Reborn and become a Great Scientist

Chapter 344 83 The first artificial nuclear fusion

Anyone who can leave their name in the history of science should not be looked down upon for their own ability and level.

Take a mistake in the history of optics, the Poisson spot, as an example. Fresnel proposed at a meeting of the French Academy of Sciences that light can be diffracted.

In order to refute his "extremely absurd" view and maintain the stable status of the particle theory of light, Poisson, a mathematics professor at the Sorbonne University, tried his best to find counterexamples and use irrefutable experimental phenomena to convince those who insist on light. Fresnel was speechless when he said this "heretical theory".

He racked his brains and finally came up with a disk experiment: if light passes through an opaque disk and can be diffracted, then a bright spot should appear in the center of the disk's shadow at a certain distance from the disk.

This was an absolutely unacceptable theory to most physicists at the time who believed that light was a particle and that light propagated along straight lines in a uniform medium.

The believers in these particle theories don't even hesitate to do experiments, because the calculation results are completely contrary to their intuition and the facts they insist on.

Poisson wanted to use this to prove that Fresnel's diffraction theory was wrong, but he did not expect that also at the French Academy of Sciences, there was a physicist named Arago who did not believe in evil.

For this simple optical experiment, the experimental equipment is not complicated to prepare.

Arago quickly found the bright spot located in the center of the disk's shadow, which was scorned by most physicists in the Academy of Sciences. He demonstrated this experimental phenomenon at a meeting of the French Academy of Sciences, which not only made Poisson and others Many scientists were speechless and proved with facts that light can be diffracted during propagation, so it should be a wave.

The bright spot in the center of the disc's shadow was not named a Fresnel spot, nor was it named after the Arago who completed the experiment. Instead, it was conventionally called a "Poisson spot", which is probably a kind of Satire.

Looking at a record of the history of physics alone, Professor Poisson, who held a high position in the French Academy of Sciences for a few years, is undoubtedly the biggest villain in the story, a representative of self-reliance without pursuing progress.

But in fact, let alone Poisson's contribution to mathematics as a mathematician, but only his contribution to physics, it is definitely not a joke about Poisson's bright spot, but a mathematical symbol - Poisson bracket.

Poisson brackets play an important role in mathematics, and also play an important role in Hamiltonian mechanics of analytical mechanics.

A century after Poisson proposed the Poisson bracket, this mathematical notation is still shining brightly in quantum mechanics, which seems to have nothing to do with him.

Dirac discovered that the correspondence between mechanical quantities in quantum mechanics is very similar to the Poisson bracket in Hamiltonian mechanics. Based on this, he invented the quantum Poisson bracket, which is the so-called commutator.

Poisson, who cannot be bypassed in the history of optics and physics because of being slapped in the face, has such an academic level, let alone Eddington, who is very famous in modern physics.

When Eddington is mentioned, the titles given to him are Einstein's best friend and staunchest supporter in the UK, the astronomer who first proved the general theory of relativity through solar eclipse observations.

However, Eddington’s contribution to physics goes far beyond that, but the reason why people always have stereotypes like the above when they mention him is because Einstein and the theory of relativity are so famous, whether they really understand it or not. You know, people always like to chat about this issue.

Eddington was the first to think from the mass-energy equation and the mass difference between four hydrogen atoms and one helium atom that mass loss can be converted into energy to continuously charge the sun's combustion. This is enough to show him. What a keen intuition I have for physics.

It's a pity that when Eddington proposed that the source of the sun's energy is nuclear fusion, it was a bit untimely.

Because the physicists and chemists at that time only knew that there were hydrogen atoms and helium atoms in the universe, but they did not know that these two elements also had their own isotopes.

Therefore, in Eddington's calculations, although it was calculated that the nuclear reaction in which four hydrogen nuclei fuse into one helium nucleus can provide enough energy to power the sun, it could not explain the conditions for the occurrence of this nuclear fusion reaction. That is to say, the temperature is much higher than the actual temperature of the sun observed in reality.

As Eddington guessed, it is true that four hydrogen nuclei fuse into one helium nucleus, but this nuclear fusion reaction is not completed in one step, but is divided into several steps.

