What is a photon, really?

David W. Snoke

Published Dec 1, 2003• 1 citation

Abstract

Our early training in physics encourages us to imagine photons as little pellets flying through the air, and to see wave-particle duality as a paradox. This view persists from the debates on quantum mechanics early in the 20th century. Much has happened in the past 80 years, however. Quantum optics and field theory have developed a very sophisticated mathematical formalism for treating photons, and this formalism affects how we view photons. Recently, physicist Carver Mead of Cal Tech published a book with a very persuasive mathematical argument of how to understand quantum jumps. He also argued that photons are not "real." In this talk, I will present, using only basic algebra, the main points of quantum optics and Carver Mead's view. These results also lead to a reconsideration of the EPR paradox.

Related papers

The Concept of the Photon—Revisited

Ashok Muthukrishnan, Marlan O. Scully, Muhammad Suhail Zubairy

concept is one of the most debated issues in the history of physical science. Some thirty years ago, we published an article in Physics Today entitled The Concept of the Photon, 1 in which we described the photon as a classical electromagnetic field plus the fluctuations associated with the vacuum. However, subsequent developments required us to envision the as an intrinsically quantum mechanical entity, whose basic physics is much deeper than can be explained by the simple 'classical wave plus vacuum fluctuations' picture. These ideas and the extensions of our conceptual understanding are discussed in detail in our recent quantum optics book. 2 In this article we revisit the concept based on examples from these sources and more.

Optics and Photonics NewsDec 19, 201718 citations

Quantum Mechanics Plan B

Stefan G. Freundt

The Quantum mechanics works but is not yet well understood. The difficulty in understanding lies not so much in the already very sophisticated mathematical formulations, but are much more rooted in the question of how the objects do that? Starting with the double-slit experiment, we will first provide the viewpoint of quantum mechanics. This leads us to the wave-particle duality. Photons have both wave and particle properties. Then we see the exact opposite: photons, electrons... are neither wave nor particle and address the question: Can we find truth from falsity? Can quantum mechanics be wrong in their conditions and yet lead to so excellent results? We then address the question of how good the mathematical prerequisites in classical physics is and how well they are fulfilled in quantum physics. Finally, we look at some very basic experiments from the point of view of the objects.

Apr 1, 20140 citations

Quantum mechanics writ large

John W. M. Bush

Some two centuries before the quantum revolution, Newton (1) suggested that corpuscles of light generate waves in an aethereal medium like skipping stones generate waves in water, with their motion then being affected by these aether waves. Times have changed. Light corpuscles are now known as photons, and the majority of physicists have dispensed with the notion of aether. Nevertheless, certain features of Newton's metaphor live on in one particular version of quantum mechanics. According to pilot wave theory, first proposed by de Broglie (2) and later developed by Bohm (3) with Einstein's encouragement, microscopic elements such as photons and electrons consist of both particle and wave, the former being guided by the latter. Although this physical picture has not been widely accepted, it has had some notable proponents, including Bell (4). Its principal appeal is that it restores realism and determinism to quantum mechanics, its weakness that the physical nature of the guiding wave field remains unclear. At the time that pilot wave theory was developed and then overtaken by the Copenhagen interpretation as the standard view of quantum mechanics, there was no macroscopic pilot wave analog to draw upon. Now there is.

Proceedings of the National Academy of SciencesSep 29, 201060 citations

The development of attitudes to the wave-particle duality of light and quantum theory, 1900–1920

John Hendry

Summary Evidence bearing on the development of the wave-particle problem for light in the period 1900–1920 is presented in order to indicate how this problem was then viewed. Particular attention is drawn to the logical force of the arguments used in the debate, and to their persuasive force in the context of current values and of the contemporary state of physics. It is shown that, despite the accumulation of strong evidence in support of wave-particle duality, and despite widespread agreement on the inadequacy of both wave and particle theories, there was little acceptance of duality. This is attributed to physicists' acceptance of the long-standing tradition requiring a physical description to be above all structurally consistent.

