5.1. Symmetry Study as Methodology for Structural Analysis in Science
About half a century ago, for the first and last time, there was hope for building a bridge across all disciplines including the humanities, science, and mathematics in the form of structuralism. The story of structuralism is probably the closest to the Biblical story of The Tower of Babel.
It is difficult to find a term of more universal use in all contemporary domains of human inquiry than “structure”. This does not mean that people who use this term can define it or explain its meaning. If asked about the meaning, people would refer to the explanation from a dictionary that structure is an organization, arrangement of parts, elements, or constituents of a complex system, considered from the point of view of the whole rather than of any particular part, etc. The terms “organization” or “arrangement”, in turn, are explained in dictionaries with the use of the word “structure”. Once we restrict the term structure to a particular discipline, we can find an increasingly precise definition of its meaning. The concept of a structure is convoluted with another concept of symmetry. Both were born in the mid 19th century to replace the traditional general ideas of form and harmony, respectively. The marriage of these concepts had, as its offspring, the formalization of the concept of structure in terms of symmetry, understood as invariance with respect to transformations.
The question about the common meaning of geometric structures considered in the different forms of geometry led to the modern general methodology for structural analysis in mathematics and mathematical sciences. This methodology involved the concept of symmetry. Up to the late 18th century, symmetry was usually conceptualized as a harmony of proportions [
38]. It can be a surprise that although its modern understanding can be traced to earlier, the precise definition of symmetry in its simplest mirror type was provided by Ernst Mach in 1872 [
38], in the same year that the entire methodology of the symmetry study was born in the Erlangen Program of Felix Klein [
39]. Klein proposed a new paradigm of mathematical study focusing not on its objects, but their transformations. His mathematical theory of geometric symmetry was understood as an investigation of invariance, with respect to transformations of the geometric space (two-dimensional plane or higher dimensional space).
Klein used this very general concept of geometric symmetry for the unification of different types of geometries (Euclidean and non-Euclidean), and the classification of different geometric structures within these geometries. The fundamental conceptual framework of Klein’s Program (which was intended by Klein as a paradigm of study, and became such paradigm on a scale not expected by him) was based on the scheme of (1) space as a collection of points → (2) the algebraic structure (group) of its transformations → and (3) invariants of the transformations, i.e., configurations of points that do not change as a whole, while their points can be permuted by transformations. Selections of algebraic substructures (subgroups) of transformations correspond to different types and levels of invariant configurations, allowing the differentiation and comparison of structural properties associated with symmetry. The classical example of mirror symmetry (symmetry with respect to the surface of the mirror) can be identified with invariance with respect to the mirror reflection, understood as a transformation of the entire space.
Klein’s work applied a new theory of groups which in the works of Arthur Cayley [
40] and Camille Jordan [
41] became a part of algebra. Klein’s Erlangen Program to classify geometries has been extended to many other disciplines of mathematics, becoming one of the most common methods of in all mathematical research. The new analytical tool was very soon adapted to studies in theoretical physics.
Group theory was originally “preconceived” in the early 19th-century work of young Evarist Galois in his study of the impossibility of solving polynomial equations of degrees higher than four (the actual definition of a group was introduced several decades later). Galois considered invariance of the solutions for equations under transformations of the set of numbers that can be substituted for the variable. This line of thinking was investigated later in the mid 19th century by James Joseph Sylvester and Arthur Cayley in the context of solving equations. This led to the natural question about the invariance of physical equations under transformations of physical coordinates.
It was quickly recognized, under the influence of the Klein Program, that in classical mechanics, the equations have to be invariant with respect to the group of transformations of coordinates, which was called the Galilean group. This group was, and is, called Galilean because it consisted of the transformations which Galileo considered several centuries earlier when he observed that the description of reality has to be independent of the choice of the position, orientation, linear motion with a constant velocity of the observer, and of the choice of the time for observation. It turns out that the equations of Newtonian mechanics are invariant with respect to the Galilean group of transformations, but curiously, Maxwell’s equations for electrodynamics are not. The latter equations turned out to be invariant with respect to another group of transformations recognized in 1905 by Henry Poincare, which he called the Lorentz group. This was the group with respect to which relativistic mechanical equations are invariant (the full group of transformations, including the Lorentz group, for which they are invariant was, in turn, called the Poincare group by Herman Minkowski in 1908).
