The speed of light in a vacuum, denoted by the symbol c , is exactly 299,792,458 meters per second (approximately 300,000 kilometers per second or about 186,000 miles per second). This value is a universal physical constant and is exact by international agreement because the meter is defined based on the distance light travels in vacuum in a fraction of a second
. This speed is the maximum speed at which information, matter, or energy can travel through space and is the same for all observers regardless of their relative motion, forming a fundamental basis of Einstein's theory of special relativity
. In summary:
- Speed of light in vacuum (c) = 299,792,458 m/s (exact)
- Approximately 300,000 km/s or 186,000 miles/s
- Universal speed limit in the universe
- Defined exactly by the SI system since 1983 based on the definition of the meter
Light slows down when passing through media other than vacuum, such as water or glass, but in vacuum, this speed is constant and fundamental.
