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We propose a new method for obtaining an effectiveFriedmann-Lema\^itre-Robertson-Walker (FLRW) cosmology from the quantum gravitydynamics of group field theory (GFT), based on the idea that an FLRW universeis characterised by a few macroscopic observables. Rather than relying onassuming a particular type of quantum state and computing expectation values insuch a state, here we directly start from relations between macroscopicobservables (defined as one-body operators) and formulate dynamics only forthose observables. We apply the effective approach to constrained quantumsystems (as developed by Bojowald and collaborators) to GFT, providing asystematic expansion in powers of $\hbar$. We obtain a kinematical phase spaceof expectation values and moments, which does not require an a priori choice ofclock variable. We identify a gauge fixing of the system which corresponds tochoosing one of the cosmological variables (with the role of extrinsiccurvature) as a clock and which allows us to rewrite the effective dynamics inrelational form. We show necessary and sufficient conditions for the resultingdynamics of expectation values to be compatible with those of classical FLRWcosmology and discuss the impact of quantum fluctuations.

Effective cosmology from one-body operators in group field theory