And, at what pressure does chemistry cease to be important, with all matter being well described using the Thomas-Fermi-Dirac (TFD) theory 18 ? Most science students learn that pressure can be an important parameter, for example in driving chemical reactions involving gases, such as the Haber-Bosch process used to convert H 2 and N 2 gas into ammonia. This process, key for the fertilizer required to feed the world's growing population at the time of its discovery, requires temperatures between 650-720 K and a pressure of 200 atm (0.02 GPa) to trigger the reaction on the iron-based catalyst. Further, students know well that natural diamonds are formed at 4.5-6 GPa, found 150-200 km below the Earth's crust. However, few students know that high-pressure high-temperature techniques, which make use of special equipment such as the Paris-Edinburgh press (max pressure ∼20 GPa) or diamond anvil cells (DACs, whose max pressure approaches 600 GPa in the latest innovationtoroidal DACs ), have been used to synthesize numerous compounds that are metastable at 1 atm. Some examples include a barium germanide, BaGe 3 , phase with a superconducting critical temperature, T c , of 4 K, synthesized at 3-13 GPa and ∼800-1500 K with a Kawai-type multi-anvil press, or a strontium-filled carbon-boron clathrate, SrB 3 C 3 , 22 formed in a DAC at 50 GPa and T >3000 K with a measured T c of 20 K at 40 GPa. Chemical stoichiometries that would be considered as exotic or even impossible at ambient conditions, become, some-1 According to the 3 rd law of thermodynamics, the entropy of a perfect homogeneous solid at 0 K is zero times, stable realities upon compression. P 3 N 5 was the only known crystalline pnictogen nitride at ambient pressure, observed in two polymorphs, an α-23 and a γ-phase, until syntheses in a DAC produced first AsN 27 (at P > 25 GPa and T > 1400 K) and then Sb 3 N 5 (at P = 32 -35 GPa and T = 1600 -2200 K).