The contact was smooth, Luo Zhi gave the coordinates of the meeting place of the other party, and the two sides agreed to meet the morning after tomorrow. A few days ago, Luo Zhi found a good Cadillac Escalade car on the road, and honestly took it for himself. The car is well adapted to the terrain and loaded. The three of them loaded up supplies and drove towards Taicang along the studied route.

On the way, Luo Zhi wanted to exchange thoughts with Liu Xuejuan about things these days.

"What do you think?" Luo Zhi asked.

"From a physical point of view, I don't have a reliable idea."

"From a physical point of view, what can move a large number of objects away?"

"It's complicated, you know, space and time don't exist independently, they're two inseparable components of the concept of 'space-time'. Minkowski discovered it a hundred years ago. So these people are on a different plane than we are now. There are many possibilities that can explain some of the circumstances, but none of them can be justified. ”

"In addition to transfer, will it be decomposition?"

"It's not decomposition, it's generally a chemical concept. Chemically, there is no essential difference between humans and animals. It doesn't make sense that so many people have disappeared and the animals are still there. ”

"You just said that there are many possibilities that could explain part of the situation?"

"Yes, those people may be in another time and space, or on another timeline, in another dimension of space. It could also be in another parallel universe. ”

"How?" Luo Zhi understood her words, but he still wanted to hear her detailed explanation, maybe he would have some suggestive ideas. Of course, Liu Xuejuan is a professional physicist, and she is just a layman. But Holmes also needs Watson sometimes.

"The space we are in is three-dimensional, and everything you see has three dimensions: length, width, and height. But in fact, three-dimensional space is just a projection of four-dimensional space in three dimensions. For example, a piece of paper, you can imagine that it is a two-dimensional space, but it is not the whole of space, but only a 'layer' in three-dimensional space, or a two-dimensional projection of three-dimensional space. The observer of the two-dimensional space can only see the things in his own space, and if a line or a figure on the paper is taken out of the paper and put into the three-dimensional, that is, the third parameter of the coordinate value is changed, and the observer in the two-dimensional space cannot see them. Similarly, if the objects in our three-dimensional space change position in the fourth dimension, we will not be able to see them. So if these people go somewhere else in the fourth dimension, it can be said that they have passed. But first, this requires an entrance to the four-dimensional space, so that these disappeared people can move in the fourth dimension, which is unrealistic. Only from the higher dimensions can the lower dimensions 'take out', and the lower dimensional objects need to have an entrance if they want to enter the higher dimensions. Just like dotting a drop of soap bubble on paper, the contact surface between this soap bubble and the paper can be seen as a three-dimensional entrance to a two-dimensional space, and if the paper man wants to move in the three-dimensional space, he can only enter through this entrance. So far, no one has actually observed the entrance to the four-dimensional space, and the four-dimensional space itself is deduced from phenomena such as gravity and the deflection of light, and no one has actually entered it. Second, if they entered through the entrance, why were they the only ones who entered? What about the things around them? ”

"Their clothes, the contents of their pockets, and the things they were holding in their hands were all gone. Doesn't that make sense? ”

Liu Xuejuan shook her head: "No, if the entrance is so big, we will definitely go in, there is no reason to think that all the people who disappeared walked in on purpose." Could it be that the entrance is just closed around you, me, and the child? That's impossible. And the people in the car are gone, so why didn't the car go in? This can only be deduced from the fact that there is an entrance only around the 'person', and that it is some force in the higher dimensional space that 'takes' them out, only 'taking' them and not 'taking' anything else. It's too hard to believe. Also, why 'take' them and not 'take' us? What is so special about us? ”

Luo Zhi also shook his head, Liu Xuejuan was right, this is impossible.

"What else is possible?"

