Emergent cosmology from quantum gravity: the universe as a quantum condensate - a podcast by Michael Haack

The construction of a quantum theory of gravity
remains an open problem despite decades of efforts.In time, the very perspective on this problem evolved.
From quantising General Relativity, the goal is nowmostly understood to be unraveling a more
fundamental microstructure of spacetime, based onnon-geometric building blocks, and to show how
spacetime and matter emerge as effective, approximatenotions. Given some candidate building blocks, the task
becomes analogous to that of extracting themacroscopic, collective behaviour of the atoms of a
condensed matter system, but even more challengingsince we cannot use the usual spacetime intuition and
no direct observational input is available to guidetheory construction.
Lacking a fundamental theory of quantum gravity,existing cosmological models which have proven
extremely successful in accounting for the observedfeatures of the very early universe (via CMB data)
remain without a solid foundation, having to make anumber of assumptions about a physical regime (close
to the big bang), where the quantum nature of gravityand spacetime is expected to be relevant. This is all the
LUDWIG-MAXIMILIANS-UNIVERSITÄT MÜNCHEN SEITE 2 VON 2more unfortunate, since the very early universe is also
where any proposed quantum theory of gravity has thehighest chance of finding its observational test-bed.
The gap needs to be bridged.In this talk I will first of all review the basic aspects of
the problem of quantum gravity, and of some currentapproaches. I will then focus on one specific formalism
for quantum gravity, so-called group field theories(strictly related to a number of other modern
approaches). I will introduce its main features, trying toclarify the nature of the suggested building blocks of
spacetime and their mathematical description. Next, Iwill outline a general strategy to extract an effective
cosmological dynamics from quantum gravity, withinthis formalism. In this setting, the universe emerges as
a quantum condensate of the fundamental “atoms ofspacetime”, and cosmology is its corresponding
hydrodynamics. Finally, I will summarize the recentresults obtained along this research direction.

Further episodes of Sommerfeld Theory Colloquium (ASC)

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Website of Michael Haack