curiosity is human nature. If you want to select some questions that have been wondering since the birth of human beings, then the question "How does the sun shine in ? " can definitely be selected. As of now, the question of
may be a bit naive. Basically, students who have passed through middle school can know the answer : nuclear fusion . Yes, the sun's light comes from nuclear fusion, but these simple three words are not so easy to obtain. They were first proposed by Arthur Eddington in the 1920s (yes, it is the one who ruthlessly suppressed Chandrasekha in the previous article), but the theory at that time was still very rough.
Arthur.Eddington
Today's article will not focus on explaining the specific situation of solar nuclear fusion, but rather introduces a very critical step in this process - "tunnel effect" (a noun in quantum theory). By what coincidence is it associated with solar nuclear fusion? The story has to start from the 20th century.
The famous British astronomer Herschel (the one who discovered Uranus), he proposed that the sun may be solid. "The light we see on the earth is because the sun has a layer of hot and dazzling atmosphere, and under the atmosphere, it may be a low-temperature solid-state planet." The evidence of his conclusion is the sun's sunspot , who believes that the sun represents the low-temperature surface revealed in the gaps in the atmosphere. This conclusion, which seems to be a little laughing now, just reflects how shallow the scientists' understanding of the sun was in that era. The idea of
was quickly overturned because it does not explain where the energy to maintain atmospheric high temperatures comes from. So, a variety of answers are coming around the core of how to maintain high temperatures. One of them is the most widely circulated, which is believed to be a giant briquette (this history has been mentioned in many popular science articles).
Because of the continuous combustion of coal balls, the sun can continue to heat and shine. At the same time, this also shows that the sun has a lifespan, that is, there will always be a day after burning. So scientists began to calculate this time. This calculation is amazing. Coal balls of the size of the sun can burn for more than a thousand years or less than two thousand years.
This conclusion is contrary to the nebula hypothesis at that time (nebula hypothesis proposed by Kant and Laplace), because the nebula hypothesis believes that the earth and the sun are almost formed together, with similar age, and the estimated life span of the earth at that time ranged from tens of millions to hundreds of millions of years, but it is definitely not only a few thousand years (this view of thousands of years is in line with the religious view of the time)
Nebula hypothesis
In addition to the above hypothesis, there are also such as "the theory of continuous fall of meteorites causing luminescence", "the theory of continuous contraction of its own radius maintaining luminosity", etc., but none of these are all The exception is that the probability of occurrence and duration cannot conform to the current situation of the earth and the sun in terms of possible occurrence probability and duration. Time came to the 1920s. At that time, the special and general relativity theory of Einstein had been born. People also discovered the transformation of atomic nucleus . So the famous astronomer Arthur Eddington stood up. He believed that the stable luminous and heating of the sun was caused by nuclear fusion inside it. Thanks to the support of Einstein's mass and energy equation, the fusion energy inside the sun can ensure that it continues to react for billions or even tens of billions of years (at that time, the mass of the sun, the surface radiation power, etc. were already known). Although
has met time, it has still been opposed by many scientists. The most core point is: During nuclear fusion, the protons and in different nuclei need to combine with each other to form a new nucleus. So how do protons overcome the powerful coulomb force ? To overcome it, you must have extremely high kinetic energy, which means extremely high temperature, at least to hundreds of millions of degrees, which is impossible for this temperature to occur relative to the sun's own situation.
Although Eddington's nuclear fusion hypothesis seems to be correct now, since human research on atomic scale laws was in a period of rapid development at that time, Eddington could not give detailed process changes.
, but it doesn't matter, someone soon rescued this difficulty.
1928, Gamov used the quantum mechanics theory that had just been born at that time to well explain "how α particle broke through the Kulun barrier during α decay", and called this phenomenon of crossing potential barriers "tunnel effect" (seeing this, some friends may already understand what's going on. In a slightly lower temperature, protons may also penetrate the potential barrier and cause nuclear fusion reaction).
and this microscopic phenomenon is common in the microscopic particle-scale world, and this tunneling effect is also easier to understand on the surface. For example, if you take off a bicycle and slide freely from a mountain, then you have to use the kinetic energy generated by the whereabouts and climb over a higher mountain without providing other power. Obviously, this is impossible in the macro world. The bicycle can rush to the same height at the top, otherwise it will not conform to the law of conservation of energy.
But if this happens in microscopic world , the situation will be different. We know the principle of inaccurate measurement , which means that the position and momentum of particles cannot be determined at the same time. Corresponding scientists have a broader inaccurate measurement principle, that is, the uncertainty relationship between energy and time. When the bicycle shrinks to a microscopic scale, it is possible that when it rushes to the hillside, its energy suddenly increases and successfully climbs over in extreme time, and then its energy returns quickly. Maybe this example is a bit unrigorous, so you don’t need to look at it carefully, just know one rough idea. But the quantum tunneling effect is an objective fact. For example, the scanning tunneling electron microscope , which is used now, uses this principle.
Animated images made by scientists using scanning tunnel electron microscope to move molecules
1932 were discovered, and the strength and weakness interactions at the microscopic scale have been proposed. So under such circumstances, American astronomer Hans Bett appeared.
Hans Bett
Relying on the above theoretical basis, he fully described the process of nuclear fusion within the sun in 1939, such as the proton-proton chain reaction in the sun but the main energy released. It uses four hydrogen nuclei to go through several steps and finally fuses into a helium nucleus, and can release quite "cost-effective" energy (after all, only the equation can be placed there, a small mass loss can release a large amount of energy). Moreover, the energy released by this combination reaction accounts for more than 80% of the total energy. In addition, there is a little carbon-nitrogen cycle energy release, which will not be introduced here.
Proton-proton chain reaction
and the reaction temperature inside the sun is directly reduced to 15 million degrees Celsius (because of the tunneling effect, protons have the opportunity to penetrate potential barriers and enter other atomic nuclei without having to put extremely high requirements for temperature). Otherwise, the sun will not be able to maintain stability because the internal temperature is too high, and it may become a hydrogen bomb and blow it up directly.
So this astronomer Hans Bet won the 1967 Nobel Prize in Physics for his important contribution to the stellar nuclear reaction mechanism. Since then, the principle that the sun relies on nuclear fusion to emit light and heat has become a household knowledge. Of course, the quantum tunneling effect is indispensable to "make a bridge" for the generation of nuclear fusion.
The content of this article ends here.
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