Open problems in gravitational physics

TL;DR

This paper explores fundamental issues and open problems in gravitational physics, questioning assumptions of General Relativity, and considers alternative formulations like Palatini gravity, emphasizing the importance of the Equivalence Principle in theory discrimination.

Contribution

It highlights the potential for disentangling metric and connection fields in gravity theories and discusses the role of the Equivalence Principle in distinguishing between competing models.

Findings

Disentangling metric and connection fields could lead to new gravitational models.

Violations of the Equivalence Principle at quantum levels may open new research directions.

Ground and space experiments could test fundamental aspects of gravity.

Abstract

We discuss some fundamental issues underlying gravitational physics and point out some of the main shortcomings of Einstein's General Relativity. In particular, after taking into account the role of the two main objects of relativistic theories of gravity, i.e. the metric and the connection fields, we consider the possibility that they are not trivially related so that the geodesic structure and the causal structure of the spacetime could be disentangled, as supposed in the Palatini formulation of gravity. In this perspective, the Equivalence Principle, in its weak and strong formulations, can play a fundamental role in discriminating among competing theories. The possibility of its violation at quantum level could open new perspectives in gravitational physics and in unification with other interactions. We shortly debate the possibility of equivalence principle measurements by ground-based and space experiments.