What Is Relativity?: An Intuitive Introduction to Einstein's Ideas, and Why They Matter

What Is Relativity? is a short, non-mathematical introduction to Einstein's special and general theories of relativity, written for general readers by astrophysicist Jeffrey Bennett. It opens with an imagined voyage to a black hole and uses that journey to correct common misconceptions, such as the idea that a black hole would suck in the Earth, before working through the central ideas: the speed of light as a cosmic speed limit, time dilation, the curvature of spacetime, and the equivalence of mass and energy expressed in E = mc2. Later chapters apply relativity to black holes and to the expanding universe, and an epilogue considers what the theory says about our place in the cosmos. Bennett stresses that relativity is not "just a theory": every major prediction has been tested to exquisite precision, and its results shape practical technologies such as the Global Positioning System. The book is illustrated and assumes no prior physics or mathematics.