The transition from classical to relativistic mechanics started to make sense as a change in the type of symmetry with different geometry (change from Euclidean geometry to the geometry of Minkowski space) and with the change in invariant physical magnitudes. In this new description of reality, the separate Galilean group invariant magnitudes of mass and energy are combined into the one Lorentz group invariant magnitude of mass-energy.
However, a bigger, Copernican-type conceptual revolution came a little bit later. The transition from classical to relativistic mechanics, in terms of the change in symmetry groups from the Galilean to the Lorentz or Poincare group, was a realization of the Klein Program in physics regarding the change in geometry. The change in the invariant physical magnitudes from separate mass and energy to united mass–energy was a welcome gift of great theoretical and practical importance (its consequence is the most famous equation of physics: E = mc2).
5.2. Copernican Revolution of Symmetry in Physics
One of the most celebrated achievements of 19th-century physics, expressed as the Law of Conservation of Energy (i.e., the First Law of Thermodynamics), was interpreted as an expression of the ontological status for an alternative form of physical entities. Energy was an alternative to matter, associated with the Law of the Conservation of Mass. Until the 19th century with the dominating Newtonian corpuscular theory of light, the concept of matter was associated with the atomistic tradition founded on the distinction matter-vacuum. It was meant, to belong in the realm of the Cartesian res extensa. The wave theory of light and the development of electrodynamics, which introduced electromagnetic waves transmitted through a vacuum, made the earlier atomistic distinction matter-vacuum meaningless.
At first, there was hope that this distinction could be retained if electromagnetic waves were the waves of the aether, an exotic form of matter filling out the entire space. The end of the 19th century was the end of this hope. Special Relativity theory eliminated aether, but also united mass and energy into mass–energy, restoring the uniform ontological status. This may explain why even today, anachronisms such as “matter and energy” finds their place in philosophical discussions when in physics, the actual ontological distinctions are along the dualisms of wave-particle or field-particle.
A Copernican revolution in the understanding of conservation laws was a consequence of one of the most important contributions to mathematical physics of all time, published in 1918 by Emmy Noether [
42] and stating that every differentiable symmetry of the action of a physical system has a corresponding conservation law. Noether showed that the conservation laws for physical magnitudes such as energy, momentum, and angular momentum are associated with transformations describing changes of reference frames, i.e., observers. Thus, it is not true that we have given, in advance, distinct physical entities with corresponding magnitudes that obey conservation laws, and for which we can find fundamental equations that are invariant with respect to some groups of symmetries.
The roles are reversed. If we have a general description of a physical system and we want to render this description objective in the sense that every theoretical observer of the system, free from the action of external forces, describes the reality the same way (i.e., the description is the same in every inertial reference-frame equivalent with respect to symmetry group transformation), then with each type of symmetry, there is a corresponding magnitude conserved in time. Conservation of energy is a consequence of invariance with respect to the time shift. Conservation of momentum is a consequence of invariance with respect to space shift. Conservation of angular momentum is a result of invariance with respect to the rotation of the reference frame.
This, in fact, answers a naïve but legitimate question: “What does make ½mv2 better than ½mv3 as the description of kinetic energy?” The answer is that the former is invariant with respect to theoretical changes of observers (i.e., reference frames) in the case of an isolated physical system in the absence of forces, while the latter is not invariant at all.
Therefore the distinguished physical magnitudes satisfying the corresponding conservation rules are determined by the choice of symmetry transformations, and those are determined by the condition of equivalence of all possible observers. Naturally, this makes the study of symmetry a central tool for scientific methodology. Physics (and science in general) looks for an objective description of reality, i.e., a description that is invariant or covariant with changes of observers. Noether’s theorem tells us that such a description can be carried out with the conserved magnitudes. This is why the expression “matter and energy” does not make sense in physics. What is the group of symmetry for which matter is invariant? What does it mean that matter is invariant?
5.3. Symmetry Climbs Comte’s Ladder
The year 1872, when the Erlangen Program was published, can be considered a starting point for the study of symmetries; this was clearly defined in terms of group theory, but not in terms of the scientific exploration of symmetries studied before the concept of symmetry was formalized. The intuitive recognition of the similarities and differences between some configurations of points and their mirror reflections generated the interest of the greatest minds for quite a long time. For instance, Immanuel Kant tried to rationalize the distinction between human left and right hands (although they are different, they are mutual mirror images), but his hypothetical argumentation that in a world in which God would have created humans with the one hand only, this hand is neither left nor right, is not very convincing. Sooner or later, humans could invent a mirror and could realize that there is an alternative form for their single hand. More important is that Kant’s reflection did not contribute much to the understanding of mirror symmetry.
