First Contact Timeline
Humanity's first contact with extraterrestrial intelligence begins with a single signal sent into space.
The Origins of Red Coast Base
The chain of events that leads to first contact begins not with a radio telescope pointed at the stars but with the Cultural Revolution in China. Ye Wenjie is the central figure whose experience shapes the entire trilogy. During this period of intense political upheaval, a young astrophysicist named Ye Wenjie witnesses violence that destroys her faith in humanity's capacity for self-governance.
Rather than being imprisoned, she is sent to work at Red Coast Base — a classified military facility operating one of the world's most powerful radio transmitters. Officially, Red Coast monitors for foreign military transmissions. Secretly, it is also part of a larger project investigating the possibility of extraterrestrial signals.
Ye Wenjie's position at Red Coast Base gives her something extraordinarily rare: access to a transmitter powerful enough to reach the stars, combined with the technical knowledge to use it, combined with a profound disillusionment with the civilization she would be putting at risk.
The Warning Signal
Years into her work at Red Coast, Ye Wenjie detects an incoming signal from an extraterrestrial source — later understood to be the Trisolaran system, roughly 4.2 light-years from Earth.
The signal is a warning. It comes from a Trisolaran individual who, at great personal risk, is attempting to alert Earth to the danger of making contact with Trisolaris. The message is clear: do not reply. The civilization sending signals is dangerous. If they locate Earth, they will come.
Ye Wenjie reads the warning. She understands it. She replies anyway.
The Reply
Her decision to respond is not impulsive. It follows from her assessment of humanity — not of Trisolaris. She has witnessed enough human cruelty to conclude that external intervention may be the only thing capable of correcting humanity's course. If an alien civilization arrives with superior technology and forces change, perhaps that is better than no change at all.
Using the Sun as a gravitational lens to amplify the signal — a technique she had previously worked out theoretically — she transmits Earth's location and an invitation.
The message travels at the speed of light toward Trisolaris. What arrives there, approximately 4.2 years later, changes everything.
The Trisolaran Response
The Trisolaran civilization receives Ye Wenjie's signal during a period of their own crisis. Their home system, with its three-sun gravitational chaos (described in detail in The Three-Body Problem in Physics), makes long-term habitability uncertain. The prospect of a new, stable home with a civilization that has just announced its coordinates and extended an invitation is extraordinary.
The Trisolarans begin mobilizing. An invasion fleet is prepared — one that will take roughly 400 years to cross the interstellar gap. And as preparation for that arrival, they deploy sophons: engineered particles that can monitor Earth in real time, suppress human scientific development, and communicate with human collaborators who share the Trisolarans' goal.
The Earth-Trisolaris Organization
In the years after the signal, a movement forms on Earth among humans who have been contacted by the Trisolarans or who independently came to believe that humanity is irredeemably corrupt. The Earth-Trisolaris Organization (ETO) is a secret network of people who welcome the invasion — either because they believe Trisolaris will be beneficial, or simply because they want humanity to fail.
The ETO operates globally, providing intelligence to Trisolaris, recruiting members, and attempting to prevent Earth from developing defenses. It is the investigation into the ETO that draws the protagonists of the first book into contact with the broader crisis.
When Humanity Learns the Truth
The public revelation that an alien fleet is en route to Earth triggers a global transformation. Governments, militaries, scientific institutions, and ordinary people all face the same impossible question: how do you respond to a threat that will arrive in four centuries, from a civilization so far ahead technologically that its surveillance particles have already rendered our secrets transparent?
The political and social response to this knowledge — the debates, the factions, the Wallfacer Project, the fleet-building programs — forms the substance of the second book. But it all begins with a single woman standing at a radio transmitter, choosing to reply to a warning that told her not to.
For the broader sweep of events across the trilogy, see Timeline of the Trilogy and Human Civilization Timeline.