After Hu Kehao, Song Huiqin, Li Hengyang, and Zhang Xiaoqiang returned to school, Hu Kehao encountered another incident. Chen Qiuhe was caught by the invigilator while carrying a note during the retaking exam. The invigilator was kind-hearted and did not report to the school, but just let Chen Qiuhe hand in the papers and leave. If he reports to the school, Chen Qiuhe will inevitably be punished by being ordered to withdraw from school. The invigilator thought that Chen Qiuhe had just taken out the note, but she didn't have time to read it, and was on the verge of cheating and not cheating, so she asked her to hand in the test paper in advance and leave the examination room. Chen Qiuhe met a benevolent and benevolent invigilator, once she encountered the school's "four famous arrests", the consequences were extremely serious, and she had to roll up the cover and leave.

Despite this, the invigilator handed the note that Chen Qiuhe was carrying to Hu Kehao. "Although the death penalty is avoided, the living crime cannot be escaped", Hu Kehao had to take this opportunity to educate Chen Qiuhe well. Chen Qiuhe received a notice from Hu Kehao and came to his office, and Hu Kehao first severely criticized and educated her, and emphasized the rules and regulations of the school and the discipline of the examination room to her again. This Chen Qiuhe drooped his head, only promised, and kept apologizing.

"There's no one else here, you tell me the truth, did you cheat at the time? Did you just take out the note? Or is it already being transcribed? Hu Kehao asked.

"The first time I took out the note, I only copied a little bit, and when the invigilator came over, I hid it. After the invigilator left, I just took out the note again, and was caught by another invigilator, who was focusing on the first invigilator and not the other invigilator. Chen Qiuhe said.

"I have emphasized the discipline of exams many times, and I have repeatedly reminded you not to cheat. Strictly speaking, you should report to the school, and you should be punished by being ordered to withdraw from school. Hu Kehao said.

"Teacher, I was wrong, I won't dare next time." Chen Qiuhe said.

"Do you regret this?" Hu Kehao asked.

"Teacher, I regret it very much, if I could turn back time, I would never carry a note." Chen Qiuhe said.

"Since it has happened, things cannot be changed, and you must learn a profound lesson...... Go back today and write a review, reflect on it seriously, and hand it over to me tomorrow. Hu Kehao said.

"Okay, teacher."

Hu Kehao remembered Professor Yang Shimo in the underground laboratory of the abandoned factory, and the delayed experiment he did could change "history", since Chen Qiuhe was so remorseful, could the "history" of her intention to cheat with a note be changed? Chen Qiuhe just took out the note at that time, but she didn't have time to read it, and she was on the verge of cheating and not cheating, that is to say, she was in a superposition state of "cheating-not cheating" at that time, wouldn't it be in line with Professor Yang's experimental research object? In order to further educate and "save" Chen Qiuhe from being lost, Hu Kehao took her to visit Professor Yang.

Professor Yang was busy in the laboratory, and Hu Kehao told him about Chen Qiuhe and asked, "Professor Yang, in the delayed experiment, after you put in the second half-lens, the history of photon motion can be changed. Chen Qiuhe now regrets cheating, can you please change this history through experiments? ”

"This has happened, where in the world is there a regret medicine to sell?" Professor Yang said.

"In the delay experiment, if the photon 'regrets' the path it has taken, it can change its path history?" Hu Kehao asked.

"In the delay experiment, the object of our study is photons, which are very microscopic, and the wave and interference phenomena are obvious. Now I am facing macroscopic things, which are very particle-oriented, very weakly fluctuating, and there is 'decoherence', and there is no interference, and I can't do delayed experiments on macroscopic things, and the history of macroscopic things cannot be changed. Professor Yang said.

"What do you mean by 'decoherence'?" Chen Qiuhe interjected a sentence next to him.

"If you've studied advanced mathematics, you should know that every vector corresponds to a spatial dimension. For example, two-dimensional coordinates (x, y) correspond to a plane, and three-dimensional coordinates (x, y, z) correspond to three-dimensional space. The lower the dimension, the easier it is to intersect. Does this understand? Professor Yang asked.

