We still teach energy, the heart of the thermo-industrial society in the footsteps of Sadi Carnot (1796-1832). How can we draw inspiration from him to explore, with the students, another future?
Image: Sadi Carnot in 1813, 17 years old, in his École Polytechnique uniform. Engraving after the painting by Léopold Boilly, published in 1878 in the reprint of « Reflections on the Motive Power of Fire », Gauthier-Villars Ed., Paris. Wikipedia
During this health crisis, which precedes other much more terrible storms caused by global warming, I essentially remained a teacher. So, the classes were held online and I have been doing the best I could. Topic: thermodynamics, i.e., the science of heat as a source of motion.
One evening after the course, I took up again the « Reflections on the Motive Power of Fire » that Sadi Carnot published at the age of 27 in 1824, 8 years before he died of cholera, and at the dawn of the Industrial Revolution. I had forgotten. I was stunned by the very first pages.
I’ve been doing physics for almost half a century. I’ve been teaching it for a quarter of a century. Always with great pleasure, in spite of growing questioning, even doubt. Beside research and more advanced courses, I teach freshmen at university. I always did. Knowledge I try to pass to coming generations was available long before I was born. Like virtually every physics teacher on Earth. Eventually I teach basic physics as I learned it. The first principle of thermodynamics is the conservation of energy. It is timeless and is applicable to everyone. So, where does this questioning and doubt now come from, when I am in class with 20-year-old people, actors of tomorrow’s world, who are already experiencing the terrible impact of the irreversible transitions that are taking place, with climate change and the collapse of biodiversity in mind?
Sadi Carnot’s “Reflections on the driving power of fire”.
So, I taught thermodynamics to freshmen this year again, with thermal machines and the Carnot cycle at the heart. In 1824, the young Sadi Carnot published his « Reflections on the driving power of fire and on the machines capable of developing this power ». In less than hundred pages, he thus founded what would become thermodynamics, so named, 20 years after his death, by William Thomson, and thus gave the steam engine a theoretical basis. Twenty years later, Rudolf Clausius also introduced entropy, which completed the picture.
In passing, Sadi Carnot rationalized and founded in theory the practices of engineers and took the measure of the effects of the whole on the changes already underway in his time, on their future developments and on the resulting transformation of the world. In hindsight, one can only admire!
« If some day the development of the fire engine extends far enough to make it inexpensive in plant and fuel, it will have all the desirable qualities and will bring about a development in the industrial arts the full extent of which is difficult to predict. »
« They (fire machines) seem destined to produce a great revolution in the civilized world. »
Two centuries later, we can measure the full extent of this great revolution. The motive power of fire, that is, the control of the heat produced by the combustion of fossil fuels, coal, oil and gas, has radically changed the world.
« The navigation of fire engines brings the farthest nations closer together in a way. It tends to bring the peoples of the earth together as if they were all living in the same land. To reduce the time, fatigue, uncertainty and danger of travel is to shorten the distance. »
Carnot had anticipated the explosion of travel and the ensuing globalization of trade in terms that are still relevant today. Already the global village is here.
Carnot and the thermo-industrial civilization
Carnot’s scientific approach is incredibly powerful. In particular, it is based on machines developed around coal mines. With this analysis comes an incredible conceptual leap:
« Wherever there is a difference in temperature, there can be production of motive power. »
Two temperatures are needed: one hot and one cold to build a thermal machine like a car engine or a thermal power plant. The hotter the hot spot, the better. The colder the cold point, the better. This is always true, including for nuclear power.
This concept is at the heart of what we increasingly call today the thermo-industrial civilization. A civilization already described in 1824 by Sadi Carnot in the introduction to his fundamental scientific text.
Humanity is burning more and more
Sadi Carnot wrote that too:
« It is from this immense reservoir that we can draw the moving force necessary for our needs; nature, by offering us fuel from all sides, has given us the ability to give birth in all times and in all places to the heat and the driving power that follows. »
To do this, we burned first trees, then coal, then gas and oil. Massively. To run more than a billion petrol and diesel-powered vehicles, and to produce the bulk of the electricity still used by nearly 90% of humanity.
Figure caption: World primary energy consumption per year. At the time of Sadi Carnot, the consumption of coal, although already essential for example in England, is still insignificant for the whole of humanity. Still no consumption of gas and oil. //ourworldindata.org/energy
The article “Thermal Engines” in the Encyclopedia Universalis written in the 20th century starts with a short introduction on gasoline and diesel engines, and immediately frames its subject by Carnot’s efficiency and its two temperatures. To teach this part of thermodynamics in this way is to be in line with Sadi Carnot’s introduction.
So I still teach, as always, the driving power of fire at the heart of the thermo-industrial civilization that is neither sustainable nor durable. And yet I do not sulk my pleasure. I teach the students these ideal thermal machines, the associated Carnot cycle and its efficiency, with entropy at the key.
It’s a piece of physics of an ever-fascinating power, subtlety and elegance. To introduce it to students is a constant privilege. Like my professors 40 years ago, in the course, I stress that mastering this knowledge is a must: “Namely for life! And even if most of you won’t be doing physics any time soon! » Of course, because there are more than a billion combustion engines in the world !
Thermo-industrial civilization: end of the game in sight
But today, I’m afraid, we’re dealing with a « wicked problem » :
« Transport is responsible for almost 30% of the European Union’s total CO2 emissions. Of these emissions, 72% come from road transport. »
In his time, Sadi Carnot clearly described the potential for progress for humanity in mastering heat to produce movement. Two centuries later, the game has been played as he anticipated. But we know today that it cannot go on like this. The brutal effects of global warming due to the carbon dioxide released into the atmosphere are there as an inevitable by-product of this immense global fire. Sadi Carnot’s program established 200 years ago is no longer a possible future for humanity.
Energy conditions everything
The lines written by Sadi Carnot were based on a scientific and rational vision of the future of his time. Today we could imagine him searching with us for another path. His vision would certainly be built on the following remarks:
- experimentally based fundamental scientific knowledge is not negotiable,
- their rational use is necessary, as the variety of responses and their difference in effectiveness in the current health crisis have shown,
- as a result, observations and forecasts such as those associated with global warming are as objective and robust as they are unpleasant.
He would probably not stop there. He was one of the researchers, who brought out a new paradigm for the future of humanity. One would think that he would be at that level of thinking again:
« It is to heat that we must attribute the great movements that strike our eyes on the earth; it is to it that we owe the agitation of the atmosphere, the rise of clouds, the fall of rain and other meteors, the currents of water that criss-cross the surface of the globe and of which man has managed to use only a small part for his own purposes. »
This first sentence of his book seems obvious to us today. Was it also obvious in his time? I don’t really know. On the one hand, he stresses the importance of natural movements due to heat, induced by the solar radiation that hits the Earth, and on the other hand, that we only have access to a small part of these energies, now called renewable energies. This remains true.
Translated with http://www.DeepL.com/Translator (free version)
Article first published in French in TheConversation: https://theconversation.com/profiles/joel-chevrier-325290/dashboard#
Teaching, exploring, learning with students... 