Young’s double-slit experiment was first demonstrated with light and was later extended to electrons and other particles. These experiments share a common geometry: something approaches the slits, passes through them, and produces an interference pattern afterward. However, monochromatic water waves, electrons, and photons are physically different, and their interactions with a real slit need not be the same. Most discussions of the double-slit experiment focus on the interference pattern collected on a screen after the slits. Some descriptions also consider what happens before the slits, including the role of an eraser or observer and the splitting of an electron or photon to interfere with itself. Much less attention is given to what happens while an electron or photon is passing through a real slit. A real slit has thickness and is made of matter. Its surfaces contain atoms, electrons, and nuclei and therefore provide an electromagnetic environment through which an electron or photon passes. An electron or photon enters the slit, travels between its surfaces, and leaves it. This raises a missing question: can an electron or photon interact with this electromagnetic environment while passing through the slit, and can such an interaction affect its motion, particularly its exiting direction? We examine experimental evidence together with geometrical and accumulated-count evidence, including the observed spacing of interference maxima, the nonlinear geometry of constant-path-difference loci, the finite number and different possible counts of interference fringes, and the accumulation of individual detection events. Figures derived from the corresponding experimental and geometrical constructions are used to make these distinctions explicit. These results motivate a global description of Young’s double-slit experiment in three physically connected regions: pre-slit, in-slit, and post-slit. We call this the global trilogy of Young’s double-slit experiment. The global trilogy places the physical slit and its electromagnetic environment explicitly between the familiar pre-slit and post-slit descriptions and provides a framework for investigating the complete process from source, through the slit, to interference and detection.
Young’s double-slit experiment was first demonstrated with light and was later extended to electrons and other particles. These experiments share a common geometry: something approaches the slits, passes through them, and produces an interference pattern afterward. However, monochromatic water waves, electrons, and photons are physically different, and their interactions with a real slit need not be the same. Most discussions of the double-slit experiment focus on the interference pattern collected on a screen after the slits. Some descriptions also consider what happens before the slits, including the role of an eraser or observer and the splitting of an electron or photon to interfere with itself. Much less attention is given to what happens while an electron or photon is passing through a real slit. A real slit has thickness and is made of matter. Its surfaces contain atoms, electrons, and nuclei and therefore provide an electromagnetic environment through which an electron or photon passes. An electron or photon enters the slit, travels between its surfaces, and leaves it. This raises a missing question: can an electron or photon interact with this electromagnetic environment while passing through the slit, and can such an interaction affect its motion, particularly its exiting direction? We examine experimental evidence together with geometrical and accumulated-count evidence, including the observed spacing of interference maxima, the nonlinear geometry of constant-path-difference loci, the finite number and different possible counts of interference fringes, and the accumulation of individual detection events. Figures derived from the corresponding experimental and geometrical constructions are used to make these distinctions explicit. These results motivate a global description of Young’s double-slit experiment in three physically connected regions: pre-slit, in-slit, and post-slit. We call this the global trilogy of Young’s double-slit experiment. The global trilogy places the physical slit and its electromagnetic environment explicitly between the familiar pre-slit and post-slit descriptions and provides a framework for investigating the complete process from source, through the slit, to interference and detection.
This work presents a structural reexamination of Young’s double-slit experiment by identifying a missing stage in its standard formulation and restoring it within a finite, geometry-based framework. The conventional treatment assumes continuous propagation, neutral boundaries, and observation on a single fixed screen, reducing the experiment to a geometric division of a continuous entity. Using exact geometry, interference is described by the condition , which defines a family of hyperbolas in space. From the triangle inequality, the number of interference fringes for monochromatic light is shown to be finite and exactly determined. The commonly observed linear fringe pattern arises from the far-field approximation and represents only a partial cross-section of this global structure. A central result of this work is the identification of the in-slit stage as a necessary part of the experiment. The slit is treated as a finite region in which particles interact with boundary-defined electromagnetic environments, leading to directional redistribution prior to propagation. This interpretation is supported by an asymmetric single-slit experiment using different materials, which produces a reversible asymmetric pattern inconsistent with a purely geometric model. The framework is extended to limiting and classical cases, including tiny apertures and diffraction phenomena such as the Poisson spot, where symmetry and lack of comparison may conceal boundary-dependent effects. The suppression of interference in which-way detection experiments is interpreted as a modification of the electromagnetic environment within the slit. These results show that interference in Young’s experiment is a finite, spatial, and timing phenomenon that cannot be fully described by post-slit geometry alone. Restoring the in-slit interaction provides a complete factual description and introduces material-dependent effects absent from standard treatments.
