Approaching the Planck Scale from a Generally Relativistic Point of View: a Philosophical Appraisal of Loop Quantum Gravity
Total Page:16
File Type:pdf, Size:1020Kb
Load more
Recommended publications
-
Quantum Simplicial Geometry in the Group Field Theory Formalism
Quantum simplicial geometry in the group field theory formalism: reconsidering the Barrett-Crane model Aristide Baratin∗1 and Daniele Oriti†2 1Centre de Physique Th´eorique, CNRS UMR 7644, Ecole Polytechnique F-9112 Palaiseau Cedex, France 2Max-Planck-Institut f¨ur Gravitationsphysik Albert Einstein Institute Am M¨uhlenberg 2, 14476, Golm, Germany, EU A dual formulation of group field theories, obtained by a Fourier transform mapping functions on a group to functions on its Lie algebra, has been proposed recently. In the case of the Ooguri model for SO(4) BF theory, the variables of the dual field variables are thus so(4) bivectors, which have a direct interpretation as the discrete B variables. Here we study a modification of the model by means of a constraint operator implementing the simplicity of the bivectors, in such a way that projected fields describe metric tetrahedra. This involves a extension of the usual GFT framework, where boundary operators are labelled by projected spin network states. By construction, the Feynman amplitudes are simplicial path integrals for constrained BF theory. We show that the spin foam formulation of these amplitudes corresponds to a variant of the Barrett-Crane model for quantum gravity. We then re-examin the arguments against the Barrett-Crane model(s), in light of our construction. Introduction Group field theories (GFT) represent a second quantized framework for both spin networks and simplicial geometry [6, 7, 9], field theories on group manifolds (or Lie algebras) producing Feynman amplitudes which can be equivalently expressed as simplicial gravity path integrals [5] or spin foam models [10], in turn covariant formulations of spin networks dynamics [1]3. -
Dimensional Topological Quantum Field Theory from a Tight-Binding Model of Interacting Spinless Fermions
This is a repository copy of (3+1)-dimensional topological quantum field theory from a tight-binding model of interacting spinless fermions. White Rose Research Online URL for this paper: http://eprints.whiterose.ac.uk/99993/ Version: Accepted Version Article: Cirio, M, Palumbo, G and Pachos, JK (2014) (3+1)-dimensional topological quantum field theory from a tight-binding model of interacting spinless fermions. Physical Review B, 90 (8). 085114. ISSN 2469-9950 https://doi.org/10.1103/PhysRevB.90.085114 Reuse Unless indicated otherwise, fulltext items are protected by copyright with all rights reserved. The copyright exception in section 29 of the Copyright, Designs and Patents Act 1988 allows the making of a single copy solely for the purpose of non-commercial research or private study within the limits of fair dealing. The publisher or other rights-holder may allow further reproduction and re-use of this version - refer to the White Rose Research Online record for this item. Where records identify the publisher as the copyright holder, users can verify any specific terms of use on the publisher’s website. Takedown If you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing [email protected] including the URL of the record and the reason for the withdrawal request. [email protected] https://eprints.whiterose.ac.uk/ (3+1)-dimensional topological quantum field theory from a tight-binding model of interacting spinless fermions Mauro Cirio,1 Giandomenico Palumbo,2 and Jiannis K. Pachos2 1Centre for Engineered Quantum Systems, Department of Physics and Astronomy, Macquarie University, North Ryde, NSW 2109, Australia 2School of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT, United Kingdom (Dated: July 15, 2014) Currently, there is much interest in discovering analytically tractable (3 + 1)-dimensional models that describe interacting fermions with emerging topological properties. -
Construction and Examples of Higher Gauge Theories∗
