The Elegant Universe: Superstrings, Hidden Dimensions, and the Quest for the Ultimate Theory

Chapter 2 explains Einstein’s theory of special relativity. Einstein began with a paradox, asking what would happen if an observer chased a light beam at light speed. According to both intuition and Newton’s laws of motion, the observer should eventually catch up to the light beam, making it appear stationary. However, in the mid-1880s, physicist James Clerk Maxwell successfully unified electricity and magnetism into a single framework called the electromagnetic field. Maxwell’s theory of electromagnetism demonstrated “that electromagnetic disturbances travel at a fixed and never-changing speed, a speed that turns out to equal that of light” (24). This led Maxwell to surmise that light is another form of electromagnetic wave and that electromagnetic waves “never slow down. Light always travels at light speed” (24). Thus, Newton’s and Maxwell’s conclusions contradicted each other.

In 1905, Einstein’s theory of special relativity resolved this contradiction by defying intuition and arguing that observers in relative motion (moving relative to each other) will always have “different perceptions of distance and of time” (25). For example, two individuals in relative motion wearing identical wristwatches will find those watches tick at different rates and will therefore not agree on the amount of time that has elapsed.