Symmetry in nature is a sign of unperturbedness. It means nothing has interfered with a natural process, and that its effects at each step are simply scaled-up or scaled-down versions of each other. For this reason, symmetry is aesthetically pleasing, and often beautiful. Consider, for instance, faces. Symmetry of facial features about the central vertical axis is often translated as the face being beautiful – not just by humans but also monkeys.
However, this is just an example of one of the many forms of symmetry’s manifestation. When it involves geometric features, it’s a case of geometrical symmetry. When a process occurs similarly both forward and backward in time, it is temporal symmetry. If two entities that don’t seem geometrically congruent at first sight rotate, move or scale with similar effects on their forms, it is transformational symmetry. A similar definition applies to all theoretical models, musical progressions, knowledge, and many other fields besides.
One of the first (postulated) instances of symmetry is said to have occurred during the Big Bang, when the observable universe was born. A sea of particles was perturbed 13.75 billion years ago by a high-temperature event, setting up anecdotal ripples in their system, eventually breaking their distribution in such a way that some particles got mass, some charge, some a spin, some all of them, and some none of them. In physics, this event is called spontaneous, or electroweak, symmetry-breaking. Because of the asymmetric properties of the resultant particles, matter as we know it was conceived.
Many invented scientific systems exhibit symmetry in that they allow for the conception of symmetry in the things they make possible. A good example is mathematics – yes, mathematics! On the real-number line, 0 marks the median. On either sides of 0, 1 and -1 are equidistant from 0, 5,000 and -5,000 are equidistant from 0; possibly, ∞ and -∞ are equidistant from 0. Numerically speaking, 1 marks the same amount of something that -1 marks on the other side of 0. Not just that, but also characterless functions built on this system also behave symmetrically on either sides of 0.
To many people, symmetry evokes an image of an object that, when cut in half along a specific axis, results in two objects that are mirror-images of each other. Cover one side of your face and place the other side against a mirror, and what a person hopes to see is the other side of the face – despite it being a reflection (interestingly, this technique was used by neuroscientist V.S. Ramachandran to “cure” the pain of amputees when they tried to move a limb that wasn’t there). Like this, there are symmetric tables, chairs, bottles, houses, trees (although uncommon), basic geometric shapes, etc.
Symmetry at its best, however, is observed in nature. Consider germination: when a seed grows into a small plant and then into a tree, the seed doesn’t experiment with designs. The plant is not designed differently from the small tree, and the small tree is not designed differently from the big tree. If a leaf is given to sprout from the mineral-richest node on the stem then it will; if a branch is given to sprout from the mineral-richest node on the trunk then it will. So, is mineral-deposition in the arbor symmetric? It should be if their transportation out of the soil and into the tree is radially symmetric. And so forth…
At times, repeated gusts of wind may push the tree to lean one way or another, shadowing the leaves from against the force and keeping them form shedding off. The symmetry is then broken, but no matter. The sprouting of branches from branches, and branches from those branches, and leaves from those branches all follow the same pattern. This tendency to display an internal symmetry is characterized as fractalization. A well-known example of a fractal geometry is the Mandelbrot set, shown below.
If you want to interact with a Mandelbrot set, check out this magnificent visualization by Paul Neave. You can keep zooming in, but at each step, you’ll only see more and more Mandelbrot sets. Unfortunately, this set is one of a few exceptional sets that are geometric fractals.
Meta-geometry & Mulliken symbols
Now, it seems like geometric symmetry is the most ubiquitous and accessible example to us. Let’s take it one step further and look at the “meta-geometry” at play when one symmetrical shape is given an extra dimension. For instance, a circle exists in two dimensions; its three-dimensional correspondent is the sphere. Through such an up-scaling, we’re ensuring that all the properties of a circle in two dimensions stay intact in three dimensions, and then we’re observing what the three-dimensional shape is.
A circle, thus, becomes a sphere; a square becomes a cube; a triangle becomes a tetrahedron (For those interested in higher-order geometry, the tesseract, or hypercube, may be of special interest!). In each case, the 3D shape is said to have been generated by a 2D shape, and each 2D shape is said to be the degenerate of the 3D shape. Further, such a relationship holds between corresponding shapes across many dimensions, with doubly and triply degenerate surfaces also having been defined.
Obviously, there are different kinds of degeneracy, 10 of which the physicist Robert S. Mulliken identified and laid out. These symbols are important because each one defines a degree of freedom that nature possesses while creating entities, and this includes symmetrical entities as well. In other words, if a natural phenomenon is symmetrical in n dimensions, then the only way it can be symmetrical in n+1 dimensions also is by transforming through one or many of the degrees of freedom defined by Mulliken.
Apart from regulating the perpetuation of symmetry across dimensions, the Mulliken symbols also hint at nature wanting to keep things simple and straightforward. The symbols don’t behave differently for processes moving in different directions, through different dimensions, in different time-periods or in the presence of other objects, etc. The preservation of symmetry by nature is not a coincidental design; rather, it’s very well-defined.
Now, if that’s the case – if symmetry is held desirable by nature, if it is not a haphazard occurrence but one that is well orchestrated if given a chance to be – why don’t we see symmetry everywhere? Why is natural symmetry broken? Is all of the asymmetry that we’re seeing today the consequence of that electro-weak symmetry-breaking phenomenon? It can’t be because natural symmetry is still prevalent. Is it then implied that what symmetry we’re observing today exists in the “loopholes” of that symmetry-breaking? Or is it all part of the natural order of things, a restoration of past capabilities?
