# Electromagnetic fields and charges in expanding universes

## TL;DR

This paper explores how electromagnetic fields and charges behave in expanding universe models, focusing on their properties, energy flow, and radiation effects in different reference frames within cosmological backgrounds.

## Contribution

It provides a detailed analysis of electromagnetic fields in expanding universes, including conformal properties and local effects using Fermi coordinates, highlighting new insights into charge acceleration and radiation.

## Key findings

- Charges following Hubble flow can radiate due to universe expansion.
- Expansion affects electromagnetic field conformal properties.
- Local inertial frames observe charge acceleration and radiation.

## Abstract

We analyze the properties of the electric and magnetic fields in different reference frames within a cosmological background space-time. First, we investigate the conformal properties of the electromagnetic fields and charge currents, discussing how the spatial curvature of the universe affects the field on different scales. Then, we analyze the effects of the expansion of the universe on local electromagnetic sources using Fermi coordinates. In particular, we investigate the energy balance and Poynting flux in this locally defined reference frame. We show that a charge following the Hubble flow in an accelerated FLRW universe is accelerated as seen by the local inertial frame, leading to non-null radiation.