The atomic nucleus is not a solid ball but a dense swarm of tiny particles called quarks, glued together by a special glue (the strong force). In light nuclei, such as calcium, this swarm is simply arranged: the numbers of the two quark types, up and down, are almost equal, like the white and black keys in an octave. Physicists explained this with a model where quarks behave like passengers on a crowded bus: each takes a seat, and there are no empty seats.

But in heavy nuclei, the balance is upset. More and more passengers pile onto the bus, and some are forced to stand, pressing together more tightly. A similar picture emerges from the modified bag model: quarks are confined in a flexible shell, and as the nucleus gets heavier, the shell stretches and the pressure inside rises. At some point, the system becomes unstable, like a balloon about to burst.

The most unexpected move is to link this picture to a black hole. It turns out that the mathematics describing the quark bag is mirror-like to the mathematics of a black hole in five-dimensional curved space. The dynamics inside such a black hole map exactly onto the behavior of quarks in our world. This strange connection has made it possible not only to understand why the periodic table ends at lead, but also to predict how the lightest particle made of pure glue, the glueball, decays.