Today, the nature of light is accounted for by one of the jewels of physics, quantum electrodynamics (QED), the fundamental theory of light and matter. Yet owing to its infinite complexity, scientists still debate how its central concept, the photon, can be reconciled with the perceived existence of light waves, emerging 200 years ago in the wake of Young's double slit diffraction experiment. Ever since, the phenomenon of diffraction has been viewed to embody the wave nature of light, leading to the schizophrenic wave-particle duality. The latter does not exist in QED which is photon based without the existence of waves. Here we introduce the new paradigm that diffraction images directly reflect the fundamental quantum states of light. This is revealed by analysis of the evolution of modern versions of Young's experiment performed with differently modified laser light and photon-based detection. In conventional quantum mechanics, corresponding to first order QED, the fundamental photon nature of light remains hidden since different quantum states produce only two basic types of diffraction patterns that may also be explained by coherent and incoherent wave superposition. The true photon based substructure of light is shown to clearly emerge through characteristic diffraction images in second order QED. The degeneracy of the first order images is lifted, the wave-particle equivalence breaks down, and the patterns directly reveal the true quantum substructure of light. This allows the replacement of the conventional concept of wave coherence by a precise order-dependent degree of coherence that quantifies the interference and diffraction behavior of all quantum states of light.
Today, the nature of light is accounted for by one of the jewels of physics, quantum electrodynamics (QED), the fundamental theory of light and matter. Yet owing to its infinite complexity, scientists still debate how its central concept, the photon, can be reconciled with the perceived existence of light waves, emerging 200 years ago in the wake of Young's double slit diffraction experiment. Ever since, the phenomenon of diffraction has been viewed to embody the wave nature of light, leading to the schizophrenic wave-particle duality. The latter does not exist in QED which is photon based without the existence of waves. Here we introduce the new paradigm that diffraction images directly reflect the fundamental quantum states of light. This is revealed by analysis of the evolution of modern versions of Young's experiment performed with differently modified laser light and photon-based detection. In conventional quantum mechanics, corresponding to first order QED, the fundamental photon nature of light remains hidden since different quantum states produce only two basic types of diffraction patterns that may also be explained by coherent and incoherent wave superposition. The true photon based substructure of light is shown to clearly emerge through characteristic diffraction images in second order QED. The degeneracy of the first order images is lifted, the wave-particle equivalence breaks down, and the patterns directly reveal the true quantum substructure of light. This allows the replacement of the conventional concept of wave coherence by a precise order-dependent degree of coherence that quantifies the interference and diffraction behavior of all quantum states of light.
The nature of light, extending from the optical to the x-ray regime, is reviewed from a diffraction point of view by comparing field-based statistical optics and photon-based quantum optics approaches. The topic is introduced by comparing historical diffraction concepts based on wave interference, Dirac’s notion of photon self-interference, Feynman’s interference of space–time photon probability amplitudes, and Glauber’s formulation of coherence functions based on photon detection. The concepts are elucidated by a review of how the semiclassical combination of the disparate photon and wave concepts have been used to describe light creation, diffraction, and detection. The origin of the fundamental diffraction limit is then discussed in both wave and photon pictures. By use of Feynman’s concept of probability amplitudes associated with independent photons, we show that quantum electrodynamics, the complete theory of light, reduces in lowest order to the conventional wave formalism of diffraction. As an introduction to multi-photon effects, we then review fundamental one- and two-photon experiments and detection schemes, in particular the seminal Hanbury Brown–Twiss experiment. The formal discourse of the paper starts with a treatment of first-order coherence theory. In first order, the statistical optics and quantum optics formulations of coherence are shown to be equivalent. This is elucidated by a discussion of Zernike’s powerful theorem of partial coherence propagation, a cornerstone of statistical optics, followed by its quantum derivation based on the interference of single-photon probability amplitudes. The treatment is then extended to second-order coherence theory, where the equivalence of wave and particle descriptions is shown to break down. This is illustrated by considering two photons whose space–time probability amplitudes are correlated through nonlinear birth processes, resulting in entanglement or cloning. In both cases, the two-photon diffraction patterns are shown to exhibit resolution below the conventional diffraction limit, defined by the one-photon diffraction patterns. The origin of the reduction is shown to arise from the interference of two-photon probability amplitudes. By comparing first- and second-order diffraction, it is shown that the conventional first-order concept of partial coherence with its limits of chaoticity and first-order coherence has the second-order analogue of partial entanglement, with its limits corresponding to two entangled photons (“entangled biphotons”) and two cloned photons (“cloned biphotons”), the latter being second-order coherent. The concept of cloned biphotons is extended to the case of n cloned photons, resulting in a 1/n reduction of the diffraction limit. In the limit of nth-order collective state are shown to propagate on particle like trajectories, reproducing the 0th-order ray-optics picture. These results are discussed in terms of the linearity of quantum mechanics and Heisenberg’s space–momentum uncertainty principle. Finally, a general concept of coherence based on photon density is developed that in first order is equivalent to the conventional wave-based picture.
