Quantum gravity poses the problem of merging quantum mechanics and general relativity, the two great conceptual revolutions in the physics of the twentieth century. The loop and spinfoam approach, presented in this book, is one of the leading research programs in the field. The first part of the book discusses the reformulation of the basis of classical and quantum Hamiltonian physics required by general relativity. The second part covers the basic technical research directions. Appendices include a detailed history of the (...) subject of quantum gravity, hard-to-find mathematical material, and a discussion of some philosophical issues raised by the subject. This fascinating text is ideal for graduate students entering the field, as well as researchers already working in quantum gravity. It will also appeal to philosophers and other scholars interested in the nature of space and time. (shrink)

Contrary to claims about the irrelevance of philosophy for science, I argue that philosophy has had, and still has, far more influence on physics than is commonly assumed. I maintain that the current anti-philosophical ideology has had damaging effects on the fertility of science. I also suggest that recent important empirical results, such as the detection of the Higgs particle and gravitational waves, and the failure to detect supersymmetry where many expected to find it, question the validity of certain philosophical (...) assumptions common among theoretical physicists, inviting us to engage in a clearer philosophical reflection on scientific method. (shrink)

Following a line of research that I have developed for several years, I argue that the best strategy for understanding quantum gravity is to build a picture of the physical world where the notion of time plays no role at all. I summarize here this point of view, explaining why I think that in a fundamental description of nature we must “forget time”, and how this can be done in the classical and in the quantum theory. The idea is to (...) develop a formalism that treats dependent and independent variables on the same footing. In short, I propose to interpret mechanics as a theory of relations between variables, rather than the theory of the evolution of variables in time. (shrink)

Facts happen at every interaction, but they are not absolute: they are relative to the systems involved in the interaction. Stable facts are those whose relativity can effectively be ignored. In this work, we describe how stable facts emerge in a world of relative facts and discuss their respective roles in connecting quantum theory and the world. The distinction between relative and stable facts resolves the difficulties pointed out by the no-go theorem of Frauchiger and Renner, and is consistent with (...) the experimental violation of the Local Friendliness inequalities of Bong et al.. Basing the ontology of the theory on relative facts clarifies the role of decoherence in bringing about the classical world and solves the apparent incompatibility between the ‘linear evolution’ and ‘projection’ postulates. (shrink)

One of the world's most renowned theoretical physicists, Carlo Rovelli has entranced millions of readers with his singular perspective on the cosmos. In Helgoland, Rovelli examines the enduring enigma of quantum theory. The quantum world Rovelli describes is as beautiful as it is unnerving. Helgoland is a treeless island in the North Sea where the 21-year-old Werner Heisenberg first developed quantum theory, setting off a century of scientific revolution. Full of alarming ideas (ghost waves, distant objects that seem to (...) be magically connected, cats that appear both dead and alive), quantum physics has led to countless discoveries and technological advancements. Today our understanding of the world is based on this theory, yet it is still profoundly mysterious. As scientists and philosophers continue to fiercly debate the theory's meaning, Rovelli argues that its most unsettling contradictions can be explained by seeing the world as fundamentally made of relationships, not substances. We and everything around us exist only in our interactions with one another. This bold idea suggests new directions for understanding the structure of reality and even the nature of consciousness. Rovelli makes learning about quantum mechanics an almost psychedelic experience. Shifting our perspective once again, he takes us on a riveting journey through the universe so we can better understand our place in it. (shrink)

Moral relativism is deeply troubling for those who believe that, without a set of moral absolutes, democratic societies will devolve into tyranny or totalitarianism. Engaging directly with this claim, Carlo Invernizzi Accetti traces the roots of contemporary anti-relativist fears to the antimodern rhetoric of the Catholic Church, and then rescues a form of philosophical relativism for modern, pluralist societies, arguing that this standpoint provides the firmest foundation for an allegiance to democracy. In its dual analysis of the relationship between (...) religion and politics and the implications of philosophical relativism for democratic theory, this book makes a far-ranging contribution to contemporary debates over the revival of religion in politics and the conceptual grounds for a commitment to democracy. It conducts the first comprehensive genealogy of anti-relativist discourse and reclaims for English-speaking readers the overlooked work of political theorists such as Hans Kelsen and Norberto Bobbio, who had articulated the bond between philosophical relativism and democracy. By engaging with attempts to replace the religious foundation of democratic values with a neo-Kantian conception of reason, this book also offers a powerful case for relativism as the strongest basis for a civic ethos that integrates different perspectives into democratic politics. (shrink)

Dans le livre Λ de la Métaphysique, en accord avec sa thèse fondamentale de la primauté ontologique de l’individu sur l’universel, Aristote refuse d’attribuer le statut de substances immatérielles et de principes premiers de la réalité aux Formes platoniciennes et aux Nombres de la tradition académicienne. Il croit que ces principes platoniciens – selon lui des universels privés de vie – doivent être remplacés par une série d’êtres vivants, d’individus doués d’intelligence, en activité contin...

In his 1956 book ‘The Direction of Time’, Hans Reichenbach offered a comprehensive analysis of the physical ground of the direction of time, the notion of physical cause, and the relation between the two. I review its conclusions and argue that at the light of recent advances in physics Reichenbach analysis provides the best account for the physical underpinning of these notions. I integrate results in cosmology, and on the physical underpinning of records and agency into Reichenbach’s account, and discuss (...) which questions it leaves open. (shrink)

A solution to the issue of time in quantum gravity is proposed. The hypothesis that time is not defined at the fundamental level (at the Planck scale) is considered. A natural extension of canonical Heisenberg-picture quantum mechanics is defined. It is shown that this extension is well defined and can be used to describe the "non-Schrödinger regime," in which a fundamental time variable is not defined. This conclusion rests on a detailed analysis of which quantities are the physical observables of (...) the theory; a main technical result of the paper is the identification of a class of gauge-invariant observables that can describe the (observable) evolution in the absence of a fundamental definition of time. The choice of the scalar product and the interpretation of the wave function are carefully discussed. The physical interpretation of the extreme "no time" quantum gravitational physics is considered. (shrink)

The claim that diversity and independence have a net positive epistemic effect on the judgments of groups has been recently defended formally by Scott Page, among others, and popularized in Surowiecki's The Wisdom of Crowds. In Meta-Induction and the Wisdom of Crowds Thorn and Schurz take issue with the claim that more diversity and independence in groups leads to better collective judgments. I argue that Thorn and Schurz's arguments are helpful in clarifying a number of over-generalizations about diversity and independence (...) that are often circulated in the social epistemology literature. I also argue that the relevant formal arguments are easily misunderstood when presented 'in a vacuum', that is, without a context of application in mind. I provide a different approach to understanding formal results in social epistemology: With the help of concrete scenarios and the formal literature, I focus on a trade-off between independence and dependence in groups. I show that the approach works well also for another principle in social epistemology; namely, the principle that 'more heads are better than few'. (shrink)

Is reality three-dimensional and becoming real (Presentism), or is reality four-dimensional and becoming illusory (Eternalism)? Both options raise difficulties. I argue that we do not need to be trapped by this dilemma. There is a third possibility: reality has a more complex temporal structure than either of these two naive options. Fundamental becoming is real, but local and unoriented. A notion of present is well defined, but only locally and in the context of approximations.

As a response to the semantic and logical paradoxes, theorists often reject some principles of classical logic. However, classical logic is entangled with mathematics, and giving up mathematics is too high a price to pay, even for nonclassical theorists. The so-called recapture theorems come to the rescue. When reasoning with concepts such as truth/class membership/property instantiation, (These are examples of concepts that are taken to satisfy naive rules such as the naive truth schema and naive comprehension, and that therefore are (...) compatible with a solution to paradox cast in the logics considered below. Other notions of similar kind can be added to the list.) if one is interested in consequences of the theory that only contain mathematical vocabulary, nothing is lost by reasoning in the nonclassical framework. This article shows that this claim is highly misleading, if not simply false. Under natural assumptions, some well-established approaches to recapture are incorrect. (shrink)

Choice can be defined in thermodynamical terms, and shown to have a thermodynamic cost: choosing between a binary alternative at temperature T dissipates an energy $$E\ge kT\ln 2$$.

This is a contribution to a book on quantum gravity and philosophy. I discuss nature and origin of the problem of quantum gravity. I examine the knowledge that may guide us in addressing this problem, and the reliability of such knowledge. In particular, I discuss the subtle modification of the notions of space and time engendered by general relativity, and how these might merge into quantum theory. I also present some reflections on methodological questions, and on some general issues in (...) philosophy of science which are are raised by, or a relevant for, the research on quantum gravity. (shrink)

Substructural logics and their application to logical and semantic paradoxes have been extensively studied. In the paper, we study theories of naïve consequence and truth based on a non-reflexive logic. We start by investigating the semantics and the proof-theory of a system based on schematic rules for object-linguistic consequence. We then develop a fully compositional theory of truth and consequence in our non-reflexive framework.

In this paper I will discuss Edmund Husserl’s critique of Franz Brentano’s interpretation of categorical judgments as Double Judgments (Doppelurteile). This will be developed mostly as an internal critique, within the framework of the school of Brentano, and not through a direct contrast with Husserl’s own theory of judgment, as presented e.g. in the Fifth Investigation. Already during the 1890s Husserl overcame the psychologistic aspects of Brentano’s approach, advocating the importance of analysing the logical structure underlying language independently from psychology. (...) Moreover, Husserl’s critique seems to be also applicable to Bertrand Russell’s analysis, which shares an important aspect of Brentano’s theory. I will try to avoid going too deep into the various theories of judgment and keep mostly to the issue of double judgments. (shrink)

According to Bohmian mechanics, we see the particle, not the pilot wave. But to make predictions we need to know the wave. How do we learn about the wave to make predictions, if we only see the particle? I show that the puzzle can be solved, but only thanks to decoherence.

The paper examines the epistemological significance of the expe- rience of estrangement caused by some types of descriptions of objects and phenomena. It shows how, today, the main productive matrix of these descriptions is formed by natural science. A distinction is drawn between a reductionist and pluralist approach to the aspect of estrangement offered by science, and subsequently analysed. The paper then puts forward an argument in support of the latter attitude.

The world appears to be well described by gauge theories; why? I suggest that gauge is more than mathematical redundancy. Gauge-dependent quantities can not be predicted, but there is a sense in which they can be measured. They describe “handles” though which systems couple: they represent real relational structures to which the experimentalist has access in measurement by supplying one of the relata in the measurement procedure itself. This observation leads to a physical interpretation for the ubiquity of gauge: it (...) is a consequence of a relational structure of physical quantities. (shrink)

The book is a comprehensive introduction to the work of the Estonian-German biologist Jakob von Uexküll. After a first introductory chapter by Morten Tønnessen and a second chapter on Uexküll's life and philosophical background, it contains four chapters devoted to the analysis of his main works; they are followed by a vast eighth chapter which deals with the influence Uexküll had on other philosophers and scientists, and by a conclusions focused on the possibility of updating Uexküll's work. The monograph combines (...) a careful reconstruction of the historical context in which the Uexküllian concepts emerged (the debate between mechanism and vitalism, contemporary scientific studies) and a thorough analysis of the philosophical contents of the Uexküllian views. As far as the key issue is concerned, Uexküll's notion of Umwelt refers to the perceptive and operative world which surrounds animal species; it is a subjective species-specific construction which provides living organisms with great security and behaviour stability. Moreover, the relationship that the animal carries out with its environment proves to be a complex system of semiotic interactions: its behaviour is not a set of mechanical reactions, but the result of a spontaneous attribution of meaning to the outside world, whose environmental elements are actively interpreted by the subject. The environment of animal species becomes a field of meaning, an exceedingly complex subjective elaboration; this can lessen the distance between animals and men, crediting both with the cognitive ability to grasp meanings and to use signs. (shrink)

Notions like meaning, signal, intentionality, are difficult to relate to a physical word. I study a purely physical definition of "meaningful information", from which these notions can be derived. It is inspired by a model recently illustrated by Kolchinsky and Wolpert, and improves on Dretske classic work on the relation between knowledge and information. I discuss what makes a physical process into a signal.

ABSTRACT The mainstreaming of environmental concerns paradoxically obscures their political dimension: as the goals of environmentalism become accepted, they are reduced to administrative problems to be solved in a purely technocratic way. This technocratic environmentalism has fueled a populist backlash that challenges the scientific basis of environmentalism. As a result, contemporary environmentalism appears to be stuck in a depoliticizing opposition between technocracy and populism. A possible way out of this depoliticizing trap consists in recognizing the intrinsic contestability of the core (...) premises on which environmentalism is based, since it is not merely the result of a straightforward application of scientifically provable facts, but also depends on normative principles and value choices. This opens the possibility for an internal pluralization of environmentalism, which shifts emphasis from the depoliticizing struggle between technocratic environmentalism and populist anti-environmentalism to the inherently political rivalry between different types of environmentalism. (shrink)