Since Christensen refuted the Bootstrap theory of confirmation in 1990, there have been some trials to improve the Hypothetico-Deductive theory of confirmation. After some trials, Gemes (1998) declared that his revised version completely overcame the difficulties of Hypothetico-Deductivism without generating any new difficulties. In this paper, I will assert that Gemes's revised version encounters some new difficulties, so it cannot be a true alternative to the Bootstrap theory of confirmation and to classical Hypothetico-Deductivism. Also I will assert that, in principle, (...) such new difficulties cannot be overcome by any trials dependent only on formal logic. (shrink)

Stoicism deserves everything that Broic$ are doing to its movement. This is because Stoics stuff the value of everything into their own heads, thus denying that external things are good and that other people have intrinsic value. Stoics are psychopathic narcissists and axiological solipsists. And this makes Stoicism easy to coopt into bro-y, shallow, self-help-y garbage.

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)

A funny, touching look at the life of a social media influencer who starts to question the #goals life she has created for herself. Every day, Élie motivates her hundreds of thousands of followers to become the best versions of themselves by posting videos of exercise routines and high-protein breakfast recipes. Far from the shy teenager that she was, she is now in a very public relationship with singer Samuel Vanasse, and together they have become one of the most popular (...) influencer couples in the country. She has succeeded. She shines. And yet, Élie worries that her life is not as flawless as she makes it seem on YouTube and Instagram. Between her obsession with the "ideal weight," her growing attraction to another man, her family's disdain for her career as a content creator and a collaboration with another influencer who Élie can't stand, a thought haunts her. What if, by trying to become everything she wanted to be, she's lost herself along the way? Suck it In and Smile is an intimate exploration of our obsession with appearances and the hypocrisies that appear when you must craft the perfect online life. (shrink)

Gravity and Grace was the first ever publication by the remarkable thinker and activist, Simone Weil. In it Gustave Thibon, the priest to whom she had entrusted her notebooks before her untimely death, compiled in one remarkable volume a compendium of her writings that have become a source of spiritual guidance and wisdom for countless individuals.

The quest for a theory of quantum gravity is usually understood to be driven by philosophical assumptions external to physics proper. It is suspected that specifically approaches in the context of particle physics are rather based on metaphysical premises than experimental data or physical arguments. I disagree. In this paper, I argue that the quest for a theory of quantum gravity sets an important example of physics’ internal unificatory practice. It is exactly Weinberg’s and others’ particle physics stance (...) that reveals the issue of quantum gravity as a genuine physical problem arising within the framework of quantum field theory. (shrink)

“Witty, acerbic, and brilliant. Halton takes on truly basic philosophical issues, but unlike the great majority of cultural critics today, he is philosophically prepared and highly competent to do so. Halton’s extraordinary work is nearly unique among current writers in its relevance, incisiveness, and philosophical power.” (Bruce Wilshire, Rutgers University) “The Great Brain Suck is a wholly original book that draws on Eugene Halton’s careful empirical and conceptual work to offer critical insights into American life and scholarship. As he details (...) the ways that the American citizen has given way to the American consumer—the ways we have been fooled by the commodity magicians of commerce—Halton provides new, sound, and fascinating perspectives on both contemporary and historic American themes.” (Russell Belk, York University). (shrink)

A striking feature of Newton’s thought is the very broad reach of his empiricism, potentially extending even to immaterial substances, including God, minds, and should one exist, a non-perceiving immaterial medium. Yet Newton is also drawn to certain metaphysical principles—most notably the principle that matter cannot act where it is not—and this second, rationalist feature of his thought is most pronounced in his struggle to discover ‘gravity’s cause’. The causal problem remains vexing, for he neither invokes primary causation, nor (...) accepts action at a distance by locating active powers in matter. To the extent that he is drawn to metaphysical principles, then, the causal problem is that of discovering some non-perceiving immaterial medium. Yet Newton’s thought has a third striking feature, one with roots in the other two: he allows that substances of different kinds might simultaneously occupy the very same region of space. I elicit the implications of these three features. For Newton to insist upon all three would transform the causal question about gravity into an insoluble problem about apportioning active powers. More seriously, it would undermine his means of individuating substances, provoking what I call ‘Newton’s Substance Counting Problem’. (shrink)

