Sadi Carnot: The Father of Thermodynamics

Born to one of the most influential families during the French Revolution, Sadi Carnot kickstarted another revolution in physics. His perfect (although theoretical) steam engine transformed the way we think about heat and work.

Transcript

Aarati Asundi (00:13)
Hi everyone, and welcome back to the Smart Tea Podcast where we talk about the lives of scientists and innovators who shaped the world. I'm Aarati.

Jyoti Asundi (00:21)
And I'm her mom, Jyoti.

Aarati Asundi (00:23)
Happy December everyone! And welcome back, Mom. You were traveling, you went off to India and everything. How's it feel to be back?

Jyoti Asundi (00:30)
Yes, I love being back. It was a good vacation. I was away for two, three weeks and I am truly glad to be back. It's a grueling journey. Door-to-door, it ends up being a little bit more than 24 hours.

Aarati Asundi (00:46)
Yeah, because India is like literally on the other side of the world.

Jyoti Asundi (00:49)
Practically, for all practical purposes, yes. So it takes a toll and the older I get, the worse it is. But I'm truly glad to be back and I'm glad at this particular moment my brain cell seems to be firing and not fogged by jet lag. 

Aarati Asundi (01:06)
Awake? ⁓ you're awake?

Jyoti Asundi (01:07)
So I am in the mood. I am in the mood for our next episode. ⁓

Aarati Asundi (01:11)
Yes, staying awake. We're going to help you stay awake with a very exciting story today.

Jyoti Asundi (01:16)
Awesome.

Aarati Asundi (01:17)
Yeah. So actually, this month, December, we have three episodes coming out. And I've ended up kind of doing a three-parter because of that. 

Jyoti Asundi (01:28)
Ooh! That's a new thing for us.

Aarati Asundi (01:31)
Yeah, so highly recommend once you listen to this one, stay tuned for the next two because they're going to build on this one. And the idea for this, of course, came from my brother Arun. Every time I put out a new episode, he's always like, when are you going to do the next physics person? And I'm like, that's not, I'm a bio person. Yes.

Jyoti Asundi (01:48)
Aha! physics, that's just what I need. That's just what my jet lagged brain needs, some physics.

Aarati Asundi (01:54)
Yeah, yeah, we're gonna keep you awake. So I started looking into the name of the person that he wanted me to do. And I was like, well, to understand that guy, you really have to understand the guy who came before him. And so I started looking into that guy. I was like, maybe this can be a two parter. And then I was like, well, to understand this guy, you have to understand the guy who came before him. So we're starting like three people back.

Jyoti Asundi (02:18)
Oh nice. Is that practically three generations then? So that... 

Aarati Asundi (02:23)
Not quite. There's...

Jyoti Asundi (02:24)
...we are spanning physics over many years?

Aarati Asundi (02:27)
Across maybe like 50 years or so, so it's not quite three generations, but ⁓

Jyoti Asundi (02:29)
⁓ wow, so the buildup of a concept over 50 years.

Aarati Asundi (02:34)
Yeah.

Jyoti Asundi (02:34)
That's fantastic. That sounds exciting already.

Aarati Asundi (02:38)
And I thought it was even more apt because we are going to be diving into the world of thermodynamics. And I was like, how perfect for December when it's all cold, we can talk about heat.

Jyoti Asundi (02:52)
Yes, yes, maybe just talking about it make us feel a little warmer than we feel right now.

Aarati Asundi (02:58)
Hopefully. So, just to note that there are so many thermodynamics people that you've probably heard of that we are not directly talking about in these three episodes. So you've probably heard of like James Prescott Joule, William Thompson, who is also known as Lord Kelvin, James Maxwell, Josiah Gibbs, Herman von Helmholtz. Like we have all of these different scientists that they're titans in this field of thermodynamics and some of them make an appearance. But today we are starting with a French scientist who is called the father of thermodynamics and his name is Sadi Carnot.

Jyoti Asundi (03:28)
Sadi Carnot?

Aarati Asundi (03:48)
Sadi is S-A-D-I.

Jyoti Asundi (03:51)
Okay.

Aarati Asundi (03:52)
And Carnot is C-A-R-N-O-T. 

Jyoti Asundi (03:51)
Carnot. Okay. Sadi Carnot. Okay.

Aarati Asundi (03:57)
Yeah, he's French, so silent T. 

Jyoti Asundi (03:59)
Got it. The T at the end is silent. Sadi Carnot. Okay.

Aarati Asundi (04:05)
I had actually never heard of him, even though he is the father of thermodynamics. Yeah.

Jyoti Asundi (04:08)
Same here. He's the father, he's the father of thermodynamics and I hadn't heard of him. These episodes are really turning out to be educational in so many ways. Fantastic.

Aarati Asundi (04:18)
Yeah, although, you know, Arun has heard of him. My brother Arun has heard of him, so of course. 

Jyoti Asundi (04:23)
Yes, he has heard of anything that is related to physics. Yeah, physics, chemistry, he's our go-to guy.

Aarati Asundi (04:31)
Yes. So Sadi was born on June 1st, 1796 at the Petit Luxembourg Palace. Sadi, as you may have realized, is not really a very French name. He was actually named after a 13th century Persian poet, Sadi of Shiraz. Yeah.

Jyoti Asundi (04:51)
Oh wow, so his parents were fairly cosmopolitan in that way.

Aarati Asundi (05:00)
Oh yes, we are going to get into his parents or his father specifically. However, a bit more about his name. When he was baptized, he was given the name Nicholas Leonard DuPont Kind of by accident.

