General Covariance and Background Independence in Quantum Gravity
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The Homological Kنhler-De Rham Differential Mechanism Part I
Hindawi Publishing Corporation Advances in Mathematical Physics Volume 2011, Article ID 191083, 14 pages doi:10.1155/2011/191083 Research Article The Homological Kahler-De¨ Rham Differential Mechanism part I: Application in General Theory of Relativity Anastasios Mallios and Elias Zafiris Department of Mathematics, National and Kapodistrian University of Athens, Panepistimioupolis, 15784 Athens, Greece Correspondence should be addressed to Elias Zafiris, ezafi[email protected] Received 7 March 2011; Accepted 12 April 2011 Academic Editor: Shao-Ming Fei Copyright q 2011 A. Mallios and E. Zafiris. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The mechanism of differential geometric calculus is based on the fundamental notion of a connection on a module over a commutative and unital algebra of scalars defined together with the associated de Rham complex. In this communication, we demonstrate that the dynamical mechanism of physical fields can be formulated by purely algebraic means, in terms of the homological Kahler-De¨ Rham differential schema, constructed by connection inducing functors and their associated curvatures, independently of any background substratum. In this context, we show explicitly that the application of this mechanism in General Relativity, instantiating the case of gravitational dynamics, is related with the absolute representability of the theory in the field of real numbers, a byproduct of which is the fixed background manifold construct of this theory. Furthermore, the background independence of the homological differential mechanism is of particular importance for the formulation of dynamics in quantum theory, where the adherence to a fixed manifold substratum is problematic due to singularities or other topological defects. -
Loop Quantum Gravity Alejandro Perez, Centre De Physique Théorique and Université Aix-Marseille II • Campus De Luminy, Case 907 • 13288 Marseille • France
features Loop quantum gravity Alejandro Perez, Centre de Physique Théorique and Université Aix-Marseille II • Campus de Luminy, case 907 • 13288 Marseille • France. he revolution brought by Einstein’s theory of gravity lies more the notion of particle, Fourier modes, vacuum, Poincaré invariance Tin the discovery of the principle of general covariance than in are essential tools that can only be constructed on a given space- the form of the dynamical equations of general relativity. General time geometry.This is a strong limitation when it comes to quantum covariance brings the relational character of nature into our descrip- gravity since the very notion of space-time geometry is most likely tion of physics as an essential ingredient for the understanding of not defined in the deep quantum regime. Secondly, quantum field the gravitational force. In general relativity the gravitational field is theory is plagued by singularities too (UV divergences) coming encoded in the dynamical geometry of space-time, implying a from the contribution of arbitrary high energy quantum processes. strong form of universality that precludes the existence of any non- This limitation of standard QFT’s is expected to disappear once the dynamical reference system—or non-dynamical background—on quantum fluctuations of the gravitational field, involving the dynam- top of which things occur. This leaves no room for the old view ical treatment of spacetime geometry, are appropriately taken into where fields evolve on a rigid preestablished space-time geometry account. But because of its intrinsically background dependent (e.g. Minkowski space-time): to understand gravity one must definition, standard QFT cannot be used to shed light on this issue. -
Who's Afraid of Background Independence?
