The constant speed of light is a cornerstone of Einstein’s theory of relativity and has profound implications for our understanding of space, time, and motion. Here’s why it’s significant:
- Universal constant: Einstein postulated that the speed of light in a vacuum is always the same—about 299,792 km/s—no matter how fast the observer or the light source is moving. This was radically different from how speeds of other objects add up in classical physics.
- Time and space are relative: Because the speed of light is constant, Einstein showed that time and space must adjust depending on motion. This leads to effects like time dilation (moving clocks tick slower) and length contraction (moving objects appear shorter), both confirmed by experiments.
- Causality is preserved: A constant speed limit (light) ensures that cause always precedes effect. No information or matter can travel faster than light, protecting the sequence of events across the universe.
- Mass-energy equivalence: The famous equation E=mc² arises from this theory. It shows that energy and mass are two forms of the same thing, with the speed of light squared acting as the conversion factor.
In essence, the constant speed of light reshaped physics, replacing the idea of absolute time and space with a unified framework—spacetime—where motion affects both.