Explain why the universe must be an isolated system to obey the law of conservation of mass.

Rudolf Clausius: The energy of the universe remains constant (1st Law of Thermodynamics) while the total entropy diverges rapidly to the infinity (2nd Law of Thermodynamics).

Explanation:

According to the German physicist Rudolph Clausius, the energy of the universe remains constant (1st Law of Thermodynamics) while the total entropy diverges rapidly to the infinity (2nd Law of Thermodynamics).

First Law of Thermodynamics is a generalization of the Principle of the Energy Conservation, originally applied to the study of mechanical systems, which states that energy cannot be created nor destroyed, but only transformed. Besides, astrophysical thoeries that endorse the idea of the existence of multiple universes, which are connected to each other, are still on trial.

The Second Law of Thermodynamics show that every real process generates entropy as a measure of irreversibilities.