What it would take to vindicate folk temporal error theory? This question is significant against a backdrop of new views in quantum gravity—so-called timeless physical theories—that claim to eliminate time by eliminating a one-dimensional substructure of ordered temporal instants. Ought we to conclude that if these views are correct, nothing satisfies the folk concept of time and hence that folk temporal error theory is true? In light of evidence we gathered, we argue that physical theories that entirely eliminate an (...) ordered substructure vindicate folk temporal error theory. (shrink)

A striking feature of Newton’s thought is the very broad reach of his empiricism, potentially extending even to immaterial substances, including God, minds, and should one exist, a non-perceiving immaterial medium. Yet Newton is also drawn to certain metaphysical principles—most notably the principle that matter cannot act where it is not—and this second, rationalist feature of his thought is most pronounced in his struggle to discover ‘gravity’s cause’. The causal problem remains vexing, for he neither invokes primary causation, nor (...) accepts action at a distance by locating active powers in matter. To the extent that he is drawn to metaphysical principles, then, the causal problem is that of discovering some non-perceiving immaterial medium. Yet Newton’s thought has a third striking feature, one with roots in the other two: he allows that substances of different kinds might simultaneously occupy the very same region of space. I elicit the implications of these three features. For Newton to insist upon all three would transform the causal question about gravity into an insoluble problem about apportioning active powers. More seriously, it would undermine his means of individuating substances, provoking what I call ‘Newton’s Substance Counting Problem’. (shrink)

This paper considers Newton’s position on gravity’s cause, both conceptually and historically. With respect to the historical question, I argue that while Newton entertained various hypotheses about gravity’s cause, he never endorsed any of them, and in particular, his lack of confidence in the hypothesis of robust and unmediated distant action by matter is explained by an inclination toward certain metaphysical principles. The conceptual problem about gravity’s cause, which I identified earlier along with a deeper problem about (...) individuating substances, is that a decisive conclusion is impossible unless certain speculative aspects of his empiricism are abandoned. In this paper, I situate those conceptual problems in Newton’s natural philosophy. They arise from ideas that push empiricism to potentially self-defeating limits, revealing the danger of allowing immaterial spirits any place in natural philosophy, especially spatially extended spirits supposed capable of co-occupying place with material bodies. Yet because their source ideas are speculative, Newton’s method ensures that these problems pose no threat to his rational mechanics or the profitable core of his empiricism. They are easily avoided by avoiding their source ideas, and when science emerges from natural philosophy, it does so with an ontology unencumbered by immaterial spirits. (shrink)

The purpose of this essay is to suggest that one of the dominant modes of thought in our society is a profound mistrust and misunderstanding of the role of business. A dominant myth in society is that business occupies the moral low ground, separate from ethics or a moral point of view. This position is characterized as the “business sucks” story, and the essay shows how the enactment of this story underlies business thinking among managers and business theorists. The (...) essay concludes with a suggestion to rethink and reinvent this story along more realistic and more empowering lines. Values based capitalism, or stakeholder capitalism, offers a better way to understand the complex role that business does and should play in modern society. (shrink)

A number of recent theories of quantum gravity lack a one-dimensional structure of ordered temporal instants. Instead, according to many of these views, our world is either best represented as a single three-dimensional object, or as a configuration space composed of such three-dimensional objects, none of which bear temporal relations to one another. Such theories will be empirically self-refuting unless they can accommodate the existence of conscious beings capable of representation. For if representation itself is impossible in a timeless (...) world, then no being in such a world could entertain the thought that a timeless theory is true, let alone believe such a theory or rationally believe it. This paper investigates the options for understanding representation in a three-dimensional, timeless, world. Ultimately it concludes that the only viable option is one according to which representation is taken to be deeply non-naturalistic. Ironically then we are left with two seemingly very unattractive options. Either a very naturalistic motivation—taking seriously a live view in fundamental physics—leads us to a very non-naturalistic view of the mental, or else views in the philosophy of mind partly dictate what is an acceptable theory in physics. (shrink)

_Gravity and Grace_ shows Weil's religious thoughts and ideas, drawn from many sources - Christian, Jewish, Indian, Greek and Hindu - and focusing on suffering and redemption. It brings the reader face to face with the profoundest levels of existence as Weil explores the relationship of the human condition to the realm of the transcendent.

