Disappearance and Emergence of Space and Time in Quantum Gravity - a podcast by MCMP Team

Daniele Oriti (Potsdam) gives a talk at the MCMP workshop "Quantum Gravity in Perspective" (31 May-1 June, 2013) titled "Disappearance and Emergence of Space and Time in Quantum Gravity". Abstract: We recall the hints for the disappearance of continuum space and time at microsopic scales, coming from classical and semi-classical gravitational physics. These include arguments for discreteness or for a fundamental non-locality, in a quantum theory of gravity. We compare how these ideas are realized in specific quantum gravity approaches, and focus in particular on the group field theory formalism, itself strictly related to other approaches, in particular loop quantum gravity. Next, we consider the emergence of continuum space and time from the collective behaviour of discrete, pre-geometric and non-spatio-temporal atoms of quantum space. After discussing the notion of emergence, with Bose condensates as one paradigmatic examples, and some specific cenceptual difficulties with the notion of emergent spacetime, we argue for spacetime as a kind fo cendsate, result of a phase transition, physically identified with the big bang. We then illustrate recent results, in the context of the group field theory framework, establishing a tentative procedure for the emergence of cosmological (homogeneous) spacetime and their effective quantum dynamics from fundamental, pre-geometric models. Last, we re-examine the conceptual issues raised by the emergent spacetime scenario in light of this concrete example.

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