Temperature measures the average kinetic energy of particles within a substance. These particles are in constant motion, and their speed correlates with the substance’s temperature. The “coldest” possible state refers to the theoretical absence or near-absence of this particle motion and energy.
Understanding Absolute Zero
Absolute zero, defined as 0 Kelvin (K), is the theoretical lowest possible temperature. This corresponds to approximately -273.15 degrees Celsius (°C) or -459.67 degrees Fahrenheit (°F). At this point, particles possess minimum possible energy, with their motion approaching a standstill. However, quantum mechanics indicates particles still exhibit minimal, unavoidable motion due to the Heisenberg Uncertainty Principle, known as zero-point energy.
Absolute zero is a theoretical limit that can be approached but never truly reached. The Third Law of Thermodynamics states no physical process can cool a system to absolute zero in a finite number of steps. As a system nears this limit, further temperature reductions become increasingly difficult. This concept is important in thermodynamics and physics, providing a baseline for understanding energy and matter.
Measuring the Coldest Temperatures
Measuring extreme low temperatures requires specialized techniques and scales. While Celsius and Fahrenheit are common, the Kelvin scale is the absolute temperature scale used in scientific contexts. The Kelvin scale sets its zero point at absolute zero, directly reflecting a system’s energy content, making it useful for scientific calculations.
Measuring such low temperatures necessitates specific instruments. Scientists often use resistance thermometers, which measure temperature based on changes in electrical resistance, or optical methods analyzing atom cloud expansion. For temperatures nearing absolute zero, advanced techniques like melting curve thermometers (0.001K to 0.5K) or nuclear-resonance thermometers (as low as 0.0000001 K) are employed.
Where Extreme Cold Occurs and How We Create It
Extreme cold exists naturally in the universe and can be created in laboratories. The coldest known natural place is the Boomerang Nebula, about 5,000 light-years from Earth. Its interior temperature is approximately -272.15°C (-457.87°F), just one degree Celsius above absolute zero. This nebula is even colder than the cosmic microwave background radiation, which is around 2.7 Kelvin.
On Earth, the coldest directly recorded temperature was -89.2°C (-128.6°F) at the Soviet Vostok Station in Antarctica in July 1983. Satellite observations indicate even colder surface temperatures on the East Antarctic Plateau, reaching an estimated -98°C (-144°F).
Scientists employ advanced techniques to achieve ultra-low temperatures in laboratories. Cryogenics uses substances like liquid helium to cool materials to a few degrees above absolute zero. Laser cooling slows atoms with precisely tuned laser light, reaching microkelvin temperatures. Further cooling can be achieved through magnetic and evaporative cooling.
The current lab record is 38 picokelvin, or 38 trillionths of a degree above absolute zero, achieved by cooling rubidium atoms. At these temperatures, matter exhibits unusual quantum phenomena, such as Bose-Einstein condensates, where atoms merge into a single quantum state, and superfluidity, where liquids flow without friction.
The Practical Uses of Extreme Cold
Achieving ultra-low temperatures has unlocked numerous practical applications. Superconductivity is a notable example, where certain materials, when cooled, conduct electricity with zero resistance. This phenomenon is utilized in medical imaging devices like MRI machines, powerful particle accelerators, and holds promise for future energy transmission with minimal loss.
Quantum computing relies on the stability of qubits, the fundamental units of quantum information, which are highly sensitive to thermal noise. Extreme cold, typically below 0.01 Kelvin, stabilizes these qubits and maintains their delicate quantum properties, allowing for complex calculations. Researchers have successfully cooled qubits to 22 millikelvin using quantum refrigerators, enhancing performance.
Cryopreservation uses ultra-low temperatures to preserve biological samples, including cells, tissues, blood, and embryos. This technique is instrumental in medical research, fertility treatments, and long-term storage, preventing degradation and maintaining viability. Extreme cold also plays a role in space exploration by cooling sensitive detectors and instruments on spacecraft, improving performance and reducing noise. These frigid conditions facilitate fundamental research, allowing physicists to study quantum phenomena and unique matter properties.