Unifying quantum theory with general relativity is challenging because of several problems related to time and to collapse in quantum measurements. In the double-slit experiment, the questions are how the momentum of the photon is transferred to a specific location on the screen and how the double slit recoils accordingly. This work investigates if these problems can be solved by adding a second time τ, which acts as an external evolution parameter, to standard four-dimensional spacetime. Within the resulting 4+1 formalism, a model for the single-photon double-slit experiment is developed. On the one hand, each spacetime associated to a value of τ relies on classical worldlines that obey local momentum conservation. On the other hand, these worldlines are allowed to readjust as a function of τ such that the quantum phenomenon of double-slit interference can be reproduced. The model explains how determinate outcomes are produced and how momentum transfer occurs in a way that satisfies the principles of relativity and local momentum conservation. As a result, the measurement problem and the problem of time evaporate, and an explanation for our experience of the present emerges. Since the presented model succeeds in explaining a key quantum phenomenon with essentially classical worldlines, this is relevant for the field of quantum gravity.
Unifying quantum theory with general relativity is challenging because of several problems related to time and to collapse in quantum measurements. In the double-slit experiment, the questions are how the momentum of the photon is transferred to a specific location on the screen and how the double slit recoils accordingly. This work investigates if these problems can be solved by adding a second time τ, which acts as an external evolution parameter, to standard four-dimensional spacetime. Within the resulting 4+1 formalism, a model for the single-photon double-slit experiment is developed. On the one hand, each spacetime associated to a value of τ relies on classical worldlines that obey local momentum conservation. On the other hand, these worldlines are allowed to readjust as a function of τ such that the quantum phenomenon of double-slit interference can be reproduced. The model explains how determinate outcomes are produced and how momentum transfer occurs in a way that satisfies the principles of relativity and local momentum conservation. As a result, the measurement problem and the problem of time evaporate, and an explanation for our experience of the present emerges. Since the presented model succeeds in explaining a key quantum phenomenon with essentially classical worldlines, this is relevant for the field of quantum gravity.
The field of quantum gravity struggles with several problems related to time, quantum measurement, nonlocality, and realism. To address these issues, this study develops a 4+1 formalism featuring a flat 4D spacetime evolving with a second form of time, τ, worldlines that locally conserve momentum, and a hypersurface representing the present. As a function of τ, worldlines can spatially readjust and influences can travel backward or forward in the time dimension along these worldlines, offering a physical mechanism for retrocausality. Three theoretical models are presented, elucidating how nonlocality in an EPR experiment, the arrival time problem, and superposition in a Mach-Zehnder interferometer can be understood within this 4+1 framework. These results demonstrate that essential quantum phenomena can be reproduced in the 4+1 formalism while upholding the principles of realism, locality, and determinism at a fundamental level. Additionally, there is no measurement or collapse problem, and a natural explanation for the quantum-to-classical transition is obtained. Furthermore, observations of a 4D block universe and of the flow of time can be simultaneously understood. With these properties, the presented 4+1 formalism lays an interesting foundation for a quantum gravity theory based on intuitive principles and compatible with our observation of time.
Conventional approaches to quantum gravity regard quantum principles, such as nonlocality and superposition, as fundamental properties of nature and therefore argue that gravity must also be quantized. In contrast, this work introduces a theory of crystallizing spacetime, which offers an alternative perspective: that both gravitational and quantum mechanical observations can be explained within a fundamentally classical framework operating beyond traditional spacetime. The theory proposes a spacetime relaxation mechanism wherein a dynamically evolving four-dimensional spacetime, populated by dynamic worldlines, relaxes as a function of the parameter τ into a standard spacetime consistent with general relativity. Simulations in the weak-gravity limit illustrate this process of spacetime and worldline relaxation. Additionally, models are developed showing that two hallmark quantum phenomena -- nonlocality in an EPR experiment and double-slit interference of a massive particle -- can be reproduced in this fundamentally classical framework by implementing Costa de Beauregard's concept of zigzag action along worldlines. The resulting crystallizing spacetime framework not only resolves the measurement problem but also provides a compelling basis for a unified theory of matter and gravity. Since this framework is grounded in concepts analogous to realism, locality, and determinism at its foundations, it brings Einstein's long-sought intuitive worldview within reach.
