The conclusion that the nuclear theory of the atom is erroneous and that in reality there is no such thing as an atomic nucleus will be difficult for the present generation of scientists to accept. The individual who has from childhood visualized the atom in the manner pictured by Bohr, who has participated in the great debates over the use of “nuclear” energy, who reads Nucleonics and the Annual Review of Nuclear Science, and who has perhaps taught classes in “nuclear physics” cannot be expected to look with enthusiasm on the prospect of life without a nucleus. We can, of course, remind him that the Bohr atom has long since vanished from the scene and that the official” atom of modern physics cannot even be imagined, so the experts say, much less pictured. We can also point out that “atomic energy” and “atomic physics,” the terms that will have to be substituted when the nucleus is discarded, are already in common use. Most of the “nuclear physicists” in the United States work, directly or indirectly, for the Atomic Energy Commission. But this will probably be cold comfort. One is not easily reconciled to the loss of an old friend in the world of ideas.
The tenacity with which the human mind clings to familiar ideas is truly remarkable. “Our first reaction” to a new mode of thought, says Lande, quoting G. Sykes, “is one of pain and distaste.33 It is quite understandable that this should be true in the metaphysical fields, religion particularly, since in these areas what one believes is paramount. Science, on the other hand, sets up an external objective standard and, at least in principle, scientists agree that any opinion which turns out to be in conflict with observed facts must be abandoned. Bridgman states the credo in these words, “In the face of a fact there is only one possible course of action for the scientist, namely acceptance, no matter how much the fact may be at variance with his anticipations, and no matter what havoc it may wreak on his carefully thought-out theories.34 It would simplify matters greatly if we could be assured that the scientific world in general would follow the principle thus laid down by Bridgman. But if we judge by past performance, we get an altogether different picture. Any new thought which is essentially nothing more than an extension or minor revision of existing theory finds the “Welcome” mat outside the door if it has any merit at all, or even if it is merely an interesting speculation, but an altogether different reception awaits any findings that challenges one of the basic tenets of current science. “Usually such new ideas are looked upon with indifference or suspicion,” says Raman, “and many years of persistent advocacy and powerful observational support are required before the investigator can hope to see his ideas generally accepted.35 Max Planck was even more pessimistic. He complained bitterly about the way his “sound arguments fell on deaf ears,” and concluded that new ideas never succeed in convincing their opponents, but must wait for a new generation of scientists to grow up.
In any event it is obvious that the case against such a popular theory as that of the nuclear atom must be extremely strong to be convincing, but the case that has been presented herein is strong; it is a prima facie case. The three preceding chapters have gone directly to the heart of the matter. It has been shown that the idea that the atoms are in contact in the solid state is nothing but an assumption, and that there are many items of evidence which indicate that this assumption is erroneous. It has been shown that there is nothing in Rutherford's findings which requires or justifies postulating the existence of a nucleus, and that in the light of what is now known about conditions in the solid, it is clear that the small but massive “something” that Rutherford located is the atom itself, not a nucleus. It has been shown that if there are any negatively-charged constituents in the atom, they cannot be electrons of the type that we observe experimentally; if such constituents exist at all, they will have to be purely hypothetical particles of a totally different and unprecedented nature. Without a nucleus and without electrons, there can be no nuclear atom of the kind postulated by present-day theory.
This is a solid and airtight case. When the nuclear theory is analyzed it is clear that it rests entirely on two assumptions: (I) that Rutherford's scattering experiments proved the existence of a nucleus, and (2) that radioactivity proves that electrons constitute one of the components of matter. Neither of these assumptions can be maintained in the light of existing physical knowledge, and the other primary assumptions of the theory-Bohr's postulates as to the behavior of the atomic electrons, and present-day ideas as to the composition of the nucleus--are preposterous without the positive proof of the existence of the nuclear structure which Rutherford and radioactivity were supposed to furnish. The theory therefore collapses. But the scientific world has been so sure of its nuclear atom for so long that there will undoubtedly be a tendency to feel that there must be a catch in it somewhere. One of the immediate reactions will no doubt be, “How can this theory be wrong when it has given us so many right answers all these years?
