The history of thermodynamics is one of the most important chapters in modern science. From the Industrial Revolution to the present day, this discipline has not only transformed physics and chemistry, but has also driven technological advances that have shaped society as we know it.
Key concepts such as energy, heat, and efficiency have evolved over centuries, with applications in areas ranging from electricity generation to the development of renewable energy, such as solar.
The importance of thermodynamics lies in its ability to explain phenomena that occur around us, such as the transfer of heat between objects or the efficiency of the engines we use in our daily lives. In addition, this branch of physics played a prominent role in solving one of the most studied problems in science: the nature of energy and how we can harness it.
Throughout its history, thermodynamics has pioneered our understanding of the physical world, linking phenomena that seemed separate and giving rise to a new way of understanding energy. To better understand this impact, it is essential to review the key moments and the scientists who have been fundamental in its development.
From ancient civilizations to the steam engine
Although the term “thermodynamics” was not coined until the 19th century, humans have been using and exploring principles related to heat and energy for millennia, long before scientific terms existed to describe them.
Ancient civilizations did not understand thermodynamics as we know it today, but they applied fundamental principles of heat and energy transfer in their everyday lives and in primitive technologies.
Ancient civilizations and the use of heat
One of the earliest applications of heat by humans dates back to the Stone Age, when our ancestors learned to control fire. Fire was one of the first sources of thermal energy used by humans and played a crucial role in human evolution.
The use of fire to cook food, heat shelters and work materials (such as hardening stone tools or smelting metals) is a clear example of how early civilizations took advantage of heat transfer to improve their quality of life.
In ancient Egypt, around 2000 BC, the heat of the sun was used to dehydrate food and to make products such as salt from salt water. The Egyptians also built rudimentary ovens that used wood as fuel for firing pottery and smelting metals. This technique spurred the development of metallurgy, especially in the creation of tools and weapons from copper and later bronze.
The Greeks and Romans, meanwhile, developed technologies that applied heat in more sophisticated ways. The Romans, for example, designed the famous hypocaust heating systems, which used the heat generated by underground furnaces to warm the air circulating under the floors and walls of their baths and buildings.
Middle Ages and the Renaissance
During the Middle Ages, particularly in the Islamic world, alchemists began to develop more advanced furnaces and use heat in rudimentary chemical processes.
In the 16th century, the Italian inventor and mathematician Giambattista della Porta described in his book Magia Naturalis the first experiments to convert heat energy into motion. Although rudimentary, his work included devices that used heat to generate small amounts of steam, although not in a system that could be used in terms of mechanical work.
Another important figure of this era was the Irish physicist Robert Boyle, known for his famous Boyle's law, which describes the relationship between the volume and pressure of a gas at constant temperature. Boyle and other scientists of the time began to conduct experiments relating heat and the motion of gases.
Steam engines
Although the first steam engines were developed in the 17th century, it was not until the 18th century that they began to be perfected.
In 1698, English engineer Thomas Savery developed a steam engine to pump water out of coal mines that marked a turning point in the evolution of the history of thermodynamics. Savery's design used steam pressure to create a vacuum, allowing water to rise through a pipe. It was one of the first examples in history of a machine that converted heat energy into useful work.
A few years later, in 1712, Thomas Newcomen improved on Savery's engine by inventing his own steam engine, known as the Newcomen engine. This device used steam to move a piston in a cylinder, which increased the efficiency of the system for pumping water.
However, the real leap forward in steam engine efficiency came in 1769, when James Watt, a Scottish engineer, introduced major improvements to Newcomen's design. Watt added a separate condenser, which significantly reduced energy losses and increased the engine's efficiency.
The leap to the Industrial Revolution
This improvement to James Watt's revolutionary engine allowed steam engines to be used not only to pump water, but also to power machinery in factories, mines, and eventually locomotives and ships.
This is where French engineer Sadi Carnot comes in, who in 1824 published "Reflections on the Motive Power of Fire", one of the founding texts of thermodynamics.
Carnot was the first to scientifically analyse how a steam engine could convert heat into work, and he did so by establishing an ideal theoretical cycle: the famous Carnot cycle. This cycle sets the limits of the efficiency of any heat engine, showing that not all heat can be transformed into work, and that there is always a loss of energy. His work was a milestone, and to this day, remains a key reference in engineering and physics.
