klassischmessbare

Klassischmessbare is an attributive German compound adjective used in physics and philosophy of science to describe quantities or properties that can be measured in a classical sense, i.e., with classical measuring devices and frameworks, as opposed to quantities that require quantum-mechanical concepts. The term appears in discussions of the classical limit, measurement theory, and debates about realism in the quantum world.

In practical terms, klassischmessbare Größen are those whose measurement statistics can be described by a joint probability distribution over a well-defined state space, aligning with classical (Kolmogorovian) probability theory. They are often associated with commuting observables, since commuting sets can (in a sense) possess simultaneous definite values and admit a joint distribution under a hidden-variable picture.

Examples commonly cited as klassischmessbare include macroscopic thermodynamic variables such as temperature, pressure, and volume, as well as coarse-grained properties like the average magnetization of a bulk material when decoherence suppresses quantum interference. By contrast, quantities displaying inherently quantum features—such as non-commutativity, contextuality, or entanglement—are typically not regarded as klassischmessbare in the strict sense.

Orthography and usage notes: In German, compound adjectives formed from klassisch and messbar can be written as klassischmessbare Größen (one word) or klassisch messbare Größen (two words), depending on styling conventions and grammatical context. The notion serves to distinguish classical-measurement notions from those that require quantum-mechanical description.