The philosophy of particle physics
by Prof. Dr. Gregor Schiemann
In 2016 the German Research Foundation set up a new research unit, led by the University of Wuppertal, which was tasked with investigating the philosophical, historical and sociological implications of activities at the world’s largest research machine, the Large Hadron Collider (LHC), at the European Organization for Nuclear Research (CERN) in Geneva. From the point of view of the philosophy of science there are three main reasons why these activities are relevant: the philosophy of science deals with the origins and fundamental structures of the world, with the conditions for the success of particle physics in generating new knowledge, and last but not least with the theoretical and practical problems associated with that success.
Discussion of all these issues shows on the one hand the remoteness of particle physics from the world in which we live, on the other hand its relevance for our conception of the world. Despite its striking successes in theory and in practice, this field of physics nevertheless raises open questions of considerable magnitude. It may well be a model for the production of knowledge within the limits of what we know.
Since 2010 the University of Wuppertal has been involved in a cooperative interdisciplinary research project ‒ funded by the German Research Foundation, the Volkswagen Foundation, and the university ‒ between elementary particle physicists and historians and philosophers of science. A further research group including sociologists of science was set up in 2016 by the German and Austrian Research Foundations (DFG & FWF) and tasked with six further projects. Total funding for these projects stands at €2.5 m for the next three years. Overall direction is in the hands of the University of Wuppertal, home university to three of the project leaders, all of whom are members of the Interdisciplinary Center for Science and Technology Studies (ICST) ‒ as is also a recently appointed junior professor for the philosophy of physics. Other project leaders are at RWTH Aachen University, the Technical University of Berlin, the University of South Carolina (USA), Karlsruhe Institute of Technology, the California Institute of Technology (Pasadena, USA), and the University of Klagenfurt in Vienna (Austria). This is the only DFG cooperative research unit involving both physics and the humanities.
Titled ‘The Epistemology of the Large Hadron Collider (LHC)’, the project in question focuses on work and results produced by the LHC at the European Organization for Nuclear Research (CERN) in Geneva ‒ a particle accelerator which is in many respects the largest piece of scientific equipment ever built. Creating collisions between particles at ultra-high energies, this measuring instrument enables empirical investigation of the basic structure of matter at a scale 100 million times smaller than that of the hydrogen atom (c. 10-10 m). Such events achieve conditions such as are thought to have existed a few billionths of a second after the origin of the universe some 13.7 billion years ago.
Question 1: Understanding matter
Viewed philosophically, research in this field is interesting for three partly contradictory reasons. First, the philosophy of science is today the branch of philosophy closest to the questions about the origin and fundamental structures of the world with which European philosophy began. Answers to these questions, which are relevant in the widest sense to the orientation of humankind, cannot be given without reference to natural science. But scientific knowledge of matter ‒ of which the experiential world ostensibly alone consists ‒ is immediately available only in mathematical constructs that are unintelligible to most people (including many scientists). Moreover, it postulates laws for its diminutive universe that are directly contrary to those of the everyday world, whose spatiotemporal reality is unequivocal. The formal structures of quantum mechanics and the results of many experiments show that this is by no means the case for individual subatomic entities. Hence the vast communication gap that opens up between the human need for orientation in the universe and the physical sciences in which the knowledge necessary for that purpose resides. The cooperation between physics and the philosophy of science seeks to bridge this gap, and although no single project of our research unit is dedicated explicitly to that end, it underlies all our concerns.
Question 2: The knowledge gained by elementary particle physics
Secondly, the philosophy of science is interested in the sheer success of elementary particle physics: the success of a structural model of matter that has proven itself in an unparalleled and exemplary fashion. The so-called standard model covers all known elementary particles, of which there are surprisingly few; it characterizes their (highly symmetrical) physical properties, and underlies the calculation of all their empirically demonstrated processes, as well as some that have as yet only been predicted. The research into the nature of matter that began in the early 20th century progressed through the application of increasingly precise technologies and highly complex formal mathematics. Both the IT that dominates, and the nuclear technology that threatens our world are by-products of that development. The triumph of the standard model as a guiding principle of research was most recently evident at CERN in 2012, with the experimental demonstration of the Higgs boson, the final building block of that paradigm.
The philosophy of science is also interested in whether, and to what extent, the conditions governing the success of scientific knowledge can be generalized. Not only in the case of the standard model, this question has historical and sociological dimensions: What drove the exceptional dynamism of the knowing process that unraveled the foundations of matter? How did it develop ‒ in a continuous line or at critical points where a research model came up against its limits? Are there such limits to research into the structure of matter as such? Might physics soon have discovered everything about the visible matter of the universe that can be discovered with its available means and instruments? Werner Heisenberg, for example, maintained that physical research into certain areas defined by objects (e.g. electrodynamics) would come to an end, after which only the technological exploitation of that knowledge (e.g. electrical engineering) would remain. What kind of knowledge is produced by elementary particle physics? Do the things it describes really exist, or are they just elements in a theoretical model that must be empirically verified? If that is the case, we can only claim to know the subatomic world when we have succeeded in measuring it experimentally. In what sense, then, can knowledge of the elementary particles and their interactions be considered true? Is this knowledge simply a matter of hypotheses that are always falsifiable and may well have equally viable alternatives? Finally, the social processes involved in the production of scientific knowledge are also of philosophical interest. The CERN experiments and their evaluation, for example, involve more than 10,000 scientists, and publications sometimes count several thousand authors. What role does the individual scientist play in such vast research collectives?
These questions – and philosophy often has more questions than answers – apply in different ways to all the research unit’s projects. Some aspects are immediately addressed in individual projects: e.g. the historical question about the origin and development of the concept of ‘virtual particles’ – non-observable particles whose properties defy the law of the conservation of energy, but which are nevertheless treated as real in the language of physicists. And a sociological project is currently inquiring into the practical conditions governing the production and establishment of new knowledge within the vast network involved in the LHC experiments.
Question 3: The problems of elementary particle physics
Thirdly, the philosophy of science is interested in the inherent problems of elementary particle physics – problems, in some cases, intimately bound up with its successes. Physics possesses the standard model with its many proven advantages; but that model harbors some not inconsiderable theoretical and experimental difficulties. It says nothing, for instance, about gravity, which is a fundamental force in the universe: the micro-level of objects described by the standard model seems to follow quite different laws from the macro-level described by gravitational theory. Hence from the perspective of physics, as well as of the philosophy of science, the world falls into (at least) two partly incompatible fields of theory – and in that respect also of reality. Could gravity be explained by an as yet undiscovered particle and thus be integrated into an expanded standard model? There are theoretical models that predict such a particle, but none has been experimentally verified. Another shortcoming is that the standard model itself comprises various theories which are not adequately unified. It postulates three forces with separate properties, although they are all constructed on the same principles. Are these, then, merely different facets of a single force? The atoms that determine our lives can likewise be explained in terms of three particles of matter (leaving neutrinos aside). Yet the standard model postulates two copies of these particles. Why this apparent excess? Other, no less serious obstacles present themselves to physicists and philosophers alike.
There is, however, a difference: physicists can pursue the solutions to their problems without the aid of the philosophy of science, just as their successes have been gained independently of that discipline. But the converse is not true: philosophical insights into physics depend on the achievements of physics. The point here, however, is that the mutual interest of the two disciplines intensifies precisely in the face of unsolved problems. And in this respect the philosophy of science has a number of different approaches, some of which focus on formal clarification of theoretical concepts – as such an entirely legitimate philosophical concern. However, where philosophy is bent on conceptual precision, physics may have a vested interest in imprecision, because this allows the sort of variant interpretations that can be an advantage in research areas that defy clear overview. Thus while certain philosophical approaches impose strict logical parameters on the reconstruction of physical theories, the theories themselves may well include pragmatic elements required to account for real phenomena. Such diverse interests can make interdisciplinary work difficult, if not impossible.
The collaboration between physics and science-focused humanities at the University of Wuppertal has consistently started from the problems as seen by physicists and worked toward a common formulation. As examples I would like to cite two research projects, one on aspects of the theoretical plurality of models, the other on the experimental use of computer simulation. Competing models usually occur in science when available theories fail to adequately meet the epistemic and aesthetic demands of scientific knowledge, or when specific phenomena – so-called anomalies – can no longer be explained in established conceptual terms. Several competing explanations for anomalies are now current; nor does contemporary physics see itself as any longer bound by the standard model – indeed, ‘Physics Beyond the standard model’ (BSM) is already a terminus technicus within the discipline. Accordingly, the investigation of the pragmatic, epistemic and aesthetic criteria for success or failure of BSM models is a prime concern of the philosophy of science. As for the philosophical aspects of computer simulation, they already possess an extensive literature which, however, rarely touches on particle physics. Simulation is essential to experimental work at the LHC, where the knowledge it produces conditions the experiments, even if it is not evident in the results. Is that an obstacle to the discovery of unknown phenomena?
Question 4: The scope of knowledge
Discussion of the threefold philosophical interest in elementary particle physics presents that discipline as remote from everyday concerns yet highly relevant to our image of the world, and at the same time as an undertaking with some important open questions. Its very success may have brought it close to the limits of the knowable. On the one hand research into the foundations of visible (baryonic) matter and the forces that mediate it seems highly advanced. On the other hand the revolutionary strides taken by astrophysics in recent decades indicate that this research only embraces some five percent of the matter and energy within the universe. Some influential hypotheses hold that the remaining ninety-five percent consists of dark matter and dark energy, for which no convincing explanation has yet been forthcoming.
Is elementary particle physics itself developing in a direction that can no longer be grasped by the terms in which research is conventionally described? One formulation of these terms is the well-known theory of scientific development proposed by Thomas S. Kuhn. If the standard model continues its triumphant course without any satisfactory solution being found either to the theoretical problems of structure or to the anomalies, the result could be a type of normative science not only informed in Kuhn’s sense by a paradigm but at the same time confronted with questions whose solution – if they have a solution – presumes major conceptual as well as arduous technological developments. Could a stable and successful paradigm coexist long-term with unsolved problems? Is this a way to conceive of knowledge at the borders of the known – or knowable?