This question is easily answered. The same thing is true of all theories that finally have to be given up after a long period of acceptance. It was true of the Ptolemaic theory and all of the others mentioned earlier in the discussion. All of these theories gave the right answers to many questions over a long period of time, but they were ultimately pronounced wrong nevertheless. It should be recognized, however, that characterizing such a theory as “wrong” does not really do it complete justice. There is no sharp line of demarcation between true and false in ordinary physical theory, because most theories are compound structures in which both truth and error are present simultaneously. Most erroneous theories contain at least some truth, otherwise they never would have been advanced in the first place; whereas most presumably correct theories contain at least a small degree of error. This is the reason why erroneous theories have often led to important scientific advances. If these theories were 100 percent wrong, they would be more likely to impede discovery of the truth than to facilitate it, but where they are partly true, this element of truth may be all that is needed for the purpose at hand. As Reichenbach puts it, Knowledge of half the truth can be a sufficient directive for the creative mind on its path to the full truth.36
The whole foundation of the science of astronomy, for instance, was laid
at a time when it was believed that the sun revolved around the earth.
We now say that this theory is wrong, and if we look upon right and wrong
as mutually exclusive, and visualize our concepts of the universe as the
answers to a series of true-false questions, the striking results obtained
from the use of the geocentric hypothesis are totally inexplicable. If
we recognize, however, that in the field of ideas we have not only pure
black and pure white, but also an infinite gradation of shades of gray,
the explanation is simple. The geocentric hypothesis can be split into
(2) The earth is the stationary component.
In the light of present knowledge, we assert that statement (2) is wrong, but we accept statement (1) as correct. A great many of the propositions with which astronomy is concerned are dependent only on assumption (1) and are not necessarily affected by the nature of assumption (2). So far as these propositions are concerned, therefore, the ancient astronomers were equally as well prepared, from the standpoint of theory, as the astronomers of today, and not until the invention of the telescope multiplied the scope and accuracy of the observational information manyfold was the need for any revision of assumption (2) apparent.
Even after a theory has been superseded by something more general, this element of truth which it contains may be sufficient to justify retaining it for use in a special field. It has been found, for example, that Newton's Laws of Motion are not a correct expression of the general situation, and for general use they must be replaced by Einstein's expressions or some equivalent. But aside from the workers in a few of the more exotic fields, all of the thousands of engineers that man our vast technological system still tune their slide rules to Newton's Laws and go about their business as if they had never heard of Einstein. We must nevertheless admit that Newton's Laws are “wrong” in the sense that they are not equal to all of the demands now made upon them, and it has been necessary to devise a theory of a wider scope.
The criterion by which we judge whether a theory is wrong in this sense, and must therefore be superseded by something more adequate, is not what it has done, but what it is now failing to do. One of the principal reasons why it is so difficult to dislodge a theory once it becomes embedded in the structure of scientific thought is the lack of general recognition of this point. The tendency is to judge currently accepted theories by their accomplishments, and not until these theories have been overwhelmed by the advance of knowledge does it bcome apparent that it is not their accomplishments but their failures that are significant in determining whether they stand or fall.
Some interesting illustrations of this point can be seen by comparing the statements made about a theory just before it was superseded with the statements made afterward. Here we find that while the same facts are being described in both cases, there is a very radical change in emphasis, so that a totally different impression is conveyed to the reader. Before the fall of the theory, the emphasis is upon its successes, and while the deficiencies or failures are mentioned, they are played down and their significance is minimized. After the fall, the emphasis is completely reversed. Now the successes of the theory are given perfunctory and patronizing comment, while the failures are portrayed as fatal weaknesses. For instance, Max Born's book The Constitution of Matter,37 published in 1923, just before wave mechanics elbowed the original Bohr theory aside, portrays this theory as a resounding success. “The correct solution was found by Bohr ..., Born assures us. Extension of the mathematical formula developed for the hydrogen spectrum to the elements beyond hydrogen was giving trouble, and Born so reports, but his tone is definitely optimistic; he speaks of “signal success” in the qualitative explanation of the spectra of these heavier elements. Furthermore, he sees bright vistas opening up ahead. In the theory of chemical combination, he tells us, “... it is to Bohr's theory of the atom that we must look for the complete solution of the problem.
Today the same picture is seen in an altogether different light. Aside from the educators, who still present pure Bohr theory to all but their most advanced classes, just as if the clock had stopped about 1920, anyone who comments on the application of the Bohr theory to spectra other than those of hydrogen and singly- ionized helium uses the term “failure” rather than Born's “signal success,” and it is well recognized that it is this failure that has determined the fate of the original Bohr theory. Whatever successes the theory may have enjoyed are from this standpoint completely irrelevant; a physical theory cannot live on the strength of its past accomplishments; it must keep abreast of the advancing tide of knowledge or give way to something else that can meet today's requirements.
It will therefore be appropriate to take a look at the nuclear theory from this standpoint, putting aside for the moment any considerations connected with the successes, real or alleged, which the theory has enjoyed, and concentrating our attention on the failures, to determine whether or not these are serious enough to suggest that the days of this theory are numbered. From a cold-blooded scientific viewpoint all this is irrelevant, since it has already been demonstrated in the preceding chapters that the nuclear theory is not a correct representation of the physical facts, and it is therefore obvious that if it has not already failed in some important aspect, it will inevitably do so sooner or later. However, the full objectives of this present work are not necessarily reached when the cold, hard facts that demonstrate the falsity of the nuclear hypothesis are assembled and laid before the scientific world. As indicated in the preceding paragraphs, there still remains a major psychological obstacle to be overcome before the full significance of these facts will be generally recognized, and in this respect it may be helpful to show that the weaknesses and failures of present-day atomic theory have by this time reached such proportions that collapse of the theory is imminent, irrespective of the conclusions reached through factual studies of the kind described in the previous chapters.
It is no secret that a large and growing number of physicists, as well as scientists in allied fields, are profoundly dissatisfied with the general state of physical theory as it now stands, and are convinced that some drastic overhauling will be necessary. David Bohm describes the situation in this manner: “Moreover, physics is now faced with a crisis in which it is generally admitted that further changes will have to take place, which will probably be as revolutionary compared to relativity and the quantum theory as these theories are compared to classical physics.38 J. R. Oppenheimer agrees, “It is clear that we are in for one of the very difficult, probably very heroic, and at least thoroughly unpredictable revolutions in physical understanding and physical theory.39
Some are openly rebellious. Cornelius Lanczos tells us defiantly, “The majority of us will not be willing to accept the particle-wave dualism.... In spite of all discouragements ... we will continue to look for a unified structure which we feel must exist behind the appearances.19 Alfred Lande joins in the attack, “We want to have a unitary theory; and (if I may use the word) even after thirty years of persuasion we still want a unitary theory.40 Philip M. Morse sums up the situation, “It is an unhappy time for theory.41
On first consideration, this chorus of disapproval might seem to contradict the statement in the introductory chapter to the effect that present-day scientists are strongly opposed to any major changes in the framework of accepted theory. But those scientists who recognize the existing situation still shy away from the clear implications of that recognition. It is obvious that changes of the magnitude which Bohm predicts, “as revolutionary compared to the quantum theory as (that theory is) compared to classical physics,” cannot leave much of the quantum theory intact. But Bohm is unable or unwilling to face the inevitable consequences of his prediction; he makes it clear that he seeks only to modify quantum theory, not to replace it. The same is true of most of the others who have taken a definite stand.
Lande, for instance, expresses much the same thoughts as Bohm. Perhaps there are some dissenters who are ready for stronger measures. D. I. Blokhintsev implies something of the kind in a recent statement, “Like many physicists all over the world I think that the well-known difficulties of the quantum field theory will be overcome only by a radical change of the very essence of the modern theory.42 In any event, irrespective of the extent to which the need for replacement rather than revision is recognized, it cannot be denied that there is a widespread feeling that existing theory is not at all satisfactory.
Since the general structure of modern physical theory is to a large extent based on the theory of the atom, the nuclear atom theory must accept a big share of the responsibility for the unsatisfactory state of physical theory in general. It is also apparent that there are major sectors of the field which an adequate atomic theory should cover that are as yet almost completely untouched. For example, a complete theory of the atom must necessarily explain the physical states of matter, yet after nearly fifty years of the nuclear theory Prof. G. Careri found it necessary to open a recent international conference on liquids with the flat statement, “We are still far from having a 'theory' of the liquid state....43
But the real testing ground for atomic theory today is what is popularly known as “elementary particle physics.” “... the future of physics,” says George Gamow, “lies in further studies and understanding of elementary particles.44 Here is a field in which atomic theory should be directly applicable; here is a rapidly expanding field in which the experimental facts are puzzling and confusing, and the help of an adequate theory is urgently needed; and here is a place where the currently accepted nuclear theory, faced with a major test of its capabilities, falls flat on its face.
The term “elementary particle” is in itself a claim to the possession of some knowledge of the structure of the atom, as it is based on the assumption, an integral part of current theory, that the atom is constructed of “parts” and that these parts cannot be further subdivided; thus they are elementary. If the nuclear atomic theory correctly portrays the structure of the atom, then it should be capable of producing the answers to the questions we find it necessary to ask with respect to the elementary particles. This point is commonly recognized, and “elementary particle physics” is classed as a subdivision of nuclear science.
How well, then, has modern atomic theory measured up to this, the most significant task now facing it? Let us ask Gamow, whose statement as to the importance of the task has just been quoted. “... for the last few decades,” Gamow replies, “not a single successful step has been made in obtaining these answers.44 This very recent evaluation of the situation was already foreshadowed years ago by keen observers who realized that the discovery of so many new “elementary” particles neither anticipated nor explained by the accepted theories raised grave doubts as to the validity of these theories. Questions like these,” said James B. Conant, “raise doubts as to whether the conceptual scheme of nuclear physics is a 'real' account of the structure of the universe,45 and Jones, Rotblat and Whitrow asked the very pertinent question, ... is this multiplicity of particles an expression of our total ignorance of the true nature of the ultimate structure of matter?46
In the light of all of the additional information that has been accumulated since these words were written, there remains little doubt but that this question must be answered in the affirmative, and that present-day atomic theory must be judged wholly inadequate for the tasks that confront it. “The physics of this century has set itself the task of interpreting all observed phenomena in terms of the behavior of atoms and molecules, and the electrical particles-electrons, protons, etc.-of which they are composed,47 says E. U. Condon. The result of this single-minded dedication of the full resources of the profession to the development of the nuclear atom theory is revealed by another statement from this same author. Speaking of the period from 1926 to 1955 he reports, “... little progress has been made in interpreting the fundamental problems of atomic theory.48 From von Weizsaecker we get this judgment, Quantum theory does not explain the characteristic properties of the different sorts of elementary particles which we know to-day. It is, therefore, certain that it must be supplemented by a new, as yet unknown theory.49
The nuclear theory has thus been weighed in the balance and found wanting. Even without the devastating disclosures of the preceding chapters, it is evident that this theory falls far short of meeting present-day demands upon it, and a drastic overhauling is inevitable. In the light of the information developed herein, however, it is clear that existing theory cannot merely be supplemented by something new as von Weizsacker suggests; it must be replaced. The nuclear theory is not simply incomplete, it is basically wrong; the atom is not so constructed.