Koray Karaca

Philosophical perspectives on ad hoc hypotheses and the Higgs mechanism

We examine physicists’ charge of ad hocness against the Higgs mechanism in the standard model of elementary particle physics. We argue that even though this charge never rested on a clear-cut and well-entrenched definition of “ad hoc”, it is based on conceptual and methodological assumptions and principles that are well-founded elements of the scientific practice of high-energy particle physics. We further evaluate the implications of the recent discovery of a Higgs-like particle at the CERN’s Large Hadron Collider for the charge of ad hocness against the Higgs mechanism.

The Strong and Weak Senses of Theory-Ladenness of Experimentation: Theory-Driven versus Exploratory Experiments in the History of High-Energy Particle Physics

In the theory-dominated view of scientific experimentation, all relations of theory and experiment are taken on a par; namely, that experiments are performed solely to ascertain the conclusions of scientific theories. As a result, different aspects of experimentation and of the relation of theory to experiment remain undifferentiated. This in turn fosters a notion of theory-ladenness of experimentation (TLE) that is too coarse-grained to accurately describe the relations of theory and experiment in scientific practice. By contrast, in this article, I suggest that TLE should be understood as an umbrella concept that has different senses. To this end, I introduce a three-fold distinction among the theories of high-energy particle physics (HEP) as background theories, model theories and phenomenological models. Drawing on this categorization, I contrast two types of experimentation, namely, “theory-driven” and “exploratory” experiments, and I distinguish between the “weak” and “strong” senses of TLE in the context of scattering experiments from the history of HEP. This distinction enables to identify the exploratory character of the deep-inelastic electron-proton scattering experiments—performed at the Stanford Linear Accelerator Center (SLAC) between the years 1967 and 1973—thereby shedding light on a crucial phase of the history of HEP, namely, the discovery of “scaling”, which was the decisive step towards the construction of quantum chromo-dynamics (QCD) as a gauge theory of strong interactions.

A case study in experimental exploration: exploratory data selection at the Large Hadron Collider

In this paper, I propose an account that accommodates the possibility of experimentation being exploratory in cases where the procedures necessary to plan and perform an experiment are dependent on the theoretical accounts of the phenomena under investigation. The present account suggests that experimental exploration requires the implementation of an exploratory procedure that serves to extend the range of possible outcomes of an experiment, thereby enabling it to pursue its objectives. Furthermore, I argue that the present account subsumes the notion of exploratory experimentation, which is often attributed in the relevant literature to the works of Friedrich Steinle and Richard Burian, as a particular type of experimental exploration carried out in the special cases where no well-formed theoretical framework of the phenomena under investigation (yet) exists. I illustrate the present account in the context of the ATLAS experiment at CERN’s Large Hadron Collider, where the long-sought Higgs boson has been discovered in 2012. I argue that the data selection procedure carried out in the ATLAS experiment illustrates an exploratory procedure in the sense suggested by the present account. I point out that this particular data selection procedure is theory-laden in that its implementation is crucially dependent on the theoretical models of high energy particle physics which the ATLAS experiment is aimed to test. However, I argue that the foregoing procedure is not driven by the above-mentioned theoretical models, but rather by a particular data selection strategy. I conclude that the ATLAS experiment illustrates that, contrary to what previous studies have suggested, there are cases of experimentation in which exploration serves to test theoretical predictions and that theory-ladenness plays an essential role in experimentation being exploratory.

Representing Experimental Procedures through Diagrams at CERN's Large Hadron Collider: The Communicatory Value of Diagrammatic Representations in Collaborative Research

The aim of this paper is to elucidate the use and role of diagrams in the design of present-day high energy physics experiments. To this end, drawing upon a prominent account of diagrammatic representations advanced by the cognitive scientists Jill Larkin and Herbert Simon, I provide an analysis of the diagrammatic representations of the data selection and acquisition procedures presented in the Technical Design Report of the ATLAS experiment at CERN’s Large Hadron Collider, where the Higgs particle was discovered in 2012. Based upon this analysis, I argue that diagrams are more useful than texts in organizing and communicating the procedural information concerning the design of the aforementioned experimental procedures in the ATLAS experiment. Moreover, I point out that by virtue of their representational features, diagrams have a particular communicatory value in the collaborative work of designing the data acquisition system of the ATLAS experiment.

Kitcher's Explanatory Unification, Kaluza-Klein Theories, and the Normative Aspect of Higher Dimensional Unification in Physics

I examine the relation between explanation and unification in both the original Kaluza–Klein theory, which originated in the works of Theodor Kaluza and Oskar Klein in the 1920s, and in the modern Kaluza–Klein theories which date back to the late 1970s and which are still considered by the majority of the physics community to be the best hope for a complete unified theory of all fundamental interactions. I use the conclusions of this case study to assess the merits of Philip Kitchers account of explanation as unification. I also draw lessons about physicists’ pursuit of the higher dimensional unification of the fundamental forces of nature. 1 Introduction 2 Kitcher on Explanatory Unification 3 A Close Look at the Kaluza–Klein Theory   3.1 Kaluzas theory: unification of gravity and electromagnetism   3.2 Kleins theory: an elucidation and elaboration of Kaluzas theory   3.3 Kleins compactification of the fifth dimension: explaining the unobserved 4 A General Overview of the Emergence of the Modern Kaluza–Klein Theories 5 Kaluza–Klein Unification Examined by Kitchers Standard of Unification 6 Concluding Remarks 1 Introduction 2 Kitcher on Explanatory Unification 3 A Close Look at the Kaluza–Klein Theory   3.1 Kaluzas theory: unification of gravity and electromagnetism   3.2 Kleins theory: an elucidation and elaboration of Kaluzas theory   3.3 Kleins compactification of the fifth dimension: explaining the unobserved   3.1 Kaluzas theory: unification of gravity and electromagnetism   3.2 Kleins theory: an elucidation and elaboration of Kaluzas theory   3.3 Kleins compactification of the fifth dimension: explaining the unobserved 4 A General Overview of the Emergence of the Modern Kaluza–Klein Theories 5 Kaluza–Klein Unification Examined by Kitchers Standard of Unification 6 Concluding Remarks

Practical Unification of Solid-State and Particle Physics in the Construction of the Higgs Mechanism

A number of philosophical accounts have been offered as to what sort of unification exists between the electromagnetic and weak interactions in the Glashow-Weinberg-Salam electroweak theory of elementary particle physics. In this paper, unlike the previous studies, I seek to address how “unity” in science might be interpreted in view of the construction process of the Higgs mechanism, which was a decisive step in the construction of the electroweak theory.

AN OPEN SINGULARITY-FREE COSMOLOGICAL MODEL WITH INFLATION

In the light of recent observations which point to an open universe (Ω0 < 1), we construct an open singularity-free cosmological model by reconsidering a model originally constructed for a closed universe. Our model starts from a nonsingular state called prematter, governed by an inflationary equation of state P = (γp - 1)ρ where γp (≃ 10-3) is a small positive parameter representing the initial vacuum dominance of the universe. Unlike the closed models universe cannot be initially static hence, starts with an initial expansion rate represented by the initial value of the Hubble constant H(0). Therefore, our model is a two-parameter universe model (γp,H(0)). Comparing the predictions of this model for the present properties of the universe with the recent observational results, we argue that the model constructed in this work could be used as a realistic universe model.

Philosophical reflections on diagram models and diagrammatic representation

Diagram models are widely used in system and software engineering to design and analyse information systems. In this article, I examine diagram models within Morgan and Morrisons ‘models as mediators’ account. I argue that even though diagram models and theoretical models differ in terms of representations they deliver, namely diagrammatic and sentential representations, respectively, as theoretical models mediate between the high-level theory and the real world, diagram models mediate between the abstract system and its concrete realisation in the world. Diagram models play this mediating role through the diagrammatic representation of the dynamic and static features of the system under consideration. Moreover, I argue why diagrammatic representation proves more efficient than sentential representation as a tool of design and analysis of information systems.

Lessons from the Large Hadron Collider for model-based experimentation: the concept of a model of data acquisition and the scope of the hierarchy of models

According to the hierarchy of models (HoM) account of scientific experimentation developed by Patrick Suppes and elaborated by Deborah Mayo, theoretical considerations about the phenomena of interest are involved in an experiment through theoretical models that in turn relate to experimental data through data models, via the linkage of experimental models. In this paper, I dispute the HoM account in the context of present-day high-energy physics (HEP) experiments. I argue that even though the HoM account aims to characterize experimentation as a model-based activity, it does not involve a modeling concept for the process of data acquisition, and it thus fails to provide a model-based characterization of the theory-experiment relationship underlying this process. In order to characterize the foregoing relationship, I propose the concept of a model of data acquisition and illustrate it in the case of the ATLAS experiment at CERN’s Large Hadron Collider, where the Higgs boson was discovered in 2012. I show that the process of data acquisition in the ATLAS experiment is performed according to a model of data acquisition that specifies and organizes the experimental procedures necessary to select the data according to a predetermined set of selection criteria. I also point out that this data acquisition model is theory-laden, in the sense that the underlying data selection criteria are determined by considering the testable predictions of the theoretical models that the ATLAS experiment is aimed to test. I take this sense of theory-ladenness to indicate that the relationship between the procedures of the ATLAS experiment and the theoretical models of the phenomena of interest is first established, prior to the formation of data models, through the data acquisition model of the experiment, thus not requiring the intermediary of other types of models as suggested by the HoM account. I therefore conclude that in the context of present-day HEP experiments, the HoM account does not consistently extend to the process of data acquisition so as to include models of data acquisition.

AN OPEN INFLATIONARY MODEL FOR DIMENSIONAL REDUCTION AND ITS EFFECTS ON THE OBSERVABLE PARAMETERS OF THE UNIVERSE

Assuming that higher dimensions existed in the early stages of the universe where the evolution was inflationary, we construct an open, singularity-free, spatially homogeneous and isotropic cosmological model to study the effects of dimensional reduction that may have taken place during the early stages of the universe. We consider dimensional reduction to take place in a stepwise manner and interpret each step as a phase transition. By imposing suitable boundary conditions we trace their effects on the present day parameters of the universe.