U City Polytechnic University, every weekend, there are many students who go out, some go back to their own homes, some go to relatives' houses, some go to other schools to meet boyfriends and girlfriends, some fall in love, and some work part-time to earn money. As a result, some students do not return home on weekends, which brings great trouble to the management of school dormitories. As a counselor majoring in applied physics, Hu Kehao is particularly afraid that students will have accidents, and safety is the top priority. On the night when Song Huiqin went out to be a tutor on the weekend, Hu Kehao organized the squad leader Li Hengyang, the secretary of the Youth League Zhang Xiaoqiang and others to check on the bed, and found that Song Huiqin and Chen Qiuhe were not there. As a class cadre, Song Huiqin herself should have joined the team of the dormitory, but she didn't expect that she was not there.

The next day, Chen Qiuhe rushed back to school from the Green Lake Harbor Community to take a retake exam for a course. Chen Qiuhe usually doesn't study seriously, loves to skip class, arrives late, and leaves early, and most of his mind is spent on dressing up, showing off and comparing, and admiring vanity. Hu Kehao couldn't contact Song Huiqin, so he investigated everywhere and found Chen Qiuhe. Chen Qiuhe said that she met Song Huiqin in the Cuihu Harbor community on Friday night, where she worked as a tutor, and they chatted a few words, and Song Huiqin went back to school.

Hu Kehao followed up the investigation and found the bus driver who Song Huiqin was riding. The driver lost consciousness after driving the car to the U City Polytechnic University that night, and the bus drove uncontrollably to the suburbs. The driver vaguely remembered that there was an abandoned factory where Song Huiqin got off the bus.

Hu Kehao took the squad leader Li Hengyang, the secretary of the Youth League Zhang Xiaoqiang and others all the way to this factory, it turned out that this was an abandoned glass factory, which was once very lively, but now it is bankrupt. The factory was dilapidated and desolate. The doors and windows were mottled and covered with a thick layer of dust. The ground was overgrown with weeds, and artemisia and dogtail grew out of the broken rubble.

They entered the factory, which was dimly lit, and what had been left of it was beginning to rot and mold, and the corners of the walls were covered with cobwebs. Rats wander leisurely inside, frightened by people, scurrying around. Li Hengyang searched every factory building, but did not find Song Huiqin. Hu Kehao looked at the dilapidated factory building, and clearly felt that this was a place infested by robbers and bad guys, and he had a hint of foreboding.

Behind a discarded machine, Li Hengyang found a secret door, pushed it with his hand, and the door did not move at all. Hu Kehao was afraid that there were bad people inside, so he asked everyone to pick up a discarded iron rod from the ground as a self-defense weapon in case of emergency. Hu Kehao came to the door, kicked the door with his foot, and shouted loudly: "Is there anyone inside?" ”

After a while, someone from inside came out, opened the secret door, poked his head out, and asked, "Who are you looking for?" Looking for Song Huiqin? She's in there, it's safe, don't worry. ”

"What are you hiding her here for? We almost called the police! Hu Kehao said.

The one who opened the door was an experimenter, who saw the three people outside, knew their intentions, and said, "We are here to do experiments, and you are welcome!" I'll go get you clothes later. The experimenter ran back, took out three clothes shielding from electromagnetic fields, and told Hu Kehao and the three of them to put them on. The function of this suit is to protect the energy of the fourth-dimensional supernatural space in the laboratory from the influence of the "yang energy" of the outside world.

Under the leadership of the experimenter, Hu Kehao and his entourage visited the "Cinema", "Swimming Pool" and "Cat House", which were the places where Professor Yang did the electron double-slit interference experiment, the water wave interference experiment and the Schrödinger cat experiment. Then, they went to another lab.