This paper considers Newton’s position on gravity’s cause, both conceptually and historically. With respect to the historical question, I argue that while Newton entertained various hypotheses about gravity’s cause, he never endorsed any of them, and in particular, his lack of confidence in the hypothesis of robust and unmediated distant action by matter is explained by an inclination toward certain metaphysical principles. The conceptual problem about gravity’s cause, which I identified earlier along with a deeper problem about (...) individuating substances, is that a decisive conclusion is impossible unless certain speculative aspects of his empiricism are abandoned. In this paper, I situate those conceptual problems in Newton’s natural philosophy. They arise from ideas that push empiricism to potentially self-defeating limits, revealing the danger of allowing immaterial spirits any place in natural philosophy, especially spatially extended spirits supposed capable of co-occupying place with material bodies. Yet because their source ideas are speculative, Newton’s method ensures that these problems pose no threat to his rational mechanics or the profitable core of his empiricism. They are easily avoided by avoiding their source ideas, and when science emerges from natural philosophy, it does so with an ontology unencumbered by immaterial spirits. (shrink)

Eternalism, the view that what we regard locally as being located in the past, the present and the future equally exists, is the best ontological account of temporal existence in line with special and general relativity. However, special and general relativity are not fundamental theories and several research programs aim at finding a more fundamental theory of quantum gravity weaving together all we know from relativistic physics and quantum physics. Interestingly, some of these approaches assert that time is not (...) fundamental. If time is not fundamental, what does it entail for eternalism and the standard debate over existence in time? First, I will argue that the non-fundamentality of time to be found in string theory entails standard eternalism. Second, I will argue that the non-fundamentality of time to be found in loop quantum gravity entails atemporal eternalism, namely a novel position in the spirit of standard eternalism. (shrink)

It has long been thought that observing distinctive traces of quantum gravity in a laboratory setting is effectively impossible, since gravity is so much weaker than all the other familiar forces in particle physics. But the quantum gravity phenomenology community today seeks to do the (effectively) impossible, using a challenging novel class of `tabletop' Gravitationally Induced Entanglement (GIE) experiments, surveyed here. The hypothesized outcomes of the GIE experiments are claimed by some (but disputed by others) to provide (...) a `witness' of the underlying quantum nature of gravity in the non-relativistic limit, using superpositions of Planck-mass bodies. We inspect what sort of achievement it would possibly be to perform GIE experiments, as proposed, ultimately arguing that the positive claim of witness is equivocal. Despite various sweeping arguments to the contrary in the vicinity of quantum information theory or given low-energy quantum gravity, whether or not one can claim to witness the quantum nature of the gravitational field in these experiments decisively depends on which out of two legitimate modelling paradigms one finds oneself in. However, by situating GIE experiments in a tradition of existing experiments aimed at making gravity interestingly quantum in the laboratory, we argue that, independently of witnessing or paradigms, there are powerful reasons to perform the experiments, and that their successful undertaking would indeed be a major advance in physics. (shrink)

In the author’s previous contribution to this journal (Rosen 2015), a phenomenological string theory was proposed based on qualitative topology and hypercomplex numbers. The current paper takes this further by delving into the ancient Chinese origin of phenomenological string theory. First, we discover a connection between the Klein bottle, which is crucial to the theory, and the Ho-t’u, a Chinese number archetype central to Taoist cosmology. The two structures are seen to mirror each other in expressing the psychophysical (phenomenological) action (...) pattern at the heart of microphysics. But tackling the question of quantum gravity requires that a whole family of topological dimensions be brought into play. What we find in engaging with these structures is a closely related family of Taoist forebears that, in concert with their successors, provide a blueprint for cosmic evolution. Whereas conventional string theory accounts for the generation of nature’s fundamental forces via a notion of symmetry breaking that is essentially static and thus unable to explain cosmogony successfully, phenomenological/Taoist string theory entails the dialectical interplay of symmetry and asymmetry inherent in the principle of synsymmetry. This dynamic concept of cosmic change is elaborated on in the three concluding sections of the paper. Here, a detailed analysis of cosmogony is offered, first in terms of the theory of dimensional development and its Taoist (yin-yang) counterpart, then in terms of the evolution of the elemental force particles through cycles of expansion and contraction in a spiraling universe. The paper closes by considering the role of the analyst per se in the further evolution of the cosmos. (shrink)

