When Albert Einstein first showed that light travels the same speed everywhere in the universe, he essentially stamped a speed limit on our universe: 670,616,629 miles per hour.
But that's not the entire story. In fact, it's just the beginning.
Before Einstein, mass - the atoms that make up you, me, and everything we see - and energy were treated as separate entities. But in 1905, Einstein forever changed the way physicists view the universe.
Einstein's Special Theory of Relativity permanently tied mass and energy together in the simple yet fundamental equation E=mc2. This little equation predicts that nothing with mass can move as fast as light.
The closest humankind has ever come to reaching the speed of light is inside of powerful accelerators like the Large Hadron Collider and the Tevatron. These colossal machines accelerate subatomic particles to more than 99.99% the speed of light, but as Physics Nobel laureate David Gross explains, these particles will never reach the cosmic speed limit.
This is because, to do so would require an infinite amount of energy to reach these speeds and, in the process, the object's mass would become infinite, which is impossible. (The reason particles of light, called photons, travel at light speeds is because they have no mass.)
Since Einstein, physicists have found that certain entities can reach superluminal (that means "faster than light") speeds and still follow the cosmic rules laid down by special relativity. While these do not disprove Einstein's theory, they give us insight into the peculiar behavior of light and the quantum realm.
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