Quantum Technology Research

time dilation , in the theory of special relativity ,
the “slowing down” of a clock as determined by
an observer who is in relative motion with
respect to that clock. In special relativity, an
observer in inertial (i.e., nonaccelerating) motion
has a well-defined means of determining which
events occur simultaneously with a given event.
A second inertial observer, who is in relative
motion with respect to the first, however, will
disagree with the first observer regarding which
events are simultaneous with that given event.
(Neither observer is wrong in this determination;
rather, their disagreement merely reflects the fact
that simultaneity is an observer-dependent
notion in special relativity.) A notion of
simultaneity is required in order to make a
comparison of the rates of clocks carried by the
two observers.