Context for Departure
The Trisolaran civilization's decision to invade Earth was not impulsive but the result of prolonged and careful evaluation. The Trisolaran world was located in the Alpha Centauri triple-star system, where the gravitational interactions of three stars made planetary orbits extremely unstable. The Trisolaran civilization had struggled through hundreds of civilizational cycles in this hostile astronomical environment — whenever the gravitational dynamics of the three stars entered a chaotic state (the "Chaotic Era"), all civilizational achievements on the planet were destroyed. The Trisolarans developed a dehydration survival strategy, allowing the entire species to be dehydrated and stored during harsh periods, then rehydrated and revived with the arrival of the next Stable Era. But this mode of survival was essentially gambling — each civilizational rebuilding could be the last.
It was this deeply ingrained survival anxiety that drove the Trisolaran civilization to commit with enormous determination to preparations for interstellar colonization. When Ye Wenjie's signal arrived and was confirmed, the Trisolaran governing body swiftly made the strategic decision to advance toward Earth. Earth possessed a stable star (the sun), with the planet in a stable orbit within the habitable zone, and environmental conditions far superior to the Trisolaran world — it was a near-perfect colonization target.
Fleet Composition and Scale
The Trisolaran fleet comprised over one thousand stellar-class warships, each of a scale and capability far exceeding what humans at the time could imagine as engineering limits. These warships' propulsion systems were based on advanced physics principles mastered by the Trisolaran civilization, capable of achieving a cruising speed of one-tenth the speed of light — while not fast on a cosmic scale, this already far exceeded humanity's technological capabilities at the time.
The fleet's departure was a massive undertaking spanning decades. The warships were not completed simultaneously but were progressively produced, organized, and dispatched over decades. The entire fleet employed a staggered departure strategy, with advance warships responsible for establishing resupply and communication relay points along the route, while subsequent warships carried more colonization materials. Throughout the voyage, the fleet maintained communication with the Trisolaran homeworld, exchanging information in real-time through the sophon system.
Notably, the Trisolaran fleet's departure preceded the sophons' arrival on Earth on the timeline. The Trisolaran civilization's strategic arrangement was two-pronged: on one hand, dispatching a physical fleet for an actual invasion; on the other, launching sophons to reach Earth first, locking down humanity's scientific development while conducting intelligence surveillance. The sophons, traveling at the speed of light, arrived on Earth more than three hundred years ahead of the fleet, thoroughly preparing the groundwork for its arrival.
The Four-Hundred-Year Countdown
News of the Trisolaran fleet's departure eventually reached human society through the Earth-Trisolaris Organization (ETO) and intelligence channels. This information struck like a bombshell, causing massive panic and chaos worldwide. For the first time, humanity faced a definitive military threat from an alien civilization — not a hypothetical scenario from science fiction, but a real fleet traveling toward Earth at one-tenth the speed of light.
Four hundred years — this was all the time humanity had. This timespan occupied a peculiarly delicate position: it was long enough that the current generation would not live to see the invasion arrive, easily fostering an illusory sense of security; yet short enough that humanity had to act immediately, since technological development requires accumulated time, and any delay could prove fatal.
Even more despairing was the existence of sophons. Even with four hundred years of preparation time, fundamental physics had been locked down by sophons. Humanity could only develop technology within existing theoretical frameworks — optimizing engineering applications but unable to achieve fundamental breakthroughs at the physics level. It was as if a civilization were permanently trapped in the Newtonian mechanics era — even given a thousand years, it could never build nuclear weapons. Through the dual strategy of fleet departure and sophon blockade, the Trisolaran civilization placed humanity in a nearly unsolvable predicament.
Impact on Human Society
After news of the Trisolaran fleet's departure became public, human society underwent profound upheaval. Different nations and groups reacted to the threat in starkly different ways. Some fell into apocalyptic panic, advocating the abandonment of all resistance; others were galvanized into unprecedented unity and determination, pushing to concentrate all of humanity's resources for defense preparations. The United Nations promptly established the Planetary Defense Council (PDC) to coordinate global resources in response to the Trisolaran threat.
The fleet's departure also gave rise to extreme ideological movements. Escapists argued that humanity should build interstellar ships and flee the solar system with the seeds of civilization; defeatists believed resistance was meaningless and advocated early surrender to the Trisolaran civilization for survival; the Adventist faction within ETO actively cooperated with the Trisolaran civilization, hoping alien forces would reform human society. These ideological currents clashed repeatedly over the ensuing centuries, profoundly influencing humanity's strategic choices.
From a macro-historical perspective, the Trisolaran fleet's departure was the watershed event marking humanity's entry into the cosmic age. Before this, while humanity had achieved preliminary space exploration, the core of civilization remained Earth-centric. The fleet's departure forced humanity to contemplate civilization's future with an urgency never before experienced — no longer whether to venture into the cosmos, but how to survive within it. This civilizational awakening was both a gift of the Three-Body Crisis and its most enduring legacy.