The "preferred-basis problem" — why does measurement produce definite outcomes in this basis rather than another — is treated in opposite ways by the interpretations of quantum mechanics: posited ab initio (spontaneous collapse), drawn from a contingent environment (decoherence), left to the choice of a framework (decoherent histories), avoided (many-worlds, pilot wave). We show that in the Time–Actualization ontology — where measurement is an instance of the universal process of actualizing quantum potentialities into events — the preferred basis is anchored in the causal past of the event, together with a readiness condition: which events that past has made ready to actualize. TA does not introduce a new selection mechanism: it identifies the environment of einselection with the already-actualized causal past — an environment that is not posited outside the formalism (unlike an external classical apparatus), but is part of the same substrate. The causal location of this environment is foliation-independent; its monitoring content depends on the couplings, not on the bare order alone. Covariance of the associated operations requires the locality hypotheses stated below. The uniqueness of outcomes is posited, not explained. Born's rule remains imported, and empirical equivalence with quantum mechanics on the causal-set substrate is a requirement still to be verified for a complete dynamics. The contribution is ontological and local to the preferred-basis question. A symmetric downstream mechanism — the redundant proliferation of the outcome into the causal future (quantum Darwinism) — in addition accounts for the inter-observer objectivity of the actualized fact, without deriving it.
The "preferred-basis problem" — why does measurement produce definite outcomes in this basis rather than another — is treated in opposite ways by the interpretations of quantum mechanics: posited ab initio (spontaneous collapse), drawn from a contingent environment (decoherence), left to the choice of a framework (decoherent histories), avoided (many-worlds, pilot wave). We show that in the Time–Actualization ontology — where measurement is an instance of the universal process of actualizing quantum potentialities into events — the preferred basis is anchored in the causal past of the event, together with a readiness condition: which events that past has made ready to actualize. TA does not introduce a new selection mechanism: it identifies the environment of einselection with the already-actualized causal past — an environment that is not posited outside the formalism (unlike an external classical apparatus), but is part of the same substrate. The causal location of this environment is foliation-independent; its monitoring content depends on the couplings, not on the bare order alone. Covariance of the associated operations requires the locality hypotheses stated below. The uniqueness of outcomes is posited, not explained. Born's rule remains imported, and empirical equivalence with quantum mechanics on the causal-set substrate is a requirement still to be verified for a complete dynamics. The contribution is ontological and local to the preferred-basis question. A symmetric downstream mechanism — the redundant proliferation of the outcome into the causal future (quantum Darwinism) — in addition accounts for the inter-observer objectivity of the actualized fact, without deriving it.
Quantum mechanics describes the potential future; general relativity describes the actualized past; the present is the process of actualization that turns the one into the other. That single move is Time–Actualization (TA), the foundational ontology set out here. TA assumes the quantum formalism and the relativistic causal structure, and derives neither: it adds no new physics, makes no new prediction, and asks to be judged on coherence and unifying power rather than on a measurement. It proposes a common ontological reading of measurement, EPR and the structural arrow of time. D5 locates the einselecting environment in the event's causal past; the couplings within that past remain imported, and the system/environment split is relocated rather than removed. In detail. The ontology is a minimal triplet (ρ, ν, ⟨P,≺⟩): a positive normalized state ρ on a local net of algebras (the conditional future potential), a primitive tempo ν (the rate of becoming), and a growing causal set ⟨P,≺⟩ (the past). What is not derived, and is named as such throughout, is the Born rule, Einstein's equations, and the constants. Eight core hypotheses yield seven consequences. A structural arrow of time, prior to thermodynamics (D1). A partial dissolution of the measurement problem (D2), with definiteness posited and the trigger open. Conditional dissolutions of EPR and the signalling worry (D3–D4), requiring a propagation law. A preferred basis anchored in the couplings carried by the causal past (D5). A conditional thermodynamic reading of the structural arrow (D6), requiring a posited bridge to physical reset, and further thermal assumptions for its value. And a conditional coherence lemma (D7): the actualization dynamics is generally covariant and no-signalling once the substrate carries the standard locality of physics. D7 claims less than the Rideout–Sorkin Bell causality condition, which is a screening-off analogue of Bell's local causality and is not inherited. We then develop the proposed physics of the tempo ν: a correspondence with a local quantum speed scale and a saturation choice, both posited. Quantum speed limits alone do not bound an ontic event count. The missing bridge must specify event resolution, additive counting and an applicable composable speed bound. The substrate cadence that reconstructs proper time is kept distinct from a system's tempo; their operational connection remains to be supplied. TA aims at empirical equivalence to quantum mechanics on a causal-set substrate. We label the admissibility requirement P5; its verification, including instrumented multi-time statistics, remains open. No distinctive prediction is claimed. The causal-set "swerve" is inherited from discreteness, generic and not specific to actualization. We close with the open dynamics, its system/substrate interface, the conditional constitution of systems, and the inherited limits of the programme.
