In 1905, a 26-year-old German physicist named Albert Einstein (then a patent clerk in Bern, Switzerland) showed how measurements of time and space are affected by motion between an observer and what is being observed. Einstein's radical theory of relativity revolutionized science. Although Einstein made many other important contributions to science, the theory of relativity alone represents one of the greatest intellectual achievements of all time. Although the concept of relativity was not introduced by Einstein, he recognised that the speed of light in vacuum is constant, i.e., the same for all observers, and an absolute upper limit to speed. This does not impact a person's day-to-day life since most objects travel at speeds much slower than light speed. For objects travelling near light speed, however, the theory of relativity shows that clocks associated with those objects will run more slowly and that the objects shorten in length according to measurements of an observer on Earth. Einstein also derived the equation, E = mc, which expresses the equivalence of mass and energy.