Recent experiments in quantum optics have demonstrated that interference patterns can arise even when the alternative paths of a photon or particle do not overlap in space or time. Such ``disjoint interference'' setups---including time-separated double slits, delayed-choice interferometers, and cross-arm quantum erasers---confirm that coherent outcomes persist without any physical contact or simultaneous existence of alternatives. From the standard quantum mechanical view, the phenomenon is attributed to the superposition of probability amplitudes in Hilbert space. Yet the absence of spatial or temporal overlap forces a deeper question: how can distinct events interfere when no exchange of energy or information occurs in spacetime? \subsection{TGIU Interpretation: Informational Resonance without Contact} Within the Universal Gravito--Informational Theory (TGIU), interference arises not from wave overlap, but from \textit{informational resonance} between coherent structures in the $(\Phi, S, \Theta_C)$ manifold---the real informational space where coherence ($\Phi$) and entropy ($S$) evolve under the TGIU Equilibrium Force (TEF). Two physically disjoint configurations can still share the same informational curvature state $\Theta_C$ and thus remain coupled through the global TEF field. When their coherence vectors align within the same equilibrium regime, interference emerges as a geometric consequence of phase alignment in informational space: \begin{equation} \Delta\Phi_C \to 0, \qquad \mathrm{TEF}_1 \approx \mathrm{TEF}_2 \quad \Rightarrow \quad \text{interference pattern in } (\Phi,S). \end{equation}
Recent experiments in quantum optics have demonstrated that interference patterns can arise even when the alternative paths of a photon or particle do not overlap in space or time. Such ``disjoint interference'' setups---including time-separated double slits, delayed-choice interferometers, and cross-arm quantum erasers---confirm that coherent outcomes persist without any physical contact or simultaneous existence of alternatives. From the standard quantum mechanical view, the phenomenon is attributed to the superposition of probability amplitudes in Hilbert space. Yet the absence of spatial or temporal overlap forces a deeper question: how can distinct events interfere when no exchange of energy or information occurs in spacetime? \subsection{TGIU Interpretation: Informational Resonance without Contact} Within the Universal Gravito--Informational Theory (TGIU), interference arises not from wave overlap, but from \textit{informational resonance} between coherent structures in the (Φ,S,ΘC) manifold---the real informational space where coherence (Φ) and entropy (S) evolve under the TGIU Equilibrium Force (TEF). Two physically disjoint configurations can still share the same informational curvature state ΘC and thus remain coupled through the global TEF field. When their coherence vectors align within the same equilibrium regime, interference emerges as a geometric consequence of phase alignment in informational space: \begin{equation} \Delta\Phi_C \to 0, \qquad \mathrm{TEF}_1 \approx \mathrm{TEF}_2 \quad \Rightarrow \quad \text{interference pattern in } (\Phi,S). \end{equation}
Introduction In recent years, numerous quantum optics experiments have demonstrated novel quantum effects based on quantum amplitude superposition. Some of these empirical observations raise disturbing questions about the nature of reality, particularly concerning quantum nonlocality. In this chapter we discuss some experiments that suggest (to us, at least) that the information void, that uncharted regime between signal preparation and outcome detection, is not well modeled by classical spacetime. Something strange seems to be lurking there. For the purposes of exposition, the sequence of experiments we discuss in this chapter does not follow the historical sequence of those experiments, We discuss first the delayed-choice quantum eraser experiment of Kim et al. (Kim et al., 2000), referred to here as KIM. This leads us to define a heuristic measure of which-path information that is central to the theme of this chapter. This leads to a discussion of Wheeler's thought experiments on the conundrum of delayed choice in physics, particularly evident in the phenomenon of galactic lensing (Wheeler, 1983), and its empirical implementation, the delayed-choice interferometer experiment of Jacques et al., referred to as JACQUES. Our final experiment in this sequence is the double-slit quantum eraser of Walborn et al. (Walborn et al., 2002), referred to as WALBORN. That experiment gives a significant challenge for quantized detector networks (QDN) to reproduce its empirical results. Such experiments have led to suggestions that interference patterns formed by particles impacting on a screen may be influenced in some way by decisions made long after those particles had landed on that screen. Our objective in this chapter is to show by a detailed QDN analysis of those experiments that quantum principles do not support these suggestions. Nevertheless, something bizarre seems to be there. There are two complementary aspects in these experiments that have deeply worried physicists. The first involves spatial nonlocality and is the point of Wheeler's concerns. Historically, it has been a great source of debate among physicists.
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.
Abstract Wave–particle duality is a counterintuitive nature of quantum physics that challenges many common-sense assumptions, and Young’s double-slit interference is a prototypical example. While most quantum erasure experiments emphasized the choice of erasing or marking the which-path information of one quantum system, we use frequency entanglement to report a nonlocal temporal double-slit interferometer such that the which-time information determines the wave-like or particle-like behaviors. Since frequency-entangled photons are created simultaneously by using spontaneous parametric down conversion, the mark of temporal distinguishability is readily prepared by delaying one of the entangled photons, and its quantum eraser is implemented by using spectrally resolved detection with a tunable delayed choice. These results may provide an alternative aspect and insight into the role of the temporal degree in quantum-light complementarity and photon interference.
