Foundations o f Physics, Vol. 24, No. 11, 1994

Debating the Final Theory A. O. Barut 1 Received May 2, 1994 Recent assertions that the present particle physics is on the path o f a "'final theory" which cannot be reduced to more fundamental ones is critically examined and confronted with a counter-thesis.

The debate is simply this: The Thesis

"We are very close to a final theory, it is almost around the corner, the ingredients are all here. We will soon know all the fundamental laws of physics, laws that cannot be explained by more basic laws, laws with unlimited validity, entirely satisfying in their completeness and consistency. There will be no mystery as far as the fundamental laws are concerned." The Counter-thesis

"The first principles of things will never be adequately known. Science is an open-ended endeavor, it can never be closed. We can do science without knowing the first principles. It does in fact not start from first principles, nor from the end principles, but from the middle. We not only change theories, but also the concepts and entities themselves, and what questions to ask. The foundations of science must be continuously examined and modified; it will always be full of mysteries and surprises." The debate is certainly not new. It must be part of the human condition that certain insights lead men to think that they have found the ultimate answers. Examples abound. The occasion for this essay is a recent version of the final theory syndrome coming from particle physics and Physics Department, University of Colorado, Boulder, Colorado 80309. 1571 0015.9018/94/1100-1571507.0o/09 1994PlenumPublishingCorporation

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cosmology, tl) These works have been extensively reviewed recently in many journals and newspapers. The ingredients of the final theory as Weinberg c2) develops in detail in his recent book are: (1)

The standard quantum mechanics.

(2)

The standard quantum electrodynamics and renormalization (QED).

(3)

The standard model of particles.

(4)

The standard cosmology to be capped with

(5)

supersymmetry and string theory.

The attribute standard in the four pillars listed above means that these theories have reached a certain standard, found widespread but not universal acceptance, but yet they are not "classical" in the dictionary sense, i.e., "of the highest quality of rank, having recognized and permanent value, of enduring interest and appeal, forming the permanent cultural achievements of mankind"; they are beset with difficulties. We do not speak, for example, of a standard mechanics, standard thermodynamics, or standard electrodynamics, they are classical. The imperfections or crucial errors (depending on one's view) of these theories are (1) The standard interpretation of quantum theory in Hilbert space formulation brings in a statistical element into the behavior of fundamental entities which prevents us from asking questions about individual happenings, hence prevents further progress. Weinberg himself states "But I admit to some discomfort in working all my life in a theoretical framework that no one fully understands. Of even greater interest it seems to me is the question whether quantum mechanics is true." (2) The standard quantum electrodynamics is necessarily perturbative, has infinities which are renormalized, which prevents us from extrapolating electromagnetic interactions to short distances. Again Weinberg: "A theory that is as spectaculary successful as QED has to be more or less correct, although we may not be formulating it just the right way." We accept of course the imperfection of our theories and try to reach more clarity by continuous examination. But to build on these foundations a very elaborate final theory is another matter. There is always the tragedy of taking not fully justified ideas as granted and sinking deeper and deeper into a quicksand in trying to repair them. The justification given is that "no one has found an alternative to quantum theory and to QED; no one has found an alternative to renormalization, and to standard model."

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Also the present tower of elaborate particle physics models with its large number of unobserved entities has gone deeper, so much so that one does not see how to modify or repair it without causing the whole tower to crumble. But at the same time those who labor on the foundations are not listened to or noticed. According to Weinberg, "Louis de Broglie and E. Schr6dinger did not contribute importantly to the further development of quantum theory." The efforts of these founders of quantum theory, and also of Einstein, was precisely to "understand" quantum theory, and to unravel, eliminate the statistical element from quantum mechanics in order to have a firmer foundation. I believe they will prove to be correct. What one accepts about quantum theory of course has an effect on all the following theories. The quantum electrodynamics (QED) is again a statistical ensemble theory with all its limitations. It makes new postulates beyond quantum mechanics that fields are quantized. We tend to elevate successful theories to the level of fundamental ultimate theories. But when they are not based on solid foundations, it is better to view them as phenomenological theories. There is nothing wrong with having phenomenological theories. This is how physics proceeds. Thus the standard electroweak model and QED, which are successful in some instances in agreeing with experiment but unable in other instances to make calculations, are best viewed as phenomenological theories, c51 Weinberg himself has contributed to the development of the notion of "effective Lagrangians." The standard model has some 24 parameters. Its unapproachable elements invented to make it a fundamental theory, namely, gauge invariance. Higgs particles, 13) color, confinement of unobserved particles, etc. bring more new problems than they can solve. It is becoming increasingly evident that the framework of particle physics as given by the five models listed above, and their further extensions, is one of extreme complexity, a very hastily built huge tower with many loose ends. Some years ago the mathematical advances in string theory lead further to the notion of the "theory of everything" (TOE) for the simple reason that the oscillations of the string could also contain gravitons. 14~ But the proponents of these theories also say that it would take fifty or a hundred years to find out if we would indeed have a TOE. In the present situation, we have as fundamental entities 6 leptons, 18 quarks, 4 vector mesons, 8 gluons, plus Higgs particles, then the new X, Y,...-particles if one goes over to grand unified theories (GUT); with supersymmetry we have gravitons and we have to double everything. The strings are supposed to leave in a super 26-dimensional space-time. Such an arena of particle physics was aptly called "particle metaphysics.''~6) Even more esoteric extensions of the whole scientific method are contemplated. 825/24/11-8

