A Brief History of Time (Delays): 50 Years of Tests of General Relativity

Michael Nowak from the Department of Physics, Washington University in St. Louis hosted this Saturday Science Lecture. Unfortunately, the recording failed, so this is merely the PowerPoint presentation with no sound. This year marks the 50th anniversary of the Hafele-Keating test of General Relativity (GR), which confirmed predictions that moving clocks and clocks that experience different gravitational potentials measure time proceeding at different rates. Since the demonstration by WUSTL Physics Professor Joseph Hafele, understanding this effect has become an important part of our everyday lives (for example, in the operation of GPS time and navigation, for which WUSTL Physics Professor Cliff Will was consulted to verify GR timing corrections!) Equally importantly, tests of General Relativity have become increasingly sophisticated, via studies such as pulsar timing and the recent imaging of a supermassive black hole by the Event Horizon Telescope. Starting with the Hafele-Keating test, Professor Nowak will summarize some of these tests and discuss how we are moving from tests of GR, itself, to using this knowledge to address problems in astrophysics and nuclear physics.