"Why is this happening?" Chen Qiuhe asked.

"In a two-dimensional plane, if two straight lines are not parallel, they must intersect. But in three-dimensional space, two lines that are not parallel do not necessarily intersect – they just need to be staggered at a certain distance in height. Therefore, the lower the dimension, the more likely it is to intersect; The higher the dimension, the lower the likelihood of intersecting. Therefore, in the electron double-slit experiment, because the phase space dimension of the electron is not high, the world in which it is located will generally intersect and project each other, so the two worlds can be perceived and related to each other, and can be superimposed and interfered with each other, which is 'coherent'. Professor Yang said.

"What if the system is complex?" Chen Qiuhe asked.

"If it is an object made up of many particles, its phase-space dimension rises dramatically, and the degree of interference between vectors decreases dramatically—just as straight lines that are not parallel to each other in three-dimensional space do not necessarily intersect. For example, Schrödinger's cat, the number of particles that compose it reaches 10 to the 27th power, such a huge particle system, the connection between the worlds is erased, so you can't see dead and alive cats! As the number of particles increases, the degree of vector coherence decreases, and this process is called 'decoherence'! Professor Yang said.

"No wonder textbooks say that microscopic particles mainly embody wave nature and interfere; Macroscopic matter is mainly particle-like and cannot interfere. Chen Qiuhe said.

"In the electron double-slit experiment, since the particle has definitely gone through the double-slit experiment, why does it not interfere when we observe, and if it does not observe, it interferes?" Hu Kehao asked.

"It's very simple, the macroscopic instrument, the macroscopic you, are made of countless particles. When you observe an electron, you have a relationship with it, and you are related to each other into a system, and the extremely high-dimensional phase space of you and the instrument is introduced, and you are in the same Hilbert space as the particle, and there is a 'decoherence' between you, and the two routes of the electron slit are no longer superimposed or entangled, so they will not interfere! Professor Yang said.

"According to this interpretation, what role does human consciousness play in observation?" Hu Kehao asked.

"I don't have to deal with the problem of consciousness collapsing the wave function here. 'Decoherence' and 'consciousness collapses the wave function' are two different theories, which are explained from another perspective and do not require the mixing and intervention of consciousness. Professor Yang said.

"If human intervention has been 'decoherent', why is it that in the delay experiment, after adding a second half-lens, the experimenter can still observe the photons interfering through two routes at the same time, which is inconsistent with the current explanation?" Hu Kehao asked.

"This ...... Because in the delay experiment, if the system composed of photons and humans has been decoherent, the photons will behave as particles, and there is a possibility of reflection or transmission after passing through two half-lenses, and the experimenter finally does not know which route the observed photons come from, and the whereabouts of the photons are not leaked and not detected by human consciousness, so there is no need for the wave function of the photons to collapse, and there will be interference in two routes at the same time......," Professor Yang said.

"In this way, consciousness is at work in the collapse of the wave function, which contradicts your interpretation......" Hu said.

"This ...... In academia, it is difficult to find a single theory that explains all phenomena. Professor Yang said.

"Since the 'macroscopic' system composed of photons and humans has not been decoherent in the delayed experiment, and the 'history' can be changed, if Chen Qiuhe, as a macroscopic system, also participates in the delayed experiment, can her cheating history be changed? She wanted to erase the stain. Hu Kehao said.

"I don't think there is any way, the note that Chen Qiuhe carried in the exam is a macroscopic object, unlike the photons in the delayed experiment, there is no superposition, it has lost its coherence, and it can't change history like the delayed experiment." Professor Yang said.

"Chen Qiuhe, in the world we live in, what has happened has become history and cannot be changed. You have to think about everything you do in the future, many times you only have one chance, don't mess around. Hu Kehao said to Chen Qiuhe. Chen Qiuhe humbly accepted the teachings.