Thermal History and Cosmic Microwave Background

This lecture covers the thermal history of the universe, focusing on the equilibrium state and the temperature of the Cosmic Microwave Background (CMB). The instructor discusses the Boltzmann equation and its relevance to understanding the behavior of particles in thermal equilibrium. The lecture emphasizes the significance of the CMB in cosmology, detailing how it provides insights into the early universe and the evolution of matter and radiation. The instructor explains the concept of luminosity distance and its connection to standard candles, which are essential for measuring astronomical distances. The relationship between the CMB temperature and the expansion of the universe is also explored, highlighting the implications for baryogenesis and the formation of structures in the cosmos. Throughout the lecture, the instructor presents mathematical formulations and physical principles that underpin these concepts, providing a comprehensive overview of the thermal dynamics that shaped the universe as we know it today.