# Nature Has No Elementary Particles and Makes No Measurements or Predictions: Quantum Measurement and Quantum Theory, from Bohr to Bell and from Bell to Bohr

## Abstract

**:**

Even in a low-brow practical account, I think it would be good to replace the word ‘measurement’, in the formulation, by the word ‘experiment’. For the latter word is altogether less misleading. However, the idea that quantum mechanics, our most fundamental physical theory, is exclusively even about the results of experiments would remain disappointing.—John Bell, “Against ‘measurement’” [1] (pp. 216–217)

## 1. Introduction

Even in a low-brow practical account, I think it would be good to replace the word ‘measurement’, in the formulation, by the word ‘experiment’. For the latter work is altogether less misleading. However, the idea that quantum mechanics, our most fundamental physical theory, is exclusively even about the results of experiments would remain disappointing.[1] (pp. 216–217)

## 2. An Outline of Concepts

In contrast to ordinary mechanics, the new quantum mechanics does not deal with a space–time description of the motion of atomic particles. It operates with manifolds of quantities [matrices] which replace the harmonic oscillating components of the motion and symbolize the possibilities of transitions between stationary states …. These quantities satisfy certain relations which take the place of the mechanical equations of motion and the quantization rules.[2] (v. 1, p. 48)

_{1}determines, by Newton’s law of gravity, the state of this body at any other point t

_{2}does not mean that the state at t

_{1}is the cause of the state at t

_{2}. One might argue that the real physical cause for any determination, including that of the initial state, A, that defines any particular case considered, is (in our language) the gravitational field defined by the Sun and other physical objects in the Solar system, as encoded in Newton’s law of gravity. In this view, a given state, A, of any single object can only be seen as a physical cause of its future states, insofar as the whole configuration of bodies and forces involved, which determines the law of motion and hence causality, is viewed as embodied in this state. The history of the system thus considered, or any of classical system, whatever a physical law or set of laws defines its causal behavior, only goes so far in a given representation, which suspends more remote causes, let alone of the ultimate cause of this history. (Assuming the ultimate cause of anything is a major philosophical problem, put aside here.) Thus, Newton bracketed the physical nature of and the causes of gravity and was (wisely) content to merely define a law of gravity in considering, as causal, the behavior of any given object under this law, and other laws of Newton’s mechanics. In considering planetary motion, all history, such as that of the emergence of the Solar system, was bracketed as well. This type of bracketing is workable on very large spatial and temporal scales, even that of the Universe itself, using Newton’s theory of gravity or general relativity, but only up to a point. The situation changes once one gets closer to the Big Bang or to considering the Big Bang itself (assumed to be a complex process in which great many things happen even if in very short time, by our measure), because of the quantum aspects and possible still other have to be considered. This leads to complexities that thus far has defeated all our efforts of resolving them.

[I]t is most important to realize that the recourse to probability laws under such circumstances is essentially different in aim from the familiar application of statistical considerations as practical means of accounting for the properties of mechanical systems of great structural complexity [in classical physics]. In fact, in quantum physics we are presented not with intricacies of this kind, but with the inability of the classical frame of concepts to comprise the peculiar feature of indivisibility, or “individuality,” characterizing the elementary processes.[2] (v. 2, p. 34)

I advocated the application of the word phenomenon exclusively to refer to the observations obtained under specified circumstances, including an account of the whole experimental arrangement. In such terminology, the observational problem is free of any special intricacy since, in actual experiments, all observations are expressed by unambiguous statements referring, for instance, to the registration of the point at which an electron arrives at a photographic plate. Moreover, speaking in such a way is just suited to emphasize that the appropriate physical interpretation of the symbolic quantum-mechanical formalism amounts only to predictions, of determinate or statistical character, pertaining to individual phenomena appearing under conditions defined by classical physical concepts [describing the observable parts of measuring instruments].[2] (v. 2, p. 64)

- (a)
- A mutual exclusivity of certain phenomena, entities, or conceptions, such as, and in particular, those of the position and the momentum measurements, which can never be performed simultaneously in view of the uncertainty relations;
- (b)
- The possibility of considering each one of them separately at any given point;
- (c)
- The necessity of considering all of them at different moments of time for a comprehensive account of the totality of phenomena that one must consider in quantum physics.

## 3. Measurement, Idealization, and Quantum Indefinitiveness

This necessity of discriminating in each experimental arrangement between those parts of the physical system considered which are to be treated as measuring instruments and those which constitute the objects under investigation may indeed be said to form a principal distinction between classical and quantum-mechanical description of physical phenomena. It is true that the place within each measuring procedure where this discrimination is made is in both cases largely a matter of convenience. While, however, in classical physics the distinction between object and measuring agencies does not entail any difference in the character of the description of the phenomena concerned, its fundamental importance in quantum theory … has its root in the indispensable use of classical concepts in the interpretation of all proper measurements, even though the classical theories do not suffice in accounting for the new types of regularities with which we are concerned in atomic physics. In accordance with this situation there can be no question of any unambiguous interpretation of the symbols of quantum mechanics other than that embodied in the well-known rules which allow us to predict the results to be obtained by a given experimental arrangement described in a totally classical way.[11] (p. 701)

_{QO}+ H

_{QI}+ H

_{QOQI}

_{QOQI}the interaction between them. In RWR view, no element of the formalism represents the ultimate nature of reality responsible for quantum phenomena, including its stratum involved in the interaction between QO and QI, responsible for the effects observed. Any such element only serves as part of the mathematics of QM that, with the help of Born’s rule, predicts such effects.

