DOCSLIB.ORG

Quantum Gravity Past, Present and Future

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Quantum Gravity Past, Present and Future Quantum Gravity past, present and future carlo rovelli vancouver 2017 loop quantum gravity, Many directions of investigation string theory, Hořava–Lifshitz theory, supergravity, Vastly different numbers of researchers involved asymptotic safety, AdS-CFT-like dualities A few offer rather complete twistor theory, tentative theories of quantum gravity causal set theory, entropic gravity, Most are highly incomplete emergent gravity, non-commutative geometry, Several are related, boundaries are fluid group field theory, Penrose nonlinear quantum dynamics causal dynamical triangulations, Several are only vaguely connected to the actual problem of quantum gravity shape dynamics, ’t Hooft theory non-quantization of geometry Many offer useful insights … loop quantum causal dynamical gravity triangulations string theory asymptotic Hořava–Lifshitz safety group field AdS-CFT theory dualities twistor theory shape dynamics causal set supergravity theory Penrose nonlinear quantum dynamics non-commutative geometry Violation of QM non-quantized geometry entropic ’t Hooft emergent gravity theory gravity Several are related Herman Verlinde at LOOP17 in Warsaw No major physical assumptions over GR&QM No infinity in the small loop quantum causal dynamical Infinity gravity triangulations in the small Supersymmetry string High dimensions theory Strings Lorentz Violation asymptotic Hořava–Lifshitz safety group field AdS-CFT theory dualities twistor theory Mostly still shape dynamics causal set classical supergravity theory Penrose nonlinear quantum dynamics non-commutative geometry Violation of QM non-quantized geometry entropic ’t Hooft emergent gravity theory gravity Discriminatory questions: Is Lorentz symmetry violated at the Planck scale or not? Are there supersymmetric particles or not? Is Quantum Mechanics violated in the presence of gravity or not? Are there physical degrees of freedom at any arbitrary small scale or not? Is geometry discrete i the small? Lorentz violations Infinite d.o.f. Supersymmetry QM violations Geometry is discrete? at Planck scale at Planck scale Strings No No Yes No No Loops No No No No Yes Hojava Lifshitz Yes Yes No No No Asymptotic safety No Yes No No No Nonlinear quantum No Yes No Yes No dynamics Your favorite … … … … … We do have existing and possibly developing empirical evidence Empirical evidence: 1: Lorentz invariance Violation of Lorentz invariance → Renormalizability Observation has already ruled out theories S. Liberati, Class. Quant. Grav. 30, 133001 (2013) Lorentz violating solutions of QG are under empirical stress Is Lorentz invariance compatible with discreteness ? Yes! Classical discreteness breaks Lorentz invariance. Quantum discreteness does not ! Cfr rotational invariance: If a classical vector component can take only discrete values only, then SO(3) is broken. But if quantum vector can have discrete eigenvalues in a SO(3) invariant theory L L(β) Lorentz invariance and quantum discreteness are compatible => Geometry is quantum geometry Empirical evidence: 2: Supersymmetry Once again, no sign of supersymmetry Solution of QG using supersymmetry are under empirical stress A point about philosophy of science: - Popper’s falsification: theories are either “OK” or “proved wrong”. - Bayesian “confirmation”: we have “degrees of confidence” in theories; these are are lowered, of enhanced, by empirical (dis-)confirmation. Karl Popper Bruno De Finetti Not seeing a giraffe in the forests of Canada during a hike, does not prove that there are no giraffes in the forests of Canada A point about philosophy of science: - Popper’s falsification: theories are either “OK” or “proved wrong”. - Bayesian “confirmation”: we have “degrees of confidence” in theories; these are are lowered, of enhanced, by empirical (dis-)confirmation. Karl