Lecture 1: Axioms of QM + Bell Inequalities

Is light transmitted by particles or waves? The basic dilemna here (which dates as far back as Newton) is to reconcile the evidence that light is transmitted by particles (called photons), with experiments demonstrating the wave nature of light. To be concrete, let us recall Young’s double-slit experiment from high school physics, which was used to demonstrate the wave nature of light. The apparatus consists of a source of light, an intermediate screen with two very thin identical slits, and a viewing screen (see picture on next page). If only one slit is open then intensity of light on the viewing screen is maximum on the straight line path and falls off in either direction. However, if both slits are open, then the intensity oscillates according to the familiar interference pattern predicted by wave theory. These facts can be qualitatively and quantitatively explained by positing that light travels in waves (as you did in high school physics).