In order to perform accurate simulations of diverse phenomena ranging from the Earth’s magnetic dynamo to the moon-forming impact to the implosion of an inertial confinement fusion capsule, it is essential to have a detailed understanding of the properties of materials under extreme conditions. This knowledge can be built primarily through two different approaches. First, one can generate these conditions in the laboratory and directly measure a material’s properties. Second, one can perform detailed calculations of a material from first principles, as in ab initio calculations. Each technique comes with its own difficulties and the scientists and engineers who pursue this knowledge are routinely forced to extend standard methods into regimes well past where they were developed.
In this talk, I will give an account of the study of hydrogen under extremes of temperature and pressure. The properties of this seemingly simple element have proven exceedingly difficult to pin down, with surprises and missteps for both experimental and theoretical approaches. I will discuss how observations and realizations from both disciplines contributed to the rich, nuanced and ultimately still-evolving understanding we have achieved today.
