Bell and Veltman at CERN, 1973. British physicist John Stewart Bell (left, 1928-1990) originated Bell's theorem in the mid-1960s, extending the EPR paradox. The inequality implies that certain types of physical theories are unable to account for all the predictions of quantum mechanics, raising philosophical questions about the limits of what is possible with such theories. Dutch physicist Martinus Veltman (right, born 1931) carried out pioneering work in theoretical physics, and was awarded the 1999 Nobel Prize in Physics (shared with former student Gerardus 't Hooft). Photographed at CERN (the European particle physics laboratory) in 1973.