Construction and examples of higher gauge theories∗ Tijana Radenkovi´cy Institute of Physics, University of Belgrade, Pregrevica 118, 11080 Belgrade, Serbia Marko Vojinovi´cz Institute of Physics, University of Belgrade, Pregrevica 118, 11080 Belgrade, Serbia Abstract We provide several examples of higher gauge theories, constructed as gener- alizations of a BF model to 2BF and 3BF models with constraints. Using the framework of higher category theory, we introduce appropriate 2-groups and 3- groups, and construct the actions for the corresponding constrained 2BF and 3BF theories. In this way, we can construct actions which describe the correct dynamics of Yang-Mills, Klein-Gordon, Dirac, Weyl, and Majorana fields coupled to Einstein-Cartan gravity. Each action is naturally split into a topological sector and a sector with simplicity constraints. The properties of the higher gauge group structure opens up a possibility of a nontrivial unification of all fields. 1. Introduction The quantization of the gravitational field is one of the fundamental open problems in modern physics. There are various approaches to this prob- lem, some of which have developed into vast research frameworks. One of such frameworks is the Loop Quantum Gravity approach, which aims to establish a nonperturbative quantization of gravity, both canonically and covariantly [1, 2, 3]. The covariant approach is slightly more general, and ∗ This work was supported by the project ON171031 of the Ministry of Education, Sci- ence and Technological Development (MPNTR) of the Republic of Serbia, and partially by the bilateral scientific cooperation between Austria and Serbia through the project \Causality in Quantum Mechanics and Quantum Gravity - 2018-2019", no. -
Aspects of Loop Quantum Gravity
Aspects of loop quantum gravity Alexander Nagen 23 September 2020 Submitted in partial fulfilment of the requirements for the degree of Master of Science of Imperial College London 1 Contents 1 Introduction 4 2 Classical theory 12 2.1 The ADM / initial-value formulation of GR . 12 2.2 Hamiltonian GR . 14 2.3 Ashtekar variables . 18 2.4 Reality conditions . 22 3 Quantisation 23 3.1 Holonomies . 23 3.2 The connection representation . 25 3.3 The loop representation . 25 3.4 Constraints and Hilbert spaces in canonical quantisation . 27 3.4.1 The kinematical Hilbert space . 27 3.4.2 Imposing the Gauss constraint . 29 3.4.3 Imposing the diffeomorphism constraint . 29 3.4.4 Imposing the Hamiltonian constraint . 31 3.4.5 The master constraint . 32 4 Aspects of canonical loop quantum gravity 35 4.1 Properties of spin networks . 35 4.2 The area operator . 36 4.3 The volume operator . 43 2 4.4 Geometry in loop quantum gravity . 46 5 Spin foams 48 5.1 The nature and origin of spin foams . 48 5.2 Spin foam models . 49 5.3 The BF model . 50 5.4 The Barrett-Crane model . 53 5.5 The EPRL model . 57 5.6 The spin foam - GFT correspondence . 59 6 Applications to black holes 61 6.1 Black hole entropy . 61 6.2 Hawking radiation . 65 7 Current topics 69 7.1 Fractal horizons . 69 7.2 Quantum-corrected black hole . 70 7.3 A model for Hawking radiation . 73 7.4 Effective spin-foam models . -
Arxiv:Gr-Qc/0303027 V1 6 Mar 2003
MATTERS OF GRAVITY The newsletter of the Topical Group on Gravitation of the American Physical Society Number 21 Spring 2003 Contents GGR News: GGR Activities, by Richard Price ....................... 3 We hear that... by Jorge Pullin ........................ 4 Institute of Physics Gravitational Physics Group, by Elizabeth Winstanley . 5 Center for Gravitational Wave Astronomy, by Mario D´ıaz .......... 6 Research Briefs: LIGO’s first preliminary science run, by Gary Sanders ........... 8 Quantization of area: the plot thickens, by John Baez ............ 12 Convergence of G Measurements – Mysteries Remain, by Riley Newman . 16 Conference reports: Brane world gravity, by Elizabeth Winstanley ................. 18 Massive black holes focus session, by Steinn Sigurdsson ........... 19 GWDAW 2002, by Peter Saulson ....................... 21 Source simulation focus session, by Pablo Laguna .............. 23 RRI workshop on loop quantum gravity, by Fernando Barbero ........ 25 Lazarus/Kudu Meeting, by Warren G. Anderson ............... 27 arXiv:gr-qc/0303027 v1 6 Mar 2003 Editor Jorge Pullin Department of Physics and Astronomy Louisiana State University 202 Nicholson Hall Baton Rouge, LA 70803-4001 Phone/Fax: (225)578-0464 Internet: [email protected] WWW: http://www.phys.lsu.edu/faculty/pullin ISSN: 1527-3431 1 Editorial Not much to report here. This newsletter is a bit late, since I wanted to wait till LIGO could report on its first science run. I want to encourage the readership to suggest topics for articles in MOG. In the last few issues articles were solicited by myself. This is not good for keeping the newsletter balanced. Either contact the relevant correspondent or me directly. The next newsletter is due September 1st. -