This paper reviews humanity's understanding of photons, the evolution of quantum mechanics and quantum electrodynamics (QED), and analyzes their physical interpretations and philosophical implications. It attempts to uncover the true nature of photons by exploring possible hidden variables in the double-slit experiment. The wave-particle duality of photons, as posited by quantum mechanics, appears to me to lack verisimilitude. By designing a thought experiment involving a photon double-slit setup, I seek to falsify the notion that photons generate coherence, or so-called wave-function superposition, within the light field between the slits and the screen. This endeavour aims to demonstrate the pure particle nature of photons. This paper further explores the intrinsic relationship between electromagnetic waves and photons by examining the wavelength of electromagnetic radiation. It posits that electromagnetic waves are fundamentally pure particle-waves. An analysis of QED elucidates the potential influence of photon momentum on photon interactions, an effect that could have profound implications for quantum information transmission. This paper explores the non-wave-particle duality of photons through the double-slit experiment and the double-slit observer experiment. The essence of photons is purely particle-like. The thought experiment of the photon double-slit experiment is pivotal in demonstrating that photons and other particles—such as electrons, atoms, and macromolecules—are purely particulate in nature. Moreover, in space, photons can interfere with each other's paths based on their momentum. This can simultaneously alter the trajectory of photons and even modify their velocity. That is to say, a photon beam possessing greater momentum may carry along a portion of photon beams with lesser momentum, propagating them over considerable distances. The wavelength of a light wave fundamentally represents the distance between consecutive photons as they queue and advance through space. A longer wavelength corresponds to a greater distance between photons, causing them to diverge more widely in space, as seen with radio waves. Conversely, a shorter wavelength implies closer proximity between photons, resulting in denser emission and a highly directional nature, as seen in gamma rays. Photons within the visible spectrum may occasionally transmit information bearing specific content. This information, conveyed via photons, can propagate over distances ranging from several metres to thousands of kilometres.
There are two opposing points of view on the nature of light: the first one manifests the wave-particle duality as a fundamental property of the nature; the second one claims that photons do not exist and the light is a continuous classical wave, while the so-called “quantum” properties of this field appear only as a result of its interaction with matter. In this paper we show that many quantum phenomena which are traditionally described by quantum electrodynamics can be described if light is considered within the limits of classical electrodynamics without quantization of radiation. These phenomena include the double-slit experiment, the photoelectric effect, the Compton effect, the Hanbury Brown and Twiss effect, the so-called multiphoton ionisation of atoms, etc. We show that this point of view allows also explaining the “wave-particle duality” of light in Wiener experiments with standing waves. We show that the Born rule for light can easily be derived from Fermi’s golden rule as an approximation for low-intense light or for short exposure time. We show that the Heisenberg uncertainty principle for “photons” has a simple classical sense and cannot be considered as a fundamental limitation of accuracy of simultaneous measurements of position and momentum or time and energy. We conclude that the concept of a “photon” is superfluous in explanation of light-matter interactions.
Abstract Objective Modern understanding of light has fluctuated between particle and wave theory. The classic double slit experiment provided crucial support of wave theory with its description of wave interference fringe patterns. To our knowledge, no significant study has been performed on light propagation in free space after exiting the slit. To further understand the double slit results we analyzed light behavior in free space using novel visualization techniques.Methods A micro-particle environment was developed that remained transparent to visible light. Coherent light was observed in this environment in settings of diffraction, refraction, and reflection.Results Experimental generation of distinct light strands after diffraction through double slits is visualized. Definitive images of discrete light strands, not waves, were noted as light propagated through free space. Light strands were visualized directly creating the pseudo-interference fringe pattern, refuting the concept of wave interference.Conclusions Novel generation and visualization of light strands confirms the particle theory of light and counters two hundred years of wave doctrine. The finding that diffractive fringe patterns and other observations of light are due to the phenomena of discrete radiating strands, not wave interference, will have implications in physics, quantum mechanics, and technology.
Any discussion of the nature of light must include a reminder that whenever we make the observation of light (photons), we only observe particle-like properties. This paper provides a reiteration that we don't need wave-like properties to scattered photons to describe phenomena such as diffraction or refraction of light. This paper updates the original ideas of Duane, later revived by Lande, which provided a description of light diffraction without making reference to a wave nature. These are updated using terminology more common to quantum electrodynamics which describes the interaction of particles in terms of the exchange of virtual photons. Diffraction is described in terms of an ensemble of distinct, probability weighted paths for the scattered photons. The scattering associated with each path results from the quantized momentum exchange with the scattering lattice attributed to the exchange or reflection of virtual photons. The probability for virtual particle exchange/reflection is dependent upon the allowed momentum states of the lattice determined by a Fourier analysis of the lattice geometry. Any scattered photon will exhibit an apparent wavelength inversely proportional to its momentum. Simplified, particle-like descriptions are developed for Young's double slit diffraction, Fraunhofer diffraction and Fresnel diffraction. This description directly accounts for the quantization of momentum transferred to the scattering lattice and the specific eigenvalues of the lattice based upon the constraints to virtual photon exchange set by the Uncertainty Principle, Δπi = h/ζi.
Young’s double slit experiments revived the wave theory of light. The standard interpretation is that the light behaves as waves before and after passing through the double slit, and the superposition of waves produces the interference pattern. Feynman called the double slit experiment the only mystery in quantum mechanics. In this article, we experimentally show the novel universal phenomena: (1) within macro-distance from the diaphragm, the light rays behave as photons and produce non-interference patterns; while near the screen, the photons produce interference patterns; (2) The non-interference patterns evolve to the interference patterns gradually in the same classical wave experiment; (3) the light is photons before and after passing through the double slit; (4) The convex lens stops the further evolution. The experiments: (1) challenge the wave theories of the light; (2) violate both Bohr’s complementarity principle and wave particle duality; (3) provide profound phenomena for developing optics and for studying the nature of light; (4) suggest that a complete theory should be able to consistently interpret all phenomena, including the non-interference pattern, the interference pattern, and the evolution from the non-interference to the interference pattern in the wave experiment; (5) show a new mystery that photons, as particles, distribute as waves.