NASA - Einstein’s Cosmic Speed Limit

NASA - Einstein’s Cosmic Speed Limit The speed of light, usually denoted by c, is a physical constant important in many areas of physics. Light and all other forms of electromagnetic radiation always travel at this speed in empty space (vacuum), regardless of the motion of the source or the inertial frame of reference of the observer. Its value is exactly 299792458 metres per second (approximately 186282 miles per second). In the theory of relativity, c interrelates space and time, and appears in the famous equation of mass--energy equivalence E = mc2. It is the speed of all massless particles and associated fields in vacuum, and it is predicted by the current theory 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 ≈ 200000 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. In most practical cases, light can be thought of as moving instantaneously, but for long distances and very sensitive measurements the finite speed of light has noticeable effects ...

Channel: YouTube Video Length: 5m 46s Date Found: Mon, Jan 24 2011 4:53 AM Category: Technology Date Produced: Mon, Jan 24 2011 4:26 AM View Count: 0