"How do you understand the concept of traversal?" The beautiful sister's lecture hall has started again, and after putting down the paintbrush, Lemidia seems to be hanging, and now she is sitting in the middle of a pile of books, wearing light pink pajamas, with a big round-framed eyes, and she looks a little cute.

"Huh?" Lin Sen's child has been overusing his brain recently, and is now in a state of rest.

"I know!" Wu Huan's children are not bad, and they have the courage to raise their hands to speak.

"Please." Lemidia is very deep in the play.

"Well, it's probably going back to the past, changing the future, going to the future and looking back at the past?" Wu Huan's answer was very conclusive.

"Not bad!" The beautiful sister praised first, and then when Wu Huan smiled shyly, she immediately splashed a basin of cold water.

"However, this is just a whimsical misunderstanding, and in fact the crossing is a very complex paradox with many logical contradictions." The beautiful sister has officially started the class.

"It's okay, it's okay~" Lin Sen comforted Wu Huan, and the ambiguous eyes of the little couple were hot.

"Oops! Don't listen to me! Dissatisfied knocked on the floor, and the two people in front of him sat up straight.

Si Qi, who was squatting on top of Lemidia's head, raised his foot and gestured with his middle finger: "Stupid dog, your movements are getting more and more skillful!" ”

Lin Sen immediately replied with a cold look, and the fierce Si Que trembled.

"Well, sit down, listen carefully, if my guess is correct, then it will definitely help solve our current trouble!" When Lemidia said this, Lin Sen and Wu Huan glanced at each other, and they were actually quite helpless in their hearts, because they also thought so after seeing the eldest lady who cut a hundred meters of sword marks with a sword a few days ago, but the result was that this eldest lady didn't know what strange disease she had, and she actually had that kind of combat effectiveness only in a dying state, and as a result, a new force immediately became a "painting expert", although she was beautiful and captivating, but she also confirmed the attributes of the vase.

So now Lin Sen really feels a deep powerlessness, in the face of Kui's overlooking power, its thoughts and thoughts have been completely beyond the reach of human beings, after the sense of powerlessness began to appear, Lin Sen has been in a state of confusion, until Lemidia suddenly started the class, saying that she found something useful.

So what exactly is this useful thing?

I saw Lemidia take out a blank piece of paper, and then said to Lin Sen and the others.

"Let's say, this is 'space.'" She stroked the surface of the white paper, and this assumption was still acceptable.

She then marked a point, then drew a straight line, and marked the right side of the line with an arrow to confirm the concept of the direction in which it extended [a line that developed from left to right].

"Now, I have created the 'line of time' within 'space'." It's the same feeling as the Creator.

Lin Sen was a little ignorant, but he listened carefully.

Wu Huan has already deserted a little, after all, the last time he was bullied by a school bully is still vivid......

"Anyway, with Lin Sen here, I'll be lazy......" When Wu Huan thought like this, Lemidia marked three more points on the line, and used A, B, and C to establish the concept of distinction from left to right.

"Suppose that A is yesterday, which can also be seen as the past that has 'passed' and 'disappeared', B is today, which also means that the present is 'in progress' and is in constant change, C is tomorrow, or more accurately, it should be the future that has not yet 'appeared' and cannot be determined. So, if you look at the concept of crossing now, how should you express it in A, B, and C? "Lemidia spoke in detail enough.

Lin Sen thought for a while, and gradually became interested, although he didn't know the reason for this interest, but he was indeed thinking about it seriously.

Picking up B and putting it in A's place is going back in time......

No, no, no......

Wrong...... If B goes back to A, then does C still exist? Can A still get the result of B?

With just a simple attempt, Lin Sen discovered the first paradox in time travel, "replacement".

"How? Did you find out? Lemidia saw Linsen's attempts and the distress of the failed attempts.

Lin Sen nodded and shook his head, after he hissed, he sat up straight and said: "If according to your assumption, the three points of ABC are on the same line, with continuity and unity, and they are very logical in all aspects, but if time can really be understood in this way, then time and space travel should be an impossible task." ”

The beautiful sister smiled, and her face showed the relief that her son could be taught.

Wu Huan was dumbfounded.

"You ...... What are you talking about? Wu Huan's brain in pure white pajamas was hit strongly again, and she strongly protested against this pure academic, communicative, because she didn't understand it at all!

