The Encyclopedia of Physics presents a broad overview of the field at a level. Focused on pure physics - which deals with the most fundamental aspects of nature such as light, sound, movement, and force - its scope of coverage is wide and significant. Complementing the coverage of pure physics topics, concise, general entries discuss interdisciplinary subjects, such as applied physics, astrophysics, biophysics, chemical physics, geophysics, and medical physics. Biographical entries present personal profiles of important physicists, past and present, and list their accomplishments. While the emphasis is on the present state of physics, the science's historical background and development are explained, as appropriate, to give perspective on current issues in physics.