100 Years of Relativistic Cosmology (1917-2017). Part I: From Origins to the Discovery of Universal Expansion (1929)

TL;DR

This paper reviews a century of cosmology, highlighting key theoretical and observational milestones from Einstein to Hubble, emphasizing the evolution of understanding about the universe's expansion and acceleration.

Contribution

It provides a comprehensive overview of the historical development of relativistic cosmology from 1917 to 1929, integrating theoretical insights and observational discoveries.

Findings

Historical overview of cosmological theories from Einstein to Hubble.

Description of the discovery of universal expansion in 1929.

Context for the subsequent development of accelerated universe models.

Abstract

We are experiencing a period of extreme intellectual effervescence in the area of cosmology. A huge volume of observational data in unprecedented quantity and quality and a more consistent theoretical framework propelled cosmology to an era of precision, turning the discipline into a cutting-edge area of contemporary science. Observations with type Ia Supernovae (SNe Ia), showed that the expanding Universe is accelerating, an unexplained fact in the traditional decelerated model. Identifying the cause of this acceleration is the most fundamental problem in the area. As in the scientific renaissance, the solution will guide the course of the discipline in the near future and the possible answers (whether dark energy, some extension of general relativity or a still unknown mechanism) should also leverage the development of physics. In this context, without giving up a pedagogical approach, we present an overview of both the main theoretical results and the most significant observational discoveries of cosmology in the last 100 years. The saga of cosmology will be presented in a trilogy. In this article (Part I), based on the articles by Einstein, de Sitter, Friedmann, Lema\^itre and Hubble, we will describe the period between the origins of cosmology and the discovery of Universal expansion (1929). In Part II, we will see the period from 1930 to 1997, closing with the old standard decelerated model. The Part III will be entirely devoted to the accelerated model of the universe, the cosmic paradigm of the XXI century.