This lecture covers the problem in special relativity, the laws of nature invariant under Lorentz transformations, the combination of space and time, the Schrödinger equation, and the Dirac equation. It also discusses the concept of holes describing antiparticles and the shortcomings of certain fermions. The instructor explains the construction of spinors, the Dirac picture extensively used in solid-state physics, and the Dirac spinor in the non-relativistic limit.