Special relativity
Albert Einstein developed his theory of special relativity by 1905, when he was a twenty-six year old clerk in the Swiss patent office. The theory accounted for the paradoxical results of certain 19th century physical experiments attempting to detect the universe's background "ether," which was supposed to be the ultimate neutral background or reference point against which the entire physical universe moved. Physicists had always assumed the ether's existence, but experiments--most notably the Michaelson-Morley experiment of the 1880s--always failed to detect it. By boldly refusing to assume the possibility of an ether and theorizing laws of motion without referring to an absolute background, Einstein's simple presumption of objects' "relativity" revolutionized the fundamental view of the physical universe in that his results utterly countered humans' intuitive view of the everyday world. In particular, humans' perception of time and distance, while quite correct for everyday life, inadequately understand these intuitive ideas when high speeds are involved. Einstein's theory says that when speed is an appreciable fraction of light's speed, or c, time passes more slowly and length shortens in the direction of motion, and so human perception fails in a fundamental way to grasp what are thought to be the intuitive ideas of time and distance.