Lavoisier’s Principle

In the context of classical mechanics, the principle of mass conservation—also known as Lavoisier’s principle—states that the mass \(M\) of a closed system is constant,

\[d M = 0 \ ,\]

that is, “nothing is created, nothing is destroyed, everything is transformed.”

• This principle was discovered by early chemists through the measurement of the mass of products and reactants in chemical reaction experiments.

• This principle ceases to hold in the framework of Einstein’s theory of relativity, which recognizes the equivalence of mass and energy: mass and energy are two representations of a single physical quantity and are part of a balance equation. In the special case of a body at rest, this reduces to the famous expression \(E = m c^2\).