Stability of Collisionless Systems

This lecture discusses the stability of collisionless systems, focusing on the entropy of such systems and the response to weak perturbations. It covers linear response theory, the Jeans instability, and the linearized equations for self-gravitating fluids. The instructor explores the concept of specific enthalpy, sound speed, and the Jeans length in fluid systems. The lecture delves into the response of homogeneous stellar systems, the Jeans instability in stellar systems, and Landau damping. It concludes with a discussion on the interpretation of density waves and the implications of Maxwellian velocity distribution functions.