Berner pointed to a dot with a cigar, and this time instead of the shadow of the cigar, he used the cigar to represent the ship, which reached another point directly from the air.

"And now?"

"Are you saying that the two-dimensional spacecraft is separated from the two-dimensional plane and flies directly in three-dimensional space?"

"Uh-huh, that's right, it jumped and entered the high-dimensional space."

"Well, it seems that this two-dimensional creature has evolved quite quickly, and it has already mastered junior high school geometry."

After Juan said a mischievous sentence, he continued to answer the question: "The hypotenuse of an isosceles right triangle is 1.414 times that of the right angle, so this distance is 1.414 light years.

"Well, a two-dimensional spacecraft traveling at the speed of light needs to fly for 1.414 years."

"Both right and wrong."

Juan frowned: "Berna, you drank too much, if every teacher is like you, using superposition to mark the exam papers, the students will have opinions." ”

"Students with poor grades don't object." Bernard replied with a quip.

He then continued: "It's all about time.

"If you look at the time of two-dimensional space, it will indeed take 1.414 years to cover this distance.

"But the problem is that this is three-dimensional space, and it has its own 'time', the time of three-dimensional space.

"To understand this, we have to start with the nature of time, which is 'movement'."

Berner motioned for Juan to pay attention to the cigar he lit in his hand.

The cigar was horizontal, slowly turned by Bernard.

"Look at the shadow of the cigar on the wall, and pay attention to the one that lights the smoke."

Berner said, turning the cigar clockwise.

Juan saw the shadow of the cigar on the wall, the one that smoked, moving in a straight line from the far left to the far right.

Berner continued to turn the cigar clockwise.

The shadow of the cigar on the wall, the one that smokes, moves in a straight line from the far right to the far left.

"Suppose a two-dimensional creature was looking at the movement of a cigarette butt on a wall, and he would conclude that the cigarette butt moved from left to right in a unit of 'two-dimensional second' time, and from right to left in one unit of 'two-dimensional second' time," Berner explains. ”

"Wait a minute," Juan interrupted, "what do you mean by 'two-dimensional seconds'?" ”

Berner explains: "The 'second' is the unit of measurement of time, and the 'two-dimensional second' is the unit of measurement of time in my hypothetical two-dimensional world, and I use this term to distinguish it from the 'second' in our three-dimensional space." ”

Juan asked suspiciously, "But what's the point, you are in three-dimensional space, turning a cigar, and the time from left to right of the cigarette butt is the same as the time of the shadow of the cigar butt on the wall, from left to right."

"So, a unit of 'two-dimensional seconds' and a unit of 'three-dimensional seconds' are equal.

"So, what's the point of distinguishing between 'two-dimensional seconds' and 'three-dimensional seconds'?"

Bernard raised the cigar in his hand and said, "Because two-dimensional seconds and three-dimensional seconds are not equal."

"Just because they're just exactly equal doesn't mean they're always equal.

"Now, I'll tell you why don't you wait, please look at the shadow of the cigarette butt again."

This time, Bernard turned the cigar clockwise so that the cigarette butt moved from the far left to the right, and then, counterclockwise, moved the cigarette back from the far right to the far left.

And the shadow of the cigarette butt on the wall, the trajectory of the movement is the same as just now.

"See what?"

Juan touched his chin and replied, "You were clockwise before, clockwise, this time clockwise, then counterclockwise."

But because the cigar is horizontal, in the two-dimensional space on the wall, the two-dimensional creature can't tell the difference, and he will think that two times are the same.

"In other words, it took 1 'two-dimensional second' to go from left to right, and 1 'two-dimensional second' to go from right to left."

Berner nodded: "That's right, so in the eyes of two-dimensional creatures, the two movements of the cigarette butt are the same, the distance traveled is the same, and the time is the same, both are 2 'two-dimensional seconds'."

"Now, the two-dimensional creature is in a two-dimensional spaceship that jumps, and he is in three-dimensional space.

Then, when he looked at the movement of the cigarette butt, he noticed that it was different.

"He would think that the previous time, it took one unit of 'two-dimensional second' time for the cigarette butt to move from left to right, and then one unit of 'two-dimensional second' time to move from right to left, for a total of two 'two-dimensional seconds'.

