Objective-collapse theory

Objective-collapse theories modify quantum dynamics with spontaneous, physical reductions of superpositions to definite outcomes, without requiring measurement or an observer.

Ghirardi–Rimini–Weber theory: A collapse model in which particles undergo rare, random position localizations that rapidly suppress macroscopic superpositions. Its localization events provide a concrete mechanism for spontaneous collapse.
Many-worlds interpretation: An interpretation of quantum mechanics in which unitary evolution produces branching, noninteracting outcomes. It explains apparent definiteness through branching rather than physical collapse.
John Stewart Bell: A physicist whose work transformed the foundations of quantum theory, including analysis of spontaneous-collapse models. Bell clarified how GRW could be understood as a physical theory rather than a measurement rule.
Matter-wave interferometry: An experimental method that reveals wave-like interference in the motion of particles or larger objects. Interference tests whether collapse destroys coherence as mass and separation increase.
Collapse-model parameter bounds: Experimental and observational limits on the strengths and length scales of spontaneous-collapse dynamics. Current bounds leave a range of collapse parameters neither excluded nor confirmed.
Continuous spontaneous localization: A collapse model that continuously and stochastically localizes mass density in space. It replaces GRW’s discrete jumps with continuous state reduction.
Copenhagen interpretation: A family of quantum interpretations that treats measurement outcomes as definite without specifying a universal collapse mechanism. It invokes measurement-related state reduction rather than an objective dynamical process.
GianCarlo Ghirardi: An Italian physicist who helped formulate the GRW spontaneous-collapse model. His work helped establish the first prominent mathematical collapse proposal.
Optomechanics: The study of interactions between mechanical motion and light, often using small resonators. Mechanical superposition experiments can test collapse at mesoscopic scales.
Energy conservation in collapse models: The problem of energy changes caused by stochastic localization in collapse dynamics. Many simple models predict heating, raising questions about conservation and physical implementation.

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