"Why?" Many people can't help but ask, "This doesn't violate the law of conservation of energy." ”

"Yes, the second type of perpetual motion machine does not violate the law of conservation of energy, but it violates another law." Ma Whistle paused, "This law that has not yet been clarified is the subject of my talk today – the second law of thermodynamics. ”

He said "not yet known", not "not yet discovered".

Compared to other disciplines, the development of thermodynamics seems to be closer to gradual. For example, the law of conservation of energy, which some scientists have been vaguely aware of for a long time, has only been clarified in recent years.

The second law of thermodynamics is also vaguely aware of the existence of some keen physicists, but they can't say it clearly, through a thin layer of window paper.

At this time, physicists only had to go back and carefully examine Carnot's theorem to realize the existence of the second law of thermodynamics.

In fact, in the original history, two or three years later, after revisiting Carnot's theorem, Clausius and Kelvin would each give their understanding of this law.

Now, Clausius and Kelvin clearly don't have that opportunity, and the horse whistle will explain the second law of thermodynamics thoroughly.

"The second law?" Faraday couldn't help but say, "Sounds interesting. ”

"The first law tells us that energy is not born and cannot be destroyed, but can only be transferred, while the second law talks about the rules of energy transfer – energy cannot be transferred at will," Ma Whistle said. ”

"Nature always restricts us more than we think." He interjected.

"The rule of this kind, to put it bluntly, is that it is impossible to transfer heat from a cold object to a hot object without causing other changes."

"After knowing the first law of thermodynamics, we look back at Carnot's theorem, and it is not difficult to find that the second law of thermodynamics is actually the premise of Carnot's theorem, and only if it is true, Carnot's theorem can be established......"

There was a lot of discussion in the audience.

The law of conservation of energy tells people that heat and work are equivalent and can be converted into each other, but Carnot's theorem describes that heat and work are not exactly the same, and work can be completely converted into heat, but not vice versa.

If both the law of conservation of energy and Carnot's theorem are correct, then it is clear that another law is needed to support the system, the second law of thermodynamics, which states that energy can be converted into each other, but it is limited by direction.

This principle is not complicated, and many physicists have understood it through Ma Whistle's statement.

"I see!"

"That's right, without this law, Carnot's theorem wouldn't have been true."

"This is really significant, and it can definitely be regarded as the second most important law of thermodynamics."

"Damn, I noticed this issue a while ago, but I didn't even think about it!" A few physicists were annoyed, "Oh God, what am I missing!" ”

"He's such a lucky guy!" Some people looked at the horse whistle on the stage and couldn't help but say sourly.

Apparently, they thought that the discovery of the second law of thermodynamics was due to luck.

That's right, the laws of physics described in such a rough way are really not technical and unconvincing.

"Of course, this is only a crude description, and it looks less like a law of physics than a philosophical maxim. ”

"Like Newton's writings, physics is a combination of philosophy and mathematics...... Therefore, in order for it to become a true law of physics, we need to elaborate it in mathematical language, and we are going to introduce a concept that can be calculated - entropy. ”

"Entropy?" The audience was confused and tried to repeat the awkward name.

Instead of using the English name of entropy known to him in his previous life, Ma Whistle used the Apache word for "primordial calamity", a religious term for the Spiritual Oracle, which the British would naturally find awkward.

"It's an Apache word that means 'primordial tribulation,' similar to original sin." "In fact, it's also a religious word, and my people have given it some religious concepts," he explained. ”

"What religion do the Apache people follow?" People can't help but be curious.

So Ma Whistle first gave a general introduction to the Spiritual Oracle Sect, and then changed the conversation: "Of course, I am not very religious advocate, and I have been advising people to follow a more rational way of thinking...... In any case, at least here, at a physics conference, let's talk less about religion. ”

There is no doubt that the religion described by the horse whistle aroused people's curiosity, and that was what he wanted.

But he didn't say much, after all, he couldn't be a missionary, and this was not the occasion to preach.

"Here, primordial calamity, or entropy, is a purely physical concept. The connotation of entropy is complex, and my understanding of it has been constantly revised from thinking about it a few years ago until now. ”

"First, let's review Kano's work."

With that, the horse whistle turned around again and wrote some formulas on the blackboard behind the podium.

"We can differentiate arbitrary thermal cycling processes and reduce them to thermal cycling processes that are superimposed by a large number of Carnot heat engines. Next, based on Kano's conclusions, we get this result......"

For many of the physicists in this room, these are familiar contents, and it is not difficult to understand.

Except, of course, for those physicists who don't understand calculus – there are such physicists.

For example, Faraday's calculus level is very questionable, and there is a high probability that he does not understand it.

Faraday came from a poor background, had little formal education, and was far from being a physicist who was proficient in mathematics, and his work was mostly in the experimental field, and it was his excellent hands-on ability and physical intuition that made him a first-rate physicist.

It can be said that among physicists of the same rank, Faraday's level of mathematics is probably the worst.

Mathematical shortcomings were also the reason why he was unable to take the study of electromagnetism further, but it was not long before the young and talented Maxwell would complete this mission for him.

After a few moments, Ma Whistle circled one of the variables in the formula and said, "This variable, or state function, is what I call 'entropy'." ”

The variable he circled was naturally Clausius entropy, which was also the earliest definition of "entropy".

“…… Now, it is not difficult to find that for an isolated system, its entropy is an irreducible value, and the entropy change must be greater than or equal to zero. The inability to reduce entropy reflects the directionality of energy transformation. ”

"The inequality here is the mathematical expression of the second law of thermodynamics." He pointed to the Clausius inequality on the blackboard.

After this operation, the physicists present had to be convinced.

If it is said that the discovery of the second law of thermodynamics can be achieved by luck, but extracting mathematical expressions from this law cannot be done without a solid foundation.

"Entropy...... I think it won't be long before the word appears in all textbooks. Thomson said with emotion.

"A great discovery!" Faraday couldn't help but applaud that, although he couldn't understand the process of mathematical derivation, with his extraordinary physical intuition, he undoubtedly felt the wonder of entropy.

"Papapa-" As he applauded, the other physicists applauded.

"Thank you." Whistle smiled and responded politely.

However, then he restrained his smile and changed his words: "However, this is not the result of my final thinking, and it is far from the true appearance of the second law of thermodynamics. ”

The applause quickly subsided, and the people looked at him in silence and amazement.

In their opinion, the lecture just now is already a model of physics, but the horse whistle tells them that this is not the result?

Facing everyone's puzzled eyes, Ma Whistle looked calm and said slowly: "We have mathematically expressed the second law of thermodynamics, but I think you have all noticed that the concept of 'entropy' does not seem to have an actual physical meaning to correspond to it. ”

"This question has been bothering me for a long time. After thinking about it for a long time, I came up with a relatively satisfactory answer, and it was because of this answer that I named the variable 'entropy' - the Apache word for 'primordial calamity'. ”

After a pause, Ma Whistle added: "Next, let's explore the nature of 'entropy'. ”