Physical theory

A physical theory is an organized set of principles and mathematical relations that predicts measurable behavior within a stated domain. It connects idealized quantities to experimental procedures, allowing observations to test more than an isolated fitted formula.

For example, Newtonian mechanics relates force to acceleration and predicts orbital motion, while general relativity changes the description of gravity when spacetime curvature becomes relevant. A theory can remain useful within its approximation regime even after a broader theory is established. Its usefulness depends on explicit assumptions, reproducible predictions and known accuracy, rather than on treating every successful approximation as exact at all scales.