Jyoti Asundi (05:12)
That's a really long handle to be given by accident.

Aarati Asundi (05:16)
Yes, I don't know where the Nicholas Leonard part came in, but the DuPont was actually his mother's maiden name...

Jyoti Asundi (05:23)
Okay.

Aarati Asundi (05:23)
...because they mistakenly thought that his maternal uncle was his father somehow. There was some screw up.  

Jyoti Asundi (05:29)
Okay. Okay.

Aarati Asundi (05:31)
So he was baptized under Nicholas Leonard DuPont. And then later on, when you're looking him up, you may find him under the name Nicholas Leonard Sadi Carnot, but he went by Sadi Carnot during his life.

Jyoti Asundi (05:44)
Okay.

Aarati Asundi (05:45)
So when Sadi was born, France was going through a massive political and military upheaval. This is the time of the French Revolution. 

Jyoti Asundi (05:55)
Mm-hmm. Those were turbulent times.

Aarati Asundi (05:59)
Very much so. And he's born right in the middle of it. Okay, so a quick history reminder of what's happening in France around this time. So in 1792, a radical political group called the Jacobins, which are led by Maximilien Robespierre, successfully abolished France's monarchy and turned France into a republic led by a main legislative body called the National Convention.

Jyoti Asundi (06:27)
Okay. 

Aarati Asundi (06:28)
Maximilien Robespierre headed the Committee of Public Safety, which basically was a de facto executive branch that was in charge of protecting France from both internal threats of rebellion and economic crisis, as well as external threats since France was at war with so many other European nations at this time.

Jyoti Asundi (06:49)
Yes.

Aarati Asundi (06:50)
And because of that, they garnered a lot of momentum during the following months, known as the Reign of Terror, as they purged France of political enemies. Over 16,000 people were executed, including of course, King Louis XVI and his wife Marie Antoinette.

Jyoti Asundi (07:09)
Yeah. It was a monarchy versus the republican way of life. And so anybody who was leaning more towards a monarchy, a style of rule, was executed. Wow, that's truly horrible.

Aarati Asundi (07:24)
Yeah, it was insane. So the Committee of Public Safety was made up of 12 members. And one of the members was Sadi's father, Lazare Carnot

Jyoti Asundi (07:38)
Oh so he was in Robespierre's National Convention. Okay. ⁓

Aarati Asundi (07:42)
Yes, he's in the Committee Safety. And he is a brilliant strategist, both as a military man and a politician. Some history books refer to him as quote, "The organizer of victory."

Jyoti Asundi (07:55)
Oh wow, okay.

Aarati Asundi (07:58)
However, although he was part of the Committee of Public Safety, he wasn't officially part of the radical Jacobins that had like overthrown the monarchy. And he quickly became disillusioned with Robespierre and his tyranny.

Jyoti Asundi (08:14)
Yeah it was extreme. It was basically... he was a terrorist, basically. Yes.

Aarati Asundi (08:20)
Yes, and Lazare Carnot was looking at this and was like, wow, OK, you're crazy.

Jyoti Asundi (08:26)
Yeah, definitely. To get a good sense of the craziness of those times, there are two really good books that bring that out. One in a very romantic style. The Baroness Orczy wrote The Scarlet Pimpernel. 

Aarati Asundi (08:43)
Oh yeah.

Jyoti Asundi (08:44)
And then the other one is, of course, Charles Dickens, The Tale of Two Cities. Both of these really captured the desperation and the utter chaotic unhinged way that aristocrats were put to death for no real apparent reason and sometimes it was just little children because they were born to that lineage potentially a threat to the republic because they had royal, quote unquote, royal blood, quote unquote...

Aarati Asundi (09:15)
Oh That's so sad.

Jyoti Asundi (09:15)
...aristocratic blood, and they were put to death because, we don't want to have any possibility of a monarchy again, that kind of thing.

Aarati Asundi (09:24)
Yeah, no road to that. Oh that's so sad. That's heartbreaking.

Jyoti Asundi (09:27)
Yeah. And false charges were brought in of political collusion to bring the monarchy back, even though there were simple people there. They were leading simple lives. were just, buried in poetry or enjoying themselves just farming and taking care of their lands and things like that. And yet they were put to death. It's terrible. It's terrible. Those two books really capture it in a very good way.

Aarati Asundi (09:54)
I can see that if anybody anywhere was even remotely connected, you might feel like I might be next on the chopping block, literally. 

Jyoti Asundi (10:04)
Correct. 

Aarati Asundi (10:05)
So on June 27, 1794, members of the National Convention decided to overthrow Robespierre. And Lazare and a few other members of the committee who were a bit more conservative helped to arrest Robespierre and his followers. Robespierre was executed a day later, ending the reign of terror, but the Committee of Public Safety lost its power. However, Lazare was quickly acquitted of doing anything wrong, so he was safe.

Jyoti Asundi (10:36=9)
He managed to save his skin.

Aarati Asundi (10:41)
Yes. That same month, the National Convention started drafting the French Constitution and established a form of government called the Directory. The Directory was made up of five members with executive power with the idea that, quote, "This executive will have the force concentrated enough that it will be swift and firm, but divided enough to make it impossible for any member to even consider becoming a tyrant."

Jyoti Asundi (11:10)
Okay, okay, trying to have multiple poles of power rather than everything concentrated into one hand.

Aarati Asundi (11:16)
Yes, instead of one president, we have five presidents.

Jyoti Asundi (11:20)
That's right.

