Law of Conservation of Mass-Energy

The Law of conservation of mass-energy is a fundamental principle in physics that states that the total mass-energy of a closed system remains constant. It combines the principles of conservation of mass and conservation of energy into a unified concept.  According to this law, the total amount of mass and energy in a closed system remains constant over time.  Mass and energy can be converted from one form to another, but the total sum is conserved.

This principle arises from Albert Einstein's theory of relativity, specifically his famous equation E=mc², where E represents energy, m represents mass, and c represents the speed of light in a vacuum (a constant value).  The equation shows that mass and energy are interchangeable and are two aspects of the same underlying physical entity.  Mass can be converted into energy, and energy can be converted into mass.  This is demonstrated in various phenomena, such as nuclear reactions, where a small amount of mass is converted into a significant amount of energy.

It's important to note that this law applies to closed systems where no mass or energy enters or leaves the system.  In reality, energy and mass can be exchanged with the surroundings, and the law can be modified to account for these interactions.  However, on a larger scale, the conservation of mass-energy remains a fundamental principle in understanding the behavior of the universe.