Coldest Temperature Ever Recorded | What Is Absolute Zero? – Popular Mechanics

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Researchers from four universities in Germany have created the coldest temperature ever recorded in a lab38 trillionths of a degree warmer than absolute zero to be exact, according to their new work, recently published in the journal Physical Review Letters.

The bone-chilling temperature only persisted for a few seconds at the University of Bremen's Center for Applied Space Technology and Microgravity, but the breakthrough could have longstanding ramifications for our understanding of quantum mechanics.

That's because the closer we get to absolute zerothe lowest possible temperature that we could ever theoretically reach, as outlined by the laws of thermodynamicsthe more peculiarly particles, and therefore substances, act. Liquid helium, for instance, becomes a "superfluid" at significantly low temperatures, meaning that it flows without any resistance from friction. Nitrogen freezes at -210 degrees Celsius. At cool enough temperatures, some particles even take on wave-like characteristics.

Absolute zero is equal to 273.15 degrees Celsius, or -459.67 degrees Fahrenheit, but most commonly, it's measured as 0 Kelvins. This is the point at which "the fundamental particles of nature have minimal vibrational motion," according to ScienceDaily. However, it's impossible for scientists to create absolute zero conditions in the lab.

In this case, the researchers were studying wave properties of atoms when they came up with a process that could lower a system's temperature by slowing particles to virtually a total standstill. For several seconds, the particles held completely still, and the temperature lowered to an astonishing 38 picokelvins, or 38 trillionths of a degree above absolute zero. This temperature is so low that it's not even detectable with a regular thermometer of any kind. Instead, the temperature is based on the lack of kinetic movement of the particles.

The mechanism at play here is "a time-domain matter-wave lens system," according to the team's research paper. A matter wave is just what it sounds like: matter that is behaving like a wave. This is part of quantum physics, where everything we previously thought we knew gets a little wobbly upon close examination. In this case, scientists used an magnetic lens to shape a quantum gas, and used that to make a matter wave focus and behave in a particular way. A regular gas is made of a loose arrangement of discrete particles, but a quantum gas is no such predictable material. In this case, the quantum gas is a perplexing state of matter called a Bose-Einstein condensate.

The lens is "tuned" using careful excitation. Think of the lenses on a pair of glasses, where the bend is designed to focus closer or further away depending on the patient's eyes. For this experiment, the scientists tuned the focus to literally infinity. Within the subset of quantum physics known as optics, this means the quantum gas confines the passing particles until they pass one at a time and at an astonishingly slow speed.

"By combining an excitation of a Bose-Einstein condensate (BEC) with a magnetic lens, we form a time-domain matter-wave lens system," the researchers write. "The focus is tuned by the strength of the lensing potential. By placing the focus at infinity, we lower the total internal kinetic energy of a BEC to 38pK."

The researchers, from the University of Bremen, Leibniz University Hannover, the Humboldt University of Berlin, and the Johannes Gutenberg University Mainz, say they envision future researchers making the particles go even slower, with a top potential "weightlessness" period of up to 17 seconds.

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Coldest Temperature Ever Recorded | What Is Absolute Zero? - Popular Mechanics