The structural characteristic that gives the distinction of left- and right-handedness was given the name of chirality by Lord Kelvin much later, but their distinction could be recognized easily thanks to our everyday experience with our hands and the gloves that have to match them. Thus, either of our hands is chiral, and they are enantiomorphs of each other, while the majority of simple organisms are symmetric with respect to all rotations and reflections, and therefore achiral.
In 1848, Louis Pasteur published one of his most important papers, explaining the isomerism of tartrates, more specifically of tartaric acid by molecular chirality (“left- or right-handedness” of molecules) [
43]. He showed that the differences in the optical properties of the solutions of this organic compound between samples synthesized in living organisms and samples synthesized artificially result from the fact that artificially synthesized molecules—although constructed from the same atoms as those in natural synthesis—have two geometric configurations; he concluded that they are symmetric with respect to the mirror reflection, but not exchangeable by spatial translations or rotations (in the same way as left and right palms of human hands); conversely, he showed that in the nature, only left-handed configurations occur. Later, it turned out that almost exclusively naturally synthesized amino acids (and therefore proteins) are “left-handed”, and sugars are “right-handed”. Artificial synthesis, if not constrained by special procedures, leads to the equal production of left and right-handedness. There is no commonly accepted explanation of this mysterious phenomenon, even today.
The chirality of organic molecules became one of the most important subjects of 19th-century biochemistry, leading to the discovery of the role of atoms of carbon in the formation of chiral molecules formulated into the Le Bel–van ’t Hoff Rule, published by these two researchers independently in 1874.
The study of symmetry in biology, particularly of chirality in complex organisms, could not have been explained in the 19th century; however, researchers published some phenomenological laws of evolution and phenotypic development of organisms, such as Bateson’s Rule. Much later Bateson’s son Gregory explained this rule in terms of information science [
44,
45].
A similar interpretation can be given to Curie’s Dissymmetry Principle. Pierre Curie made so many important contributions to physics and chemistry that this fundamental principle of great philosophical importance is rarely invoked. The outdated original formulation, using the term “dissymmetry” instead of the now commonly used “asymmetry”, was: A physical effect cannot have a dissymmetry absent from its efficient cause [
46]. This rather unintuitive principle has very important consequences in biology and chemistry. The real importance of these early developments could be fully appreciated half a century later when it became fully clear, thanks to advances in physics (elementary particle theory), that the study of the conditions for maintaining symmetry is no more important than the study of breaking symmetry.
By the mid 20th century, the study of symmetry became a fundamental tool for mathematics, physics, chemistry, and several branches of biology. This can explain the explosion of the interest in symmetry among philosophers. The swing of the pendulum of the dominating philosophical interests between the tendency to seek an objective methodology for philosophical inquiry, inspired by scientific methodology, and the calls for freedom of the use of introspective, and therefore subjective, phenomenal experience, reached the apex of the former. The most influential expression of the alignment of the humanities with science was in structuralism.
5.4. Structuralism or Many Structuralisms?
Although the generic term “structuralism” was already in use in the late 19th century in the context of mental structures in the psychology of Wilhelm Wundt (for instance, in the description of Wundt’s position by his student Edward B. Titchener), the beginnings of structuralism, understood as a broad methodological perspective, can be traced most directly to the works of Ferdinand de Saussure on linguistics (more specifically his lectures from 1907–1911, posthumously published by his disciples in 1916 as
Course in General Linguistics [
47]). The emphasis on the structural characteristics of language and their synchronous analysis prompted increased interest in the meaning of the concept of structure, although de Saussure himself used the term “system” rather than “structure”. It is only speculation, but it seems that the words “structure” and “system” gained their popularity in the 19th century in parallel to the decline in the use of the term “form”, due to the latter’s luggage of associations to its use in diverse meanings in philosophy through the centuries. Through the association with de Saussure, the concept of a structure acquired an implicit characteristic of synchrony. In disciplines in which diachrony was fundamental, such as biology, the preferred dynamical concept of morphogenesis, popularized by Goethe, appended the idea of structure expressed as morphology. We should not be deceived by terminological preferences. In all cases, the central concept was of a structure, viewed either statically or dynamically; by the end of the 19th century, this concept had replaced in science the concept of form. Klein’s Erlangen Program, originally formulated for geometry, provided the pattern of a methodological tool for mathematics, and soon later, for physics.