The last point – of natural order – is allegorical with, as well as is exemplified by, a geological process called anastomosis. This property, commonly of quartz crystals in metamorphic regions of Earth’s crust, allows for mineral veins to form that lead to shearing stresses between layers of rock, resulting in fracturing and faulting. Philosophically speaking, geological anastomosis allows for the displacement of materials from one location and their deposition in another, thereby offsetting large-scale symmetry in favor of the prosperity of microstructures.
Anastomosis, in a general context, is defined as the splitting of a stream of anything only to rejoin sometime later. It sounds really simple but it is a phenomenon exceedingly versatile, if only because it happens in a variety of environments and for an equally large variety of purposes. For example, consider Gilbreath’s conjecture. It states that each series of prime numbers to which the forward difference operator has been applied always starts with 1. To illustrate:
2 3 5 7 11 13 17 19 23 29 … (prime numbers)
Applying the operator once: 1 2 2 4 2 4 2 4 6 … (successive differences between numbers)
Applying the operator twice: 1 0 2 2 2 2 2 2 …
Applying the operator thrice: 1 2 0 0 0 0 0 …
Applying the operator for the fourth time: 1 2 0 0 0 0 0 …
And so forth.
If each line of numbers were to be plotted on a graph, moving upwards each time the operator is applied, then a pattern for the zeros emerges, shown below.
This pattern is called that of the stunted trees, as if it were a forest populated by growing trees with clearings that are always well-bounded triangles. The numbers from one sequence to the next are anastomosing, only to come close together after every five lines! Another example is the vein skeleton on a hydrangea leaf. Both the stunted trees and the hydrangea veins patterns can be simulated using the rule-90 simple cellular automaton that uses the exclusive-or (XOR) function.
Now, what does this have to do with symmetry, you ask? While anastomosis may not have a direct relation with symmetry and only a tenuous one with fractals, its presence indicates a source of perturbation in the system. Why else would the streamlined flow of something split off and then have the tributaries unify, unless possibly to reach out to richer lands? Either way, anastomosis is a sign of the system acquiring a new degree of freedom. By splitting a stream with x degrees of freedom into two new streams each with x degrees of freedom, there are now more avenues through which change can occur.
Particle physics simplies this scenario by assigning all forces and amounts of energy a particle. Thus, a force is said to be acting when a force-carrying particle is being exchanged between two bodies. Since each degree of freedom also implies a new force acting on the system, it wins itself a particle, actually a class of particles called the Nambu-Goldstone (NG) bosons. Named for Yoichiro Nambu and Jeffrey Goldstone, the particle’s existence’s hypothesizers, the presence of n NG bosons in a system means that, broadly speaking, the system has n degrees of freedom.
How and when an NG boson is introduced into a system is not yet a well-understood phenomenon theoretically, let alone experimentally! In fact, it was only recently that a mathematical model was developed by a theoretical physicist at UCal-Berkeley, Haruki Watanabe, capable of predicting how many degrees of freedom a complex system could have given the presence of a certain number of NG bosons. However, at the most basic level, it is understood that when symmetry breaks, an NG boson is born!
The asymmetry of symmetry
In other words, when asymmetry is introduced in a system, so is a degree of freedom. This seems only intuitive. At the same time, you’d think the axiom is also true: that when an asymmetric system is made symmetric, it loses a degree of freedom – but is this always true? I don’t think so because, then, it would violate the third law of thermodynamics (specifically, the Lewis-Randall version of its statement). Therefore, there is an inherent irreversibility, an asymmetry of the system itself: it works fine one way, it doesn’t work fine another – just like the split-off streams, but this time, being unable to reunify properly. Of course, there is the possibility of partial unification: in the case of the hydrangea leaf, symmetry is not restored upon anastomosis but there is, evidently, an asymptotic attempt.
However, it is possible that in some special frames, such as in outer space, where the influence of gravitational forces is weak if not entirely absent, the restoration of symmetry may be complete. Even though the third law of thermodynamics is still applicable here, it comes into effect only with the transfer of energy into or out of the system. In the absence of gravity (and, thus, friction), and other retarding factors, such as distribution of minerals in the soil for acquisition, etc., symmetry may be broken and reestablished without any transfer of energy.
The simplest example of this is of a water droplet floating around. If a small globule of water breaks away from a bigger one, the bigger one becomes spherical quickly; when the seditious droplet joins with another globule, that globule also reestablishes its spherical shape. Thermodynamically speaking, there is mass transfer, but at (almost) 100% efficiency, resulting in no additional degrees of freedom. Also, the force at play that establishes sphericality is surface tension, through which a water body seeks to occupy the shape that has the lowest volume for the correspondingly highest surface area (notice how the shape is incidentally also the one with the most axes of symmetry, or, put another way, no redundant degrees of freedom? Creating such spheres is hard!).
A godless, omnipotent impetus
Perhaps the explanation of the roles symmetry assumes seems regressive: every consequence of it is no consequence but itself all over again (self-symmetry – there, it happened again). This only seems like a natural consequence of anything that is… well, naturally conceived. Why would nature deviate from itself? Nature, it seems, isn’t a deity in that it doesn’t create. It only recreates itself with different resources, lending itself and its characteristics to different forms.
A mountain will be a mountain to its smallest constituents, and an electron will be an electron no matter how many of them you bring together at a location. But put together mountains and you have ranges, sub-surface tectonic consequences, a reshaping of volcanic activity because of changes in the crust’s thickness, and a long-lasting alteration of wind and irrigation patterns. Bring together a unusual number of electrons to make up a high-density charge, and you have a high-temperature, high-voltage volume from which violent, permeating discharges of particles could occur – i.e., lightning. Why should stars, music, light, radioactivity, politics, manufacturing or knowledge be any different?
With this concludes the introduction to symmetry. Yes, there is more, much more…