Popper Bruno De Finetti Not seeing a giraffe in the forests of Canada during a hike, does not prove that there are no giraffes in the forests of Canada But if for thirty years nobody sees a giraffe… And we have now heard that supersymmetry is “going to be seen soon” for more than thirty years…. Empirical evidence: 3: Lab experiments Analog systems Test the consequences of an assumption. Not the assumption themselves. Planck scale effects NOT predicted by most QG theories in the lab Violations of QM suggested by QG Quantum property Can falsify the hypothesis that the of the metric gravitational field is classical. Is the metric a Can falsify the hypothesis that the quantum entity? gravitational field is classical. S Bose, A Mazumdar, GW Morley, H Ulbricht, M Toroš, M Paternostro, A Geraci, P Barker, MS Kim, G Milburn: A Spin Entanglement Witness for Quantum Gravity, 2017. C Marletto, V Vedral: An entanglement-based test of quantum gravity using two massive particles, 2017. Empirical evidence: 4: The Sky a) Early Universe: “Quantum cosmology” b) Black holes: Disruption of the photon ring Planck Stars Quantum Cosmology A: In the early universe, quantum gravity effects cannot be disregarded These leave traces in the current universe. Few degrees of freedom. Gravity is quantum, spacetime is dynamical Schrödinger equation → Wheeler de Witt equation Absence of a preferred time variable. Quantum Cosmology H: How to understand quantum theory of “the whole”. All degrees of freedom of the Universe. Absence of external observer? The problems raised by this would exist also if relativistic gravity did not exist. Quantum Cosmology A is a totally different problem from Quantum Cosmology H Large activity to describe the physics of the very early universe, and find traces in the CMB Notice: this is all physics of few degrees of freedom! Great effort to find testable consequences of the theories in course b) Black holes Small effects pile up over time - Wide quantum fluctuations of the metric Giddings - Boson condensate of low energy gravitons Dvali - Fluctuations of the causal structure allowing black hole to decay Haggard, Barrau, Vidotto, CR - Wide quantum fluctuations of the metric Theoretical reason: to bring information out of the hole Observable consequence: Event Horizon Telescope Possibly visible distortion of the photon ring Imaging an Event Horizon: Mitigation of Scattering toward Sagittarius A* Fish et al 2014 - Fluctuations of the causal structure allowing black hole to decay /KPMQYUMK 5EJYCT\UEJKNF 3WCPVWOTGIKQP 5EJYCT\UEJKNF /KPMQYUMK Exploding holes /KPMQYUMK 3WCPVWOTGIKQP 5EJYCT\UEJKNF /KPMQYUMK Exploding holes At MG2 and in a paper ’79-’81 Frolov, Vilkovinski ‘79 Sean A. Hayward in ’06 Stephen, t’Hooft, Whithing ‘93 Valeri Frolov In ’05 Ashtekar, Bojowald ’05 [see M. Smerlak’s talk] Grigori A. Vilkovisky (left) Modesto ‘06 In ’93 Abhay Ashtekar Hayward ’06 Cristopher R. Stephens Martin Bojowald 2 Hajicek Kieffer ’01 1 Gerard ’t Hooft region 3 Haggard, Rovelli ’15 Bernard F. Whiting Figure 2: Penrose diagram for the gravitational collapse inside the event horizon (Region 1 and region 2) and outside the event horizon (Region3). Solving the constraints equations (9) we obtain the known results for the classical dust matter gravi- tational collapse [8]. 2GravitationalcollapseinAshtekarvariables In this section we study the gravitational collapse in Ashtekar variables [12]. In particular we will express the Hamiltonian constraint inside and outside the matter and the constraints P1 and P2 in terms of the symmetric reduced Ashtekar connection [13], [14]. 