Structural Realism and Evolution

In studying the history of physics, especially the formation of physical theories and concepts, one will discover that development always takes place on two different layers — on a formal, mathematical level on the one hand, and as a conceptual, verbal formulation on the other. In my book, ‘Die Entdeckung des Unvorstellbaren’ [1], this is explained in detail.

The layers are not only different in their language — mathematical here, upscale vernacular there — but also in their development. New theories arise only on the first layer, in the form of tangible mathematical relationships between experimentally accessible quantities. But thereby, further quantities requiring interpretation also come into play. Often, a satisfying understanding of the significance of these additional variables lags behind, such as in the perception of the electromagnetic field or the probability amplitude in quantum mechanics.
Some differences can also be seen in the state of examinations and enhancements by a more comprehensive theory. The basic equations of a theory always remain valid and useful; however, the interpretation and meaning of the quantities involved may change. Newtonian mechanics still serves for the calculation of the motion of classical bodies at velocities considered small compared to that of light, and Maxwell's fundamental equations and their offshoots continue to provide the right results for all electrical and magnetic phenomena of our everyday lives. If there should be a change at this formal mathematical level, then it occurs in time periods that we have not yet passed.

The meaning of new quantities, which are introduced into the equations by some mathematical symbols, may, however, enable significant developments over the centuries. For example, in the 17th Century, light was considered as a ray of corpuscles, i.e. very small particles of matter. At the beginning of the 19th Century, however, one came to the conclusion that light is a wave in the ether, an all-pervasive subtle substance, and then, at the beginning of the 20th Century, Albert Einstein showed that light is neither a wave nor a particle, but a ray of ‘a finite number of energy quanta localized at points in space which move without dividing and which can be absorbed and created only as a whole’. With another ingenious idea that led to the theory of special relativity, Einstein could furthermore explain that the concept of ether was totally unnecessary, and thus, a substance in the inventory of concepts in physics had simply disappeared. Likewise, it was only some 50 years ago that the concept of ‘caloric’ vanished; for a long time many had assumed that this substance was responsible for the heat of a material body, until the theory that heat is a random motion of atoms or molecules of a substance finally prevailed, and nobody spoke further about caloric.

You may call the first layer that of mathematical relations and structures, and the second the layer of the substances. History clearly shows that on the structural layer, one always has more solid ground under one’s feet than on the substantive. Current research takes place at the structural layer; this provides the best prospect for a consensus, and this is, in fact, always achieved when the experiments speak clearly. But heated discussions can give the interpretation to the question — what do they mean, these newly gained insights about new entities of this world and its properties? As a matter of fact, the discussion about the interpretation of quantum mechanics is still in progress.

The French physicist Henri Poincaré has described these two layers already, in his 1904 book ‘Science and Hypothesis’ [2]. Inspired by the reading of this book, in 1989, the English philosopher John Worrall formulated the thesis that ‘our scientific theories do not provide objective, but a structural approach to the world’, and thus introduced ‘Structural Realism’ [3]. As is typical for any philosophical position, this again split into numerous refinements, which can roughly be divided into ‘epistemic’ and ‘ontic’ variants. They differ in their claim about the ‘carriers of the structures’, i.e. the objects for which we recognize the relations. In the epistemic variants, it is claimed that we cannot recognize them in principle, in the ontic variants they do not exist at all.

As absurd as the ontic variations appear at first (at least to a physicist), one should not forget that the caloric and the ether recall situations in which, even with substances that do not exist, one could achieve quite respectable explanations for a certain time. Why do we feel assured that the objects of our present theories really exist? Perhaps in the distant future, some of these will suffer the same fate as the caloric. In a radical form, this ‘argument of the pessimistic meta-induction’ may even lead to an anti-realism, in which a correspondence between our theories and the reality is negated.

On the other hand, no one can deny the predictive and explanatory success of science, and the impressive development of ever more sophisticated technical equipment constitutes, for the outsider, a strong sign of a correspondence between our theories and reality. However, it is always the knowledge of the relations and structures that are exploited, not our view on the ontological status of entities. If we are playing with a camera, experimenting with quanta, we can do that successfully, because we know what the consequences of our actions are on the object, how the possible states of the object are related by our actions. The question of what a camera or a quant is does not arise. Thus, it is not the structures, but the carriers of the structures which give rise to many problems. That is what we have also seen in the history of physics.