Aarati Asundi (11:22)
So five members of the directory. And guess who was one of the members of the directory?

yoti Asundi (11:27)
Oh! Was Carnot one of them?

Aarati Asundi (11:30)
Yeah! Lazare Carnot. 

Jyoti Asundi (11:30)
Wow, wow. up there in terms of political power. Okay, okay, got it.

Aarati Asundi (11:36)
Yes. Yes. Very, very influential guy. So he served as a member of the directory until 1797 during which time Sadi was born. In 1797, three members of the Directory formed a coup, and Lazare and one other member was ousted. 

Jyoti Asundi (11:54)
Okay.

Aarati Asundi (11:55)
Lazare was sent into exile in Switzerland, but he came back to France when Napoleon rose to power...


Jyoti Asundi (12:02)
Oh yes!

Aarati Asundi (12:02)
...and he was made Minister of War.

Jyoti Asundi (12:05)
He is a very strong personality then. 

Aarati Asundi (12:09)
Yes.

Jyoti Asundi (12:09)
Very powerful person for those times.

Aarati Asundi (12:12)
He was a huge military politician, like political figure this time. And Sadi is born into this family that has so much influence over what is happening in France at the time. 

Jyoti Asundi (12:24)
Yes, okay.

Aarati Asundi (12:26)
But Sadi is like four years old now. So I found a really cute story that was written by Sadi's younger brother, Hippolyte and he tells stories of how young Sadi used to go with his father to Napoleon's residence and was put in the care of Madame Josephine Bonaparte, his wife while Lazare conducted business with Napoleon.

Jyoti Asundi (12:52)
Napoleon's wife is babysitting him. 

Aarati Asundi (12:55)
Yeah, basically.

Jyoti Asundi (12:56)
Oh wow, while the guys are doing their guy things and fighting and coming up with war strategies, Napoleon's wife is babysitting Sadi.

Aarati Asundi (13:06)
Yes. So there was one really cute story where Hippolyte tells the story of when Sadi was about four years old at Napoleon's residence watching Madame Bonaparte and her lady friends at a pond rowing boats. And then Napoleon suddenly appears and starts splashing water at the women. 

Jyoti Asundi (13:30)
Just being playful.

Aarati Asundi (13:31)
Yeah. So Sadi got really mad and shouted at Napoleon calling him a "Beast of a First Consul". which was...

Jyoti Asundi (13:40)
Oh my god!

Aarati Asundi (13:41)
Napoleon's title was First Consul. 

Jyoti Asundi (13:44)
Ha ha ha ha ha. It's like he's protecting his protector. He's so loyal.

Aarati Asundi (13:51)
Yeah! This is, know, how dare you splash water at this lovely ladies rowing their boats. 

Jyoti Asundi (13:56)
Yes, who's taking care of me? That's beautiful.

Aarati Asundi (13:59)
Yeah! So really funny.

Jyoti Asundi (14:02)
That's so cute. Yes.

Aarati Asundi (14:02)
Just the cutest little story of this little four-year-old yelling at Napoleon. And Napoleon also thought the whole thing was hilarious. Like, ⁓ very cute. Yeah. So cute.

Jyoti Asundi (14:16)
Nice.

Aarati Asundi (14:17)
However after a while, Napoleon also started to become a bit too power hungry for Lazare's liking. Napoleon crowned himself Emperor of France, which Lazare was not okay with.

Jyoti Asundi (14:29)
Yeah, the whole idea of the ⁓ reign of terror and the French Revolution that preceded Napoleon was that there would be no monarchy, there would be polarization of multiple poles of power, it would be a republic... 

Aarati Asundi (14:45)
Checks and balances everywhere. 

Jyoti Asundi (14:47)
Checks and balances everywhere, it would be a republic. And now Napoleon, under the guise of being in the republic, is now becoming a dictator which again is another way of being a bad monarchist.

Aarati Asundi (15:02)
Yes and so, Lazare didn't agree with Napoleon becoming emperor, and so he resigned from his position. But he kept himself busy, so aside from being an accomplished military man and politician, he was also a brilliant mathematician and physicist.

Jyoti Asundi (15:21)
So this Lazare guy is a brilliant war strategist, he is extremely high in terms of political power. In addition to that, he's a mathematician and a physicist. 

Aarati Asundi (15:35)
Yes. All of this rolled into one person.

Jyoti Asundi (15:36)
Wow. wow. The fact- but wait, hang on. And in addition to the fact, in addition to all this, the fact that he named his young son Sadi after a Persian poet shows you he has a philosophical bent and he bent towards literature. So he's basically, well educated..

Aarati Asundi (15:59)
Very worldly.

Jyoti Asundi (16:01)
Wow, wow, what a man, huh? And a peaceful guy. He didn't like any of these people who were basically being terrorists under the name of a new way of life. And he didn't like a monarchist and he didn't like dictators. So a very well balanced thought process going on there.

Aarati Asundi (16:21)
Yes, and I see that theme a lot, you know? Like the more educated you are, the more you see of the world, the more like he was one of those people who had just seen a lot, read a lot, knew a lot. And he was like, what are we all fighting for, guys? Like, work towards peace, work towards something that works in terms of political strategy and power. I agree, there shouldn't be one guy calling himself king or emperor or whatever. So let's... the best way to do it is to have these multiple, like you said, polls of power, checks and balances. And it's like, listen to the guy who knows so much about the world. Listen to him.

