# Quantum Gravity

This series consists of talks in the area of Quantum Gravity.

## Seminar Series Events/Videos

Nov 13 2019 - 3:30pm
Room #: 394
Speaker(s):
Scientific Areas:
Nov 14 2019 - 2:30pm
Room #: 301
Speaker(s):
Scientific Areas:
Nov 15 2019 - 2:00pm
Room #: 294
Speaker(s):
Scientific Areas:

## Minimum length scenarios that maintain continuous symmetries

Thursday Nov 07, 2019
Speaker(s):

It has long been argued that combining the uncertainty principle with gravity will lead to an effective minimum length at the Planck scale. A particular challenge is to model the presence of a smallest length scale in a manner which respects continuous spacetime symmetries. One path for deriving low-energy descriptions of an invariant minimum length in quantum field theory is based on generalized uncertainty principles. Here I will consider the question how this approach enables one to retain Euclidean or even Lorentzian symmetries.

Collection/Series:
Scientific Areas:

## Dimensionally Restricted Causal Sets

Thursday Oct 31, 2019
Speaker(s):

We study dimensionally restricted non-perturbative causal set quantum dynamics in two and three spacetime dimensions with non-trivial global spatial topology.  The causal set sample space is generated from causal embeddings into latticisations of flat background spacetimes with global spatial topology $S^1$ and

Collection/Series:
Scientific Areas:

## Central extension in gravity

Thursday Oct 24, 2019
Speaker(s):

The asymptotic symmetry charge algebra of certain class of spacetimes could have a nontrivial central extension, which measures the non-equivariance of the charges of the large gauge transformations. The Cardy formula of the dual CFT has been famously used to derive black hole entropy. However, it remains obscure from the point of view of gravity why such a constant on the gravitational phase space could encode the information about the density of black hole micro-states, and what the degrees of freedom accounting for the black hole entropy truly are.

Collection/Series:
Scientific Areas:

## No entailing laws, but enablement in the evolution of the biosphere

Thursday Oct 17, 2019
Speaker(s):

Biological evolution is a complex blend of ever changing structural stability, variability and emergence of new phenotypes, niches, ecosystems. We wish to argue that the evolution of life marks the end of a physics world view of law entailed dynamics.

Collection/Series:
Scientific Areas:

## Evaporating Black-to-White Hole

Thursday Oct 10, 2019

What is the ultimate fate of black holes? Since the discovery of Hawking evaporation process, the issue has been much discussed. Loop quantum gravity suggests that black hole could ultimately turn into white holes. In this talk, we investigate several possible mixed scenario where black holes first evaporate to a Planckian size before tunnelling to white holes. We build various spacetime models, taking Hawking backreaction into account, and we discuss some aspects of the expected phenomenology.

Collection/Series:
Scientific Areas:

## Time and the brain

Thursday Sep 26, 2019
Speaker(s):

Time is one of the most basic features of nature which has been extensively discussed in philosophy and physics. In contrast, time is rather neglected in neuroscience; here time is only conceived in terms of our perception and cognition of time. That leaves open the relevance of time itself, that is, how the brain constitutes its own temporal dynamics and how that is relevant for, for instance, consciousness and other mental features like self.

Collection/Series:
Scientific Areas:

## The cosmological non-constant and Cartan's spiral staircase

Thursday Sep 19, 2019
Speaker(s):

We review recent efforts to turn the cosmological constant into a dynamical variable without an ungainly proliferation of free parameters. In a cosmological setting where parity invariance is imposed (along with homogeneity and isotropy) this leads to phenomenological disaster. However, in this theory it is possible to construct parity violating Friedman models due to torsion, a re-enactment of "Cartan's spiral staircase".

Collection/Series:
Scientific Areas:

## Spacetime and higher-spin symmetries in the de Sitter S-matrix

Thursday Sep 05, 2019
Speaker(s):

I will discuss the problem of an observer's S-matrix in de Sitter space, i.e. the mapping between fields on the initial and final horizons of a de Sitter static patch. I will show how the S-matrix of free massless fields can be packaged in a spinor-helicity language. This involves “cheating” the static patch’s painfully low symmetry, by relating each horizon separately to global, de Sitter-invariant data.

Collection/Series:
Scientific Areas:

## General Covariance and Causal Sets

Thursday Aug 29, 2019
Speaker(s):

If General Relativity emerges from quantum gravity, then general covariance, the gauge invariance of GR, will emerge with it. We can ask, within any approach to the problem of quantum gravity, what is the “precursor” principle or precept that will give rise to — or manifest itself as — general covariance in the large scale semi-classical approximation?
Given how important the understanding of general covariance (or lack of it!) was in the development of GR we might expect that thinking about this question will be similarly important in the development of quantum gravity.

Collection/Series:
Scientific Areas:

## Algebraic construction of interacting QFT models on causal sets

Thursday Aug 22, 2019
Speaker(s):

In this talk I will report on recent progress in building QFT models on causal sets. The framework I'm using is that of perturbative algebraic quantum field theory (pAQFT). It was developed for rigorous study of perturbative QFT in the continuum, but can also be applied in the situation where spacetime is replaced by a discrete structure. Causality plays a key role in pAQFT, so it is natural to apply it to causets.

Collection/Series:
Scientific Areas: