How do scientists cool objects to absolute zero?

Category: Physics
Published: May 31, 2013

By: Christopher S. Baird, author of The Top 50 Science Questions with Surprising Answers and physics professor at West Texas A&M University

Nothing can be cooled to a temperature of exactly absolute zero. The temperature of an object is a measure of the average random motion energy (kinetic energy) of its atoms. Absolute zero is the temperature at which all of an object's atoms have been brought to a dead stop relative to each other. This temperature is denoted by the number zero on absolute temperature scales such as Kelvin. Absolute zero is more of a fundamental limit than a reachable temperature. Absolute zero can never be perfectly reached because of quantum fluctuations. Perfectly stopping every atom at a distinct point would require fixing the exact location and momentum of the atom, which is not physically possible according to the Heisenberg Uncertainty Principle. Every quantum system has a non-zero ground state energy which is the lowest possible state. This is nature's way of enforcing the Heisenberg Uncertainty Principle. Additionally, thermodynamics states that perfectly cooling an object to absolute zero would require an infinite number of steps. Despite the inaccessibility of a temperature at exactly absolute zero, scientists have been able to get very close. The Low Temperature Laboratory at Aalto University cooled a piece of rhodium metal to 0.0000000001 K using a nuclear demagnetization refrigerator. A nuclear demagnetization refrigerator cools a material by aligning the spin of nuclei using a strong magnetic field.

A temperature of exactly absolute zero is fundamentally impossible to reach. However, researchers have been able to reach very close to absolute zero. Public domain image, source: NOAA.

Topics: absolute zero, cold, cooling, low temperature, nuclear demagnetization, temperature