The speed of light in a vacuum 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 denoted by the symbol "c" and is the maximum speed at which all energy, matter, and information in the universe can travel
. This speed is exact by definition because the meter is defined based on the distance light travels in vacuum in 1/299,792,458 of a second
. The constancy of the speed of light, regardless of the motion of the source or the observer, is a fundamental postulate of Einstein's theory of special relativity
. While light travels at this speed in a vacuum, it can slow down when passing through materials such as water or glass, but this does not change the universal constant speed of light in vacuum
. In summary:
- Speed of light in vacuum: 299,792,458 m/s (exact)
- Approximate equivalents: 300,000 km/s or 186,000 miles/s
- Symbol: c
- It is the universal speed limit for all matter and information