2.1 Ashtekar variables In LQG the fundamental variables are the Ashtekar variables:theyconsistofanSU(2) connection i a Aa and the electric field Ei ,wherea, b, c, =1, 2, 3aretensorialindicesonthespatialsectionand ··· a i, j, k, =1, 2, 3areindicesinthesu(2) algebra. The density weighted triad Ei is related to the ···i a 1 abc j k i j triad ea by the relation Ei = 2 ϵ ϵijk eb ec .Themetricisrelatedtothetriadbyqab = ea eb δij . Equivalently, ab a b ij det(q) q = Ei Ej δ . (10) ! i a The rest of the relation between the variables (Aa,Ei )andtheADMvariables(qab,Kab)isgivenby i i b ij Aa = Γa + γ KabEj δ (11) i where γ is the Immirzi parameter and Γa is the spin connection of the triad, namely the solution of i i j k Cartan’s equation: ∂[aeb] + ϵjk Γ[aeb] =0. The action is 1 3 a a i S = dt d x 2Tr(E A˙ a) N N a N i , (12) κγ Σ − − H − H − G " " # $ where N a is the shift vector, N is the lapse function and N i is the Lagrange multiplier for the Gauss a a i a constraint i.WehaveintroducedalsothenotationE[1] = E ∂a = Ei τ ∂a and A[1] = Aadx = i i a G A τ dx .Thefunctions , a and i are respectively the Hamiltonian, diffeomorphism and Gauss a H H G 4 /KPMQYUMK 3WCPVWOTGIKQP 5EJYCT\UEJKNF /KPMQYUMK A technical result in classical GR: The following metric is an exact vacuum solution, of the Einstein equations outside a finite spacetime region (grey), plus an ingoing and outgoing null shell, I The metric is determined by two constants: ds2 = F (u, v)dudv + r2(u, v)(d✓2 + sin2✓dφ2) − III II v u F (u ,v )=1,r(u ,v )= I − I . Region I I I I I I 2 vI < 0. 3 32m r r r F (u, v)= e 2m 1 e 2m = uv. Region II r − 2m I ⇣ ⌘ 1 uI uI Matching rI (uI ,vI )=r(u, v) u(uI )= 1+ e 4m . vo 4m 3 ⇣ ⌘ 32m rq Region III F (uq,vq)= e 2m ,rq = vq uq. rq − Black hole fireworks: quantum-gravity effects outside the horizon spark black to white hole tunneling Hal Haggard, CR I I ➜ Choose a “Boundary” surface around the quantum region. /KPMQYUMK 3WCPVWOTGIKQP 5EJYCT\UEJKNF /KPMQYUMK Spin network Spinfoam Primordial black holes! A real-time FRB 5 Figure 2. The full-Stokes parameters of FRB 140514 recorded in the centre beam of the multibeam receiver with BPSR. Total intensity, and Stokes Q, U,andV are represented in black, red, green, and blue, respectively. FRB 140514 has 21 7% (3-σ)circularpolarisation ± averaged over the pulse, and a 1-σ upper limit on linear polarisation of L<10%. On the leading edge of the pulse the circular polarisation is 42 9% (5-σ)ofthetotalintensity.Thedatahavebeensmoothedfromaninitialsamplingof64µsusingaGaussianfilteroffull-width ± half-maximum 90 µs.
Load more

Recommended publications
  • What Can We Learn from Shape Dynamics? International Loop Quantum Gravity Seminar
    What can we learn from shape dynamics? International Loop Quantum Gravity Seminar Tim A. Koslowski University of New Brunswick, Fredericton, NB, Canada November 12, 2013 Tim A. Koslowski (UNB) What can we learn from shape dynamics? November 12, 2013 1 / 19 Outline 1 Motivation from 2+1 diemsnional qunatum gravity to consider conformal evolution as fundamental 2 Conformal evolution is different from spacetime (i.e. abandon spacetime) 3 Generic dynamical emergence of spacetime in the presence of matter (i.e. regain spacetime) Tim A. Koslowski (UNB) What can we learn from shape dynamics? November 12, 2013 2 / 19 Introduction and Motivation Tim A. Koslowski (UNB) What can we learn from shape dynamics? November 12, 2013 3 / 19 Motivation Canonical metric path integral in 2+1 (only known metric path integral) ab p necessary: 2+1 split and CMC gauge condition gabπ − t g = 0 R 2 ab R ab a pπ c i dtd x(_gabπ −S(N)−H(ξ)) Z = [dgab][dπ ][dN][dξ ]δ[ g − t]δ[F ] det[FP ]e R 2 A R A i dtd x(_τAp −Vo(τ;p;t)) = [dτA][dp ]e [Carlip: CQG 12 (1995) 2201, Seriu PRD 55 (1997) 781] where: τA are Teichm¨ullerparameters, Vo(τ; p; t) denotes on-shell volume, which depends explicitly on time t ) QM on Teichm¨ullerspace, phys. Hamilt. Vo(τ; p; t) [Moncrief: JMP 30 (1989) 2907] Fradkin-Vilkovisky theorem: [cf. Henneaux/Teitelboim: \Quantization of Gauge Systems"] \Partition function depends on gauge fixing cond. only through the gauge equivalence class of gauge fixing conditions." for a discussion and some examples of non-equivalence [see Govaerts, Scholtz: J.Phys.
