Entropy

From Conservapedia

Entropy is a measure of disorder or information content in a system, first postulated by Lazare Carnot in 1803.

The second law of thermodynamics states that entropy will always increase over time within a closed system, defining a closed system as one in which neither matter nor energy may enter or leave.

Entropy is undeniable and yet creates perhaps insurmountable difficulties for many modern theories of physics. For example, it renders time asymmetric, resulting in an arrow of time that is difficult to reconcile with the theory of relativity. Entropy casts doubt on whether physical laws or the speed of light are invariant and perpetual.

Perhaps because entropy confounds so much other contemporary theory in physics, there is very little theoretical work on entropy today.

Contents 1 Definitions 1.1 Thermodynamic definition 1.2 Statistical mechanics definition 1 1.3 Statistical mechanics definition 2 2 See also 3 References

Definitions

Thermodynamic definition

In classical thermodynamics, if a small amount of energy dQ is supplied to a system from a reservoir held at temperature T, the change in entropy is given by

For a measurable change between two states i and f this expression integrates to

Statistical mechanics definition 1

If a system can be arranged in W different ways, the entropy is

S = k_BlogW

where k_B is Boltzmann's constant.

Statistical mechanics definition 2

Label the different states a thermodynamic system can be in by . If the probability of finding the system in state i is p_i, the entropy is

This definition is closely related to ideas in information theory, where the definition of information content is very similar to the definition of entropy.

See also

• History of the development of entropy

References