Dimension is a mathematical concept.

Its mathematical significance is that in a space, several parameters are required to be able to determine a position. Only one parameter is needed to determine the position, which is called one-dimensional space, and two-dimensional space is called two-dimensional space, and the space we are in needs three coordinate parameters of length, width and height to determine the specific position, so it is called three-dimensional space.

What kind of space is one-dimensional space, the answer is a straight line. In a straight line, only one parameter is needed to determine the specific position, so the straight line is one-dimensional space, while in a plane, two axes of X and Y are needed to locate the two-dimensional space.

By analogy, three parameters are required for three-dimensional space and four parameters for four-dimensional space.

But for us living in three-dimensional space, we can't directly touch four-dimensional space because of the different dimensions, so four-dimensional space is just a concept that exists in mathematics for us. It's real, but we don't have an intuitive understanding of it.

There is no doubt that the four-dimensional space is a bizarre world for us living in the three-dimensional space, and it is impossible to peek into its internal form of existence with the known senses.

However, we can make an analogy between two-dimensional space and three-dimensional space, three-dimensional space is relative to four-dimensional space, and its existence is like a person in three-dimensional space looking at two-dimensional space, so what is the result?

Suppose there is a group of creatures in the two-dimensional realm, and they are also extremely technologically advanced, and their cities also have vehicles similar to cars, but this kind of transportation is speeding against the ground, because they have no concept of height. You can't get off the ground. Airplanes are a means of transportation that would never have been possible in their world.

But if suddenly there is a magical force from the outside world that is exerted into the two-dimensional realm, everything in the two-dimensional realm will have a "height" overnight. Then this phenomenon is very magical.

For beings in the two-dimensional realm, they may not be able to understand the meaning of "height". But standing in the three-dimensional world, we can see that they are just like the cars in our world, although they can only speed against the ground, but they actually have a height. It's just that in such a world, they still can't make such a thing as an airplane.

This world is between two-dimensional space and three-dimensional space, and it is defined as two-point five-dimensional space.

What is the difference between two-dimensional space and three-dimensional space, the most basic is that three-dimensional space has more information than two-dimensional space.

For example, a piece of paper is laid on the ground in three-dimensional space, which is two-dimensional space, and a plate of mosquito coils is placed on the paper. Under the illumination of the light, the threads of the mosquito coil are projected onto the paper. Suppose that the creature in the two-dimensional space has the same complete perspective as us, and the mosquito coil projection it sees is also a thread, then at this time we turn the mosquito coil over a side, and the thread direction of the mosquito coil projection changes, standing in the perspective of the three-dimensional creature, of course, we know that this is still the original mosquito coil, but the two-dimensional creature sees not the original mosquito coil.

This is the reason for the information asymmetry, and the two-dimensional organisms with less information cannot judge that the two mosquito coil projections actually originate from the same mosquito coil as we do.

Here's a simple example. However, in reality, a two-dimensional creature cannot have a complete perspective like us, nor can it see the complete thread of mosquito coils, it only sees a "wall" in front of it that can never be overcome.

There's a concept involved here. That is, the space at high latitudes is completely visible to the space at low latitudes.

This means that from a high-latitude perspective, it is possible to observe low-latitude space at a glance. In simple terms. Suppose a piece of paper is the two-dimensional realm, draw a circle on the paper. Then for the two-dimensional creatures inside the circle, they are trapped by a closed wall. It is never possible to see the world outside the circle, and the two-dimensional beings outside the circle will never know what is happening inside the circle.

But standing in three-dimensional space, we can easily know everything inside and outside the circle. Because for us, there is such a dimension as "height", which allows us to look down on them directly.

In the same way, if there is a closed sphere in our three-dimensional space that has existed since the beginning of the formation of the world, the people inside the sphere will not be able to know what is happening outside the sphere, and the people outside will not know what is happening inside the sphere. However, for the "people" of the higher dimension of the four-dimensional realm, they are able to use an additional dimension that they can comprehend to observe us completely.

The two-dimensional realm is not sealed for the three-dimensional realm, and similarly, the three-dimensional realm is not secret for the four-dimensional realm. That's all it takes!

If a person has a four-dimensional perspective, then everything he sees is perspective, and there are no secrets to him in this world.

In addition, low-latitude space cannot defend against high-latitude space.

It means that there is a circle in the two-dimensional world that is indestructible for two-dimensional beings, and this circle can never be destroyed, but for the people of the three-dimensional world, this circle cannot form any obstacles, and we can easily use the weapon of "height" to cross into the circle!

Well, no matter how strong the defenses of two-dimensional space are, it doesn't mean anything to us. Because its existence itself has a fatal flaw! Similarly, even if we build an absolutely strong defense in three-dimensional space, we cannot stop the invasion of four-dimensional creatures.

