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Fellows Directory

James Cronin

Professor James Cronin ForMemRS

Foreign Member

Elected: 2007


James Cronin was a Nobel Prize-winning nuclear physicist who discovered charge parity (CP) violation with co-researcher, Val Logsdon Fitch. CP violation implies that a reaction run in reverse does not merely retrace the path of the original reaction, challenging the long-held theory that the laws of symmetry and conservation are unbreakable.

Prior to James’s work, physicists widely accepted the invariance of time and the conservation of charge and physical properties, or parity. James and Val’s research on the decays of neutral subatomic particles called K mesons (or kaons) demonstrated, however, that charge and parity are not, in fact, conserved during weak particle interactions. To account for this anomaly, they established the concept of CP symmetry — an equal offset of charge to compensate for any parity violation.

James and Val shared the 1980 Nobel Prize in Physics for demonstrating that subatomic particles are not indifferent to time. James later conducted research into cosmic rays at the Pierre Auger Observatory in Argentina.

Professor James Cronin ForMemRS died on 25 August 2016.


  • Nobel Prize in Physics

    Jointly with Val Logsdon Fitch for the discovery of violations of fundamental symmetry principles in the decay of neutral K-mesons.