The University of Chicago has been the site of some important experiments and academic movements. In economics, the university has played an important role in shaping ideas about the free market and is the namesake of the Chicago school of economics, the school of economic thought supported by Milton Friedman and other economists. The university's sociology department was the first independent sociology department in the United States and gave birth to the Chicago school of sociology. In physics, the university was the site of the Chicago Pile-1 (the first self-sustained man-made nuclear reaction, part of the Manhattan Project), of Robert Millikan's oil-drop experiment that calculated the charge of the electron, and of the development of radiocarbon dating by Willard F. Libby in 1947. The chemical experiment that tested how life originated on early Earth, the Miller–Urey experiment, was conducted at the university. REM sleep was discovered at the university in 1953 by Nathaniel Kleitman and Eugene Aserinsky.