Simon Allzén

Astrophysics is a scientific field with a rich ontology of individual processes and general phenomena that occur in our universe. Despite its central role in our understanding of the physics of the universe, astrophysics has largely been ignored in the debate on scientific realism. As a notable exception, Hacking (Philos Sci 56(4):555–581, 1989) argues that the lack of experiments in astrophysics forces us to be anti-realist with respect to the entities which astrophysics claim inhabit the universe. In this paper, I investigate the viability of astrophysical realism about black holes, given other formulations of entity realism, specifically Cartwright’s (How the Laws of Physics Lie. Oxford University Press, 1983), and Chakravartty’s (A Metaphysics for Scientific Realism: Knowing the Unobervable. Cambridge University Press, 2007) versions of entity realism. I argue that on these accounts of entity realism, you cannot be a realist with respect to black holes, and likewise, if you want to be a realist about black holes, you cannot be an entity realist of these particular strands.

I explore the process of changes in the observability of entities and objects in science and how such changes impact two key issues in the scientific realism debate: the claim that predictively successful elements of past science are retained in current scientific theories, and the inductive defense of a specific version of inference to the best explanation with respect to unobservables. I provide a case-study of the discovery of radium by Marie Curie in order to show that the observability of some entities can change and that such changes are relevant for arguments seeking to establish the reliability of success-to-truth inferences with respect to unobservables.

One of the core charges against explanationist scientific realism is that is too epistemically optimistic. Taking the charge seriously, some realists offer alternative forms of scientific realism – semi-realism and theoretical irrealism – designed to be more modestin their epistemic claims. In this paper, I consider two cases in cosmology and astrophysics that raise novel issues for both views: semi-realism is argued to end up making astrophysics metaphysically inflated when confronted with cases regarding the existence and evolution of galaxies and other astrophysical objects that cross the cosmic event horizon; theoretical irrealism is argued to be in serious tension with standard evidential reasoning in the context of the dark matter problem.

It is widely believed that science is in the business of finding out what the world is really like. The philosophical version of this belief is scientific realism -- a doctrine about science that tells us that we ought to believe that the best theories in science are true, and that the world is occupied with the objects that those theories contain. If scientific realism was not correct, the argument goes, the incredible success of science would be a miracle. The best explanation for the success of science however, is not that it is a miracle, but that scientific theories are true. This argument is an instance of inference to the best explanation, or IBE. Skeptics have questioned why scientific success must imply its truth given that there are so many abandoned, false scientific theories in the history of science that were nevertheless successful. One of the controversies in the debate between scientific realists and anti-realists surrounds the legitimacy of reasoning in accordance with IBE. Realists need IBE to be a justified and reliable guide to truth. In this compilation thesis, I address various questions related to IBE and scientific realism. Paper 1 argues that scientific realism without IBE loses too much of its epistemic optimism, and that it in some contexts even becomes more pessimistic than the most prominent rival philosophical doctrine about science -- constructive empiricism. To avoid deflating realism, I argue, a defense of IBE is necessary. Paper 2 addresses whether methodological similarities between science and metaphysics force scientific realists to also be realists with respect to metaphysics. If IBE is legitimate, it should not only be valid in science, but also in metaphysics, effectively inflating the ontology that scientific realists are rationally bound to accept. I argue against this conclusion. Paper 3 offers a proof of concept regarding a novel way to justify inferences to unobservable objects. Paper 4 establishes a novel critique of non-probabilistic versions of IBE in scientific realism.

Scientific realism driven by inference to the best explanation (IBE) takes empirically confirmed objects to exist, independent, pace empiricism, of whether those objects are observable or not. This kind of realism, it has been claimed, does not need probabilistic reasoning to justify the claim that these objects exist. But I show that there are scientific contexts in which a non-probabilistic IBE-driven realism leads to a puzzle. Since IBE can be applied in scientific contexts in which empirical confirmation has not yet been reached, realists will in these contexts be committed to the existence of empirically unconfirmed objects. As a consequence of such commitments, because they lack probabilistic features, the possible empirical confirmation of those objects is epistemically redundant with respect to realism.

The main purpose of this paper is to refute the metaphysicians ‘methodological continuation’ argument supporting epistemic realism in metaphysics. This argument aims to show that scientific realists have to accept that metaphysics is as rationally justified as science given that they both employ inference to the best explanation, i.e. that metaphysics and science are methodologically continuous. I argue that the reasons given by scientific realists as to why inference to the best explanation is reliable in science do not constitute a reason to believe that it is reliable in metaphysics. The justification of IBE in science and the justification of IBE in metaphysics are two distinct issues with only superficial similarities, and one cannot rely on one for the other. This becomes especially clear when one analyses the debate about the legitimacy of IBE that has taken place between realists and empiricists. The metaphysician seeking to piggyback on the realist defense of IBE in science by the methodological continuation argument presupposes that the defense is straightforwardly applicable to metaphysics. I will argue that it is, in fact, not. The favoured defenses of IBE in scientific realism make extensive use of empirical considerations, predictive power and inductive evidence, all of which are paradigmatically absent in the metaphysical context. Furthermore, I argue that the metaphysician, even if the realist would concede to the methodological continuation argument, fails to offer any agreed upon conclusions resulting from its application in metaphysics. As a result, the scientific realist is not committed to believing that there is metaphysical knowledge.