Shulou(Shulou.com)11/24 Report--

1900 is the first year of the 20th century, and modern physics has developed for nearly 300 years since the time of Galileo.

Over the past 300 years, physicists have worked tirelessly to explore the mysteries of nature, opening up many research fields such as mechanics, optics, heat, electromagnetism, and so on. A large number of talented physicists such as Newton, Faraday, Maxwell, Boltzmann and so on emerged. By 1900, people had figured out the laws of the solar system, discovered the periodic table of elements, invented steam engines and generators, and even invented radio communications.

Mankind's understanding and transformation of the world reached an unprecedented height. at that time, many physicists confidently believed that man already knew nature like the back of his hand, and that man's exploration of physics was coming to an end. the universe will no longer have secrets in human eyes.

In 1900, the German physicist Max Planck (1858-1947) had just turned 42, but he was already full of honor. After graduating from his PhD at the age of 21, Planck first taught at his alma mater, the University of Munich, and then returned to his hometown, Kiel University. With his excellent work in the field of thermodynamics, he came to the capital Berlin in 1889 as director of the Institute of theoretical Physics of the University of Berlin, and in 1894 he was elected a member of the Prussian Academy of Sciences.

Planck, who is honored by Max Planck, is already a very successful physicist in the eyes of the world, but he often recalls what his college physics teacher, Von Yoli, said to him. At that time, he was bent on studying physics, so he applied to transfer from the mathematics department to the physics department. Feng Yoli unexpectedly told him that the physics building had been built, and all that was left was to repair the edges and corners in some remote corners. There is no great future.

Although Planck was not persuaded by these words, they took root in his heart, and he often wondered whether physics was really coming to an end. In the year when he was elected academician, Planck decided to attack blackbody radiation, a famous problem in physics at that time. He hoped to overcome this problem, even if it was to repair the edges and corners of the building, he had to repair the most difficult part.

When an object is heated, it glows. For example, red-hot iron gives off orange-yellow light in the dark. At that time, physicists already knew that "light" is electromagnetic waves, luminescence is radiating electromagnetic waves, and the energy carried by electromagnetic waves is the measured "heat".

Red iron emits visible light in fact, anything with a temperature above absolute zero (- 273.15 ℃) glows, but not all the "light" they emit is visible light. Only light with a wavelength of 400 to 700 nm is visible light, that is, electromagnetic waves that can be recognized by human eyes. Electromagnetic waves in other bands are invisible and cannot be seen by human beings.

For example, although human beings are also glowing, they emit infrared light that is invisible to the naked eye. Objects emit strong visible light only when heated to more than 500 ℃.

The range of visible light in the electromagnetic spectrum the phenomenon of luminescence and heating of objects has a proper term in physics-thermal radiation.

The higher the temperature, the stronger the radiation capacity. Thermal radiation does not seem to be complicated. according to reason, people already had perfect theories of optics, heat, statistical mechanics and electromagnetism at that time, and it should not be a difficult problem to explain this phenomenon, but surprisingly, it turned out to be a big problem at that time.

In order to study thermal radiation, an ideal situation is conceived. If an object can absorb all external light, it will glow as much as possible when it is heated. This is the ideal thermal radiation, also known as blackbody radiation. The concept of "blackbody" was put forward by Planck's teacher Kirchhoff in 1862.

The reason why an object is black is that it can absorb light without reflecting light. Obviously, the blackest object can absorb all the light shining on its surface and does not reflect it at all. This is the "blackbody".

At first, blackened platinum sheets were used as blackbodies. Later, German physicist Wayne came up with a more ingenious way to make blackbody: find a heat-resistant closed box with blackened inner wall and make a small hole in the box, because the light shot into the hole is fully absorbed. So this hole is a "blackbody".

At that time, the relation curve between the wavelength of blackbody radiation and radiation energy has been obtained through experiments. For an ideal thermal radiation, this curve is certain and only varies with temperature.

Blackbody radiation spectrum curve (https://www.chem17.com/tech_news/detail/2195430.html) at different temperatures, but in the theoretical explanation, we can not find a suitable formula to describe this curve. Physicists derive two formulas through classical thermodynamics and statistical mechanics, called Wayne formula and Rayleigh-kins formula, but these two formulas can only explain half of the curve and can not give the energy density distribution of the whole curve. Classical physics seems to be powerless on this issue.

By 1900, Planck had been studying blackbody radiation for six years. As a thermodynamics expert, braving the halo of academicians of the Academy of Sciences, Planck is still under great pressure after six years of struggle. It seems that his efforts are out of proportion to his returns. It is still unknown whether he can achieve results. Is it going to take a lifetime to spend his whole life on this issue?

