Special relativity unlocked the secrets of the stars and revealed the fantastic quantities of energy stored deep inside the atom. But the seed of relativity was planted when Einstein was only 16 years old and asked himself a childlike question: What would a beam of light look like if you could race alongside it? According to Newton, you could catch up to any speeding object if you moved quickly enough. If you could catch up to a light wave, Einstein realized, it would look like a wave frozen in time. But even as a teenager, he knew that no one had ever seen a frozen light wave before. In fact, such a wave makes no physical sense.
When Einstein studied Maxwell’s theory of light, he found something that others missed—that the speed of light always appears the same, no matter how quickly you move. Einstein then boldly formulated the principle of special relativity: The speed of light is a constant in all inertial frames (frames that move at constant velocity).
No longer were space and time absolutes, as Newton thought. Space compresses and clocks tick at different speeds throughout the universe.