Clock time

A great article in New Scientist last week coincided with a trip to Saltholme and an encounter with the rabbit from Alice in Wonderland. The article says that we invented clock time based on the rotation of the Earth. This is not constant and unchanging. Sixty five years ago a clock was invented that used the frequency of a particular types of light as a "pendulum" and this led to the redefinition of the second. New and better clocks allow the second to be measured with greater precision. This should allow for testing of physics theories with even greater precision. For example it would allow further tests to see whether gravitational and inertial masses are really the same.