Annals of ScienceJan 1, 198033 citations

Understanding Photons in Quantum Physics - A clear, modern scientific article to resolve common conceptual confusions

purnendu nath bala

This work provides a conceptual clarification of the photon within modern quantum physics. While the experimental behavior of photons is well established, conceptual confusion persists regarding their wave-particle nature, wavelength attribution, and energy without mass. The article presents an interpretation-safe account of photons as quantum excitations of the electromagnetic field, resolving common misconceptions without proposing new physics.

Jan 11, 20260 citations

Quantum Mechanics

Peter E. Hodgson

The difﬁculties of the old quantum theory were largely dispelled by the development of quantum mechanics in the 1920s. First Heisenberg (1925) developed the rather abstract matrix mechanics and soon after Schro¨dinger (1926; see also Eckart, 1926) developed the physically more appealing wave mechanics. Subsequently he showed them to be mathematically equivalent. The physicists were greatly relieved; now they had once again a mathematical formalism that enabled the results of experiments to be calculated. It was possible to move forward. It is certainly a very elegant and indeed beautiful formalism, and does enable the results of many physical measurements to be calculated with great accuracy. It is used daily by atomic and nuclear physicists; there is no other way to make calculations. From the earliest days there has been intense debate about the interpretation of quantum mechanics, and it shows no signs of being settled; if anything it is becoming more intense over the years. As Penrose has remarked, no one understands quantum mechanics. Feynman (1967; see also Sykes, 1994) also admitted that ‘nobody understands quantum mechanics’, and Einstein once remarked: ‘I have thought a hundred times as much about the quantum problems as I have about general relativity theory’ (Pais, 1994, p. 57). It should therefore be evident that the most that can be done here is to try to show where the real difﬁculties lie, and how the failure to recognize that quantum mechanics is an essentially statistical theory has led to a series of confusing quantum paradoxes. It is just these paradoxes that have often been used to support theological speculations. It is useful to ask what ‘understanding quantum mechanics’ actually means. Certainly it means being able to calculate the results of many measurements. The same applies to Newton’s theory of gravitation, which we understand in the sense that we can use it as a basis of calculation, although we do not really understand the gravitational force itself. Very often, especially in modern physics, the mathematical formalism does not give us the sort of intuitive physical feeling for what is going on that we often obtain from classical mechanics. Perhaps we can never achieve more than this for quantum mechanics. In classical mechanics we can assume that a property that is measured objectively exists prior to the interaction of the measuring apparatus with the observed system. Quantum mechanics, however, ‘is incompatible with the proposition that measurement discovers some unknown but pre-existing property’ (Peres, 1997, p. 14). There is an important distinction between mysteries and absurdities. We may be forced to live with mysteries, but there is no reason why we should put up with absurdities such as the wave-particle duality, tunnelling through potential barriers, acausal events and the collapse of the wave function. These are the quantum paradoxes that will be discussed later on. They arise within the Copenhagen interpretation of quantum mechanics and are solved by other interpretations. These alternative interpretations enable us to make conjectures about what is going on, even though we cannot understand it in detail. This is acceptable and a stimulus to further research. It is certainly difﬁcult enough to understand quantum mechanics, but there is no need to try to visualize logical absurdities in the effort to do so. Quantum mechanics is a mathematical formalism that makes it possible to calculate the results of some experiments. Anything more than this, such as questions about the interpretation of what is measured and whether it tells us what is actually going on in the system being studied, belongs to philosophy. Thus we are concerned here with what is essentially a philosophical debate; if it were just a matter of physics the debate would have been settled long ago. One of the difﬁculties is that it invokes the results of experiments and uses the language of quantum mechanics. Inevitably this language uses philosophical terms and then it is easy to give the impression that the philosophical propositions are in some way entailed by the physical results. These in turn can inﬂuence theological thinking. In order to be quite clear which arguments are justiﬁed and which are not, it is essential to separate the three levels of discourse: physical, philosophical and theological. Our task is to relate these together, and this immediately raises the traditional problems of the philosophy of science, including the relation of experiment to theory, and of theory to explanation. We begin by discussing experiments, distinguishing between those that are real and those that are imaginary.

Routledge eBooksSep 8, 20170 citations