Maddury Somayazulu, an experimental physicist who goes by Zulu, could only hope that being close would be good enough. In an equipment-crammed room at Argonne National Laboratory in Illinois, he was huddled with postdoctoral researcher Zachary Geballe over a plum-sized cylindrical gadget called a diamond anvil cell. Inside was a dust speck’s worth of the rare-earth metal lanthanum and a bit of hydrogen gas, which theorists had predicted could morph into a novel compound under the enormous pressure of 2.1 million atmospheres. That is more than half the pressure at the center of Earth and, more relevant on that June 2017 day, near the limits of the cell’s capacity to compress its contents between its two pebble-sized diamonds—among the hardest materials in nature. As the scientists turned the cell’s screws up to 1.7 million atmospheres, they felt them tighten. The diamonds, already warped by the pressure, could break. “Okay, that’s it. We can’t go any higher,” Somayazulu said. “Let’s try to synthesize here and see what happens.”