Quantum quirk: Scientists pack atoms together to prevent collisions in atomic clock

Quantum quirk: Scientists pack atoms together to prevent collisions in atomic clock: "How exactly does high interaction energy—the degree to which an atom's behavior is modified by the presence of others—prevent collisions? The results make full sense in the quantum world. Strontium atoms are a class of particles known as fermions. If they are in identical energy states, they cannot occupy the same place at the same time—that is, they cannot collide. Normally the laser beam used to operate the clock interacts with the atoms unevenly, leaving the atoms dissimilar enough to collide. But the interaction energy of atoms packed in optical tubes is now higher than any energy shifts that might be caused by the laser, preventing the atoms from differentiating enough to collide."