Jyoti Asundi (16:57)
Yes, absolutely. What path of life would lead to greater good the entire society? That's what he's looking at. And he has the ability to do so because he's so well educated and he's really looked at the world from multiple angles. ⁓ So that's a wonderful gift. What a gift he was to France at that time.

Aarati Asundi (17:22)
Yes. So once he resigns, he starts working on his math and physics. He throws himself into that. In 1801, he published a paper on geometry, which contains several theorems, including one that's now known as Carnot's theorem. And in 1803, he published another paper called Fundamental Principles of Balance and Motion, which aimed to explain equilibrium and motion through geometric reasoning.

Jyoti Asundi (17:49)
Wow! Yeah, he's doing groundbreaking research. Wonderful. Setting the foundations.

Aarati Asundi (17:57)
But he also used his skills to engineer modified versions of fortification systems to protect garrisons during times of war. So he was also using his engineering skills for, you know, more political strategies and...

Jyoti Asundi (18:10)
Very practical purposes. Yeah.

Aarati Asundi (18:12)
Yeah, war strategies and things like that.

Jyoti Asundi (18:13)
Yeah, no, France is going through turbulent times. You need to protect the garrisons. Yes, so he's using his knowledge for that as well. A very practical guy.

Aarati Asundi (18:25)
Yeah. And he's in fact such a great mathematician that today you can find his name as one of 72 French scientists with their names written around the Eiffel Tower.

Jyoti Asundi (18:39)
Oh wow! He is immortalized for posterity there on the Eiffel Tower. Wow, that's a great honor. What a big name he is. Wow.

Aarati Asundi (18:49)
So hugely, hugely influential figure. And now, Sadi, this little child, is growing up with this remarkable father and all the connections that the family had with all of its advantages. 

Jyoti Asundi (19:04)
Yes.

Aarati Asundi (19:06)
His father actually, in 1897, dropped everything to personally homeschool Sadi and his younger brother, in science, math, and art and music. So like we were saying.

Jyoti Asundi (19:17)
Yes, he's doing the right thing, bringing up the kids the way he wants it done.

Aarati Asundi (19:23)
Yeah, and teaching them to probably go and look at all these different cultures, literature, and study poetry from different places. 

Jyoti Asundi (19:28)
Yes, yes, learn, learn from different perspectives. Yes.

Aarati Asundi (19:33)
Yeah. Sadi showed a lot of promise. And in 1812, he was admitted to the Polytechnic School in Paris at the age of 16, which was the youngest possible age that anyone could be accepted to that school.

Jyoti Asundi (19:47)
Nice.

Aarati Asundi (19:48)
He was taught by some great names like Joseph Louis Gay-Lussac, who was the one who discovered that water is made of two parts hydrogen and one part oxygen. 

Jyoti Asundi (19:58)
Whoa. What times.

Aarati Asundi (20:00)
And he did a lot of work on alcohol water mixtures. So I think that maybe if you're a bartender or anything, you might have heard of his name. And then another one of his teachers was Siméon Denis Poisson, who was a great mathematician and physicist. And he was also taught by André-Marie Ampère, who worked on electromagnetism and is where we get the unit of amps. 

Jyoti Asundi (20:25)
Amps. Yes, the amps come from Ampere. Okay. This is a guy who has really strong influences in his life. Wow.

Aarati Asundi (20:35)
Yes, really learning from the cream of the crop.

Jyoti Asundi (20:38)
Absolutely. Yeah, this is absolute privilege, actually. He's growing up in great privilege.

Aarati Asundi (20:46)
However, things take a turn when in 1814 Napoleon's empire was collapsing because he had faced a few big military defeats and sensing his vulnerability, the allied forces of Russia, Austria, Prussia, and the German state Wurttemberg seized the opportunity to try to take Napoleon down once and for all and they invaded France and attacked Paris with the hopes of getting rid of Napoleon once and for all. Sadi, who's in Paris studying the Polytechnic Institute, he gathers his fellow students and joins the effort to defend Paris but they were greatly outnumbered. Lazare, the father, also returned to help Napoleon and was briefly named Minister of the Interior, but it was all a lost cause. And Paris fell on March 31st, 1814. Napoleon was deposed and the monarchy restored with King Louis XVIII taking the throne.

Jyoti Asundi (21:50)
Oh wow, okay. Hmm.

Aarati Asundi (21:52)
Yeah. So we all just went in a big circle here. 

Jyoti Asundi (21:54)
and back to monarchy.

Aarati Asundi (21:56)
And back to monarchy. Yeah.

Jyoti Asundi (21:57)
After all the reign of terror and everything, it's back to monarchy.

Aarati Asundi (22:01)
Yeah. But now because Lazare had thrown his lot in with Napoleon, he was forced into exile in Madgeburg, Germany, where he spent the rest of his life.

Jyoti Asundi (22:12)
Okay.

Aarati Asundi (22:13)
Meanwhile, Sadi is not exiled. He manages to graduate from the Polytechnic School and then he goes on to enroll in the School of Applied Artillery and Military Engineering in Metz, specializing in engineering. He graduated from the two-year program in 1816 and then joined the French Army's Corps of Engineers. However, because of his family's strong association with Napoleon, Sadi's military career prospects were very limited. He couldn't go far.

Jyoti Asundi (22:45)
Yes, correct because now he's a questionable force basically. 

Aarati Asundi (22:51)
Yeah.

Jyoti Asundi (22:51)
It's like, well, you were with Napoleon, cannot, your loyalty is questionable.

