General Relativity and Cosmology: Unsolved Questions and Future Directions

TL;DR

This paper reviews the current status of General Relativity in cosmology, examining its successes, challenges, and future directions, highlighting the need for potential revisions to address unresolved questions and observational conflicts.

Contribution

It provides a comprehensive overview of GR's self-consistency, observational support, and challenges in cosmology, outlining future research directions and potential revisions.

Findings

GR remains the dominant gravitational theory supported by observations.

There are unresolved conflicts and phenomena challenging GR in cosmology.

Future developments may require revising or replacing aspects of GR.

Abstract

For the last 100 years, General Relativity (GR) has taken over the gravitational theory mantle held by Newtonian Gravity for the previous 200 years. This article reviews the status of GR in terms of its self-consistency, completeness, and the evidence provided by observations, which have allowed GR to remain the champion of gravitational theories against several other classes of competing theories. We pay particular attention to the role of GR and gravity in cosmology, one of the areas in which one gravity dominates and new phenomena and effects challenge the orthodoxy. We also review other areas where there are likely conflicts pointing to the need to replace or revise GR to represent correctly observations and consistent theoretical framework. Observations have long been key both to the theoretical liveliness and viability of GR. We conclude with a discussion of the likely developments over the next 100 years.