The double-slit experiment strikingly demonstrates the wave-particle duality of quantum objects. In this famous experiment, particles pass one-by-one through a pair of slits and are detected on a distant screen. A distinct wave-like pattern emerges after many discrete particle impacts as if each particle is passing through both slits and interfering with itself. Here we present a temporally- and spatially-resolved measurement of the double-slit interference pattern using single photons. We send single photons through a birefringent double-slit apparatus and use a linear array of single-photon detectors to observe the developing interference pattern. The analysis of the buildup allows us to compare quantum mechanics and the corpuscular model, which aims to explain the mystery of single-particle interference. Finally, we send one photon from an entangled pair through our double-slit setup and show the dependence of the resulting interference pattern on the twin photon's measured state. Our results provide new insight into the dynamics of the buildup process in the double-slit experiment, and can be used as a valuable resource in quantum information applications.
This article presents a conceptual interpretation of the double-slit experiment using Feynman's path integral formulation. Rather than treating a quantum particle as a point-like object following a single trajectory, the particle's propagation is viewed as a distributed structure in 4D spacetime. In the path-integral picture, this structure is represented by a coherent sum over possible paths between emission and detection. From this perspective, the observed interference pattern emerges from the phase relationships between these possible spacetime paths. The article distinguishes between propagation and interaction. Propagation is described as an extended 4D process, while measurement appears as a localized spacetime event within a 3D spatial slice, producing the point-like detections observed in the double-slit experiment. The aim is not to propose a new physical theory or to explain the mechanism of collapse, but to provide an intuitive geometric interpretation of the standard quantum formalism and its relationship between quantum propagation, interference, and localized measurement outcomes. This is a conceptual essay and interpretive synthesis, not a proposal of a new physical theory.
This work presents a unified, interpretive account of quantum interference and delayed-choice experiments that applies equally to photons and massive particles. Rather than invoking spacetime trajectories, wave–particle duality, retrocausality, or collapse postulates, the paper locates quantum interference in the coherent evolution of internal, pre-geometric degrees of freedom defined over classical spacetime. Within this framework, “which-path” questions are not merely unanswered but fundamentally ill-posed: interference arises from global coherence of an internal field subject to experimental boundary conditions, while spacetime itself remains single-valued and classical at laboratory scales. The approach reproduces all standard quantum-mechanical predictions without modification and is explicitly interpretive rather than predictive. A central result is a unified explanation of why interference occurs across disparate physical systems—photons, electrons, atoms, and molecules—while decoherence manifests through system-dependent physical mechanisms. Photons and massive particles differ in how internal coherence is lost (e.g., electromagnetic absorption versus collisional and thermal interactions), but not in the underlying principle. Delayed-choice experiments are reinterpreted without paradox: changes to the apparatus modify boundary conditions for the internal field rather than retroactively altering particle histories. By removing spacetime paths from the fundamental ontology, the framework offers a consistent, path-free account of interference, decoherence, and localized detection that preserves the empirical success of quantum mechanics while clarifying its conceptual foundations.
The double slit experiment (DSE) is known as an important cornerstone in the foundations of physical theories such as Quantum Mechanics and Special Relativity. A large number of different variants of it were designed and performed over the years. We perform and discuss here a new verion with the somewhat unexpected results of obtaining interference pattern from single-slit screen. This outcome, which shows that the routes of the photons through the array were changed, leads one to discuss it, using the equivalence principle, in terms of geodesics mechanics. We show using either the Brill's version of the canonical formulation of general relativity or the linearized version of it that one may find corresponding and analogous situations in the framework of general relativity.