There’s more to physics than nonrelativistic quantum mechanics.

Many of the advances in string theory have been generated by the discovery of new duality symmetries connecting what were once thought to be distinct theories, solu-tions, processes, backgrounds, and more. Indeed, duality has played an enormously important role in the creation and development of numerous theories in physics and numerous fields of mathematics. Dualities often lie at those fruitful intersections at which mathematics and physics are especially strongly intertwined. In this paper I describe some of these dualities and unpack some of their philosophical conse-quences, focusing primarily on string-theoretic dualities. I argue that dualities fall uncomfortably between symmetries and gauge redundancies, but that they differ in that they point to genuinely new deeper structures