"Different timelines. Time is relative, I don't know if you have read the theory of relativity, the inference is a little tedious, but the conclusion is simple: the observed time of objects in relative motion is different. The relative velocity in everyday life is too small to feel the difference in time. But if your relative speed with mine reaches sub-light, let's say, one-half of the speed of light, then our time difference is more than a dozen percent. The higher the speed, the more different the time. If someone were moving at close to the speed of light relative to us, the moment they felt it would seem to us for many years. So, if the people who disappeared were moving at a high speed relative to us, by the time they came back we might be very old, and they might have only been a few seconds later. That is, these people come to our future. ”

"But this is nothing more than a movement in the overall concept of 'space-time,' and in space, we can still see them."

"Yes, it seems you understand what 'plane' means. There is no pure space, and there is no pure time, the two can only exist when they are combined. If those people really reach our future, that is, they are not only moving in our space, but also in our time. It all depends on the relative velocity. ”

"Understood, so if that's the possibility, we just have to observe them. Even if they were moving at the speed of light, they could still be seen in only ten days. ”

"Not necessarily. If it was really that high speed, they would have gone a long way by now. And they don't shine on their own, and they can only see the sunlight reflected by them. When astronomical telescopes are not available, it is difficult to see them. But we don't really need to see them. It's also hard to justify this possibility. If these people really disappear in an instant, then their speed will be very high, not to mention that acceleration will kill them, even to accelerate so many people to such a speed, the amount of energy required is also incredibly magnitude. Where did so much energy come from? And then again, the question: why are we still here? ”

Luo Zhi smiled. The three of them, as well as the two people on the steamer in Yangshan Port, are indeed still in place. What's so special about these five people?

"What else?"

"There are parallel universes. Do you understand the concept? ”

"Understood. The concept was originally developed in the interpretation of the 'single-electron double-slit interference' experiment. It is a completely new logical explanation of the uncertainty of quantum mechanics. ”

"Yes, your knowledge of physics is very good. Haha, why didn't our school ask you to be a teacher? By the way, I will tell the students how to open someone's fingerprint lock and how to scare the poor little animal with a big gun. Liu Xuejuan suddenly teased.

Luo Zhi also smiled, he was used to this sudden and cute turn of her, and he also enjoyed this kind of teasing.

"Don't be funny, it's okay to go to your school and talk about the content behind, if you talk about physics, you have to let people blow it out."

"Yes, come to us to talk about fingerprints, and go to the public security university to talk about physics, anyway, I don't have to worry about eating, haha."

"Cut, now it's all about reaching out to get the rice, isn't the car we are driving now just a sheep? What kind of lectures do you still need to teach? ”

"Really, by the way, I became a rare rich man in the world. Let's just say the three of us, how much money do you think you have now? ”

"Money? Who's going to use that? It's just a piece of paper. I said, Mr. Liu, if you really like this thing, I'll go find some for you, and it will be your tuition for my class. ”

"Hmph, I don't want your stinky money. I have it myself! Ha ha! ”

The two laughed relatively loudly, and Yu Guannan also laughed in the back seat as if he didn't understand.

"Let's move on to parallel universes, there's nothing else going on right now anyway. I know where the concept comes from, but don't understand the deeper theory. ”

"There are no in-depth theories, and most of the research on parallel universes is still in the stage of mathematical simulation, and there are not too many experiments to confirm the authenticity of this theory. Tell me what you know, it's not my specialty, and I don't know much. ”

"Okay. In the history of the development of quantum mechanics, there is a very famous experiment called the 'single-electron double-slit interference' experiment. It is to shoot an electron like a bullet at a wall with two gaps, and classical physics holds that this electron can only pass through one of the two gaps at a time, either through the left gap or through the right one. However, the experiment turned out that the electron had passed through the wall and interfered. Only two electrons pass through different slits at the same time to interfere with each other, how can one electron pass through two slits at the same time? Just like when we play billiards, a ball can only go into one of the two bottom pockets at a time, and it is impossible to go into both the left bottom pocket and the right side at the same time.