One of the great challenges for 21st century physics is to quantize gravity and generate a theory that will unify gravity with the other three fundamental forces of nature. This paper takes the (heretical) point of view that gravity may be an inherently classical, i.e., nonquantum, phenomenon and investigates the experimental consequences of such a conjecture. At present there is no experimental evidence of the quantum nature of gravity and the likelihood of definitive tests in the (...) future is not at all certain. If gravity is, indeed, a nonquantum phenomenon, then it is suggested that evidence will most likely appear at mesoscopic scales. (shrink)

The central thesis of this paper is that contemporary theoretical physics is grounded in philosophical presuppositions that make it difficult to effectively address the problems of subject-object interaction and discontinuity inherent to quantum gravity. The core objectivist assumption implicit in relativity theory and quantum mechanics is uncovered and we see that, in string theory, this assumption leads into contradiction. To address this challenge, a new philosophical foundation is proposed based on the phenomenology of Maurice Merleau-Ponty and Martin Heidegger. Then, (...) through the application of qualitative topology and hypernumbers, phenomenological ideas about space, time, and dimension are brought into focus so as to provide specific solutions to the problems of force-field generation and unification. The phenomenological string theory that results speaks to the inconclusiveness of conventional string theory and resolves its core contradiction. (shrink)

In March 2015, a Falun Gong practitioner began an extended email assault on an Australian academician, an academician who had written about the confrontation between this practitioner’s movement and the People’s Republic of China in ways that the practitioner deemed overly critical of Falun Gong. This person demanded that the academician retract her article, implicitly threatening to defame her, her university, and the journal in which her piece appeared, and, possibly, file a lawsuit if she did not accede to his (...) demands. Though most non-specialists think of Falun Gong as a peaceful spiritual exercise group unjustly persecuted by Chinese authorities, it has a dark, little-known history of forcibly silencing critics. In turn, this pattern of repression is tied in with an esoteric theory of karma which prompts practitioners of Falun Gong to actively seek persecution and martyrdom. (shrink)

Although general relativity is a predictively successful theory, it treats matter as classical rather than as quantum. For this reason, it will have to be replaced by a more fundamental quantum theory of gravity. Attempts to formulate a quantum theory of gravity suggest that such a theory may have radical consequences for the nature, and indeed the fate, of spacetime. The present article articulates what this problem of spacetime is and traces it three approaches to quantum gravity (...) taking general relativity as their vantage point: semi-classical gravity, causal set theory, and loop quantum gravity. (shrink)

Spacetime functionalism is the view that spacetime is a functional structure implemented by a more fundamental ontology. Lam and Wüthrich have recently argued that spacetime functionalism helps to solve the epistemological problem of empirical coherence in quantum gravity and suggested that it also (dis)solves the hard problem of spacetime, namely the problem of offering a picture consistent with the emergence of spacetime from a non-spatio-temporal structure. First, I will deny that spacetime functionalism solves the hard problem by showing that (...) it comes in various species, each entailing a different attitude towards, or answer to, the hard problem. Second, I will argue that the existence of an explanatory gap, which grounds the hard problem, has not been correctly taken into account in the literature. (shrink)

The search for a quantum theory of the gravitational field is one of the great open problems in theoretical physics. This book presents a self-contained discussion of the concepts, methods and applications that can be expected in such a theory. The two main approaches to its construction - the direct quantisation of Einstein's general theory of relativity and string theory - are covered. Whereas the first attempts to construct a viable theory for the gravitational field alone, string theory assumes that (...) a quantum theory of gravity will be achieved only through a unification of all the interactions. However, both employ the general method of quantisation of constrained systems, which is described together with illustrative examples relevant for quantum gravity. There is a detailed presentation of the main approaches employed in quantum general relativity: path-integral quantisation, the background-field method and canonical quantum gravity in the metric, connection and loop formulations. The discussion of string theory centres around its quantum-gravitational aspects and the comparison with quantum general relativity. Physical applications discussed at length include the quantisation of black holes, quantum cosmology, the indications of a discrete structure of spacetime, and the origin of irreversibility. This book will be of interest to researchers and students working in relativity and gravitation, cosmology, quantum field theory and related topics. It will also be of interest to mathematicians and philosophers of science. (shrink)

