LECTURES BY
CLIFFORD M. WILL

Popular Talks

Was Einstein Right?
Black Holes, Waves of Gravity, and other Warped Ideas of Dr. Einstein

Colloquia

Was Einstein Right? A Centennial Assessment
On the Unreasonable Effectiveness of post-Newtonian Theory in Gravitational Physics
Testing General Relativity in the Strong-Field Dynamical Regime
The Cosmic Barber: Counting Gravitational Hair in the Solar System and Beyond

Lectures suitable for undergraduate physics students

The Search for Black Holes
The Search for Gravity Waves


Popular Talks

Was Einstein Right? (also in French as Einstein, avait-il raison?)

How has the most celebrated scientific theory of the 20th century held up under the exacting scrutiny of planetary probes, radio telescopes, and atomic clocks? After 100 years, was Einstein right? In this lecture we relate the story of testing relativity, from the 1919 measurements of the bending of light to the 2016 detection of gravity waves'. We will show how a revolution in astronomy and technology led to a renaissance of general relativity in the 1960s, and to a systematic program to try to verify its predictions. We will also demonstrate how relativity plays an important role in daily life.
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Black Holes, Waves of Gravity, and other Warped Ideas of Dr. Einstein (also in French as Trous noirs, vagues de gravité, et autres idées tordues de professeur Einstein)

Einstein's theories of relativity have had a major impact on everything from popular culture to everyday life to basic science. Songs, plays and movies proclaim Einstein as the symbol of genius, while users of GPS navigation devices unknowingly take account of Einstein's relativistic warpage of time. Two of the crazier ideas that come from Einstein's theories are Gravitational Waves and the Black Hole. Today, international teams of scientists are on a quest to verify these ideas. Using large-scale detectors on the ground they have detected Einstein's gravity waves and are using them to reveal the hidden secrets of black holes. Gravitational waves provide a remarkable new tool for ``listening'' to Einstein's cosmic symphony.
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Colloquia/Seminars

Was Einstein Right? A Centennial Assessment

Einstein formulated general relativity 100 years ago. Although it is generally considered a great triumph, the theory's early years were characterized by conceptual confusion, empirical uncertainties and a lack of relevance to ordinary physics. But in recent decades, a remarkably diverse set of precision experiments has established it as the "standard model" for gravitational physics. Yet it might not be the final word. We review a century of measurements that have verified general relativity, and describe some of the opportunities and challenges involved in testing Einstein’s great theory in strong-field regimes and in gravitational waves.
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On the Unreasonable Effectiveness of post-Newtonian Theory in Gravitational Physics

The first indirect detection of gravitational waves involved a binary system of neutron stars. Within a few years, the first direct detection may also involve binary systems -- inspiralling and merging binary neutron stars or black holes. This means that it is essential to understand in full detail the two-body problem in general relativity, a notoriously difficult problem with a long and troubled history. One approach has been the "post-Newtonian approximation", which treats slow-motion and weak-field conditions. Yet recent results have shown that the post-Newtonian approximation often remains valid well into the relativistic strong-field regime. We will describe the many arenas in which post-Newtonian theory has been unreasonably effective, including binary pulsars, "kicks" imparted to newly formed black holes, and the gravitational wave signal from merging compact binaries.
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Testing General Relativity in the Strong-Field Dynamical Regime

General relativity has been well-tested in the weak-field slow-motion regime of the solar system. In binary pulsar systems, some tests of strong-field aspects of the theory have been carried out. In the future, testing GR in the strong-field, highly dynamical regime will be an important theme in experimental relativity. We describe a number of possible tests that could be carried out, including tests using astrophysical phenomena around black holes, tests using gravitational waves, and tests of black hole no-hair theorems using high-precision observations of stars orbiting our galactic center black hole.

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The Cosmic Barber: Counting Gravitational Hair in the Solar System and Beyond

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 measurements of the angular-momentum hair of the Earth 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 measuring 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.
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Lectures suitable for undergraduate physics students

The Search for Black Holes

One of the most remarkable predictions of Einstein's general theory of relativity is the Black Hole, a region of warped spacetime left over from the catastrophic collapse of a star from which nothing, not even light, can escape. What is a Black Hole and what are its properties? Do Black Holes really exist? Have gravitational-wave observatories recently given us the ``smoking gun'' for the existence of black holes?
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The Search for Gravity Waves

In 2016 a new form of astronomy began, called ``gravitational-wave astronomy''. General relativity predicts that moving matter produces gravitational radiation, and that the most intense sources of waves will be cosmic cataclysms such as the collapse of stars, or the collisions of black holes. In this lecture, we describe the nature and properties of gravitational waves, and the network of gravitational wave observatories that have recently detected these waves. Gravitational waves provide a remarkable new tool for ``listening'' to Einstein's cosmic symphony.
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