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I What can we learn from the Carlofest speakers' list?

  1. Mar 4, 2016 #1


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    Try to estimate the range of ideas represented by this collection of speakers (all but two are already confirmed for the 22-27 May conference). It covers not only Quantum Gravity and Cosmology but also Noncommutative Geometry, Foundations of Quantum Mechanics, Philosophy of Science, and more. Should be a very interesting group of talks and discussions!

    Abhay Ashtekar - Institute for Gravitation and the Cosmos, PennState, US

    John Baez - University of California Riverside, San Diego, US

    Fernando Barbero - Spanish National Research Council, Madrid, Spain

    Aurelian Barrau - LPSC, Grenoble, France

    Eugenio Bianchi - Institute for Gravitation and the Cosmos, PennState, US

    Jeremy Butterfield - Cambridge, UK

    Alain Connes - College de France, Paris, France

    Bianca Dittrich - Perimeter Institute for Theoretical Physics, Waterloo, Canada

    John Earman - University of Pittsburgh, US

    Laurent Freidel - Perimeter Institute for Theoretical Physics, Waterloo, Canada

    Chris Isham* - Imperial College, London, UK

    Ted Jacobson - University of Maryland, US

    Jerzy Lewandowski - University of Warsaw, Poland

    Stefano Liberati - INFN and SISSA, Trieste, Italy

    Etera Livine - ENS, Lyon, France

    Ezra Ted Newman - University of Pittsburgh, US

    Daniele Oriti - Albert Einstein Institute, Berlin, Germany

    Jorge Pullin - Louisiana State University, Baton Rouge, US

    Michael Reisenberger - Universidad de Montevideo, Uruguay

    Simon Saunders - University of Oxford, UK

    Rafael Sorkin* - Perimeter Institute for Theoretical Physics, Waterloo, Canada

    Lee Smolin - Perimeter Institute for Theoretical Physics, Waterloo, Canada

    Thomas Thiemann - Institute for Quantum Gravity, Erlangen-Nurnberg, Germany

    *to be confirmed
    Last edited: Mar 4, 2016
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  3. Mar 4, 2016 #2


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    Carlo Rovelli was born in 1956, so he celebrates his 60th birthday this year. His work covers a remarkable range from Quantum Gravity to Quantum Foundations to the Philosophy of Cosmology and includes bestselling books on the History of Science and Modern Physics for general audience. I think this is a great list of speakers and that it reflects his significant contributions over this broad range
  4. Mar 4, 2016 #3


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    to take just one example: Oriti can, I think, be relied on to present results from a very interesting bunch of recent papers by his group at the Albert Einstein Institute.

    To mention just a few:
    Gielen S., Oriti D., Quantum cosmology from quantum gravity condensates: cosmological variables and lattice-refined dynamics, New J. Phys. 16 (2014), 123004, arXiv:1407.8167.
    Bouncing cosmologies from quantum gravity condensates
    Daniele Oriti, Lorenzo Sindoni, Edward Wilson-Ewing
    (Submitted on 26 Feb 2016)
    We show how the large-scale cosmological dynamics can be obtained from the hydrodynamics of isotropic group field theory condensate states in the Gross-Pitaevskii approximation. The correct Friedmann equations are recovered in the semi-classical limit for some choices of the parameters in the action for the group field theory, and quantum gravity corrections arise in the high-curvature regime causing a bounce which generically resolves the big-bang and big-crunch singularities.
    4 pages
    Emergent Friedmann dynamics with a quantum bounce from quantum gravity condensates
    Daniele Oriti, Lorenzo Sindoni, Edward Wilson-Ewing
    (Submitted on 18 Feb 2016)
    We study the effective cosmological dynamics, emerging as the hydrodynamics of simple condensate states, of a group field theory model for quantum gravity coupled to a massless scalar field and reduced to its isotropic sector. The quantum equations of motion for these group field theory condensate states are given in relational terms with respect to the scalar field, from which effective dynamics for spatially flat, homogeneous and isotropic space-times can be extracted. The result is a generalization of the Friedmann equations, including quantum gravity modifications, in a specific regime of the theory. The classical Friedmann equations of general relativity are recovered in a suitable semi-classical limit for some range of parameters of the microscopic dynamics. An important result is that the quantum geometries associated with these GFT condensate states are non-singular: a bounce generically occurs in the Planck regime. For some choices of condensate states, these modified Friedmann equations are very similar to those of loop quantum cosmology.
    58 pages

