"Necklaces" of ultracold atoms have provided new evidence to support a nearly 100-year-old quantum theory.In 1931, physicists were trying to use quantum mechanics to explain why some materials are magnetic. Then, a young physicist named Hans Bethe looked at a single row of electrons. Each electron's spin can point up or down. Bethe worked out the math for how such a row behaves and found that if a few spins in the row flip, they can stick together and travel down the row as a single unit.Decades later, physicists found that Bethe's method also works for larger particles moving along a line, such as atoms. If those particles attract each other, the math predicts they will bind into clusters c...