Disappearance and emergence of space and time in quantum gravity

Abstract

We discuss the hints for the disappearance of continuum space and time at microscopic scale. These include arguments for a discrete nature of them or for a fundamental non-locality, in a quantum theory of gravity. We discuss how these ideas are realized in specific quantum gravity approaches. Turning then the problem around, we consider the emergence of continuum space and time from the collective behaviour of discrete, pre-geometric atoms of quantum space, and for understanding spacetime as a kind of "condensate", and we present the case for this emergence process being the result of a phase transition, dubbed "geometrogenesis". We discuss some conceptual issues of this scenario and of the idea of emergent spacetime in general. As a concrete example, we outline the GFT framework for quantum gravity, and illustrate a tentative procedure for the emergence of spacetime in this framework. Last, we re-examine the conceptual issues raised by the emergent spacetime scenario in light of this concrete example.

As below, so before: ‘synchronic’ and ‘diachronic’ conceptions of spacetime emergence

“…30 For details on QCH, see, Markopoulou (2009), for quantum graphity, see: Konopka et al (2008). 31 Geometrogenesis is also described in group field theory, which is an active research program that utilises, and is useful for, various other approaches to QG, including LQG and causal set theory (Freidel, 2005;Oriti, 2009Oriti, , 2014. E state via Hamiltonian evolution, and the two states are supposed to be of the same system, being the entire universe.…”

Incubating a future metaphysics: quantum gravity

“…In these special cases, the theory describes structures which correspond, roughly, to the geometry of our familiar experiences. Because of these features, Huggett and Wüthrich (2013) and Oriti (2014) claim that spacetime is emergent from the spin-networks of LQG. I will follow the convention of the literature and will continue to say "spacetime emergence" though, in the case of LQG, it might be more accurate to say "space emergence" given that the weave-states only encode the geometry of the three-dimensional hyper-surfaces of spacetime.…”

A Givental-like formula and bilinear identities for tensor models

“…From the start tensor models were also related to the group field theory (GFT) approach to quantum gravity [21,41,43]. This approach implements a sum over spin networks of loop quantum gravity [22] as a quantum field theory defined on a Lie group.…”