Susskind emphasizes that if this tensor is zero, the space is flat (regardless of how strange the coordinates look). If it is non-zero, space is curved.

: The full 2012 Stanford lecture series, which served as the foundation for the book, is available for free on the Official Theoretical Minimum Website The Theoretical Minimum | Sample Chapters

Old PDFs stop at the Schwarzschild metric.

"General Relativity: The Theoretical Minimum" by Leonard Susskind and André Cabannes serves as an accessible, hands-on introduction to Einstein's theory for independent learners. The text covers foundational topics including the equivalence principle, tensor calculus, and black hole physics, bridging the gap between popular science and academic, graduate-level textbooks. Access the companion lecture series and course materials via The Theoretical Minimum . General Relativity (Fall, 2012) | The Theoretical Minimum

The term "Theoretical Minimum" was first introduced by physicist Richard Feynman, who used it to describe the minimum amount of information required to understand a particular topic in physics. The idea is to strip away unnecessary complexity and focus on the essential principles, equations, and concepts that underlie a theory.

where Rμν is the Ricci tensor, R is the Ricci scalar, gμν is the metric tensor, G is the gravitational constant, c is the speed of light, and Tμν is the stress-energy tensor.