# Ultrarelativistic heavy ion collisions: the first billion seconds

## TL;DR

This paper reviews the history and scientific goals of ultrarelativistic heavy ion collisions, emphasizing the discovery of quark-gluon plasma and connections to cosmology, neutron stars, and matter under extreme conditions.

## Contribution

It provides a historical overview and discusses recent progress in understanding the QCD phase diagram and related phenomena in heavy ion physics.

## Key findings

- Discovery of quark-gluon plasma properties
- Connections to cosmology and neutron star physics
- Insights into the QCD phase diagram

## Abstract

I first review the early history of the ultrarelativistic heavy ion program, starting with the 1974 Bear Mountain Workshop, and the 1983 Aurora meeting of the U.S. Nuclear Science Committee, just one billion seconds ago, which laid out the initial science goals of an ultrarelativistic collider. The primary goal, to discover the properties of nuclear matter at the highest energy densities, included finding new states of matter -- the quark-gluon plasma primarily -- and to use collisions to open a new window on related problems of matter in cosmology, neutron stars, supernovae, and elsewhere. To bring out how the study of heavy ions and hot, dense matter in QCD has been fulfilling these goals. I concentrate on a few topics, the phase diagram of matter in QCD, and connections of heavy ion physics to cold atoms, cosmology, and neutron stars.