  The first three sections of this article contain a broad brush summary of the
profound changes in the notion of time in fundamental physics that were brought
about by three revolutions: the foundations of mechanics distilled by Newton in
his Principia, the discovery of special relativity by Einstein and its
reformulation by Minkowski, and, finally, the fusion of geometry and gravity in
Einstein's general relativity. The fourth section discusses two aspects of yet
another deep revision that waits in the wings as we attempt to unify general
relativity with quantum physics.