    [Show full text]
  • D-Instantons and Twistors
    Home Search Collections Journals About Contact us My IOPscience D-instantons and twistors This article has been downloaded from IOPscience. Please scroll down to see the full text article. JHEP03(2009)044 (http://iopscience.iop.org/1126-6708/2009/03/044) The Table of Contents and more related content is available Download details: IP Address: 132.166.22.147 The article was downloaded on 26/02/2010 at 16:55 Please note that terms and conditions apply. Published by IOP Publishing for SISSA Received: January 5, 2009 Accepted: February 11, 2009 Published: March 6, 2009 D-instantons and twistors JHEP03(2009)044 Sergei Alexandrov,a Boris Pioline,b Frank Saueressigc and Stefan Vandorend aLaboratoire de Physique Th´eorique & Astroparticules, CNRS UMR 5207, Universit´eMontpellier II, 34095 Montpellier Cedex 05, France bLaboratoire de Physique Th´eorique et Hautes Energies, CNRS UMR 7589, Universit´ePierre et Marie Curie, 4 place Jussieu, 75252 Paris cedex 05, France cInstitut de Physique Th´eorique, CEA, IPhT, CNRS URA 2306, F-91191 Gif-sur-Yvette, France dInstitute for Theoretical Physics and Spinoza Institute, Utrecht University, Leuvenlaan 4, 3508 TD Utrecht, The Netherlands E-mail: [email protected], [email protected], [email protected], [email protected] Abstract: Finding the exact, quantum corrected metric on the hypermultiplet moduli space in Type II string compactifications on Calabi-Yau threefolds is an outstanding open problem. We address this issue by relating the quaternionic-K¨ahler metric on the hy- permultiplet moduli space to the complex contact geometry on its twistor space. In this framework, Euclidean D-brane instantons are captured by contact transformations between different patches.
    [Show full text]
  • Shape Dynamics
    Shape Dynamics Tim A. Koslowski Abstract Barbour’s formulation of Mach’s principle requires a theory of gravity to implement local relativity of clocks, local relativity of rods and spatial covariance. It turns out that relativity of clocks and rods are mutually exclusive. General Relativity implements local relativity of clocks and spatial covariance, but not local relativity of rods. It is the purpose of this contribution to show how Shape Dynamics, a theory that is locally equivalent to General Relativity, implements local relativity of rods and spatial covariance and how a BRST formulation, which I call Doubly General Relativity, implements all of Barbour’s principles. 1 Introduction A reflection on Mach’s principle lead Barbour to postulate that rods and spatial frames of reference should be locally determined by a procedure that he calls “best matching,” while clocks should be locally determined by what he calls “objective change.” (For more, see [1].) More concretely, Barbour’s principles postulate lo- cal time reparametrization invariance, local spatial conformal invariance and spatial covariance. The best matching algorithm for spatial covariance and local spatial conformal invariance turns out to be equivalent to the imposition of linear diffeo- morphism and conformal constraints Z Z 3 ab 3 H(x) = d xp (Lx g)ab; C(r) = d xr p; (1) S S Tim A. Koslowski Perimeter Institute for Theoretical Physics, 31 Caroline St. N, Waterloo, Ontario, Canada New address: Department of Mathematics and Statistics, University of New Brunswick Fredericton, New Brunswick E3B 5A3, Canada e-mail: [email protected] 1 2 Tim A.
    [Show full text]
  • On the Axioms of Causal Set Theory
    On the Axioms of Causal Set Theory Benjamin F. Dribus Louisiana State University [email protected] November 8, 2013 Abstract Causal set theory is a promising attempt to model fundamental spacetime structure in a discrete order-theoretic context via sets equipped with special binary relations, called causal sets. The el- ements of a causal set are taken to represent spacetime events, while its binary relation is taken to encode causal relations between pairs of events. Causal set theory was introduced in 1987 by Bombelli, Lee, Meyer, and Sorkin, motivated by results of Hawking and Malament relating the causal, conformal, and metric structures of relativistic spacetime, together with earlier work on discrete causal theory by Finkelstein, Myrheim, and 't Hooft. Sorkin has coined the phrase, \order plus number equals geometry," to summarize the causal set viewpoint regarding the roles of causal structure and discreteness in the emergence of spacetime geometry. This phrase represents a specific version of what I refer to as the causal metric hypothesis, which is the idea that the properties of the physical universe, and in particular, the metric properties of classical spacetime, arise from causal structure at the fundamental scale. Causal set theory may be expressed in terms of six axioms: the binary axiom, the measure axiom, countability, transitivity, interval finiteness, and irreflexivity. The first three axioms, which fix the physical interpretation of a causal set, and restrict its \size," appear in the literature either implic- itly, or as part of the preliminary definition of a causal set. The last three axioms, which encode the essential mathematical structure of a causal set, appear in the literature as the irreflexive formula- tion of causal set theory.
