Since the Scientific Revolution, the period from roughly 1500 to 1700 during which modern science was born, physicists have worked toward uncovering a single theory capable of uniting all the fundamental forces into a single equation and explaining the basic nature of matter and energy. This theory is sometimes called a Theory of Everything. Establishing this theory has been a gradual process. Isaac Newton contributed to that process in the late seventeenth century when he proclaimed a universal theory of gravity, which led to his insights into the nature of light. Almost 200 years later, James Clerk Maxwell developed a set of four equations that successfully integrated electricity and magnetism into a single force known as electromagnetism.
Twentieth-century physicists made the greatest contributions to the Theory of Everything. In 1905, Albert Einstein revolutionized our understanding of reality when he declared that the speed of light is a constant. This theory led to many surprising deductions, including the theory that space and time are not separate entities. With this theory, the idea of “spacetime” was born. A decade later, Einstein toppled Newton’s universal theory of gravity by defining gravitational force as the curvature of space and time.
Einstein’s theories helped make sense of the largest aspects of the universe—movement in space and time, and the speed of light. Another group of physicists helped make sense of the smallest aspects of the universe—tiny subatomic particles. With the discovery of the strong force and the weak force in the 1930s, electromagnetism and the laws governing subatomic particles were named quantum mechanics.
In just thirty years, physicists had made gigantic leaps toward an integrated understanding of the cosmos. But there was one large problem: the laws didn’t match up. Physicists quickly discovered that quantum mechanics was fundamentally incompatible with Einstein’s general theory of relativity. Theories of the small simply did not agree with theories of the large, which suggested some massive defect in physicists’ formulation of the universe’s laws.
Both quantum mechanics and general relativity had been experimentally confirmed time and again, and for many years physicists could make no sense of the inconsistency between them. Many scientists had trouble believing that the universe operates according to two separate, contradictory sets of laws, but all attempts to reconcile quantum mechanics with general relativity met with frustration and failure. Because combining the two sets of laws seemed impossible, physicists tended to study one at the expense of the other. Pursuing a divide-and-conquer-style course toward truth, they studied the laws governing either the ultramicroscopic or the massive, but seldom both. Finally, in the last thirty years, the development of string theory and M-theory have given physicists a satisfactory way to merge the large with the small.
String theory had existed for a decade in cruder forms before it became popular in the mid-1980s when, in 1984, scientists John Schwarz and Michael Green published a groundbreaking paper that launched the first superstring revolution.
Brian Greene, author of The Elegant Universe, was an instant convert to string theory. He was convinced that particle physics was at an end. Despite the difficulty of proving the theory, Greene believed, as did many of his colleagues, that the basic ingredient of the universe was not zero-dimensional point particles, but rather tiny one-dimensional strands of string that vibrate in different patterns.
Greene earned his undergraduate degree from Harvard. He was a first-year graduate student and Rhodes Scholar at Oxford University when Schwarz and Green published their groundbreaking paper. Greene is now a professor of physics and mathematics at Columbia University, where he is also the codirector of Columbia’s Institute for Strings, Cosmology, and Astroparticle Physics (ISCAP). Greene’s The Elegant Universe was phenomenally successful, selling three-quarters of a million copies worldwide and becoming a Pulitzer Prize finalist in 2000. In 2003, Greene hosted a three-part NOVA special, also called “The Elegant Universe,” which drew twice the average audience for a NOVA program and won a 2004 Peabody Award for broadcast excellence. Greene’s follow-up to The Elegant Universe, The Fabric of the Cosmos: Space, Time, and the Texture of Reality, was on the New York Times bestseller list for ten weeks. The Washington Post has called Greene “the single best explainer of abstruse concepts in the world today.”
To this day, physicists cannot experimentally test and verify superstring theory’s predictions. The equations remain so complex that physicists must content themselves with approximations. While string theory has a long way to go, its promise will determine the future of physics in the twenty-first century. In The Elegant Universe, Greene shows how string theory offers a single theory capable of synthesizing quantum mechanics and general relativity.