Information about the principle that Einstein took as a starting point for developing his general theory of relativity
So what is gravity in Einstein’s theory? The answer: in part, an illusion; in part, an aspect of geometry.
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
About the different roles played by mass, and the weak equivalence principle
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.