The Routledge Companion to Philosophy of Physics

Eleanor Knox, Alastair Wilson

• Publisher: Routledge
• Year: 2021
• ISBN:
  9781317227137
• Edition: 1
• Topic: Philosophy
• Subtopic: Philosophy History & Theory

The Routledge Companion to Philosophy of Physics is a comprehensive and authoritative guide to the state of the art in the philosophy of physics. It comprisess 54 self-contained chapters written by leading philosophers of physics at both senior and junior levels, making it the most thorough and detailed volume of its type on the market – nearly every major perspective in the field is represented.The Companion's 54 chapters are organized into 12 parts. The first seven parts cover all of the major physical theories investigated by philosophers of physics today, and the last five explore key themes that unite the study of these theories.I. Newtonian Mechanics
II. Special Relativity
III. General Relativity
IV. Non-Relativistic Quantum Theory
V. Quantum Field Theory
VI. Quantum Gravity
VII. Statistical Mechanics and Thermodynamics
VIII. Explanation
IX. Intertheoretic Relations
X. Symmetries
XI. Metaphysics
XII. CosmologyThe difficulty level of the chapters has been carefully pitched so as to offer both accessible summaries for those new to philosophy of physics and standard reference points for active researchers on the front lines. An introductory chapter by the editors maps out the field, and each part also begins with a short summary that places the individual chapters in context. The volume will be indispensable to any serious student or scholar of philosophy of physics.

Part I

Newtonian Mechanics

Introduction to Part I

In both physics and philosophy of physics, our study usually begins with Newtonian physics. Whether it’s resolving the forces on objects on a slope, or contemplating the justification for Newton’s postulation of absolute space, the theory provides a fertile ground for pedagogical exploration. And within physics, of course, knowledge of this theory is crucial; despite being superseded in various domains by relativistic and quantum physics, Newtonian physics remains accurate enough in many domains that it still provides us with many of our best physical models. But why should we study the foundations and philosophy of a superseded theory? What might the aims and outcomes of such an enterprise be?

One thing is clear: if we think of the philosophy of Newtonian physics as an exploration of the metaphysics of a non-actual possible world governed by Newtonian laws, the ink spilled on the topic is wasted. After all, Newtonian theories can’t account for the existence of stable matter. So what justifies the enduring popularity of the subject? In part, the answer lies with the theory’s familiarity: after all that exposure in school we take ourselves to have an intuitive understanding of Newtonian mechanics. This means that thinking about the foundations is more straightforward; even though in many ways the structures of Newtonian theories are more complex than those of relativistic ones, the concepts come more easily. Moreover, the connection between Newtonian theory and empirical results is largely unproblematic. This value goes well beyond pedagogy. In order to think about theories that test the very bounds of our physical and mathematical understanding, we need clear heuristics for theory interpretation: how should we think about differences that are, in principle, not empirically detectable? What role do concepts like “force” or “inertia” play in our theories? What kinds of consideration determine what we should say about the spacetime of a theory? The chapters in this section suggest answers to many of these questions, and hence hold morals for further theories discussed in subsequent chapters.

In Chapter 1, Ryan Samaroo explores the conceptual structure of Newton’s theory. One might be forgiven for thinking that Newton’s primary achievement lies in giving an empirically accurate model of terrestrial and astronomical motion, but Samaroo argues that the conceptual achievements of the theory go beyond this: Newton provides principles that have a special character and that articulate and apply in a special way concepts of quantity of matter, motion, space, and time. While these principles and the concepts they articulate require adjustment in the light of more recent theories, they represent nonetheless a paragon of the kind of theorizing required for modern physics as we understand it.

Samaroo works primarily in the familiar framework of forces and acceleration used by Newton himself, but part of the enduring importance of the theory stems not from Newton’s own mathematical framework, but from the great re-renderings of the theory offered by Lagrange and Hamilton in the late 18th and early 19th centuries. The Lagrangian and Hamiltonian formulations of classical mechanics look, at least on the surface, quite different, both from each other and from Newton’s original theory. The later formulations are particularly important because they provide a framework not just for Newtonian physics, but for the relativistic and quantum theories that were later developed. But although all three formulations are usually thought of as notational variants, the relation between them is far from obvious. Jill North’s chapter explores these relations and asks widely applicable questions about the notions of theory, formulation, equivalence, and fundamentality.

