Quantum Gravity on the Computer

5 Mar 2018, 09:00 → 9 Mar 2018, 18:00 Europe/Stockholm

122:026 (Nordita, Stockholm)

Lisa Glaser (Radboud University), Sebastian Steinhaus (Perimeter Institute)

Venue

Nordita, Stockholm, Sweden

Scope

One of the big challenges of non-perturbative quantum gravity is the complexity of the dynamics. Discrete approaches can only show a non-trivial dynamics and approximate the continuum when a large number of degrees of freedom is taken into account. Over the last decades numerical tools have stimulated and accelerated developments in many fields of theoretical physics, which is why we want to apply them to non-perturbative quantum gravity. The goal of this workshop is to bring together researchers from quantum gravity already working with numerical methods, those that want to start working with numerical methods and practitioners of numerics in other fields of physics to kick-start the development of numerical techniques and to establish new collaborations and research projects. Timetable Slides from talks and Posters [If you have slides or posters and want to have them available on this page, please send them to info@nordita.org]

Participants

Quantum Gravity computators (click to enlarge). "I think this is the beginning of a beautiful friendship."

Invited Speakers

Sumati Surya, Raman Research Institute, Bangalore Benjamin Bahr, University Hamburg Antonia Zipfel, Florida Atlantic University, Boca Raton Steffen Gielen, University of Nottingham David Edward Bruschi, University of York

Jan Ambjørn, Niels Bohr Institute, Copenhagen Bianca Dittrich, Perimeter Institute, Waterloo Andrzej Goerlich, Jagiellonian University, Krakow Jack Laiho, Syracuse University, New York

Giulia Gubitosi, Radboud University, Nijmegen Parampreet Singh, Louisiana State University, Baton Rouge Will Cunningham, Northeastern University, Boston

Application

If you want to apply for participation in the workshop, please fill in the application form. You will be informed by the organizers shortly after the application deadline whether your application has been approved. Due to space restrictions, the total number of participants is strictly limited. (Invited speakers are of course automatically approved, but need to register anyway.)

Application deadline: 12 January 2018

There is no registration fee.

Sponsored by:

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 706349.

pictures Chip_and_spacetime_v3_bw_text.png Chip_and_spacetime_v3_text.png

Monday 5 March

1 Registration

2 Welcome

3 Plan of workshop

4 The universe as a quantum gravity condensate

Bridging the gap from the Planck scale to cosmological scales is the ultimate challenge for quantum gravity, but doing so would allow us to connect the microscopic physics of quantum gravity to observation through cosmology. In the group field theory (GFT) approach, a promising working hypothesis has been that a macroscopic universe emerges from a "condensate" of many interacting (Planck-scale) degrees of freedom of quantum geometry. I will give an introduction into the GFT formalism and discuss the approximations that have been employed, in analogy to normal Bose-Einstein condensates, in order to obtain simple, analytically solvable equations for the emergent cosmology. Most of these approximations are crude, and numerical techniques may indeed be necessary for justifying them, thus providing more solid foundations for the connection of GFT to the universe. I will also discuss how GFT might one day pass the main test for any theory of the early universe: explaining the pattern of the cosmic microwave background.

Speaker: Steffen Gielen

5 Discussion

6 Lunch break

7 Challenges in canonical Loop Quantum Gravity

By now, the foundations of loop quantum gravity are well understood. However, only a very limited number of predictions have been derived from full LQG due to the complicated nature of the dynamics. To tackle this problem it will be inevitable to further develop efficient numerical methods and construct effective models. In my talk I will discuss several recent approaches in which numerical methods play a key role. Amongst others I will discuss the semi-classical dynamics of cosmological states and symmetry reduction in the case of spherical symmetry.

Speaker: Antonia Zipfel

8 Discussion (on talks)

9 Coffee break

10 Dynamic afternoon: new possibilities for QG?

11 Poster session

12 Welcome reception

Tuesday 6 March

13 Quantum information for relativistic and quantum physics

Quantum information has shaped physics and science in the past decades. On the one hand, quantum information studies the theoretical aspects of information theory when quantum systems are employed. On the other, quantum information promises technological revolutions far beyond our current capabilities. These include quantum computers, quantum communications and quantum cryptography. Regardless of the approach considered, quantum information is well described and characterized by quantum mechanics. Experiments have been so far successfully explained by quantum physics alone. However, they are now reaching regimes where relativity cannot be ignored. A completely novel approach needs to be taken in order to give correct predictions at the overlap of relativity and quantum science; these will provide us with better ways to characterize our future technologies, our theory and, ultimately, our ability to test the fundamental laws of nature. We present recent advances in the field of relativistic quantum information. We focus our attention on theoretical aspects and predictions of possible experiments that can test the role of paradigmatic quantum information resources, such as entanglement, in phenomena that occur at the overlap of relativity and quantum physics. In particular we focus on a recently proposed gravitational wave antenna based on micrometer-size Bose Einstein Condensates. We then discuss the role of the information theoretical aspects of the proposal, such as optimisation of, and ultimate bounds on, measurements, which are paramount for the success of the technology. We conclude with an overlook on future directions and applications.