It was a natural consequence that the tools used in science for structural analysis in terms of symmetry found their way to psychology, anthropology, and philosophy.
The clearest programmatic work
Structuralism by Jean Piaget, published originally in 1968, refers explicitly to the concept of the group of transformations, although very little of the formal apparatus was presented there [
48,
49]. On the other hand, Piaget, in his work on developmental psychology, used this methodology explicitly. For instance, he based his theory of child development on the so-called Klein’s “Four-group”. The works of others, for instance, Claude Levi-Strauss, also directly employed the methods developed as a consequence of the Erlangen Program, and included the use of Klein’s group too [
50].
This was the time in which structuralism was triumphant, but also a time of great confusion. The popularity of structuralism made its name a buzzword, and everything written at that time with the word “structure” was (and unfortunately still frequently is) associated with structuralism. Of course, nobody owns the name of structuralism and there is nothing wrong with using it for different purposes. However, mixing these different uses and the resulting misattributions of views are errors.
Piaget should be prized for the popularization of the idea of structuralism as a broad philosophical direction of thought, but his postulate to use the concept of a structure as a bridge between the scientific and humanistic forms of inquiry was preceded by the short but very influential 1952 book
Symmetry, written by Hermann Weyl [
51]. Weyl did not use the name structuralism, but demonstrated the use of the method of Klein’s Erlangen Program in studying structures from mathematics, physics, crystallography, and biology, to art, design, etc. In his view, the study of structures was the study of the invariants of transformations (more exactly, groups of transformations).
It was a time when both terms “structure” and “symmetry” had already established fundamental roles in mathematics, physics, chemistry, and biology. A more elaborate exposition of these roles in the present context of their unifying power is presented by the author elsewhere, in the study of the question “What is a structure?”, carried out with the use of, or reference to, rather advanced mathematical formalisms [
52]. However, to prevent confusion, it is necessary to disentangle some ideas before we proceed to further discussion of the methodological tools that structuralism, based on the symmetry concept, can offer for transdisciplinary studies.
Piaget’s book
Structuralism generated enormous interest among readers belonging to a very wide audience, although in its Conclusion, he already complains that “[…] one can only be disturbed by the current modishness of structuralism, which weakens and distorts it” [
49] (p. 137). Thus, the book was intended as a means to clarify the confusion that often comes with popularity. Unfortunately, it also generated a lot of misunderstandings, possibly partially because of the differences between its original French edition and its English translation. In the following, I will refer to the English version. This could have been prevented if Piaget gave a reference to the much earlier book
Symmetry by Herman Weyl (whose different book on a different subject he quoted).
Piaget prizes Klein’s Erlangen Program as “a prime example of the scientific fruitfulness of structuralism” [
49] (p. 22) and provides its explanation, but makes it so oversimplified that it does not make much sense. Statements such as “Groups are systems of transformations; but more important, groups are so defined that transformation can, so to say, be administered in small doses, for any group can be divided into subgroups and the avenues of approach from any one to any other can be marked out” [
49] (p. 21), or “Group structure and transformation go together. However, when we speak of transformation, we mean an intelligible change, which does not transform things beyond recognition at one stroke, and which always preserves invariance in certain respects” [
49] (p. 20) are nonsensical. What is meant by “preserves invariance in certain respects”?
Piaget made it clear that structuralism, or to use his words, “structuralism in general”, is a descendant of Klein’s Erlangen Program: “In this little book we shall, therefore, confine ourselves to the kinds of structuralism that are to be met in mathematics and the several empirical sciences, already a sufficiently venturesome undertaking. […] But first we must elaborate somewhat on the definition of the structuralism in general that is here proposed, else it will be hard to understand why a notion as abstract as that of a ‘system closed under transformation’ should raise such high hopes in all domains of inquiry” [
49] (p. 6).
This may explain the bizarre formulation of his presentation of Klein’s ideas, which he might have considered easier to understand for those who abhor abstraction. Whatever his intention, some of his statements are confusing, and some are confused. For instance, in the passage “Indeed, all known structures – from mathematical groups to kinship systems — are, without exception, systems of transformation. But transformation need not be a temporal process {…}” [
49] (p. 11), he is obviously right in that symmetry is an invariance with respect to transformations that do not have to be temporal, and that what is invariant is structure; however, it is the invariant of a group of transformations, not a “system of transformations.”
