Mr. Lu Xun once said, "When I see short sleeves, I immediately think of white arms, the whole body, the raw organs, the intercourse, hybridization, and illegitimate children." It is only at this level that the imagination of the Chinese people can make such a leap forward (from "Little Miscellaneous Feelings", originally published in the December 17, 1927 issue of the weekly "Silk Language", Vol. 4, No. 1)".

From Lake Como to "Star Wars", from "Star Wars" to aliens, Chen Muwu's performance seems to perfectly confirm Lu Xun's above-mentioned famous words that he has not had time to say.

But in the end, the matter of aliens was definitely not Chen Muwu's sudden explosion of association and whim, but his own deliberate doing.

Zi said: "If you are a threesome, you must have my teacher." ”

Now the situation around Chen Muwu is similar, and among the three of them on the shore of Lake Como, there is also an "expert" who has a lot of experience and achievements in alien research.

This man was certainly not himself, nor Dirac, who "kept his ears open to the outside and read only physics", but another Italian physics professor, Fermi.

Fermi's achievements in physics include the discovery of transuranic elements, but the discovery of slow neutron nuclear fission, the construction of the first nuclear reactor in human history "CP-1 (Chicago Pile 1)", and the training of many successors for the development and inheritance of human physics.

But what many people may not know is that Fermi also studied the topic of "whether aliens exist", and proposed a paradox named after him, "Fermi's paradox".

Fermi was not only a physicist, he was also interested in astronomy.

Otherwise, he would not have become good friends with Hubble after he went to the United States, and helped him advance the feasibility of winning the Nobel Prize in physics for his astronomical achievements.

Also during a walk to lunch, Fermi and several colleagues talked about UFO reports at the time, as well as the possibility of faster-than-light travel, in a casual conversation.

Because it was a small talk, after a few words, everyone's conversation moved to other topics, but after the meal was served, Fermi blurted out this sentence, "But, where is everyone?" ”

The people in his sentence refer to aliens that may exist on other planets in the universe.

Fermi was not the first person to put forward Fermi's paradox, the real first was that at the David Faraday Institute, when Chen Muwu wanted to "accidentally" discover the superconducting magnetic effect, he mentioned to Wells, who was accompanied by Huxley, the pioneer of Sulian spaceflight, Tsiolkovsky.

He once mentioned such an incident implicitly and euphemistically in his unpublished manuscripts.

"Paul, Professor Fermi, I'm not a drinker, I just drank a cup of coffee in the morning, so I'm not talking nonsense.

"I just thought of an interesting thing, why do we humans deny the existence of intelligent beings on other planets in the universe? I think there are only two reasons:

"The first is because if there are such creatures, they will visit the earth;

"The second is that if such civilizations exist, then they will give us some hints of their existence."

Chen Muwu was not shy about the contents of Tsiolkovsky's manuscript, which he had not yet written.

Dirac and Fermi were confused from the beginning, how could Dr. Chen suddenly say something about aliens?

The two of them now looked at the Asians who were talking with a puzzled expression, waiting for Chen Muwu to continue.

And Dr. Chen did not disappoint: "But, does it mean that aliens really don't exist?" I don't think so.

"It only takes a simple calculation to see some contradictions.

"First of all, from astronomical observations, there are billions of stars in the Milky Way that resemble the Sun.

"Then among these stars, there should also be some planets like the Earth, that is, as long as there is enough atmospheric pressure, liquid water can exist on the surface of the planet.

"And many of these stars and their planets are older than the sun. If terrestrial planets also developed like Earth, then there should be intelligent life on some of them that may have developed a long time ago.

"Since 1905, when Dr. Albert Einstein proposed his theory of relativity, people have begun to consider the possibility of interstellar travel. Those planets developed earlier than we did, and they should have developed faster than we did, and perhaps some of these civilizations had already explored ways to travel the stars.

"Even if they could not travel at the speed of light, or even much slower than that, the Milky Way could have been fully traversed in a few million years.

"And many stars like the Sun are billions of years older than the Sun.

"Putting all of the above together, we should have reason to believe that Earth has already been visited by extraterrestrial civilizations, or at least by their probes.

"But there is no convincing evidence on the planet that this has ever happened."

Before, when Chen Muwu hadn't elaborated on his thoughts in detail, the expressions on Dirac and Fermi's faces were unclear.

But now, he had finished all the thoughts in his heart, and the two of them had become dumbfounded.

Dirac even made a rare joke: "Aliens exist, of course aliens exist, aren't you a living example, Chen?" ”

"Paul, don't be kidding."

It is rare to experience humor from this dull Englishman, but in the face of Dirac's accusations, Chen Muwu will categorically not admit it.

He admits that he is an alien one second, and he is estimated to be captured the next second, and maybe the mysterious 51st area in the United States will appear in advance because of his existence.

Besides, I'm not an alien at all, so why should I admit it?

However, Chen Muwu's drunkard didn't mean to drink, and it didn't matter what Dirac said, he had been waiting for Fermi's response.

In addition to his achievements in physical research, Fermi also has another unique skill, that is, his estimation level is particularly high.

Of course, the estimation mentioned here is certainly not a simple and boring question such as "how many meters is the height of this tree" and "how heavy is the mass of this watermelon", but a qualitative and semi-quantitative estimation of the problem through dimensional analysis, using simple and limited known information to calculate those seemingly incalculable quantities, and make reasonable guesses accordingly.

It is only necessary to break down a large problem into several related and easier to solve minor problems, and then estimate them one by one to get an approximate value.