Speaker: David Bruschi

14 Coffee break

15 Lattice QCD and Quantum Gravity

The methods and results of Lattice Quantum Chromodynamics are reviewed. This includes a review of algorithms, effective field theory, and results relevant for particle physics. What we might be able to learn about gravity from this is discussed.

Speaker: Jack Laiho

16 Discussion (on talks)

17 Lunch break

18 Talk 4 (Observables)

Speaker: Bianca Dittrich

19 Discussion (on talks)

20 Coffee break

21 Provocation

Speaker: Giulia Gubitosi

22 Discussion: brainstorming on observables and connection

Wednesday 7 March

23 Wave function renormalization in QG

Using the bosonic string as an example I discuss the conceptional problem wave function renormalization imposes on a lattice regularization of QG, and thus on putting QG on a computer.

Speaker: Jan Ambjørn

24 Coffee break

25 Deep Learning in Quantum Gravity

Is it worthwhile to study quantum gravity using deep learning? In causal set quantum gravity, it is useful for measuring discrete observables in Monte Carlo simulations. We have found that though there does not yet exist a general analytical expression for a causal set's manifold dimension, we can train a deep neural network in under five minutes to identify the correct value with over 99% accuracy. Remarkably, when trained with only 100-element Minkowski causal sets, the network can still correctly identify the dimension for those generated from other manifolds and those with larger sizes. We will discuss the types of problems for which deep learning is well suited, and also look at how one constructs a supervised learning algorithm using the TensorFlow package for Python. Finally, we will conclude by discussing how these methods may be trivially extended to study other discrete geometric properties.

Speaker: Will Cunningham

26 Discussion (on talks)

27 Lunch break

28 Causal Set Quantum Gravity on the Computer

I will discuss the role of numerical simulations in the causal set approach to quantum gravity. Because of the inherent non-locality of the graphs, the limits and complexity of simulations can far exceed that associated with finite valency graphs. On the other hand, fairly small graphs contain far richer geometric information than one might imagine. The overall goal is to present some of the broad numerical challenges faced in the causal set approach. I will begin with examples of geometric observables in the theory and how simulations give us practical estimates for manifoldlikeness. I will then discuss a class of continuum inspired dynamics which are studied using MCMC simulations. An approach that has been successful in 2d is to limit the full sample space of causal sets by spacetime dimension and topology. I will then describe some very recent work where this is extended to the class of cylindrical 2d geometries using a "lattice gas" model of causal sets.

Speaker: Sumati Surya

29 Discussion (on talks)

30 Coffee break

31 Conference dinner

Thursday 8 March

32 Renormalization in symmetry-restricted spin foam models with curvature

We study the renormalization group flow in the Euclidean EPRL-FK spin foam model for quantum gravity in a truncation. This extends previous results which were carried out in a hypercuboidal setting, where a non-trivial fixed point was found. In the extended setting presented in this talk, some local curvature excitations are permitted, and we find that the fixed point still exists, with similar properties. We discuss the implications, as well as the connection to restoration of broken diffeomorphism symmetry in this setting.

Speaker: Benjamin Bahr

33 Coffee break

34 Numerical Loop Quantum Cosmology

One of the key predictions of loop quantum gravity is that classical differential geometry of GR is replaced by a discrete quantum geometry at the Planck scale. In this talk we will discuss the way numerical simulations of quantum spacetime is far more challenging than the ones in classical spacetime. We will then discuss some novel procedures to overcome these challenges and discuss various numerical results. These results show that big bang singularity in isotropic and anistropic spacetimes are resolved and that prove validity of an effective spacetime description. The latter has been extensively used to understand new physics at the Planck scale and signatures in cosmic microwave background.

Speaker: Parampreet Singh

35 Discussion (on talks)

36 Lunch break

37 Causal Dynamical Triangulations on the Computer

Causal Dynamical Triangulations (CDT) is a background independent approach to quantum gravity which introduces a lattice regularization. In this talk, we will describe computational methods of CDT, particularly the Monte Carlo algorithm. We will discuss what we can measure and, based on that, what phase structure we observe. We will present how to extract the effective action for a scale factor, which is of physical interest, using the covariance matrix method and the transfer matrix method. Finally, we will highlight some aspects of code parallelization with the aim at improving the performance and speeding up the thermalization stage.

Speaker: Andrzej Goerlich

38 Discussion (on talks)

39 Coffee break

40 Discussion: voice of the young

Friday 9 March

41 Wrap-up talks

42 Discussion on all aspects of the workshop: roadmap