THE ARROW OF TIME has been directly measured by two groups
of physicists, one at CERN in Geneva
(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 not 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.)