Loop and Spin Foam Quantum Gravity: a Brief Guide for Beginners
AEI-2006-004 hep-th/0601129 January 18th, 2006 Loop and Spin Foam Quantum Gravity: A Brief Guide for Beginners Hermann Nicolai and Kasper Peeters Max-Planck-Institut f¨ur Gravitationsphysik Albert-Einstein-Institut Am M¨uhlenberg 1 14476 Golm, GERMANY hermann.nicolai, [email protected] Abstract: We review aspects of loop quantum gravity and spin foam models at an introductory level, with special attention to questions frequently asked by non-specialists. arXiv:hep-th/0601129 v2 16 Feb 2006 Contributed article to “An assessment of current paradigms in the physics of fundamental interactions”, ed. I. Stamatescu, Springer Verlag. 1. Quantum Einstein gravity ics approach [7], addresses several aspects of the problem that are currently outside the main focus The assumption that Einstein’s classical theory of of string theory, in particular the question of back- gravity can be quantised non-perturbatively is at the ground independence and the quantisation of geom- root of a wide variety of approaches to quantum etry. Whereas there is a rather direct link between gravity. The assumption constitutes the basis of sev- (perturbative) string theory and classical space-time eral discrete methods [1], such as dynamical tri- concepts, and string theory can therefore rely on fa- angulations and Regge calculus, but it also implic- miliar notions and concepts, such as the notion of a itly underlies the older Euclidean path integral ap- particle and the S-matrix, the task is harder for LQG, proach [2, 3] and the somewhat more indirect ar- as it must face up right away to the question of what guments which suggest that there may exist a non- an observable quantity is in the absence of a proper trivial fixed point of the renormalisation group [4–6]. -
The Philosophy and Physics of Time Travel: the Possibility of Time Travel
University of Minnesota Morris Digital Well University of Minnesota Morris Digital Well Honors Capstone Projects Student Scholarship 2017 The Philosophy and Physics of Time Travel: The Possibility of Time Travel Ramitha Rupasinghe University of Minnesota, Morris, [email protected] Follow this and additional works at: https://digitalcommons.morris.umn.edu/honors Part of the Philosophy Commons, and the Physics Commons Recommended Citation Rupasinghe, Ramitha, "The Philosophy and Physics of Time Travel: The Possibility of Time Travel" (2017). Honors Capstone Projects. 1. https://digitalcommons.morris.umn.edu/honors/1 This Paper is brought to you for free and open access by the Student Scholarship at University of Minnesota Morris Digital Well. It has been accepted for inclusion in Honors Capstone Projects by an authorized administrator of University of Minnesota Morris Digital Well. For more information, please contact [email protected]. The Philosophy and Physics of Time Travel: The possibility of time travel Ramitha Rupasinghe IS 4994H - Honors Capstone Project Defense Panel – Pieranna Garavaso, Michael Korth, James Togeas University of Minnesota, Morris Spring 2017 1. Introduction Time is mysterious. Philosophers and scientists have pondered the question of what time might be for centuries and yet till this day, we don’t know what it is. Everyone talks about time, in fact, it’s the most common noun per the Oxford Dictionary. It’s in everything from history to music to culture. Despite time’s mysterious nature there are a lot of things that we can discuss in a logical manner. Time travel on the other hand is even more mysterious. -
Erich Kretschmann As a Proto-Logical-Empiricist: Adventures and Misadventures of the Point-Coincidence Argument
