Reborn and become a Great Scientist

Chapter 89 37 Poor Cavendish

After waiting for Rutherford to lose his temper, Chen Muwu responded sincerely: "Director, please allow me to finish my sentence.

"In our country, there is a famous saying called 'experiment is the only criterion to test whether the theory is correct or not'."

In order to avoid being lucky by the god of river crabs, Chen Muwu also thoughtfully changed a few words in it.

"If Millikan hadn't done the precise photoelectric effect experiment, and Peter and Blackett had photographed the trajectories of recoil electrons in the cloud chamber, then people would never have believed that light, which has always been considered as an electromagnetic wave , will actually have the properties of particles.

"Similarly, regarding the conjecture about whether electrons are a kind of wave, you only need to design an experiment as you said to test whether the conjecture is correct or not.

"The most convenient way to verify whether an electron is a wave is to see if it can produce interference or diffraction phenomena like light."

Obviously, Rutherford had listened to Chen Muwu's words: "'Experiment is the only criterion for testing whether a theory is correct or not', um...Chen, who said this sentence? He said it really well! I I think they can make this sentence into a slogan and hang it in the Cavendish laboratory."

Chen Muwu's head was full of black lines, why Rutherford was only interested in this sentence!
"Uh... Director, this is the result of brainstorming by the working people."

Rutherford thought quietly for a while, and even picked up Chen Muwu's pen and draft paper from the table, and made a few calculations on them.

Then he continued to ask: "If electrons are really a kind of wave, according to the formula you gave, even electrons with an energy of only one electron volt, the corresponding wavelength is only about one nanometer.

"This value is much smaller than the wavelength of visible light, so it cannot easily obtain interference or diffraction patterns after passing through double or single slits like visible light... Wait!
"Looking at it this way, the wavelength of an electron with an energy of one electron volt should be on the same order of magnitude as the wavelength of X-rays. That is to say, it is completely possible to let electrons enter the crystal like the crystal diffraction experiment of X-rays. See if there is a diffraction pattern on the photographic film to detect whether the electron is a wave or not?"

Seeing the calm expression on Chen Muwu's face sitting firmly on the Diaoyutai, Rutherford finally realized: "Chen, have you thought about this experiment for a long time?"

Chen Muwu smiled without saying a word, then nodded.

"I knew it," the increasingly excited Rutherford even put his hands on Chen Muwu's shoulders, "I knew it, Chen, you are a genius!"

After all, he was still a young man in his 20s, and Rutherford's compliment made Chen Muwu feel a little ecstatic.

But before the latter had time to be happy for a long time, the former poured a ladle of cold water on his head again.

"Unfortunately, Chen, I'm sorry," Rutherford smoked a pipe and calmed down, "I'm afraid I won't let you do this experiment, I mean, at least in the recent period of time, you I can't do this experiment yet."

Ok?
Hearing the word "sorry", Chen Muwu felt that something was wrong. After the whole content of Rutherford's words, Chen Muwu felt that his head suddenly became bigger.

"Director, why is this?"

Unconsciously, there was anxiety in his tone.

Rutherford said with a look of regret: "To be honest, Chen, although you have described electronic fluctuations in a hype, but this new electronic theory you put forward, or it should be called conjecture, has not convinced me. I am pessimistic about the success of this experiment and have little confidence.

"It can't be that every time you put forward a theory for granted, I have to arrange a new experiment, right?

"You know, doing an experiment is not something you can do with a flash of inspiration and a pat on the head. If you want to do a good experiment, you must be fully prepared, and you must have the persistence to endure repeated failures. And the powerful spirit of repeating the previous futile work again and again.

"Furthermore, the electron diffraction experiment you mentioned is not the same as the previous gamma ray scattering experiment. There are too many aspects that require money."

"But," Chen Muwu wanted to argue for himself, he really didn't want the electron diffraction experiment to be aborted like this, "but director, you don't need any special equipment for this experiment? Electron beam cathode ray tube, an accelerating electric field, and then a metal crystal, and finally a few photosensitive films are enough!"

But Rutherford still shook his head stubbornly: "Chen, you have committed a common problem of people your age, that is, you are too young and naive.

"Do you think that doing this experiment is similar to doing X-ray crystal scattering? You only need to prepare the ray source, crystal, and photographic film, and put them in the corresponding positions to get the corresponding diffraction pattern?"

Chen Muwu nodded.

"That's what I thought at first, so I think you've come up with a genius idea.

"However, after I calmed down, I realized that electrons are not gamma rays after all. Their penetrating power is not strong, and they cannot propagate unimpeded in the air like electromagnetic waves. Molecules collide and ionize, which can have a big impact on the experiment.

"However, if you want to do your experiment, you must keep the electron beam, diffraction crystal and photographic film in a high vacuum state, and all of them are indispensable. And this level of vacuum is not yet reached in our laboratory.

