In 1905 Albert Einstein suggested that light was a particle, not a wave, defying two hundred years of experiments. Werner Heisenberg's Uncertainty Principle and Erwin Schrödinger's infamous dead-or-alive cat are similarly strange. As Niels Bohr said, if you weren't shocked by quantum theory, you didn't really understand it. In 1925 the quantum pioneers nearly all hailed from upper-middle-class academic families, most were German, and their average age was twenty-four. Their irrational, romantic spirit inspired their will to test science to its limits.