Glossary
The working vocabulary
The words ACT uses, grouped by role. Where a word carries a claim, its tag is the Claim Ledger’s status for that claim and links to the row; the ledger governs.
What exists, and what happens
- The field
- The one real object. A quantum system is one composite wave of a quantum field, with internal structure the way a sound wave contains its harmonics. ontology
- Modes
- The field’s structure. For a free, translation-invariant field the dynamics select its Fourier modes; a single photon “in two places” is one excitation of one two-lobed mode. established physics
- Superposition
- The composition of that one wave: its modes, or more generally its components in the decomposition the dynamics select. Not many things, and not ignorance of one. Interpretive
- Components
- The terms of the one wave in a given decomposition. vocabulary
- Two senses of “real”
- Components are real as the structure of the one wave: amplitude, interference while no record is released, later anchoring of what a record left unrecorded. An alternative is real as fact only when a released record has made it actual. The unselected alternatives keep the first and never acquire the second; anchoring picks out, it does not remove (The Picture). vocabulary
- Alternatives
- The sectors of the pointer observable that the record architecture resolves — what a detector can register. Exclusivity attaches here: one alternative per event. vocabulary
- The actual history
- The one sequence of anchored records. The definite, temporal, causal world is this history, not the wave alone. Written one mark at a time: one photon, one click, never both (the Mark). vocabulary
- Anchoring
- The bath’s taking of a record irreversibly, which, on the one actual history, makes one alternative actual. Anchoring adds a determination; it does not reduce the wave, and the field’s global evolution is never modified. mechanism
- Anchored event
- One record, one fact, now in causal time. Events are progressive where records accumulate: each released record is an anchoring. mechanism
- Particle
- An anchored event: the localized mark a mode of the field leaves in a detector’s record, and the chain of such marks called a track. Not a second kind of thing; the field is always a wave. ACT’s framing
- Wave–particle duality
- Dissolved. Wave is what exists; particle is what happens. A cloud-chamber track is one spherical wave and a straight line of condensation events (Mott 1929); anchoring is analogous to nucleation — a phase change in the record, not in the field. ACT’s framing
- Not yet in time
- Before the bath, a mode has structure but no temporal causal history; its evolution can be run either way. The pre-anchored state does not yet constitute a determinate temporal history of localized events. Interpretive
- Causal time
- The order among anchored events. Elapsed, recorded time exists only as anchored events; the Schrödinger parameter orders structure, not events. Interpretive
- Mass as a clock
- A massive excitation’s phase turns at its rest-energy rate $mc^2/\hbar$. Mass gives the field a clock; anchoring gives the clock its readings. Interpretive
- One history actual
- ACT’s one primitive commitment: of the possible record histories, one is the case. Stated, not derived; the Mark shows the marks, and this says that one history of them is actual (the Mark). Postulate
The mechanism
- The bath
- The photons, phonons and detector modes already present in the world: a continuum of modes coupled to the system. ACT’s mechanism; no new field is added. Its thought experiment is the Rock: a slab that nothing reads kills the fringes, in proportion to how lossy it is. Established
- Quantum Brownian motion
- The Caldeira–Leggett and Feynman–Vernon description of a system in a fluctuating, dissipating bath. Supplies noise, damping and record formation from one spectral density. established physics
- Spectral density $J(\omega)$
- How the bath’s modes are distributed in frequency. An anchoring bath needs weight down to low frequencies, so that records can spread without coming back; a field with a mass gap cannot anchor. Derived
- Decoherence
- The passing of a mode’s relative phase into the bath. In ACT it is built in: the phase in which a mode enters causal time, presumed by the mechanism rather than added to it. Its rate can be dialled: the Valves. ACT’s framing
- Decoherence exponent $\Phi_A$
- The noise-kernel term of the influence functional, $|\mathcal F|=e^{-\Phi_A}$. Nonnegative always; unbounded in a Markov bath with persistent separation. Derived
- Fluctuation–dissipation
- The relation tying the bath’s noise to its damping. One spectral density fixes both, so decoherence cannot be dialled without dialling the dissipation. established physics
- Detector/observer effect
- Detectors and observers anchor events because they are coupled to the bath, not because they observe. A detector is a device built to couple a signal into a continuum, with amplification; a rock will do (the Rock). Established
- The Legendre point
- Where the passage from the Lagrangian (structure, no privileged time) to the Hamiltonian (states in time) picks out a time. The bath sits there: with a bath the passage is forced and directed. ACT’s framing
When a record becomes a fact
- Record
- A state of environmental degrees of freedom correlated with the system’s pointer observable. A record that can still be read back coherently is not yet a fact. definition
- Record architecture
- The accessible algebra of the detector together with the carriers it releases. An instrument is supported by the records when its outcomes are classical functions of released records. definition
- Recoverable phase distinguishability $\Phi_{\rm irr}$
- Paper I’s measure of irreversibility: how well the relative phase of two alternatives can still be told apart through the accessible algebra, $\Phi_{\rm irr}=-\ln[\mathcal D(t)/\mathcal D(0)]$. It cannot be inflated by operations on the system alone. Definition
- Accessible algebra $\mathcal A_{\rm acc}$
- The observables the apparatus can physically act on or read, fixed by detector architecture, causal locality and the environmental partition. Quantum-trajectory theory needs the same specification. Position
- Release
- A record is released when it commutes with every observable in the system’s accessible future, including through any return path. Nothing the system can do afterwards recombines the phase it carried away. Release completes a mode’s entry into causal time. The experiments that fix this boundary, and the earlier event rules they rule out, are set out on the Evidence page, under Where the event can sit. Definition
- Released record
