Let's take a trip through the history of thermodynamics, the branch of physics that studies heat, energy and how they are transformed.
To understand how we came to know so much about this topic, it is important to know the great minds who made important discoveries.
We are going to talk about the most prominent scientists in thermodynamics, their lives, some curiosities, and the fundamental role they played in the evolution of this science.
Sadi Carnot (1796-1832) – The father of thermodynamics
Let's start with one of the most important, the Frenchman Sadi Carnot .
Carnot is considered one of the pioneers of thermodynamics, although he did not live to see the full development of this science, as he died young at the age of 36, a victim of cholera. Carnot was born in Paris, into a family with strong political and scientific connections, which allowed him to study at the best institutions of the time, such as the École Polytechnique in Paris.
What makes Carnot so important is that he was the first to understand how heat engines worked, that is, those that convert heat into work.
In his famous book "Reflections on the Motive Power of Fire" (1824), he proposed that steam engines could not operate without a temperature difference between a hot and a cold source. Basically, the steam engine needed a "current" of heat from the hot to the cold to do useful work.
Additionally, Carnot introduced the concept of the "Carnot cycle," a theoretical cycle that described how to operate the most efficient heat engine possible.
A curious fact about Carnot is that he was never fully appreciated in his time. In fact, he died in anonymity, and only years later would his ideas be fully recognized and understood.
He was rather a visionary who, although he died young, left a mark that would change the course of physics.
James Prescott Joule (1818-1889) – The man of energy
Let us now turn to a very well-known name: James Prescott Joule , an English physicist who was born into a wealthy family.
The Joule family owned a brewery, but James proved to be more of a scientist than a beer lover from a young age. He is credited with the famous law of conservation of energy, a basic element of thermodynamics.
Joule performed experiments in which he demonstrated that mechanical energy and heat are related , that is, they can be transformed into one another. This discovery led to the formulation of the first principle of thermodynamics, which states that energy is neither created nor destroyed, it is only transformed.
He did this by carrying out rather rudimentary but ingenious experiments, such as the famous water mill experiment, where he measured the heat generated by stirring water using a system of weights and pulleys.
The curious thing about Joule is that, despite having carried out such important experiments, he was not a formal academic scientist. Joule did not work at any university, but was self-taught and financed his own experiments, even building his own laboratory equipment.
He also loved science so much that he even measured the temperature of the water while on holiday in the Alps.
Rudolf Clausius (1822-1888) – The Lord of Entropy
Another essential name in the history of thermodynamics is the German physicist Rudolf Clausius .
We owe Clausius the concept of entropy , a word you've probably heard in physics or chemistry class. He was born in a small town in what is now Poland, but studied in Berlin and later taught at German universities.
In 1850, Clausius reformulated the ideas of Carnot and Joule, proposing the second law of thermodynamics , which states that in any natural process, the entropy of the universe always increases. Entropy, simply put, is a measure of disorder: the more entropy, the more chaotic a system is.
Clausius realized that although energy is conserved (first principle of thermodynamics), the quality of that energy changes, and there is always some that is "lost" as unusable heat.
Clausius also played an important role in unifying the study of heat with electricity and the kinetic theory of gases. In fact, he was a key proponent of atomic theory when it was still controversial.
William Thomson (Lord Kelvin) (1824-1907) – The man of extreme cold
Now let's talk about a British scientist who is practically a legend, William Thomson , better known as Lord Kelvin . You've probably heard of degrees Kelvin, the unit of temperature measurement that bears his name. Well, Lord Kelvin was one of the greatest physicists of his time and contributed a lot to thermodynamics.
Kelvin was one of the first to establish an absolute temperature scale , what we know today as the Kelvin scale. On this scale, absolute zero (-273.15 ºC) is the lowest possible temperature, where molecules have no kinetic energy and everything stops.
This was a milestone because until then, all temperature scales were relative, such as degrees Celsius or Fahrenheit.
Kelvin also worked with Joule on the famous Joule-Thomson experiment, where they demonstrated that when a gas expands without doing work, its temperature decreases, a key phenomenon for understanding how to cool gases and therefore create modern refrigeration systems.
As a curious fact, Kelvin was passionate about submarine cables, and helped install the first transatlantic telegraph cable, which allowed instant communication between Europe and America.
He was not just a theorist, but enjoyed applying his knowledge of physics to engineering and practical technology.
Ludwig Boltzmann (1844-1906) – The statistician of atoms
Let us now move on to a very interesting and, for many, tragic character: the Austrian physicist Ludwig Boltzmann .
Boltzmann is known as the creator of statistical mechanics , a theory that explains how the macroscopic properties of systems, such as temperature and pressure, arise from the interactions of many individual particles.
Boltzmann was one of the first to defend the idea that matter is composed of atoms and molecules, something that we take for granted today, but which was highly debated in his time.
Using this idea, he was able to explain the second law of thermodynamics in terms of probability: systems tend toward disorder (increase in entropy) because particles are statistically more likely to be distributed in a disordered manner than in an ordered manner.
Sadly, Boltzmann had a difficult personal life. Despite his brilliant contributions to physics, he was heavily criticized by some of his colleagues who did not accept the idea of atoms.
This pressure, along with other personal problems, led him to commit suicide in 1906. Today, Boltzmann is remembered as one of the fathers of modern physics, and his equation S=k⋅lnW, which relates entropy to probability, is engraved on his tombstone.
Josiah Willard Gibbs (1839-1903) – The Master of Free Energy
Next on our list is American Josiah Willard Gibbs , a scientist who was a genius in mathematics and physics, but who lived a fairly quiet life without many eccentricities.
Gibbs was not that famous in his time, partly because his work was very abstract, but his ideas are fundamental to modern thermodynamics and chemistry.
Gibbs introduced the concept of free energy , which is a measure of the amount of useful work a system can perform. Gibbs free energy provides insight into how chemical reactions and thermodynamic processes occur. It enabled scientists to predict which reactions would be spontaneous and which would not.
Although Gibbs did not travel much, preferring to stay in his laboratory at Yale, his contributions spread throughout the world.
Curiously, he was so modest that when his colleagues tried to give him a prize, he felt uncomfortable and refused it. Even so, his name is fundamental in the history of thermodynamics.