The coldest stuff in the universe was made on Earth

Cool a gas low enough and its atoms stop behaving like a crowd of individuals. On June 5, 1995, Eric Cornell and Carl Wieman at JILA (a NIST–University of Colorado lab) chilled rubidium atoms to about 20 billionths of a degree above absolute zero — roughly 170 nanokelvin.

Getting there took two stages. First, laser cooling: beams tuned just below the atoms’ resonance strike them head-on, each photon nudging them slower until a swarm of fast-moving atoms is slowed to a near crawl. Then evaporative cooling finishes the job — the atoms are held in a magnetic trap whose walls are gradually lowered so the hottest, most energetic atoms escape, carrying heat away and leaving the rest colder, exactly as a cup of coffee cools as steam departs.

At that temperature the atoms collapsed into a single quantum entity, a Bose–Einstein condensate, behaving as one superatom. Satyendra Nath Bose and Albert Einstein had predicted it back in 1924–25, a roughly 70-year wait for the experiment to catch up to the theory.

This state could never have existed naturally anywhere in the universe.

Months later, Wolfgang Ketterle independently produced a condensate in sodium; he shared the 2001 Nobel Prize in Physics with Cornell and Wieman. Nothing in nature gets that cold — even deep space hovers around 2.7 kelvin.

The payoff was a new toolkit. Because every atom occupies one quantum state, condensates gave rise to atom lasers, to “slow light” experiments that brake a beam to bicycle speed, and to ultra-precise sensors and atomic clocks.