"It followed from the special theory of relativity that mass and energy are both but different manifestations of the same thing — a somewhat unfamiliar conception for the average mind." -Albert Einstein You've heard and seen it plenty of times: Einstein's most famous equation, E = mc2. I've taken you inside this equation before, which lays out how much energy is stored in matter-at-rest, and tells you how much energy you need to create matter in the first place.