Richard Dawid

We provide a philosophical reconstruction and analysis of the debate on the scientific status of cosmic inflation that has played out in recent years. In a series of critical papers, Ijjas et al. have questioned the scientificality of the current views on cosmic inflation. Proponents of cosmic inflation have in turn defended the scientific credentials of their approach. We argue that, while this defense, narrowly construed, is successful against Ijjas et al., the latter's reasoning does point to a significant epistemic issue that arises with respect to inflation. A broadening of the concept of theory assessment is needed to address that issue in an adequate way.

We claim that, as it stands, the Deutsch–Wallace–Everett approach to quantum theory is conceptually incoherent. This charge is based upon the approach’s reliance upon decoherence arguments that conflict with its own fundamental precepts regarding probabilistic reasoning in two respects. This conceptual conflict obtains even if the decoherence arguments deployed are aimed merely towards the establishment of certain ‘emergent’ or ‘robust’ structures within the wave function: To be relevant to physical science notions such as robustness must be empirically grounded, and, on our analysis, this grounding can only plausibly be done in precisely the probabilistic terms that lead to conceptual conflict. Thus, the incoherence problems presented necessitate either the provision of a new, non-probabilistic empirical grounding for the notions of robustness and emergence in the context of decoherence, or the abandonment of the Deutsch–Wallace–Everett programme for quantum theory

String theory currently is the only viable candidate for a unified description of all known natural forces. This article tries to demonstrate that the fundamental structural and methodological differences that set string theory apart from other physical theories have important philosophical consequences. Focussing on implications for the realism debate in philosophy of science, it is argued that both poles of that debate face new problems in the context of string theory. On the one hand, the claim of underdetermination of scientific theory by the available empirical data, which is a pivotal element of empiricism, loses much of its plausibility. On the other hand, the dissolution of any meaningful notion of an external ontological object destroys the basis for conventional versions of scientific realism. String theory seems to suggest an intermediate position akin to Structural Realism that is based on a newly emerging principle, to be called the principle of theoretical uniqueness.

According to an argument by Colin Howson, the no-miracles argument is contingent on committing the base-rate fallacy and is therefore bound to fail. We demonstrate that Howson’s argument only applies to one of two versions of the NMA. The other version, which resembles the form in which the argument was initially presented by Putnam and Boyd, remains unaffected by his line of reasoning. We provide a formal reconstruction of that version of the NMA and show that it is valid. Finally, we demonstrate that the use of subjective priors is consistent with the realist implication of the NMA and show that a core worry with respect to the suggested form of the NMA can be dispelled.

Scientific theories are hard to find, and once scientists have found a theory, H, they often believe that there are not many distinct alternatives to H. But is this belief justified? What should scientists believe about the number of alternatives to H, and how should they change these beliefs in the light of new evidence? These are some of the questions that we will address in this article. We also ask under which conditions failure to find an alternative to H confirms the theory in question. This kind of reasoning is frequently used in science and therefore deserves a careful philosophical analysis. 1 Introduction2 The Conceptual Framework3 The No Alternatives Argument4 Discussion I: A Quantitative Analysis of the No Alternatives Argument5 Discussion II: The Number of Alternatives and the Problem of Underdetermination6 ConclusionsAppendix AAppendix B

This paper proposes a revision of our understanding of causation that is designed to address what Hartry Field has suggested is the central problem in the metaphysics of causation today: reconciling Bertrand Russell’s arguments that the concept of causation can play no role in the advanced sciences with Nancy Cartwright’s arguments that causal concepts are essential to a scientific understanding of the world. The paper shows that Russell’s main argument is, ironically, very similar to an argument that Cartwright has put forward against the truth of universal laws of nature. The paper uses this insight to develop an account of causation that does justice to traditional views yet avoids the arguments of Russell.

