The science of matter and energy and their interactions; SYN. physical science, natural philosophy.
Branch of science concerned with the laws that govern the structure of the universe, and the investigation of the properties of matter and energy and their interactions. For convenience, physics is often divided into branches such as atomic physics, nuclear physics, particle physics, solid-state physics, molecular physics, electricity and magnetism, optics, acoustics, heat, thermodynamics, quantum theory, and relativity. Before the 20th century, physics was known as natural philosophy.