# A Cosmological basis for E=mc^2

## TL;DR

This paper explores the cosmological significance of the gravitational horizon R_h=ct, proposing it as fundamental to physics by linking it to the origin of rest-mass energy through gravitational binding energy.

## Contribution

It introduces a novel perspective connecting the gravitational horizon R_h=ct with the origin of rest-mass energy via gravitational binding energy calculations.

## Key findings

- The gravitational binding energy of a mass at the horizon equals mc^2.
- Particles near R_h have energy transitioning from rest to escape energy.
- The R_h=ct cosmology aligns well with observational tests.

## Abstract

The Universe has a gravitational horizon with a radius R_h=c/H coincident with that of the Hubble sphere. This surface separates null geodesics approaching us from those receding, and as free-falling observers within the Friedmann-Lemaitre-Robertson-Walker spacetime, we see it retreating at proper speed c, giving rise to the eponymously named cosmological model R_h=ct. As of today, this cosmology has passed over 25 observational tests, often better than LCDM. The gravitational/Hubble radius R_h therefore appears to be highly relevant to cosmological theory, and in this paper we begin to explore its impact on fundamental physics. We calculate the binding energy of a mass m within the horizon and demonstrate that it is equal to mc^2. This energy is stored when the particle is at rest near the observer, transitioning to a purely kinetic form equal to the particle's escape energy when it approaches R_h. In other words, a particle's gravitational coupling to that portion of the Universe with which it is causally connected appears to be the origin of rest-mass energy.