There are two major divisions of physics: classical and modern. Within classical physics, the major subdivisions are mechanics, thermodynamics, acoustics, optics, electricity and magnetism. The subdivisions of modern physics consist of chaos theory, relativity, string theory, cryogenics, crystallography and nanotechnology. The field also includes quantum-level, atomic, molecular, chemical, computational, high-energy, high-pressure and laser physics.
Classical physics is often described as the study of physics on the macroscopic level, meaning questions are generally investigated without the aid of highly technological equipment, such as electron microscopes. The inception of classical physics dates back to the late 1500s. Mechanics is the oldest subdivision of classical physics. The field is inspired by the work of Isaac Newton.
The study of modern physics takes place at the sub-microscopic level. This division of physics investigates the behavior of very small particles, such as electrons and atoms. Modern physics developed in the early 1900s when physicists began to realize that the laws of classical physics did not always hold true for sub-microscopic particles. Notable advances in modern physics include Einstein's theories of relativity and Heisenberg's principle of indeterminacy. Because even the world's most advanced microscopes cannot make sub-microscopic particles visible, expensive tools and equipment, such as particle accelerators, are required to explore the world at this level.