The first step is the fusion of two hydrogen nuclei into a deuterium nucleus, simultaneously releasing a positron and an electron neutrino:

H+H→D+e+ν.

The second step of the nuclear reaction is that deuterium, the product of the first step, continues to fuse with hydrogen nuclei to generate helium-3, and at the same time releases a photon:
D+H→He+γ.

The third step of the reaction is the reaction that ultimately generates helium nuclei. The main way is that two helium-3 fuse to generate one helium-4 and two hydrogen atoms:

He+He→He+Ｈ+Ｈ.

Of course, in the third step, there are other ways for lithium, beryllium and boron to participate in the reaction, and the entire cycle may also be a carbon-nitrogen-oxygen cycle involving carbon, nitrogen, and oxygen.

But the latter two nuclear reactions account for a relatively small proportion in the sun, and the most important ones are the three steps mentioned above.

In general, when these three-step reactions are combined, six hydrogen nuclei are fused into one helium nucleus, and two more hydrogen nuclei are released at the same time.

Subtracting two hydrogen nuclei from both sides of the reaction at the same time results in the fusion of four hydrogen nuclei into one helium nucleus, which is exactly the same as the nuclear reaction equation Eddington originally guessed.

But the only difference between the two is that the nuclear reaction proposed by Eddington is completed in one step, while the real nuclear reaction in the sun is divided into several steps.

In this way, the requirements for the reaction environment are no longer so stringent, and there will no longer be a contradiction between the theoretical temperature and the actual temperature that differs by several orders of magnitude.

The reason why Eddington failed to think further that the nuclear fusion reaction in the sun proceeds in steps is not because of his lack of imagination, but because when he proposed this theory, both deuterium and helium-3 It has not yet been discovered by scientists.

In the original space and time, as the first of the three major discoveries in nuclear physics in 1932, deuterium was discovered by Yuri of the United States in the same year.

Helium-3 was discovered even later than deuterium. It was not only based on Yuri's discovery of deuterium, but also had to wait until the particle accelerator was invented.

Mark Oliphant, an Australian student in the Cavendish Laboratory, used the accelerated particle accelerator in the Cockcroft-type particle accelerator invented by Cockcroft and Walter in 1934. Deuterons bombarded hydrogen, and the trajectory of helium-3 nuclei was photographed for the first time in a cloud chamber. ——No matter in which time and space, with the advent of particle accelerators and deuteron nuclei, Rutherford would always think about accelerating hydrogen nuclei to deuterium, or accelerating deuterium nuclei to hydrogen atoms.

The difference is that Chen Muwu withstood the pressure and did not do this experiment.

As a new student, Olyphant followed the instructions completely and completed the experiment of discovering helium-3.

In addition, the nuclear reaction in which two deuterium and hydrogen nuclei collided to generate helium-3 nuclei completed by Olyphant in the Cavendish Laboratory was also the first successful nuclear fusion in the history of human physics.

It was not until 1939 that helium-3 was separated from helium gas for the first time.

A clever woman cannot make a meal without rice, and Eddington would never have been able to directly guess the correct equation for nuclear reactions in the sun without knowing the existence of deuterium and helium-3.

People have always been curious about where the endless energy in the sun comes from. This is why Bohr proposed that energy is not conserved in the sun.

Later, even though the particle accelerator had been invented for more than ten years, human physicists still couldn't figure out the conditions under which nuclear fusion reactions should occur.

In 1943, more than a year had passed since Pearl Harbor. The United States and Japan were at war in the Pacific, and the "Manhattan Project" to develop the atomic bomb was also in full swing in the United States.

At this time, Oppenheimer, the physics chief of the Manhattan Project, was still struggling with a very serious problem.

Atomic bomb explosions rely on nuclear fission, but in the high temperature and pressure generated by the release of energy after nuclear fission, hydrogen and other lighter nuclei are likely to fuse into nuclei with greater mass and release a large amount of energy.

- Just like what happens all the time in the sun, hydrogen fuses to become deuterium, and hydrogen and deuterium fuse to form helium-3.

The earth is divided into three parts ocean and seven parts land. There are many more deuterium atoms in sea water than in air.

