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If you ask a 19th-century physicist why some matter can conduct electricity and some matter does not, the best answer he can give you is only synonymous repetition.
This video is an excerpt from the live broadcast of Professor Yuan Lanfeng on the theme of "Principles and Technologies of Quantum Information" on September 11, 2021
(Why has quantum, which was proposed a hundred years ago, suddenly become a hot topic |? Technology Yuan Ren)
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This video was released on October 1, 2021 and has reached 10,000 likes
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Why do some substances conduct electricity? For example, copper and aluminum can conduct electricity, right? They are very good conductors, some substances do not conduct electricity, for example, wood and plastic it does not conduct electricity, and then later we will find that some substances are semiconductors, such as silicon and germanium, some substances are superconductors, such as some metals at low temperatures, these problems are completely unexplainable by traditional theories.
If you ask a 19th-century physicist why some matter can conduct electricity and some matter does not conduct electricity, the best answer he can give you is to say that the electrons in those materials that can conduct electricity are free, and the electrons are not free in the non-conductive matter.
But if you think about it, is this really an explanation? It doesn't actually explain anything, it's just synonymous repetition, because it just tells you that if you can conduct electricity, you call it a free electron, and if you can't conduct electricity, you call it an unfree electron.
So you have to ask him if you can predict it? Can you tell me why the electrons in copper and aluminum are free, and the electrons in wood and plastic are not free? The answer is that because it can't predict at all, so this theory is just playing a word game, and only after quantum mechanics have we developed a whole new set of theories, called the energy belt theory, the energy of the energy, the tie of the belt, the band of the band, this band theory is able to let you do calculations, can accurately predict which substances can conduct electricity, which substances do not conduct electricity.
We can also invent new substances, such as semiconductors and superconductors, and then quantum mechanics can not only explain the phenomena that already exist in the real world, but it can also invent some new devices, such as lasers and light-emitting diodes, which everyone often uses, for example, I now use this laser pointer, this is quantum mechanics, with the effects of quantum mechanics to create, if there is no quantum mechanics, you can not understand the phenomenon of lasers at all.
Therefore, all the technological achievements of modern society are inseparable from quantum mechanics. So if you're going to ask, what's the use of quantum mechanics, right? This is a very layman's question, which means that you definitely don't know anything about quantum mechanics, and if you know a little about quantum mechanics, you certainly won't ask this kind of question.