However, this experiment has indeed proved that the same electron passes through two gaps at the same time in the course of an experiment. In the classical Copenhagen interpretation of this experiment, quantum mechanics explains this phenomenon in terms of probability, that is, the mechanical quantity of a microscopic particle does not have a definite value when it is in a certain state. Its velocity, position, momentum, energy, and so on are all indeterminate, but have a series of possible values, each of which occurs with a certain probability. Like our macroscopic objects, such as a person, his speed, position, etc., are determined at all times, and I am driving here, so it is impossible to be in the back seat at the same time. But microscopic particles are different, it is possible to be both here and there at the same time, and there is a certain probability here or there, uncertain. In this way, it is possible for that electron that pierced the wall to pass through both the left and right gaps at the same moment. And when the observer goes to determine which gap the electron has passed through, he will always find the electron in one of them, and in this observation, the electron is on the left and not on the right; The next time you look at it, the electron may be on the right, but not on the left. Even if two instruments measure at the same time, it is not possible to detect electrons in both slits at the same time.

This is even more anomalous, many people scratch their scalps for this, which is simply counterintuitive. Originally, it was weird enough that an electron could pass through two gaps at the same time. Now add that if you don't measure, electrons can pass through two slits at the same time, and as long as you measure, electrons can only pass through one of the slits, as if people's measurement behavior changes the state of motion of electrons. What a thing. ”

Luo Zhi himself couldn't help laughing, and he continued:

But the results of the experiment are clearly there, and there is no doubt about it. One can only look for theories that explain this phenomenon. The mathematical framework of quantum mechanics, the 'wave function', explains this maddening phenomenon. The wave function can describe the probability of the spatial distribution of microscopic particles with uncertainty. According to the principles of quantum mechanics, the state of motion of an electron exists in the form of a wave function. When people do not observe electrons, there is a probability that electrons exist at the positions of both slits; However, once it is measured, for example, the position of the electron in the left gap, the probability of it in that position is 1, and the probability in other positions is 0. Mathematically, at the moment of measurement, the wave function of the electron 'collapses' to that position. This is the most mysterious and questionable aspect of quantum mechanics: observation can change the state of being.

Philosophically, this is, of course, idealistic, and many people are not convinced. Even the technical details of the 'collapse' of the wave function have caused a lot of controversy. For example, when exactly did the 'collapse' occur? Does it happen at the moment of measurement, or does it not happen until the photons from the measurement result enter the human eye and form an image on the retina? Therefore, even if the wave function 'collapse' is mathematically explained, it is still widely questioned. Many people believe that quantum mechanics cannot be called physics when it uses this way to explain experimental phenomena, but at most it is nothing more than a set of complex and cumbersome calculation methods. This method of interpretation has led to the fact that no one can 'understand' quantum mechanics, but only gives people a way of computing that can describe the results of experiments. ”

Luo Zhi took a breath, and Liu Xuejuan looked at him with very appreciative eyes. Without further thought, he continued:

Here comes an even more bizarre explanation. The American physicist Everett proposed that to explain this phenomenon, we can start by 'not collapsing' the wave function, that is, at any time, the wave function is true, the motion state of the electron is in the form of probability, and the wave function will not 'collapse' to a certain position. After the measurement, the electrons are still in the left and right slots, in a state of 'superposition'. So why can people only observe that electrons are in a certain position? This is because the human world is also in a state of 'superposition'. When the electrons pass through the double slit, the two 'superimposed' worlds separate, and in one world, the electrons pass through the left slit and in the other world, the electrons pass through the right slit. The point is that worlds that were originally 'superimposed' together are separated by observational activity: those who observe in the former world see electrons in the left slit, and those who observe in the latter world see electrons in the right slit.

