Quantum Gravity

Quantum gravity is concerned with unifying Einstein's general theory of relativity with quantum theory into a single theoretical framework. At Perimeter Institute, researchers are actively pursuing a number of approaches to this problem including loop quantum gravity, spin foam models, asymptotic safety, emergent gravity, string theory, and causal set theory. We are also particularly interested in experimental implications of these different proposals. As the aim is a unification of the laws of physics into a single theory, the search for quantum gravity overlaps with other areas such as cosmology, particle physics and the foundations of quantum theory.

Displaying 973 - 984 of 1399

PHYS 781 - Lecture 14

Niayesh Afshordi University of Waterloo
November 04, 2014

PIRSA:14110049
Cosmology

Quantum Gravity

Strong Gravity
Complex Loop Quantum Cosmology

Jibril Ben Achour Ludwig-Maximilians-Universität München (LMU)
October 30, 2014

PIRSA:14100047
Quantum Gravity
Is B-Mode Polarization of the CMB the Holy Grail of Inflation?

Robert Brandenberger McGill University - Department of Physics
October 16, 2014

PIRSA:14100002
Quantum Gravity
Observables and Change in Totally Constrained Systems

Karim Thebault Ludwig-Maximilians-Universität München (LMU)
September 18, 2014

PIRSA:14090004
Quantum Gravity
Firewalls- A GR perspective

Bill Unruh University of British Columbia
September 04, 2014

PIRSA:14090066
Quantum Gravity
Physical Hilbert space for the affine group formulation of 4D, gravity of Lorentzian signature.

Eyo Ita US Naval Academy and Cambridge University (DAMTP)
July 31, 2014

PIRSA:14070033
Quantum Gravity
Gravity, an unexpected journey: from thermodynamics to emergent gravity, Lorentz breaking and back...

Stefano Liberati SISSA International School for Advanced Studies
June 19, 2014

PIRSA:14060002
Quantum Gravity
Analogue Models of Gravity: The ubiquitous space-time

Stefano Liberati SISSA International School for Advanced Studies
June 18, 2014

PIRSA:14060000
Quantum Gravity
Last gasp ‎of a black hole: why unitary evaporation must be non-monotonic

Matteo Smerlak Capital Fund Management S.A.
May 29, 2014

PIRSA:14050027
Quantum Gravity
From locally covariant QFT to quantum gravity

Katarzyna Rejzner University of York
May 15, 2014

PIRSA:14050004
Quantum Gravity
On the role of the extra kinetic term coupling ƛ in classical Hořava-Lifshitz gravity

Luis Pires Radboud Universiteit Nijmegen
May 08, 2014

PIRSA:14050061
Quantum Gravity
Group Field Theory in dimension 4 - ε

Sylvain Carrozza University of Burgundy
May 01, 2014

PIRSA:14050001
Quantum Gravity

PHYS 781 - Lecture 14

Niayesh Afshordi University of Waterloo
November 04, 2014

PIRSA:14110049
Cosmology

Quantum Gravity

Strong Gravity
Complex Loop Quantum Cosmology

Jibril Ben Achour Ludwig-Maximilians-Universität München (LMU)
October 30, 2014

PIRSA:14100047
Quantum Gravity
We study in the context of loop quantum cosmology the effect of the analytic continuation that sends the Barbero-Immirzi parameter to a purely imaginary value. We show that this construction leads once again to a bouncing scenario, in which however the contracting and expanding phases on each side of the bounce are not symmetrical. Moreover, the minimal volume reached by the universe and the critical matter density become naturally independent of the Barbero-Immirzi parameter. This analytic continuation was first proposed in the context of black hole entropy calculation, and constitutes a proposal for defining a theory of self-dual quantum gravity in terms of the complex Ashtekar connection and for solving the so-called reality conditions. We expect that the systematic investigation of this analytic continuation in various setups will eventually lead to new insights on the status of the quantum states of complex Ashtekar gravity.
Is B-Mode Polarization of the CMB the Holy Grail of Inflation?

