In this dissertation I make three different claims concerning the role that symmetries and conservation laws played in particle physics in the 1950s and the 1960s, during the early history of the discipline. First, I provide a historical contribution outlining the main developments that took place in particle physics during these two decades. Secondly, I make a technical point about the manner in which symmetries and conservation laws relate to each other in different physical theories. Finally, I make a philosophical point, which concerns the ways in which scientists decide what theories deserve to be developed further, and what research programs ought to be
The main historical contribution in the dissertation comes in chapter 2. The central claim in this chapter is that symmetries and conservation laws played a central role in particle physics during the 1950s and 1960s. Although this claim is not controversial, my analysis adds a nuance that is frequently overlooked in the literature. As I show, different authors used symmetries and conservation laws in different ways, giving rise to different research programs.
Chapters 3 and 4 contain the main technical point in the dissertation. My claim here is that the nature of the relation between symmetries and conservation laws is different in different physical theories. In particular, I provide an account of the differences that obtain between the cases of quantum and classical mechanics, and the reasons why these differences obtain.
My claim in these two chapters is that in quantum mechanics, unlike in classical mechanics, Noether’s theorems are not needed in order to derive a conservation law from a symmetry. As a result of this, the nature of the relation between symmetries and conservation laws is different in the two theories in the following two ways. In classical mechanics, on the one hand, the relation between symmetries and conservation laws is restricted to some theories and some symmetry transformations. In quantum mechanics, on the other hand, no such restrictions obtain. In this case, however, symmetries have further consequences that can be used for practical purposes and have no classical analogue.
Having argued that symmetries and conservation laws played a crucial role during the early history of particle physics, and that the nature of the connection between symmetries and conservation laws varies from theory to theory, I go on to show how different accounts of the nature of this connection were used to sustain different research programs in particle physics, and to investigate how the particle physics community chose between different options available. I consider, in particular, a historical case-study that concerns two different attempts to use symmetries and conservation laws in order to develop a theory for the strong nuclear interaction. This allows me to support the main philosophical claim in the dissertation, which comes in chapters 5 and 6.
This final contribution concerns the manner in which decision-making operates in science. My claim here is that a small number of criteria, which are known in the literature as epistemic values, provide the basis on which scientists make decisions about the evaluation and development of scientific theories. As my case-study on the strong nuclear force illustrates, however, these criteria lend themselves to different interpretations, and this raises the question of what grounds the integrity of scientific decision-making. I conclude by suggesting that we answer this question by turning the social organization of science.