Event Description
In the final stage of the Three-Body story, the narrative's scope expands to encompass the fate of the entire universe. Cheng Xin and Guan Yifan learned that the universe was originally ten-dimensional, possessing incomparably elegant physical laws. But throughout the long history of the cosmos, wars between countless civilizations led to the widespread use of dimensional weapons — higher-dimensional spaces were continuously reduced to lower dimensions, from ten to nine, eight, and progressively down to the current three dimensions (with some regions already reduced to two).
An even more serious problem was mass loss. Many advanced civilizations, seeking their own continuation, created "pocket universes" — miniature universe spaces independent of the main universe — and transferred matter from the main universe into these pocket spaces for storage. While this protected individual civilizations, it caused the total mass of the main universe to continuously decrease. When the main universe's mass fell below a critical threshold, the universe would be unable to re-collapse after expanding to its limit, making another Big Bang impossible — the universe would expand forever, ultimately reaching heat death and total annihilation.
The Return Movement was born from this crisis. A call transcending civilizational boundaries spread across the cosmos: all civilizations should return the mass stored in their pocket universes to the main universe, allowing it to complete the collapse-explosion-expansion cycle and thereby achieve rebirth. This was a moral choice concerning the fate of the entire universe.