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The Elegant Universe

Brian Greene


Part III: The Cosmic Symphony

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Chapter 6: Nothing but Music: The Essentials of Superstring Theory

The standard model, which describes the elementary particles of the universe as amorphous, zero-dimensional points, is not comprehensive because it ignores gravity. Superstring theory, on the other hand, describes the most basic ingredients of matter as Planck-length strings that vibrate perpetually, like tiny rubber bands.

Before explaining why only string theory can resolve the conflict between general relativity and quantum mechanics, Greene supplies a brief history of the origins of string theory. In 1968, theoretical physicist Gabriele Veneziano was trying to understand the strong nuclear force when he made a startling discovery. Veneziano found that a 200-year-old formula created by Swiss mathematician Leonhard Euler (the Euler beta function) perfectly matched modern data on the strong force. Veneziano applied the Euler beta function to the strong force, but no one could explain why it worked.

Two years later, Yochiro Nambu, Holger Nielsen, and Leonard Susskind unveiled the physics beneath Euler’s strictly theoretical formula. By representing nuclear forces as vibrating, one-dimensional strings, these physicists showed how Euler’s function accurately described those forces. But even after physicists understood the physical explanation for Veneziano’s insight, the string description of the strong force made many predictions that directly contradicted experimental findings. The scientific community soon lost interest in string theory, and the standard model, with its particles and fields, remained unthreatened.

Then, in 1974, John Schwarz and Joel Scherk studied the messenger-like patterns of string vibration and found that their properties exactly matched those of the gravitational force’s hypothetical messenger particle. Schwarz and Scherk argued that string theory had failed to catch on because physicists had underestimated its scope.

But the enthusiasm faded fast, for string theory’s conflicts with quantum mechanics remained unresolved. Then, in 1984, Schwarz and Michael Green declared that string theory was capable of explaining all four forces and all matter as well. String theory, they said, was not a strong force theory, but a quantum theory that also included gravity. Shwarz’s and Green’s reinterpretation marked the first-ever quantum mechanical theory of the gravitational force.

In 1984, Brian Greene started graduate school at Oxford University. The reaction to Schwarz’s and Green’s discovery was to influence the direction of his research for the next two decades. Greene came to believe that particle physics had no future: only string theory, he believed, could explain all properties of the microworld. String theory can make numeric predictions that the standard model, which is too flexible to explain the properties of elementary particles, can only assume.

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