Can Geodesics in Extra Dimensions Solve the Cosmological Horizon Problem?

TL;DR

This paper proposes a non-inflationary mechanism where signals traveling through extra dimensions can connect distant regions of the universe faster than light confined to our three-dimensional space, addressing the horizon problem.

Contribution

It introduces a novel solution to the horizon problem using extra-dimensional null geodesics, bypassing the need for inflation.

Findings

Extra-dimensional geodesics can connect distant points more quickly.

A signal can leave and return to our brane via extra dimensions.

This mechanism can explain causal contact without inflation.

Abstract

We demonstrate a non-inflationary solution to the cosmological horizon problem in scenarios in which our observable universe is confined to three spatial dimensions (a three-brane) embedded in a higher dimensional space. A signal traveling along an extra-dimensional null geodesic may leave our three-brane, travel into the extra dimensions, and subsequently return to a different place on our three-brane in a shorter time than the time a signal confined to our three-brane would take. Hence, these geodesics may connect distant points which would otherwise be ``outside'' the four dimensional horizon (points not in causal contact with one another).