The question of the coldest thing ever recorded has two distinct answers: one found in space and the other achieved in a specialized laboratory on Earth. Temperature is fundamentally a measure of the average motion, or kinetic energy, of a substance’s atoms and molecules. The search for the ultimate cold is a quest to completely halt this microscopic movement.
Absolute Zero: The Theoretical Limit
Absolute zero is the theoretical limit of cold and the foundational point for the Kelvin temperature scale. Defined as 0 Kelvin (K), it is equivalent to approximately -273.15 degrees Celsius (°C) or -459.67 degrees Fahrenheit (°F). At absolute zero, atoms possess the lowest possible amount of energy, and all classical thermal motion has ceased.
It is a core principle of thermodynamics that reaching this precise zero-point is physically impossible, regardless of the cooling method used. The nearer a system gets to 0 K, the more challenging it becomes to extract the remaining thermal energy. This is due to the third law of thermodynamics, which implies that a system must always retain some minimal, residual kinetic energy, known as zero-point energy.
The Kelvin scale is useful in science because it begins at absolute zero, meaning there are no negative temperatures on this scale. Unlike the Celsius or Fahrenheit scales, the Kelvin scale is anchored to the fundamental physics of energy and motion. Scientists measure temperatures in the ultra-cold regime using the Kelvin scale, often expressing them in terms of nanokelvin (nK) or picokelvin (pK), which represent billionths and trillionths of a degree, respectively.
The Coldest Thing Ever Made: The Picokelvin Record
The record for the coldest temperature ever measured was not set in space but in a laboratory, achieving an astonishing 38 picokelvin above absolute zero. This temperature, just 38 trillionths of a degree above 0 K, was reached by a team of German researchers using a cloud of rubidium atoms. The experiment required extreme isolation from all sources of heat and motion, necessitating a highly specialized cooling process.
The atoms were first cooled to about two billionths of a degree above absolute zero using laser cooling and evaporative cooling techniques. This process transitioned the rubidium gas into a unique state of matter called a Bose-Einstein condensate (BEC). To achieve the final, record-breaking temperature, the researchers needed to eliminate the effect of gravity, which otherwise causes the atoms to move and heat up.
The final stage of cooling involved placing the apparatus inside the European Space Agency’s Bremen drop tower, which simulates a microgravity environment. For a few seconds of free-fall, the researchers rapidly switched a magnetic field on and off, allowing the BEC to expand and cool without the interference of gravity. This adiabatic decompression technique brought the atoms’ collective motion to a near-complete standstill, resulting in the 38 picokelvin record.
Quantum Effects at Extreme Cold
When matter is cooled to temperatures in the picokelvin range, it enters the exotic state of a Bose-Einstein condensate (BEC), where the rules of classical physics begin to break down. In this state, a cloud of individual atoms begins to behave as a single entity, or one “super-atom”. This collective, wave-like behavior is a quantum mechanical phenomenon apparent only when the thermal energy is nearly eliminated.
The ultracold temperatures are a necessary condition for studying fundamental physics, such as the nature of gravity and quantum mechanics. For instance, a BEC can be used to create highly sensitive sensors for measuring tiny forces, like gravity, with unprecedented precision. The ability to slow down the atoms’ motion allows scientists to observe these quantum properties for a longer duration.
The atoms in a BEC are all in the same quantum state, which means their wave functions overlap perfectly, making the behavior of the entire group predictable. This macroscopic quantum state is the goal of ultra-low temperature physics research. By pushing the limits of cold, researchers gain insights into the universe’s most fundamental laws, which are often obscured by thermal noise at warmer temperatures.
The Coldest Place in the Cosmos
Moving outside the laboratory, the coldest known natural location in the universe is the Boomerang Nebula, situated about 5,000 light-years from Earth in the constellation Centaurus. This young planetary nebula has been measured to have a temperature of approximately 1 Kelvin, which is about -272 °C. The Boomerang Nebula holds this record because it is expanding outward at an extremely high speed, causing its gas to cool rapidly through adiabatic expansion.
This temperature is even colder than the background radiation, known as the Cosmic Microwave Background (CMB). The CMB is the remnant heat from the Big Bang, uniformly bathing the universe in a thermal glow of about 2.7 Kelvin. Any object in deep space not near a star or other heat source will eventually cool down to this 2.7 K temperature, which represents the natural thermal floor of the cosmos.
The Boomerang Nebula is the only known object that has achieved a temperature below the CMB, essentially acting as a cosmic refrigerator. Its rapid expansion acts as a natural cooling mechanism that outpaces the warmth being absorbed from the surrounding CMB radiation. For comparison, the average temperature of the Moon’s shadowed surface only plunges to about -233 °C (40 K), demonstrating the Boomerang Nebula’s exceptional coldness.
The Coldest Place on Earth
The coldest temperature recorded naturally on Earth was measured at the Vostok Station in Antarctica. On July 21, 1983, Soviet researchers recorded -89.2 °C (-128.6 °F) at the remote outpost, which remains the official record for a direct, ground-level measurement. This extreme cold results from the station’s high elevation on the Antarctic Plateau, extended winter darkness, and the absence of any nearby ocean to moderate the temperature.
Even lower temperatures have been observed by satellite instruments across the East Antarctic Plateau. These remote sensing measurements, recorded between Dome Argus and Dome Fuji, showed surface temperatures dropping to as low as -98 °C (-144 °F). However, these are not considered official world records because they are satellite-derived surface temperatures, not direct air temperature measurements taken at a standardized height.
These satellite readings indicate the temperature of the snow surface itself, which can be colder than the air just above it. To achieve such a low temperature, the air must be extremely dry and still, allowing the ground to effectively radiate its heat directly into space. The conditions on the high-altitude, inland ice sheet of Antarctica create the most frigid natural climate on Earth.