WELL, THIS IS THE 21ST CENTURY, YOU KNOW: Scientists Create Metallic Hydrogen. “Metallic hydrogen could potentially enable rockets to get into orbit in a single stage, even allowing humans to explore the outer planets. Metallic hydrogen is predicted to be ‘metastable’ — meaning if you make it at a very high pressure then release it, it’ll stay at that pressure. A diamond, for example, is a metastable form of graphite. If you take graphite, pressurize it, then heat it, it becomes a diamond; if you take the pressure off, it’s still a diamond. But if you heat it again, it will revert back to graphite.”