"Cavendish's current vacuum pump is still the Sprenger mercury pump made by Sir Thomson and Aston more than ten years ago. The vacuum it can provide is far from enough for your electrons. The free path is so long that it can be emitted from the cathode through the acceleration of the potential difference and the diffraction of the crystal, and finally shoot onto the photographic film.

"I heard that the American General Electric Company invented a vacuum pump with more advanced technology, but unfortunately, we can't afford it!

"If we are as rich as the Yankees, or even half as rich as them, then I will never refuse your proposal for an experiment.

"But it's almost the end of the year, and the fall semester of the new academic year is about to start, and there will be a few new students entering the laboratory. Cavendish really doesn't have much money in his books to allow you to buy that vacuum pump. It's an experiment."

When money was mentioned, the expression on Rutherford's face became more and more helpless.

From the experimental environment and experimental equipment, Chen Muwu has seen the poverty of the Cavendish Laboratory.

But he didn't expect the actual situation to be even poorer than what he saw.

With a budget of more than 9000 pounds a year, it was spent in August and began to be carefully calculated. No wonder Rutherford said "because we have no money, so we have to think".

It seems that this is not because of his modesty, but because he really has no money!
Ugh!
……

After Rutherford left the meeting room, Chen Muwu gradually calmed down.

The director's words are not rough, every word he said is the truth.

Regarding electron diffraction, Chen Muwu only saw the diffraction patterns of Davidson, Ge Mo and Jr. Thomson in textbooks when he was studying quantum mechanics, but he did not go into details about how these two experiments were done. from.

That's why he took electrons for granted as electromagnetic waves like X-rays, and completely ignored the fact that electrons exposed to air would collide with air molecules, produce ionization, and affect the experimental results.

Jiang was still old and hot, and after only a few minutes of thinking, Rutherford was able to point out Chen Muwu's problem to the point.

After such a quick call from him, Chen Muwu suddenly realized that he had really thought too little.

He felt that after his time travel, because everything went so smoothly, he couldn't help but feel a little swayed recently.

Being scolded by Rutherford also sounded a wake-up call for Chen Muwu, that is, even though he knows about the future scientific development, he must guard against arrogance and impetuosity in scientific research and be down-to-earth.

In the original time and space, after de Broglie proposed the concept of matter waves, when Langevin asked him how to verify the existence of matter waves, de Broglie, like Chen Muwu, proposed the experiment of electron diffraction.

But one reason is that people think that this French aristocrat is just a newcomer in physics who has not even obtained a Ph.D., and his statement is too unreasonable. Electrons are electrons and cannot be waves.

The second is that it was really difficult to achieve the degree of vacuum that allowed electrons to successfully diffract in crystals on the European continent at that time.

So even though de Broglie has given the experimental method of crystal diffraction, no one is willing to do this experiment.

Even in the private laboratory of his elder brother, Maurice de Broglie, the sixth Duke of de Broglie, no one was willing to pay attention to the little prince's nonsense.

Collinden Davidson and Lester Germer, who first discovered crystal diffraction of electron beams, had already started to do related experiments before de Broglie proposed the concept of matter waves in 1924.

It's just that their experiments were not originally intended to prove the existence of matter waves in a prophetic way, but only to detect the impact of electron bombardment on metals.

During this period, although Davidson published several experimental results, he had no idea that de Broglie, who was far away in Europe, had already proposed the idea of ​​matter waves.

Until 1926, Davidson married again and took his second wife to England for honeymoon. By chance, he attended a local physics meeting and found that Born was holding the experimental data he had published a few years ago. Talking about de Broglie's matter wave, Davidson realized that there is a concept of matter wave.

Since then, Davidson, who returned to the United States, and Thomson Jr., who participated in this meeting, used low-speed electrons and high-speed electrons in their respective laboratories to design electron beam crystal diffraction that can verify the matter wave theory. experiments, and finally achieved positive experimental results.

If Davidson hadn’t done the experiment of electron bombardment on the metal surface by accident, and Born happened to see the result of this experiment and announced it at the conference, then maybe people’s experimental verification of matter waves is still far away.

This is enough to show how unpopular de Broglie's matter wave theory was when it was first proposed.

It has been eighteen or nineteen years since the photon theory was put forward, and finally confirmed to exist after the experimental verification of the photoelectric effect and the Compton effect.

People are just now believing that light, which has long been thought to be a wave, is also a particle.

Now I want them to believe that the electron, which is originally a kind of particle, is also a kind of wave. Of course, there will be very strong resistance.

Although Rutherford reprimanded Chen Muwu, and then rejected his experiment request, it is estimated that compared with the cynicism and ridicule that De Broglie received at the beginning, the attitude of the director of the Cavendish experiment can be regarded as good. Very amiable!

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(End of this chapter)