Registration Room: 122:026

Welcome Room: 122:026

Plan of workshop Room: 122:026

The universe as a quantum gravity condensate

• Steffen Gielen

Room: 122:026 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.

Discussion Room: 122:026

Lunch break Room: 122:026

Challenges in canonical Loop Quantum Gravity

• Antonia Zipfel

Room: 122:026 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.

Discussion (on talks) Room: 122:026

Coffee break Room: 122:026

Dynamic afternoon: new possibilities for QG? Room: 122:026

Poster session Room: AlbaNova entrance foyer

Welcome reception Room: AlbaNova entrance foyer

Quantum information for relativistic and quantum physics

• David Bruschi

Room: 122:026 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.

Coffee break Room: 122:026

Lattice QCD and Quantum Gravity

• Jack Laiho

Room: 122:026 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.

Discussion (on talks) Room: 122:026

Lunch break Room: 122:026

Talk 4 (Observables)

• Bianca Dittrich

Room: 122:026

Discussion (on talks) Room: 122:026

Coffee break Room: 122:026

Provocation

• Giulia Gubitosi

Room: 122:026

Discussion: brainstorming on observables and connection Room: 122:026

Wave function renormalization in QG

• Jan Ambjørn

Room: 122:026 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.

Coffee break Room: 122:026

Deep Learning in Quantum Gravity

• Will Cunningham

Room: 122:026 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.

Discussion (on talks) Room: 122:026

Lunch break Room: 122:026

Causal Set Quantum Gravity on the Computer

• Sumati Surya

Room: 122:026 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.

Discussion (on talks) Room: 122:026

Coffee break Room: 122:026

Conference dinner Room: Restaurant "Eriks Gondolen"

Renormalization in symmetry-restricted spin foam models with curvature

• Benjamin Bahr

Room: 122:026 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.

Coffee break Room: 122:026

Numerical Loop Quantum Cosmology

• Parampreet Singh

Room: 122:026 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.

Discussion (on talks) Room: 122:026

Lunch break Room: 122:026

Causal Dynamical Triangulations on the Computer

• Andrzej Goerlich

Room: 122:026 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.

Discussion (on talks) Room: 122:026

Coffee break Room: 122:026

Discussion: voice of the young Room: 122:026

Wrap-up talks Room: 122:026

Discussion on all aspects of the workshop: roadmap Room: 122:026