Kenneth Snelson Exhibition The Nature of Structure

The New York Academy of Sciences, January – April 1989

Snelson’s Atom

Essay by Hans Christian von Baeyer

Snelson’s atom is a conceptual model that agrees in some respects with the conventional picture accepted by physicists, and differs in others. The point of departure for both is the image of a tiny central nucleus carrying a positive electrical charge and most of the weight of the atom, surrounded by an envelope with equal and opposite charge and negligible weight, and consisting of electrons. The two models differ principally in the description and configuration of the electrons in the outer layer of the atom.

The word model is used differently by artists and physicists. in the late nineteenth century it still meant “mechanical model”, i. e. a real, palpable object that might be too small to be seen, but that nevertheless had the attributes of familiar objects. By means of such mechanical models, physicists tried to understand the material world, including atoms, light, heat, and even electrical and magnetic forces. But in this century it has become clear that this approach is too restrictive. The atom and its inaccessible inner workings are described by means of mathematical equations that do not correspond to the palpable, visual models of the artist. But the word model has remained in the scientific vocabulary. So when a physicist speaks of a model, he may be referring to a hypothetical object, or to a purely mathematical construct.

The physicist’s model of the atom, in particular, has evolved by stages into an exceedingly abstract conception. The original image of electrons as members of a miniature planetary system, which still serves as the universally recognized graphic symbol for an atom, was replaced by the vague notion of electron waves, which later yielded to clouds of charge shrouding the nucleus. Today the convcntional model has lost most of its palpability. It is described by a mathematical formula, the Schr6dinger equation, from which, by well established rules, predictions about the atom and its interactions with light and other particles can be made with exquisite precision.

The Schr6dinger equation incorporates remnants of the older ideas, including the electrical attraction between the electrons and the nucleus, the mutual repulsion of electrons, the centrifugal force accompanying orbital motion, and small magnetic effects caused by charges in motion. In addition there are features that have no counterparts in the everyday world. The Heisenberg uncertainty principle that blurs the electrons’ paths beyond recognition, their intrinsic magnetism, their indistinguishability, the exclusion principle that prevents them from occupying identical orbits, and, above all, the probabilistic, rather than definitive, nature of the whole description – all these are built into the Schr6dinger equation. The model has been so successful that physicists don’t question it any longer, even though it has lost its appeal to common sense.

Snelson’s atomic model retains some of the mechanical quality of the older models. Electron orbits, rather than being hypothetical lines or clouds, are real, three-dimensional objects that look like rings, or halos. They combine some properties of matter with those of waves: They are matter-waves. The most significant departure from conventional quantum-mechanical models lies in the arrangement of these rings. instead of being centered on the nucleus, they lie on the surfaces of spheres, like circles drawn on a balloon with a felt tip pen. A typical atom consists of several nested spheres, each of which carries several rings representing electron orbits on its surface.

Snelson’s electronic rings possess a fundamental rigidity: They cannot interpenetrate each other the way quantum-mechanical charge clouds can. It is here that Snelson locates the origin of solidity – of the inability of two macroscopic objects, like stones and chairs, to occupy the same space at the same time. Each ring is thought of as a miniature magnet, with adjacent ones carrying I opposite polarity so that they attract each other. A sphere covered as completely as is geometrically possible with identical electronic rings is a rigid structure, held together by the electrical attraction of the nucleus, and by magnetism, and kept from collapsing by the impenetrability of its components.

The original impetus for Snelson’s mode.1, and one of its highlights, is its treatment of periodicities that have their exact analogues in the periodicities of Mendeleev’s table of elements. The periodic table starts at hydrogen with one electron, and then proceeds, by adding one positive charge to each successive nucleus, and one electron to the outer shell of the corresponding atom, through the list of the known elements. The properties of the chemicals in this list exhibit certain striking periodicities: after two, then six, eight, ten … entries, the regular progression repeats with elements that display very similar characteristics. This pattern gives the periodic table its name, and is accounted for in the conventional model of the atom. Snelson found a similar pattern by experiments with magnetic rings. It turns out that you can build rigid structures from two rings, and from 5, 8, 10, 14, 18, or 32. With the exception of the number five, which is an imperfection, the sequence is the same as that of the periodic table. The meaning of this circumstance for Slielson’s atom is that once you reach such a structure in your progression through the periodic table, you cannot fit another halo onto the outermost sphere, and will be forced to start a new, larger sphere and thus start a new period.

The conception of confined electrons as impenetrable rings allows Snelson to extend his atomic model to the analogues of complex molecules and crystals. In this way he arrives at a palpable mechanical model of solid matter.