Classical physics derived from quantum mechanics: Feynman Path Integral

Classical Mechanics and Relativity: Lecture 5 0:00 Introduction 2:35 Fermat's Principle 9:57 Variational principles 17:16 Double slit experiment 21:38 Quantum interference 25:08 Feynman Path Integral 31:12 Quantum trajectories 38:26 Classical Action of quantum paths 42:36 Path integral representation of wavefunction 44:17 Classical path from quantum interference Theoretical physicist Dr Andrew Mitchell presents an undergraduate lecture course on Classical Mechanics and Relativity at University College Dublin. This is a complete and self-contained course in which everything is derived from scratch. In this lecture I make the connection between classical mechanics and quantum mechanics. By analogy to Fermat's principle of least time in the theory of optics, and by considering a generalization of the double slit experiment, I introduce Feynman's Path Integral formulation of quantum mechanics. From it, I derive the principle of least action, and hence all of classical mechanics. Full lecture course playlist: https://www.youtube.com/playlist?list=PLotxEOxVaaoKDo2GFPZsg04p3OnlwYBkR Course textbooks: "Classical Mechanics" by Goldstein, Safko, and Poole "Classical Mechanics" by Morin "Relativity" by Rindler