A35 Lectures 20-21 - Lecture 20 Strong Gravity Thursday Einsteins Theory of General Relativity(GR New theory of gravitation(builds from Newton GR is

A35 Lectures 20-21 - Lecture 20 Strong Gravity Thursday...

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Lecture 20: Strong Gravity Thursday, April 16, 2009 Einstein’s Theory of General Relativity (GR) - New theory of gravitation (builds from Newton). GR is needed. - Passes all tests, and predicts some new phenomena (which seem to be correct): o Gravitational waves o Black holes - GR is the theory of gravity that underpins our study of the universe as a whole ( cosmology ) - It is difficult to test for GR in the laboratory – the Universe is the only place where some of these ideas can be measured. - Black holes: The evidence for astronomical black holes is strong, but it does not (yet) test the details of GR. Black holes are a scientific frontier. (Picking up from last time) - Discovery of planets around other stars (also discovery of invisible stars:) o Periodic shifts in the Doppler velocity of a star are evidence for invisible planets/stars. This points in the direction of a binary system. Velocity shifts = gravitational force from another mass. o There are many planets around other stars o Few of these are “visible” – their presence is inferred from the small velocity shifts they induce in the stars they orbit.
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