    For an overview and other recent papers relating to the QG condensates approach, there's this useful review by Oriti's associates, Gielen and Sindoni:
    Quantum cosmology from group field theory condensates: a review
    Steffen Gielen, Lorenzo Sindoni
    (Submitted on 25 Feb 2016)
    We give, in some detail, a critical overview over recent work towards deriving a cosmological phenomenology from the fundamental quantum dynamics of group field theory (GFT), based on the picture of a macroscopic universe as a "condensate" of a large number of quanta of geometry which are given by excitations of the GFT field over a "no-space" vacuum. We emphasise conceptual foundations, relations to other research programmes in GFT and the wider context of loop quantum gravity (LQG), and connections to the quantum physics of real Bose-Einstein condensates. We show how to extract an effective dynamics for GFT condensates from the microscopic GFT physics, and how to compare it with predictions of more conventional quantum cosmology models, in particular loop quantum cosmology (LQC). No detailed familiarity with the GFT formalism is assumed.
    46 pages, 5 figures, invited review for SIGMA Special Issue on Tensor Models, Formalism and Applications

    ==quote http://arxiv.org/pdf/1602.08104.pdf page 39==
    In the second approach, one tries to interpret corrections to an effective Friedmann equation (arising, for instance, from different types of GFT interactions) as matter fields or as an effective cosmological constant. This possibility was outlined in [66] where we point for further reference. It is potentially very interesting, as it may, for example, raise a hope to solve the cosmological constant problem through GFT condensates, but has not been explored much so far.

    some more of the "condensate" papers cited in this review
    [63] Gielen S., Quantum cosmology of (loop) quantum gravity condensates: An example, Class. Quantum Grav. 31 (2014), 155009, arXiv:1404.2944.
    [64] Gielen S., Perturbing a quantum gravity condensate, Phys. Rev. D 91 (2015), 043526, arXiv:1411.1077.[65] Gielen S., Identifying cosmological perturbations in group field theory condensates, JHEP 1508 (2015),010, arXiv:1505.07479.
    [66] Gielen S., Oriti D., Quantum cosmology from quantum gravity condensates: cosmological variables andlattice-refined dynamics, New J. Phys. 16 (2014), 123004, arXiv:1407.8167.
    [67] Gielen S., Oriti D., Sindoni L., Cosmology from Group Field Theory Formalism for Quantum Gravity,Phys. Rev. Lett. 111 (2013), 031301, arXiv:1303.3576.
    [68] Gielen S., Oriti D., Sindoni L., Homogeneous cosmologies as group field theory condensates, JHEP 1406 (2014), 013, arXiv:1311.1238.

    This is one of the new developments occurring in LQG.
    Last edited: Mar 5, 2016
  5. Mar 6, 2016 #4


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    to take another example, Bianca Dittrich is another of the invited Carlofest speakers. might she bring up this new research?

    Can chaos be observed in quantum gravity?
    Bianca Dittrich, Philipp A. Hoehn, Tim A. Koslowski, Mike I. Nelson
    (Submitted on 10 Feb 2016)
    Full general relativity is almost certainly non-integrable and likely chaotic and therefore almost certainly possesses neither differentiable Dirac observables nor a reduced phase space. It follows that the standard notion of observable has to be extended to include non-differentiable or even discontinuous generalized observables. These cannot carry Poisson-algebraic structures and do not admit a standard quantization. This has deep consequences for a quantum theory of gravity, which we investigate in a simple model for a system with Hamiltonian constraint that fails to be completely integrable. We show that basing the quantization on standard topology precludes a semiclassical limit and can even prohibit any solutions to the quantum constraints. Our proposed solution to this problem is to refine topology such that a complete set of Dirac observables becomes continuous. In the toy model it turns out that a refinement to a polymer-type topology, as e.g. used in loop quantum cosmology, is sufficient. Basing quantization of the toy model on this finer topology, we find a complete set of quantum Dirac observables and a suitable semiclassical limit.
    4 pages + references

