The Conservation of Mass-Energy in the Expanding Cosmos

This paper explores the principle of mass-energy conservation within the framework of the Big Bang theory and the expansion of the universe. It examines how the foundational law of conservation of energy, which states that energy cannot be created or destroyed, applies to the cosmos as a whole. Drawing upon Albert Einstein's mass-energy equivalence (E=mc^2), the article argues that the total sum of mass and energy in the universe has remained constant since the initial singularity. It clarifies the distinction between rest mass and relativistic mass, utilizing the more precise relativistic energy equation (E=γ m_0 c^2) to explain how energy and mass are interconvertible. The paper concludes that while the universe is expanding, causing matter to spread out, the fundamental quantity of mass-energy remains unchanged, aligning with established laws of physics.