Do Atoms Exist ?

By W. R.
Thompson, F.R.S.
NOT far from the main entrance of the Kensington Science Museum there is a small room containing a most interesting exhibit of the results of research work on radioactivity. The central place in the exhibit is occupied by the remarkable piece of apparatus called a cloud-chamber, invented by Professor
C. T. R. Wilson, which enables the tracks of the constituent elements of the atom, such as a-particles, electrons or positrons, to be photographed.
The physical principle involved is simple. The amount of water-vapour air can contain depends partly on its temperature: the lower the temperature of the air the less water-vapour it will contain. If the air at a certain temperature is completely saturated and the temperature falls, it first becomes super-saturated, but eventually the excess water vapour suddenly condenses forming water. If the air is perfectly clean, there can be some fall in temperature, producing super-saturation, without condensation. But if the saturated air contains dust the slightest fall in temperature causes the excess water vapour to condense on the dust particles, so that we have the formation of fog or mist.
In the Wilson cloud-chamber, the particles emitted from various substances pass through a gas containing a little moisture. This gas is allowed to expand, which cools it. Particles of water vapour then condense to form a mist along the path of the o-partide. The impression given by the photographs is certainly that of small solid particles, bouncing off one another when they collide, just like minute billiard balls.
The Rutherford-Bohr theory of the atom as a nucleus around which there exists a number of electrons in " shells " also appears to lend itself well to pictorial representation. The accounts of it that one reads convey, and seem intended to convey, the idea of a microscopic solar system, with particles as real as the sun and the planets, which We could see in their assigned places if we could but invent a sufficiently highpower microscope. It is said that Lord Rutherford's method of dealing with experimental facts always involved a direct visual picture of the phenomena, and we can hardly suppose he attached no ontological value to it.
Other very distinguished scientists hold similar views.
0 0 0 Sir Frederick Gowland Hopkins in his presidential address to the Royal Society in 1933, asserted that the mental constructions ,of the earlier chemists have been shown by X-ray studies to be " no mere diagrams for heuristic use." " Where, for instance, they conceived of a carbon chain, there is an actual chain; where they pictured a ring, a ring is there; and the proved actuality extends to not a few details." His successor, Sir William Bragg, agreed with him.
Biology, though it is a genuine science, deals with real objects, not, of course, in their individuality, but, nevertheless, as material unities. The idea that these objects of the senses can be decomposed with elements refractory to sensory apprehension is repugnant to the Biologist. Taking one consideration with another, he tends, therefore, to prefer microscopic billiard balls which he can imagine, to unimaginables like " Wavicles " (which, it is said, can be truly described either as waves spreading throughout space or particles concentrated almost into points), in spite of the un doubted philosophical difficulties into which the reifying of " atoms " lands him. The writer therefore in his recent book, Science and Commonsense, came down, after some hesitation, on the atomistic side of the fence.
Further consideration has led him to modify these views slightly. Some theories that purport to explain how things behave and have in fact been as successful as anyone could expect, have been extracted from imaginative representations so fantastic that no one would ever take them seriously as pictures of the real world : a celebrated case being that of Clerk Maxwell's electro-magnetic theory, elaborated, said the late J. W. N. Sullivan, out of " a jungle of vortices, idle wheels and particles " (Great Victorians). Such " limiting cases " show clearly that imaginative representations in scientific theory simply constitute a " manuductio."
We cannot think without the help of images. Our thought about the constitution of material things is bound to be full of imagery.
If, by the help of this imagery, we can produce a rational construction from which observed conditions can be deduced we may consider our effort to have been successful.
On the other hand, we must realise quite clearly that the success of that theory does not in any sense guarantee the ontological status of the imagery used in its construction. The imagery may be ridiculous or self-contradictory; that does not matter, provided the concepts it helps us to form, constitute a rational assemblage from which we can deduce consequences verifiable in Nature.
It may indeed be said (I think J. Maritain has said somewhere) that the more absurd the imagery, the better, since we are less likely to objectify an absurdity than something that looks very like an element of the world we know.
On the other hand, it is obvious that unless the process of theoretical construction is understood, for what it is, both scientists and the public may be led to attempt to picture the unpicturable, believing that science requires them to do this, and reducing their minds to pulp in the process. The experience with relativity and kindred theories proves that this is a very real danger. As Professor Stebbing showed, in a book recently reviewed in these columns, the efforts of some of our leading scientists to explain what science is doing,
simply led the unfortunate layman more deeply into the fog.
We should therefore be extremely grateful to Professor Herbert Dingle for the lucid and entertaining study of scientific theory contained in his book, Through Science to Philosophy (Humphrey Milford, Clarendon Press pp. vi and 363, 15s. net).
Professor Dingle thinks, as I think, that scientific men have been talking in a manner that is injurious to public mentality.
He believes, as I believe, that this is due in the main, to the fact that they themselves do not understand exactly what they are doing.
He feels, as I do, that when we once come to understand the process of scientific theorising, the paradoxes with which some of our scientific leaders have been stupefying us, are perceived to be mere illusions.
Professor Dingle has, as it seems to me, a remarkably comprehensive knowledge of physical theory. He is an admirable writer, deeply interested in his argument and carrying the reader along by his en thusiasm, in spite of the technicalities of the problems with which he deals. He makes a great effort to be clear and, generally speaking, succeeds.
To give an idea of his viewpoint, we may take an extract concerning the theory of heat, from the chapter on Causality.
In their attempts to correlate the facts about heat, says Professor Dingle, " physicists conceived the idea that every material body was composed of myriads of small particles, or corpuscles, which could not possibly be seen, but whose kinetic energy constituted the sensible heat of the body. It was then quite easy to describe the simpler thermal phenomena; for instance, conduction of heat along a bar was attributed to collisions between the corpuscles, in which the faster ones at the hot end imparted some of their kinetic energy to their neighbours which in turn passed it on to the farther end of the bar."
At first sight, says Professor Dingle, "this appears to reduce the phenomena of heat to mechanics." Not only this, " but still rasher conclusions were drawn, with implications whose inconsistency was either unrealised or ignored." When the contradictions were pointed out, the defenders of the theory were unable to give a satisfactory answer; yet felt that the theory could not be abandoned.
Their difficulties arose from their failure to realise that the corpuscles, since they were simply postulated for the purpose of explanatory theory, could not, legitimately, be credited with properties other than those required for that purpose. Physical theory proceeds, in fact, from a mental construct or ens rationis which contains, virtually, the situation it is desired to explain. Our difficulties arise merely from our irresistible tendency to reify these mental entities, adding to the characteristics they have been granted for theoretical ends, attributes designed to bring them into the world of reality.