A new pyramid-like shape always lands the same side up
In 360 BCE, Plato envisioned the cosmos as an arrangement of five geometric shapes: flat-sided solids called polyhedra. These immediately became important objects of mathematical study. So it might be surprising that, millennia later, mysteries still surround even the simplest shape in Plato’s polyhedral universe: the tetrahedron, which has just four triangular faces. One major open problem, for instance, asks how densely you can pack “regular” tetrahedra, which have identical faces. Another as