27 September 17

Happy Mass-Energy Equivalence Day! On this date in 1905, Albert Einstein submitted his paper "Does the Inertia of a Body Depend Upon Its Energy Content?" to Annalen der Physik. This paper explained the mathematical derivation of the famous equation E = mc², stating that the total energy of any object is equal to its mass times the square of the speed of light. Prior to Einstein's theories of relativity, the mass of an object was generally considered to be just solid stuff that interacted with other objects according to the mechanical principles of Newton's "laws of motion." But the basic concept from Einstein's most famous equation is that "mass is just a super-concentrated form of energy and, moreover, these things can turn from one form to the other and back again." And so began completely new understandings of our whole universe and how it holds together!