A number of philosophers have argued in favour of extended simples on the grounds that they are needed by fundamental physics. The arguments typically appeal to theories of quantum gravity. To date, the argument in favour of extended simples has ignored the fact that the very existence of spacetime is put under pressure by quantum gravity. We thus consider the case for extended simples in the context of different views on the existence of spacetime. We show that the (...) case for extended simples based on physics is far more complex than has been previously thought. We present and then map this complexity, in order to present a much more textured picture of the argument for extended simples. (shrink)

‘Quantum Gravity’ does not denote any existing theory: the field of quantum gravity is very much a ‘work in progress’. As you will see in this chapter, there are multiple lines of attack each with the same core goal: to find a theory that unifies, in some sense, general relativity (Einstein’s classical field theory of gravitation) and quantum field theory (the theoretical framework through which we understand the behaviour of particles in non-gravitational fields). Quantum field theory and general (...) relativity seem to be like oil and water, they don’t like to mix—it is fair to say that combining them to produce a theory of quantum gravity constitutes the greatest unresolved puzzle in physics. Our goal in this chapter is to give the reader an impression of what the problem of quantum gravity is; why it is an important problem; the ways that have been suggested to resolve it; and what philosophical issues these approaches, and the problem itself, generate. This review is extremely selective, as it has to be to remain a manageable size: generally, rather than going into great detail in some area, we highlight the key features and the options, in the hope that readers may take up the problem for themselves—however, some of the basic formalism will be introduced so that the reader is able to enter the physics and (what little there is of) the philosophy of physics literature prepared. I have also supplied references for those cases where I have omitted some important facts. Hence, this chapter is intended primarily as a catalyst for future research projects by philosophers of physics, both budding and well-matured. (shrink)

The quest for a theory of quantum gravity is usually understood to be driven by philosophical assumptions external to physics proper. It is suspected that specifically approaches in the context of particle physics are rather based on metaphysical premises than experimental data or physical arguments. I disagree. In this paper, I argue that the quest for a theory of quantum gravity sets an important example of physics’ internal unificatory practice. It is exactly Weinberg’s and others’ particle physics stance (...) that reveals the issue of quantum gravity as a genuine physical problem arising within the framework of quantum field theory. (shrink)

The remarkable connections between gravity and thermodynamics seem to imply that gravity is not fundamental but emergent, and in particular, as Verlinde suggested, gravity is probably an entropic force. In this paper, we will argue that the idea of gravity as an entropic force is debatable. It is shown that there is no convincing analogy between gravity and entropic force in Verlinde’s example. Neither holographic screen nor test particle satisfies all requirements for the existence of (...) entropic force in a thermodynamics system. As a result, there is no entropic force in the gravity system. Furthermore, we show that the entropy increase of the screen is not caused by its statistical tendency to increase entropy as required by the existence of entropic force, but in fact caused by gravity. Therefore, Verlinde’s argument for the entropic origin of gravity is problematic. In addition, we argue that the existence of a minimum size of spacetime, together with the Heisenberg uncertainty principle in quantum theory, may imply the fundamental existence of gravity as a geometric property of spacetime. This provides a further support for the conclusion that gravity is not an entropic force. (shrink)

The gravity-related model of spontaneous wave function collapse, a longtime hypothesis, damps the massive Schrödinger Cat states in quantum theory. We extend the hypothesis and assume that spontaneous wave function collapses are responsible for the emergence of Newton interaction. Superfluid helium would then show significant and testable gravitational anomalies.

This paper is in three sections. The first establishes that Newton, in spite of a well-known passage in a letter to Richard Bentley of 1692, did believe in action at a distance. Many readers may see this merely as an act of supererogation, since it is so patently obvious that he did. However, there has been a long history among Newton scholars of allowing the letter to Bentley to over-ride all of Newton’s other pronouncements in favour of action at a (...) distance, with devastating effects on our understanding of related aspects of his physics and his theology. Furthermore, this misconceived scholarly endeavour shows no sign of abating. The second section then offers a historical reconstruction, based on Newton’s writings, of how, when and why he began to accept actions at a distance and make them one of the cornerstones of his physics. Finally, using this chronological account of Newton’s use of actions at a distance, the paper re-assesses the claims of B. J. T. Dobbs that Newton’s important manuscript, De gravitatione et aequipondio fluidorum, was written, not in the late 1660s or early 1670s as was previously supposed, but during the composition of the Principia, in 1684 or 1685.Keywords: Isaac Newton; Action-at-a-distance; Gravity; Force; Aether; Attraction. (shrink)

