It was recognized almost from the original formulation of general relativity that the theory was incomplete because it dealt only with classical, rather than quantum, matter. What must be done in order to complete the theory has been a subject of considerable debate over the last century, and here I just mention a few of the various options that have been suggested for a quantum theory of gravity. The aim of what follows is twofold. First, I address worries about the (...) consistency and physical plausibility of hybrid theories of gravity—theories involving a classical gravitational field and quantum matter fields. Such worries are shown to be unfounded. These hybrid theories—mongrel gravity—in fact comprise the only current, actual theories of gravity that incorporate quantum matter, and they also offer legitimate promise as tools for discovering the full theory of gravity. So my second aim is to highlight these theories as providing an interesting example of scientific revolution in action. I begin to try to draw some philosophical lessons from mongrel gravity theories, but more importantly I try to convince philosophers of physics that they should pay more attention to them. (shrink)

In this paper, I consider the relationship between Inference to the Best Explanation and Bayesianism, both of which are well-known accounts of the nature of scientific inference. In Sect. 2, I give a brief overview of Bayesianism and IBE. In Sect. 3, I argue that IBE in its most prominently defended forms is difficult to reconcile with Bayesianism because not all of the items that feature on popular lists of “explanatory virtues”—by means of which IBE ranks competing explanations—have confirmational import. (...) Rather, some of the items that feature on these lists are “informational virtues”—properties that do not make a hypothesis \ more probable than some competitor \ given evidence E, but that, roughly-speaking, give that hypothesis greater informative content. In Sect. 4, I consider as a response to my argument a recent version of compatibilism which argues that IBE can provide further normative constraints on the objectively correct probability function. I argue that this response does not succeed, owing to the difficulty of defending with any generality such further normative constraints. Lastly, in Sect. 5, I propose that IBE should be regarded, not as a theory of scientific inference, but rather as a theory of when we ought to “accept” H, where the acceptability of H is fixed by the goals of science and concerns whether H is worthy of commitment as research program. In this way, IBE and Bayesianism, as I will show, can be made compatible, and thus the Bayesian and the proponent of IBE can be friends. (shrink)

Different versions of the A-theory of time are traditionally defined in terms of whether everything is present, or whether there are also past and future things. In this paper I argue that the traditional way of defining A-theories should be abandoned. I focus on the traditional definition of presentism, according to which always, everything is present. First, I argue that there are good reasons to reject all the most plausible interpretations of the predicate ‘is present’ as it appears in the (...) traditional definition of presentism. It follows that there are also good reasons to reject the most plausible interpretations of the traditional definitions of the other A-theories. I then argue that there is a better way of defining the A-theories, in terms of the question of whether existence has a beginning and an end. Finally, I argue that what goes for the traditional definition of presentism goes for the traditional definition of its modal analogue actualism, according to which necessarily, everything is actual : there are good reasons to reject the traditional definition of actualism in favour of a definition in terms of contingent existence. (shrink)

Howson famously argues that the no-miracles argument, stating that the success of science indicates the approximate truth of scientific theories, is a base rate fallacy: it neglects the possibility of an overall low rate of true scientific theories. Recently a number of authors has suggested that the corresponding probabilistic reconstruction is unjust, as it concerns only the success of one isolated theory. Dawid and Hartmann, in particular, suggest to use the frequency of success in some field of research \ to (...) infer a probability of truth for a new theory from \. I here shed doubts on the justification of this and similar moves and suggest a way to directly bound the probability of truth. As I will demonstrate, my bound can become incompatible with the assumption specific testing and Dawid and Hartmann’s estimate for success. (shrink)

This paper investigates some of the philosophical and conceptual issues raised by the search for a quantum theory of gravity. It is critically discussed whether such a theory is necessary in the first place, and how much would be accomplished if it is eventually constructed. I argue that the motivations behind, and expectations to, a theory of quantum gravity are entangled with central themes in the philosophy of science, in particular unification, reductionism, and the interpretation of quantum mechanics. I further (...) argue that there are —contrary to claims made on behalf of string theory— no good reasons to think that a quantum theory of gravity, if constructed, will provide a theory of everything, that is, a fundamental theory from which all physics in principle can be derived. (shrink)

Is philosophy useful for physics? Many physicists and philosophers believe that it is; but there are those who challenge the usefulness of philosophy for science. Three major objections can be identified in their reasoning: 1. Philosophy’s death diagnosis, which states that philosophy is dead and has nothing new to teach us. 2. Historic-agnostic argument/challenge, which states that there is no historical evidence for the claim that philosophy is useful for science, or if it is, it is unknown to us. 3. (...) The division of property argument, which states that philosophy and science are two distinct fields. The purpose of this article is to respond to these three objections by examining the case study of the relationship between general relativity and philosophy. By looking at the history of the formation and development of general relativity, we will argue that: 1. Philosophy has led to a refinement and deep understanding of the important concepts of covariance and invariance. 2. There is clear historical evidence for the positive influence of philosophy on the development of the core concepts of general relativity, as one of the most important physical theories, as well as the undeniable evidence for the key role of some philosophers in the development of the theory. 3. Physics and philosophy, in seeking answers to fundamental questions, are two highly intertwined fields. (shrink)

I explore Leibnizian themes in the theoretical physicist's pursuit of a quantum cosmology by examining Smolin's program based on the elimination of ideal elements. These constructs are formal mathematical structures of a physical theory that require for their interpretation the existence of objects external to the system treated by the theory. After introducing some necessary background information, I discuss the particulars of Smolin's definition of ideal elements and analyze his motivations and arguments for the elimination of ideal elements. I then (...) survey and assess his two specific proposals for the construction of a quantum cosmology. The former stems from the canonical approach to the development of a quantum theory of gravity; the latter consists of a series of hypotheses framing a speculative fundamental theory of the universe. Finally, I consider the explicit links and debts of Smolin's program to Leibniz's philosophy. (shrink)

In the last two centuries, a better understanding of nature and significant advances in science and technology have led to the emergence of new and exciting ideas and approaches. Almost all of them are known as the product of contemporary science. Ideas such as evolution in biology, the ideas about the beginning of the universe (models based on the existence of a starting point for the universe or otherwise), and the idea of parallel worlds in physics. Although these ideas have (...) flourished in the context of modern science, they contain important philosophical backgrounds and as a result, have some important philosophical consequences. In this article, a historical review of the writings and works of Ibn Sina shows that each of these ideas has been presented similarly since ancient times in natural philosophy. Therefore, their position is more philosophical than scientific. Using these theories without considering their metaphysical and non-experimental assumptions will lead to misconceptions. Many of the challenges between science and religion stem from not considering the limits of empirical science and a lack of attention to the metaphysical assumptions of scientific theories. In this article, we will explain Ibn Sina's reasons for or against these theories as one of the first people to explicitly examine the scientific and philosophical aspects of these theories. Ibn Sina's scientific accuracy and admirable scientific spirit can be enlightening for contemporary scholars. (shrink)

One of Julian Barbour’s main aims is to solve the problem of time that appears in quantum geometrodynamics (QG). QG involves the application of canonical quantization procedure to the Hamiltonian formulation of General Relativity. The problem of time arises because the quantization of the Hamiltonian constraint results in an equation that has no explicit time parameter. Thus, it appears that the resulting equation, as apparently timeless, cannot describe evolution of quantum states. Barbour attempts to resolve the problem by allegedly eliminating (...) time from his interpretation of QG. In order to evaluate the efficacy of his solution, it is necessary to ascertain in what sense time has been eliminated from his theory. I proceed to do so by developing a form of conceptual analysis that is applicable to the concept of time in physical theories and applying this analysis to Barbour’s account. (shrink)