2005 Richard Conn Henry1 Where does E = mc2 Summary: © 2005 Richard Conn Henry1 Where does E = mc2 come from? Richard Conn Henry, The Johns Hopkins University, Baltimore MD he location of an eventone beat of your heart, sayis given by its three space coordinates, and its time coordinatebut, if we want to use the same units for all of those 4 numbers we will require a units conversion factor: if there are c centimeters in one second, the conversion factor is c cm/sec, and the location of a heartbeat is given by the set of numbers (x, y, z, ct) , where all four quantities are now in units of centimeters. Of course we don't yet know the value of c, but - we would like to find that out! The famous Pythagorean Theorem states that ds2 = dx2 + dy2 for a right triangle, where dx designates a length in the x direction. Let us GUESS that for two heartbeats, that are separated in our (at least apparently) four-dimensional universe by dx, dy, dz, cdt( ), the Pythagorean Theorem expands to: ds2 = dx2 + dy2 Collections: Physics