Group field theory and its cosmology in a matter reference frame

Understand

While the equations of general relativity take the same form in any coordinate system, choosing a suitable set of coordinates is essential in any practical application.

• This poses a challenge in background-independent quantum gravity, where coordinates are not a priori available and need to be reconstructed from physical degrees of freedom.
• We review the general idea of coupling free scalar fields to gravity and using these scalars as a "matter reference frame." The resulting coordinate system is harmonic, i.e.
• it satisfies harmonic (de Donder) gauge.