Thus far, we can talk about the confusing formulation of some claims. The real problem starts when Piaget makes claims that are meaningless or explicitly inconsistent with the mathematical description of structures as invariants of transformations: “In short, the notion of structure is comprised of three key ideas: the idea of wholeness, the idea of transformation, and the idea of self-regulation” (p. 6). While the idea of transformation (in the mathematical description realized by transformations understood as functions of a specific type) is fundamental for structures, and we can interpret wholeness as the result of invariance, the idea of self-regulation does not have any meaning in the structures of mathematics or physics. By introducing the idea of self-regulation, Piaget resurrects the ghost of the systemic, organismic conceptual framework without giving self-regulation any formal meaning.
A similar problem of the error of commission can be identified in the Conclusion, where Piaget writes, in the context of all possible structures: “
There is no structure apart from construction, either abstract or genetic” [
49] (original emphasis, p. 140) and “The problem of genesis is not just a question of psychology; its framing and its solution determine the very meaning of the idea of structure. The basic epistemological alternatives are predestination or some sort of constructivism” [
49] (p. 141). Here, Piaget makes the mistake of mixing two levels of the discourse.
There is nothing in the general inquiry of the structures defined as invariants of transformations that commits us to a particular epistemological or ontological position. These commitments in works of contributors are always posterior to the study of structures. Naturally, from the position of his Genetic Epistemology, transformations can be interpreted as types of constructions, and with this interpretation comes the interpretation of structures as constructs [
49,
53]; however, this is the result of his commitment, not an inherent feature of structures. In any case, Piaget’s interpretation seems artificial when we consider the symmetries of physics. For instance, transformations from the Galileo group or Lorentz group are transitions between potential observers (reference frames). Not only can these transitions hardly be considered constructions, but the transition from Newtonian to Relativistic Mechanics—which, in hindsight, we can associate with the transition from the Galilean to the Lorentz group—was a discovery made against the expectations and the will of physicists involved. Later, we had a string of major discoveries in physics that consisted of surprising cases of breaking symmetry.
Thus far we had examples of ramifications in the understanding of structures and related forms of structuralism. There is no reason to claim that one form is better than the other. We just have to choose one and, in this paper, it is the one that is based on the concept of symmetry, initiated by the Erlangen Program of Klein, and is free from any additional assumptions or interpretations. The reason for the choice is that the task for this paper is to build a bridge between the Two Cultures, and to search for patterns in developing a transdisciplinary methodology.
Thus, it was clarified that we have more than one structuralism, and the one that serves our purpose the best is derived from the Erlangen Program. However, this does not eliminate the confusion. Another source of misunderstanding is a false belief that our preference excludes directions of inquiry of special importance. An example of the apparent contestant to the role of a methodological tool for transdisciplinarity is category theory, introduced in 1945 by Samuel Eilenberg and Saunders MacLane in a long, epoch-making paper,
General Theory of Natural Equivalences [
54]. The misunderstanding is in the relationship between these two directions of thought. First, it should be made clear that the more important idea of this famous paper is that of a functor, understood as a transition between categories that are, themselves, auxiliary concepts.
For those who are familiar with the research genealogy of the subject in which Emmy Noether was a mentor for MacLane, and Felix Klein for Emmy Noether, it should not be a surprise that the work of Eilenberg and MacLane was intended as a continuation of the Erlangen, as this quotation from the Introduction tells us: “The invariant character of a mathematical discipline can be formulated in these terms. Thus, in group theory all the basic constructions can be regarded as the definitions of co- or contravariant functors, so we may formulate the dictum: The subject of group theory is essentially the study of those constructions of groups which behave in a covariant or contravariant manner under induced homomorphisms. More precisely, group theory studies functors defined on well specified categories of groups, with values in another such category. This may be regarded as a continuation of the Klein Erlanger Programm, in the sense that a geometrical space with its group of transformations is generalized to a category with its algebra of mappings” [
54].
Thus, the two directions of thought are not only not in competition, but one is an extension of the other. This may generate a question about whether the the Category and Functor Theory is a better choice for a methodological tool for transdisciplinarity. The answer is that it is a matter of preference. The theory of structures based on symmetry is just less abstract. Most of the research in physical sciences and, of course, in other disciplines is carried out at this lower level of abstraction, so there is no compelling reason to go further. There is a close analogy of the relationship between these two programs of inquiry and the pair of algebraic structures of groups and monoids (the former are special cases of the latter type). In mathematics, if you can carry out something using exclusively groups, you do not introduce the concept of a monoid. If it turns out that there is a need for generalization, you can always achieve it; however, you then have to pay the price of some lost tools that require the eliminated assumptions (in this case, the reversibility of morphisms and the methods of set theory).
