speed-of-light

In 1887, Michelson and Morley tried to measure Earth's motion through the ether and found nothing. That null result demolished a century of physics and paved the way for Einstein.

If the speed of light were dramatically lower — say, 100 km/h — relativistic effects would dominate everyday life. Cars would gain mass as they accelerated, time would dilate for joggers, and the universe would look profoundly different.

Nothing with mass can reach the speed of light. But shadows, spots of light, and the expansion of the universe can move faster than light without violating physics. Here's the strange truth about superluminal motion.