D. RICKLES WHO’S AFRAID OF BACKGROUND INDEPENDENCE? ABSTRACT: Background independence is generally considered to be ‘the mark of distinction’ of gen- eral relativity. However, there is still confusion over exactly what background independence is and how, if at all, it serves to distinguish general relativity from other theories. There is also some con- fusion over the philosophical implications of background independence, stemming in part from the definitional problems. In this paper I attempt to make some headway on both issues. In each case I argue that a proper account of the observables of such theories goes a long way in clarifying mat- ters. Further, I argue, against common claims to the contrary, that the fact that these observables are relational has no bearing on the debate between substantivalists and relationalists, though I do think it recommends a structuralist ontology, as I shall endeavour to explain. 1 INTRODUCTION Everybody says they want background independence, and then when they see it they are scared to death by how strange it is ... Background independence is a big conceptual jump. You cannot get it for cheap... ([Rovelli, 2003], p. 1521) In his ‘Who’s Afraid of Absolute Space?’ [1970], John Earman defended New- ton’s postulation of absolute, substantival space at a time when it was very un- fashionable to do so, relationalism being all the rage. Later, in his World Enough and Space-Time, he argued for a tertium quid, fitting neither substantivalism nor relationalism, substantivalism succumbing to the hole argument and relational- ism offering “more promissory notes than completed theories” ([Earman, 1989], p. -
Arxiv:1911.01307V1 [Gr-Qc] 4 Nov 2019 What ‘True Names’ This Article Refers to These By
Lie Theory suffices to understand, and Locally Resolve, the Problem of Time Edward Anderson Abstract The Lie claw digraph controls Background Independence and thus the Problem of Time and indeed the Fundamental Nature of Physical Law. This has been established in the realms of Flat and Differential Geometry with varying amounts of extra mathematical structure. This Lie claw digraph has Generator Closure at its centre (Lie brackets), Relationalism at its root (implemented by Lie derivatives), and, as its leaves, Assignment of Observables (zero commutants under Lie brackets) and Constructability from Less Structure Assumed (working if generator Deformation leads to Lie brackets algebraic Rigidity). This centre is enabled by automorphisms and powered by the Generalized Lie Algorithm extension of the Dirac Algorithm (itself sufficing for the canonical subcase, for which generators are constraints). The Problem of Time’s facet ordering problem is resolved. 1 dr.e.anderson.maths.physics *at* protonmail.com 1 Introduction Over 50 years ago, Wheeler, DeWitt and Dirac [6, 4] found a number of conceptual problems with combining General Relativity (GR) and Quantum Mechanics (QM). Kuchař and Isham [11] subsequently classified attempted resolutions of these problems; see [14] for a summary. They moreover observed that attempting to extend one of these Problem of Time facet’s resolution to include a second facet has a strong tendency to interfere with the first resolution (nonlinearity). The Author next identified [15, 20] each facet’s nature in a theory-independent manner. This is in the form of clashes between background-dependent (including conventional QM) and background-independent Physics (including GR). -
Chapter 9: the 'Emergence' of Spacetime in String Theory
Chapter 9: The `emergence' of spacetime in string theory Nick Huggett and Christian W¨uthrich∗ May 21, 2020 Contents 1 Deriving general relativity 2 2 Whence spacetime? 9 3 Whence where? 12 3.1 The worldsheet interpretation . 13 3.2 T-duality and scattering . 14 3.3 Scattering and local topology . 18 4 Whence the metric? 20 4.1 `Background independence' . 21 4.2 Is there a Minkowski background? . 24 4.3 Why split the full metric? . 27 4.4 T-duality . 29 5 Quantum field theoretic considerations 29 5.1 The graviton concept . 30 5.2 Graviton coherent states . 32 5.3 GR from QFT . 34 ∗This is a chapter of the planned monograph Out of Nowhere: The Emergence of Spacetime in Quantum Theories of Gravity, co-authored by Nick Huggett and Christian W¨uthrich and under contract with Oxford University Press. More information at www.beyondspacetime.net. The primary author of this chapter is Nick Huggett ([email protected]). This work was sup- ported financially by the ACLS and the John Templeton Foundation (the views expressed are those of the authors not necessarily those of the sponsors). We want to thank Tushar Menon and James Read for exceptionally careful comments on a draft this chapter. We are also grateful to Niels Linnemann for some helpful feedback. 1 6 Conclusions 35 This chapter builds on the results of the previous two to investigate the extent to which spacetime might be said to `emerge' in perturbative string the- ory. Our starting point is the string theoretic derivation of general relativity explained in depth in the previous chapter, and reviewed in x1 below (so that the philosophical conclusions of this chapter can be understood by those who are less concerned with formal detail, and so skip the previous one). -
String Field Theory, Nucl