Also, helium in the air is not very stable, but is slightly more stable than deuterium in sea water.

What Oppenheimer is worried about is that if after the atomic bomb explodes, a chain reaction occurs that is beyond human control, hydrogen changes to deuterium, hydrogen and deuterium change to helium-3... and so on, the water in the ocean and the air in the atmosphere All will be ignited, and the earth will fall into endless burning and eventually destroy.

Oppenheimer himself did not dare to bear such serious consequences. He could only go to Bole Compton, who suggested to the military that he should be the general manager of physics, to discuss this possible matter.

Both of them are very pessimistic about this, and feel that rather than letting the adventure activities they personally participate in send all humans on the earth into the abyss of eternal destruction, it is better to passively accept the enslavement notice of NaC.

However, the military was pressing hard. Einstein and other scientists jointly wrote a letter to Roosevelt, saying that Germany was also stepping up its development of the atomic bomb, a mass murderer that did not respect martial ethics.

They had to get ahead of the Germans and produce the key that might open the door to hell.

In the end, it was Compton who made the decision. If the calculated results confirmed that the probability of the earth being destroyed by an atomic bomb exceeded [-] per thousand, then he would stop the Manhattan Project.

Fortunately, in the end, Compton's calculation results were lower than the value set by Compton. The Manhattan Project could continue smoothly, and I was lucky enough to experience what "thunder, rain, and dew are all a blessing from the Lord" in my childhood.

By 1943, the world's top physicists were still worried about whether nuclear fusion would destroy the earth. So in 1927, the American astronomer named Hervey was unreasonably worried that the sun would one day explode. .

Seeing Chen Muwu sitting opposite him with a solemn expression and saying nothing, the Times reporter quietly wrote something in his notebook.

"After I raised this question, China Chen from Cambridge University said nothing and fell into deep thinking for a long time. It seemed that the problem of solar explosion was very serious and made him very entangled."

After the reporter wrote this paragraph, he planned to remind Chen Muwu aloud that after all, he came to Cambridge this time with a certain political mission.

The British people cannot be allowed to panic just because an American astronomer said "possible". They start to panic all day long, worrying about the end of the world every day.

What the British government means is that astronomers must stand up at this time. Regardless of whether their speech is correct or wrong, it must have the effect of stabilizing people's hearts.

That’s why the interviews in Cambridge were handed over to The Times, which to a certain extent represents the government’s voice. Those who went to the Royal Observatory in Greenwich were also other reporters from the newspaper.

The reporter who came to Cambridge even made a plan to work hard on reporting to help Chen Muwu look decent if he said something that was not conducive to stabilizing public sentiment.

"Dr. Chen..."

"Ah, ah!" Chen Muwu raised his head when he heard the call, with an apology on his face, "I'm sorry, Mr. Reporter, I was thinking about some issues just now, and I neglected you inadvertently.

"You're here to ask my opinion on the American astronomer's suggestion that the sun may explode at any time, right?
"My point of view on this is that this matter is completely nonsense. The sun above our heads is very stable. Even if a small island on our planet in the Pacific explodes, there is no possibility of the sun exploding.

"I think the astronomer may have misjudged the source of the sun's energy for the entire solar system.

"In the early 20s, Professor Eddington, director of the Cambridge University Observatory, was the first to propose that nuclear fusion might be going on inside the sun, with four hydrogen nuclei fused into one helium nucleus, and the reduced mass converted into energy. But because This reaction temperature is much higher than the temperature of the sun, so it is doubted and denied by other physicists.

"A few years ago, several colleagues and I discovered the hydrogen isotope deuterium in the David Faraday Laboratory in London. So the nuclear reaction in the sun is probably not completed in one step, but is completed in several steps? For example, Say two hydrogen nuclei fuse to produce a deuterium nucleus, and then the two deuterium nuclei further fuse to produce a helium nucleus? In this way, will the temperature decrease?
"Scientific research cannot rely solely on guesswork. I plan to simulate possible nuclear fusion reactions in the sun in the Cavendish Laboratory as soon as possible, and then announce the results to the public as soon as possible, using experimental facts to dispel everyone's recent fears. .”

(End of this chapter)