6. Mass-Energy Equivalence
Mass-energy equivalence, better known by its formula E = mc², is the concept that the mass of an object or system is a measure of its energy content. In some measure, this discovery led to the creation of the atomic bomb.
Why, Einstein, of course! While he was not the first to propose a relationship between mass and energy, he was the first to interpret mass-energy equivalence as a fundamental principle that follows from the relativistic symmetries of space and time.