Exchange forces lie at the base of some of the most striking explanatory successes of modern physics.An exchange interaction, for instance, is held to be responsible in some key sense for the chemical bond.An exchange force is the origin of ferromagnetism, providing the force that lines up individual spins into an overall pattern.In nuclear physics an exchange force is characteristic for the description of nucleon-nucleon forces.And, in perhaps the most far-reaching example, an exchange interaction is taken as definitional for the quantum field-theoretic description of nature, in which not only the fundamental forces (gravity, electromagnetism, the weak and strong nuclear forces), but also such non-fundamental ones as that operative between pairs of superconducting electrons in a lattice, are traced to the exchange of field quanta.In all these cases, moreover, exchange forces are a peculiarly quantum mechanical phenomenon, something characteristic of the new era that began in 1925 and continues into the present.And as a peculiarly quantum mechanical phenomenon, they are central to the new understanding of matter and force that was ushered in by the theory.For such a central concept, the historical origins of exchange forces are distinctly unclear.What was the path by which these diverse manifestations of exchange-in atomic physics, in condensed matter, in nuclear physics, in quantum field theory-came to go by the same name?Indeed, what is the common thread running through all these uses?The very notion of exchange is nebulous.Consider the following definition from a technical dictionary: exchange [QUANT MECH] (1) Operation of exchanging the space and spin coordinates in a Schrodinger--Pauli wave function representing two identical particles; this operation must leave the wave function unchanged, except possibly for a sign.(2) Process of exchanging a real or virtual particle between two other particles.'Here two distinct meanings of the term 'exchange' are on offer.The first notion
Exchange forces lie at the base of some of the most striking explanatory successes of modern physics.An exchange interaction, for instance, is held to be responsible in some key sense for the chemical bond.An exchange force is the origin of ferromagnetism, providing the force that lines up individual spins into an overall pattern.In nuclear physics an exchange force is characteristic for the description of nucleon-nucleon forces.And, in perhaps the most far-reaching example, an exchange interaction is taken as definitional for the quantum field-theoretic description of nature, in which not only the fundamental forces (gravity, electromagnetism, the weak and strong nuclear forces), but also such non-fundamental ones as that operative between pairs of superconducting electrons in a lattice, are traced to the exchange of field quanta.In all these cases, moreover, exchange forces are a peculiarly quantum mechanical phenomenon, something characteristic of the new era that began in 1925 and continues into the present.And as a peculiarly quantum mechanical phenomenon, they are central to the new understanding of matter and force that was ushered in by the theory.For such a central concept, the historical origins of exchange forces are distinctly unclear.What was the path by which these diverse manifestations of exchange-in atomic physics, in condensed matter, in nuclear physics, in quantum field theory-came to go by the same name?Indeed, what is the common thread running through all these uses?The very notion of exchange is nebulous.Consider the following definition from a technical dictionary: exchange [QUANT MECH] (1) Operation of exchanging the space and spin coordinates in a Schrodinger--Pauli wave function representing two identical particles; this operation must leave the wave function unchanged, except possibly for a sign.(2) Process of exchanging a real or virtual particle between two other particles.'Here two distinct meanings of the term 'exchange' are on offer.The first notion
It is commonly said that exchanging two identical particles is equivalent to rotating one of them by one revolution. The present note shows that, in this equivalence, both the exchange and the rotation are purely mathematical operations—symbolic manipulations of the wave function, made during the design phase of an experiment. Neither occurs in the physical spacetime in which the experiment runs. While in general, “exchange” and “rotation” refer to physical processes, in the context of this equivalence, they do not. The key observation is that either one can return the system to its original state perfectly—which is possible only for a mathematical operation, not for a real physical process. At best, it is an idealized physical process—the limiting case of a real one. However, in this equivalence, those two mathematical operations cannot even be considered as limiting cases, because their very definitions are purely mathematical. A physical process—real or idealized—is a function of time. Neither exchange (as particle label-swap) nor rotation (as frame coordinate transformation) has the time variable. The very meaning of “process” is the set of intermediate steps. Therefore: no time, no process. They are proposed mathematical properties of possible physical worlds. Mathematical properties—once well-defined or proved—are always true within their formal system. However, those properties can be inapplicable in some worlds. Therefore, it is possible to use physical experiment to test whether they apply in this physical reality. But they are still not physical processes within any particular spacetime. While Euclidean geometry is mathematical, the statement “this world follows Euclidean geometry if we define straight lines as paths of light” is physical, because it is possible to be falsified by experiment. Still, the geometric assertions never refer to any physical processes. As the operations are purely mathematical, the equivalence itself is likewise mathematical. Moreover, since either operation can exist without the other, the equivalence is not a logical necessity, but a convention.
