# The theory of gravitation: A tale of many questions and few answers

## TL;DR

This paper explores unresolved fundamental questions in gravity theory, focusing on observer effects, vorticity-radiation relationships, and gravitational wave sources, highlighting areas needing further research.

## Contribution

It provides a comprehensive discussion on key unresolved issues in gravity, emphasizing the role of different observers and the physical properties of gravitational wave sources.

## Key findings

- Tilted observers detect dissipation in isentropic systems
- Vorticity may be linked to radiation with observable consequences
- Summary of current knowledge on gravitational wave sources

## Abstract

We discuss on different issues pertaining the theory of gravity, which pose some unresolved fundamental questions. First we tackle the problem of observers in general relativity, with particular emphasis in tilted observers. We explain why these observers may detect dissipative processes in systems which appear isentropic to comoving observers. Next we analyze the strange relationship between vorticity and radiation, and underline the potential observational consequences of such a link. Finally we summarize all the results that have been obtained so far on the physical properties of the sources of gravitational radiation. We conclude with a list of open questions which we believe deserve further attention.