Erich Kretschmann as a Proto-Logical-Empiricist: Adventures and Misadventures of the Point-Coincidence Argument Marco Giovanelli Abstract The present paper attempts to show that a 1915 article by Erich Kretschmann must be credited not only for being the source of Einstein’s point-coincidence remark, but also for having anticipated the main lines of the logical-empiricist interpretation of general relativity. Whereas Kretschmann was inspired by the work of Mach and Poincaré, Einstein inserted Kretschmann’s point-coincidence parlance into the context of Ricci and Levi-Civita’s absolute differential calculus. Kretschmann himself realized this and turned the point-coincidence ar- gument against Einstein in his second and more famous 1918 paper. While Einstein had taken nothing from Kretschmann but the expression “point-coincidences”, the logical empiricists, however, instinctively dragged along with it the entire apparatus of Kretschmann’s conven- tionalism. Disappointingly, in their interpretation of general relativity, the logical empiricists unwittingly replicated some epistemological remarks Kretschmann had written before General Relativity even existed. Keywords: Erich Kretschmann, Point Coincidence Argument, Moritz Schlick, General Relativity, Logical Empiricism, Conventionalism 1. Introduction In the early 1980s, John Stachel (Stachel, 1980) and John Norton (Norton, 1984) famously shed new light on Einstein’s celebrated, yet somewhat cryptic, claim that all physical measurements amount to a determination of space-time coincidences, such as the matching of a pointer with a scale, or, if the world consisted of nothing but particles in motion, the meetings of their world-lines. In Einstein’s published writings, this remark — which Stachel has success- fully labeled the “point-coincidence argument” — amounts to the requirement of “general covariance”: since all coordinate systems necessarily agree on coin- cidences, that is, in everything observable, there is no reason to privilege one coordinate system over another. -
Symmetry and Entropy of Black Hole Horizons
Nuclear Physics B 744 (2006) 1–13 Symmetry and entropy of black hole horizons Olaf Dreyer, Fotini Markopoulou, Lee Smolin ∗ Perimeter Institute for Theoretical Physics, 35 King Street North, Waterloo, ON N2J 2W9, Canada Department of Physics, University of Waterloo, Waterloo, ON N2L 3G1, Canada Received 31 August 2005; accepted 3 February 2006 Available online 31 March 2006 Abstract We argue, using methods taken from the theory of noiseless subsystems in quantum information theory, that the quantum states associated with a Schwarzschild black hole live in the restricted subspace of the Hilbert space of horizon boundary states in which all punctures are equal. Consequently, one value of the Immirzi parameter matches both the Hawking value for the entropy and the quasi normal mode spectrum of the Schwarzschild black hole. The method of noiseless subsystems allows us to understand, in this example and more generally, how symmetries, which take physical states to physical states, can emerge from a diffeomorphism invariant formulation of quantum gravity. © 2006 Published by Elsevier B.V. 1. Introduction This paper is concerned with two distinct problems in background independent formulations of quantum gravity. First, how one can recover the semiclassical Bekenstein–Hawking results [1,2] in the context of results about the entropy of horizons and surfaces in loop quantum gravity [3–6]. Second, how the description of spacetime in terms of classical general relativity emerges from the quantum theory. Up till now, these problems have been treated in isolation. Here we propose a perspective that relates them, and also addresses a technical issue concerning the black hole entropy. -
A Measure of Change Brittany A
University of South Carolina Scholar Commons Theses and Dissertations Spring 2019 Time: A Measure of Change Brittany A. Gentry Follow this and additional works at: https://scholarcommons.sc.edu/etd Part of the Philosophy Commons Recommended Citation Gentry, B. A.