Abstract One of the outstanding differences between classical theory and quantum mechanics is the importance which the latter attaches to the identity of particles. Although perfectly well realised before the introduction of modern quantum theory, the fact that two electrons are experimentally indistinguishable did not introduce any novel features into the dynamics of many electron systems on Bohr’s theory. However, Heisenberg showed that these identity relations are of fundamental importance in many body problems, and was able to explain the formerly very puzzling characteristic of the spectrum of neutral helium, its division into two non-combining term systems. Owing to the identity of the particles, the wave function representing such a system must have certain symmetry properties; for the particles known in Nature this symmetry characteristic is that the function be either symmetric or anti-symmetric in the co-ordinates of the particles. For particles with a spin such as the electron and proton, only antisymmetry is allowed (Pauli’s principle), while for α-particles the wave function must be symmetrical. Since Heisenberg’s explanation of the helium spectrum the theory of anti-symmetric electron wave functions has been extended to describe the general features of the spectra of all atoms, while it appears from the work of Heitler and London that the theory is of fundamental importance in the explanation of chemical combination between atoms. Again, in furnishing a new statistics it is an essential feature of the theory of metals. As the effect of the identity relations depends on the fact that exchanging the electrons does not alter the system in any way, these effects are known as exchange phenomena.
Conventional many-body quantum theory considers, as a rule, a system of particles in the mean field interacting through two-body forces. Recently it was suggested that in nuclear physics many-body forces, first of all three-body ones, are important for saturation of nuclear matter and for many details of nuclear structure. We consider possible influence of three-body forces, regardless of their origin (bare nucleon interactions or effective medium phenomena), on many-body dynamics. The new effects include, but are not limited to, renormalization of pairing and other two-body forces, enhancement of anharmonicity for collective modes, and special features of shell model calculations.
The mind–matter relationship remained in the domain of philosophers for aeons. However, the inquisitiveness of the scientific minds has always been trying to understand the science behind its various functions. The scientific temper ushered in by the Renaissance about the 15th century saw the scientists exploring this problem from a science point of view. Technological advances during the later part of the 20th century enabled neuroscientists to explore and localise functions of the brain. However, the most difficult has been understanding the origin of a conscious experience scientifically or materialistically. Despite the delineation of many functions of the brain, the origin of conscious experience, the qualia, in the material brain remains elusive, so much so it came to be called the holy grail of neuroscience. Heisenberg wrote: ‘Physics entered the domain of philosophy with the emergence of consciousness in quantum observation, which incidentally opened the door for reconciliation of science and philosophy’,[1] an event which enabled the predictions of Snow of the merging of arts and sciences.[2,3] Quantum mechanics is a branch of physics relating to very small particles – subatomic particles – electrons, photons, and everything in the submolecular realm, being the smallest units in matter. Quantum theory is the most fundamental theory of matter available at present. Some basic concepts of quantum physics need to be understood. These include “superposition”, where in subatomic particles exist either as waves or particles in a dual nature, never simultaneously. They exist as waves in more than one place at a time and once an observer observes or interferes with (such as measuring) their superposition state collapses to particle state. Quantum entanglement is the phenomenon that occurs when a group of particles which are generated, interact with or share special proximity such that they remain connected even when separated by vast distances. Consciousness is a manifestation of quantum process. Q mind or Q consciousness comprises a group of hypotheses proposing that quantum mechanical phenomena such as entanglement and superposition may play an important part in the functions of the brain and could thus explain the origin of consciousness. Several theories of quantum consciousness have been proposed. Wigner proposed the idea that quantum mechanics has something to do with the workings of the mind and proposed that the wave function collapse in the interaction with conscious observation creates consciousness.[4] Vitiello and Freeman[5] proposed quantum field theory (QFT) of brain states. This theory deals with systems and provides formal elements from which a standard description of brain activity can be inferred. According to QFT, particles are only excited states or simply manifestations of a field. Every particle has its own field that covers all of the universe, which means that, according to QFT, all of the electrons of the universe belong to the same field and could be regarded as one. Bohm formulated the QFT as a deeper theory of quantum theory plus relativity.[6] He viewed mind and matter as projections into our explicate order underlying the implicate order. Quantum brain dynamics (QBD) hypothesis explains the function of the brain within the framework of QFT.[7] It is not yet known exactly how quantum superpositions and their collapse result in the genesis of the raw feels of consciousness, the qualia. Feynman stated ‘if you think you understand quantum mechanics then you do not!’