Quick Answer
The coldest known place in the universe is the Boomerang Nebula, about 5,000 light-years from Earth, where temperatures drop to roughly 1 kelvin (−272°C) — colder even than the natural background of space itself. Most of space sits at about 2.7 K, the leftover warmth of the Big Bang, but the rapidly expanding gas of the Boomerang Nebula chills itself below that. The very coldest temperatures of all, however, are made by humans in laboratories.
It is natural to assume that deep space is the coldest thing there is. But “cold” has a baseline even in the vacuum, and one remarkable object manages to beat it. This guide explains how cold the universe normally is, why the Boomerang Nebula is colder than its surroundings, the astonishing temperatures achieved in labs, and what the ultimate cold — absolute zero — really means.
How Cold Is the Universe Normally? (the CMB at 2.7 K)
Empty space is not at absolute zero. It is bathed in the cosmic microwave background (CMB) — the faint afterglow of the Big Bang, radiation that has been cooling for nearly 14 billion years as the universe expanded. Today it fills all of space with a temperature of about 2.725 kelvin, which is roughly −270°C.
This means that anything floating in deep space, far from any star, will naturally settle toward that temperature of about 2.7 K, warmed ever so slightly by this universal background glow. For a long time, this seemed to set the floor for how cold any natural place could be — until astronomers found somewhere colder.
The Boomerang Nebula — Colder Than Space Itself
The Boomerang Nebula, located about 5,000 light-years away in the constellation Centaurus, holds the record for the coldest known natural place in the universe. Measurements put its temperature at around 1 kelvin — about −272°C — which is actually below the 2.7 K temperature of the cosmic background radiation. It is, as far as we know, the only known natural object colder than the Big Bang’s afterglow.
How a nebula gets colder than its surroundings
How can anything be colder than the background of space that surrounds it? The answer is the same principle that makes an aerosol can feel cold as it sprays. The Boomerang Nebula is formed by a dying central star flinging out gas at enormous speed — around 150 kilometres per second. As that gas rushes outward, it expands rapidly, and expanding gas cools (a process called adiabatic expansion). The gas is being flung out and expanding so quickly that it chills below the surrounding background faster than it can reabsorb heat from it. Astronomers measured this by watching how the cold gas absorbs the cosmic microwave background passing through it — the nebula casts a “cold shadow” against the warmer background.
The Coldest Place Made by Humans (labs near absolute zero)
As cold as the Boomerang Nebula is, humans have done far better. In physics laboratories, scientists routinely chill matter to temperatures thousands of times colder than anything found in nature, using techniques like laser cooling and magnetic evaporative cooling to slow atoms almost to a standstill.
These experiments reach into the nanokelvin range — billionths of a degree above absolute zero — and some have pushed even lower, into trillionths of a degree. NASA’s Cold Atom Laboratory aboard the International Space Station creates some of the coldest known spots, exploiting weightlessness to chill clouds of atoms into exotic states of matter called Bose–Einstein condensates. So the coldest places in the known universe are not in deep space at all — they are inside human-built apparatus on and above the Earth.
What Absolute Zero Actually Means
All of these temperatures are measured against the same ultimate reference point: absolute zero, which is 0 kelvin, or −273.15°C. Temperature is fundamentally a measure of how much atoms and molecules jiggle and move. The hotter something is, the more its particles move; the colder it is, the less. Absolute zero is the theoretical point at which this thermal motion reaches its absolute minimum.
This is the floor of the temperature scale — you cannot get any colder, because there is no “less than no motion.” It is also why the kelvin scale starts there. What would happen to ordinary matter, like the air around us, if it were brought near this ultimate cold is exactly the scenario we explore in what if the atmosphere liquefied at absolute zero.
Why Nothing Can Reach Exactly 0 K
Here is a deep truth of physics: nothing can ever actually reach absolute zero. This is a consequence of the third law of thermodynamics, which implies that removing the last bit of heat from a system would take an infinite number of steps. No matter how clever the cooling method, you can always get closer but never quite arrive.
There is also a quantum reason. Even at absolute zero, particles would retain a tiny irreducible motion called zero-point energy — a consequence of quantum uncertainty, which forbids a particle from having both a perfectly defined position and zero momentum. So absolute zero is best understood as a limit that matter forever approaches but can never truly touch — the asymptote at the bottom of the temperature scale.
Q&A
The coldest temperatures ever achieved are in laboratories, where scientists have cooled atoms to within a few trillionths of a degree (picokelvin) of absolute zero. These are far colder than any natural place, including the Boomerang Nebula, which sits at about 1 kelvin.
Yes. The natural background of space is about 2.7 kelvin, but the Boomerang Nebula is colder, at roughly 1 kelvin, because its rapidly expanding gas chills below the background. Human laboratories are colder still, reaching billionths and trillionths of a degree above absolute zero.
At absolute zero, the thermal motion of particles would reach its theoretical minimum. Matter can enter exotic quantum states, such as Bose–Einstein condensates, where atoms behave as a single quantum entity. However, true absolute zero cannot actually be reached, and a small quantum zero-point motion always remains.
The coldest natural air temperature reliably recorded on Earth’s surface was about −89°C at Vostok Station in Antarctica, with satellite data suggesting pockets of the Antarctic Plateau may reach near −98°C. That is frigid, but still vastly warmer than space or laboratory temperatures.
The Bigger Question
Understanding extreme cold leads to a fascinating thought experiment: what would happen to the very air we breathe if it were chilled toward absolute zero? At those temperatures, the gases of the atmosphere would condense into liquids and then freeze solid. We follow that scenario step by step in what if the atmosphere liquefied at absolute zero.
For a real, everyday taste of extreme cold, see our companion article on liquid nitrogen, and explore more temperature extremes on the Extreme Physics hub.
Watch the absolute zero scenario to see what the ultimate cold would do to our world.