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I made a short answer below, but I think it is necessary to write an article to talk about it in detail, because this is a basic concept. Understanding the concept of quantum accurately is of great benefit to deepening the understanding of quantum mechanics and the essential difference between quantum mechanics and classical mechanics.
concept
Quantum is not a concept on microscopic particles such as molecules, atoms, electrons and protons. If any physical quantity has a lowest indivisible unit, such a physical quantity is quantized, and its smallest unit is called quantum.
In traditional mechanics, our physical quantities are all continuous. Taking energy as an example, we can ask for energy of 1 joule, energy of 0. 1 joule and energy of 0.00000 1 joule. It seems that as long as we are happy (as long as scientific and technological means are developed enough), we can ask for infinitesimal energy. But quantum mechanics tells us that it is impossible for you to want infinitesimal energy, because energy is quantized, and it has the smallest indivisible energy unit. You can't be any smaller here. All energy is an integer multiple of this minimum energy.
Not only energy, but also many physical quantities. The mechanical system based on such a model is called quantum mechanics ~
origin
In fact, the idea of energy continuity in classical mechanics seems very realistic. Some physical quantities we usually perceive, whether temperature, energy, length or speed, seem to be as small as we want, but have you ever thought about it? This is actually very unreasonable. In the mathematical model, we can use the concepts of infinitesimal and limit to approach a number infinitely, but in our real life, in this world made of matter, is there really such a thing to correspond to infinitesimal? Since it is infinitesimal, how can there be an entity corresponding to it? Because you are infinitesimal, you should be smaller than all the numbers that appear, so since you appear, it is definitely not the smallest infinitesimal.
In our daily life, we don't feel this discontinuity, because we usually deal with these problems on a large scale. Just like the images and photos you see on your mobile phone or computer screen now, they seem to be continuous, but in fact they are all made up of pixels. You take a photo with a camera with 6.5438+0.3 million pixels, which means that this photo is composed of 6.5438+0.3 million pixels.
In the past, the problems dealt with by physics were all macroscopic, and whether those physical quantities were continuous or discrete (that is, quantized) had little influence on them until they encountered the problem of blackbody radiation. Simply put, blackbody radiation is to make an object absorb different electromagnetic waves, see what changes have taken place in the temperature and spectrum of the object, and then give a formula to describe this phenomenon. This problem seems simple, but classical physics just can't give a perfect formula. At that time, there were two theories to explain this phenomenon: one was suitable for short wave, and the long wave was inconsistent with the experimental data; The other is suitable for long wave, but it is not consistent with the experiment in short wave.
Planck
Just when physicists were at a loss, Planck's brain hole suddenly opened wide: I don't care what the principle is, don't your two formulas just apply to one short wave and one long wave? Then I will put your two formulas together regardless of the theoretical significance. In short, at least let this formula look consistent with the experiment first. Then Planck spelled out a formula himself, and then Planck found an amazing thing: the premise of this formula is that he must regard energy as a fragment, that is to say, he can no longer regard energy as a completely continuous thing, and energy is composed of many smallest energy fragments, so Planck called it an energy quantum. This is the first time that the concept of quantum has officially appeared in front of people.
Gjoleka, Djali I Abazit
Although Planck solved the problem of blackbody radiation through the assumption of energy quantization, he himself (including most physicists at that time) was unwilling to accept this assumption, and the world of classical physics was continuous. This quantization assumption is completely deviant and even completely destroys the previous world. It is amazing to look at Newton's laws of motion and Maxwell's equations. That wonderful harmony is physics. How can energy be discontinuous? No, there must be a deeper reason that we haven't found yet. We must find the deeper reason for this quantization from classical physics. That's what mainstream physicists at that time thought, including Planck, the father of quantum mechanics. Now he wants to strangle his ugly child himself, but obviously, no matter how hard they try, their work is in vain.
It is understandable that the older generation of physicists are homesick, but the younger generation is not. Right is right, wrong is wrong. I want to know the truth. I don't care what the truth looks like, beauty or ugliness. We have the courage to abandon everything.
Einstein stood up first.
Planck and Einstein
Planck is the biological father of quantum mechanics, but this biological father was ready to abandon it as soon as he was born. Einstein saw quantum mechanics as if he saw a gifted but incomprehensible child, so Einstein took the initiative to raise and educate him. Quantum mechanics grew up slowly under Einstein's care, so that later he had the ability to move Gan Kun and make the whole physical world dark.
Adoptive father and godfather Einstein, quantum mechanics will be discussed later.
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