Earth’s inner core has long challenged researchers because seismic waves do not move through it uniformly. Compressional waves generated by earthquakes travel roughly 3 to 4 percent faster along Earth’s rotation axis than they do across the equator. This directional difference, called seismic anisotropy, also varies with depth. Near the outer boundary of the inner core, anisotropy is relatively weak, typically around 2 percent or less. Deeper toward the center, the effect becomes much stronger, rising to about 4 to 6 percent. Understanding why this directional behavior intensifies with depth remains a major problem in Earth science. Two leading explanations have been proposed. One argues that the shapes of grains or inclusions inside the core become aligned, a mechanism known as shape preferred orientation. The other points to lattice preferred orientation, in which the crystal structures themselves line up as the material undergoes deformation. An overview of the experimental setup at DESY in Hamburg reveals the vacuum chamber housing the high-temperature diamond anvil cell: The cell’s orange colour comes from the light it emits at …