Its significance is far broader than its role in describing a property of electromagnetic waves. The speed of light is considered a fundamental constant of nature. In particular, the value for the speed of light in a vacuum is now defined as exactly 299,792,458 metres per second. The measurement, which many scientists say is impossible to make, could resolve the long-standing question of whether the speed of light is uniform in all directions. speed of light, speed at which light waves propagate through different materials. For all that success, one major hurdle remains: directly testing the one-way speed of light. In the late 1990s and early 2000s, photons set a record for slowest measured speed of light at 17 meters per second and froze in their tracks for one-thousandth of a second ( SN: 1/27/01, p. But they weren’t done putting light through its paces. Speed of light definition, a fundamental universal constant, the speed at which light and all forms of electromagnetic radiation travel in a vacuum. The result, which still holds up, helped scientists redefine the standard length of the meter ( SN: 10/22/83, p. In the late 1600s, he was obsessed with some strange. That 1972 experiment measured the two-way speed of light, or the average speed of photons that traveled from their source to a reflective surface and back. The first person to realize that light does indeed have a speed at all was an astronomer by the name of Ole Romer. A New Figure for the Cosmic Speed Limit – Science News, December 2, 1972Ī group at the National Bureau of Standards at Boulder, Colo., now reports an extremely accurate measurement using the wavelength and frequency of a helium-neon laser.… The result gives the speed of light as 299,792.4562 kilometers per second.
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