Lin Sen smiled slightly and explained in a more vivid way: "You can understand it this way, if you are A when you were a child, you are B now, you are C in the future, and your growth is in a process from A to B and then to C, so although it deviates a little from what we just said, it is not too much, then you think about it, if you go back to the past, then what will happen?" ”

Wu Huan frowned and thought for a while, and then naturally replied: "Of course, change the past, and then be a better me?" ”

Lemidia laughed dryly, Lin Sen tried to keep smiling, he knew clearly, Wu Huan still didn't understand.

OvO？

How is it wrong? Wu Huan looked at the two of them stupidly.

Although Lin Sen didn't think it was too necessary, he still wanted to work hard. So he said, "Have you ever wondered how you went back in time?" Do you directly replace you with your existing memories like a game file, or do you help you as a stranger as a bystander? ”

"This ......" Wu Huan understood...... That's right? What is the state of me back in the past?

If you follow your personal wishes, you must want to directly fit into your past self and start over with your conscious reading files, but when you really do something, according to more realistic considerations, it is more likely to go back to the past and see another self.

Wu Huan understood this, but she didn't notice Lin Sen's expression.

Lin Sen is thinking much more now than Wu Huan, he not only knows the various possibilities of time and space travel, but also has many contradictions.

Lemidia took the pen and drew a circle with a diameter between A and B, and the first paradox appeared.

"Loop! If we develop on a single line, then when B returns to the position of A, replacing the past A with a fit produces A1 with the idea of B, then if the timeline is unified and unique, when A1 develops to the position of B that was originally crossed by time advancement, the paradox arises! At this time, will the B1 obtained by the development and evolution of A1 continue to advance to obtain C1, or will it fall into an endless cycle and start crossing again and create A2? After all, the timeline is the basis of the same, only we change, people walking on the same road, even if we turn back to the starting point, then after the switchback again, will the turnback happen again at the point? ”

Lemidia's words began to get very complicated.

Even Lin Sen was now in a state of contemplation and distress, but Wu Huan, who didn't have much understanding of this and had a lot less doubts and considerations, asked rhetorically, "Will it?" If I go back in time and change myself, why should I travel back in time in the future? Haven't I already achieved my goal? ”

Lemidia shook her head, she looked at Wu Huan with a serious expression and said seriously: "Has it been reached?" ”

“……？” Wu Huan couldn't understand it at all, is the seemingly simple problem of time travel really that complicated?

When Wu Huan was at a loss, Lin Sen suddenly raised his hand to take Lemidia's pen, and then drew another line under the circle, and a new timeline with the center of the two points of AB as a vertical parallel appeared.

On the new timeline, A1, B1, and C1 are marked.

This is the only explanation, and it is exactly what Lin Sen is experiencing now.

Lemidia nodded: "By the way, new time, new space, everything is new, in order to jump out of the paradox, the B that has been crossed is no longer the original timeline." ”

Wu Huan pouted, snorting angrily and clutching the pillow for a while.

Lin Sen touched her head and explained with a smile: "Let's put it this way, if you go back to when you were a child, and then you choose to commit suicide, can you still cross over?" Or is the intention of suicide really achievable? Figuratively, if you go back to the time before your parents knew each other and kill your father, will you disappear? If you disappear, how can you kill your father? ”

Wu Huan was ignorant, but he finally touched the contradiction, is there a forbidden place in this spiral of time that cannot be touched?

"Therefore, if time is linear, unique, and unified, then it is not feasible to go back to the past, or we go back to the past itself as a repetition in the development of time, and this repetition will not be changed, cannot be changed, unless we jump out and start from ourselves and recreate a timeline!" When Lin Sen said this, on the one hand, he was explaining to Wu Huan, and on the other hand, he was also arguing his own understanding.

Vaguely, Lin Sen already understood something, but why me? Why is it that every time it is because of my death, it has caused a heavy load and a re-creation? What timeline am I on now?

Or is it just a hoax in itself, just a little trick on memory?

……

If cognition is a circle, then the more you know and the bigger the circle becomes, the more problems you have to face.

The current Lin Sen is in this state.

Wu Huan's small circle was much smaller, she understood a little, but quickly asked rhetorically: "What about going to the future?" Can't that be done either? ”

Lin Sen was thinking seriously, and he didn't answer.

Lemidia gave the answer: "Yes, but you don't have yourself in the future, in fact, it's more like a hibernation, you are separated from the world, you fall into a deep sleep, and when you wake up, you arrive in the future, but this is completely different from the naïve idea that you expect to see your future family." Of course, there is a premise for all this, that is, you are unique and unified, and space and time themselves are also unique and unified. ”

Some of Wu Huan's little fantasies were ruthlessly broken, she had always looked forward to the ability to travel through time and space, but now it seems that it may just be a fantasy......