After obtaining his Ph.D. at Harvard University under Julian Schwinger, he worked at the IBM Research Laboratory in Yorktown, New York until 1964.
He then worked at the Department of Theoretical Physics at the University of Geneva, Geneva, Switzerland, until 1966, and became full professor at the Department of Physics, University of Denver, Denver, Colorado.
He has been on the editorial and advisory boards and standing committees for several conferences on mathematical and theoretical physics and journals, and on the Panel of Assessors ARC, Australian National Funding DEET.
He has made frequent visits, long and short term, at the Institute for Advanced Study, Princeton, New Jersey, the Department of Theoretical Physics, University of Geneva, CERN (Geneva), University of Connecticut (Storrs, Connecticut), ETH (Honggerberg, Zurich), Institut des Hautes Etudes Scientifiques (Bures-sur-Yvette, France), and the Ilya Prigogine Center for Statistical Mechanics and Complex Systems, University of Texas at Austin, United States.
He received a National Science Foundation Fellowship 52–53 and was a Shell Oil Fellow 56–57 at Harvard University.