zeroth law of thermodynamics

The zeroth law of thermodynamics is a fundamental principle in physics that establishes the concept of thermal equilibrium. It states that if two systems are each in thermal equilibrium with a third system, then they are also in thermal equilibrium with each other. This means that if two objects are at the same temperature and are in equilibrium with a third object, all three objects share the same temperature. This law is crucial for the meaningful use of thermometers to define temperature scales. The zeroth law was formally stated by Ralph Fowler in the 1930s, after the first, second, and third laws had already been established, and it serves as a foundational concept for the other laws.1