Primordial flat frame -- a new view on inflation

Abstract

Models of inflationary cosmology admit a choice of the metric for which geometry becomes flat Minkowski space in the infinite past. In this primordial flat frame all mass scales vanish in the infinite past and quantum scale symmetry is realized. The cosmological evolution is dominantly described by the slow increase of a scalar field which sets the scale of all masses. We construct the primordial flat frame for standard models of inflation as Starobinski inflation or chaotic inflation. In particular, we discuss the evolution of inhomogeneous solutions in the neighborhood of the homogeneous isotropic background solution and their relation to the observable primordial fluctuation spectrum. Our observed inhomogeneous Universe can be extrapolated back to the infinite past in physical time. There is no physical big-bang singularity -the latter reflects only a singular choice of "field coordinates".

Quantum gravity and scale symmetry in cosmology

“…Both conformal time η and the combination A are invariant under Weyl scalings. For many observables the independence from the choice of the metric frame has been demonstrated explicitly [44,[100][101][102][103][104][105][106][107][108][109][110]. Weyl scalings change the geometry without affecting observables.…”