4. Energy, mass, and light

Abstract

By the beginning of the twentieth century, our understanding of matter was completely transformed by the great discoveries of electromagnetism and relativity. ‘Energy, mass, and light’ outlines Einstein’s special theory of relativity of 1905, which describes what happens when objects move at speeds close to the speed of light. The theory transformed our understanding of the nature of space and time, and matter through the equivalence of mass and energy. In 1916, Einstein extended the theory to include gravity in the general theory of relativity, which revealed that matter affects space by curving space around it.