In the nineteenth century it was discovered that matter could not get colder than –273.15 degrees in the Celsius scale. A new temperature scale named Kelvin – after physicist William Thomson, Lord Kelvin – renumbered Celsius to assign zero to that newfound lower bound. Zero degrees Kelvin corresponds to the absolute zero of temperature, the absolute cold.

At the absolute zero all motion ceases to exist. The random movement of the microscopic constituents of matter ceases, and every degree of freedom remains frozen and under control. This is certainly not a pleasant place to be, but those are the idyllic conditions for errorless machine performance, in which computers, precision instruments, compasses, and diagnosis tools will work unaffected by the detrimental effects of thermal noise.

As appealing as it seems, the absolute zero is unreachable. Even in deep space, the background radiation filling the whole Universe since the Big Bang “keeps the vibe” at 3 K. If you were lucky enough to get to some interstellar objects made of expanding gases, like the Boomerang nebula, you could get cooler than that and drop to 1 K. Indeed, cooling by expansion of gases is the principle behind freezers and air conditioning, and it also explains why spray deodorants are so cold. The principle was discovered (again) by Lord Kelvin and had a central role in the development of thermodynamics, the physics of heat and cold. Learning to direct heat pushed steam trains forward while schemes to procure cold revolutionized the industry and commerce of food and products. At a more fundamental level, it propelled low-temperature labs worldwide into a hectic race to get closer and closer to the unreachable absolute zero. This race holds the key to understanding why we are now reaching temperatures of only millionths of billionths of a degree (and dropping).

In 1908, the physicist Heike Kamerlingh Onnes got himself a prominent place in the competition, achieving a record temperature of 2.4 K with the liquefaction of helium. However, Onnes was not interested in the record itself, rather his motivation was confirming the existing theories about the behavior of metals at very low temperatures. He did not, however, find what he expected.