Gravitational Lensing: Testing Relativity and Exploring the Cosmos

Einstein's general theory of relativity predicts that mass and energy warp space and time.  One consequence is that light passing near a massive object will be deflected, an effect called "gravitational lensing".  In 1919, the Eddington Experiment provided the first experimental test of general relativity: a measurement of the deflection of starlight by the sun's gravity during a total eclipse.  Since then, gravitational lensing has evolved from experimental test to experimental tool in astronomy.  In this presentation, I will describe the theory behind gravitational lensing, the history of the Eddington experiment — including my own efforts as a participant in the Modern Eddington Experiment in 2024, and modern applications of gravitational lensing in astronomy.