AA tries to comfort Cheng Xin about her role in the destruction of the solar system as they make their 287 light-year journey to DX3906 that takes roughly 52 hours in their frame of reference.
Upon landing on the more habitable planet in the system, which they call Planet Blue, they are greeted by the civilian cosmologist who was aboard Gravity hundreds of years ago, Guan Yifan. He is not sure what happened to the Trisolaran fleets or Yun Tianming, but he received the broadcast from Halo and was there to meet them and take them back to one of the worlds that the galactic humans had founded.
Even though this part of space is dangerous, Cheng Xin insists on waiting for Yun Tianming, and when Yifan’s ship detects activity on a nearby planet, Cheng Xin accompanies him to investigate.
While en route, Yifan tells Cheng Xin more about the realities of the universe, including that civilizations routinely use the laws of physics as a means of attack, often using dimensional attacks. Some civilizations have even found ways to live in lower dimensions while attacking ones in higher dimensions, just as a means of survival at any cost. Finally, he tells her the theory that the universe was once ten-dimensional and light speed approaches infinity, but the endless dimensional attacks have brought the universe to its current state. They reach “Planet Grey” and see 5 black lines radiating from the planet, which Guan Yifan calls “death lines.” These lines are made from extremely advanced curvature propulsion engines and the speed of light inside them is 0 and they have a possibility of rupturing, especially if they come in contact with other curvature propulsion trails. He recommends that they get away from them as quickly as possible.
As they make their way back to Planet Blue, they receive a message from AA saying that Yun Tianming is there with her and he has brought her another even grander gift. Cheng Xin is awestruck and they make their way down to the planet, but the reunion is not meant to be as the death lines rupture and they find themselves traveling at the new, slower speed of light inside the black domain that was created by the rupture. Because his computers can’t work at reduced lightspeed, Guan Yifan needs to start the process of booting the slower, but heavily parallized neural computer to help them bring life support back online. This process takes over 12 days, so they will need to temporarily hibernate to preserve oxygen. This process is ultimately successful, but comes at a great cost, as they have traveled at the new lightspeed for almost 19 million years, meaning that Cheng Xin’s chance to meet with Yun Tianming has long since passed.
Cheng Xin and Guan Yifan are able to reduce their speed and make their way down to the planet to search for any signs, when Cheng Xin remembers what Luo Ji had taught her and AA, that the only way to preserve a message over great spans of time was words carved into stone, and they eventually find a message left to them from AA and Yun Tianming:
- WE LIVED A HAPPY LIFE TOGETHER
- WE GIVE YOU A LITTLE
- SURVIVE THE COLLAPSE INSIDE
- GO TO THE NEW
They find a rectangular doorway on the planet and upon entering it, they are greeted by Sophon and their own pastoral, pocket universe. The hope is that they will be able to stay in the mini-universe outside of time until such time the universe has a chance to reset with another big bang and they’re able to experience the edenic, 10-dimensional universe. During their stay in the mini-universe they receive a broadcast from a faction called the Returners who say that the universe will not be able to reset due to the mass that has been taken into the pocket universes and the only way to allow it to happen is to return the mass to the main universe.
Cheng Xin and Guan Yifan decide to dismantle their universe and return the mass with the hope that enough other inhabitants of pocket universes will do the same to save the universe from an eventual heat death. The three of them take a ship and set out to explore leaving behind only a databank of human and Trisolaran knowledge and a self-sustaining fish bowl that will travel outside to the new universe.