1 THE PURPOSE OF THIS ESSAY
It is a long established practice to employ two kinds of mechanics in explaining how nature behaves and why she does so, classical and quantum. Classical mechanics successfully explains the external relationships which obtain between the objects we encounter in our experience. It takes these objects to be material points possessed of a mass and described by their location with respect to a relatively fixed system of reference. Their motion, attributed to their interaction with all other objects, is then described by the change of that location with time as measured by a clock at rest in the chosen system of reference. The focus of classical mechanics is to determine the future location of these natural objects from their known location at the present time. Therefore, classical mechanics conceives of nature as a fully interactive, and completely deterministic, system of moving material points.
That natural objects also have an inside is as immediate an experience as is that they have an outside. Because any attempt to directly experience the inside of things by breaking them up only reveals the external relationship between the resulting pieces, the scientific project takes the inside of natural objects to be no different from their outside. From the earliest of times, objects were thus conceived to consist of certain constitutive entities and their inside was reduced to the external relationships which obtain between those entities. Quantum mechanics successfully ascertains the relationships that these constituents must have to each other if they are to fully explain those properties of natural objects which are attributable to their inside. Unlike classical mechanics, however, this mechanics is not deterministic. The future of a system governed by this mechanics cannot precisely be determined from its present; only the probability of a possible future for it can be precisely ascertained.
The problem is that, although not immediately accessible to our unaided senses, the constituents of natural objects were nevertheless universally conceived to be of the same kind with the objects we routinely encounter in our experience and the mechanics describing their motion ought consequently to have been classical. That it was not, bothered the founding fathers of quantum mechanics immensely. The great controversy concerning the difference between the two mechanics and the apparent need for using both of them consumed the scientific community of the time for the better part of a quarter century and became known as the great crisis in physics.
The older generation, represented by Planck, Einstein and Schrödinger, focused upon the puzzling fact that objects of the same nature should be described by two different theories and attributed the probabilistic character of quantum mechanics to a temporary failure of that theory to completely capture the external relationships extended by the constituents of matter to each other. The younger generation, represented by Heisenberg and Dirac, believed the new mechanics to be a complete description of those constituents and focused instead on developing a mathematical structure capable of accounting for all known experiments involving them. Bohr, stood alone in this debate bestriding the two camps. He believed with the younger generation that the new theory was complete as given but understood the significance of the philosophical issues raised by the older generation.
However, when the creators of quantum mechanics insisted that their theory was in fact complete, they only meant to say that no questions beyond those included therein were permissible. They took the position that, while the constituents of natural things were indeed of the same nature with the things that they constituted, one could not however access them experimentally as completely as one could natural things. We could, for instance, allow a single linearly polarized photon to impinge upon a tourmaline crystal and then seek for it beyond the crystal. The result of doing so is that we sometimes find the photon on the other side of the crystal and sometimes we do not. When we do, the photon polarization is found to be perpendicular to the crystal’s optical axis. But, we are not allowed to inquire about the manner in which the passage actually occurs and how the polarization changes during that passage:
The reasons why a given photon will traverse or not the crystal, and the manner in which its direction of polarization will change when it does traverse it, cannot be experimentally examined and are therefore to be considered extraneous to the scientific domain.
P.A.M. Dirac, The Principles of Quantum Mechanics (1930)
According to Dirac, the experimental examination of the passage is forbidden by the uncontrollable perturbation such examination would inflict upon the photon whose progress through the crystal we wish to follow:
We must assume that there exists a limit to the delicacy of our observational equipment, and consequently a lower limit for the degree of perturbation which accompanies the observation itself, that is intrinsic to the nature of things, a limit which cannot be surpassed through better observational technique.
The position is that questions which require direct observation of a quantum object for their answer would have to be excluded from the theory because the inevitable mismatch between the size of the experimental equipment one would use to observe such an object and the size of the object under observation renders a specific answer impossible by uncontrollably disturbing that object; only the probability of such specific answers is possible. It is not that the photon does not actually pass through the crystal as any other particle would through a corresponding obstacle, but rather that we are not allowed to know the specifics of its passage through the crystal because we cannot experimentally follow it on its course without uncontrollably disturbing its motion. There is an insurmountable limit to our knowledge of a quantum object.
By taking this epistemological position, the founders of quantum theory succeeded in creating a mathematical structure able to account for all experiments conducted to investigate the constituents of matter, but left the question concerning the need for employing two mechanics exactly where they found it. Therefore, while the original discomfort with the need to have two distinct mechanics subsided eventually, it never did fully disappear. A cottage industry of occasional papers endeavoring to render the unconventional character of the new mechanics palatable lives peacefully alongside mainstream science. While it offered over the years highly imaginative explanations of how the statistical nature of the theory comes about, this industry never managed to convincingly dispose of the issue as witnessed by its continued existence; people still feel a compulsion to seek an interpretation of quantum mechanics:
Nearly 90 years after the theory’s development, there is still no consensus in the scientific community regarding the interpretation of the theory’s foundational building blocks.