Robert Brandenberger McGill University - Department of Physics
October 16, 2014

PIRSA:14100002
Quantum Gravity
I will discuss why the search for B-Mode Polarization of the Cosmic Microwave Background (CMB) is very important for early universe cosmology, but that a discovery of such a polarization mode is in no way a confirmation of inflationary cosmology.
Observables and Change in Totally Constrained Systems

Karim Thebault Ludwig-Maximilians-Universität München (LMU)
September 18, 2014

PIRSA:14090004
Quantum Gravity
We isolate an important physical distinction between gauge symmetries which exist at the level of histories and states, and those which exist at the level of histories and not states. This distinction is characterised explicitly using a generalized Hamilton-Jacobi formalism within which a non-standard prescription for the observables of classical totally constrained systems is developed. These ideas motivate a `relational quantization' procedure which is different from the standard `Dirac quanization'. In particular, relational quantization of totally constrained systems leads to a formalism with superpositions of energy eigenstates and an enlarged set of quantum observables. These `Kucha\v{r} observables' can change independently of each other, and thus are associated with measurable quantities in excess of the `perennials' of the standard Dirac approach.
Firewalls- A GR perspective

Bill Unruh University of British Columbia
September 04, 2014

PIRSA:14090066
Quantum Gravity
This talk will examine the Firewall argument and a number of possible approaches to it, with a variety of simple examples to try to clarify various aspects of the arguments.
Physical Hilbert space for the affine group formulation of 4D, gravity of Lorentzian signature.

Eyo Ita US Naval Academy and Cambridge University (DAMTP)
July 31, 2014

PIRSA:14070033
Quantum Gravity
The authors have revealed a fundamental structure which has been hidden within the Wheeler-DeWitt (WDW) constraint of four dimensional General Relativity (GR) of Lorentzian signature in the Ashtekar self-dual variables. The WDW equation can be written as the commutator of two geometric entities, namely the imaginary part of the Chern-Simons functional Q and the local volume element V(x) of 3-space. Upon quantization with cosmological constant, the WDW equation takes on the form of the Lie algebra of the affine group of transformations of the straight line, with Q and V(x) playing the role of the generators for the Lie algebra. The generators are Hermitian, which addresses the issue of the implementation of the reality conditions of GR at the quantum level. Additionally, the irreducible unitary representations (IUR) implement the positivity of the spectrum of the volume operator V(x) at the quantum level This development has led to the existence of elements of the physical Hilbert space for four dimensional gravity of Lorentzian signature, the full theory, in the form of irreducible, unitary representations of the affine group of transformations of the straight line. The affine Lie algebraic structure of the WDW equation remains intact even in the presence of nongravitational fields. This feature has led to the extension of the affine group formulation to elements of the physical Hilbert space for gravity coupled to the full Standard Model of particle physics, quantized on equal footing. Work on the physical interpretation of the states with respect to gauge-diffeomorphism invariant observables, and spacetime geometries solving the Einstein equations is in progress. The journal reference for these results are as follows: - The first result has been published in CQG 30 (2013) 065013 - The second result has just been published in Annals of Physics Journal Vol.343, pages 153-163, April 2014
Gravity, an unexpected journey: from thermodynamics to emergent gravity, Lorentz breaking and back...

Stefano Liberati SISSA International School for Advanced Studies
June 19, 2014

PIRSA:14060002
Quantum Gravity
Thermodynamical aspects of gravity have been a tantalising puzzle for more than forty years now and are still at the center of much activity in semiclassical and quantum gravity. We shall explore the possibility that they might hint toward an emergent nature of gravity exploring the possible implications of such hypothesis. Among these we shall focus on the possibility that Lorentz invariance might be only a low energy/emergent feature by discussing viable theoretical frameworks, present constraints and open issues which make this path problematic. In the end we shall focus on black hole thermodynamics in Lorentz breaking gravity by presenting some recent results that seems to hint towards a surprising resilience of thermodynamics aspect of gravity even in these scenarios.
Analogue Models of Gravity: The ubiquitous space-time

Stefano Liberati SISSA International School for Advanced Studies
June 18, 2014

PIRSA:14060000
Quantum Gravity
Analogies have played a very important role in physics and mathematics, as they provide new ways of looking at problems that permit cross-fertilization of ideas among different branches of science. An analogue gravity model is a generic dynamical system (typically but not always based on condensed matter physics) where the propagation of excitations/perturbations can be described via hyperbolic equations of motion possibly characterized be one single metric element for all the perturbations. We shall review the historical development of this field, some of the systems proposed, and discuss several applications of this fruitful analogy mainly in the context of black hole physics and cosmology. While typical applications are in the realm of classical and quantum field theory on curved spacetime, I shall in the end also discuss recent developments which may provide insights about the possible nature of gravitational dynamics in emergent gravity scenarios.
Last gasp ‎of a black hole: why unitary evaporation must be non-monotonic

