physics

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. Before the 19th century, physics was known as natural philosophy.

Classical physics consisted of the study of heat, light, electricity, magnetism, optics, acoustics, and mechanics. Since the turn of the 20th century quantum mechanics and relativity have transformed all areas of physics. Today, physics is often divided into branches such as nuclear physics, particle physics, quantum physics, theoretical physics, and solid-state physics. The study of the planets, stars, and their interactions is known as astrophysics, the physics of the Earth is called geophysics, and the study of the physical laws relating to living organisms is called biophysics.