Labs on Earth have made the coldest stuff in the universe

The coldest matter known in the universe has been made in laboratories on Earth, beginning on 5 June 1995, when Eric Cornell and Carl Wieman at JILA in Boulder, Colorado, created the first Bose–Einstein condensate from rubidium atoms cooled below 170 billionths of a degree above absolute zero.

Before photographing it, the team took the atoms down to about 20 nanokelvin, then the lowest temperature ever achieved and some 300 times colder than any other laboratory had reached. NIST’s account records that condensation first appeared at 10:54 a.m. The result was a ball of about 2,000 atoms, roughly 20 microns across, behaving as a single quantum “superatom”. Gas atoms at room temperature move at around 1,000 miles per hour; the ordinary atoms surrounding the condensate drifted at about 3 feet per hour.

“This state could never have existed naturally anywhere in the universe,” Cornell said.

Nature does not come close. Space is bathed in the Big Bang’s leftover radiation at about 2.7 kelvin, and the coldest known natural object, the Boomerang Nebula, has an outflow that has cooled significantly below that background. A 20-nanokelvin condensate is over 100 million times colder than empty space. Laboratories have kept pushing lower since:

• 1995: JILA reaches 20 nK; Wolfgang Ketterle independently makes a condensate from sodium atoms.
• 2001: Ketterle shares the Nobel Prize in Physics with Cornell and Wieman.
• 2003: Ketterle’s MIT group reaches 500 picokelvin.
• 2021: a German-led team drops a condensate of about 101,000 atoms in free fall and uses magnetic lensing to cut its internal kinetic energy to an effective 38 picokelvin, reported in Physical Review Letters.

That last figure describes how slowly the atoms move relative to each other rather than the temperature of a sample sitting in thermal equilibrium, so it is a different kind of record from the 1995 and 2003 figures.