If you spend a lifetime, you will spend a lifetime! Planck made up his mind. It is better to solve one major problem than to solve ten ordinary problems. Planck knew that the problem was crucial to physics as a whole. No matter what the cost, he decided to find a theoretical explanation for blackbody radiation.

Planck knows very well that classical physics cannot solve this problem. It seems that some changes must be made, and it is not clear whether the change is big or small, but this step must be taken.

So Planck decided to abandon the rules of classical physics and cobble together a formula. No matter where the formula comes from, first find a formula that matches the experimental curve, and then look for the physical connotation behind the formula.

Planck started with Wayne's formula, combined with the experimental curve that has been familiar with for six years, after some deliberation, and finally, using the method of mathematical interpolation, he really came up with a formula, this formula can fully explain the whole blackbody radiation curve, exactly! This result makes Planck ecstatic, but makes him more nervous and anxious. He has seen the dawn of hope, but he seems to be in the darkness before dawn. He must find the physical mystery behind this formula to meet the real dawn.

The next few weeks, the busiest and most stressful weeks of Planck's life, were devoted to this formula, and he was not content to find it just by accident. His goal was to derive it. His brain kept running at high speed, figuring out the secret behind the formula day and night, and gradually, a completely unexpected picture became clear in his mind-could the energy be discontinuous? He kept asking himself.

No one has ever asked this question in classical physics, or no one has ever realized that it is a problem. Everyone subconsciously thinks that energy must be continuous, just as we deal with a smooth curve in mathematics, we can take the value of any point on the curve. However, the picture in Planck's mind kept telling him that in order to derive this formula, the energy must be discontinuous! In the end, Planck made a painful decision to accept the discontinuity of energy, no matter how incompatible it was with classical physics.

On December 14, 1900, at a meeting of the Berlin Academy of Sciences, Planck read out a paper entitled "Energy Distribution in the blackbody Spectrum", in which he put forward the earth-shaking quantization hypothesis of energy: the energy of electromagnetic radiation is not continuous, but one by one. He called this share of the energy unit "energy quantum". From then on, quantum theory was officially born.

In Planck's hypothesis, just as matter is made up of atoms, the energy of electromagnetic waves is actually made up of parts of energy quantum, and the energy carried by each energy quantum can be expressed by a simple formula:

Estrangh v

Where: v is the electromagnetic wave frequency Atrah is a new physical constant proposed by Planck, which is called the Planck constant (h ≈ 6.262 × 10-34J ·s).

The concept of quantization of energy is a brand-new concept that no one has ever thought of. There is no place for this concept in the building of classical physics. Planck's teacher thought the physics building was nearing completion, but perhaps Planck himself did not realize that he had shoveled the first shovel of earth for the foundation of a new building and made the first brick. The new physics building is called quantum mechanics.

The term quantum mechanics corresponds to classical mechanics, which is Newtonian mechanics, which studies the law of motion of objects in the macro world, while quantum mechanics studies the law of motion of particles in the micro world. The dividing line between macro and micro depends on the Planck constant.

Planck constant is a symbolic constant of quantum mechanics, which can reflect the spatial scale and energy quantization characteristics of microscopic systems, so it has also become an important parameter to define the scope of application of classical physics and quantum mechanics. When the influence of Planck constant tends to 00:00, the problem of quantum mechanics will degenerate into a problem of classical physics.

The definition of kilogram is determined by Planck constant, and its principle is that the mechanical force required by a moving mass of 1 kg is converted into an electromagnetic force that can be expressed by Planck constant, and then the mass is calculated by the mass-energy conversion formula.

Because the Planck constant is very small, its influence on macroscopic objects and macroscopic motion is basically zero, which is why we do not see quantum effects in our daily life, so people always mistakenly think that energy is continuous.

Thanks to the small Planck constant, the Planck constant makes our everyday world orderly and disciplined, and if you enter the quantum world, the vagaries of chaos there may make you completely confused and have no more rules to follow.

Of course, at that time, physicists did not know that Planck only built the first brick, the building of quantum mechanics, and needed more talented physicists to build it bit by bit.

Wen Yuan: "telling Quantum Science to teenagers" author: Gao Peng part of the picture source network copyright belongs to the original author. Editor: Zhang Runxin this article comes from Wechat official account: Origin Reading (ID:tupydread), author: Gao Peng, Editor: Zhang Runxin

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