The current status of string theory is assessed quite differently by most of the theory’s exponents than by the majority of physicists in other fields. While the former tend to have a high degree of trust in string theory’s viability, the latter largely share a substantially more skeptical point of view. This article argues that the controversy can be best understood in terms of a paradigmatic rift between the two sides over their understandings of theory assessment. An attempt is made to evaluate the two conflicting paradigms on their own terms. †To contact the author, please write to: Institute Vienna Circle, University of Vienna, Universtitätscampus Spitalgasse 2‐4, Hof 1, 1090 Vienna, Austria; e‐mail: [email protected].

This article investigates the implications of string theory for the conception of scientific theory confirmation. The classical understanding of theory confirmation is based on the assumption that scientific theory building is underdetermined by the available empirical data. Several arguments are presented, which suggest a devaluation of this ‘principle of scientific underdetermination’ in the context of string theory. An altered conception of scientific progress emerges that is not based on the notion of theory succession.

String theory currently is the only viable candidate for a unified description of all known natural forces. This article tries to demonstrate that the fundamental structural and methodological differences that set string theory apart from other physical theories have important philosophical consequences. Focussing on implications for the realism debate in philosophy of science, it is argued that both poles of that debate become untenable in the context of string theory. On one side the claim of underdetermination of scientific theories, which represents a pivotal element of empiricism, looses its appeal. On the other side the dissolution of any meaningful notion of an external ontological object destroys the basis for conventional versions of scientific realism. String theory seems to suggest an intermediate position akin to Structural Realism that is based on a newly emerging principle, to be called the principle of theoretical uniqueness. An appreciation of string theory’s considerable impact on basic conceptions of philosophy of science can also contribute to a clearer picture of string theory’s status and relevance in a scientific context.

String theory has by now maintained a highly influential position in high energy physics for more than a quarter of a century. The present article analyses the reasons for the considerable trust exponents of string theory have in their theory even though it has neither found empirical confirmation nor a complete formulation up to this point. It is argued that this trust can be understood in terms of an emerging new conception of theory assessment that relies strongly on the identification of limitations to the underdetermination of scientific theory building. The second part of the paper makes the point that another conspicuous element of string theoretical reasoning, the prominent role of the notion of a final theory, can be understood in terms of this altered notion of theory assessment as well.

It has been argued in Dawid that physicists at times generate substantial trust in an empirically unconfirmed theory based on observations that lie beyond the theory’s intended domain. A crucial role in the reconstruction of this argument of “non-empirical confirmation” is played by limitations to scientific underdetermination. The present paper discusses the question as to how generic the role of limitations to scientific underdetermination really is. It is argued that assessing such limitations is essential for generating trust in any theory’s predictions, be it empirically confirmed or not. The emerging view suggests that empirical and non-empirical confirmation are more closely related to each other than one may expect at first glance.

The discovery of the Higgs particle required a signal of 5σ significance. The rigid application of that condition is a convention that disregards more specific aspects of the given experiment. In particular, it does not account for the characteristics of the look elsewhere effect in the individual experimental context. The paper relates this aspect of data analysis to the question as to what extent theoretical reasoning should be admitted to play a role in the assessment of the significance of empirical data

Progress in elementary particle physics in recent decades has changed the status of the visible phenomena in the context of scientific research. Empiricist positions in philosophy of science, which put particular emphasis on the pre-eminence of the visible regime, are affected by this development. In spite of its less radical claims, constructive empiricism turns out to run into more serious problems than straightforward instrumentalism. The constructive empiricist’s emphasis on the scientist’s aims makes it essential for her to provide a satisfactory motivation for scientific inquiry. This, however, seems difficult to achieve on an empiricist basis in the case of elementary particle physics.

