## The basics of general relativity

### The elevator, the rocket, and gravity: the equivalence principle

Information about the principle that Einstein took as a starting point for developing his general theory of relativity

### Gravity: from weightlessness to curvature

So what is gravity in Einstein’s theory? The answer: in part, an illusion; in part, an aspect of geometry.

### …that all coordinate systems are created equal

Why, in general relativity, all observers are on an equal footing – and why, nevertheless, you can say that the earth orbits the sun, but not the other way around

### Inertial and Gravitational Mass

About the different roles played by mass, and the weak equivalence principle

### A subtle change in direction: Geodetic precession

In Einstein’s theory, gravity is related to spacetime curvature. This text explores what curvature is – and how the way it influences geometry can be measured directly, with the help of gyroscopes.