There is one aspect of symmetry and structure studies that is worth mentioning here. The Theory of Categories and Functors has its role in mending the historical division of research on symmetries between Felix Klein and Sophus Lie. Klein, in his Erlangen Program, explicitly renounced the exploration of symmetries described by continuous groups studied by Lie, and left it to his friend [
39]. This led to the study of continuous symmetries in terms of the so-called pseudogroups. Emmy Noether’s two famous theorems regarding the relationship between symmetries and conservation laws of physics were in the conceptual framework of continuous symmetries [
42]. Moreover, there is a parallel direction of research in physics initiated by the work of Lie within mathematics—the study of dynamic systems, culminating in the works of René Thom—especially his 1972
Structural Stability and Morphogenesis [
55]—and in the complexity studies of the members of Santa Fe Institute focusing on complex adaptive systems. Although the two directions of research initiated by Klein and Lie have many differences in their methodologies, they do not compete but complement each other. Unforunately, the perception of the general audience of their supposed opposition is biased by the differences in terminology (e.g., structure vs. complex system).
5.5. Is the Paradise of Structuralism Lost?
The swing of the pendulum reversed its direction and in the late 20th century, structuralism lost its dominating position to competitors; however, its importance can be seen in the name of this reversed swing as “Post-structuralism”. Some of this criticism is naïve. For instance, structuralism was criticized as “ahistorical,” “static,” “too much formalized,” and “too much restrictive for the freedom of expression”.
The view of the ahistorical characteristic is most likely a result of mistaken association with the views of Ferdinand de Saussure. In the context of linguistics, de Saussure distinguished the two modes of inquiry: diachronic and synchronic. The synchronic perspective focuses on the structure at some particular moment. However, in a more general context, there is nothing precluding the evolution of structures, as is commonly done in physics. We can see here why the inquiry of structures using the methodology of symmetry is so effective. Structures are invariants of transformations and they are distinguished from their environment by being invariant. Their existence is a resolution of the opposition between change (diachrony) and identity (synchrony). This is the key distinction between structuralism based on symmetry invariance and its other types or versions.
More justified is the objection to the lack of interest in the explanation of the origin of structures considered in the studies of Levi-Strauss and others. The missing evolutionary or dynamic theory of structures can be blamed on these authors, but it is more a matter of the misunderstanding of the mathematical tools than of their absence. Physics and chemistry possess powerful, exact dynamic theories of their structures in terms of group theory and symmetry, so there is no good reason to believe that such a dynamic approach is impossible in other disciplines of philosophy. The most convincing explanation of the shortcomings identified in the applications to the study of culture and society is probably that the mathematical tools of symmetry theory found little use in works of the most prominent propagators of structuralism. Symmetry was more a metaphor for the literary treatment of the subject than an actual study of the invariants of groups of transformations [
56].
Symmetry can easily be identified in the studies of visual arts and music. The structural study of music initiated by Pythagoreans found its way to medieval philosophy via Neoplatonic authors, and then to the works of the founders of modern science such as Johannes Kepler. The music of heavens, understood literally as music produced by the motion of the planets, was a mathematical model of the universe. An example of the highest-quality contemporary study of symmetries in art in a cross-cultural perspective can be found in the book
Symmetries of Culture: Theory and Practice of Plane Pattern Analysis by Dorothy K. Washburn and Donald W. Crowe [
57].
At this time, group theory in the context of symmetries had already become an everyday tool for all physicists and had assumed a permanent place in university curricula for studies in physics, chemistry, and biology [
58]. A statement from an article published in Science in 1972 by a future Nobel Prize laureate in Physics Philip Warren Anderson stating that “It is only slightly overstating the case to say that physics is the study of symmetry” was an expression of a commonly accepted truth [
12].
The study of symmetry became a fundamental methodological tool. Anderson’s article not only closed the century of its development, but also included another very important message. Anderson emphasized the role of “breaking symmetry” and of the hierarchical structure of reality. He demonstrated that, at least in the perspective of physics, reality has a hierarchic structure of increasing complexity and that the transition from one level of complexity to the next is associated with breaking symmetry, understood as a transition from one group of symmetry to another of a lower level. Thus, not only is the study of symmetry important, but so are the ways in which it changes.
