"All that matter ... in one Big Bang ...," & other cosmological singularities

TL;DR

This paper reviews the historical development of cosmological singularities, clarifies the original Big Bang concept, and discusses recent theoretical advances and new types of singularities arising from modified gravity theories.

Contribution

It provides a historical perspective on the origin of the Big Bang idea and offers an updated classification of various cosmological singularities including those from modified gravity models.

Findings

Clarification of the original Big Bang concept and its evolution.

Introduction of new singularities from modified gravity theories.

Updated classification of cosmological singularities.

Abstract

The first part of this paper contains a brief description of the beginnings of modern cosmology, which, the author will argue, was most likely born in the Year 1912. Some of the pieces of evidence presented here have emerged from recent research in the history of science, and are not usually shared with the general audiences in popular science books. In special, the issue of the correct formulation of the original Big Bang concept, according to the precise words of Fred Hoyle, is discussed. Too often, this point is very deficiently explained (when not just misleadingly) in most of the available generalist literature. Other frequent uses of the same words, Big Bang, as to name the initial singularity of the cosmos, and also whole cosmological models, are then addressed, as evolutions of its original meaning. Quantum and inflationary additions to the celebrated singularity theorems by Penrose, Geroch, Hawking and others led to subsequent results by Borde, Guth and Vilenkin. And corresponding corrections to the Einstein field equations have originated, in particular, $R^2$, $f(R)$, and scalar-tensor gravities, giving rise to a plethora of new singularities. For completeness, an updated table with a classification of the same is given.