Metallization of hydrogen and the essential differences between dynamic and static compression

In 1935 Wigner and Huntington (WH) predicted that at density D$_{\mathrm{Thry}}=$0.62 mole H/cm$^{3}$, ``very low temperatures,'' and a pressure greater than 25 GPa, \textit{bcc} H$_{2}$ undergoes an isostructural phase transition directly to H with an associated insulator-metal transition (IMT). In 1996 metallic fluid H was made under dynamic compression in a cross over from H$_{2}$ to H that completes at D$_{\mathrm{exp}}=$0.64 mole H/cm$^{3}$, 140 GPa and T $\sim$ 2600 K. The Free-electron Fermi temperature T$_{\mathrm{F}}=$220,000 K and T/T$_{\mathrm{F}}=$0.012\textless \textless 1, as for ordinary metals at 300 K. To date solid metallic hydrogen has yet to be made at static pressures up to $\sim$360 GPa at T $\sim$ 300 K. This difference between electrical conductivity of H$_{2}$ compressed dynamically and statistically begs the question of why fluid H at 140 GPa and $\sim$3000 K becomes metallic at 0.64 mol H/cm$^{3}$, the density predicted by WH for their IMT at low T; whereas metallization of solid H$_{2}$ or H near 300 K is yet to be achieved experimentally at pressures up to $\sim$360 GPa? The answer is systematic differences induced by the rate of application of pressure in the two methods. Slow compression at $\sim$300 K strengthens solid H$_{2}$ by inducing intermolecular bonds, which impede dissociation, metallization and perhaps even thermal equilibrium. Fast dynamic compression of liquid H$_{2}$ up to $\sim$3000 K precludes formation of intermolecular H-H bonds, which permits fluid H$_{2}$ to weaken to dissociation and thus metallization at 140 GPa. Dynamic- and static-compression effects on materials will be compared in the context of how they effect metallization of hydrogen.