    Could be a significant new development, IMO.
  6. Mar 6, 2016 #5


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    another example, Alain Connes known for using Noncommutative Geometry (NCG) to realize the standard model particles, could discuss the deeper understanding of time (as arising from the state of the system, i.e what is taken as the universe, rather than existing independently) that has emerged in a number of papers since this seminal work with Rovelli:
    Von Neumann Algebra Automorphisms and Time-Thermodynamics Relation in General Covariant Quantum Theories
    A. Connes, C. Rovelli
    (Submitted on 14 Jun 1994)
    We consider the cluster of problems raised by the relation between the notion of time, gravitational theory, quantum theory and thermodynamics; in particular, we address the problem of relating the "timelessness" of the hypothetical fundamental general covariant quantum field theory with the "evidence" of the flow of time. By using the algebraic formulation of quantum theory, we propose a unifying perspective on these problems, based on the hypothesis that in a generally covariant quantum theory the physical time-flow is not a universal property of the mechanical theory, but rather it is determined by the thermodynamical state of the system ("thermal time hypothesis"). We implement this hypothesis by using a key structural property of von Neumann algebras: the Tomita-Takesaki theorem, which allows to derive a time-flow, namely a one-parameter group of automorphisms of the observable algebra, from a generic thermal physical state. We study this time-flow, its classical limit, and we relate it to various characteristic theoretical facts, as the Unruh temperature and the Hawking radiation. We also point out the existence of a state-independent notion of "time", given by the canonical one-parameter subgroup of outer automorphisms provided by the Cocycle Radon-Nikodym theorem.
    25 pages

    This is basically Rovelli's idea of 'thermal time'. Connes seems to have given it his blessing.

    Two of Connes' collaborators recently posted this;
    On Unification of Gravity and Gauge Interactions
    Ali H. Chamseddine, Viatcheslav Mukhanov
    (Submitted on 6 Feb 2016)
    The tangent group of the four dimensional space-time does not need to have the same number of dimensions as the base manifold. Considering a higher dimensional Lorentz group as the symmetry of the tangent space, we unify gravity and gauge interactions in a natural way. The spin connection of the gauged Lorentz group is then responsible for both gravity and gauge fields, and the action for the gauged fields becomes part of the spin curvature squared. The realistic group which unifies all known particles and interactions is the SO(1,13) Lorentz group whose gauge part leads to SO(10) grand unified theory and contains double the number of required fermions in the fundamental spinor representation. We briefly discuss the Brout-Englert-Higgs mechanism which breaks the SO(1,13) symmetry first to SO(1,3)×SU(3)×SU(2)×U(1) and further to SO(1,3)×SU(3)×U(1) and gives very heavy masses to half of the fermions leaving the others with light masses.
    11 pages

    "Since the Dirac operator plays a fundamental role in this setting, it is natural to look for connections between this construction and that of noncommutative geometry. In addition, the need to add Higgs scalar fields suggests that a total unification of gravity, gauge and Higgs fields within one geometrical setting, should be possible by replacing the continuous four- dimensional manifold by a noncommutative space which has both discrete and continuous structures [5]. This possibility and others will be the subject of future investigations."

    The program is to unify gravity with the standard model. GR with QFT. They've made a fair amount of progress.
    Last edited: Mar 24, 2016
  7. Mar 6, 2016 #6


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    Etera Livine is one of the invited speakers and he just came out with what I think is a fascinating extension of spin networks and LQG
    I wonder if the participants at Carlofest will get to discuss it.
  8. Mar 12, 2016 #7


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    Another of the speakers, Stefano Liberati, is a recognized authority on QG phenomenology. Here's his author profile (some 5000 citations to his work)
    He recently co-authored a paper describing TABLETOP experiments (some being currently built) able to detect QG effects and prospects for constraining QG theories by observation.
    Tests of Quantum Gravity induced non-locality via opto-mechanical quantum oscillators
    Alessio Belenchia, Dionigi M. T. Benincasa, Stefano Liberati, Francesco Marin, Francesco Marino, Antonello Ortolan
    (Submitted on 7 Dec 2015)
    Several quantum gravity scenarios lead to physics below the Planck scale characterised by nonlocal, Lorentz invariant equations of motion. We show that such non-local effective field theories lead to a modified Schr\"odinger evolution in the nonrelativistic limit. In particular, the nonlocal evolution of opto-mechanical quantum oscillators is characterised by a spontaneous periodic squeezing that cannot be generated by environmental effects. We discuss constraints on the nonlocality obtained by past experiments, and show how future experiments (already under construction) will either see such effects or otherwise cast severe bounds on the non-locality scale (well beyond the current limits set by the Large Hadron Collider). This paves the way for table top, high precision experiments on massive quantum objects as a promising new avenue for testing some quantum gravity phenomenology.
    5 pages, 1 figure
  9. Mar 24, 2016 #8


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    Incidentally Rovelli's wide audience physics book came out 1 March and has been something of a physics and cosmology best seller for much of the month.
    Today I checked the Amazon page and it was #8 in all the books, of all sorts, that Amazon sells.
    In case you might be interested Greg has an interview with Rovelli in the Insights section:
    Last edited: Mar 24, 2016
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