Physical Principles: Quantum Mechanics

Abstract

The practitioners of Western physics believed that they had reached the climax of their art by the end of the nineteenth century. When a young Max Planck turned to the study of physics, he was warned that the field was virtually closed and that no significant or fundamental discoveries remained to be made. These views are certainly understandable taken from the perspective of the nineteenth-century practitioner. Appreciating the certainty of this view and then following the path by which the ideas of classical physics were replaced provides one of the best historical examples confirming the ideas put forth in the first section. The quite surprising rise of modern physics (which is comprised of quantum and relativistic theory) from the monolith of classical physics followed from a fundamental shift in assumptions and a fresh view of the physical state space. As we will see in the following discussion, a shift in the paradigm from the macroscopic to the microscopic nature of the Universe leads to a reevaluation of the empirical evidence already at hand. The experimental evidence could not be understood (or better, properly linked to a formal model) until the simplifying assumptions on which the treatment of mechanics was based were revisited and revised. The new mechanical constructs that reflect both a shift in the way the state space is viewed and how the observables are linked to a formal theoretical model compose the language and concepts of modern physics. As such they are the foundation of modern natural science. We will follow the historical development of the quantum theory as an example of model making and will use this perspective as our approach for learning the details of the field.