Aarati Asundi (22:56)
And so now he's gone from this state of being like in this very highly influential, very powerful family to kind of the opposite. Like he has no power. Nobody's willing to give him a chance. He was bounced around various posts to examine fortifications and write reports, but none of his recommendations were taken seriously. So after a couple of years of not being able to advance in his career path, Sadi decided to take a leave of absence and studied to join the General Staff Corps. He passed the exams in 1819 and stayed on call for military duty. However, he started spending most of his time pursuing his own interests in physics. 

Jyoti Asundi (23:37)
Okay.

Aarati Asundi (23:38)
And he started attending lectures in chemistry and physics at the Sorbonne and College de France. 

__________________________________________________________________________________________________________________

Aarati Asundi (23:51)
Hi everyone, Aarati here. I hope you're enjoying the podcast. If so, and you wish someone would tell your science story, I founded a science communications company called Sykom, that's S-Y-K-O-M, that can help. Sykom blends creativity with scientific accuracy to create all types of science, communications, content, including explainer videos, slide presentations, science, writing, and more. We work with academic researchers, tech companies, nonprofits, or really any scientists. To help simplify your science, check us out at sykommer.com. That's S-Y-K-O-M-M-E-R.com. Back to the story.
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Aarati Asundi (24:38)
Here, as he's learning about things, he starts to become interested in steam engines. 

Jyoti Asundi (24:43)
Oh nice, yes the industrial revolution is just round the corner.

Aarati Asundi (24:47)
Yes, it's just started. Steam engines are still relatively new. And in a basic steam engine, how it works is you input heat by burning coal or fuel. T

Jyoti Asundi (25:01)
Yeah.

Aarati Asundi (25:02)
This heat goes to a water boiler which generates steam and the steam drove pistons, which did the work.

Jyoti Asundi (25:09)
Yes.

Aarati Asundi (25:10)
The steam then left the pistons, now at a cooler temperature, traveled to a condenser, which condensed the steam back into liquid water, and this water was taken back to the boiler, and the process is repeated.

Jyoti Asundi (25:24)
Yes, okay. Mm-hmm. Steam power.

Aarati Asundi (25:27)
Yeah, steam power. It was a revolutionary thing.

Jyoti Asundi (25:31)
Yes.

Aarati Asundi (25:32)
And people started building trains and ships and all these other machines that are now powered by the steam engine. But despite this, no one really understood exactly how they worked from a physics standpoint. They were like, OK, we know the steam is somehow doing the work. But how? How is heat from steam able to do physical work?

Jyoti Asundi (25:53)
Yes.

Aarati Asundi (25:54)
So Sadi is looking at this. And he proposed that the work that was being done by the engine was a result of the temperature falling when the steam cooled down as it interacted with the pistons. That loss of heat is what is doing the work.

Jyoti Asundi (26:14)
Because the heat that is being lost by the steam is being actually transferred over to the piston. That energy is being converted to the energy that moves the pistons actually.

Aarati Asundi (26:28)
Yes, well, we know that now. He did not know that.

Jyoti Asundi (26:31)
Oh! We did not know that. So I'm jumping the gun when I say that.

Aarati Asundi (26:34)
No, because this is really good, actually, because this was so hard for me to wrap my head around because they did not know about energy or, the transformation of energy. They didn't know about that.

Jyoti Asundi (26:47)
Energy can be in different forms, yes. That concept is not known. 

Aarati Asundi (26:52)
It's not there at all.

Jyoti Asundi (26:53)
And we are studying, we are looking at that point in the history of physics. 

Aarati Asundi (26:59)
Yeah. So it was really hard for me to kind of wrap my head around how he came to this conclusion, because it was like, if you don't know that heat has energy, how are you able to make this conclusion that heat's the one that is doing the work, that this drop in temperature is the thing that is driving the work? So it was really, really interesting to kind of try to put myself in his headspace of like, ⁓ but we don't know about energy, but we don't know about it.

Jyoti Asundi (27:27)
Yeah, but that's genius to be able to make that connection.

Aarati Asundi (27:32)
Somehow, but he did not- since he didn't know about energy. He didn't know that heat was being transformed at all. He actually thought that heat was a separate kind of entity that did the work. It wasn't heat Transforming into something it was heat was...

Jyoti Asundi (27:51)
Heat itself.

Aarati Asundi (27:51)
...its own thing that was doing the work. Yeah.

Jyoti Asundi (27:53)
Yes, doing the actual work. Yeah, yes.

Aarati Asundi (27:57)
And so actually he thought that heat was this invisible kind of liquid that existed. 

Jyoti Asundi (28:04)
Ha! Inside the steam.

Aarati Asundi (28:06)
Inside the system, basically. Heat is this invisible liquid called caloric. And this was the thing that was doing the work.


Jyoti Asundi (28:16)
Okay.

Aarati Asundi (28:17)
But yeah, you were right. It is actually genius that he figured this out. No other physicist had even hinted that it could be this fall in temperature that is doing the work. 

Jyoti Asundi (28:29)
Yes.

Aarati Asundi (28:30)
And he also proposed that the greater the fall in temperature, the more work could be done.

Jyoti Asundi (28:36)
Correct, correct, the differential, yes.

Aarati Asundi (28:39)
Mm-hmm. So with that understanding, he started to think about what the most perfect, most efficient steam engine might look like. Because steam engines were and still are very inefficient. You burn tons and tons of coal, and then most of that heat that is generated is lost as waste. It's not put towards doing any work.

Jyoti Asundi (29:03)
Of course. Yeah. Yeah you can't really transfer it over to making steam. Correct.