The causal-set programme proposes that spacetime is, at bottom, a discrete poset whose Lorentzian geometry emerges, endowed with a covariant sequential growth dynamics. It leaves open, however, two points that an ontology must settle: the status of the "becoming" of growth (a computational procedure or a real process?), and the basis of its quantum version (quantum sequential growth, QSG, does not specify the basis of the histories). We show that the theory Time–Actualization (TA) proposes an ontological answer: becoming is posited as real actualization, while the basis is selected by the couplings carried by the causal past, where that monitoring supplies a sharp basis. This identifies an environment within the ontology; it does not derive its coupling content or construct the full quantum dynamics. We present the interface as a consistency bridge, not a refoundation. The emergent geometry and its Hauptvermutung remain inherited, and the dynamical law of actualization remains open. The proposed unification concerns a common process reading of flashes, system actualizations and causal-set growth; their different rates still require an explicit interface.
The preferred-basis problem and the definite-outcome aspect of the measurement problem persist even when the detector is modeled unitarily. Experimental data are represented in a Boolean event algebra of mutually exclusive records, while the theoretical description employs a noncommutative operator algebra with continuous unitary symmetry. This change of mathematical structure constitutes the core of the ``cut'': a necessary interface from group-based kinematics to set-based counting. In the Operationally Induced Preferred Basis (OIPB) framework, the basis relevant for recorded outcomes is not fixed by the system Hamiltonian but induced by the measurement interface -- the detector channel together with its coarse-grained readout. The Born rule follows from Gleason-type uniqueness (Gleason for projections in d>2 and Busch's extension for POVMs including d=2), as the unique probability measure consistent with additivity over exclusive events and basis-independence of the unitary sector. A compact qubit-pointer model yields an induced unsharp POVM E±=21(1±ησz) with sharpness η fixed by pointer resolution, explicitly demonstrating detector-induced basis selection. OIPB aligns with decoherence and operational theories while diverging from collapse models (no spontaneous reductions) and the Many-Worlds Interpretation (no ontological branching). Empirical distinctions arise through POVM tomography, Wigner-friend incompatibility tests, and superposition stability bounds. Nested-observer paradoxes are resolved by a non-composability lemma: joint assignment of outcome propositions is possible only if a joint instrument exists. This relocates the origin of randomness to the stochasticity of the interface rules.
Environmental decoherence is central to contemporary accounts of quantum measurement, yet its relation to definite outcomes remains disputed. This review distinguishes four explanatory demands: interference suppression, preferred-basis selection, operational objectivity, and outcome actualization. It compares open-system formalism and experimental evidence with the principal philosophical accounts of definiteness. In nonrelativistic models, environmental entanglement disperses phase coherence into inaccessible correlations, rendering the reduced system–apparatus state approximately diagonal in an interaction-selected pointer basis. Experiments support this loss of locally observable interference, while einselection and redundant environmental records explain the stability and intersubjective accessibility of macroscopic properties. These achievements neither convert an improper mixture into ignorance about an actual result nor select one component of the global state. Everettian interpretations reject global uniqueness, Bohmian mechanics adds an actual configuration, objective-collapse theories modify the dynamics, and QBist or pragmatist approaches revise quantum-state semantics. Decoherence is therefore indispensable to the formation of classical records but insufficient, by itself, for an interpretation-neutral derivation of unique actualization. Its foundational significance lies in identifying where unitary dynamical explanation ends and an ontological, dynamical, or semantic account of definiteness must begin.
