We have made places colder than space
The cosmic microwave background is 2.7 kelvin. Laboratories have cooled matter to nanokelvin, far below the temperature of deep space.
The universe is full of leftover radiation at 2.725 kelvin. A rock in deep shadow exchanges heat with that bath and cannot sit below it for long without work being done. Laser cooling and evaporative cooling are that work. They have produced Bose-Einstein condensates at nanokelvin, a billionth of a degree above absolute zero, millions of times colder than the background radiation.
The Nobel prizes of 1997 and 2001 mark the two steps: cooling and trapping atoms with light, then crossing into quantum degeneracy. The record has since been pushed toward picokelvin in specialised systems. Nanokelvin is already enough for the sentence.
Caveats
- 'Space' is not uniformly cold. A surface in sunlight, even far from the Sun, can be hot. The comparison is with the microwave background, the temperature of the shade.
- The chilled sample is tiny, a cloud of atoms. The achievement is temperature, not a refrigerator you could stand in.
Sources
- 1Anderson M. H. et al.. Observation of Bose-Einstein condensation in a dilute atomic vapor. Science 269, 1995.