[8] Pribram proposed the holonomic brain theory (quantum holography). He invoked quantum mechanics to explain the higher-order processing by the mind. Pribram provided evidence on how much of the processes in the brain take place in a distributed fashion.[9,10] The composite model of Pribram-Bohm of holoflux hypothesis addresses observed phenomenon of non-locality both spacially and temporally. Bose and Einstein, who first predicted Bose Einstein condensate proposed that water at dendritic membrane surfaces might operate by structuring condensation,[11] supporting QBD. Penrose and Hamoreff proposed the orchestrated-objective reduction (ORCH-OR) in 1989 through 2013. According to them, the microtubules in the neurons (neurotubules), the tubulin protein polymer at the site of quantum collapse, leads to conscious experience. The quantum superposed states which develop in the tubulins remain coherent and recruit more superposed tubulins until a mass-time-energy threshold is reached. At this point, self-collapse or objective reduction occurs, which is equated to a discrete conscious event. Cascades of ORCH-OR events give rise to the stream of consciousness.[12,13] Penrose suggested that objective reduction represents neither randomness nor algorithmic processing but instead a non-computable influence in spacetime geometry from which mathematical understanding and, by later extension, consciousness derives.[14] Quantum vibrations in the microtubules proposed by Bandyopadhyay[15] have been shown to be source of conscious experience by corroborating the Penrose-Hemeroff’s ORCH-OR hypothesis.[13,16] In April 2022, the results of two related experiments at the University of Alberta and Princeton University, announced at The Science of Consciousness conference, provided further evidence to support quantum processes operating within microtubules. However, in another experiment, Gregory D. Scholes and Aarat Kalra of Princeton University used lasers to excite molecules within tubulins, causing a prolonged excitation to diffuse through microtubules further than expected, which did not occur when repeated under anaesthesia.[17,18] Beck and Eccles considered quantum mechanics at the synaptic level. If Orchestrated objective reduction (ORCH-OR) theory is applicable, a similar phenomenon in the microtubules at the presynaptic level, the axon terminal could be invoked for the genesis of consciousness.[19] A recent study by scientists at Trinity College, Dublin, in October 2022,[20] suggests that quantum processes underlie the cognitive and conscious brain functions. The brain–mind operational architectonics is the boundary between and integration point of quantum physics and eastern metaphysics and that it may inspire building a richer and more inclusive paradigm of the brain–mind relation, where quantum physics and eastern metaphysics are inherently intertwined. A body of empirical evidence[21-24] supports these possibilities, strengthening the proposal that the mind–brain relationship may be partially quantum. Quantum information theory clarifies the distinction between the unobservable mind and the observable brain and supports a solid physical foundation for consciousness research. With all these theories trying to explain and understand the theoretical/hypothetical framework for consciousness to explain the subjective experience of consciousness, the experts of this field feel it is still a long way to bridge the gap between current neurobiological and physical–mathematical concepts with their associated quantum–mind theories. Though there is still a long way to go for explaining conscious experience scientifically, when ever this happens, it will become one of the benchmarks in science. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest. Use of artificial intelligence (AI)-assisted technology for manuscript preparation The authors confirm that there was no use of artificial intelligence (AI)-assisted technology for assisting in the preparation of the manuscript and no images were manipulated using AI.
The effect of spin exchange collisions on the internal variables (orientation, alignment, etc.) of colliding atoms is discussed, with particular emphasis on the role played by the Pauli principle. The calculation presented is valid for distinguishable or identical particles, and the initial introduction of an effective exchange hamiltonian for the spins is avoided. The one-atom density matrix of the internal variables is calculated after collision, in an operatorial form which enables the discussion of various physical effects. The first term in the density matrix evolution is a transfer term which does not originate from particle indistinguishability. The following terms are indeed introduced by the Pauli antisymmetrization principle applied to electrons and nuclei, and they can be described as electronic or nuclear apparent magnetic field (or electric gradient). In addition, terms arising from the combined exchange of electrons and nuclei are obtained, in particular from the exchange of identical whole atoms (bosons in the case of hydrogen). The evolution equations for the density operators are applied to a few particular cases in order to evaluate spin exchange effects in various situations : weak or strong hyperfine decoupling, Zeeman or hyperfine resonances, etc...
This article describes the origin of wave-particle duality of matter which has led to the birth of quantum mechanics. We argue that the presence of exchange interaction among particles is indispensable for the manifestation of their 'wave-like' behavior. We intend to justify different attributes of their wave character via the exchange interaction. In short, the most fundamental (and unknown) issue in quantum mechanics has been clarified. This article MUST be read together with our other articles, arXiv:1409.7156 and J. Phys.: Cond. Matter 25, 382205 (2013) {the links to these are provided}, for proper appreciation of our ideas. This replacement is a linguistic refinement/elaboration of text of the manuscript and the suppl. info. (like a pedagogical description).