String's the Thing

Physicist Brian Greene charts the development of this "theory of everything" that ties general relativity and quantum mechanics together. Physicist Gabriel Veneziano saw something in a 200-year-old mathematical equation that no one else had. There were problems: "unruly equations" and mathematical calculations that didn't add up. John Schwarz and Michael Green worked out the anomalies, but no one has been able to overcome the fact that strings are so small that the theory is untestable.