In some ways, quantum mechanics and classical physics are strikingly different. These differences, explained in this series, are: ODD PHENOMENA: Subatomic particles follow laws unknown to classical physics, such as Heisenberg's uncertainty principle. Unlike classical determinism, the quantum world is indeterminate (not subject to exact measurement), and partakes of wave-particle duality, so that matter cannot be interpreted exclusively as either waves or particles. Fundamental particles are measured by means of statistical probability. Moreover, a single particle, which sometimes appears to take several different paths at once, exists in a superposition of possible states. STRANGE EXPERIMENTS: Physicists come in two styles: the experimentalists and the theorists. Theorists often devise thought experiments, like the famous EPR paradox and Schr"odinger's cat, to test their reasoning. Experimentalists often work with particle accelerators (sometimes called atom smashers) in which high-speed beams of particles hit targets inside massive collider detectors at energies up to several TeV (trillion electron volts). Only at these energies are certain short-lived particles (such as baryons and hadrons) produced. CURIOUS INTERPRETATIONS: The Copenhagen interpretation, the many-worlds view, and the undivided wholeness approach all try to explain quantum mechanical phenomena. Some physicists also look to string theory, which says that matter is made up of tiny strings. Others search for a unified field theory, which would unite the forces of gravity and electromagnetism with the strong force (holding the atomic nucleus together) and the weak force (which breaks up the nucleus), all as manifestations of a single force. Still, others think the explanations lie in hidden variables not yet discovered.