# Spacetime instability due to quantum gravity

## TL;DR

This paper investigates how quantum gravity causes exponential growth in gravitational waves, leading to potential universe collapse, and proposes methods to manage these runaway modes in different cosmological backgrounds.

## Contribution

It introduces a novel approach to control quantum gravity-induced instabilities by contour selection and mode removal, with implications for cosmology and astrophysics.

## Key findings

- Quantum gravity causes exponentially growing gravitational waves.
- A contour method can exclude problematic modes in Minkowski space.
- Runaway modes can be managed in expanding universes based on Hubble dynamics.

## Abstract

We show that quantum gravity yields exponentially growing gravitational waves. Without a mechanism to stop these modes from growing, the universe would go through a gravitational collapse. For Minkowski background, we propose a solution by choosing an integration contour in Fourier space that does not enclose the problematic modes, thus preventing them from showing up in the effective theory. It turns out that this is only possible when the modes are removed altogether. For an expanding universe, we argue that the runaway modes can be managed accordingly to the dynamics of the Hubble constant, leading to important implications for astrophysics.