A generalized and unifying viewpoint to both general relativity and quantum mechanics and information is investigated. It may be described as a generaliztion of the concept of reference frame from mechanics to thermodynamics, or from a reference frame linked to an element of a system, and thus, within it, to another reference frame linked to the whole of the system or to any of other similar systems, and thus, out of it. Furthermore, the former is the viewpoint of general relativity, (...) the latter is that of quantum mechanics and information. Ciclicity in the manner of Nicolas Cusanus (Nicolas of Cusa) is complemented as a fundamental and definitive property of any totality, e.g. physically, that of the universe. It has to contain its externality within it somehow being namely the totality. This implies a seemingly paradoxical (in fact, only to common sense rather logically and mathematically) viewpoint for the universe to be repesented within it as each one quant of action according to the fundamental Planck constant. That approach implies the unification of gravity and entanglement correspondiing to the former or latter class of reference frames. An invariance, more general than Einstein's general covariance is to be involved as to both classes of reference frames unifying them. Its essence is the unification of the discrete and cotnitinuous (smooth). That idea underlies implicitly quantum mechanics for Bohr's principle that it study the system of quantum microscopic entities and the macroscopic apparatus desribed uniformly by the smmoth equations of classical physics. (shrink)

We present a reformulation of loop quantum gravity with a cosmological constant and no matter as a Fermi-liquid theory. When the topological sector is deformed and large gauge symmetry is broken, we show that the Chern–Simons state reduces to Jacobson’s degenerate sector describing 1+1 dimensional propagating fermions with nonlocal interactions. The Hamiltonian admits a dual description which we realize in the simple BCS model of superconductivity. On one hand, Cooper pairs are interpreted as wormhole correlations at the de Sitter (...) horizon; their number yields the de Sitter entropy. On the other hand, BCS is mapped into a deformed conformal field theory reproducing the structure of quantum spin networks. When area measurements are performed, Cooper-pair insertions are activated on those edges of the spin network intersecting the given area, thus providing a description of quantum measurements in terms of excitations of a Fermi sea to superconducting levels. The cosmological constant problem is naturally addressed as a nonperturbative mass-gap effect of the true Fermi-liquid vacuum. (shrink)

This qualitative study presents an analysis of the experiences of a teacher who had recently left working in an England state funded primary school. Using reflective lifeworld methodology, this study explored the teacher’s struggle to be authentic in the context of state funded education. Three prominent themes were identified as: 1) enhancement of every learner; 2) systemic oppression; and 3) tensions in being a teacher. The study concludes that being authentic as a teacher was experienced as being incompatible with the (...) current educational system. (shrink)

The space-time expansion has a new perspective on the universe phenomena. In this article, the key features of the Space-Time Expansion Theory are summarized and discussed, with three postulates incorporating different insights into the behavior of space-time expansion, gravity, space-time curvature, and time itself. Gravity is not an attraction; it is a push. Inertia, free fall, the principles of the theory of relativity and some other phenomena support the author’s assertions. The expansion of space-time is universal, occurs everywhere, (...) and produces gravity instead of counteracting it. Being immersed in the same space-time acceleration, we only perceive the disturbance caused by the matter, which is the massive objects push. This study aims to offer scientists an alternative investigation. “Gravitation is not attraction; it’s a push.” All in accordance with hydrodynamic gravitation and expanding Universe. (shrink)

This is a nontechnical overview of how various approaches to quantum gravity suggest modifications to the way we conceptualize space and time. A theory of quantum gravity is needed to reconcile quantum physics with general relativity, our best theory for gravity. The most popular approaches to quantum gravity are string theory and loop quantum gravity. So far, no approach has been empirically successful, and there is no commonly accepted theory. Thus, the conclusions presented here are (...) tentative. Many approaches suggest that space and time—or perhaps, it is better to talk about spacetime—might not be fundamental. Various views on how to think about time in quantum gravity are briefly presented. (shrink)

