Syllabus

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Course Description

There was an explosion in our understanding of physics at the turn of the 20th century. Einstein imagined riding along with a light wave and realized as a consequence that parts of the foundation of our understanding of physics, e.g. our notion of time, need to be revised when we take into account objects moving near the speed of light. Thus began special relativity. Simultaneously, a collection of physicists realized together that some physical observables, like the energies of an electron orbiting the nucleus, are not well described by a continuum of values, but rather by discrete quantum jumps. Incorporating this discreteness into physical models also required an upheaval of the bedrock of physics, classical mechanics, and led to the invention of quantum mechanics.

In retrospect, one way to capture these two revolutions is to say that they each introduced a new fundamental physical scale, captured by a constant of nature. These are the speed of light, c, and Planck's constant, ℏ. As you turn on these constants you move from classical mechanics to special relativity and quantum mechanics respectively, see the Figure. If you do an experiment where they are both relevant at once you move towards the upper right corner of the Figure and the end of the modern physics era, the discovery of quantum field theory.

A third revolution, which built more slowly but with inexorable strength, was the study of many particles through thermodynamics and statistical mechanics. Unlike relativity and quantum mechanics, which changed what we think the world is made of, statistical mechanics changed how we approach the description and quantification of the world. We left behind detailed understanding of a few objects, and turned towards a much broader understanding of bodies with ∼10²³ constituents.

The goal of this course is to combine these three revolutions to understand the interaction of light and matter. This necessitates a deep understanding of classical and quantum waves. The rich questions of how light transfers energy to matter and how matter radiates light will motivate every aspect of the course and lead us to applications in particle physics, nuclear physics, optical and molecular physics, condensed matter physics, and astronomy.