In the world of physics, unlike in everyday life, laws are not meant to be broken. These natural laws are the backbone of our understanding of the universe. Among them, the Second Law of Thermodynamics stands out as both crucial and mysterious, celebrating its 200th anniversary this year.

The Second Law, in simple terms, tells us that heat flows from hot to cold, that every action produces some waste and that order naturally turns into disorder. Imagine spilling a bag of marbles – they scatter chaotically, never spontaneously reassembling. This tendency towards disorder is a key idea in the Second Law, often referred to as entropy.

Two hundred years ago, French engineer Sadi Carnot was trying to make steam engines more efficient. Steam engines were the driving force of the Industrial Revolution, powering factories, trains and ships. Carnot’s work laid the foundation for the Second Law, even though it took scientists another two decades to fully grasp its significance.

Carnot discovered that the efficiency of a heat engine – like the steam engines of his time – depends on the temperature difference between its heat source and its cooling part. He showed that no engine could ever be 100% efficient because some energy is always lost as waste heat, a concept central to the Second Law.

Despite its age, the Second Law is still not fully understood. It’s like a puzzle with pieces that fit together in different ways, depending on how you look at them.

Scientists have formulated many versions of the Second Law, trying to capture its essence. Percy Bridgman, a physicist, famously said: “There have been nearly as many formulations of the Second Law as there have been discussions of it.”

The Second Law, in simple terms, tells us that heat flows from hot to cold, that every action produces some waste and that order naturally turns into disorder

The Second Law is everywhere in our daily lives. It explains why your hot coffee cools down, why air conditioners and refrigerators work, and even why time seems to move in one direction – from past to future. British astrophysicist Arthur Eddington highlighted its importance, saying any theory that goes against the Second Law is doomed to fail.

Think of the Second Law as a universal truth, like a wise old teacher who reminds us that in every process, there is always some loss. This loss is what prevents perpetual motion machines – hypothetical machines that could work forever without any energy input – from being possible.

The Second Law also predicts a rather gloomy future for the universe. It suggests that over time, all energy will eventually spread out evenly, and everything will reach the same temperature. This idea, known as the “heat death of the universe”, means that in the very distant future, all processes will stop, and the universe will be in a state of eternal rest.

In recent years, scientists have linked the Second Law to information theory, exploring how processing information produces waste heat, much like physical processes. This modern angle keeps the Second Law at the forefront of scientific inquiry.

While the Second Law has not been rigorously proved in every context, it has withstood numerous challenges. It remains a guiding principle in understanding the natural world, from the smallest particles to the vast cosmos.

As we celebrate the 200th anniversary of the Second Law of Thermodynamics, we recognise its profound impact on science and technology. It’s a reminder that even the simplest truths can unlock the deepest mysteries of the universe. Whether it’s in cooling a drink or predicting the fate of the cosmos, the Second Law continues to shape our understanding of how the world works.

Mohamed Daoud is a public engagement expert.

Sound Bites

•        Researchers have developed a precise method to measure temperatures of electronic devices using neutrons. By utilising the Doppler broadening effect in neutron resonance absorption and a high-powered laser to create 100-nanosecond neutron pulses, they achieved exceptional temporal resolution. Tests on silver and tantalum samples accurately recorded their characteristic information and temperatures.

•        Physicists are developing quantum microscopy to record electron movement at the atomic level with unprecedented spatial and temporal resolution. This method could allow scientists to develop materials more precisely than ever before.

DID YOU KNOW?

•        In the realm of quantum mechanics, particles can become entangled, meaning the state of one particle instantly influences the state of another, no matter how far apart they are. This phenomenon puzzled even Einstein, who referred to it as “spooky action at a distance”.

•        Certain materials, when cooled to very low temperatures, can conduct electricity without any resistance. This phenomenon, known as superconductivity, was discovered in 1911 and has applications in MRI machines and maglev trains.

•        Physics is governed by several conservation laws, such as the conservation of energy, momentum and angular momentum, which state that these quantities remain constant in an isolated system. These principles are fundamental to understanding physical interactions.

•        Certain liquids, like helium-4 when cooled below a critical temperature, flow without viscosity. This superfluidity allows them to climb walls and defy gravity, providing insights into quantum mechanics.

•        Scientists believe that the universe started in a state of low entropy at the Big Bang, which allows for the increasing entropy we observe as the universe expands and evolves.

•        At the smallest scales, space-time is thought to be extremely turbulent, a concept known as quantum foam. This idea was proposed by John Wheeler and suggests that space-time is not smooth but frothy and chaotic.