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Echoing C. N. Yang's statement ~6~ that "particle physics is in trouble, deep trouble," I believe we must go back to the sources, to the foundations, to the completion of the basic theories left unfinished. It has been emphasized again and again since Kant that the foundations of science must be continuously examined. As Ren6 Thorn c7) recently states, "it is a mistake to think that science can always advance without worrying about its foundations." So therefore I come back now to our antithesis. About exactly 200 years ago, George Christoff Lichtenberg observed: "One should often study that what most people forget, overlook, or what is assumed to be known so that it is not worth to be investigated. Nothing is more harmful to the progress of science than to think that one knows what in fact one does not know. This mistake is made usually by the inventors of numerous new hypothesis." Fortunately for science, there are always people at any given time who try to examine carefully the foundations. To point out the difficulties of the thesis of our debate is not enough. In order to defend the antithesis one must show that there are other alternatives. Theories cannot be tested by experiments alone; they must be tested against other theories. I believe that the completion of quantum theory and of quantum electrodynamics will also change profoundly the foundations and direction of particle physics. The idea of an electromagnetic origin of weak and strong interactions has been around since the beginnings of particle physics in the early thirties, and vigorously reviewed and developed in the last decade. But it has remained generally unnoticed in particle physics literature as evidenced by remarks that "no one has proposed an alternative to quantum theory, QED, and to standard model." I am reminded of what a certain master of the Balliol College, Benjamin Jowett, has said, "I am the master of this college/What I know not is not knowledge." Quantum theory and quantum electrodynamics are unfinished because standard probabilistic interpretation of quantum mechanics and special theory of relativity are (nearly) incompatible, because we cannot describe single individual events, because we cannot extrapolate electromagnetic forces to short distances, because of infinite electromagnetic zero-point energy in the universe, and so on. In fact, contrary to what many think, the electromagnetic interactions are not completely known. It is the duty of theoretical physics to first complete such a universal and successful theory as electrodynamics. The simple insight is that the nonperturbative short-distance behavior of electromagnetic interactions between leptons is such that they can manifest themselves as "weak" and

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"strong" interactions which are precisely of very short range. Such myths that "/~-decay is something that is not allowed to happen through any known kind of force, hence is evidence for a new kind of force in nature, ''c2~ or that nuclear forces are too strong, hence cannot be electromagnetic, or that electrons have no room in nuclei, they are too big, etc. have all been answered.(8) What is attempted here is a return to common sense, a humble approach to physics in the great traditions of classical physics of causality, clarity, rationality, consistency, and objectivity. It is attributed to Niels Bohr the saying "This idea is crazy, but not crazy enough to be true." I think rather that when we really understand it, physics is comprehensible, simple, not bizarre or awkward, not full of invented jargons "simplex sigillum veri." Irrationality and dogmatism must be avoided. The return to common sense contains a deterministic quantum theory of single events such that the probabilistic quantum mechanics appears as an ensemble average, the elimination of the line dividing classical and quantum physics, a deterministic Q E D as a classical relativistic field theory which allows the extrapolation of electromagnetic forces to short distances, which in turn can reveal the "weak" and "strong" manifestations of electromagnetism. Hence the possibility of building up of all the "particles" from just electrons and neutrons. ~8~ The approach is so conservative that it may appear as revolutionary. But in fact it makes less assumptions than the standard theories. In any case these ideas will show that there is not only one mainstream way to particle physics, but there are other simpler avenues as well. Not everything is fully proven in this approach but this is even more so for the claims of standard approach. Even if we can extend a bit further our causal, classical deterministic electromagnetism to quantum electrodynamics and to weak and strong interactions, this will not be a final theory. It is a simplification which removes some paradoxes, but the very nature of the absolutely stable particles, electron and neutrino, their charge, mass .... are elusive and still mysteriously unknown. We recall that the "concept" of electron itself has undergone more than half a dozen different paradigms in the last hundred years. And of course the frontiers everywhere are still unknown. "Cosmic ignorance does not diminish us, it ennobles us." J. G. Taylor, examining the "theory of everything" (TOE) claims of superstring theories, recently came also to the conclusion that T O E cannot happenJ 81 For a more philosophical and comprehensive discussions we refer to recent volumes of Barron ~~ and Lindley. oH)

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REFERENCES

1. S. W. Hawking, "The end of theoretical physics," Cambridge Inaugural Lecture, 1978; S. W. Hawking, A Brief History of Time (Bantam, New York, 1988). 2. S. Weinberg, Dreams of a Final Theory (Random House, New York, 1993); S. Weinberg, "The answer to (almost) everything," New York Times, March 8, 1993. 3. Leon Lederman and Dick Teresi, The God Particle: If the Universe Is the Answer, What Is the Question (Houghton Mifflin, New York, 1993). 4. M. B. Green, H. H. Schwartz, and E. Witten, Superstrings (Cambridge University Press, Cambridge, 1989). 5. S. S. Schweber, Phys. Today, November 1993. 6. John Horgen, "Particle metaphysics," Sci. Am., February 1994, p. 97. 7. R. Thorn, Ann. Fond. L. de Broglie 18, 370 (1993). 8. See the reviews: A. O. Barut, Ann. Phys. 43, 83 (1986); T. Grandy, Jr., Found. Phys. 23,. 461 (1993). 9. J. G. Taylor, "On theories of everything," Found. Phys. 23, 239 (1993). 10. J. D. Barrow, Theories of Everything (Clarendon Press, Oxford, 1991). 11. David Lindley, The End of Physics. The Myth of a Unified Theory (Basic Books, New York, 1993).