Lyshastighet

Lyshastighet, often denoted by the symbol c, is the speed at which light travels in a vacuum. This fundamental constant in physics is approximately 299,792,458 meters per second. It is the maximum speed at which all energy, matter, and information in the universe can travel. The speed of light is not only the speed of visible light but also the speed of all electromagnetic radiation, including radio waves, microwaves, infrared, ultraviolet, X-rays, and gamma rays.

The concept of a finite speed of light was first proposed in the 17th century and experimentally confirmed in the 19th century. Albert Einstein's theory of special relativity, published in 1905, established the speed of light in a vacuum as a universal constant, independent of the motion of the observer or the source of the light. This principle is a cornerstone of modern physics and has profound implications for our understanding of space, time, and gravity.

When light travels through a medium other than a vacuum, such as water or glass, its speed is reduced. This reduction in speed is described by the refractive index of the medium. However, the speed of light in a vacuum, c, remains the ultimate speed limit. The precise value of c is now used to define the meter, the SI unit of length. One meter is defined as the distance traveled by light in a vacuum during a time interval of 1/299,792,458 of a second.