Aarati Asundi (29:10)
Yeah.

And so, Sadi was like, how do I create an engine where 100 % of heat is used to do work?

Jyoti Asundi (29:18)
Yes.

Aarati Asundi (29:19)
So he starts digging into understanding the math behind the relationship between heat and work. And he came up with a theoretically perfect heat engine that worked in a reversible cycle, which is now known as the Carnot cycle.

Jyoti Asundi (29:35)
So hang on, hang Sadi is the one coming up with the Carnot cycle, just for me to get it clear in my head. His father Lazare Carnot and he is Sadi Carnot. And on the Eiffel Tower, you have the name Carnot. Which Carnot are they referring to? 

Aarati Asundi (29:52)
It is Lazare. Yeah. On the Eiffel Tower...

Jyoti Asundi (29:53)
It is?

Aarati Asundi (29:54)
Yeah, I looked into it. Yeah. They're... Yeah, on the Eiffel Tower, they're referring to Lazare Carnot. Yeah.

Jyoti Asundi (30:01)
OK, but then Sadi Carnot was also a force in his own right.

Aarati Asundi (30:07)
Yes. So he comes up Carnot cycle, and the cycle has four stages. So, imagine there's a cylinder that has a piston in it, and between the bottom of the piston and the end of the cylinder, there's some gas. 

Jyoti Asundi (30:24)
Okay.

Aarati Asundi (30:25)
So, in the first stage of Carnot's cycle, you have a process that's called an isothermal expansion. Isothermal means the temperature is being held constant. 

Jyoti Asundi (30:37)
Yes.

Aarati Asundi (30:38)
So the cylinder that has the piston in it is kept next to a reservoir of heat that is being held at a constant temperature. 

Jyoti Asundi (30:48)
Okay.

Aarati Asundi (30:49)
So now this heat is flowing from the reservoir into the cylinder that has the gas and the gas starts to expand. And that pushes the piston outwards or upwards, right? Because as the gas is expanding, you're doing work on the piston. It's pushing the piston.

Jyoti Asundi (31:09)
Correct.

Aarati Asundi (31:11)
This is basically the equation PV=nRT. They knew about that. 

Jyoti Asundi (31:16)
Oh! they did know that. Okay, okay.

Aarati Asundi (31:18)
Yeah. They knew that there's this relationship between pressure and volume and temperature. And so if temperature is being held constant, when volume increases, the pressure has to decrease. And they knew that's how it's working.

Jyoti Asundi (31:31)
Okay. 

Aarati Asundi (31:32)
Heat is added to the system, temperature remains constant, volume is increasing because the gas is pushing the piston outwards. 

Jyoti Asundi (31:41)
Yes.

Aarati Asundi (31:42)
So then in step two, we have what is called an adiabatic expansion. So adiabatic now means that the cylinder is insulated. So no heat is allowed to go in and out of the gas.

Jyoti Asundi (31:55)
Okay, okay.

Aarati Asundi (31:57)
And it's an expansion. So the gas keeps expanding. It keeps pushing the piston outwards because we had that constant temperature volume is increasing, but pressure has to decrease in order for the temperature to be kept the same. And so for that to happen, for pressure to decrease, you have to push the piston out even more. 

Jyoti Asundi (32:19)
Yeah, yeah, yeah.

Aarati Asundi (32:21)
So no heat is being added in step two, but pressure is decreasing and this also causes the gas to cool down. Okay? So then in step three, we have an isothermal compression. again, isothermal means the temperature of the cylinder is being held constant. Now though, the gas is at a slightly cooler temperature than when we started. So a reservoir of a cooler is being held near the cylinder.

Jyoti Asundi (32:52)
Okay.

Aarati Asundi (32:53)
And now the reverse of what was happening in step one is happening in step three.

Jyoti Asundi (32:58)
Yes, the release now.

Aarati Asundi (33:00)
Yeah. So before we were using heat to push the piston outwards and do work. Now we're doing work to push the piston back inwards. So when that happens, it starts to squeeze the gas. But...

Jyoti Asundi (33:17)
Yeah, pressure increasing, yes.

Aarati Asundi (33:17)
...temperature has to be constant. Yeah, but temperature has to be constant. So if pressure is increasing, volume has to decrease, right?

Jyoti Asundi (33:24)
Yes, correct, correct.

Aarati Asundi (33:26)
And now heat is going in the opposite direction into the reservoir. 

Jyoti Asundi (33:30)
Yes, into the reservoir. Yes.

Aarati Asundi (33:33)
Yes. And then finally, step four is called an adiabatic compression. And it's essentially, again, the reverse of what happened in step two. So the cylinder is insulated, so no heat can enter or leave. The piston keeps on squeezing inwards. 

Jyoti Asundi (33:49)
Increasing the pressure.

Aarati Asundi (33:51)
Yeah. And that increases the temperature of the gas. And then we're back to step one.

Jyoti Asundi (33:56)
Yes, so it circles back to step one. Got it.

Aarati Asundi (34:00)
Yeah. 

Jyoti Asundi (34:00)
All right yeah

Aarati Asundi (34:01)
So that's his cycle. And it's important to remember that this is a purely theoretical idea. 

Jyoti Asundi (34:08)
Yes, yes, because how would you actually design a system where there is no loss? 

Aarati Asundi (34:15)
Yes.

Jyoti Asundi (34:15)
Even with the best of insulation and everything, you don't have a system where there is no loss of heat and there is no loss of pressure and all of that. 

Aarati Asundi (34:25)
Yeah, and there's friction and all this other stuff.

