Typically, classical physics encompasses topics at an atomic level (or larger). Physical theories (or laws), physicists, etc. Classical physics is causal; complete knowledge of the past allows computation of the future. Classical physics is a group of physics theories that predate modern, more complete, or more widely applicable theories. Some day that everything pre-1905 is classical, and everything afterwards is modern. The energy of blackbody radiation is not shared evenly by all wavelengths of light. Any object with a temperature above absolute zero emits light at all wavelengths. As StringJunky said, one of them is Classical vs Quantum. Not so in quantum physics. The defnition I prefer, and have heard most often, is that every branch of physics that does not utilize a quantum treatment is classical, and any physics that is based on quantum mechanics is modern. Classical Physics Classical physics includes the traditional branches and topics that were recognized and well-developed before the beginning of the 20th century— classical mechanics, acoustics, optics, thermodynamics, and electromagnetism. are can be* separated into two realms, Classical Physics and Modern Physics. Modern physics is an effort to understand the underlying processes of the interactions with matter, utilizing the tools of science and engineering. If the physics does not include quantum mechanics, it's classical. If the object is perfectly black (so it doesn't reflect any light), then the light that comes from it is called blackbody radiation.. (Chaos theory is irrelevant to this statement; it talks about how well you can do with incomplete knowledge.) If a currently accepted theory is considered to be modern, and its introduction represented a major paradigm shift, then the previous theories, or new theories based on the older paradigm, will often be referred to as belonging to the realm of "classical physics". This chapter focuses on the aspects of classical physics that lead to modern physics. Likewise, complete knowledge of the future allows precise computation of the past. So modern physics includes both relativity and quantum mechanics. 1. Blackbody Radiation. In general, the term is used to refer to any branch of physics either developed in the early 20th century and onward, or branches greatly influenced by early 20th century physics. THREE FAILURES OF CLASSICAL PHYSICS. Another term is "modern physics", which is a time divide, basically at 1905, when Einstein introduced relativity. Physics can be defined as the study of matter and energy. The Problems with Classical Physics By the late nineteenth century the laws of physics were based on Mechanics and the law of Gravitation from Newton, Maxwell's equations describing Electricity and Magnetism, and on Statistical Mechanics describing the state of large collection of matter. The laws that unify physics refer to particular physical quantities. It discusses two areas of modern physics—special relativity and quantum theory. So classical … There are a few varying definitions of what separates classical physics from modern physics.