**Copyright Information:**All rights reserved to Prof. Leonard Susskind, Stanford University.

### Lecture Description

Summary: Leonard Susskind demonstrates that Einstein's field equations become wave equations in the approximation of weak gravitational fields. The solutions for these equations create the theory of gravity waves. Professor Susskind demonstrates how Einsteins's equations can be linearized in the approximation of a weak gravitational field. The linearized equation is a wave equation, and the solution to these equations create the theory of gravitational radiation and gravity waves. Gravity waves represent waves in the curvature of spacetime and thus are effectively tidal forces that change over time. Gravity waves propagate at the speed of light. A rotating binary pulsar is the most likely source of detectable gravity waves. Professor Susskind closes the final lecture of the course by developing the Einstein-Hilbert action for general relativity, and discussing how minimizing this action leads to the Einstein field equations. Topics: - Weak gravitational fields - Gravitational radiation - Gravity waves - Einstein-Hilbert action for general relativity Recorded on December 3, 2012.

### Course Index

- The Equivalence Principle and Tensor Analysis
- Tensor Mathematics
- Riemannian Geometry: Flatness and Curvature
- Geodesics, Gravitational Fields, & Special Relativity
- The Metric for a Gravitational Field
- Schwarzschild Radius & Black Hole Singularity
- Falling into a Black Hole: The Event Horizon
- Black Hole Formation, Penrose Diagrams & Wormholes
- Einstein Field Equations of General Relativity
- Gravity Waves: Gravitational Radiation & Einstein-Hilbert Action

### Course Description

General relativity is the geometric theory of gravitation published by Albert Einstein in 1916 and the current description of gravitation in modern physics. General relativity generalizes special relativity and Newton's law of universal gravitation, providing a unified description of gravity as a geometric property of space and time, or spacetime. In particular, the curvature of spacetime is directly related to the energy and momentum of whatever matter and radiation are present. This course uses the physics of black holes extensively to develop and illustrate the concepts of general relativity and curved spacetime. This series is the fourth installment of a six-quarter series that explore the foundations of modern physics. In this quarter, Leonard Susskind focuses on Einstein's General Theory of Relativity.