1 String field theory W. TAYLOR MIT, Stanford University SU-ITP-06/14 MIT-CTP-3747 hep-th/0605202 Abstract This elementary introduction to string field theory highlights the fea- tures and the limitations of this approach to quantum gravity as it is currently understood. String field theory is a formulation of string the- ory as a field theory in space-time with an infinite number of massive fields. Although existing constructions of string field theory require ex- panding around a fixed choice of space-time background, the theory is in principle background-independent, in the sense that different back- grounds can be realized as different field configurations in the theory. String field theory is the only string formalism developed so far which, in principle, has the potential to systematically address questions involv- ing multiple asymptotically distinct string backgrounds. Thus, although it is not yet well defined as a quantum theory, string field theory may eventually be helpful for understanding questions related to cosmology arXiv:hep-th/0605202v2 28 Jun 2006 in string theory. 1.1 Introduction In the early days of the subject, string theory was understood only as a perturbative theory. The theory arose from the study of S-matrices and was conceived of as a new class of theory describing perturbative interactions of massless particles including the gravitational quanta, as well as an infinite family of massive particles associated with excited string states. In string theory, instead of the one-dimensional world line 1 2 W. Taylor of a pointlike particle tracing out a path through space-time, a two- dimensional surface describes the trajectory of an oscillating loop of string, which appears pointlike only to an observer much larger than the string. -
The Hole Argument for Covariant Theories 6 2.1 Theory, Models, Covariance and General Covariance
The Hole Argument for Covariant Theories Iftime, M.∗, Stachel, J. † Abstract The hole argument was developed by Einstein in 1913 while he was searching for a relativistic theory of gravitation. Einstein used the lan- guage of coordinate systems and coordinate invariance, rather than the language of manifolds and diffeomorphism invariance. He formulated the hole argument against covariant field equations and later found a way to avoid it using coordinate language. In this paper we shall use the invariant language of categories, mani- folds and natural objects to give a coordinate-free description of the hole argument and a way of avoiding it. Finally we shall point out some im- portant implications of further extensions of the hole argument to sets and relations for the problem of quantum gravity. Keywords: General Relativity, Differential Geometry ∗School of Arts and Sciences, MCPHS, Boston, MA, USA †Department of Physics and Center for Philosophy and History of Science, Boston, MA, USA arXiv:gr-qc/0512021v2 8 Apr 2006 1 Contents 1 The Hole Argument in General Relativity 3 1.1 TheOriginalHoleArgument . 3 1.2 The Hole Argument for Inhomogeneous Einstein’s Field Equations 5 2 The Hole Argument for Covariant Theories 6 2.1 Theory, Models, Covariance and General Covariance . ... 6 2.2 Background Independent vs Background Dependent Theories.. 7 2.3 TheHoleArgumentforGeometricObjects . 8 2.4 Blocking the Formulation of the Hole Argument . 11 3 Conclusion 11 4 Acknowledgements 12 2 1 The Hole Argument in General Relativity 1.1 The Original Hole Argument In Einstein’s most detailed account of the hole argument [3], G(x) represents a metric tensor field that satisfies the field equations in the x-coordinate system and G′(x′) represents the same gravitational field in the x′-coordinate system. -
Quantum Gravity: a Primer for Philosophers∗
Quantum Gravity: A Primer for Philosophers∗ Dean Rickles ‘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.1 I have also supplied references for those cases where I have omitted some important facts. -
Einstein's Hole Argument
Einstein's Hole Argument Alan Macdonald Luther College Decorah, Iowa 52101 [email protected] February 17, 2020 Much improved version of Am. J. Phys. 69, 223-225 (2001) Abstract In general relativity, a spacetime and a gravitational field form an indi- visible unit: no field, no spacetime. This is a lesson of Einstein's hole argument. We use a simple transformation in a Schwartzschild spacetime to illustrate this. On the basis of the general theory of relativity . space as opposed to \what fills space" . has no separate existence. There is no such thing as an empty space, i.e., a space without [a gravitational] field. Space-time does not claim existence on its own, but only as a structural quality of the field. Albert Einstein, 1952. Introduction. What justification can be given for Einstein's words,1 writ- ten late in his life? The answer to this question has its origin in 1913, when Einstein was searching for a field equation for gravity. Einstein was aware of the possibility of generally covariant field equations, but he believed { wrongly, it turned out { that they could not possess the correct Newtonian limit. He then proposed a field equation covariant only under linear coordinate transforma- tions. To buttress his case against generally covariant field equations, Einstein devised his hole argument, which purported to show that no generally covariant field equation can be satisfactory. When Einstein discovered his fully satisfac- tory generally covariant field equation for general relativity in 1915, it became apparent that there is a hole in the argument.2 The twin and pole-in-the-barn \paradoxes" of special relativity3 are invalid arguments whose elucidation helps us better understand the theory. -
