#DEFINITION OF ENTROPY MOVIE#

The question of why entropy increases until equilibrium is reached was answered very successfully in 1877 by a famous scientist named Ludwig Boltzmann. While the second law, and thermodynamics in general, is accurate in its predictions of intimate interactions of complex physical systems behave, scientists are not content with simply knowing how a system behaves, but want to know also why it behaves the way it does.

#DEFINITION OF ENTROPY MOVIE#

For example, the orbiting of the planets around the Sun may be thought of as practically reversible: A movie of the planets orbiting the Sun which is run in reverse would not appear to be impossible. Some processes in nature are almost reversible. Such processes are irreversible: An ice cube in a glass of warm water will not spontaneously form from a glass of cool water. For example, a glass of warm water with an ice cube in it will have a lower entropy than that same system some time later when the ice has melted leaving a glass of cool water. When bodies of matter or radiation, initially in their own states of internal thermodynamic equilibrium, are brought together so as to intimately interact and reach a new joint equilibrium, then their total entropy increases. Thermodynamic entropy has a definite value for such a body and is at its maximum value. A body of matter and radiation eventually will reach an unchanging state, with no detectable flows, and is then said to be in a state of thermodynamic equilibrium. Irreversibility is described by a law of nature known as the second law of thermodynamics, which states that in an isolated system (a system not connected to any other system) which is undergoing change, entropy increases over time. Mixing coffee and burning wood are 'irreversible'.

If a movie that shows coffee being mixed or wood being burned is played in reverse, it would depict processes impossible in reality. A more physical interpretation of thermodynamic entropy refers to spread of energy or matter, or to extent and diversity of microscopic motion. The word 'entropy' has entered popular usage to refer a lack of order or predictability, or of a gradual decline into disorder. For example, cream and coffee can be mixed together, but cannot be 'unmixed' a piece of wood can be burned, but cannot be 'unburned'. In thermodynamics, entropy is a numerical quantity that shows that many physical processes can go in only one direction in time.

Definition of entropy