Luo Ji broke the wall of himself, he understood the axioms of the universe, he understood why the three-body people wanted to kill him, and he also understood the meaning of the last sentence that Ye Wenjie said when he met him, yes, he understood.

Luo Ji has penetrated the truth, and as for how to verify this truth, Luo Ji has his own decision.

He contacted Kanter, his contact for the Planetary Defense Council at the International Joint Conference, and when he saw him again, Rogue said to Kanter: "All these years, your hair has turned gray. ”

"At least for many years to come, it won't continue to be in vain." Kante said with a smile, in the past, he always looked polite and thoughtful in front of Luo Ji, and it was the first time Luo Ji saw such a sincere smile, and from his eyes, Luo Ji saw the unspoken words: You finally started working.

"I need a safer place." Luo Ji said.

"That's no problem, Dr. Luo Ji, do you have any other requirements for that place?"

"There are no requirements other than safety, absolute safety."

"Doctor, there is no such thing as an absolutely safe place, but we can do it very closely, but I need to remind you that such places are often underground, so the comfort aspect ......"

"I don't have to worry about comfort, but this place should be in my country."

"No problem, I'll do it right away."

As Kanter was about to leave, Roche stopped him, pointed out the window to the Garden of Eden, which was completely covered in snow and ice, and said, "Can you tell me the name of the place?" I'm going to miss it here. ”

……

After more than ten hours of closely guarded travel, Luo Ji arrived at his destination, and as soon as he stepped out of the car, he immediately knew where it was—a spacious but low hall in the shape of an underground garage, from which Luo Ji started his new dream life five years ago, and now, after five years of alternating nightmares and sweet dreams, he is back to the starting point.

Among the people who greeted him was Zhang Xiang, who was the young man who sent him away with Shi Qiang five years ago, since Shi Qiang hibernated due to illness, he is now the person in charge of security here, and after five years, he has become a lot older, and he looks like a middle-aged man.

The one who drove the elevator was still an armed police soldier, of course, not the one he was back then, but Luo Ji still had a sense of intimacy in his heart. In fact, the old-fashioned elevator has been replaced with a fully automatic one, and there is no need for human operation, and the soldier just pressed the "-10" button, and the elevator descended to the ground.

The underground building has apparently been renovated, the ventilation ducts in the corridors are hidden, the walls are covered with moisture-resistant tiles, and all traces of the past, including civil air defense slogans, have disappeared.

The ten basement floors have all become Luo Ji's residences, although the comfort is incomparable to the place he just left, but it is equipped with complete communication and computer facilities, as well as a conference room with a remote video conferencing system, making this place like a headquarters.

The administrator specifically pointed out a type of light switch in the room to Luo Ji, each with a small sun symbol on it. The administrator said that this type of lamp, called sun lamp, must be turned on for no less than five hours a day, which was originally a kind of labor protection equipment for mine workers, which can simulate the sun's rays, including ultraviolet rays, to supplement sunlight for people who have been underground for a long time.

……

The next day, at Luo Ji's request, astronomer Albert Ringer came to the tenth basement floor.

After seeing Ringer, Luo Ji said: "You first observed the track of the trimaran fleet?" ”

"No, it's not me, it's General Fitzrow, it's him who asked me to observe the Three-Body World."

Luo Ji said: "What I want to talk to you about has nothing to do with this, I have also done astronomy, but I have not gone deeper, and now I am already enthusiastic about this major." First of all, I would like to ask a question: If there are other observers in the universe except for the three-body problem, has the position of the earth been exposed so far? ”

"Nope."

"Are you so sure?"

"Yes."

"But the earth has already interacted with the three-body world."

"This kind of low-frequency communication can only expose the general direction of the Earth and the Three-Body World in the Milky Way, as well as the distance between the Earth and the Three-Body World, that is, if there is a third-party receiver, then what they may know through these communications is that there are two civilized worlds 4.22 light-years apart in this area of the Orion Arm of the Milky Way, but the precise location of these two worlds is still unknown.