Jyoti Asundi (34:27)
Yes, all this other stuff going, so many other forces in play. Makes sense.

Aarati Asundi (34:31)
So somehow or another, you know, heat's gonna leave or, you know, it's not going to be as efficient. So this is very theoretical. And even today, like with this knowledge, knowing about Carnot cycle and everything, our most efficient heat engines are only 40 to 45 % efficient. So less than half of the heat that we put in is actually turned into work.

Jyoti Asundi (34:56)
Being converted into work and all that. Wow, with a 50 % waste, a system with 50 % waste of energy.

Aarati Asundi (35:02)
Yep. More than. Yep. Yeah, but now that we have this ideal, this theoretical ideal that Carnot has come up with, we can use it as a standard to judge the efficiency of heat engines because now we know what 100 % efficient engine in theory would look like.

Jyoti Asundi (35:19)
What can be done in theory. Yes.

Aarati Asundi (35:22)
The other reason that the Carnot cycle is important is because it introduced the idea of reversibility. That if we could ignore and get rid of things like friction and heat loss, then the processes in step one and three are exactly reverse...

Jyoti Asundi (35:39)
Correct.

Aarati Asundi (35:29)
...and the processes in step two and four are exactly reverse.

Jyoti Asundi (35:42)
Right, right. So back and forth, the idea that it can go back and forth, the whole transfer of energy or in this, well, they don't know the idea of energy yet, but the concept of work going back and forth. Yeah. 

Aarati Asundi (35:56)
Yes, exactly. So you have this perfect machine that works in a never-ending cycle, and you could either use it as a heat engine where put in heat and you get out work, or you could use it in the reverse direction as a heat pump by putting in work and getting out heat. 

Jyoti Asundi (36:14)
Wow. Nice. Nice. Nice. The reversibility between the two heat and work. Yes. Yes.

Aarati Asundi (36:19)
Yeah, so that was another big concept that, you know, he laid the foundation for. 

Jyoti Asundi (36:23)
He laid the foundation for that. Okay.

Aarati Asundi (36:27)
Sadi, at his own personal expense, published this theoretical engine in a short book called Reflections on the Motive Power of Fire and Machines, fitted to develop that power and he published this in 1824. Unfortunately, though, his paper was largely ignored his time. There are a couple of reasons maybe for why. The first was that his writing style wasn't very accessible to the steam engineers who might have actually done something with it. It was very math heavy, a lot of theoretical proposals and nothing very practical that could be used directly. And secondly, Sadi himself was a very introverted man. He didn't like publicity, and so he probably wouldn't have pushed it very far either. 

Jyoti Asundi (37:18)
So it's not reaching its targeted audience, really speaking.

Aarati Asundi (37:23)
It's not reaching his targeted audience, and he's also not making a big fuss about it. He's also not trying to...

Jyoti Asundi (37:27)
Okay, yeah, he just, this is more about his own personal quest.

Aarati Asundi (37:32)
Yeah, because I mean, I think we're both actually the same way. Like, if we want people to know about something, we tell the person who we know is an extrovert and let them go run off and...

Jyoti Asundi (37:41)
Yes, let them go publish the thing. Yes, yes, yes.

Aarati Asundi (37:44)
Yeah, but he wasn't even doing that. He wasn't really like, you know... Apparently one of his rules of conduct was, "Say little about what you know and nothing at all about what you don't know."

Jyoti Asundi (37:57)
Hmm. hmm. In fact, it reminds me another great physicist, Dr. Feynman.

Aarati Asundi (38:04)
Oh! Richard Feynman. 

Jyoti Asundi (38:06)
Yeah, and there's a beautiful clip on YouTube about him saying how- he won the Nobel Prize, by the way- and he said the Nobel Prize is not the real prize. The people honoring you, that's not the real prize. The real reward for your work is that discovery, that pushing that boundary, finding out something new. You did something that allowed you to find out something new. And that's the reward. Then whether people recognize you for it, whether they honor you for it, none of it matters. It's all about the actual discovery that I found this out. And now we as humanity know something more about this process than we knew before my work. That's the reward. That's it. That's it. And that's

Aarati Asundi (39:01)
That takes a very big person, because I know if I made some discovery, I'd want everybody to bow down and be like, yes, I'm the one. Yeah.

Jyoti Asundi (39:07)
Yes, yes. No, but those are the people who truly, truly love science.

Aarati Asundi (39:13)
Yeah, those are the great ones. Those are the ones.

Jyoti Asundi (39:15)
Yeah the fact that this discovery helps humanity is their reward.

Aarati Asundi (39:22)
very much like Charles Goodyear we were talking about where he just...

Jyoti Asundi (39:26)
That's right.

Aarati Asundi (39:27)
...you know, gave away his patents, gave away his licenses, and was just like, as long as it helps people, I'm happy enough. 

Jyoti Asundi (39:33)
That's right. That's right. That's the reward.

Aarati Asundi (39:36)
Mm-hmm. Unfortunately though, Sadi did not live long enough to see his work recognized. So he quit his job in the army in 1828, which left him without an income or a pension. Presumably, he continued to work on steam engines. There is one hint that says, that in 1830, there was a directory of alumni from the Polytechnic School in Paris that was published. And it lists Sadi as a maker of steam engines. 

Jyoti Asundi (40:08)
Oh okay, okay.

Aarati Asundi (40:09)
So that's really the only clue that we have as to what he was up after he quit the army in 1828. And then in 1832, Sadi contracted scarlet fever and was sent to a sanatorium just south of Paris. And although he seemed to be getting better, Paris was then struck by an epidemic of cholera.

