It's Finally Settled: Absolute Zero Is Impossible

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Just how cold can it get? The answer may be more important than you think: scientists study absolute zero to figure out all the wacky stuff that happens to molecules when the chilly temperatures slow them way down. But up until recently, absolute zero has had a shadow of controversy surrounding it, one that two researchers decided to take head-on. Grab your scarves and coat for this one.


What All the Fuss is About

Absolute zero is the lowest temperature that is theoretically possible—0 Kelvin, or about -273.15 degrees Celsius. Entropy, on the other hand, is the measure of disorder in a system. In 1906, as described by New Scientist, the German chemist Walther Nernst put forward the principle that, as a system's temperature approaches absolute zero, the system's entropy goes to zero. In 1912, he added the unattainability principle, stating that absolute zero is actually impossible to reach. Taken together, the principles form the third law of thermodynamics. However, the third law of thermodynamics has not been considered a law by some—it has remained controversial for decades. But a new study from researchers at the University College London may just settle the matter once and for all.

The problem is this: at 0 Kelvin, a system has minimal motion—but not a lack of motion altogether. That's because of the Heisenberg uncertainty principle, which states that we can't know both the exact position and momentum of a particle at the same time. There may still be small fluctuations of movement. So, how could a system's entropy go down to zero?

The short answer: it can't.

Solving the Riddle

A new study from researchers Jonathan Oppenheim and Lluís Masanes sheds light on this riddle, by showing that reaching 0 Kelvin is physically impossible. Think of it this way: as described by Science Alert, the cooling of a system is essentially the "shoveling" out of heat from that system into the surrounding environment. But cooling has its limits, determined by how many steps it takes to shovel the heat out, and the size of the surrounding environment. You can only reach absolute zero, then, if you have both infinite steps and an infinite surrounding environment.

Dr. Lluís Masanes told IFL Science that their study shows "it is impossible to cool a system to absolute zero in a finite time" and that they "established a relation between time and the lowest possible temperature. It's the speed of cooling."

The researchers used quantum mechanics to arrive at their conclusion, viewing the cooling process as a computation, according to IFL Science. A longstanding debate about the third law of thermodynamics has finally been put to bed.

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