The Svedberg, Stockholm, 1953. Gift of John Edsall. The Svedberg (1884–1971) Swedish biochemist The Svedberg was awarded the Nobel Prize at the relatively young age of 42 for his observation of Brownian motion, which proved the existence of molecules. As strange as it may sound today, molecules were considered theoretical constructs in some circles, rather than concrete realities, until Svedberg’s work provided indirect observation of molecules in motion. Svedberg, however, is most famous for his development of one instrument—the ultracentrifuge. This device spins samples in a carousel at speeds of up to 100,000 revolutions per minute. The great forces produced cause the different components of the sample to separate according to molecular mass, with substances higher in molecular weight settling at the bottom and lighter molecules at the top. Svedberg used the ultracentrifuge to measure the molecular weights of large molecules, such as proteins and other biopolymers, showing some to have molecular weights in the millions. Svedberg spent most of his career at the University of Uppsala, and later in his career he turned his attention to nuclear chemistry.