A Short History of the Missing Mass and Dark Energy Paradigms

TL;DR

This paper reviews the historical development of cosmological models, focusing on the discovery and understanding of dark matter and dark energy, which now constitute the majority of the Universe's mass-energy content.

Contribution

It provides a comprehensive historical overview of the evolution of the missing mass and dark energy paradigms over the twentieth century.

Findings

Stars account for about 1% of the Universe's mass

Dark matter makes up approximately 30%

Dark energy constitutes around 66% of the Universe's total mass-energy

Abstract

In 1900 it was believed that almost 100% of the mass of the Universe resided in stars. Now, in the year 2000, such stars (and cold gas) are known to account for only ~1% its mass. The remaining mass of the Universe is thought to reside in hot baryons (~3%), cold dark matter (~30%) and dark energy (~66%). The present paper traces the evolution of our thinking about the density of the Universe during the Twentieth Century, with special emphasis on the of the discovery of cold dark matter.