Matteo Smerlak Capital Fund Management S.A.
May 29, 2014

PIRSA:14050027
Quantum Gravity
I will describe the relationship between radiated energy and entanglement entropy of massless fields at future null infinity (the "Page curve") in two-dimensional models of black hole evaporation. ‎I will use this connection to derive a general feature of any unitary-preserving evaporation scenario: the Bondi mass of the hole must be non-monotonic. Time permitting, I will comment on time scales in such scenarios.
From locally covariant QFT to quantum gravity

Katarzyna Rejzner University of York
May 15, 2014

PIRSA:14050004
Quantum Gravity
Locally covariant quantum field theory (LCQFT) has proven to be a very successful framework for QFT on curved spacetimes. It is natural to ask, how far these ideas can be generalized and if one can learn something about quantum gravity, using LCQFT methods. In particular, one can use the relative Cauchy evolution to formulate the notion of background independence. Recently we have proven that background independence in this sense holds for effective quantum gravity, formulated as a perturbative QFT. Remarkably, the formalism of LCQFT can be extended to structures more general than spacetimes. The essential feature is the presence of the causal structure. An example application would be QFT on causal sets (work in progress).
On the role of the extra kinetic term coupling ƛ in classical Hořava-Lifshitz gravity

Luis Pires Radboud Universiteit Nijmegen
May 08, 2014

PIRSA:14050061
Quantum Gravity
We study the classical constraint algebra of Hořava-Lifshitz gravity, where due to the breaking of 4d diffeomorphism symmetry, there is a new dimensionless coupling absent in GR and whose role is not yet clear. Starting from two apparently contradictory results, we show how the role of the extra coupling differs between the projectable and non-projectable versions of the theory. In particular, we see how in the latter, it gives rise to a non-trivial constraint algebra, akin to the conditions seen in the CMC gauge of GR.
Group Field Theory in dimension 4 - ε

Sylvain Carrozza University of Burgundy
May 01, 2014

PIRSA:14050001
Quantum Gravity
Rank 3 tensorial group fields theories with gauge invariance condition appear to be renormalizable on dimension 3 groups such as SU(2), but also on dimension 4 groups. Building on an analogy with ordinary scalar field theories, I will generalize such models to group dimension 4 - ε, and discuss what this might teach us about the physically relevant SU(2) case.

Title	Speaker(s)	Date	Talk Type	Info link
PHYS 781 - Lecture 14	Niayesh Afshordi	2014-11-04	Course	View details
Complex Loop Quantum Cosmology	Jibril Ben Achour	2014-10-30	Scientific Series	View details
Is B-Mode Polarization of the CMB the Holy Grail of Inflation?	Robert Brandenberger	2014-10-16		View details
Observables and Change in Totally Constrained Systems	Karim Thebault	2014-09-18	Scientific Series	View details
Firewalls- A GR perspective	Bill Unruh	2014-09-04	Scientific Series	View details
Physical Hilbert space for the affine group formulation of 4D, gravity of Lorentzian signature.	Eyo Ita	2014-07-31	Scientific Series	View details
Gravity, an unexpected journey: from thermodynamics to emergent gravity, Lorentz breaking and back...	Stefano Liberati	2014-06-19	Scientific Series	View details
Analogue Models of Gravity: The ubiquitous space-time	Stefano Liberati	2014-06-18	Scientific Series	View details
Last gasp ‎of a black hole: why unitary evaporation must be non-monotonic	Matteo Smerlak	2014-05-29	Scientific Series	View details
From locally covariant QFT to quantum gravity	Katarzyna Rejzner	2014-05-15	Scientific Series	View details
On the role of the extra kinetic term coupling ƛ in classical Hořava-Lifshitz gravity	Luis Pires	2014-05-08	Scientific Series	View details
Group Field Theory in dimension 4 - ε	Sylvain Carrozza	2014-05-01	Scientific Series	View details

Quantum Gravity

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