Do intergalactic magnetic fields imply an open universe?

TL;DR

The paper argues that the presence of primordial magnetic fields observed today suggests the universe is likely marginally open, based on their survival through cosmic evolution in different cosmological models.

Contribution

It demonstrates how primordial magnetic fields can survive in an open universe but not in flat or closed models, providing a new cosmological constraint.

Findings

Magnetic fields survive inflation in open universes

Magnetic fields fail to survive in flat or closed universes

Primordial magnetic fields imply a marginally open universe

Abstract

The detection of magnetic fields at high redshifts, and in empty intergalactic space, support the idea that cosmic magnetism has a primordial origin. Assuming that Maxwellian electromagnetism and general relativity hold, and without introducing any `new' physics, we show how the observed magnetic fields can easily survive cosmological evolution from the inflationary era in a marginally open Friedmann universe but fail to do so, by a very wide margin, in a flat or a marginally closed universe. Magnetic fields evolve very differently in open and closed Friedmann models. The existence of significant magnetic fields in the universe today, that require primordial seeding, may therefore provide strong evidence that the universe is marginally open rather than marginally closed.