Molecules are hot. They zip, spin and vibrate with frenetic motion. They jiggle and twist on the inside and bounce on the outside, imparting structure and physical properties to nearly everything that exists. But by achieving temperatures colder than any in the natural world, physicists can almost stop these speed demons cold.
![In an ultracold cloud held in place by lasers in a lab at the University of Freiburg, lithium and cesium atoms form tightly bound molecules.](https://i0.wp.com/www.sciencenews.org/wp-content/uploads/2008/12/9317.jpg?resize=300%2C261&ssl=1)
![](https://i0.wp.com/www.sciencenews.org/wp-content/uploads/2008/12/9319.jpg?resize=300%2C185&ssl=1)
Like surgeons who slow a beating heart by packing ice around a patient’s chest, physicists have recently coaxed molecules into ultracold states in which motion is nearly gone. Researchers are left with intriguing, exquisitely controllable new specimens to poke and prod, enabling experiments that would be impossible with everyday hot molecules that rotate and vibrate at their usual frenzied pace.