This way of thinking of the 'superposition' of the two worlds can also explain the famous paradox of quantum mechanics, 'Schrödinger's cat'. 'Schrödinger's cat' means that, according to the principles of quantum mechanics, it is uncertain whether an atom decays at a certain moment, and there is a certain probability of decay or not, just like the electron that passes through the double slit, and it is possible for this atom to decay and not decay at the same time without observation. If there is a large box, and a small box with poison gas sealed, whether the poison gas is released depends on whether the atoms decay or not. Put atoms, a cat, and the small box in the big box and close the lid of the big box. In this way, people will not be able to observe what is going on inside the big box. And according to the experiments of electron slits, it is known that once the atom is observed, it can be determined whether the atom decays, the wave function 'collapses', and there is no uncertainty. In this observation, the atom decayed, and the next observation, the atom did not decay, but each observation can only have a definite result. In this experiment, it is simplified to simply opening the lid of the large box and one can see whether the atoms are decaying or not.

Now the paradox comes: first, without opening the lid of the big box, that is, without observing, the atoms are in a state of both decay and non-decay at the same time, but is the poison gas released? Is the cat dead or not? You little atom can do this and that at the same time, but a cat can't be dead at the same time.

Second, without opening the lid of the big box, the life and death of the cat is uncertain and can only be described by the wave function, but once the lid is opened, it is only possible to observe one result, the wave function 'collapses', and the life and death of the cat are decided, either dead or alive. And whether it is dead or alive, no one can predict. This time the lid was opened, and the cat died; The next time I open the lid, the cat is still alive. The poor cat existed in a state of both life and death, but humans opened the lid to determine its life and death, and whether it would survive or not was unpredictable, so it was impossible to resign itself to fate. The observed behavior changes the cat's state of being.

The theory of the 'superimposed' world saved the poor cat. The life and death of cats are 'superimposed', and observational activities lead to the separation of the 'superimposed' worlds: in one world, the cat is alive, and in the other, the cat is dead. People who observed in the former world saw the cat alive, and people who observed in the latter world saw the cat dead.

It's as simple as that, the wave function will not 'collapse', the Schrödinger equation of quantum mechanics always holds, it is the quantum process that creates the 'two worlds', and these two worlds will exist completely independently and evolve in parallel independently.

This is a parallel universe. ”

Luo Zhi said so much in one breath, and felt a little out of breath. Liu Xuejuan applauded him:

"It's so clear, I've really gained knowledge. Even though I knew this before, it was like I had been baptized by thought. You're amazing! ”

"After the prize, I know so much. But I don't really believe in this theory. ”

"Why?"

"Because according to this interpretation, the world is not simply two 'superimposes', but countless 'superpositions'!" There is only one electron and two gaps in the 'single electron double-slit interference' experiment, but what if there are countless gaps? What if there are an infinite number of electrons? The results of each observation are not necessarily the same, so there are countless 'superimposed' worlds? This is just an experiment, and countless parallel universes have been created, and there are too many quantum processes to count! Moreover, these 'superimposed' worlds are all real, and none is a little more important than the others. It's unbelievable. And most importantly, observations separate worlds that would otherwise be 'superimposed'. Again, this does not circumvent the trap of the act of observation altering the nature of the world. ”

"That's true, but there is no experiment that negates this theory, and mathematically, the concept of 'infinity' is also manageable."

"I understand, but there are no macroscopic experiments that can confirm this theory, everything is microscopic and mathematical."

"Not exactly, most of the research is still microscopic and mathematical. But physicists at the University of California, Santa Barbara, have taken the experiment from the microscopic to the macroscopic level, and their test object has reached the width of a human hair, which is by no means an elementary particle, but the result is still the same: the test object is in two quantum states at the same time. ”

But the theory of parallel universes does not fully explain our current situation, if there are some quantum processes that lead to the emergence of certain parallel universes, why do people go to other universes? Could it be that the difference between these two or more parallel universes is that in one universe people are on Earth and in the other universe people are elsewhere? ”

"Yes, as I said, all possibilities can only explain part of the situation, and none of them can justify themselves."

Luo Zhi felt tired. He also pondered the reasons for the disappearance of human beings and, most importantly, whether the process was reversible and whether people could come back. But he didn't even have a clue.

Both of them were silent, except for the sound of the engine and Yu Guannan's sleeping breathing in the car.