When no one is looking, a particle has near limitless potential: it can be nearly anywhere. But measure it, and the particle snaps to one position. How do subatomic objects shed their quantum weirdness? Experts in the field of physics, including David Z. Albert, Sean Carroll, Sheldon Goldstein, Ruediger Schack, and moderator Brian Greene, discuss the history of quantum mechanics, current theories in the field, and possibilities for the future.