    [Show full text]
  • BEYOND SPACE and TIME the Secret Network of the Universe: How Quantum Geometry Might Complete Einstein’S Dream
    BEYOND SPACE AND TIME The secret network of the universe: How quantum geometry might complete Einstein’s dream By Rüdiger Vaas With the help of a few innocuous - albeit subtle and potent - equations, Abhay Ashtekar can escape the realm of ordinary space and time. The mathematics developed specifically for this purpose makes it possible to look behind the scenes of the apparent stage of all events - or better yet: to shed light on the very foundation of reality. What sounds like black magic, is actually incredibly hard physics. Were Albert Einstein alive today, it would have given him great pleasure. For the goal is to fulfil the big dream of a unified theory of gravity and the quantum world. With the new branch of science of quantum geometry, also called loop quantum gravity, Ashtekar has come close to fulfilling this dream - and tries thereby, in addition, to answer the ultimate questions of physics: the mysteries of the big bang and black holes. "On the Planck scale there is a precise, rich, and discrete structure,” says Ashtekar, professor of physics and Director of the Center for Gravitational Physics and Geometry at Pennsylvania State University. The Planck scale is the smallest possible length scale with units of the order of 10-33 centimeters. That is 20 orders of magnitude smaller than what the world’s best particle accelerators can detect. At this scale, Einstein’s theory of general relativity fails. Its subject is the connection between space, time, matter and energy. But on the Planck scale it gives unreasonable values - absurd infinities and singularities.
    [Show full text]
  • Causal Dynamical Triangulations and the Quest for Quantum Gravity?
    Appendices: Mathematical Methods for Basic and Foundational Quantum Gravity Unstarred Appendices support Part I’s basic account. Starred Appendices support Parts II and III on interferences between Problem of Time facets. Double starred ones support the Epilogues on global aspects and deeper levels of mathematical structure being contemplated as Background Independent. If an Appendix is starred, the default is that all of its sections are starred likewise; a few are marked with double stars. Appendix A Basic Algebra and Discrete Mathematics A.1 Sets and Relations For the purposes of this book, take a set X to just be a collection of distinguishable objects termed elements. Write x ∈ X if x is an element of X and Y ⊂ X for Y a subset of X, ∩ for intersection, ∪ for union and Yc = X\Y for the complement of Y in X. Subsets Y1 and Y2 are mutually exclusive alias disjoint if Y1 ∩ Y2 =∅: the empty set. In this case, write Y1 ∪ Y2 as Y1 Y2: disjoint union.Apartition of a set X is a splitting of its elements into subsets pP that are mutually exclusive = and collectively exhaustive: P pP X. Finally, the direct alias Cartesian product of sets X and Z, denoted X × Z, is the set of all ordered pairs (x, z) for x ∈ X, z ∈ Z. For sets X and Z,afunction alias map ϕ : X → Z is an assignation to each x ∈ X of a unique image ϕ(x) = z ∈ Z. Such a ϕ is injective alias 1to1if ϕ(x1) = ϕ(x2) ⇒ x1 = x2, surjective alias onto if given z ∈ Z there is an x ∈ X such that ϕ(x) = z, and bijective if it is both injective and surjective.
