Absolute Zero
Today, absolute zero. The University of Houston presents this series about the machines that make our civilization run, and the people whose ingenuity created them.
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The question: “How cold is it possible to get?” has a curious history. The scientific revolution was becoming intense by the end of the seventeenth century. And issues that we now bundle into the science of thermodynamics were arising as new questions. How cold indeed!
Most scientists did feel that there must be a limit. But where? Then, in 1714, Daniel Fahrenheit gave us a reliable thermometer. We now had a temperature scale that went from the boiling of water down to below freezing. And it was clear that temperatures kept right on getting colder below his zero point. We now had an arrow pointing to that bottom temperature.
It was about this same time that elements of what would one day become the ideal gas law were afoot. A French physicist named Amontons had noticed that air had a certain springiness. And that springiness kept decreasing with the temperature. Surely springiness would end somewhere.
Of course we had no idea that air could eventually freeze. And it’d be many years before we had a full ideal gas law. But, when we did have that law, it pointed to a limit at minus 273.15 degrees Celsius. (In today’s Kelvin temperature scale we call that Zero degrees.)
And so reaching Zero degrees Kelvin in the laboratory became a sort of unattainable holy grail. Why? Well, the colder anything gets, the less active – the less disordered – are its molecules. Perfect cold means the least entropy. Almost perfect quiet.
The German scientist, Nernst, came to grips with this problem in the early twentieth century. And he concluded that any process that reduced entropy would leave some disorder behind. So he formulated a Third Law of Thermodynamics. It says – and I quote: “It is impossible for any process, no matter how idealized, to reduce the entropy of a system to its absolute-zero value in a finite number of operations.”
Walther Hermann Nernst (Image Courtesy of Wikimedia Commons)
That meant we’d never see absolute zero – not in the laboratory – not in the universe. (In fact, astronomers have discovered a spot in a distant nebula where the temperature reaches one degree Kelvin. Close, but no cigar.)
Boomerang Nebula at 1o Kelvin (Image courtesy of Wikimedia Commons)
Of course that doesn’t stop us ever-curious humans from seeing just how close we can get. A German team contrived a process, too complex to describe here, in 2018. It got them to a temperature of – get this – thirty-eight trillionths of a degree Kelvin.
As a young boy in Minnesota, I experienced thirty-five below on a winter hike. And I was suitably impressed. But, no longer a boy, I now see that as 236 degrees Kelvin. Suddenly that feels downright toasty.
I’m John Lienhard, at the University of Houston, where we’re interested in the way inventive minds work.
(Theme music)
Sources:
I was lured (mentally) into doing this episode when I found the following source on my bookshelf: Erwin Schrodinger, Statistical Thermodynamics: Cambridge University Press, 1964, Chapter 3 “Discussion of the Nernst Theorem”
Third law of thermodynamics - Wikipedia
Guillaume Amontons - Wikipedia
Lowest artificial temperature | Guinness World Records
This Episode first aired on August 12, 2026.