Observation of the Final Boundary Condition: Extragalactic Background Radiation and the Time symmetry of the Universe

TL;DR

This paper explores how a closed, time-symmetric universe could produce a significantly higher extragalactic background radiation than observed, offering a potential test for the universe's boundary conditions and challenging the notion of time symmetry.

Contribution

It demonstrates that in a closed universe with time symmetric boundary conditions, the optical extragalactic background radiation would be at least twice the contribution from observed galaxies, providing a testable prediction.

Findings

Time symmetric boundary conditions imply higher EGBR levels.

Electromagnetic radiation can propagate unabsorbed into the recollapsing phase.

Current observations are consistent with the lower bound of the predicted excess EGBR.

Abstract

This paper examines an observable consequence for the diffuse extragalactic background radiation (EGBR) of the hypothesis that if closed, our universe possesses time symmetric boundary conditions. For simplicity, attention is focused on optical wavelengths. The universe is modeled as closed Friedmann- Roberston-Walker. It is shown that, over a wide range of frequencies, electromagnetic radiation can propagate largely unabsorbed from the present epoch into the recollapsing phase, confirming and demonstrating the generality of results of Davies and Twamley. As a consequence, time symmetric boundary conditions imply that the optical EGBR is at least twice that due to the galaxies on our past light cone, and possibly considerably more. It is therefore possible to test experimentally the notion that if our universe is closed, it may be in a certain sense time symmetric. The lower bound on the "excess" EGBR in a time symmetric universe is consistent with present observations. Nevertheless, better observations and modelling may soon rule it out entirely. In addition, many physical complications arise in attempting to reconcile a transparent future light cone with time symmetric boundary conditions, thereby providing further arguments against the possibility that our universe is time symmetric.