The interval AB in the diagram to the right is "time-like" (that is, there is a frame of reference in which event A and event B occur at the same location in space, separated only by their occurring at different times, and if A precedes B in that frame then A precedes B in all frames: there is no frame of reference in which event A and event B occur simultaneously). To put it another way, information propagates to and from a point from regions defined by a light cone. Such a violation of causality has never been recorded. If something could move faster than light, this ratio would not be a real number. Due to special relativity's time dilation, the ratio between an external observer's perceived time and the time perceived by an observer moving closer and closer to the speed of light approaches zero. If information could travel faster than c in one reference frame, causality would be violated: in some other reference frames, the information would be received before it had been sent, so the "effect" could be observed before the "cause". A light sensor traveling near the speed of light would also find that colours of lights ahead were shifted toward the violet end of the spectrum and of those behind were redshifted, so that the Lorentz transformations and classical explanations of frequency shifting are in harmony. Observers traveling at large velocities will find that distances and times are distorted in accordance with the Lorentz transforms however, the transformations distort times and distances in such a way that the speed of light remains constant. This logic is the basis of the theory of special relativity. Because of this fact, one can view c as a fundamental physical constant. If one combines this observation with the principle of relativity, one concludes that all observers will measure the speed of light in vacuum as being the same, regardless of the reference frame of the observer or the velocity of the object emitting the light. One consequence of the laws of electromagnetism (such as Maxwell's equations) is that the speed c of electromagnetic radiation does not depend on the velocity of the object emitting the radiation thus for instance the light emitted from a rapidly moving light source would travel at the same speed as the light coming from a stationary light source (although the color, frequency, energy, and momentum of the light will be shifted, which is called the relativistic Doppler effect). 4.1 Ancient, medieval and early modern theories.3.5 "Faster-than-light" observations and experiments.3.4 Accelerated frames of reference and general relativity.3.3 Interaction with transparent materials.3.1 Constant velocity from all inertial reference frames.General relativity explains how a gravitational potential can affect the apparent speed of distant light in a vacuum, but locally light in a vacuum always passes an observer at a rate of c. The ratio of c to the observed phase velocity is called the refractive index of the medium. The speed of light when it passes through a transparent or translucent material medium, like glass or air, is slower than its speed in a vacuum. In imperial units, the speed of light is about 670,616,629.2 miles per hour or 983,571,056 feet per second, which is about 186,282.397 miles per second, or roughly one foot per nanosecond. The approximate value of 3×10 8 m/s is commonly used in rough estimates. The fundamental SI unit of length, the metre, has been defined since October 21, 1983, as the distance light travels in a vacuum in 1/299,792,458 of a second any increase in the precision of the measurement of the speed of light would certainly refine the definition of the metre, but not alter the numerical value of c. More generally, it is the speed of anything having zero rest mass. It is the speed of all electromagnetic radiation, including visible light, in a vacuum. The speed of light in a vacuum is an important physical constant denoted by the letter c for constant or the Latin word celeritas meaning "swiftness". For other uses of "speed of light", see speed of light (disambiguation) For other uses, see Lightspeed (disambiguation).
0 Comments
Leave a Reply. |