Scientists Reach Record Temperature of 9.7 Picokelvins in Orbit
Physicists on China's Tiangong space station measured an equivalent temperature of 9.7 picokelvins, about 280 billion times lower than the background temperature of space. The researchers report in the journal Science that it is the lowest equivalent temperature ever measured.
Scientists reach record temperature of 9.7 picokelvins aboard China's Tiangong space station, according to a paper published in the journal Science. That is 0.0000000000097 kelvins, an equivalent temperature about 280 billion times lower than the background temperature of space.
The researchers call it "to our knowledge, the lowest equivalent temperature ever measured."
How cold is cold
Even empty space is not completely cold. Leftover radiation from the birth of the Universe some 13.8 billion years ago keeps the average background temperature around 2.7 kelvins, or -270.45 degrees Celsius (-454.81 Fahrenheit).
Absolute zero, or zero kelvins, is the theoretical lower limit. Unlike the speed of light, it cannot be reached at all. The closer scientists get, the harder it becomes to remove the remaining thermal energy.
Why the experiment went to orbit
The team wanted to make a Bose-Einstein condensate, an exotic state of matter. It forms when certain atoms are cooled to just fractions of a degree above absolute zero. The atoms then act collectively, their individual quantum states merging into one coherent whole.
That lets researchers study quantum behavior on a much larger scale than single atoms allow. Condensates can also support extremely sensitive measurements of the physical world, potentially helping scientists probe fundamental laws of the Universe.
On Earth, gravity makes it increasingly difficult to cool atoms this far. In orbit, the problem is much smaller.
Previous records
NASA created the first Bose-Einstein condensate in orbit aboard the International Space Station in 2018, cooling a cloud of rubidium atoms to 100 nanokelvins. The previous record stood at 38 picokelvins. It was set during a free-fall experiment in Germany's Bremen Drop Tower and described in a 2021 paper.
The method
Physicists Xiaoji Zhou and Xuzong Chen of Peking University and Weibiao Chen of the Chinese Academy of Sciences led the new work. They used the prolonged microgravity on Tiangong to push cooling further.
They started with a cloud of rubidium-87 atoms, an isotope well suited to laser cooling and to making condensates. Lasers cooled the atoms, which were held in an optical trap inside an apparatus called the Cold Atom Physics Rack.
Next came evaporative cooling. The most energetic atoms are allowed to escape, leaving the rest with less energy. It works much like a cup of coffee cooling as its most energetic molecules leave as vapor.