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.
Young’s double slit experiments have been descripted by wave theories, i.e., before and after passing a double slit, the light is waves. Now, we extend the double slit experiments to the comprehensive double slit experiments by utilizing Shield (showing the light is not wave), Metal tube (showing the light is not EM waves), Blocker (showing the light is particles), combination of Shield and Blocker (showing the light is particles), Photon-Chamber (showing the light is particles which produce both non-interference patterns and interference patterns), and Lens (showing the light is particles which produce non-wave and wave patterns). We propose two Postulates: “Postulate on light: light is photons before and after passing through double slit” and “Postulate on lens: light behaves same before and after passing through lens”. Then, we show the novel phenomena of the comprehensive double slit experiments: (1) the light is photons before and after passing through a double slit; (2) photons form both the non-interference patterns and the interference patterns; (3) the non-interference patterns gradually evolve to the interference patterns in the same experiment. We refer to the novel phenomena as “PhotoWave phenomena” that are universal. The comprehensive double slit experiments provide the novel phenomena for developing theoretical model further to study: (1) the nature of the light; (2) the Feynman’s mystery of the double slit; (3) the wave-particle duality; and (4) the wave theories of the light; (5) applications. A complete description should explain all the comprehensive double slit experiments consistently.
Young’s double slit experiments have been descripted by wave theories, i.e., before and after passing a double slit, the light is waves. Now, we extend the double slit experiments to the comprehensive double slit experiments by utilizing Shield (showing the light is not wave), Metal tube (showing the light is not EM wves), Blocker (showing the light is particles), combination of Shield and Blocker (showing the light is particles), Photon-Chamber (showing the light is particles which produce both non-interference patterns and interference patterns), and Lens (showing the light is particles which produce non-wave and wave patterns). We propose two Postulates: “Postulate on light: light is photons before and after passing through double slit” and “Postulate on lens: light behaves same before and after passing through lens”. Then, we show the novel phenomena of the comprehensive double slit experiments: (1) the light is photons before and after passing through a double slit; (2) photons form both the non-interference patterns and the interference patterns; (3) the non-interference patterns gradually evolve to the interference patterns in the same experiment. We refer to the novel phenomena as “PhotoWave phenomena” that are universal. The comprehensive double slit experiments provide the novel phenomena for developing theoretical model further to study: (1) the nature of the light; (2) the Feynman’s mystery of the double slit; (3) the wave-particle duality; and (4) the wave theories of the light; (5) applications. A complete description should explain all the comprehensive double slit experiments consistently.
Young’s double slit experiments have been descripted by wave theories, i.e., before and after passing a double slit, the light is waves. Now, we extend the double slit experiments to the comprehensive double slit experiments by utilizing Shield (showing the light is not wave), Metal tube (showing the light is not EM wves), Blocker (showing the light is particles), combination of Shield and Blocker (showing the light is particles), Photon-Chamber (showing the light is particles which produce both non-interference patterns and interference patterns), and Lens (showing the light is particles which produce non-wave and wave patterns). We propose two Postulates: “Postulate on light: light is photons before and after passing through double slit” and “Postulate on lens: light behaves same before and after passing through lens”. Then, we show the novel phenomena of the comprehensive double slit experiments: (1) the light is photons before and after passing through a double slit; (2) photons form both the non-interference patterns and the interference patterns; (3) the non-interference patterns gradually evolve to the interference patterns in the same experiment. We refer to the novel phenomena as “PhotoWave phenomena” that are universal. The comprehensive double slit experiments provide the novel phenomena for developing theoretical model further to study: (1) the nature of the light; (2) the Feynman’s mystery of the double slit; (3) the wave-particle duality; and (4) the wave theories of the light; (5) applications. A complete description should explain all the comprehensive double slit experiments consistently.
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 now explained here, making the current, „probabilistic interpretation‟, a past history. 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 explained as 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. We know that even the purest monochromatic laser source has a „line-width ‟ of a few Giga-Hertz, or at least a few kilo-Hertz. So in the particle-interference-experiments, they are these wide bands of waves which pass through both the slits, even in the case of single photon states, and interfere physically. This physical interference of the wide bands of pre-quantum-waves determines the position and time of emergence of the „particle‟. Thus, form the theoretical view-point, there are only the waves, and waves alone; and the „particle ‟ is a specific situation of constructive-superimposition of all the spectral-components of pre-quantum-waves; so there is no wave-particle-duality.