(quantum mechanics) The phenomenon in which a wavefunction — initially in a superposition of several different possible eigenstates — appears to reduce to a single one of those states after interaction with an observer: the reduction of the physical possibilities into a single possibility as seen by an observer.

(genealogy) The phenomenon in which ancestral inbreeding causes the number of a descendant’s distinct ancestors to be smaller than that predicted by a binary tree (∑ᵢ₌₁ⁿ 2ⁱ, where n represents the number of generations).

(cricket) A succession of batsmen or batswomen getting out without adding many runs to the team's score.

A mysterious and widespread phenomenon of the sudden disappearance of colonies of bees.

(history) The transition from the Bronze Age to the Iron Age in the eastern Mediterranean and southwestern Asia, characterised by the collapse of the Hittite, Egyptian, Mycenean and Canaanite civilisations.

A proposed alternative to a black hole whose collapse continually slows down, and that does not form an event horizon

plural of eternally collapsing object

A transition in the Aegean Region, Southwestern Asia and the Eastern Mediterranean from the Late Bronze Age to the Early Iron Age that historians believe was violent, sudden, and culturally disruptive.