But it has turned out to be remarkably difficult to achieve experimentally and to predict theoretically. Even though hydrogen is the simplest element to understand in its atomic and molecular states, it's condensed states are perhaps the most difficult to understand of all the elements because of the quantum nature of the protons. There is general agreement, based upon theoretical simulations and experiments using shock waves, that hydrogen forms a metallic fluid at high temperatures. But experiments using diamond anvil cells at room temperature have reached pressures ten times the original prediction by Wigner and Huntington, still with no firm evidence of metallization.
All results point to a remarkable ability of hydrogen to avoid becoming a metal.
Theoretical studies are attempting to provide guidance toward unraveling the puzzles. Work done with D. M. Ceperley, V. Natoli, I. Souza, and M. Staedele. Recent reviews include R. J. Hemley and N. Ashcroft, Physics Today, vol. See, for example, V. D. Natoli, et al., Phys.