PROTONS AND ANTIPROTONS HAVE THE SAME MASS to within one part in 10 billion. Harvard physicists Gerald Gabrielse (617-495-4381) and Anton Khabbaz and their Bonn collaborators are able to make this comparison by loading a single antiproton and a single proton (saddled with two electrons, in order to make the proton into a negatively charged object) and lets them orbit (simultaneously) around an ion trap under the influence of a strong magnetic field. One has no reason to believe the proton and antiproton masses would be different, but this stringent new measurement constitutes the best test yet (by a factor of 10; see Update 218) of the CPT theorem (C stands for charge conjugation, P for parity inversion, and T for time reversal), which says that physics should not discriminate between particles, on the one hand, and antiparticles moving backwards in time on the other. These new results will be reported next week (paper I6.05) at the APS Division of Atomic, Molecular, and Optical Physics meeting in Santa Fe, NM.