The Quest for the Ultimate Cold
Imagine the cold inside a freezer at 0°F (-18°C). It’s chilly, but with warm clothes, you can handle it. Now consider the freezing -76°F (-60°C) of the Antarctic winter, harsh enough to damage human skin. Then there’s the unimaginable cold of outer space, which measures -454°F (-270°C).
However, an unexpected fact is that the coldest spots in the universe are not in space. They are, in fact, in many university physics departments. Over the past decades, scientists have been devising methods to get ever closer to the chilliest conceivable temperature: absolute zero.
The quest for absolute zero began in the early 1700s. Guillaume Amontons, a French physicist, proposed that since temperature gauges the heat in a system, there must be a minimum temperature. He estimated it to be -454°F (-270°C), a guess impressively close to the real figure.
Fast forward to 1848, when Scottish-Irish physicist William Thomson, popularly known as Lord Kelvin, built upon Amontons’ idea. He introduced the “absolute” temperature scale suitable for all substances. On this Kelvin (K) scale, he designated absolute zero as 0, eliminating negative values. From his experiments, Kelvin deduced that this temperature would equal -459.4°F (-273°C).
William Thomson (Lord Kelvin), 1906
Absolute zero or 0 Kelvin corresponds to -459.67°F, or -273.15°C. It’s where a system reaches its minimum energy. But does motion cease at absolute zero? No, atoms still display minute movements due to quantum physics effects, and internal atomic activities like electron, proton, and neutron movements persist, regardless of the cold.
However, there’s a caveat: achieving absolute zero is impossible. The work required to extract heat from a substance grows exponentially the colder you aim to go. Hitting 0 Kelvin would demand infinite work.
Common freezers use power to reduce temperatures, with the most advanced models reaching -112°F (-80°C). But a more straightforward method to attain far lower temperatures is to pressurize helium gas, and then release it through a nozzle. This action produces liquid helium, chilling to about -452°F (-269°C), only 7°F (4°C) above absolute zero. Dip an item in this substance, and its temperature drops significantly.
In the late 1980s, physicists Claude Cohen-Tannoudji, Steven Chu, and William Phillips found a novel way to edge even closer to absolute zero. They targeted gases like caesium or rubidium in a vacuum chamber with laser pulses, counteracting the atoms’ movement direction. Repeating this process, they dramatically reduced the atoms’ speed. This deceleration, given that heat is tied to atomic movement, resulted in a record low temperature of 40 microkelvin, just fractions above absolute zero. This groundbreaking cooling technique earned them the 1997 Nobel Prize in Physics.
Then, in the early 1990s, physicists Eric Cornell, Carl Wieman, and Wolfgang Ketterle went further. Their evaporative cooling method involved using lasers to decelerate atoms and remove the warmer ones. This left only the coldest atoms, reaching temperatures in the nanokelvin range. This achievement, even colder than the 1980s record, brought them the Nobel Prize in 2001.
These milestones unlocked the gateway to the enigmatic quantum realm, where particles exhibit bizarre behaviors like existing simultaneously in multiple locations or showcasing entanglement over vast distances. Observing such quantum phenomena requires minimal external disturbances. With nearly all heat eradicated and atoms at a standstill, exploration within the quantum domain became viable.
While reaching a billionth of a degree above absolute zero is impressive, there’s ongoing research into a revolutionary device: the quantum fridge. By harnessing quantum mechanics, this machine aims to explore an even colder and more mysterious realm.
Absolute zero, equivalent to -459.67°F or -273.15°C, represents the lowest possible temperature where atoms nearly cease movement. While space is cold at -454°F (-270°C), the closest approximations to absolute zero have been achieved in university labs. Due to energy constraints and quantum mechanics, reaching this temperature is impossible. In the late 1980s and 1990s, physicists used innovative laser techniques to cool atoms to near-standstill, earning two Nobel Prizes. This exploration has unveiled the mysterious quantum realm, where particles exhibit strange behaviors. Recent research is now focused on the “quantum fridge,” aiming to push the boundaries of cold even further.
Words of wisdom
“Nothing happens until something moves.” —Albert Einstein
“Not only is the universe stranger than we think, it is stranger than we can think.” —Werner Heisenberg
“Science makes people reach selflessly for truth and objectivity; it teaches people to accept reality, with wonder and admiration, not to mention the deep awe and joy that the natural order of things brings to the true scientist.” —Lise Meitner
“Before I came here, I was confused about this subject. Having listened to your lecture, I am still confused—but on a higher level.” —Enrico Fermi