Jyoti Asundi (40:33)
One disease after the other, that is hard for the body withstand.

Aarati Asundi (40:39)
Yes, and unfortunately he could not. So within days of contracting cholera, Sadi passed away on August 24th, 1832. He was only 36 years old.

Jyoti Asundi (40:53)
Oh that is so young.

Aarati Asundi (40:55)
Yeah. And even more unfortunately for us, for the world, because he had died of cholera, his possessions were considered contaminated. And so most of his notebooks and mathematical papers were destroyed.

Jyoti Asundi (41:08)
No way. Oh no!

Aarati Asundi (41:10)
Yeah. And so we actually lost a lot of his, you know, genius and his thoughts that were probably in those papers.

Jyoti Asundi (41:18)
Oh my God. Oh my God. So a big loss for humanity then. Sadi's death in two, three ways. The fact that he died so young, the fact that he was an introvert so he didn't publish his work, and then the fact that his disease caused the people surrounding him to destroy everything that he had.

Aarati Asundi (41:40)
Yeah. So he did publish his Carnot cycle, that steam engine. He self-published that. And actually the only reason that we really know about Sadi Carnot today is because fortunately, two years after his death in 1834, a classmate of his from the Polytechnic School named Paul Émile Clapeyron translated Sadi's work from French into English...

Jyoti Asundi (42:06)
Okay. 

Aarati Asundi (42:06)
...and published his own book on heat engines that referenced Sadi's work. So by the 1840s and 50s, Clapeyron's translation of Sadi Carnot's work made its way into the hands of some budding physicists, including William Thomson, AKA Lord Kelvin, at the University of Cambridge. This is, of course, before he became known as Lord Kelvin.

Jyoti Asundi (42:33)
Okay.

Aarati Asundi (42:34)
William Thompson refined and expanded on Carnot's works and coined the term "thermodynamics", which encompasses the study of the relationships between heat, work, temperature, and energy.

Jyoti Asundi (42:47)
Nice, nice.

Aarati Asundi (42:48)
And so that is why Sadi Carnot is often called "The Father of Thermodynamics".

Jyoti Asundi (42:54)
Nice.

Aarati Asundi (42:54)
The guy William Thomson who coined the term actually was inspired by Sadi Carnot's work. 

Jyoti Asundi (42:59)
Yes, and drew his understanding of the field from there, yes.

Aarati Asundi (43:06)
Yeah. Sadi's work also made its way into the hands of a young German physicist named Rudolf Clausius. And that is who we're going to be talking about next episode. So stay tuned.

Jyoti Asundi (43:21)
I can't wait. From France to Germany. Ok. This is beautiful. This is beautiful. In spite of all the political turmoil, power switching hands back and forth between monarchy, republic, dictatorship and all that, science is still there, going strong. 

Aarati Asundi (43:39)
Mm-hmm. Science is moving on. Yep.

Jyoti Asundi (43:42)
Science is moving on and truly critical things are happening right at the cusp of the Industrial Revolution. A wonderful story. A foundational story. 

Aarati Asundi (43:54)
Part one, part one. 

Jyoti Asundi (43:54)
I can't wait for part two and part three. I can't wait for it. 

Aarati Asundi (43:58)
Yeah, it's gonna be great. 

Jyoti Asundi (43:59)
Yes, yes, December is going to be a fun month.

Aarati Asundi (44:02)
Yeah, hopefully kept you awake through your jet lag and...

Jyoti Asundi (44:05)
Oh yes, absolutely. This was, yeah, because I had to have my brain cells firing. Yeah, physics is not my forte, so I had to kind of be right on top of it.

Aarati Asundi (44:14)
I think you got it. I think you got it. 

Jyoti Asundi (44:17)
Thank you. 

Aarati Asundi (44:17)
I also tried to make it very easy to understand, although,


Jyoti Asundi (44:19)
No, you are a wonderful storyteller. You break down really very complex topics into understandable bites, which I really appreciate.

Aarati Asundi (44:32)
This one was a little bit easy because it was like, don't have to get into all these like really crazy kinetic energy, potential energy kind of things. 

Jyoti Asundi (44:40)
Mm-hmm, mm-hmm.

Aarati Asundi (44:41)
So I don't have to go into that because he didn't know about that. But then at the same time, it's really hard to understand his....

Jyoti Asundi (44:45)
But that's the foundation. 

Aarati Asundi (44:47)
Yeah, it's really, that's how we're taught it right from the beginning. And so it's really hard for me to understand how he came up with some of these things without knowing this. I'm like, how do you...

Jyoti Asundi (44:58)
Yeah, that's the genius mind, right? That leaps from this known to unknown that requires a genius. It's not that methodical plodding that goes on in most cases. This is like a true leap of faith, a true leap of creativity. 

Aarati Asundi (45:16)
Mm-hmm. So come back for part two in two weeks. 

Jyoti Asundi (45:19)
Yes. Yes. We'll be visiting Rudolf Clausius in Germany next. Perfect.

Aarati Asundi (45:27)
Thanks for listening. If you have a suggestion for a story we should cover or thoughts you want to share about an episode, reach out to us at smartteapodcast.com. You can follow us on Instagram, TikTok, and Blue Sky @smartteapodcast and listen to us on Spotify, Apple Podcasts, YouTube, or wherever you get your podcasts. And leave us a rating or comment. It helps us grow. New episodes are released every other Wednesday. See you next time.