Precision Cosmology with the Lightest Elements

TL;DR

This paper reviews the importance of Big Bang Nucleosynthesis, especially deuterium abundance, in precision cosmology, highlighting historical developments and future prospects for improving our understanding of the early universe.

Contribution

It provides a comprehensive overview of BBN research evolution and discusses upcoming advancements in primordial element abundance measurements.

Findings

Deuterium abundance measurements are crucial for constraining cosmological models.

Recent developments have significantly improved the precision of BBN predictions.

Future observations are expected to refine our understanding of the early universe.

Abstract

This is a transcript of the joint talk we gave at the Sixth Gruber Cosmology Conference at Yale University on 3 October 2025. We describe the key role played by Big Bang Nucleosynthesis (BBN) in today's `Precision Cosmology', focusing in particular on the precise determination of the primordial abundance of deuterium. We describe the development of the ideas and methods of BBN research from their beginnings more than 75 years ago to the latest developments, and conclude with a forward look to likely advances expected towards the end of the current decade.