A visualization of galactic settlement

[tmazanec1]

https://www.centauri-dreams.org/2021/06/...ettlement/

VERY conservative assumptions fill the galaxy in 1 Eon.

[Bear]

I don't get why the commenters think this model requires some ultra-stable political organization or unified civilization with a millions-of-years-long agenda to colonize the galaxy.

The model says a colonized world is expected to send out a colony vessel, if it has a suitable target within ten light years and hasn't done so more than nine times total or at all in the previous hundred thousand years.

A hundred thousand years is a long damn time. That doesn't even imply that these sequential colony ships would be sent out by the same species, let alone by some eternally-enduring political order or according to some galaxy-spanning imperative that endures for millions of years.

That's more like, "Every hundred thousand years or so we can expect that some civilization that values expansion will arise, at a time when building an interstellar colony ship is technologically possible, and endure long enough to actually launch one before it collapses or gets destroyed by its neighbors."

I wouldn't even expect individuals descended from the same colony to recognize one another as the same species, if both were five or six colony-worlds removed from it via different lines of descent. They'd probably recognize that they were related somehow, but not even guess how recent the last common ancestor might be. And as for political continuity? That's just out the window.

And anyway, I would be thinking in terms of systems colonized rather than planets, because the vast majority would be in habitats not on planets.

So I think you wind up colonizing systems more-or-less by default whenever they pass by close enough that its (uncolonized) oort cloud intersects your (colonized) one and even just one or two, out of MILLIONS OR BILLIONS, of habitats in the intersecting volume expands out to one of these valuable unclaimed bodies, at a moment when it's nearby, overcoming whatever delta-vee separates them. So with a spacefaring culture that inhabits its star's oort cloud I'd expect *EVERY* star that wanders into close range, to wind up colonized. Even accidentally, if colonies are captured by the passing star.

[selden]

I agree. Those arbitrarily long intervals between colonization attempts have always seemed speciously long to me, determining an upper bound on the total time, with no effort to try to put error bars on them. I’ve come across this argument before, although I don‘t recall where I saw it last.

[stevebowers]

I like to assume that the various stars in a wave of colonisation can talk to each other, so they will exchange data about whether nearby stars are colonised or not. Perhaps some colonies would be colonised in secret by rival factions, but I would assume they'd broadcast the fact of their presence at some point, to deter rival claimants to the territory.

[selden]

Don’t forget about the Diamond Network. Supposedly they’ve colonized many red dwarf systems which happen to be near those systems settled by bionts, and I don’t think they bothered to publicize their presence.
ETA:
Oops. Sorry, I answered out of context. *sigh* Ignore me,

[Bear]

I like to assume that the various stars in a wave of colonisation can talk to each other, so they will exchange data about whether nearby stars are colonised or not. Perhaps some colonies would be colonised in secret by rival factions, but I would assume they'd broadcast the fact of their presence at some point, to deter rival claimants to the territory.

I dunno....  If our own past is anything to judge by, rival powers may be in a race to ''claim" good colonization targets.  If you tell your neighbor where you want to colonize, you run the risk that your neighbor will go there first just to cut you off. 


The point of the model is that the rate of colony reproduction doesn't actually matter that much.  All of these worlds are continually moving into new spaces relative to each other as they orbit the galaxy.  Worlds continue to have access to a frontier because unsettled worlds drift into range.  If it takes them a hundred thousand years to send a colony ship, all that means is that there's more un-colonized systems that have drifted into range among them when the next ship goes out.  They're "filling in" inside ALMOST the same boundaries that they'd be "filling in" inside if they sent out a colony ship literally every year, because the boundaries are defined by the movement of colonized worlds relative to each other regardless of how fast you get to one once it's inside the boundary.

Instead of a steadily advancing wavefront where everything within is one hundred percent occupied, nothing more than ten lightyears inside should even bother trying to colonize anything ever again because no frontier worlds will ever be available to it again, and everything outside the wavefront is unclaimed and mostly unreachable....  you get a situation where the wavefront is not very rigidly defined, everybody within thousands of lightyears of the front has fairly egalitarian access to frontier systems, and the "vanguard" or "boundary" out there where six generations of colony world have gone to higher relative-velocity worlds, is so far beyond the generally-known 'front' that they aren't even competing for the any of the same frontiers that other folks' great-grand-colonies might even get close to.  


The comparison between this once-in-a-hundred-thousand-years model and a once-in-a-hundred-years model actually isn't that big a difference.  Your once-in-a-hundred-year colony ships live in a galaxy where a colony might get ten chances, total, to launch one because after that everything's too far out of range to the frontier or already claimed to the interior.  Your once-in-a-hundred-thousand-year colony ships live in a galaxy where a colony *still* gets ten chances to launch one, all to nearby uninhabited worlds, even though by the time the last one goes it's thousands of lightyears inside the 'wavefront' of colonization.  The ultimate rate of reproduction is the same because colony ships getting produced a thousand times more slowly are getting produced on a thousand times as many worlds, 999/1000 of which would be "out of the running" in the fast-building scenario.

[Bear]

Ultimately there are two growth laws here: Exponential growth of biology, economics, etc, and cube-law growth of bounded space. Cube law growth ultimately bounds exponential growth, and while that's true, the exponent doesn't matter.

The observation here is that galactic orbits mean the cube expands *REGARDLESS* of the rate of exponential growth. Whether the exponent is high (once a century) or low (once in ten millennia) we ultimately wind up expanding within the same cube-law limit, and have access to the same set of worlds.