Fifteen years ago, I was a physicist hard at work hunting for a theory of nature that would unify the very big and the very small. There was good reason to hope. The great and the good were committed. 1 Even Einstein, who recognized that our understanding of reality is necessarily incomplete, had spent the last 20 years of his life searching for a unified field theory that would describe the two main forces we see acting around us—gravity and electromagnetism—as manifestations of a single force. For him, such a mathematical theory represented the purest and most elegant expression of nature and the highest achievement of the human intellect. 2 Modern critics say that Einstein and other giants of 20th-century physics failed because their models didn't include all particles of matter and their fundamental interactions. But are we really getting any closer? Do we dare ask whether the search is fundamentally misguided? 3 Could belief in a physical theory that unifies the secrets of the material world—a "hidden code" of nature—be the scientific equivalent of the religious belief in oneness held by the billions who go to churches every day? 4 Even before what we now call physics existed, ancient Greek philosophers pondered whether the diversity of nature could radiate from a single source, a primal (原始的) substance. Pythagoras and his followers believed that nature was a mathematical puzzle, constructed through ratios and patterns that combine integers, and that geometry was the key to deciphering it. The idea of mathematics as a fundamental gateway to nature's secrets re-emerged during the late Renaissance. 5 Galileo Galilei (伽利略) made it clear that the mathematical description of nature succeeds only through the painstaking application of the scientific method, where hypotheses are tested by experiments and observations and then accepted or rejected.