- A record that has been released; the carrier of actuality. For a free output field every record is released as it forms. Theorem in class
- Readability
- How well a record can be read from an environment fragment. It can fall after release, through scrambling, without un-anchoring anything: release is what actuality needs; readability is what objectivity needs. Paper II
- Record algebra
- The algebra generated by the released records. It is commutative, and its points (the characters of the commutative algebra) are the possible record histories. Which algebra a detector has is set by the coupling: an apparatus picks out components of the wave, never the outcome, and a Stern–Gerlach magnet sorts along its own axis (the Filter). Theorem in class
- Exclusivity
- One alternative per event. A stated commitment in Paper I; a theorem in the record-algebra class of Paper II. Theorem in class
- CP-divisibility
- The property of the accessible dynamics under which $\Phi_{\rm irr}$ cannot decrease. The event law is stated in that scope; where it fails, phase is returning and no hazard is defined. Scope condition
When, what, which
- The event law
- Three answers in the bath’s own terms: when an event can occur (release, at a rate set by irreversible record production), what can be registered (the alternatives the record architecture supports), and which occurs (Born weights). Theorem in class
- Instrument
- The family of completely positive maps the records support, one per outcome. In general the event law is the path measure of the instrument. established physics; selected by the record architecture
- Event intensity $\lambda_r$
- For counting records, $\lambda_r=\mathrm{Tr}[L_r^\dagger L_r\rho_c]$, built from the bath’s own jump operators. For an atom emitting into open space, $\gamma\langle e|\rho_c|e\rangle$. Theorem in class
- Hazard $h=\dot\Phi_{\rm irr}$
- The event rate in the quantum-nondemolition case, where $L_\pm=\sqrt\Lambda P_\pm$ and the evolution before the event is outcome-neutral. The survival probability is $S=e^{-\Phi_{\rm irr}}$. Derived (QND)
- Stopped process
- $\rho_S(t)=S\,\rho^{\rm coh}+(1-S)\sum_kP_k\rho(0)P_k$: the ensemble of runs not yet anchored and runs anchored reproduces the reduced dephasing exactly. Decoherence is anchoring seen in the ensemble. Derived (QND)
- Outcome-neutrality
- The hypothesis that waiting for the first event does not bias the alternatives. With ensemble agreement it forces the Born weights in the nondemolition model. hypothesis of Prop. 2
- Born weights, forced
- $p_k=\mathrm{Tr}[P_k\rho]$. Forced by the one-wave law, one history, support certainty for joint records, no signalling for every division into here and elsewhere, refinable records and continuity, by Zurek’s argument in Barnum’s form (the flagship, Appendix A; the proof in full in Paper II, Appendix A). The martingale descent of the conditioned weights is the consistency check with the master equation. Forced
- Selection theorem
- In a fast-record probe model, fragment records support only classical post-processings of the localization instrument, and no coherent momentum-kick instrument. It identifies which unraveling the records support; which is actual then follows from the one-history postulate. Its role is ontological, not empirical. Conditional theorem
- Unraveling
- A stochastic-trajectory representation of a master equation. Many reproduce the same ensemble; the record architecture fixes which one is physical where the selection theorem applies, and the apparatus-free case is open. established physics
- Outcome dependence
- The outcome at one end of an entangled pair depends on the record at the other: the other end anchors from what is left of the one structure. ACT’s nonlocality is this and nothing more. Stated
- Parameter independence
- No outcome depends on how the distant detector was set; why the correlations carry no signal. established physics (no-signalling)
Objects on the formal spine
- Lagrangian, action
- One action over whole field histories, with no privileged time. Structure. established physics
- Hamiltonian
- States at a time, evolving forward. For an open mode the generator is a semigroup with no physical inverse. established physics
- Closed time path, influence functional
- The Schwinger–Keldysh doubling of histories and the Feynman–Vernon result of integrating out a Gaussian bath: a retarded dissipation kernel (causal order) and a noise kernel (decoherence), tied by fluctuation–dissipation. established physics
- Lindblad form
- The Markov generator of an open system’s reduced dynamics. Its jump operators $L_r$ are the bath’s own and build the event law. established physics
- Conditioned state $\rho_c$
- The state given the record so far: the quantum filter, which reproduces the unconditioned dynamics in the ensemble. established physics
- Collision model
- A system meeting fresh environment slices one at a time; the setting in which Paper II’s theorems are proved and every number checked. established physics
- Fewster–Verch instruments
- Measurement schemes for quantum fields in compact spacetime regions, with causal factorization: records in causally disjoint regions commute and need no order. The route to a covariant record history. established physics; covariant release open
How claims are held
- Option B
- ACT’s stance: global unitary dynamics are never modified; anchoring adds a determination. Not a collapse model. Commitment
- Corroborated, not singled out
- ACT’s standing with experiment: its mechanism measured, its event boundary fixed, its placement never refuted, and no experiment able to single it out from the other interpretations that keep unitary quantum mechanics (Evidence). Stated
- The four thought experiments
- The Evidence page’s argument in four performed pictures: the Rock (a lossy slab that nothing reads still kills the fringes: a bath, not an observer, keeps the record), the Valves (the rate at which the fringes fade can be dialled), the Filter (an apparatus picks components out of one wave, as a radio picks a station out of the air, and no event occurs until a record is released) and the Mark (single marks build a wave’s fringes when no record of the path was kept, and a particle pattern when one was). evidence
- Interpretive layer
- Three readings on which no proof depends: not yet in time; superposition as the composition of one wave; mass as the field’s clock. The proofs hold without them; the picture of what exists is built on them. Interpretive
- Open
- Five problems, listed with what would close each: covariant release, selection without an apparatus, non-Markovian release, the energy ledger of a single event, and the alignment conjecture. Open