We present an operational account of quantum measurement in which outcome definiteness and irreversibility arise from causal structure, decoherence, and computational constraints rather than from fundamental collapse. We show that in any globally unitary quantum system with environmental coupling and nontrivial causal partitioning, no physically realizable observer can access all information pathways simultaneously. As a result, observer-dependent descriptions—definite outcomes for embedded observers and coherent superpositions for external observers—are mutually consistent and cannot lead to operational contradiction. This framework resolves Wigner-type measurement paradoxes and clarifies the origin of irreversibility without modifying quantum mechanics.
We present an operational account of quantum measurement in which outcome definiteness and irreversibility arise from causal structure, decoherence, and computational constraints rather than from fundamental collapse. We show that in any globally unitary quantum system with environmental coupling and nontrivial causal partitioning, no physically realizable observer can access all information pathways simultaneously. As a result, observer-dependent descriptions—definite outcomes for embedded observers and coherent superpositions for external observers—are mutually consistent and cannot lead to operational contradiction. This framework resolves Wigner-type measurement paradoxes and clarifies the origin of irreversibility without modifying quantum mechanics.
Quantum measurement is widely regarded as paradoxical due to the apparent role of observers, wave function collapse, and mutually inconsistent descriptions of reality. We argue that these paradoxes are not intrinsic to quantum mechanics, but arise from a category error: treating observer-dependent inferences as observer-independent physical facts.We introduce a causality-first framework in which quantum states represent open causal structures, and measurement corresponds to a scale-dependent transition to causal closure. No privileged observer, stochastic collapse mechanism, or many-worlds ontology is required. Within this framework, celebrated paradoxes such as Wigner’s Friend and the Frauchiger–Renner no-go theorem dissolve, as their contradictions rely on an implicit violation of causal consistency.Our proposal does not modify quantum dynamics nor introduce new postulates. Instead, it clarifies when quantum processes may enter causal chains. The result is a realist, observer-independent account of measurement that preserves standard quantum theory while eliminating its most persistent conceptual pathologies.
Quantum mechanics lacks a physical definition of measurement, observer, probability, and experienced time. These notions are instead treated as primitive or interpretation-dependent, leading to persistent foundational problems including the measurement problem, the origin of the Born rule, observer disagreement in Wigner’s Friend scenarios, the arrow of time, and apparent information loss in black hole evaporation. In this work, we show that these problems share a single missing ingredient: the absence of an operational definition of observers as bounded physical systems. We define observers as physically realizable systems capable of forming irreversible internal records under unitary dynamics. Measurement is identified with record formation, probability with record redundancy, experienced time with record accumulation, and irreversibility with computational inaccessibility rather than non-unitarity. Using decoherence and quantum Darwinism, we show that the number of accessible, decoherence-stable records associated with an outcome scales with the squared amplitude, yielding the Born rule from record counting without invoking collapse, subjective probability, or additional axioms. Observer-relative paradoxes dissolve once outcome definiteness is indexed to record formation rather than to the global quantum state. Reconstruction of global quantum information is shown to require exponential resources, rendering measurement and black hole evaporation operationally irreversible despite global unitarity. The resulting framework closes quantum mechanics conceptually by eliminating undefined primitives, without modifying its mathematical structure or introducing new dynamical postulates.
We present a unitary and operational account of quantum measurement in which outcome irreversibility arises from computational complexity rather than fundamental nonunitarity. Measurement is modeled as a two-stage physical process. First, local interactions dynamically select a pointer basis in which stable classical records are formed via decoherence. Second, subsequent local scrambling dynamics distribute these records globally across a finite quantum memory register. Using explicit circuit constructions based on local random circuits that form approximate unitary k-designs, we show that measurement records are encoded in high-order nonlocal correlations. We prove that reversing such records requires quantum circuits of exponential depth, even allowing ε-approximate reconstruction. This establishes a quantitative complexity barrier rendering outcome reversal physically unrealizable despite global unitarity. We apply the framework to multi-register (Wigner-type) scenarios and show that no physically realizable operation can expose inconsistency between distinct register-relative descriptions. Finally, we prove a conditional no-go theorem excluding any global collapse mechanism compatible with unitary dynamics, locality, and computational feasibility. Measurement irreversibility is therefore shown to be an emergent, complexity-protected phenomenon within standard quantum mechanics
Wigner’s Friend scenarios expose a foundational tension in quantum theory between unitary evolution and the existence of definite measurement outcomes experienced by observers. This paper proposes an Observer-First Interpretation (OFI) in which quantum states are treated as observer-relative informational constructs constrained by evidence accessibility and record boundaries. Within this framework, the friend’s measurement produces a single definite outcome through irreversible informational compression into a stable internal record, while an external observer lacking access to this record may consistently describe the laboratory as unresolved or coherent. Apparent paradoxes arise only when observer-indexed state assignments are illegitimately combined as if they represented simultaneous global facts. By enforcing observer-relative state attribution, the framework resolves Wigner’s Friend and related observer paradoxes without modifying the formalism or empirical predictions of quantum mechanics.
We present a unitary and operational account of quantum measurement in which outcome irreversibility arises from computational complexity rather than fundamental nonunitarity. Measurement is modeled as a two-stage physical process. First, local interactions dynamically select a pointer basis in which stable classical records are formed via decoherence. Second, subsequent local scrambling dynamics distribute these records globally across a finite quantum memory register. Using explicit circuit constructions based on local random circuits that form approximate unitary k-designs, we show that measurement records are encoded in high-order nonlocal correlations. We prove that reversing such records requires quantum circuits of exponential depth, even allowing ε-approximate reconstruction. This establishes a quantitative complexity barrier rendering outcome reversal physically unrealizable despite global unitarity. We apply the framework to multi-register (Wigner-type) scenarios and show that no physically realizable operation can expose inconsistency between distinct register-relative descriptions. Finally, we prove a conditional no-go theorem excluding any global collapse mechanism compatible with unitary dynamics, locality, and computational feasibility. Measurement irreversibility is therefore shown to be an emergent, complexity-protected phenomenon within standard quantum mechanics.
The quantum measurement problem arises from a structural asymmetry in standard formulations of quantum mechanics: while unitary evolution is treated as fundamental, irreversible events are introduced only through ad hoc postulates. As a result, measurement, decoherence, and probability appear conceptually disconnected. In this work, we propose a minimal reformulation in which irreversible interaction events are taken as ontological primitives. An event is defined as a completely positive, trace-preserving map that is not equivalent to any unitary transformation. Unitary evolution emerges as an effective description valid between events. Within this framework, quantum measurement is not a special process but a particular class of irreversible events with outcome-resolving structure. The Born rule arises naturally from the statistical structure of event realizations, and environmental decoherence is reinterpreted as a high density of irreversible events. No collapse postulate, observer-dependent rule, or modification of quantum dynamics is required. This formulation provides a unified and physically grounded resolution of the measurement problem and establishes a conceptual foundation for event-based extensions connecting quantum theory with spacetime and gravity.