The speed of light as a limit
Light in vacuum travels at a fixed speed, about 300,000 kilometres per second, and this speed is the same for every observer regardless of how fast the source or the observer is moving. That last point is the surprising one, and it is the experimental fact special relativity is built on. Because energy is needed to accelerate any object with mass, and the energy required grows without limit as the speed of light is approached, no massive object can reach it. Nothing carrying information or energy travels faster, which sets a hard boundary on what can influence what.
Why it matters
It converts a fact about light into a structural limit on cause and effect throughout the universe.
Also written: speed of light, light speed
Where it comes up
Read about The speed of light as a limit on Wikipedia
Sources
- Speed of light English Wikipedia
- Michelson-Morley experiment English WikipediaThe 1887 experiment that found no change in the measured speed of light.
- Speed of light Britannica