"The next time, it took one unit of 'two-dimensional second' time for the cigarette butt to move from left to right, and then time was reversed by one unit of 'two-dimensional second' to make the cigarette butt retreat from right to left, for a total of 0 'two-dimensional seconds'."

"What? Turn back the clock! This is impossible, time can only go forward, it is impossible to turn back. ”

"If you use the time of a low-dimensional space to understand the motion of a high-dimensional space, you will have the result of going back in time."

"But it's just clockwise and counterclockwise, and if you put it upright, you can do it in a two-dimensional plane."

"Don't talk to me, Juan, I'm just using the analogy of the movement of a cigar.

"In fact, as long as motion involves a dimension that is not known in low-dimensional space, low-dimensional time cannot explain that motion."

As Juan scratched his head in thought, Bernard continued: "Objects move from one place to another at a certain speed over time.

"The speed of motion of this object is a function of space and time, and whether it is uniform or variable, it can be expressed by the variables of space and time.

"When space is constant, but there are two different movements of the same absolute velocity, then time can only be added to the absolute value, that is, negative time is allowed."

Juan tugged at his hair and said, "But that's not right, in fact, there is no time for negative values in three-dimensional space. ”

"You're right, in the example, there is no negative value in 3D time, but there is a negative value in 2D time."

Juan continued to tug at his hair, but his green hair was tough enough not to be plucked out by him.

He muttered, "What does that mean?" ”

"That proves that time in two-dimensional space is irrelevant to time in three-dimensional space," Berner said.

Further, the time of the low-dimensional space and the time of the high-dimensional space are also irrelevant.

"Although they are sometimes equal, they are definitely not proportional, not tenfold, hundredfold or whatever, but it doesn't matter at all."

Juan gave up pulling his hair, and at the same time gave up thinking, choosing to accept it calmly.

He followed the answer he found on the Internet and said: "Time is attached to space, there is no time without space, and different dimensional spaces will naturally have different movements, and there will inevitably be different times."

"Berner, you are so long-winded, you might as well tell me the conclusion."

"I hope you understand, that's why I said that."

"I don't need to understand, I just have to recite the conclusion. In the past, when I was in college, I had to memorize the answers to subjects that I didn't understand. ”

"Where did the answer come from?"

"Ah, this, haha, it's nice today."

Without dwelling on some of the obvious, Berner continued:

"Let's go back to the space jump we discussed earlier, now, how much 'two-dimensional time' does it take for a two-dimensional spacecraft to travel from this point through three-dimensional space directly to that point?"

Juan replied, "I don't know." Because the spacecraft is separated from the original two-dimensional space and moves in a three-dimensional space that is completely unrelated to time, there is no two-dimensional time there, so it is impossible to calculate. ”

"No, the ship still has two-dimensional time, inside it."

Juan was at a loss: "So, or 1.414 years?" ”

Berner shook his index finger: "You forgot the 'clock slows down'."

According to Einstein's special theory of relativity, especially the theory of slow ruler shrinkage put forward in it. When an object is moving at a speed close to the speed of light, time around the object slows down rapidly and space shrinks rapidly. When the speed of motion of an object is equal to the speed of light, time stops and space shrinks to points, i.e., zero space-time appears.

"Of course, only objects with zero resting masses can reach the speed of light, and no object can exceed the speed of light. A spacecraft with mass is at most close to the speed of light, but it is absolutely not at all.

"However, as long as there is speed, there is a 'clock slow ruler shrinking' effect. The faster the speed, the more obvious the effect.

"If the spacecraft reaches 0.9 times the speed of light and completes this 1.414 light-year voyage, the time inside it will only pass for about ten seconds.

"In other words, it took only ten seconds for the spacecraft to go from the start to the end of the jump."

Juan was surprised: "0.9 times the speed of light, ten seconds, and a distance of 1.414 light years?!" ”

Berner patted the wall and said, "It's 2 light years."

"To the creatures who were still in two-dimensional space, the spacecraft, ten two-dimensional seconds after disappearing from this point, appeared at another point two light-years away.

"But this spaceship, in fact, is not faster than light.

"It's a spatial jump."