M. Schlosshauer, J. Kofler, & A. Zeilinger A Snapshot of Foundational Attitudes Toward Quantum Mechanics (2013)
Clearly, there is something hidden behind the split of science into two mechanics, something we failed to understand, something that will not go away just because the formalism of quantum theory transforms itself continuously into that of classical theory as the size of its object grows large and because using them together in this fashion appears to work. It is the purpose of this essay to seek after that something. The essay is therefore focused on understanding why the division into two mechanics occurred, one describing natural things and another describing their constituents; whether the split was accidental or a necessary consequence of the structure of the scientific project; whether science can still return to the status quo ante-crisis and then surpass the divide by developing a monolithic structure which encompassed the divided halves within its boundaries; and whether anybody should even want to do so.
We shall take our clue for how to examine the structure of the scientific project in search for that something from the following observation. To talk, as the epistemological position does, about disturbing quantum objects subjected to observation is to concede that such objects are already there to be subsequently disturbed. That raises the question of what these objects were like before they were thus observed. From the very beginning, the epistemological position took it tacitly for granted that the constituents of things existed objectively and were much like the things that they constituted, but was subsequently forced to burden those constituents with properties which rendered them quite unlike anything we had ever encountered in our experience. For instance, we recall that anytime an observation of a photon’s polarization is attempted with the help of a tourmaline crystal, the photon is found to be in one of two possible states but that we cannot predict which of those polarization states obtains. To deal with this situation, quantum mechanics was forced to conceive of the photon prior to the act of observation as Being in both those states of polarization at the same time. This suggests that the objects we encounter in our experience and the objects which we have assumed would constitute them must be ontologically quite different. The epistemological position concerning the limit of our knowledge about the constituents of matter thus becomes an ontological one concerning their Being. The fundamental question is no longer how much can one know about the constituents of things but rather what exactly are they? What, for instance is a photon or an electron? The question is not concerned with the way in which the electron is different from a photon, or any other atomic object for that matter, but rather with the thinghood of either of them. It is not about their specific attributes—such as mass, charge, spin—but about their being something rather than nothing at all and the manner in which they are something.
Postponing the ontological question in favor of an epistemological one concerning the bounds of human knowledge by forbidding questions concerning the Being of constituents of matter was perhaps the right thing to do at the time; it enabled the scientific community to focus all its energies on much needed theoretical development rather than allowing it to dissipate that energy in endless discussions concerning the nature of the objects the community was studying. In time, however, the development of theory became all-consuming and questions concerning the nature of the constituents of things were forgotten. As a place holder for this legitimate question, the scientific community began to think of these constituents as abstract entities corresponding to elements of the theory they were developing and of the theory as simply a model. If the theory fitted the experimental results, or so the argument went, then the ontological nature of the entities involved in that theory was not really of much practical importance and the fact that the mechanics describing them was not classical mechanics was something the community would have to simply learn to accept.
But this casual drifting into abstraction at the detriment of ontology will not do. It is not reasonable to take the constituents of things as abstract entities and still insist that those things are real; the constituents themselves must have some measure of objective reality if they are to serve the purpose for which they had been conceived of in the first place. Therefore, asking about their Being is not only legitimate but also necessary. Moreover, without a clear idea of what the constituents are, it is not even possible to assign a precise meaning to the proposition, so fundamental to the epistemological position, that only those statements be allowed into science which can be verified by experimental measurement. Conventionally, an experimental measurement involves approaching the thing whose properties one attempts to measure with the experimental apparatus one uses for that purpose. However, in the case of the constituents of things, such a procedure would not be directly possible because, by the very presuppositions of the theory describing them, they are abstract entities, and abstractions cannot not be encountered. The ontological question concerning the Being of a quantum object thus requires that we re-examine not only what we mean by an electron but also what quantum mechanics means by an experiment designed to measure its properties.
By thus revisiting the structure of modern science with particular attention to its ontological side the essay finds that the constituents of matter are different from the ordinary objects we encounter in our daily experience and that ignoring the difference not only demands that quantum mechanics should be strange, but it also explains why it is strange in the particular way in which it is so. The principle of complementarity, the quantization of energy, the statistical character of the theory, the superposition principle, the reduction of the wave function, and the entanglement of states are all the direct result of misrepresenting the particular manner in which atomic entities are.
But, questions concerning the Being of the objects constituting the realm of a science properly belong to philosophy rather than to science:
The scientific methods have been developed precisely in order to explore beings. But they are not suited for examining the Being of these beings.
Martin Heidegger, Phenomenological Interpretation
of Kant’s Critique of Pure Reason (1927)
By raising the ontological question, this essay is therefore forced to employ a language which is neither all philosophical nor all scientific. For all that, the essay is not properly philosophy of science either because that discipline appears to be dominated by a community which is no longer engaged in questioning research; for them quantum mechanics is a fact that must be analyzed, not a question to be answered. To the extent that we employ philosophical questioning to seek the meaning of our science, we are rather in the tradition of the founding fathers of quantum mechanics who most certainly did.