Speed of light in vacuum: CODATA Value

CODATA Value: speed of light in vacuum The speed of light in vacuum is 3 × 108 m/s. The vacuum is a space where there is no matter or in which the pressure is so low that any particles in the space do not affect any processes being carried on there. Around 1676, Danish astronomer Ole Roemer became the first person to prove that light travels at a finite speed. When comparing the speed of light in vacuum with the speed of light in air, the speed of light in air is 1.0003 times slower than the speed of light in a vacuum. For example, light traveling through Earth's atmosphere moves almost as fast as light in a vacuum, slowing down by just three ten-thousandths of the speed of light.