  The progression of time can be understood by assuming that the Hubble
expansion takes place in 4 dimensions rather than in 3. The flow of time
consists of the continuous creation of new moments, new nows, that accompany
the creation of new space. This model suggests a modification to the metric
tensor of the vacuum that leads to testable consequences. Two cosmological
tests are proposed, but they present both experimental and theoretical
problems. A more practical and immediate test is based on a predicted lag in
the emergence of gravitational radiation when two black holes merge. In such
mergers (as recently observed by the LIGO team), a macroscopic volume (millions
of cubic kilometers) of space is created in the region in which the
gravitational wave is generated; this one-time creation of new space should be
accompanied by the creation of detectable level of new time, resulting in a
time delay that could be observed as a growing lag in the emission of the wave
as the merger takes place
