We recover the effective topology of spacetime using the notion of record from the decoherent histories approach to Quantum Theory. From a series of (gedanken) experiments, we obtain the set of possible events, grouped into sub-sets that corresponds to histories, but with no other information such as (causal) order or any notion of proximity. This corresponds to tomography of the "effective" spacetime, that is done in an operational way. Making certain assumptions about these records, and using the existence of upper bound in the speed of transfer of matter and information, we recover the full partial (causal) order up to certain ambiguities. The partially ordered set of events corresponds to an "effective" causal set which is a discretized version of spacetime with the causal relation as defining feature. We conclude with a derivation of the topology of this effective discretized spacetime.
We recover the effective topology of spacetime using the notion of record from the decoherent histories approach to Quantum Theory. From a series of (gedanken) experiments, we obtain the set of possible events, grouped into sub-sets that corresponds to histories, but with no other information such as (causal) order or any notion of proximity. This corresponds to tomography of the "effective" spacetime, that is done in an operational way. Making certain assumptions about these records, and using the existence of upper bound in the speed of transfer of matter and information, we recover the full partial (causal) order up to certain ambiguities. The partially ordered set of events corresponds to an "effective" causal set which is a discretized version of spacetime with the causal relation as defining feature. We conclude with a derivation of the topology of this effective discretized spacetime.
The tomographic histories approach is presented. As an inverse problem, we recover in an operational way the effective topology of the extended configuration space of a system. This means that from a series of experiments we get a set of points corresponding to events. The difference between effective and actual topology is drawn. We deduce the topology of the extended configuration space of a ‘classical ’ (i.e. non-relativistic) system, using certain concepts from the consistent histories approach to Quantum Mechanics, such as the notion of a record. A few remarks about the case of a relativistic system, preparing the ground for a forthcoming paper sequel to this, are made in the end. 1 Introduction with Motivational Remarks In the standard formulation of relativity theory, the spacetime topology is a priori fixed by the theorist to that of a continuous manifold; hence, it is not an observable entity. Only the metric structure is traditionally supposed to be dynamically variable. With the exception of Wheeler’s celebrated, but largely heuristic, spacetime foam scenario
We provide a precise definition and analysis of quantum causal histories (QCHs). A QCH consists of a discrete, locally finite, causal pre-spacetime with matrix algebras encoding the quantum structure at each event. The evolution of quantum states and observables is described by completely positive maps between the algebras at causally related events. We show that this local description of evolution is sufficient and that unitary evolution can be recovered wherever it should actually be expected. This formalism may describe a quantum cosmology without an assumption of global hyperbolicity; it is thus more general than the Wheeler–De Witt approach. The structure of a QCH is also closely related to quantum information theory and algebraic quantum field theory on a causal set.
General relativity (GR) is naturally organized around spacetime events and their causal order, whereas quantum field theory (QFT) is formulated in terms of states, operators, and unitary evolution, without an intrinsic criterion for when a quantum process becomes a definite spacetime fact. We propose an event-centered framework in which events are locally irreversible records generated by quantum-environment interactions and serve as an interface between quantum dynamics and relativistic spacetime structure. Event anchoring is characterized operationally by three jointly sufficient conditions: local classicalization, redundant environmental recording, and irreversibility against recovery. Their joint satisfaction defines local generative freezing. We realize these criteria in an explicit repeated-collision open-system model. The model is illustrative rather than a derivation from relativistic QFT, but it remains globally unitary and yields the freezing time in closed form. For all admissible tolerances, local classicalization is certified no later than channel-level irrecoverability, and generically earlier. Full anchoring occurs only when both irrecoverability and the required record redundancy have been reached, producing irrecoverability-limited and redundancy-limited regimes. At the level of anchored records, physical history is therefore represented as a partially ordered causal skeleton of frozen events on which effective field-theoretic descriptions operate. The framework addresses event anchoring--when a candidate outcome becomes a stable spacetime fact--while remaining compatible with standard QFT and relativistic causality. It does not derive the Born rule or solve single-outcome selection, which belong to the separate problem of event generation.
