The Universe Within 12.5 Light Years

One particular "feel" that people often get wrong: on a scale of up to around 1000 light years in each dimension (on the order of a million stars, or a hundred thousand sun-like stars - I haven't done the integrals over the density), the placement of star systems is largely homogenous. Most galaxy-scale structure (such as the spiral arms, or core vs rim) only starts becoming significant when you get bigger than that.

Now there are 2 caveats to this - first, there is a measurable density difference as you get closer to the galactic plane. And second, globular clusters do do their own thing.

What this means for fiction is that you must commit to either:

* The overwhelming majority of systems must be irrelevant; relevant systems are hundreds of lightyears apart (it is trivial to disappear into uncharted systems assuming you can maintain your spacecraft), and galactic structure does matter. Or,

* If even a modest percentage of systems are to be relevant, then you can't care about galaxy-scale structure at all. And you need to have something stopping people from gratuitously flying out of bounds (this might be as simple as "no compatible languages and no compatible fuel pumps").

That's interesting, so fiction would be more realistic if they always have distances of hundreds of lightyears apart?

But that means that galaxy-scale structure actually does matter, right? A hundred thousand sun-like stars isn't all that much, I'm guessing only a small percentage-points of those would have a planet in the correct orbit for terraforming, and you'd need to go outside your proposed 1000 LY volume?

Your writing style reminds me of Brandon Sanderson

If you want to exact match to earth in our solar system line conditions , i.e. G-5 star with a rocky plant in the water zone and not too close to a binary if any - you would end up with only few possibilities in 1000Ly

However say red dwarfs with moons of closely orbiting gas giants, and many other combinations could in theory be sustain life easily .

We can learn from history on earth, economics is the reason why cities or outposts form and die, even when they are very hostile or very unsuitable and expensive to make it work.

Space would be no different, people would be happy to setup an outpost on Betelgeuse despite its impending supernova if they can say get away from regulation or it cheaper to make things for some other reason, or there is ideal low gravity planet with the right conditions for growing some thing even it would normally be considered hostile .

Thanks so much, I love your comments here!