Preface: An Invitation

An evolving set of lecture notes on the many-body problem — classical and quantum, condensed or not — written concepts-first, asking why before we calculate.

Voyage is an ongoing series of lecture notes on the many-body problem, written in a deliberately conceptual voice — concepts before notation, why before how. This is its preface; chapters will join over time.

Dear Observer,

in these notes, we will always ask why and never calculate without first thinking carefully about what we expect. Our focus is on physics, concepts, geometry, symmetries, and methods. Concepts will come first, then notation — so that it becomes easier to open any book, regardless of its formalism, and understand everything. Finally, it is not only true that if you cannot teach it, you do not understand it, but also that if you cannot use it, you have wasted your time.

So, what are we interested in? We will be interested in many-body systems — whether classically or quantum mechanically, whether in a condensed state or not, from the lens of mathematics to the technology of the future. Nothing in these notes is guaranteed to be true, but at least we will judge it together. Join me on this everlasting journey.