Coldest Temperature Ever: 10 Picokelvin in Space Explained

What is the coldest temperature ever recorded?

The coldest temperature ever reported is an equivalent temperature of 9.7 picokelvin, set aboard China's space station and published in the journal Science on 5 November 2026 ^[1][2]. A picokelvin is one trillionth of a kelvin, so the atoms were less than ten-trillionths of a degree above absolute zero ^[2].

The research paper, titled "Quantum gases below 10 picokelvin in space", reports a Bose-Einstein condensate (BEC) of 2.0 × 10^4, or 20,000, atoms that reached that equivalent temperature with a free expansion time of 7.0 seconds ^[1]. The team used rubidium atoms ^[2][3].

Science's news report says the result lowered the coldest temperature ever achieved by a factor of four ^[2]. Ernst Rasel, a quantum physicist at Leibniz University Hannover whose team recorded the previous record in 2021, told Science: "I congratulate the scientists. I'm very impressed" ^[2].

Many headlines round the figure to 10 picokelvin. Both numbers appear in coverage: the paper reports below 10 pK, and Science's reporter describes the final atomic speeds as equivalent to about 10 pK ^[1][2].

How cold is 10 picokelvin compared with space?

Far colder than anything in nature that astronomers know of. Empty space is filled with the cosmic microwave background, which NASA measures at about 2.725 kelvin ^[5]. Dividing 2.725 K by 9.7 pK shows that the background glow of the Universe is roughly 280 billion times warmer than the atoms on Tiangong.

Absolute zero, 0 kelvin, is minus 273.15 °C or minus 459.67 °F ^[4]. On those scales the new record is indistinguishable from absolute zero, which is why physicists use kelvin and its tiny subdivisions:

• Nanokelvin (nK): one billionth of a kelvin. Early BEC experiments reached about 100 nK ^[2].
• Picokelvin (pK): one trillionth of a kelvin. Space experiments are now in this range ^[1][2].

Reaching exactly zero is thought to be impossible. One version of the third law of thermodynamics says reaching absolute zero would take an infinite number of steps, Saibal Mitra, a physicist interviewed by Live Science, explained ^[4].

How did scientists reach 10 picokelvin?

By trapping rubidium atoms with lasers in microgravity, letting the hottest ones escape, then letting the rest spread out gently ^[2][3]. According to Science's account, the steps were ^[2]:

1. Trap: about 2 million rubidium atoms were held in an inner optical trap 54 micrometres wide, formed where two intense laser beams cross. The lasers ran at 5 watts.
2. Evaporate: the power was eased down to 0.2 milliwatts, letting the more energetic atoms escape. The remaining 20,000 atoms cooled to 3 nK.
3. Expand: the atoms were allowed to spread into a wider trap 124 micrometres across, which reduced how strongly they interacted. In the end they moved at less than 100 micrometres per second.

"We keep the same number of atoms. Only the interaction energy changes," said Xuzong Chen of Peking University, the instrument's chief scientist ^[2]. The Shanghai Institute of Optics and Fine Mechanics adds that evaporative cooling in an optical trap works less well in microgravity, so the team used an extra magnetic gradient to help produce the condensate ^[3].

The instrument is the Cold Atom Physics Rack in the station's Mengtian laboratory module, launched in 2022 ^[2][3]. The institute says its developers shrank a ground system of about 20 cubic metres and 10 tonnes into a flight instrument of about 0.7 cubic metres and half a tonne ^[3].

Is 9.7 picokelvin a real temperature?

It is an equivalent temperature that describes how slowly the atoms move, not a reading on a thermometer ^[3]. The Shanghai institute states that the 9.7 pK figure "characterizes the atoms' extremely slow expansion" and does not mean the equipment or its surroundings reached the same temperature ^[3].

The research paper itself uses the phrase "equivalent temperature" ^[1]. Scientists estimate it from how fast the released cloud of atoms spreads; slower spreading means lower energy ^[2][3]. Science gives the final speeds as less than 100 micrometres per second ^[2]. Phys.org's report on the paper gives an uncertainty range of 7.0 to 12.9 pK around the 9.7 pK value ^[7].

That distinction matters when comparing records. The earlier record of 38 pK, and NASA's 52 pK, are likewise effective temperatures inferred from how fast the cloud expands, so the comparison is between like quantities, although the experiments differ in method ^[2][6][7]. Comparisons with the temperature of a fridge, a planet or deep space are useful for scale, but not precise physics.

Why was the record set in space instead of on Earth?

Gravity pulls ultracold atoms downward, which forces scientists to hold them in stronger traps that keep them warmer ^[2][3]. Science explains that gravity squeezes the atoms against the fields suspending them, driving their temperature up ^[2]. In orbit, the trap can be made much weaker and the atoms observed for longer ^[3].

MIT physicist Wolfgang Ketterle, a 2001 Nobel laureate, put the seven-second observation in perspective: "On Earth, it would fall down by about 250 meters, so it would actually crash to the ground unless you have a vacuum chamber, which is 250 meters high" ^[3].

Earlier attempts to escape gravity included dropping atom chips down towers and flying them on suborbital rockets ^[2]. NASA launched its Cold Atom Laboratory to the International Space Station in 2018 ^[2], and a Bose-Einstein condensate made on the station reached effective temperatures as low as 52 pK, reported in Nature Communications in 2022 ^[6]. The previous record, 38 pK with 2 seconds of free expansion, came from an atom-chip magnetic trap in microgravity ^[1]; Science News describes it as a drop-tower experiment published in 2021 ^[6].

The Chinese instrument differs because it uses optical traps, made of laser light, rather than magnetic ones ^[1][2]. The paper notes that optical traps had not been used to prepare such quantum gases in microgravity before ^[1].

What is a Bose-Einstein condensate?

A Bose-Einstein condensate is a state of matter in which very cold atoms crowd into a single quantum wave and behave collectively ^[2][3]. Science compares it to the photons in a laser beam, and notes that atoms in a BEC can flow without resistance and create interference patterns ^[2].

Satyendra Nath Bose and Albert Einstein predicted condensates in 1924; two teams first made them in 1995, one with rubidium-87 and one with sodium-23, work recognised with the 2001 Nobel Prize in Physics ^[2]. Live Science describes the condensate as behaving akin to a single atom ^[4].

Because the effects are visible on scales far larger than single atoms, BECs let researchers study quantum behaviour directly ^[3]. For a beginner-friendly introduction to related ideas, see Quantum Computing Explained for Beginners: What It Is and What It Is Not. For another space-science story from this week, see Euclid Telescope Data Release: What ESA's New Map Shows.

What could ultracold atoms in space be used for?

Mainly precision measurement and quantum simulation; the researchers and independent experts describe these as directions for future work ^[2][3].

• Testing gravity: long expansion times are ideal for interference experiments that could test whether gravity pulls on all types of atoms equally, as general relativity assumes, Science reports ^[2]. "The 7 seconds is an even more important figure of merit than the 10 picokelvin," said Holger Mueller of UC Berkeley ^[2].
• Atom interferometers: Rasel told the Shanghai institute that their sensitivity increases with the square of the time atoms spend in the instrument, and that such tools could help measure Earth's gravity field and test dark matter models ^[3].
• Quantum simulation: the team plans optical lattices, grids of laser spots that mimic a crystal, to simulate effects related to high-temperature superconductivity ^[2][3].
• Mixed atoms: Hélène Perrin of Sorbonne Paris Nord University noted that optical traps can hold atoms in different internal states at once ^[2].

Weibiao Chen of the Shanghai institute told Science the rack is "open for the international community" ^[2]. None of these applications has been demonstrated with this instrument yet.