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The von Neumann entropy formula is an extension of the Gibbs entropy formula to the quantum mechanical case. It has been shown [ 1 ] that the Gibbs Entropy is equal to the classical "heat engine" entropy characterized by d S = δ Q T {\displaystyle dS={\frac {\delta Q}{T}}\!} , and the generalized Boltzmann distribution is a sufficient and ...
The statistical definition of entropy defines it in terms of the statistics of the motions of the microscopic constituents of a system — modelled at first classically, e.g. Newtonian particles constituting a gas, and later quantum-mechanically (photons, phonons, spins, etc.). The two approaches form a consistent, unified view of the same ...
An equivalent definition of entropy is the expected value of the self-information of a variable. [1] Two bits of entropy: In the case of two fair coin tosses, the information entropy in bits is the base-2 logarithm of the number of possible outcomes — with two coins there are four possible outcomes, and two bits of entropy. Generally ...
Thus the definitions of entropy in statistical mechanics (The Gibbs entropy formula = ) and in classical thermodynamics (=, and the fundamental thermodynamic relation) are equivalent for microcanonical ensemble, and statistical ensembles describing a thermodynamic system in equilibrium with a reservoir, such as the canonical ensemble, grand ...
The entropy of is defined as [30] [31] [32] = (), where f ( x ) log f ( x ) {\textstyle f(x)\log f(x)} is understood to be zero whenever f ( x ) = 0 {\textstyle f(x)=0} . This functional can be maximized, subject to the constraints that the distribution is properly normalized and has a specified mean and variance, by using variational ...
In thermodynamics, entropy is a numerical quantity that shows that many physical processes can go in only one direction in time.For example, cream and coffee can be mixed together, but cannot be "unmixed"; a piece of wood can be burned, but cannot be "unburned".
Entropy is a measure of uncertainty or randomness in a probability distribution. For a Bernoulli random variable X {\displaystyle X} with success probability p {\displaystyle p} and failure probability q = 1 − p {\displaystyle q=1-p} , the entropy H ( X ) {\displaystyle H(X)} is defined as:
The entropy is thus a measure of the uncertainty about exactly which quantum state the system is in, given that we know its energy to be in some interval of size . Deriving the fundamental thermodynamic relation from first principles thus amounts to proving that the above definition of entropy implies that for reversible processes we have: