Quantum Gravity and Property of the very early Universe

TL;DR

This paper explores how nonperturbative quantum gravity, particularly through the exact renormalization group equation, impacts early universe models, suggesting it removes initial singularities and determines cosmological time without conflicting with existing cosmological success.

Contribution

It applies nonperturbative quantum gravity via ERGE to early universe cosmology, revealing singularity avoidance and a unique origin of cosmological time.

Findings

Universe becomes free from initial singularity

Cosmological time origin is uniquely determined

Results are consistent with current cosmological observations

Abstract

As is well known, the universally accepted theory as quantum gravity (QG) doesn't exist. One of the main reasons for that is that quantized general relativity is perturbatively nonrenormalizable. But there are several theories whose low-energy effective action is general relativity such as super string theory, supergravity and so on. On the other hand there is the prospect that quantized general relativity will become consistent nonperturbatively, for example by way of the $\epsilon$ - expanded analysis in 2 + $\epsilon$ gravity and the implication of the exact renormalization group equation (ERGE) and so on. Thus, the reason that we can't check which is right, is because of no constraint from experiments. By the way, the early Universe can be considered a good laboratory for QG, because of the high energy scale. In this period it is thought that the effect of QG governed the Universe. Therefore to construct the Universe model out of consideration of a certain type of QG can be thought of the test of the theory. Here the result of quantized general relativity, which is treated nonperturbatively by ERGE, is checked. The application of QG improved Einstein equation to the very early Universe shows several characteristic properties. At first the Universe become free from the initial singularity. The second is the origin of the cosmological time is uniquely decided. Furthermore this result doesn't destroy the success that the current cosmology attained.