The 19th century held further mathematical developments of relevance to Newtonian mechanics, although it took some years for this relevance to be widely recognized. Geometrical techniques more commonly used in relativity can be equally well applied to Newtonian theories, and can help to elucidate the spacetime structures of the theory. Jim Weatherall’s chapter explores these structures; using geometrical ideas more usually encountered in relativity, he considers what we should say about Newtonian spacetime structure. This involves a modern look at the debate between Leibniz and Clarke over the existence of absolute substantival space. As Howard Stein pointed out in 1967, thinking about the structure of Newtonian spacetime allows us to understand that it’s possible for both Leibniz and Clarke to be right: Newton overreached in postulating absolute space but was nonetheless correct that some absolute structure is required by his theory to support the existence of absolute accelerations.

While Newton may have been right about the need for absolute structures in his own theory, contemporary strategies do not entirely close the debate between substantivalism (which holds that space or spacetime is an entity in its own right) and relationism (which holds that space is reducible to the relations between bodies). What becomes clear is that for Leibniz (and later Mach) to be correct, a new, relationist theory is needed which can replicate the empirical results of Newtonian mechanics without commitment to spatiotemporal structure. Mach’s legacy had to wait until the early 1980s for a spatially relationist theory to emerge through the work of Julian Barbour and Bruno Bertotti. In Barbour’s chapter for this volume, he explores the possibility of going beyond their original theory, and developing a classical theory which gives a truly relational account of both space and time. This chapter is more technical than the others in this section, so the reader not familiar with the physics and mathematics is advised to start with the earlier entries.

1

Newtonian Mechanics

Ryan Samaroo

The theory that we now know as “Newtonian mechanics” is Newton’s science of matter in motion, and its philosophical significance, in a sentence, is this: Newton gave us more than just an empirically successful theory of mechanics – he gave us an account of what knowledge of the physical world should look like, one that remains with us. But what is this account of physical knowledge? What is it that remains with us? Various answers to these questions have been given and they concern the methodological character of the laws of motion. What is methodologically rational about them? What is their distinctive feature? These are the questions on the table.

The structure of this chapter is as follows. I will begin by introducing the laws of motion, the relations among them, and the spatiotemporal framework that is implicit in them. Then I will turn to the question of their methodological character. This has been the locus of philosophical discussion from Newton’s time to the present, and I will survey the views of some of the major contributors. A theme running through this section is that there is something in the spirit of Kant’s analysis of Newtonian physics that is worth preserving, though distilling what that is is an open problem. I will conclude by showing that while Newtonian mechanics motivates a number of philosophical ideas about force, mass, motion, and causality – and through this, ideas about space and time – the laws are themselves the outcome of a philosophical or critical conceptual analysis. Therefore, taking some care to understand how the theory grew out of Newton’s analysis of the conceptual frameworks of his predecessors and contemporaries is valuable for its insights into the nature of that activity.

A word about the scope of this chapter is in order. It is worth recalling that Principia contains two theories: the theory of mechanics and the theory of universal gravitation. The former is found in a few pages...

Table of contents

• Cover
• Half Title
• Series Page
• Title Page
• Copyright Page
• Table of Contents
• List of Figures, Boxes, and Tables
• Notes on Contributors
• Introduction
• Section A: Theories
• Part I Newtonian Mechanics
• Part II Special Relativity
• Part III General Relativity
• Part IV Non-Relativistic Quantum Theory
• Part V Quantum Field Theory
• Part VI Quantum Gravity
• Part VII Statistical Mechanics and Thermodynamics
• Section B: Themes
• Part VIII Explanation
• Part IX Intertheoretic Relations
• Part X Symmetries
• Part XI Metaphysics
• Part XII Cosmology
• Index