Earth

In the AiO universe, Earth is humanity's dying home world and the origin point of a six-century-long conspiracy for immortality.

By 2026 AD, humanity had advanced to a Type II Kardashev civilization; a massive energy-harvesting structure in the solar system intercepted the vast majority of the Sun's photons. Consequently, Earth was deprived of visible and ultraviolet light, causing photosynthesis to cease, circadian rhythms to collapse, continental ecosystems to turn into barren wastes, and the climatic boundaries between the poles and the equator to blur completely.

The "strong-interaction noise" left behind by the extraction of glueballs caused persistent DNA damage, slashing the maximum human lifespan by five to six years every two decades and narrowing the window for reproduction; interstellar colonization shifted from a means of expansion to a prerequisite for species survival. Surface city clusters degenerated into the ruins of a dying home world, while the surviving population migrated into underground domes and artificial light zones.

Nominally, Earth and Mars maintained a dual-core administration under a United Colonial Government, linked by quantum tunneling gates and orbital stations. In reality, however, the Zhu Foundation had spent six centuries operating in the shadows to monopolize glueball purification, immortality-granting DNA symbionts, and interstellar power. The glowing metal mistaken for an "elixir of immortality" during the transition from the Jianwen to the Yongle reign of the Ming Dynasty was, in fact, a glueball-hadron hybrid crystal—a substance that accelerated scientific progress while simultaneously giving rise to the Foundation.

Today, Earth is the birthplace of the state doctrine declaring the "Dyson-style interception of starlight" a necessary sacrifice, as well as a homeland that countless people look back upon but can never return to. Though it no longer shines, it remains the first tombstone in the causal loop of the entire AiO universe.