Cronin, James Watson (1931-...), an American nuclear physicist, shared the 1980 Nobel Prize for physics with fellow American Val Fitch (see Fitch, Val Logsdon). They were awarded the prize for an experiment that suggested that reversing the direction of time would not produce an exact reversal of certain reactions involving subatomic particles. Their research on subatomic particles known as kaons revealed that the fundamental laws of symmetry in nature, which include time reversal, could be violated. Before this, physicists had assumed that the direction of time would not affect the way in which reactions work. Although scientists still do not fully understand this result, they use it to explain why matter dominates antimatter in the universe. See Subatomic particle; Antimatter.