Loop Quantum Gravity
QUANTUM GRAVITY Loop gravity combines general relativity and quantum theory but it leaves no room for space as we know it – only networks of loops that turn space–time into spinfoam Loop quantum gravity Carlo Rovelli GENERAL relativity and quantum the- ture – as a sort of “stage” on which mat- ory have profoundly changed our view ter moves independently. This way of of the world. Furthermore, both theo- understanding space is not, however, as ries have been verified to extraordinary old as you might think; it was introduced accuracy in the last several decades. by Isaac Newton in the 17th century. Loop quantum gravity takes this novel Indeed, the dominant view of space that view of the world seriously,by incorpo- was held from the time of Aristotle to rating the notions of space and time that of Descartes was that there is no from general relativity directly into space without matter. Space was an quantum field theory. The theory that abstraction of the fact that some parts of results is radically different from con- matter can be in touch with others. ventional quantum field theory. Not Newton introduced the idea of physi- only does it provide a precise mathemat- cal space as an independent entity ical picture of quantum space and time, because he needed it for his dynamical but it also offers a solution to long-stand- theory. In order for his second law of ing problems such as the thermodynam- motion to make any sense, acceleration ics of black holes and the physics of the must make sense. -
Regarding the 'Hole Argument' and the 'Problem of Time'
Regarding the ‘Hole Argument’ and the ‘Problem of Time’ Sean Gryb∗1 and Karim P. Y. Th´ebault†2 1Institute for Mathematics, Astrophysics and Particle Physics, Radboud University, Nijmegen, The Netherlands 2Department of Philosophy, University of Bristol, United Kingdom December 5, 2015 Abstract The canonical formalism of general relativity affords a particu- larly interesting characterisation of the infamous hole argument. It also provides a natural formalism in which to relate the hole argu- ment to the problem of time in classical and quantum gravity. In this paper we examine the connection between these two much dis- cussed problems in the foundations of spacetime theory along two interrelated lines. First, from a formal perspective, we consider the extent to which the two problems can and cannot be precisely and distinctly characterised. Second, from a philosophical perspective, we consider the implications of various responses to the problems, with a particular focus upon the viability of a ‘deflationary’ attitude to the relationalist/substantivalist debate regarding the ontology of space- time. Conceptual and formal inadequacies within the representative language of canonical gravity will be shown to be at the heart of both the canonical hole argument and the problem of time. Interesting and fruitful work at the interface of physics and philosophy relates to the challenge of resolving such inadequacies. ∗email: [email protected] †email: [email protected] 1 Contents 1 Introduction 2 2 The Hole Argument 3 2.1 A Covariant Deflation . .3 2.2 A Canonical Reinflation . .6 3 The Problem of Time 13 3.1 The Problem of Refoliation . -
The Hole Argument and Some Physical and Philosophical Implications
Living Rev. Relativity, 17,(2014),1 ,)6).' 2%6)%73 http://www.livingreviews.org/lrr-2014-1 doi:10.12942/lrr-2014-1 INRELATIVITY The Hole Argument and Some Physical and Philosophical Implications John Stachel Center for Einstein Studies, Boston University 745 Commonwealth Avenue Boston, MA 02215 U.S.A. email: [email protected] Accepted: 17 November 2013 Published: 6 February 2014 Abstract This is a historical-critical study of the hole argument, concentrating on the interface between historical, philosophical and physical issues. Although it includes a review of its history, its primary aim is a discussion of the contemporary implications of the hole argument for physical theories based on dynamical, background-independent space-time structures. The historical review includes Einstein’s formulations of the hole argument, Kretschmann’s critique, as well as Hilbert’s reformulation and Darmois’ formulation of the general-relativistic Cauchy problem. The 1970s saw a revival of interest in the hole argument, growing out of attempts to answer the question: Why did three years elapse between Einstein’s adoption of the metric tensor to represent the gravitational field and his adoption of the Einstein field equations? The main part presents some modern mathematical versions of the hole argument, including both coordinate-dependent and coordinate-independent definitions of covariance and general covariance; and the fiber bundle formulation of both natural and gauge natural theories. By abstraction from continuity and di↵erentiability, these formulations can be extended from di↵erentiable manifolds to any set; and the concepts of permutability and general permutability applied to theories based on relations between the elements of a set, such as elementary particle theories.