    [Show full text]
  • Twistor Theory at Fifty: from Rspa.Royalsocietypublishing.Org Contour Integrals to Twistor Strings Michael Atiyah1,2, Maciej Dunajski3 and Lionel Review J
    Downloaded from http://rspa.royalsocietypublishing.org/ on November 10, 2017 Twistor theory at fifty: from rspa.royalsocietypublishing.org contour integrals to twistor strings Michael Atiyah1,2, Maciej Dunajski3 and Lionel Review J. Mason4 Cite this article: Atiyah M, Dunajski M, Mason LJ. 2017 Twistor theory at fifty: from 1School of Mathematics, University of Edinburgh, King’s Buildings, contour integrals to twistor strings. Proc. R. Edinburgh EH9 3JZ, UK Soc. A 473: 20170530. 2Trinity College Cambridge, University of Cambridge, Cambridge http://dx.doi.org/10.1098/rspa.2017.0530 CB21TQ,UK 3Department of Applied Mathematics and Theoretical Physics, Received: 1 August 2017 University of Cambridge, Cambridge CB3 0WA, UK Accepted: 8 September 2017 4The Mathematical Institute, Andrew Wiles Building, University of Oxford, Oxford OX2 6GG, UK Subject Areas: MD, 0000-0002-6477-8319 mathematical physics, high-energy physics, geometry We review aspects of twistor theory, its aims and achievements spanning the last five decades. In Keywords: the twistor approach, space–time is secondary twistor theory, instantons, self-duality, with events being derived objects that correspond to integrable systems, twistor strings compact holomorphic curves in a complex threefold— the twistor space. After giving an elementary construction of this space, we demonstrate how Author for correspondence: solutions to linear and nonlinear equations of Maciej Dunajski mathematical physics—anti-self-duality equations e-mail: [email protected] on Yang–Mills or conformal curvature—can be encoded into twistor cohomology. These twistor correspondences yield explicit examples of Yang– Mills and gravitational instantons, which we review. They also underlie the twistor approach to integrability: the solitonic systems arise as symmetry reductions of anti-self-dual (ASD) Yang–Mills equations, and Einstein–Weyl dispersionless systems are reductions of ASD conformal equations.
    [Show full text]
  • Physics Needs Philosophy. Philosophy Needs Physics. Carlo Rovelli
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by PhilSci Archive Physics needs philosophy. Philosophy needs physics. Carlo Rovelli Extended version of a keynote talk at the XVIII UK-European Conference on the Foundation of Physics, given at the London School of Economics the 16 July 2016 Published on Foundations of Physics, 48, 481-491, 2018 Abstract 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. 1. Against Philosophy is the title of a chapter of a book by one of the great physicists of the last generation: Steven Weinberg, Nobel Prize winner and one of the architects of the Standard Model of elementary particle physicsi. Weinberg argues eloquently that philosophy is more damaging than helpful for physics—although it might provide some good ideas at times, it is often a straightjacket that physicists have to free themselves from. More radically, Stephen Hawking famously wrote that “philosophy is dead” because the big questions that used to be discussed by philosophers are now in the hands of physicistsii.
    [Show full text]
  • Loop Quantum Gravity: the First 25 Years Carlo Rovelli
    Loop quantum gravity: the first 25 years Carlo Rovelli To cite this version: Carlo Rovelli. Loop quantum gravity: the first 25 years. Classical and Quantum Gravity, IOP Publishing, 2011, 28 (15), pp.153002. 10.1088/0264-9381/28/15/153002. hal-00723006 HAL Id: hal-00723006 https://hal.archives-ouvertes.fr/hal-00723006 Submitted on 7 Aug 2012 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Loop quantum gravity: the first twenty five years Carlo Rovelli Centre de Physique Th´eorique de Luminy∗, Case 907, F-13288 Marseille, EU (Dated: January 27, 2011) I give a synthetic presentation of loop quantum gravity. I spell-out the aims of the theory and compare the results obtained with the initial hopes that motivated the early interest in this research direction. I give my own perspective on the status of the program and attempt of a critical evaluation of its successes and limits. I. INTRODUCTION The history of quantum gravity is full of great hopes later disappointed. I remember as a young student sitting in a major conference where a world-renowned physicists Loop gravity is not quite twenty-five years old, but announced that the final theory of quantum gravity and is getting close to such a venerable age: several basic everything had finally been found.