3.1 Interference of a Single Photon The kinds of study originally conducted by Thomas Young - in particular, the celebrated "double slit" experiment that we briefly examined in Chapter 1 (see Fig. 1) - provide a capacity to reveal far more than the wave nature of light, important as that is. True enough, the observed characteristic fringe pattern, when monochromatic light passes through two closely spaced slits onto a screen, appears to be simply explicable on the basis of waves from each slit undergoing constructive and destructive interference at different positions on the screen. Yet, astonishingly, these patterns of interference are still exhibited when individual photons of a low-intensity input beam reach the screen one at a time, showing that it cannot in fact be a matter of different photons having to interfere with each other. Indeed, Dirac enunciated the general principle that photons can never directly interact with each other. The double slit and other such experiments indicate that each photon interacts in a delocalized, wave-like manner with both slits at the same time. Successive experiments build interference patterns that conform to an exact mathematical distribution formula, but the position at which an individual photon is detected in any particular instance cannot be predicted; this is a quintessential illustration of quantum uncertainty. Using the path integral approach of quantum theory, the phenomenon is more accurately represented by introducing a summation over all possible routes between the source and the screen on which the pattern appears, signifying an entire "lifetime" for each photon involved in the experiment. This relates to the fact that the actual trajectory is unknown without an observation, and thus we only obtain the probabilities of the photon striking the screen at different positions and times; all trajectories (potentialities) must be considered in a superposition. Each route is considered equally probable, and the variation in phase produces quantum interference. The differences in phase of each trajectory, at varying positions on the screen, generates the fringe pattern. An intriguing variation on this experiment involves "marking" the photons so that the actual route of each photon to the screen is known. Remarkably, in such a case, the fringe patterns do not appear because quantum interference cannot occur. A consequence of the observation of the photon route is an effect that, in other quantum mechanical connections, is known as a collapse of the wavefunction. However, it is possible for the fringe patterns to reappear when information on the route of the photons is lost; this is known as a quantum eraser.
The particle-interference-experiments, with the photons and electrons have clearly shown that they are always detected as localized ‘particles’; and the density of their detections exhibit a pattern similar to the interference of waves. This experimental-observation is alternatively interpreted here, different from the current, ‘probabilistic interpretation’. The ‘particle’ is first mathematically characterized as an ‘impulse function’ in space; and then Fourier-transformed into the wave-number-domain, as a wide band of constituent-waves as shown in the fig. 1&2. The ‘particle’ is an ‘event’ of constructive-superimposition of a wide band of ‘pre-quantum-waves’. This ‘event’ occurs in space at regular distances; and at regular instances in time. In the particle-interference-experiments, they are the wide band of ‘pre-quantum-waves which interfere physically. This physical interference of the pre-quantum-waves determines the position and time of emergence of the ‘impulse in space’ detectable as the ‘particle’. In the real-world-situation, the ‘pre-quantum-waves of a wide bandwidth arrive from all the directions, so the amplitude and phase of every constituent wave keep changing; so the place of constructive superimposition of all the spectral-components, keep varying unpredictably; and only the ‘probability’ of detection in a given volume is possible in practice. Thus, form the theoretical view-point, there are only the pre-quantum-waves; and ‘particle’ is a specific situation of constructive-superimposition of all the spectral-components of pre-quantum-waves; so there is no wave-particle-duality. The ‘probabilistic-interpretation’ is only a ‘practical-limitation’, detector being able to detect only the ‘particle’, and not the spectrum of constituent waves.
This work addresses the long-standing claim that interference phenomena—most notably in double-slit–type experiments—cannot be physically modeled without invoking wave propagation or particles following multiple trajectories. We show that this claim rests on an implicit restriction to local, dynamical descriptions acting between emission and detection. We introduce a minimal framework in which detection events are treated as discrete realizations occurring at an absorbing boundary, while the observed interference pattern arises from global structural admissibility constraints of the full experimental configuration. The model does not attempt to generate or predict individual detection events. Instead, it characterizes the statistical distribution of outcomes as a property of realization closure rather than of local evolution in transit. Within this approach, interference patterns are understood as emergent statistical signatures of global realization structure, not as evidence of propagating waves, hidden variables, or oscillatory dynamics in space. The framework preserves all empirical features of standard interference experiments while avoiding assumptions about intermediate physical processes that are neither observed nor required by theory. This work is consistent with relativistic and quantum no-go results concerning photon trajectories, localization, and in-flight observables. It complements earlier structural interpretations of light and realization by providing a concrete, physically explicit model demonstrating how stable interference statistics arise without propagation. The contribution clarifies the precise sense in which interference is modelable, and the sense in which it is not: individual events remain intrinsically unpredictable, while their global organization is physically intelligible at the level of realization structure. The model introduces no new forces, fields, or modifications of established equations, and is intended as a refinement of conceptual foundations rather than a replacement of existing formalisms.