On Wang Miao's fifth login to Three Body, the world has advanced dramatically: the old pyramid is gone, the landscape is filled with reflective modern structures, and a giant moon now dominates the sky. A homeless violinist identifies himself as Einstein and explains that earlier Trisolaran efforts to predict the suns failed because classical mechanics needed a correction from general relativity. Even with better equations and modern computers, however, the results have not saved him or the civilization, and Einstein has become a discarded prophet.

Following Einstein's directions, Wang goes behind the UN Headquarters and finds a ceremony for a colossal Pendulum Monument. The secretary general tells Wang that the monument is both a memorial and a tombstone for nearly two hundred civilizations' attempts to solve the three-body problem. When Wang presents Wei Cheng's mathematical model, the science advisor praises its ingenuity but says many stronger models have already been tested, and the conclusion is definitive: the three-body system is chaotic and cannot be predicted in any usable way. This revelation destroys the central hope that Trisolaran civilization could survive by finally discovering orderly celestial laws.

The secretary general then explains why even technological progress cannot secure Trisolaran survival. The giant moon is actually a fragment of the planet itself, created in the "great rip," when three suns passed so close to Trisolaris that tidal forces tore the planet apart during Civilization 191. One fragment became the dead companion world, the surviving "mother planet" barely recovered, and life needed ninety million years to evolve again before Civilization 192 appeared.

The situation proves even worse than a single catastrophe. Astronomers have discovered that the system once had twelve planets and that the other eleven were all consumed by the suns. They have also learned that the suns' outer layers expand and contract over immense cycles, making planetary capture more likely; another expansion is predicted in about one thousand years. Because Trisolaris cannot predict the stars well enough and cannot trust long-term survival in its own system, the leadership concludes that the only remaining strategy is to leave and find another world.

The pendulum is set in motion as a symbol of Trisolaran civilization's struggle against cosmic chaos. A message then appears announcing that Civilization 192 will itself be destroyed 451 years later, but that it has achieved a historic turning point by proving the three-body problem unsolvable and changing Three Body's goal to "Head for the stars; find a new home." After logging out, Wang rests briefly and logs in again, only to see an urgent notice that the Three Body servers are about to shut down and will proceed directly to the final scene.