In fact, the mutual determination of positions through such interactive communication can only be achieved between stars that are very close to each other, such as the Sun and the Three-Body Problem, and for third-party observers who are slightly farther away, even if we interact directly with them, we cannot determine each other's positions. ”

"Marking the position of a star to other observers in the universe is far less simple than one might think, so let's use an analogy: when you fly over the Sahara Desert in a plane, a grain of sand in the desert below shouts at you, 'I'm here,' and you hear it, can you determine the location of the grain of sand on the plane? There are nearly 200 billion stars in the Milky Way, which is almost a desert of stars. ”

Luo Ji nodded, as if relieved, "I understand, that's right." ”

"What's right?" Ringer asked, puzzled.

Luo Ji didn't answer, but asked, "So, with our technical level, how can we mark the position of a star in the universe?" ”

"With locatable VHF electromagnetic waves, which should reach or exceed the visible light frequency, send out the message at stellar power. Simply put, it's about letting the star twinkle and turning it into a cosmic beacon in itself. ”

"It's far beyond our technical capabilities."

"No, Li Yang's detection system already has a certain emission function, and if that system is fully completed, it will be more conducive to the transmission of stellar information."

"Or there is another way, but the level of technology required to interpret this kind of location information is much higher than that of humans, and even ...... I think it's also higher than the three-body civilization. ”

"Tell me about it."

"The relative position of the stars is an important piece of information, and if you designate a region of space in the Milky Way that contains a large enough number of stars, probably a few dozen, then the relative arrangement of these stars in this three-dimensional space is almost unique in the universe, like a fingerprint."

"I kind of got it to me: if you send out information about the relative position of the star you want to indicate and the surrounding stars, and the receiver compares it with the star map, the position of the star is determined."

"Yes, but it's not that simple, the recipient needs to have a three-dimensional model of the entire Milky Way, a model that contains all the hundreds of billions of stars, accurately indicating their relative positions. That way, after receiving the information we sent, they can search through this huge database and find the space that matches the location composition we send. ”

"It's really not easy, it's equivalent to recording the relative position of every grain of sand in a desert."

"There is more difficult, the Milky Way is different from the desert, it is in motion, the position between the stars is constantly changing, the later the position information is received, the greater the error caused by this position change, which requires that database to have the ability to predict the position changes of all the hundreds of billions of stars in the Milky Way, theoretically fine, but in practice, oh my God......"

But for higher-level hunters, this is not a problem.

"Is it difficult for us to send this kind of location information?"

"It's not difficult, because we only need to have a limited number of star position compositions, and now think about it, with the average star density of the outer spiral arms of the Milky Way, a position composition of thirty stars is enough, or even less, which is just a small amount of information."

"Okay, now let me ask the third question: You seem to have found hundreds of other stars with planets outside the solar system?"

"So far, five hundred and twelve."

"What's closest to the sun?"

"244J2E1, 16 light-years according to the Sun."

"I remember that the numbers were set like this: the numbers in front of them represent the order in which they were discovered, J, E, and X represent Jupiters, terrestrial planets, and other types of planets, respectively, and the numbers after the letters represent the number of such planets."

"Yes, 244J2E1 means that there are three planets, two Jupiteriums and one terrestrial planet."

Luo Ji thought for a moment and shook his head, "It's too close." What about further afield, such as ...... 50 light years or so? ”

"187J3X1, 49.5 light-years from the Sun."

"This is good, can you make a composition of the position of this star?"

"Absolutely."

"How long does it take? Need help? ”

"All you need is a computer with internet access, and I can do it here, according to the composition of thirty stars, and I can give it to you tonight." "What time is it? Isn't it night? ”

"Dr. Luo Ji, I think it should be morning."

Ringer went to the computer lab next door, and Luo Ji called Kanter and Zhang Xiang again, and he first told Kanter that he wanted to ask the Planetary Defense Council to hold a hearing on the wall-facing plan as soon as possible.