Explore fundamental cosmological concepts in this third lecture from the Perimeter-SAIFR-IFT Journeys into Theoretical Physics program, delivered by Rogerio Rosenfeld from IFT-UNESP/ICTP-SAIFR. Delve into advanced topics in cosmology as part of a comprehensive series designed to introduce theoretical physics concepts to students and researchers. Build upon previous foundational knowledge while examining key principles that govern the structure and evolution of the universe. Gain insights from an expert perspective on modern cosmological theory and its applications in understanding the cosmos. Access this educational content as part of the broader Journeys into Theoretical Physics initiative, which brings together leading physicists to share cutting-edge knowledge in theoretical physics disciplines.