I discuss the statistical mechanics of gravitating systems and in particular its cosmological implications, and argue that many conventional views on this subject in the foundations of statistical mechanics embody significant confusion; I attempt to provide a clearer and more accurate account. In particular, I observe that (i) the role of gravity in entropy calculations must be distinguished from the entropy of gravity, that (ii) although gravitational collapse is entropy-increasing, this is not usually because the collapsing matter itself (...) increases in entropy, and that (iii) the Second Law of thermodynamics does not owe its validity to the statistical mechanics of gravitational collapse. (shrink)

Philosophers of physics and physicists have long been intrigued by the analogies and disanalogies between gravitational theories and gauge theories. Indeed, repeated attempts to collapse these disanalogies have made us acutely aware that there are fairly general obstacles to doing so. Nonetheless, there is a special case space-time dimensions) in which gravity is often claimed to be identical to a gauge theory. I subject this claim to philosophical scrutiny in this article. In particular, I analyse how the standard disanalogies (...) can be overcome in dimensions, and consider whether really licenses the interpretation of gravity as a gauge theory. Our conceptual analysis reveals more subtle disanalogies between gravity and gauge, and connects these to interpretive issues in classical and quantum gravity. 1 Introduction1.1 Motivation1.2 Prospectus2 Disanalogies3 Three-dimensional gravity and gauge3.1 gravity3.2 Chern–Simons3.2.1 Cartan geometry3.2.2 Overcoming obst-gauge via Cartan connections3.3 Disanalogies collapsed4 Two More Disanalogies4.1 What about the symmetries?4.2 The phase spaces of the two theories5 Summary and Conclusion. (shrink)

Analogue Gravity Phenomenology is a collection of contributions that cover a vast range of areas in physics, ranging from surface wave propagation in fluids to nonlinear optics. The underlying common aspect of all these topics, and hence the main focus and perspective from which they are explained here, is the attempt to develop analogue models for gravitational systems. The original and main motivation of the field is the verification and study of Hawking radiation from a horizon: the enabling feature (...) is the possibility to generate horizons in the laboratory with a wide range of physical systems that involve a flow of one kind or another. The years around 2010 and onwards witnessed a sudden surge of experimental activity in this expanding field of research. However, building an expertise in analogue gravity requires the researcher to be equipped with a rather broad range of knowledge and interests. The aim of this book is to bring the reader up to date with the latest developments and provide the basic background required in order to appreciate the goals, difficulties and success stories in the field of analogue gravity. Each chapter of the book treats a different topic explained in detail by the major experts for each specific discipline. The first chapters give an overview of black hole spacetimes and Hawking radiation before moving on to describe the large variety of analogue spacetimes that have been proposed and are currently under investigation. This introductory part is then followed by an in-depth description of what are currently the three most promising analogue spacetime settings, namely surface waves in flowing fluids, acoustic oscillations in Bose-Einstein condensates and electromagnetic waves in nonlinear optics. Both theory and experimental endeavours are explained in detail. The final chapters refer to other aspects of analogue gravity beyond the study of Hawking radiation, such as Lorentz invariance violations and Brownian motion in curved spacetimes, before concluding with a return to the origins of the field and a description of the available observational evidence for horizons in astrophysical black holes. (shrink)

There is a philosophical tradition of arguing against presentism, the thesis that only presently existing things exist, on the basis of its incompatibility with fundamental physics. I grant that presentism is incompatible with special and general relativity, but argue that presentism is not incompatible with quantum gravity, because there are some theories of quantum gravity that utilize a fixed foliation of spacetime. I reply to various objections to this defense of presentism, and point out a flaw in Gödel's (...) modal argument for the ideality of time. This paper provides an interesting case study of the interplay between physics and philosophy. (shrink)

Physics seems to tell us that there are four fundamental force-fields in nature: the gravitational, the electromagnetic, the weak, and the strong (or interactions). But it also seems to tell us that gravity cannot possibly be a force-field, in the same sense as the other three are. And yet the search for a grand unification of all four force-fields is today one of the hottest pursuits. Is this the result of a simple confusion? This article aims at clarifying this (...) situation by (i) reviewing the gauge-field programme and its conception of unification of force-fields, (ii) examining the various attempts at a gauge theory of gravity, and (iii) articulating the nature of "gauging" and using it to explain the difference between gravity and the other force-fields. (shrink)