The Diffuse Light of the Universe - On the microwave background before and after its discovery: open questions

TL;DR

This paper reviews the history, interpretation challenges, and open questions surrounding the Cosmic Microwave Background, questioning its status as definitive evidence of the Big Bang and exploring alternative explanations.

Contribution

It critically examines the assumptions and interpretations of the CMB, highlighting unresolved issues and proposing alternative perspectives within cosmological theories.

Findings

Highlights uncertainties in CMB interpretation

Discusses historical and alternative explanations

Identifies open questions in cosmology

Abstract

In 1965, the discovery of a new type of uniform radiation, located between radiowaves and infrared light, was accidental. Known today as Cosmic Microwave background (CMB), this diffuse radiation is commonly interpreted as a fossil light released in an early hot and dense universe and constitutes today the main 'pilar' of the big bang cosmology. Considerable efforts have been devoted to derive fundamental cosmological parameters from the characteristics of this radiation that led to a surprising universe that is shaped by at least three major unknown components: inflation, dark matter and dark energy. This is an important weakness of the present consensus cosmological model that justifies raising several questions on the CMB interpretation. Can we consider its cosmological nature as undisputable? Do other possible interpretations exist in the context of other cosmological theories or simply as a result of other physical mechanisms that could account for it? In an effort to questioning the validity of scientific hypotheses and the under-determination of theories compared to observations, we examine here the difficulties that still exist on the interpretation of this diffuse radiation and explore other proposed tracks to explain its origin. We discuss previous historical concepts of diffuse radiation before and after the CMB discovery and underline the limit of our present understanding.