Advances in Physics These reviews are sometimes complemented by a "Perspectives" section which publishes shorter articles that may be controversial, with the intention of stimulating debate. The intended audience consists of physicists, materials scientists, and physical chemists working in universities, industry, and research institutes. Broad, interdisciplinary coverage includes topics ranging from condensed matter physics, statistical mechanics, quantum information, cold atoms, and soft matter physics to biophysics. The impact factor for "Advances in Physics" 18.062 in 2013, ranking it first in the discipline of condensed matter physics. This journal is indexed in the following databases: Advances in Physics Advances in Physics is a bimonthly
Action (physics) (see also below). The action is defined by an integral, and the classical equations of motion of a system can be derived by minimizing the value of that integral. This simple principle provides deep insights into physics, and is an important concept in modern theoretical physics. "Action" was defined in several now obsolete ways during the development of the concept. Expressed in mathematical language, using the calculus of variations, the evolution of a physical system (i.e., how the system actually progresses from one state to another) corresponds to a stationary point (usually, a minimum) of the action. Several different definitions