The subjective Everettian approach to quantum mechanics presented by Deutsch and Wallace fails to constitute an empirically viable theory of quantum phenomena. The decision theoretic implementation of the Born rule realized in this approach provides no basis for rejecting Everettian quantum mechanics in the face of empirical data that contradicts the Born rule. The approach of Greaves and Myrvold, which provides a subjective implementation of the Born rule as well but derives it from empirical data rather than decision theoretic arguments, avoids the problem faced by Deutsch and Wallace and is empirically viable. However, there is good reason to cast doubts on its scientific value

String theory has played a highly influential role in theoretical physics for nearly three decades and has substantially altered our view of the elementary building principles of the Universe. However, the theory remains empirically unconfirmed, and is expected to remain so for the foreseeable future. So why do string theorists have such a strong belief in their theory? This book explores this question, offering a novel insight into the nature of theory assessment itself. Dawid approaches the topic from a unique position, having extensive experience in both philosophy and high-energy physics. He argues that string theory is just the most conspicuous example of a number of theories in high-energy physics where non-empirical theory assessment has an important part to play. Aimed at physicists and philosophers of science, the book does not use mathematical formalism and explains most technical terms.

In the absence of empirical confirmation, scientists may judge a theory's chances of being viable based on a wide range of arguments. The paper argues that such arguments can differ substantially with regard to their structural similarly to empirical confirmation. Arguments that resemble empirical confirmation in a number of crucial respects provide a better basis for reliable judgement and can, in a Bayesian sense, amount to significant \textit{non-empirical} confirmation. It is shown that three kinds of non-empirical confirmation that have been specified in earlier work do satisfy those conditions.

The paper discusses major implications of high energy physics for the scientific realism debate. The first part analyses the ways in which aspects of the empirically well-confirmed standard model of particle physics are relevant for a reassessment of entity realism, ontological realism and structural realism. The second part looks at the implications of more far-reaching concepts like string theory. While those theories have not found empirical confirmation, if they turned out viable, their implications for the realism debate would be more substantial than those of the standard model.

String dualities establish empirical equivalence between theories that often look entirely different with respect to their basic ontology and physical structure. Therefore, they represent a particularly interesting example of empirical equivalence in physics. However, the status of duality relations in string physics differs substantially from the traditional understanding of the role played by empirical equivalence. The paper specifies three important differences and argues that they are related to a substantially altered view on the underdetermination of theory building.

Moritz Schlick’s interpretation of the causality principle is based on Schlick’s understanding of quantum mechanics and on his conviction that quantum mechanics strongly supports an empiricist reading of causation in his sense. The present paper compares the empiricist position held by Schlick with Bas van Fraassen’s more recent conception of constructive empiricism. It is pointed out that the development from Schlick’s understanding of logical empiricism to constructive empiricism reflects a difference between the understanding of quantum mechanics endorsed by Schlick and the understanding that had been established at the time of van Fraassen’s writing.

String theory has not even come close to a complete formulation after half a century of intense research. On the other hand, a number of features of the theory suggest that the theory, once completed, may be a final theory. It is argued in this chapter that those two conspicuous characteristics of string physics are related to each other. What links them together is the fact that string theory has no dimensionless free parameters at a fundamental level. The paper analyses possible implications of this situation for the long term prospects of theory building in fundamental physics.

We discuss the proposal by Sebens and Carroll to derive the Born rule in Everettian quantum mechanics from a principle they call ‘ESP-QM’. We argue that the proposal fails: ESP-QM is not, as Sebens and Carroll argue, a ‘less general version’ of an independently plausible principle, ESP, and can only be motivated by the empirical success of quantum mechanics, including use of the Born rule. Therefore, ESP-QM cannot have the status of a meta-theoretical principle of reasoning and provides no viable basis for deriving the Born rule.

It is argued that the evolution of fundamental microphysics throughout the twentieth century is characterised by two interrelated developments. On the one hand, the experimental signatures which confirm theoretical statements are moving towards the fringes of the phenomenal world and, at the same time, leave increasingly wide spaces for entirely theoretical reasoning with little or no empirical interference. On the other hand, assessments of limitations to scientific underdetermination gain importance within the theoretical process

It is argued that the evolution of fundamental microphysics throughout the twentieth century is characterised by two interrelated developments. On the one hand, the experimental signatures which confirm theoretical statements are moving towards the fringes of the phenomenal world and, at the same time, leave increasingly wide spaces for entirely theoretical reasoning with little or no empirical interference. On the other hand, assessments of limitations to scientific underdetermination gain importance within the theoretical process