Bertrand Russell offers a clear, non-technical introduction to Einstein’s special and general theories of relativity, explaining how the constancy of the speed of light forces us to rethink absolute space and time, and how gravity is better understood as the curvature of space-time. Through everyday analogies and careful reasoning he guides the general reader from the limitations of common sense to the philosophical consequences of a universe in which measurements of distance and duration depend on the observer’s motion.

First published in 1925, the book remains a model of lucid popular science writing. Russell’s characteristic clarity and dry wit make difficult ideas approachable without oversimplification, and while later discoveries have refined some details, the core exposition still serves as an excellent starting point for anyone seeking to grasp the conceptual revolution Einstein set in motion.