Quantum physics is the golden child of modern science. It is the basis of our understanding of atoms, radiation, and so much else, from elementary particles and basic forces to the behavior of materials. But for a century it has also been the problem child of science: it has been plagued by intense disagreements between its inventors, strange paradoxes, and implications that seem like the stuff of fantasy. Whether it's Schr?dinger's cat--a creature that is simultaneously dead and alive--or a belief that the world does not exist independently of our observations of it, quantum theory challenges our fundamental assumptions about reality.