(2019). Time: A Measure of Change. (Doctoral dissertation). Retrieved from https://scholarcommons.sc.edu/etd/5247 This Open Access Dissertation is brought to you by Scholar Commons. It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of Scholar Commons. For more information, please contact [email protected]. Time: A Measure of Change By Brittany A. Gentry Bachelor of Arts Houghton College, 2009 ________________________________________________ Submitted in Partial Fulfillment of the Requirements For the Degree of Doctor of Philosophy in Philosophy College of Arts and Sciences University of South Carolina 2019 Accepted by Michael Dickson, Major Professor Leah McClimans, Committee Member Thomas Burke, Committee Member Alexander Pruss, Committee Member Cheryl L. Addy, Vice Provost and Dean of the Graduate School ©Copyright by Brittany A. Gentry, 2019 All Rights Reserved ii Acknowledgements I would like to thank Michael Dickson, my dissertation advisor, for extensive comments on numerous drafts over the last several years and for his patience and encouragement throughout this process. I would also like to thank my other committee members, Leah McClimans, Thomas Burke, and Alexander Pruss, for their comments and recommendations along the way. Finally, I am grateful to fellow students and professors at the University of South Carolina, the audience at the International Society for the Philosophy of Time conference at Wake Forest University, NC, and anonymous reviewers for helpful comments on various drafts of portions of this dissertation. -
Time in Cosmology
View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Philsci-Archive Time in Cosmology Craig Callender∗ C. D. McCoyy 21 August 2017 Readers familiar with the workhorse of cosmology, the hot big bang model, may think that cosmology raises little of interest about time. As cosmological models are just relativistic spacetimes, time is under- stood just as it is in relativity theory, and all cosmology adds is a few bells and whistles such as inflation and the big bang and no more. The aim of this chapter is to show that this opinion is not completely right...and may well be dead wrong. In our survey, we show how the hot big bang model invites deep questions about the nature of time, how inflationary cosmology has led to interesting new perspectives on time, and how cosmological speculation continues to entertain dramatically different models of time altogether. Together these issues indicate that the philosopher interested in the nature of time would do well to know a little about modern cosmology. Different claims about time have long been at the heart of cosmology. Ancient creation myths disagree over whether time is finite or infinite, linear or circular. This speculation led to Kant complaining in his famous antinomies that metaphysical reasoning about the nature of time leads to a “euthanasia of reason”. But neither Kant’s worry nor cosmology becoming a modern science succeeded in ending the speculation. Einstein’s first model of the universe portrays a temporally infinite universe, where space is edgeless and its material contents unchanging. -
SPACE, TIME, and (How They) MATTER: a Discussion of Some Metaphysical Insights About the Nature of Space and Time Provided by Our Best Fundamental Physical Theories
SPACE, TIME, AND (how they) MATTER: A Discussion of Some Metaphysical Insights about the Nature of Space and Time Provided by Our Best Fundamental Physical Theories Valia Allori Northern Illinois University Forthcoming in: J. Statchel, G.C. Ghirardi (eds.). Space, Time, and Frontiers of Human Understanding. Springer-Verlag Abstract This paper is a brief (and hopelessly incomplete) non-standard introduction to the philosophy of space and time. It is an introduction because I plan to give an overview of what I consider some of the main questions about space and time: Is space a substance over and above matter? How many dimensions does it have? Is space-time fundamental or emergent? Does time have a direction? Does time even exist? Nonetheless, this introduction is not standard because I conclude the discussion by presenting the material with an original spin, guided by a particular understanding of fundamental physical theories, the so-called primitive ontology approach. 1. Introduction Scientific realists believe that our best scientific theories could be used as reliable guides to understand what the world is like. First, they tell us about the nature of matter: for instance, matter can be made of particles, or two-dimensional strings, or continuous fields. In addition, whatever matter fundamentally is, it seems there is matter in space, which moves in time. The topic of this paper is what our best physical theories tell us about the nature of space and time. I will start in the next section with the traditional debate concerning the question of whether space is itself a substance or not.