Lord Kelvin and the second law of thermodynamics
In 1848, British physicist William Thomson, better known as Lord Kelvin, made another major breakthrough in the history of thermodynamics by proposing the absolute temperature scale, known today as the Kelvin scale. This scale was crucial because it allowed us to unify the way we measure temperature around the world, and it is still fundamental in modern science and engineering. Later, Lord Kelvin also worked on what would become one of the most revolutionary ideas in thermodynamics: the second law.
The second law of thermodynamics states that in any process involving a transfer of energy, there will always be an increase in the entropy of the system, i.e. "disorder" or "chaos." This principle is key to understanding why certain processes are irreversible. For example, when a hot cup of coffee cools down, it is impossible for it to warm up again on its own; the energy is dissipated and cannot be fully recovered.
This idea of entropy introduced a concept that challenged classical notions of physics: not all processes are perfectly reversible, and there is always some “loss” of energy in the form of heat. This understanding was not only key to physics, but also laid the groundwork for a greater appreciation of energy efficiency, a concept of growing importance in today’s context of sustainability and resource conservation.
Joule and Clausius: A modern understanding of energy
In parallel to Lord Kelvin's work, another prominent physicist, James Prescott Joule, performed key experiments that led to a greater understanding of the equivalence between heat and work. Until the mid-19th century, many scientists believed in the existence of a substance called "caloric," which was responsible for heat transfer. However, Joule proved that heat was not a substance, but a form of energy.
Joule's work was instrumental in the formulation of the first law of thermodynamics, also known as the law of conservation of energy. This law states that energy is neither created nor destroyed, but simply transformed from one form to another. This principle is crucial in understanding any physical system, from internal combustion engines to biological systems.
Another essential name of this period is that of the German physicist Rudolf Clausius, who in 1855 refined the concept of entropy and deepened the understanding of reversible and irreversible processes. Clausius was the first to introduce the Clausius inequality, which mathematically formalised the second law of thermodynamics and allowed scientists to advance in the understanding of the most complex thermodynamic systems.
Willard Gibbs and the graphical representation of thermodynamics
One of the most significant advances in the history of thermodynamics came from the American physicist Willard Gibbs. In 1876, Gibbs published his masterpiece "On the Equilibrium of Heterogeneous Substances", where he presented a methodology for graphically representing thermodynamic systems.
Gibbs' work made it possible to visualize how variables such as energy, entropy, temperature, pressure, and volume interact in a system.
Gibbs' graphical approach was revolutionary because it allowed a more accessible and practical way to study complex systems, particularly those involving chemical reactions. This method is key in chemical thermodynamics and remains relevant today, especially in the study of multiphase systems and the prediction of the spontaneity of reactions.
From classical thermodynamics to renewable energies
The impact of thermodynamics was not limited to heat engines in the 19th century. In the 20th century, thermodynamics began to have applications in a variety of broader fields, including internal combustion engines, gas turbines, and refrigeration systems. Understanding the principles of energy efficiency and heat transfer was key to the development of technologies that are still fundamental to modern life today.
One of the fields where thermodynamics plays an essential role is in the development of renewable energies, particularly solar thermal energy. At the end of the 18th century, the Swiss physicist Horace Bénédict de Saussure built the first solar collector, a device that captured solar radiation and converted it into heat. This invention was pioneering and demonstrated that solar energy could be used to generate heat, laying the foundations for the development of modern solar technologies.
Today, solar thermal plants, which use mirrors or lenses to concentrate sunlight and generate steam, rely entirely on the principles of thermodynamics to maximize their efficiency. The steam resulting from these systems drives a turbine, producing electricity. The second law of thermodynamics also plays a key role here, as it imposes limits on the efficiency of converting thermal energy into useful work. As the world moves toward a more sustainable future, the efficient use of solar energy and other renewable sources has become essential, and thermodynamics will continue to be a key tool in this effort.
The philosophical roots of thermodynamics
The fascination with heat and energy is not unique to the modern era. The ancient Greeks, for example, were already debating the nature of heat and the elements that made up the universe. Philosophers such as Heraclitus postulated that fire was one of the fundamental elements, along with earth, water and air.
Later, thinkers such as Leucippus and Democritus introduced the idea of atomism, a theory that held that all matter was composed of tiny, indivisible particles called atoms. Although this theory was not directly related to thermodynamics in its early days, later developments in statistical mechanics during the 19th and 20th centuries linked these two branches of physics.
Statistical mechanics, which emerged as an extension of thermodynamics, allowed scientists to explain how the macroscopic behavior of systems, such as temperature or pressure, emerged from the microscopic interactions of atoms and molecules. This relationship between the large and the small is a reminder of how scientific advances are often built on centuries of philosophical thought and discovery.