This estimation method is also named after Fermi, and is known as the "Fermi problem".

A classic example is "How many piano tuners are there in Chicago?"

This is a question that Fermi overheard while chatting with his colleagues while presiding over the construction of the Chicago No. 1 Pile at the University of Chicago.

Without specific statistics, the question seemed uncertain, and the conversation quickly turned to something else.

But Fermi doesn't think so, he thinks that he only needs to adopt a few assumptions to divide and conquer the problem.

About nine million people live in Chicago;

In Chicago, on average, there are two people per household;

In about twenty families, one family needs to have a piano tuning done regularly;

Pianos that are regularly tuned need to be tuned once a year;

Each piano tuner tunes the piano for each time, plus the time spent on the road and back, which takes about two hours;

Each piano tuner works eight hours a day, five days a week, or about fifty weeks a year.

With these assumptions in mind, we can roughly extrapolate the number of pianos that need to be tuned in Chicago each year:

(9 million people) / (2 people / family) × (1 piano / 20 × (piano adjusted 1 time/1 year) = 225,000 piano movements per year in Chicago.

I don't know if the number of more than 200,000 is too much or too little for Chicago, a big city in the United States.

But no matter how much, it can say another thing, that is, there are many good five-star citizens in the city of Chicago, and everyone loves to do some hand, especially finger movements, either sitting in front of the piano and playing the piano elegantly, or outputting frantically on the typewriter in their arms.

In the same way, it can be calculated that the average piano tuner tunes 1,000 pianos per year.

If you divide the two numbers above, you can easily get that there are about 225 tuners in Chicago.

Fermi saw this as a pastime outside of his work at building a nuclear reactor, and after a few minutes of thought, he made the same judgment to his colleagues.

Because he is a newcomer who has just arrived in the United States for a few years, and he is in an airborne leadership position, although he has a Nobel Prize, Fermi's position is still not very secure.

So after listening to Fermi's speculation, some people were very unconvinced and went to a famous musical instrument store in Chicago to find the owner and piano tuner to investigate.

After a lot of hard work, he got the data that there were about 290 piano tuners in Chicago, which was not much different from Fermi's estimate in a few minutes.

Of course, Fermi's most remarkable estimate was not the elegant but boring question of a Chicago piano tuner.

That was on the night of July 16, 1945, after the most famous "Trinity" atomic bomb experiment was successfully detonated at the range of the Los Alamos Laboratory in New Mexico.

As Oppenheimer was busy uttering his famous phrase, "Now I am the Grim Reaper, the destroyer of the world," Fermi, who was also at the observation site near the atomic bomb site, did something else.

Holding a handful of scraps of paper that had been prepared long ago, he suddenly jumped up and threw them into the air, and the air waves generated by the atomic bomb explosion quickly swept away the pieces of paper.

Fermi ran a few steps on the heel, estimating the yield of a nuclear explosion based on the distance the piece of paper was rolled out.

He estimated that the explosion would release the equivalent of 10,000 tons of TNT.

The official result was 25,000 tons of TNT.

In other words, the difference between Fermi's estimates and the official results is less than ten times, and the two are in the same order of magnitude.

Chen Muwu suddenly brought up the question of whether this alien exists or not by Lake Como after seeing Fermi today, in order to throw bricks and lead to jade, so that he could also make a qualitative and semi-quantitative estimate of this.

Historically, it was Fermi who estimated this matter and obtained a "number of high-IQ civilizations on other planets in the galaxy that may have come into contact with us", and then found that there was a contradiction between the overestimation of the existence of extraterrestrial civilizations and the lack of relevant evidence on Earth, so there was the "Fermi Paradox" named after him.

Sure enough, after listening to Chen Muwu's description of the question and Dirac's "humorous" answer, Fermi fell into a deep state of thought.

Chen Muwu was looking forward to his answer, and looking at the "tour guide" standing still, Dirac only felt crazy again.

Dr. Chen's mind is occasionally a little wild, so how can anyone really think seriously about the obvious joke he asks about aliens?

It is no wonder that after modern times, the level of physics in Italy declined rapidly.

Even this kind of rectum can be a professor, doesn't that mean something?

Chen Muwu waited expectantly for Fermi's response to this question, but after a few minutes passed, the other party still did not make progress.

It can be seen that Fermi is indeed thinking about the problem, but maybe Chen Muwu is not facing Fermi's complete body, and the calculation that is not worth mentioning for him in the future is a somewhat difficult difficulty to overcome in front of the current Fermi.

In that case, there is no need to wait any longer.

Dirac, who wanted to enjoy the mountains and rivers, had just been delayed at the front desk of the hotel, and Chen Muwu didn't want his good friend to continue to stay in place and waste time because of his own problems.

"Forget it, Professor Fermi, this is just my unintentional words, please don't take it too seriously. Let's continue to explore the great scenery around Lake Como, whether aliens exist or not, it doesn't affect our lives. ”

But Fermi was like a tendon in Dirac's eyes, and the expression on his face was still serious: "Dr. Chen, I think you have a really good question. It's interesting to me at least, and I'd like to look into it when I get back. ”

Chen Muwu can't control other people's brains to think about something, since Fermi wants to continue researching, let him go.

The alien question he raised was not useless, at least since then, Chen Muwu and Dirac have never heard some lame words in their ears, and they can finally quietly enjoy the lake and mountains of Lake Como and the Alps.

This year's Nobel Prize in Physics was announced, and unfortunately, none of the book's readers won the prize.

Just kidding.

As an aside, it's like a bunch of condensed matter physics predictions in advance......

(End of chapter)