A patch of a spiral galaxy, a few thousand light-years across. One or more civilisations launch self-replicating probes. Each probe that reaches an unclaimed star builds a seed factory, mines the system, and eventually builds more probes.
Every colony knows only what light has told it. When a colony launches a probe or is founded, it broadcasts that fact at c (the faint rings). Neighbours that haven't heard yet may target the same star — a duplicate arrival. Cooperative strains also follow a protocol: the nearest colony you can see has the right of claim. Knowledge in this sim is never stored; it is computed from event times and distances, so every decision is made on a genuinely out-of-date picture. Select a colony and press “View from its light cone” to see the galaxy exactly as that colony perceives it: stars as they were, probes where they appear to be.
Colonies extract matter (richer in the metal-heavy inner galaxy and near nebulae), grow industry up to a cap set by starlight, and split output between probes and a Dyson swarm. Swarms dim the star (it glows infrared instead) and raise energy for industry and research. Once a colony has nowhere left to expand, it stops mining and turns to computation. Mass is conserved: rock becomes infrastructure, swarms, defences and probes; wreckage falls back as rubble. Probes obey the rocket equation, so speed costs propellant, and exhaust is the one real loss. When the rock runs out, hungry colonies dismantle their own swarms.
Each colony researches on its own; the first to reach a breakthrough (Drive, Range, Fabrication, Fidelity, Stellar Engineering) broadcasts it. The bright ring is that news spreading at lightspeed — colonies upgrade only when it reaches them. Big bright stars wrapped in swarms tend to become the research hubs.
Replication is imperfect, and long-lived colony minds drift too. Each colony carries four heritable traits: loyalty (cohesion with its own civilisation), aggression (stance toward other civilisations), expansion drive, and a protocol dialect.
Colonies keep their dialect in sync with the same-civ neighbours they can see, but isolated or peripheral regions drift together. When a cluster can no longer parse its parent's broadcasts it splinters into a new civilisation with its own name, colour, research and founding doctrine. Claims are only intelligible within a civilisation, so borders produce collisions.
Strains with aggression above 0.6 raid other civilisations with heavy, slow-to-build warships. Strains whose loyalty falls below 0.2 go feral: they prey on everyone, never build swarms, and keep their research to themselves. Any colony that sees hostility nearby (a feral system, or a recent conquest by another civ, by the light that has reached it) arms up and sends white hunter warships to retake those systems. Fidelity research slows all drift.
Dust lanes (dark patches) destroy probes in transit. Massive O/B stars go supernova; the blast front travels at c and sterilises colonies within ~45 ly, leaving a remnant and freshly enriched matter that gets recolonised.
Drag pan · Wheel/pinch zoom · Click inspect · Space pause · V cycle colour mode · T/P/C toggle layers · F fit · O light-cone view of selection · Esc exit. Tip: slow down to ~50–100 yr/s and zoom in to watch light-lag in action.
Auto-pause (top bar) stops the clock and flies the camera to events you choose — supernovae, feral outbreaks, first contact and more. Hover or tap any underlined label, legend entry or tech name for what it models and the numbers behind it.