It turns out the Hadron may be the black hole.
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NASA's Chandra X-ray Observatory has found a cosmic "ghost" lurking around a distant supermassive black hole. This is the first detection of such a high-energy apparition, and scientists think it is evidence ...
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(PhysOrg.com) -- When it comes to nonlocal correlations, some correlations are more nonlocal than others. As the subject of study for several decades, nonlocal correlations (for example, quantum entanglement) ...
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(PhysOrg.com) -- It is the most famous scientific equation in history, framed by Einstein more than a century ago. But what does e=mc˛ actually stand for? And how does it explain the relationship between energy, mass and ...
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(PhysOrg.com) -- Integral has captured one of the brightest gamma-ray bursts ever seen. A meticulous analysis of the data has allowed astronomers to investigate the initial phases of this giant stellar explosion, ...
Astrophysicists explore a blazar
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An international team of astrophysicists using telescopes on the ground and in space have uncovered surprising changes in radiation emitted by an active galaxy. The picture that emerges from these first-ever ...
Physicists Propose Method for Entangling Moving Material Particles
Jan 16, 2009 |
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(PhysOrg.com) -- When physicists experiment with quantum entanglement, they usually work with photons, the intangible particles of light. In the past few years, however, scientists have begun to broaden their ...
