The likely course
Run the research baseline and the two waves tell different stories.
The first hundred thousand years. Machines need only raw material, so almost every star is a target. Their front moves at about five percent of light speed and covers several thousand light-years. People who still need Earth-like worlds barely move. Their ships can cross about fifteen light-years at a time, and a suitable world is often farther than that, so the front waits for stars to drift into range.
The descendants’ turn. As settlers learn to live around ordinary stars, in built habitats, the share of systems open to them climbs from about five percent to sixty. From then on the pace is set by how long each new settlement takes to launch the next ship, and the front settles near one percent of light speed.
The crossing. Machines reach the Galactic Center in roughly half a million years and enclose ninety-nine percent of the Galaxy’s stars in 1.2 to 1.5 million. The human wave reaches the center in about two million years and encloses nearly everything in five to six million. The thin outer disk fills last.
Even the slow scenario fills the Galaxy in under a hundred million years, a small fraction of its age. This is the arithmetic behind the claim on the first page: had anyone begun, the evidence would be everywhere.
Riding with the machines
The Seed ships scenario is the one this project favors. Both waves ride the same small ships, at three percent of light speed and fifteen light-years to a hop. People do not cross as passengers. They cross as frozen embryos aboard the small ships that carry a self-copying factory, and are born and raised at the destination. Such a ship is tens of times lighter than a worldship, a vessel big enough to carry generations of living crew, and it can stop wherever a factory can, so the human wave no longer waits for Earth-like worlds. If every seeded settlement succeeded, the human wave would reach its first ten systems within about three percent of the machines’ time.
The gap you see between the two waves in this scenario rests almost entirely on one number: the share of settlements whose first generation, raised by machines, comes through. It is set here at seventy percent. Nothing we know fixes it, and the findings explain why it is the weakest part of the design.
How to read the maps
Four things to keep in mind when reading the maps above. The reasoning behind them is in the Findings.
- Range matters far more than the share of settleable stars. Once about four suitable systems lie within one hop, adding more makes no difference to the front’s speed; below about one, the front moves only as fast as the stars drift. A machine wave able to use five percent of systems moves exactly as fast as one able to use ninety.
- Range is a matter of endurance, not fuel. A longer crossing at the same speed burns no more fuel; it only takes longer. So the length of a hop is set by how long a ship can fly and still work, and no fuel depots are needed along the way. In the Sun’s own neighborhood this means the first wave goes out from the Sun directly, as the Neighborhood page shows.
- The early milestones are local. The first ten, thousand and million systems all lie inside the Sun’s own region of the model. They measure how fast a front moves here, not whether it crosses the Galaxy. The first test of that is a hundred million systems.
- The first-ten-systems times run about eleven percent early, because the model counts star systems while the readout counts stars.
Many civilizations, not one
Set Color by to Lineage drift and let it run past a billion years. The Galaxy does not turn as a solid wheel. Stars nearer the center lap those farther out, and settlements that began as neighbors are drawn into arcs and then into rings. A signal from the frontier takes tens of thousands of years to reach the Sun. No capital can govern that, and no fleet can hold it together. A galaxy-wide polity is not physically available.
There is a second lesson, and it is sharper. In this model each settlement succeeds or fails on its own. Real seeded settlements would not. One flawed way of raising the first generation fails the same way at every destination, because every ship carries the same instructions. Crewed colonies carry adults who can improvise around a fault. Seeded ones carry the fault.
Both lessons point the same way. What spreads through the Galaxy is not a government. It is a pattern: the habits of belonging, authority and repair written into the first settlements and copied outward by each one that follows. That pattern has to be right, and it has to be more than one pattern, before the branching begins.
Marsism: designing the pattern
How the model works
The Galaxy is about twenty thousand regions, each roughly 650 light-years across, laid out as a two-armed barred disk: Sun at 8.2 kiloparsecs, scale length 2.6 kiloparsecs, circular speed 238 km/s. Each region orbits at its own rate, so the map shears over time. It is a schematic of the disk on the Galaxy page, simplified to two arms. In each region the local front speed comes from the formula of Carroll-Nellenback and colleagues:
Here f is the settleable share, ρ the local density of systems, d the longest hop, v the cruise speed, Tp the time to launch again and p the share of settlements that launch. D₁ is the chance that a target lies ahead within range, and τc the wait for a stellar encounter. A finite settlement lifetime lowers each region’s occupancy and slows the front. Regions vary by a random factor, and a few turn inward and stop expanding.
The map leaves out the halo and globular clusters, vertical structure, competition between lineages, catastrophes, other civilizations and the jump to other galaxies. Times are statistical front arrivals, not the dates of individual missions.
Sources
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