Where does collapse collide?

Collapse in the lung is the loss of air from part or all of the lung so that the tissue deflates and its air spaces close, a state also called atelectasis. Laennec's 1819 treatise De l'auscultation médiate described the airless, collapsed lung among the chest conditions his new stethoscope could detect, and Duggan and Kavanagh's 2005 review Pulmonary atelectasis set out how it arises under anaesthesia and injury and how it is imaged and reversed. The referent is deflated lung tissue in a living body, and it has nothing in common with a quantum state reducing on measurement, matter falling together under gravity, or a society losing its complexity.[1][2]

Unit

One collapsed lung or lobe, scaled by the volume or fraction of lung that has lost air

Recovery means

A collapsed lung can re-expand when air re-enters, through deep breathing, physiotherapy, or ventilation

Measured by

Detected on chest imaging such as X-ray or CT and by reduced oxygenation, and quantified as the volume of lung involved

Collapse of the wavefunction is the abrupt change by which a quantum system, described before measurement as a spread of possible outcomes, jumps to the single definite result that is observed. Von Neumann's 1932 Mathematische Grundlagen der Quantenmechanik gave this the formal rule now called the projection postulate, separating the smooth evolution of the undisturbed state from the discontinuous jump at measurement. The referent is a mathematical change of state in quantum theory, tracked by the probabilities of measurement outcomes, and it is a different thing from a lung deflating, a star imploding, or a civilization breaking down.[3]

Unit

One measurement event, scaled by the probabilities assigned to the possible outcomes

Recovery means

Not applicable

Measured by

Inferred from the statistics of repeated measurements, which match the probabilities predicted before collapse

Gravitational collapse is the runaway inward fall of a body's matter when its own gravity overwhelms whatever pressure had been holding it up, driving the material toward ever higher density. Oppenheimer and Snyder's 1939 paper On continued gravitational contraction gave the first relativistic account of a massive star contracting without limit once its support fails, the process now understood to form black holes. The referent is the mechanical implosion of astrophysical matter, measured by mass, radius, and density over time, and it is unrelated to a deflated lung, a quantum state reducing on measurement, or the decline of a society.[4]

Unit

One collapsing body, scaled by its mass, radius, and density over time

Recovery means

Not applicable

Measured by

Modelled from mass and equation of state, and inferred observationally from supernovae, compact remnants, and gravitational waves

Societal collapse is the rapid loss of an established level of social, political, and economic complexity, leaving a simpler and smaller society in its place. Tainter's 1988 book The Collapse of Complex Societies defined it this way and argued that societies collapse when the added complexity they invest in stops returning enough benefit to be worth its cost. The referent is a historical decline in the organisation of a human society, studied through archaeological and documentary records, and it does not describe a lung emptying of air, matter imploding under gravity, or a quantum state reducing on measurement.[5]

Unit

One society over a span of time, scaled by measures of its social and political complexity

Recovery means

Not applicable

Measured by

Reconstructed from archaeological and historical evidence of settlement, population, trade, and administration