In a recent article in these Proceedings (1) Professor G. N. Lewis has suggested that the conflict between the quantum theory of light and the known facts of interference might be resolved by assuming that an atom never emits a quantum of light except to another atom, the possibility of transmission of the quantum being determined by the nature of the paths connecting the two atoms in such a manner that the transmission will not occur if forbidden by the known laws of interference. The idea is made more plausible by describing such transmissions with the help of Minkowski's four-dimensional geometry of relativity.
In a recent article in these Proceedings (1) Professor G. N. Lewis has suggested that the conflict between the quantum theory of light and the known facts of interference might be resolved by assuming that an atom never emits a quantum of light except to another atom, the possibility of transmission of the quantum being determined by the nature of the paths connecting the two atoms in such a manner that the transmission will not occur if forbidden by the known laws of interference. The idea is made more plausible by describing such transmissions with the help of Minkowski's four-dimensional geometry of relativity.
In the perspective of classical theory it is the ability of light to interfere and diffract which above all prevents us from believing that light consists of a sort of classical particles, perhaps pointlike. Even if we took the standpoint that propagating light fields in free space did consist of streams of pointlike entities, these can certainly not be robust in their interaction with material particles, although this was suggested by the scientist G. N. Lewis who in 1926 coined the name photon for Einstein’s light quanta [144]. Despite the fact that the idea of the existence of uncreatible and indestructible “light atoms” has turned out to be untenable, the theory of classical optics shows reminiscences of particle behavior in situations where the finite wavelength of light is negligible.
In an earlier number of these Proceedings, (1) Professor G. N. Lewis adopted an extreme form of the light quantum theory, in which the light quanta are assumed to travel in straight lines except when deflected by matter, the facts of interference being explained by the assumption that the quanta do not go to those places where the wave theory forbids the action of radiation. As a crucial test between this and other theories of light, Professor Lewis proposed an experiment in which the absence of light quanta, traveling over a particular path which leads to the center of of an interference band on a screen, would produce an unbalanced torque on a reflecting mirror.
The following views regarding the mode of transmission of light are of so unorthodox a character that I set them down with some reluctance; but it seems to be generally admitted that the paradox of quantum theory cannot be resolved without doing violence to one or more of our cherished common notions.Some of the consequences of the theory that I am going to advance are repugnant to common sense, yet, searching in vain for an alternative and finding no physical fact of optics or of thermodynamics in opposition to the theory, I have come to regard it as a natural and indeed inevitable extension of Einstein's principle of relativity.Let me start with two statemefits which seem now to be well supported by experiment, although perhaps not entirely demonstrated.They are, however, the postulates upon which the following theory is built.
Physicists have spent many centuries developing theories for light. It is a problem that was tackled by the best of the best (Newton and Einstein) and many, many others. Understanding the quantum nature of light is complex, but it is something every one of us should understand to be a well-educated individual. It encompasses some of the most bizarre features of quantum mechanics. We begin our encounter with light in this chapter focusing on examples that include partial reflection of light from glass, single-slit diffraction, two-slit diffraction, mirrors, diffraction gratings, and lenses.
Abstract This article examines models and theories of energy and matter behaviour developed in microscopic experiments of quantum mechanics; the branch of physics relating to the very small, which studies the physical properties of nature at atomic scales and subatomic particles. It is based on the idea that energy, at the sub-atomic level, can only be emitted and absorbed in discrete amounts - small units – called “quanta”. We begin by remembering that the ideas of the philosopher Democritus, on the assumption of a finite division of matter, led to the search for the atom, allowing the development of what is now known as physics. It is particularly discussed how the understanding of electricity made it possible to affirm and discover the nature of the atom, not as Democritus thought, but that its existence as a basic component of matter could be verified. In this text, we make a path of experiments and ideas that led to the current model of the atom, and that allowed the development of a theory about its nature and properties. Finally, conclusions on this brief study are presented.
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.