There is no description of what happens to the system between the initial observation and the next measurement. …The demand to “describe what happens” in the quantum-theoretical process between two successive observations is a contradiction in adjecto, since the word “describe” refers to the use of classical concepts, while these concepts cannot be applied in the space between the observations; they can only be applied at the points of observation.[28] (pp. 57, 145)

It is very difficult to modify our language so that it will be able to describe these atomic processes, for words can only describe things of which we can form mental pictures, and this ability, too, is a result of daily experience. Fortunately, mathematics is not subject to this limitation, and it has been possible to invent a mathematical scheme—the quantum theory [e.g., QM]—which seems entirely adequate for the treatment of atomic processes.[33] (p. 11).

## 4. Quantum Measurement as Entanglement

_{1}and S

_{2}, forming an EPR pair (S

_{1}, S

_{2}), allows one by means of a measurement performed on S

_{1}to make predictions, with probability one, concerning S

_{2}. In the present view, S

_{2}is only defined once the corresponding measurement is performed, but not when the prediction concerning it is made, which makes it even more difficult and rigorously impossible to speak of any independent properties of S

_{2,}however predicted, because there is no S

_{2}, in the first place, until it is measured. There is only the independent, RWR-type, reality, ultimately responsible for the existence of S

_{2}, when it is measured, and secondly, even then S

_{2}is still an RWR-type entity, which means that no physical properties can be attributed to it as such. These properties could only be attributed to the instrument used. As predictions at a distance, these predictions may be called “quantum-nonlocal” [7]. They do not, however, entail any instantaneous transmission of physical influences between such events, “a spooky action at a distance” [spukhafte Fernwirkung], famously invoked by Einstein [37] (p. 155). As such, they may be called Einstein-local. Einstein-locality would prohibit such an action, as would relativity, although the concept of Einstein-locality, or the locality principle, which implies that physical systems can only be physically influenced by their immediate environment, is independent of relativity.

_{1}and S

_{2}lead to the situation in which possible future measurements can be handled by the mathematics of entangled states in the formalism of QM and expectation catalogs they enable. Accordingly, in the present view, only quantum states, $\psi $-functions, can be entangled, but there is something in the ultimate nature of reality responsible for quantum phenomena that requires this entanglement. If one assumes an independent existence of quantum objects between measurements, which is possible even in RWR-type interpretations, then one could say that they become entangled, although, if one adopts an RWR-type interpretation, the nature of the reality defining this entanglement is beyond representation or knowledge or even conception. $\psi $-functions never represent either the ultimate reality responsible for quantum phenomena or quantum phenomena and thus the outcomes of measurements. They do not represent these outcomes even if one adopts a realist view of $\psi $-functions as representing what happens between measurements because one needs Born’s rule added to the formalism to predict the probabilities of these outcomes, described by classical physics.

After a preliminary measurement of the momentum of the diaphragm, we are in principle offered the choice, when an electron or photon has passed through the slit, either to repeat the momentum measurement or to control the position of the diaphragm and, thus, to make predictions pertaining to alternative subsequent observations. It may also be added that it obviously makes no difference, as regards observable effects obtainable by a definitive experimental arrangement, whether our plans of considering or handling the instruments are fixed beforehand or whether we prefer to postpone the completion of our planning until a later moment when the particle is already on its way from one instrument to another.[2] (v. 2, p. 57).

## 5. “Perhaps the Biggest Change of All the Big Changes in Physics”: Quantum Measurement, Quantum Objects, and Elementary Particles in QFT

_{4}is the identity matrix)

^{+}, W

^{−}, and Z, or strong (gluons).

^{†}, each lowering or increasing a number of particles in a given state by one. In RWR-type interpretations, these operators do not represent any physical reality: they only enable one to calculate the probabilities or statistics of the outcomes of experiments, just as the wave functions do in quantum mechanics. Both, to return to Schrödinger’s language, provide expectation-catalogs for the outcomes of possible experiments. Those provided by QFT give probabilities or statistics of the appearance of quantities associated with other types of particles even in experiments initially defined by a particle of a given type. In QFT regimes, it is, again, meaningless to ever speak of a single electron even in the hydrogen atom.

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## Acknowledgments

## Conflicts of Interest

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**MDPI and ACS Style**

Plotnitsky, A. Nature Has No Elementary Particles and Makes No Measurements or Predictions: Quantum Measurement and Quantum Theory, from Bohr to Bell and from Bell to Bohr. *Entropy* **2021**, *23*, 1197.
https://doi.org/10.3390/e23091197

**AMA Style**

Plotnitsky A. Nature Has No Elementary Particles and Makes No Measurements or Predictions: Quantum Measurement and Quantum Theory, from Bohr to Bell and from Bell to Bohr. *Entropy*. 2021; 23(9):1197.
https://doi.org/10.3390/e23091197

**Chicago/Turabian Style**

Plotnitsky, Arkady. 2021. "Nature Has No Elementary Particles and Makes No Measurements or Predictions: Quantum Measurement and Quantum Theory, from Bohr to Bell and from Bell to Bohr" *Entropy* 23, no. 9: 1197.
https://doi.org/10.3390/e23091197