We provide a unified operational framework for the study of causality, non-locality and contextuality, in a fully device-independent and theory-independent setting. Our work has its roots in the sheaf-theoretic framework for contextuality by Abramsky and Brandenburger, which it extends to include arbitrary causal orders (be they definite, dynamical or indefinite). We define a notion of causal function for arbitrary spaces of input histories, and we show that the explicit imposition of causal constraints on joint outputs is equivalent to the free assignment of local outputs to the tip events of input histories. We prove factorisation results for causal functions over parallel, sequential, and conditional sequential compositions of the underlying spaces. We prove that causality is equivalent to continuity with respect to the lowerset topology on the underlying spaces, and we show that partial causal functions defined on open sub-spaces can be bundled into a presheaf. In a striking departure from the Abramsky-Brandenburger setting, however, we show that causal functions fail, under certain circumstances, to form a sheaf. We define empirical models as compatible families in the presheaf of probability distributions on causal functions, for arbitrary open covers of the underlying space of input histories. We show the existence of causally-induced contextuality, a phenomenon arising when the causal constraints themselves become context-dependent, and we prove a no-go result for non-locality on total orders, both static and dynamical.
The Causal Set hypothesis for Quantum Gravity asserts that the smooth Lorentzian spacetime manifold of General Relativity is only an approximation to a fundamental microscopic discrete structure: a locally-finite partially-ordered set. The points of this set are akin to the point-events of the spacetime manifold, and the order-relations among these points are akin to the causal-relations among these point-events. The local-finiteness condition implies a fundamental discreteness and provides an important [conformal] factor needed for the continuum approximations. In this dissertation, we address two aspects toward the formulation of a quantum dynamics for causal sets. The first aspect concerns the dynamics of a zero-mass classical scalar field on a background causal set, Poisson-sampled from an Alexandrov interval in (1 + 1)-dimensional Minkowski spacetime. Our numerical simulations suggest that actions can be defined for such a scalar field, expressed solely in terms of the causal set and the scalar field, which approximates the corresponding classical action on the continuum Minkowski spacetime. This result may help us describe matter and gauge fields in a local and Lorentz-invariant way on a causal set, a discrete structure now being considered as the arena for spacetime physics. More importantly, it may help us formulate an action for the causal set itself, which would be used in a sum-over-histories approach to describe the quantum dynamics of causal sets. The second aspect concerns Quantum Measure Theory, a new approach to quantum dynamics inspired by the sum-over-histories approach, which is better suited to formulating the dynamics of causal sets and of other alternative structures for spacetime. To better understand the mathematical structure underlying this new approach, we derive some algebraic identities involving the sum-rules of the Quantum Measure and its generalizations. We conclude with a discussion on possible applications and open problems concerning these aspects.
This paper presents SCAR, short for Space-Time Causal Associative Record, as a speculative hypothesis for a discrete causal-information substrate of spacetime. The central proposal is that a qualifying entanglement-producing direct causal interaction writes a persistent relational record, called a SCAR, into an underlying causal structure. We define a finite covariant history space whose physical elements are unlabeled isomorphism classes of causal orders decorated by local quantum-process classes and SCAR records. Each SCAR contains a relational record label, a local-unitary-invariant persistence sector, and a bounded magnitude determined by entanglement. A label-invariant statistical history ensemble is proposed, with a minimal action that couples causal-link structure to the concentration of SCAR magnitude. The framework is explicitly presented as a finite toy model and hypothesis rather than an established theory of physics. It does not derive the Born rule, Lorentz symmetry, an effective spacetime metric, general relativity, quantum field theory, or an empirical prediction for the observed universe. Its immediate purpose is to formulate a falsifiable research program in which covariance, quantum consistency, continuum emergence, and phenomenology can be tested progressively.