Variants of the ontic structural realism are thus quite intensely discussed in the philosophy of modern physics (see e.g. [5] and the literature therein), on the basis of the findings in quantum mechanics and quantum field theory. In quantum mechanics, for example, one becomes acquainted with entities which lack a property that we naturally expect from an object existing in reality — that all its measurable traits should possess definite values. A rigid body, for instance, has at any time a certain position, and equally certain values for its speed and orientation, in space. The state of a quantum, however, is comprehensively characterized by a function which only contains information about possible, in many cases quantized, values of the traits, and their probabilities of being realized, e.g. in a measurement. Furthermore, a so-called entangled state, e.g. of two quanta, poses difficult questions about the individuality of the individual quanta. All of these aspects are incorporated into the discussion of ontic structural realism by the philosophers of physics.

Amazingly enough, however, the fact that our cognitive ability is a product of evolution is nowhere taken into account - but that should not be ignored. Of course, it is difficult to draw compelling conclusions from that fact. It may happen that conflicting observations can be viewed with the same rights as compatible with an evolutionary origin, but that has to be expected: evolution includes adaptation to the environment, and a characterization of a particular environment can rarely be achieved so precisely that a stringent conclusion can be drawn. There may, at most, be fairly plausible arguments.

For instance, it is highly plausible that we, as humans, are better at the detection of rules and relationships than understanding the nature of things. In order to survive, rules have been more important than the objects themselves. It was crucial that man could spark and feed a fire — what fire actually is was of secondary importance. The knowledge of whether such rules and relations are functioning is always preserved and cannot be returned. This also includes the knowledge that a theory is consistent with observations within impressively wide limits. Therefore, the dominance of structures and relations in the light of biological and cultural evolution is not surprising.

Concerning our access to the entities of the world, one can state, in the light of the evolutionary origin of our cognitive ability, at least the following: First, one has to be aware of limits or restrictions; however, one should not believe that one could recognize these boundaries from the outset. Secondly, our exposure during the evolution may be reflected in the nature of our cognitive ability; there may be gradations in the ‘epistemic access’. Entities of the ‘world of medium dimensions’, i.e. of our everyday world, to which we have adapted during evolution, are certainly more accessible for us than those of the worlds of the smallest and largest dimensions. We have developed an imagination for particles of ‘human’ size because we constantly deal with such entities (see e.g.[ 6]). Quanta, however, have been found to be objects which are incomparable to anything that we know from our progress during evolution. Therefore, they are unimaginable to us. Here, the limitation of our evolutionary origins becomes manifest, and, considering that future generations will develop an even deeper understanding of the nature of the quanta, one may conclude that we may never know definitively what the carriers of the structures are in ‘realness’. Any speculation about an end of the development towards an increasingly better understanding makes no sense, because we are certainly not provided with the appropriate concepts and ideas.

Thus, the consideration of the evolutionary origin of our cognitive ability adds a new aspect to the discussion about the interpretation of quantum mechanics. One can come to terms with the Copenhagen interpretation of quantum mechanics, especially with the idea of the non-reality of quanta; you do not have to escape to other interpretations, such as the many-worlds interpretation, in order to save one’s classic world view.

By this consideration, the fronts in the debate about structural realism are also shifted. The dominance of the relations and structures remains preserved, and appears even greater. Reality and non-reality get a contour — non-reality now belongs to the ‘true nature’ of nature, and reality appears only at a complex level. The epistemic accessibility of structures and relations is obviously more far-reaching than our imagination, which was only confronted in the course of evolution with the objects of everyday life. At the layer of structures, we will comprehend the world better and better; on the layer of objects, the entities will become more and more alien to us.

1. Josef Honerkamp: "Die Entdeckung des Unvorstellbaren - Einblicke in die Physik und ihre Methode", Spektrum Akademischer Verlag, 2010

2. Henri Poincaré: "Wissenschaft und Hypothese", (autorisierte deutsche Ausgabe von F. und L. Lindemann), Teubner, Leipzig, 1904

3. John Worrall: "Structural Realism: the Best of Both Worlds", Dialectica, Vol. 43, 99, 1989

4. Structural realism:  http://plato.stanford.edu/entries/structural-realism/

5. Michael Esfeld and Vincent Lam: “Ontic structural realism as a metaphysics of objects”, in Alisa and Peter Bokulich (eds.): Scientific structuralism. Dordrecht: Springer 2011. Chapter 8. Paper available at
http://philsci-archive.pitt.edu/5531/

6. Vollmer, Gerhard (2005), "How is it that we can know this world? New arguments in evolutionary epistemology," in Darwinism & Philosophy, (eds.) V. Hösle and Christian Illies, Notre Dame, IND: University of Notre Dame Press.




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