In the laboratory, where are Professor Yang and Song Huiqin doing experiments? They didn't even do their job and played in it! There are three boards in the court, all of which are placed on the ground at a forty-five degree angle. The first board is in the lower left corner, equipped with a mechanism that can bounce the ball vertically and cause it to be reflected, or it can cause the ball to enter the board and be transmitted. The second board is on the top left and the third board is on the bottom right, both of which are facing the first board and both can only reflect the ball. Song Huiqin held a racket in his hand and hit a tennis ball hard, the ball went along the guide rail, touched the board with a 45-degree inclination, rebounded, the trajectory changed, and it moved vertically upward, and then it encountered a second board, and it rebounded again, becoming a horizontal movement. Experimenter A in front saw the ball and reported to Professor Yang: "Eventually, the ball is moving horizontally. ”

Professor Yang saw Hu Kehao and the three coming, held their hands tightly, welcomed them, and invited Hu Kehao to play. Like Song Huiqin's method, Hu Kehao held a racket in his hand and hit a tennis ball hard, the ball went along the guide rail, touched the board at a 45-degree angle, and did not rebound, but drilled into the board and transmitted. It turns out that there is a mechanism inside the board, and the force of hitting the tennis ball does not exceed the set threshold, and the tennis ball will reflect; If the force exceeds the set threshold, the tennis ball will be transmitted. Whether the force exceeds the threshold is 50% probability, so whether the tennis ball is reflected or transmitted accounts for 50% probability. After Hu Kehao saw the tennis ball radiating from the board, it continued to move in the horizontal direction, and when it encountered the board in front of him, it reflected again and changed to a vertical movement. Experimenter B at the top saw the ball and reported to Professor Yang: "Eventually the ball is moving vertically. ”

Professor Yang put a fourth board with a mechanism in the upper right, which can reflect the ball and also make the ball transmit, and asked the squad leader Li Hengyang to play the ball. In the same way of hitting the ball, I saw that the ball touched the first board and was reflected, and the upward movement touched the second board, and after the reflection, it became a horizontal movement, and when it touched the fourth board, it was transmitted again, and it came out again, and the experimenter A recorded it and reported to Professor Yang: "The final ball moves in the horizontal direction." ”

Professor Yang took off the fourth board with a mechanism and asked Zhang Xiaoqiang, the secretary of the Youth League, to continue the experiment. I saw that the tennis ball was projected first, and then reflected. When the ball left the third board and had not yet reached the end, Professor Yang quickly put on the fourth board with a mechanism, and the tennis ball touched this board, and finally the transmission occurred again. Experimenter B at the top took notes and reported to Professor Yang: "Eventually, the ball is moving vertically. ”

"Professor, we did the same experiment four times, what does that mean?" Hu Kehao asked.

"This experiment tells us that when a tennis ball encounters the first board with a mechanism, it will either be reflected or transmitted, and only one route can be chosen, and the probability of each route is 50%. Similarly, when a tennis ball encounters a second board with a mechanism at the end of the upper right, it will either be reflected or transmitted, and only one route can be chosen, and the probability of each route is 50%. Two of our experimenters either saw a ball moving horizontally or vertically. Professor Yang said.

"If the subject of the experiment changes, for example, if you do the same experiment with electrons or photons, will the results change?" Song Huiqin thought of the strange phenomenon in the electronic double-slit experiment and asked Professor Yang.

"That's a good question, let's continue the experiment." Professor Yang said.

The assistant adjusted the experimental equipment through an automated system, and the four boards in the court became four mirrors, all placed on the ground at a 45-degree angle. The first mirror, painted semi-silver-plated, is a semi-lenticular and is placed in the lower left. Light can be reflected or transmitted, with a 50% probability of each. How does this work? Most mirrors have a thick metal plating, and when the incident light hits the mirror, the light will be reflected. If the metal plating is thin enough, then part of the incident light will be reflected, and the other part of the light will pass through the metal plating and transmit, this kind of mirror is called a semi-silver-plated mirror. As with the previous board, the second mirror is placed on the top left and the third mirror is placed on the bottom right, both of which only reflect light. The fourth mirror, also a semi-lens, is placed on the upper right and can be removed or fitted as needed.

This is the famous Einstein spectroscope experimental device, which is an upgrade of the electronic double-slit experimental device.