# Dark Energy, $H_0$ and Weak Gravity Conjecture

## TL;DR

This paper explores how cosmological observations, particularly the Hubble constant discrepancies, could test the Weak Gravity Conjecture by linking early dark energy phenomena with quantum gravity principles.

## Contribution

It proposes a novel connection between early dark energy models and the Weak Gravity Conjecture, suggesting cosmological tests for quantum gravity theories.

## Key findings

- Early dark energy may decay into relativistic matter, affecting $H_0$ measurements.
- WGC fields supporting cosmic acceleration could produce relativistic matter after traversing Planckian distances.
- Potential link between resolving $H_0$ discrepancies and fundamental quantum gravity principles.

## Abstract

We point out that the physics at the extreme IR---cosmology---might provide tests of the physics of the extreme UV---the Weak Gravity Conjecture. The current discrepancies in the determination of $H_0$ may hint at a modification of $\Lambda$CDM. An extension which may fit better comprises of an early contribution to dark energy which `decays' into relativistic matter. On the other hand the discourse on WGC to date suggests that fields which support cosmic acceleration may produce relativistic matter after they traverse a $\sim$ Planckian distance in field space. We explain how this offers a simple realization of the requisite cosmic phenomenology. Thus if the resolution of $H_0$ discrepancies is really early dark energy that ends with a shower of relativistic matter and the current ideas on WGC are indicative, this may be a rare opportunity to link the two extreme limits of quantum field theory.