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"The existence of the universe is really amazing, and the alien civilization's understanding of space far exceeds that of human beings!"

This is Su Yuan's sigh after reading some of the previous information.

Mankind's understanding of multidimensional space is still limited to mathematics, and the extraterrestrial civilizations that gave rise to Gaia and Alaya have a more detailed understanding of the invisible high-latitude space. In their technology, there are even large weapons that use high latitudes as shields or means of attack, although they have only learned to use the four-dimensional space, but have not mastered the higher dimensions. But it's already staggering.

Su Yuan didn't know how much damage the Dao Four-Dimensional Weapon could cause, but just thinking about it already made people feel chills.

In the information provided by Alayya. There is an ominous mention of space weapons, and the defense has a "four-dimensional protective shield". The attacks include the "Space Cage" that is similar to the four-dimensional protective shield that specifically locks the enemy inside, and the "Space Rift" that completely tears through the three-dimensional space.

However, it is a pity that only these terms appear, and there are no specific principles and parameters.

Of course, Su Yuan also has an expectation, that is, he hopes to find a way to repair space in alien technology, since alien civilizations can use "space" as a weapon to attack the enemy, why don't they have the technique of reverse repairing space?

……

In the next few days, Su Yuan immersed himself in obscure materials. With Alayah, the "mentor", by her side, her understanding of space can be described as a day by day.

Although she had only scratched the surface of the four-dimensional space so far, and was at best at the beginning stage, according to Alayya, this knowledge was only something that should be mastered in the first year of junior high school in her mother civilization, but Su Yuan already felt very satisfied.

The conversation with Alayah was more of an inquiring attitude, as if a door to a new world suddenly opened, immersing her in a new atmosphere.

Meantime. Su Yuan hurriedly went back to the countryside with Su Caiwei, and this time back, Su Caiwei officially introduced her to her relatives in her hometown. Those relatives saw that Su Caiwei had found her daughter, and they all congratulated her. At the same time, she also asked for warmth from Su Yuan's experience in the past ten years, which made her have the heart to retreat, but it was not good to snub the enthusiasm of her relatives. It's not embarrassing for a while.

After staying in the countryside for a day, Su Yuan said goodbye to his grandparents, uncles and others. She returned to the Longmen community and continued her learning progress.

……

December 20th. It is a very important day, and in my memory, the first "World Boundary Sniffer" on the World Continent will be completed in the hands of Gao Jun and Charlene in the afternoon of this day.

At that time, Su Yuan will be able to know whether he has jumped the boundary of the world, whether he can change in the future depends on today, in order to wait for this day to come, Su Yuan has been worried for a long time.

As soon as the light of the morning light shone into the room, Su Yuan opened his crystal clear eyes. After a simple wash, and without even eating much, she ran towards Riverside City.

At the entrance of Binhe University of Technology, the white car was parked under the shade of a tree, the air conditioning was on in the car, the windows were slightly open, Su Yuan was wearing a pair of sunglasses on his face, and he was holding a loaf of bread and a bottle of mineral water in his hands.

It was close to noon, and it was her lunch.

From time to time, cars passed by her, turned right onto another road, or headed straight for the riverside polytechnic school gate.

"It seems that there are quite a lot of cars coming in and out of the school every day. She had only been waiting for more than an hour before she saw more than a dozen cars entering.

Thinking so, she grunted and drank water, just then an off-road vehicle drove by and stopped not far in front of her. Seeing the person getting off the off-road vehicle, Su Yuan stopped drinking water and looked ahead in surprise.

The driver was a man in his thirties, with dark skin and a rough appearance, which made people see at a glance that he was a hard stubble.

The young man who got out of the car was the one who caught Su Yuan's attention, and it turned out to be Wei Hefeng!

"This guy has a bouquet of flowers in his hand, is he going to pursue me in the school?" Thinking of Chu Wei and Feng's "pursuit" for him, Su Yuan felt a burst of amusement.

Wei Hefeng said that he was a single, at least he didn't want to get married so early, and he had to pretend to pursue Su Yuan in order to cope with his parents' forced marriage. However, when he knew that Su Yuan already had a boyfriend, he immediately dispelled this idea and turned around and left very freely.

On the surface, this is the case, but Su Yuanzhi, who has experienced the danger of life and death, said that Wei and Feng are not as simple as they seem on the surface.

Judging from the fact that he brought a team of heavily armed men and horses that day, and had the power to talk to the military, his identity could not be simple, he pretended not to see himself when he saw himself, and deliberately let himself and others go, and it can also be seen that he at least has a kind side to himself.

It's just that why did he want to get close to him, and helped himself at a critical moment?

This mystery has been brewing in Su Yuan's heart. (To be continued......)