Core quantum postulates including the superposition principle and the unitarity of evolutions are natural and strikingly simple. I show that—when supplemented with a limited version of predictability (captured in the textbook accounts by the repeatability postulate)—these core postulates can account for all the symptoms of classicality. In particular, both objective classical reality and elusive information about reality arise, via quantum Darwinism, from the quantum substrate. This approach shares with the Relative State Interpretation of Everett the view that collapse of the wavepacket reflects perception of the state of the rest of the Universe relative to the state of observer’s records. However, our “let quantum be quantum” approach poses questions absent in Bohr’s Copenhagen Interpretation that relied on the preexisting classical domain. Thus, one is now forced to seek preferred, predictable, hence effectively classical but ultimately quantum states that allow observers keep reliable records. Without such (i) preferred basis relative states are simply “too relative”, and the ensuing basis ambiguity makes it difficult to identify events (e.g., measurement outcomes). Moreover, universal validity of quantum theory raises the issue of (ii) the origin of Born’s rule, pk=|ψk|2, relating probabilities and amplitudes (that is simply postulated in textbooks). Last not least, even preferred pointer states (defined by einselection—environment—induced superselection)—are still quantum. Therefore, unlike classical states that exist objectively, quantum states of an individual system cannot be found out by an initially ignorant observer through direct measurement without being disrupted. So, to complete the ‘quantum theory of the classical’ one must identify (iii) quantum origin of objective existence and explain how the information about objectively existing states can appear to be essentially inconsequential for them (as it does for states in Newtonian physics) and yet matter in other settings (e.g., thermodynamics). I show how the mathematical structure of quantum theory supplemented by the only uncontroversial measurement postulate (that demands immediate repeatability—hence, predictability) leads to preferred states. These (i) pointer states correspond to measurement outcomes. Their stability is a prerequisite for objective existence of effectively classical states and for events such as quantum jumps. Events at hand, one can now enquire about their probability—the probability of a pointer state (or of a measurement record). I show that the symmetry of entangled states—(ii) entanglement—assisted invariance or envariance—implies Born’s rule. Envariance also accounts for the loss of phase coherence between pointer states. Thus, decoherence can be traced to symmetries of entanglement and understood without its usual tool—reduced density matrices. A simple and manifestly noncircular derivation of pk=|ψk|2 follows. Monitoring of the system by its environment in course of decoherence typically leaves behind multiple copies of its pointer states in the environment. Only pointer states can survive decoherence and can spawn such plentiful information-theoretic progeny. This (iii) quantum Darwinism allows observers to use environment as a witness—to find out pointer states indirectly, leaving systems of interest untouched. Quantum Darwinism shows how epistemic and ontic (coexisting in epiontic quantum state) separate into robust objective existence of pointer states and detached information about them, giving rise to extantons—composite objects with system of interest in the core and multiple records of its pointer states in the halo comprising of environment subsystems (e.g., photons) which disseminates that information throughout the Universe.
Quantum theory shows that natural laws cannot be understood as ruling single events since the latter occur randomly. Nevertheless, the physical world shows everywhere order whose source cannot be represented by the latter. It is shown that this order is due to the presence of quantum correlations. Since their e↵ect is to reduce the space of the possible events, they can be considered as causal factors. However, being correlations, they do not display the dynamic character that would be required in order to produce a determinate e↵ect. This is why they need additional local factors in order to concur to the production of a certain event. If not so, this would even imply a violation of Einstein’s locality since correlations could be used by themselves to transmit superluminal signals. Due to such a character of correlation, they can be understood as kind of potential reality needing actual (and local) context to be e↵ective. This allows also a distinction that is classically unknown between locality and globality. Such a distinction solves the important problem of measurement showing that ultimately we have irreversible local processes while globally everything is still reversible. In particular, it is a shift of information that can explain this local phenomenon. In fact, quantum systems are essentially information and also the measurement process is ultimately a dealing with information: information processing (preparing a system), information sharing (coupling a system with an apparatus) and information selection (detecting). State, observable and property appear as equivalence classes of these three procedures, respectively. Finally, the distinction between interpreted and uninterpreted ontology is considered in a Kantian perspective, but it is also shown that the approach supported here is rather a critical realism.