    [Show full text]
  • Annual Report 2013 NARODOWE CENTRUM BADAŃ JĄDROWYCH NATIONAL CENTRE for NUCLEAR RESEARCH
    Annual Report 2013 NARODOWE CENTRUM BADAŃ JĄDROWYCH NATIONAL CENTRE FOR NUCLEAR RESEARCH ANNUAL REPORT 2013 PL-05-400 Otwock-Świerk, POLAND tel.: 048 22 718 00 01 fax: 048 22 779 34 81 e-mail: [email protected] http://www.ncbj.gov.pl Editors: N. Keeley K. Kurek Cover design: S. Mirski Secretarial work and layout: G. Swiboda ISSN 2299-2960 Annual Report 2013 3 CONTENTS FOREWORD ............................................................................................................................................................ 5 I. GENERAL INFORMATION ................................................................................................... 7 1. LOCATIONS ...................................................................................................................... 7 2. MANAGEMENT OF THE INSTITUTE ............................................................................ 7 3. SCIENTIFIC COUNCIL ..................................................................................................... 8 4. MAIN RESEARCH ACTIVITIES ................................................................................... 11 5. SCIENTIFIC STAFF OF THE INSTITUTE .................................................................... 13 6. VISITING SCIENTISTS .................................................................................................. 15 7. PARTICIPATION IN NATIONAL CONSORTIA AND SCIENTIFIC NETWORKS .. 23 8. DEGREES ........................................................................................................................
    [Show full text]
  • Modified Newtonian Dynamics
    Faculty of Mathematics and Natural Sciences Bachelor Thesis University of Groningen Modified Newtonian Dynamics (MOND) and a Possible Microscopic Description Author: Supervisor: L.M. Mooiweer prof. dr. E. Pallante Abstract Nowadays, the mass discrepancy in the universe is often interpreted within the paradigm of Cold Dark Matter (CDM) while other possibilities are not excluded. The main idea of this thesis is to develop a better theoretical understanding of the hidden mass problem within the paradigm of Modified Newtonian Dynamics (MOND). Several phenomenological aspects of MOND will be discussed and we will consider a possible microscopic description based on quantum statistics on the holographic screen which can reproduce the MOND phenomenology. July 10, 2015 Contents 1 Introduction 3 1.1 The Problem of the Hidden Mass . .3 2 Modified Newtonian Dynamics6 2.1 The Acceleration Constant a0 .................................7 2.2 MOND Phenomenology . .8 2.2.1 The Tully-Fischer and Jackson-Faber relation . .9 2.2.2 The external field effect . 10 2.3 The Non-Relativistic Field Formulation . 11 2.3.1 Conservation of energy . 11 2.3.2 A quadratic Lagrangian formalism (AQUAL) . 12 2.4 The Relativistic Field Formulation . 13 2.5 MOND Difficulties . 13 3 A Possible Microscopic Description of MOND 16 3.1 The Holographic Principle . 16 3.2 Emergent Gravity as an Entropic Force . 16 3.2.1 The connection between the bulk and the surface . 18 3.3 Quantum Statistical Description on the Holographic Screen . 19 3.3.1 Two dimensional quantum gases . 19 3.3.2 The connection with the deep MOND limit .
    [Show full text]
  • Does Time Differ from Change? Philosophical Appraisal of the Problem of Time in Quantum Gravity and in Physics
    Studies in History and Philosophy of Modern Physics 52 (2015) 48–54 Contents lists available at ScienceDirect Studies in History and Philosophy of Modern Physics journal homepage: www.elsevier.com/locate/shpsb Does time differ from change? Philosophical appraisal of the problem of time in quantum gravity and in physics Alexis de Saint-Ours Université Paris Diderot – CNRS, Laboratoire SPHERE, UMR 7219, Bâtiment Condorcet, case 7093, 5 rue Thomas Mann, 75205 Paris cedex 13, France article info abstract Article history: After reviewing the problem of time in Quantum Gravity, I compare from a philosophical perspective, Received 16 December 2013 both Carlo Rovelli's and Julian Barbour's (before Shape Dynamics) understanding of time in Quantum Received in revised form Gravity and in dynamics in general, trying to show that those two relational understandings of time 10 March 2015 differ. Rovelli argues that there is change without time and that time can be abstracted from any change Accepted 15 March 2015 whereas Barbour claims that some motions are better than others for constituting duration standards Available online 27 October 2015 To my father and that time is to be abstracted from all change in the universe. I conclude by a few remarks on Bergson's criticism of physics in the light of those debates trying to show that both Rovelli and Barbour Keywords: give surrationalist (as Bachelard understood it) answers to the critique of spatialized time in Physics. Time & 2015 Elsevier Ltd. All rights reserved. Change Barbour Rovelli Bergson Lautman When citing this paper, please use the full journal title Studies in History and Philosophy of Modern Physics 1.
    [Show full text]