In his classic book the dragons of eden, astronomer carl sagan tidily summarized the central challenge scientists face when they try to formulate grand new theories: "Remarkable claims require remarkable proof." One of the most remarkable claims made in modern times comes from string theory, which holds that everything in the universe is composed of tiny vibrating strings of energy. In this view, every particle in your body, every speck of light that lets you read these words, and every packet of gravity that pushes you into your chair is just a variant of this one fundamental entity. Over the past three decades, string theory has increasingly captured the imagination of physicists. Hundreds of researchers around the world now hammer away at its equations every day, trying to make the different parts of the theory hang together. They, like me, consider it the greatest step forward in science since Albert Einstein and Max Planck introduced the key ideas of relativity and quantum mechanics about a century ago.
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