The history of quantum mechanics begins with wanting to understand how atoms and molecules interact with radiation. Predictions from classical physics were incomplete, and so a different empirically oriented set of physical theories emerged that were created to fit experimental observation. This is an important point: while expressed mathematically, and ultimately validated to an extremely high level of experimental accuracy, these descriptions were arrived at not via a comprehensive understanding of underlying physical reality but more instead through determining the general shape of the mathematical boundaries such theories required.