THE ARROW OF TIME has been directly measured by two groups of physicists, one at CERN in Geneva (http://www.cern.ch/cplear/Welcome.html) and one at Fermilab (http://fnphyx-www.fnal.gov/experiments/ktev/ktev.html) near Chicago. Time reversal (T) is one of those symmetries, along with charge conjugation (or C, the operation which turns particles into antiparticles) and parity (or P, the reversal of a particle's coordinates from x,y,z to -x,-y,-z) that were once thought to be preserved in interactions at the atomic level. But then experiments showed that P, C, and the combination CP were not sacred. And since the triple symmetry of CPT is still thought to be valid, T by itself was thought to be vulnerable. That is, it is now thought that physics does differentiate between the forward or backward movement of time. The two groups have now seen evidence for this T violation in the observed decay rates for neutral K mesons. (Science, 2 Oct.; Science News, 31 Oct.)