5.6. Symmetry as a Unification Tool
The role of symmetry and its breaking is equally fundamental in physics and other scientific disciplines today as it was half a century before, while structuralism in the humanities has gone through a period of strong denial (seen in the proudly declared dissents of those who, like Umberto Eco, were considered structuralists, or in the frequent denunciations of its ineffectiveness). However, recently, there has been increased interest in structuralism, not only in philosophy but also in social sciences and economics [
59].
One of the reasons for the revival of the interest in structuralism and symmetry outside of scientific disciplines—where they both remained at the center of attention without any decline in interest—was the growing recognition that practically every complex system retains its identity only as a structure, not as an aggregation of elements. For instance, every living organism replaces its chemical substrates in a time incomparably shorter than its life span, which applies, of course, to the human organism. Every social organization goes through a similar process of exchange. This naturally led to the claim that, because of this universal feature of complex systems and because of deficiency in the description of complexes in terms of their simple components, the actual, real status should be given to structures, not their substrates.
We can already find the same way of thinking in Weyl’s book which, in 1952, initiated an interest in symmetry: “We found that objectivity means invariance with respect to the group of automorphisms. Reality may not always give a clear answer to the question of what the actual group of automorphisms is, and for the purpose of some investigations, it may be quite useful to replace it by a wider group” [
51].
There is possibly a legitimate concern regarding backlash against structuralism, which generated such strong polarization of views within The Two Cultures. If we want to use the methodology that was denounced in the past as faulty, this may lead to yet another story of The Tower of Babel. The answer is that the use of symmetry in humanistic or cultural contexts was misguided by the lack of appropriate methodological tools.
The most typical misunderstanding in attempts to extend the methodology of symmetry studies, in geometry to other contexts, is a consequence of misinterpretation of Klein’s Program. Klein did not consider arbitrary transformations of the plane (or set of points on which geometry is defined), but only those that preserve the underlying geometric structure. This very important but very frequently ignored aspect of the Program was clearly described in Weyl’s book popularizing symmetry in the general audience: “What has all this to do with symmetry? It provides the adequate mathematical language to define it. Given a spatial configuration ℑ, those automorphisms of space which leave ℑ unchanged form a group Γ, and
this group describes exactly the symmetry possessed by ℑ. Space itself has the full symmetry corresponding to the group of all automorphisms, of all similarities. The symmetry of any figure in space is described by a subgroup of that group.” [
51]
Even in recent books popularizing symmetry studies within the restricted domain of geometry, we can find statements exhibiting a lack of understanding of this aspect of Klein’s Program. Therefore, everywhere in textbooks we find statements such as “Symmetry of a geometric object consisting of some set of points A is every transformation of a space S, i.e., bijective function from S to itself, that leaves A unchanged.” In these cases, the authors are talking about “groups of symmetries” as groups of all arbitrary transformations leaving object A unchanged. Of course, these “symmetries” and “groups of symmetries” would only be useful in very limited situations. If symmetry is just one particular collection of transformations, then every two squares of the different centers would have different symmetries. In addition, we have to consider separate “symmetries” transformations that leave all points of a square identical, but arbitrarily permute all other points.
The beauty and power of Klein’s Program are in the recognition of what is important for the study of symmetry. We have a more general group of transformations of a particular type, i.e., determined by a specific type of the structure (geometric, topological, algebraic, etc.); then, we look for the subgroup of transformations that leave our object unchanged, even if particular points within the object have different images through the transformations. The difference would emphasize the importance of the pre-defined total group of transformations which typically is a proper subgroup of the group of all transformations. Weyl calls it the group of symmetries for the entire space: “Space itself has the full symmetry” [
51]. Only then we can make a selection of the subgroup describing a specific symmetry.
This is the point where we can find the sources of the doubts about the applications of symmetry in cultural studies. In the geometric context, everyone, even those who did not understand the method in its generality, automatically considered only subgroups of the group of all isometries, i.e., transformations preserving the metric (distance) characterizing a particular type of geometry. In application to the humanities, the choice of the symmetry group was arbitrary, guided only by the desired result. The presence of arbitrary choices of transformations generated resentment, expressed in the form of claims that Levi-Strauss and others using this methodology could not get anything new beyond that which they entered into consideration. However, this is more of an aberration of the structuralistic way of thinking than the norm [
60].