University of Cambridge > Talks.cam > Scott Lectures > Scott Lecture II - The Cosmic Barber: Counting Gravitational Hair in the Solar System and Beyond

Scott Lecture II - The Cosmic Barber: Counting Gravitational Hair in the Solar System and Beyond

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According to general relativity, every self-gravitating object has “hair”, an array of multipole moments of various types that characterize the body’s exterior geometry. In alternative theories of gravity, bodies could also be endowed with more exotic tresses, such as scalar hair. We review how solar system experiments, such as light deflection and time-delay measurements, have placed stringent limits on scalar hair. We describe how experiments such as GRACE have measured with high precision the vast head of Newtonian hair possessed by the Earth. We discuss how the angular-momentum hair of the Earth has been measured by Gravity Probe B and the LAGEOS project. At the relativistic extreme, black holes are almost bald, possessing only two strands of general relativistic hair, and we describe ways of counting those follicles in the future, by tracking stars orbiting very close to our galactic center black hole, and by using gravitational waves to measure how newly formed black holes shed their unruly hair.

This talk is part of the Scott Lectures series.

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