Where does opacity collide?

In stellar physics, opacity is the resistance that stellar material offers to the passage of radiation through it: the higher the opacity, the harder it is for energy to flow outward as light, which shapes a star's temperature structure and how it burns. Eddington's 1922 On the Absorption of Radiation inside a Star introduced a coefficient of opacity for the matter inside a star and placed it at the centre of stellar structure. Kramers' 1923 On the theory of X-ray absorption and of the continuous X-ray spectrum derived the absorption law behind it, and Rosseland's 1924 Note on the Absorption of Radiation within a Star defined the averaged quantity now called the Rosseland mean opacity. Here opacity is a physical property of matter and radiation, gauged as an absorption coefficient, and it has nothing to do with a firm hiding its books, a name that resists substitution, or a rule about database transactions.[1][2][3]

Unit

A mass absorption coefficient: energy absorbed per unit mass of material along a path

Recovery means

Not applicable

Measured by

Computed from atomic absorption physics, tabulated as opacity against temperature and density, and constrained by stellar models and laboratory plasma experiments

In the philosophy of language, referential opacity is the failure of a term inside a context to be freely swapped for another term naming the same thing without changing whether the whole statement is true. Quine's 1943 Notes on Existence and Necessity set out this failure of substitution in statements about necessity and belief, and he later named such positions referentially opaque in Word and Object (1960). In a transparent context, if two names pick out the same object then either name will do; in an opaque one, for example inside 'believes that' or 'necessarily', substituting an equal name can turn a truth into a falsehood. Here opacity is a logical property of a linguistic context, not a physical barrier to radiation, a firm's level of disclosure, or a property of concurrent programs.[4][5]

Unit

A position in a statement, judged by whether co-referring terms may be substituted there while preserving truth

Recovery means

Not applicable

Measured by

Tested by substituting co-referring terms into the position and checking whether the truth value is preserved

In finance and economics, opacity is the difficulty outsiders face in observing the true value and risk of a firm's assets from available information. Morgan's 2002 Rating Banks: Risk and Uncertainty in an Opaque Industry argued that banks and insurers are inherently more opaque than other firms, evidenced by how often bond raters disagree over them and how lopsided those splits are. Here opacity is a property of a firm and its information environment, tied to disclosure, asset complexity, and the cost of monitoring, and it is gauged by proxies such as rating disagreement or how prices react to news. This is a claim about what markets can see, not an absorption coefficient inside a star, a substitution rule for names, or a correctness criterion for software.[6]

Unit

A firm's degree of information hiddenness, on a relative scale across firms

Recovery means

Not applicable

Measured by

Proxied by disagreement among bond raters, dispersion in analyst forecasts, bid-ask spreads, and price responses to disclosure

In computer science, opacity is a correctness condition for transactional memory: it requires that all transactions, including those that eventually abort, appear to run one after another in an order consistent with real time, and that even an aborted transaction never observes an inconsistent state. Guerraoui and Kapałka's 2008 On the correctness of transactional memory defined opacity and argued that weaker database criteria such as serializability are not enough for in-memory transactions, because a doomed transaction that reads inconsistent data can still crash the whole program before it aborts. Here opacity is a safety property of a concurrent execution, satisfied or not by a given history, and it is unrelated to radiation inside a star, hidden corporate value, or the substitution of names in a sentence.[7]

Unit

A yes-or-no property of a concurrent execution history

Recovery means

Not applicable

Measured by

Established by proving a history admits a valid sequential ordering, or checked by model checking and runtime verification

In postcolonial theory, opacity refers to the right not to be made transparent to another's understanding, set against demands for full comprehension. This meaning comes from Glissant (1997) in Poetics of relation.[8]

Unit

Recovery means

Measured by