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After
more than 100 years of debate featuring the likes of Einstein himself,
physicists have finally offered up mathematical proof of the third law of
thermodynamics, which states that a temperature of absolute zero cannot be
physically achieved because it's impossible for the entropy (or disorder) of a
system to hit zero.

While
scientists have long
suspected that there's an intrinsic 'speed limit' on the act of
cooling in our Universe that prevents us from ever achieving absolute zero (0
Kelvin, -273.15°C, or -459.67°F), this is the strongest evidence yet that our
current laws of physics hold true when it comes to the lowest possible
temperature.

"We
show that you can't actually cool a system to absolute zero with a finite
amount of resources and we went a step further, we then conclude that it is
impossible to cool a system to absolute zero in a finite time, and we
established a relation between time and the lowest possible temperature. It's
the speed of cooling." one of the team, Lluis Masanes from University
College London, told
IFLScience.

What
Masanes is referring to here are two fundamental assumptions that the third law of
thermodynamics depends on for its validity. The first is that in order
to achieve absolute zero in a physical system, the system's entropy has to also
hit zero. The second rule is known as the unattainability principle,
which states that absolute zero is physically unreachable because no system can
reach zero entropy.

The
first rule was proposed by German chemist Walther Nernst in 1906, and while it
earned him a Nobel Prize in Chemistry, heavyweights like Albert Einstein and Max Planck weren't
convinced by his proof, and came up with their own versions of the
cooling limit of the Universe.

This
prompted Nernst to double down on his thinking and propose the second rule in
1912, declaring absolute zero to be physically impossible. Together, these
rules are now acknowledged as the third law of thermodynamics, and while this
law appears to hold true, its foundations have always seemed a little rocky -
when it comes to the laws of thermodynamics,
the third one has been a bit of a black sheep.

"[B]ecause earlier arguments focused only on specific mechanisms or were crippled by questionable assumptions, some physicists have always remained unconvinced of its validity," Leah Crane explains forNew Scientist.

In
order to test how robust the assumptions of the third law of thermodynamics
actually are in both classical
and quantum systems, Masanes and his colleague Jonathan Oppenheim decided
to test if it is mathematically possible to reach absolute zero when restricted
to finite time and resources.

Masanes
compares this act of cooling to
computation - we can watch a computer solve an algorithm and record
how long it takes, and in the same way, we can actually calculate how long it
takes for a system to be cooled to its theoretical limit because of the steps
required to remove its heat.

You
can think of cooling as effectively 'shovelling' out the existing heat in a
system and depositing it into the surrounding environment. How much heat
the system started with will determine how many steps it will take for you to
shovel it all out, and the size of the 'reservoir' into which that heat is being
deposited will also limit your cooling ability.

Using
mathematical techniques derived from quantum information theory - something
that Einstein had
pushed for in his own formulations of the third law of thermodynamics
- Masanes and Oppenheim found that you could only reach absolute zero if you
had both infinite steps and an infinite reservoir and that's not exactly
something any of us are going to get our hands on any time soon.

This
is something that physicists have
long suspected, because the second
law of thermodynamics states that heat will spontaneously move from a
warmer system to a cooler system, so the object you're trying to cool down will
constantly be taking in heat from its surroundings and when there's any amount
of heat within an object, that means there's thermal motion inside, which
ensures some degree of entropy will always remain.

This
explains why, no matter where you look, every single thing in the Universe is
moving ever so slightly - nothing in existence is completely still
according to the third law of thermodynamics. The researchers say they
"hope the present work puts the third law on a footing more in line with
those of the other laws of thermodynamics", while at the same time
presenting the fastest theoretical rate at which we can actually cool something
down.

In
other words, they've used maths to quantify the steps of cooling, allowing
researchers to define set speed limit for how cold a system can get in a finite
amount of time and that's important, because even if we can never reach
absolute zero, we can get pretty damn close, as
NASA demonstrated recently with its Cold Atom Laboratory, which can
hit a mere billionth of a degree above absolute zero, or 100 million times
colder than the depths of space.

At
these kinds of temperatures, we'll be able to see strange atomic behaviours
that have never been witnessed before. And being able to remove as much heat
from a system is going to be crucial in the race to finally build a functional quantum
computer and the best part is, while this study has taken absolute zero off the
table for good, no
one has even gotten close to reaching the temperatures or cooling
speeds that it's set as the physical limits - despite some
impressive efforts of late.

"The work is important - the third law is one of the fundamental issues of contemporary physics, it relates thermodynamics, quantum mechanics, information theory - it's a meeting point of many things." Ronnie Kosloff at the Hebrew University of Jerusalem, Israel who was not involved in the study, toldNew Scientist.

The
study has been published in

*Nature Communications.*
This post was written by Usman Abrar. To contact the
writer write to iamusamn93@gmail.com.
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