A Curious Explanation of Some Cosmological Phenomena

TL;DR

This paper explores how the Milne model, a phenomenological cosmological theory, can explain observations without dark sectors, potentially offering insights into developing a final theory of gravitation.

Contribution

It highlights unnoticed coincidences suggesting that a theory excluding the energy-stress tensor from dynamics could resolve key cosmological issues.

Findings

Milne model explains observations without dark matter or dark energy.

The model avoids horizon, flatness, and cosmological constant problems.

Insights from coincidences may guide the development of a final gravitational theory.

Abstract

While observational cosmology has shown tremendous growth over the last decade, deep mysteries continue to haunt our theoretical understanding of the ingredients of the concordance cosmological model, which are mainly `dark'. More than 95 percent of the content of the energy-stress tensor has to be in the form of inflaton, dark matter and dark energy, which do not have any non-gravitational or laboratory evidence and remain unidentified. Moreover, the dark energy poses a serious confrontation between fundamental physics and cosmology. This makes a strong case to discover alternative theories which do not require the dark sectors of the standard approach to explain the observations. In the present situation, it would be important to gain insight about the requirements of the `would be' final theory from all possible means. In this context, the present paper highlights some, hitherto unnoticed, interesting coincidences which may prove useful to develop insight about the `holy grail' of gravitation. It appears that the requirement of the speculative dark sectors by the energy-stress tensor, is indicative of a possible way out of the present crisis appearing in the standard cosmology, in terms of a theory wherein the energy-stress tensor does not play a direct role in the dynamics. It is shown that various cosmological observations can be explained satisfactorily in the framework of one such theory $-$ the Milne model, without requiring the dark sectors of the standard approach. Moreover, the model evades the horizon, flatness and the cosmological constant problems afflicting the standard cosmology. Though Milne's theory is an incomplete, phenomenological theory, and cannot be the final theory of gravitation, nevertheless, it would be worthwhile to study these coincidences, which may help us develop insight about the would-be final theory.