[Space] The Galactic Empire according to GURPS Space

[Michael Thayne]

I got curious about something: what happens if you use the world-building rules in GURPS Space to try to populate a "galactic empire" analogous to the empires in Star Wars, Asimov's Foundation series, or the Imperium of Man from Warhammer 40k: the defining feature is an empire covering most or all of the Milky Way. This requires starships that (at a minimum) can cross hundreds of parsecs in a day. Furthermore, to allow a well-settled empire, the requisite technology needs to have been around for thousands of years. TL11 is probably a good choice for tech level, but for simplicity, we'll assume that population densities don't increase past TL10 (because GURPS Space leaves any such increases at the discretion of the GM. Furthermore, because Space doesn't have any rules for the population size of Dyson spheres, we'll assume planets are not disassembled to create megastructures, though an asteroid belt at carrying capacity might resemble the early stages of such a structure.

Given thousands of years to colonize the galaxy, it's likely that a majority of valuable galactic real estate will be settled, and not only settled, but at carrying capacity. Given the way the rules for populations work in Space, the overwhelming majority of the galaxy's population will live on just two types of "worlds": garden worlds and asteroid belts. Both types will have mean carrying capacities over a billion. The question then is, how many such places exist in the galaxy? The above fictional "galactic empire" settings I've cited canonically have millions of settled worlds, but it's not clear to me if anything less than billions is plausible for our galaxy. That gives you a galactic population in the quintillions. How on earth do you manage such a population? I'm not sure. I have some thoughts, but I'm going to let others comment first.

[mr beer]

If the choices are garden worlds or asteroid belts, well garden worlds might be vanishingly rare and/or require lengthy and expensive terraforming. But yeah sure there are probably billions of asteroid belts around. Your choice as to why there are only millions or if you prefer, sure billions, why not?

[David Johnston2]

It's worth remembering that even if you have a galactic milieu that has colonized all the valuable real estate...asteroid belts aren't really valuable real estate. They'll only be inhabited if they have both a positive RVM, and convenient location in the vicinity of a well-inhabited world to import their minerals. While the long term the asteroid belt's habitation may grow to dwarf the near-by Garden World, nobody would have colonized it in the first place without an export market already existing.

[Rupert]

It depends on how many thousands of years the galaxy as a whole has been in reach, and on whether rich TL10+ people breed at faster than replacement rates when colonising new worlds.

If the population grows slowly, and travel is as fast and cheap as a galaxy-wide empire implies, it's quite possible that only the very best worlds are even considered for colonisation, let alone actually colonised aggressively. Why settle for hard graft on a planet no more friendly than Earth because it's a day or two away, when a week's travel gets you a perfect Eden?

[ericthered]

Originally Posted by Rupert

It depends on how many thousands of years the galaxy as a whole has been in reach, and on whether rich TL10+ people breed at faster than replacement rates when colonising new worlds.

It also depends on if its economical to export billions of people across the galaxy. There are settings where most worlds are going to be decedents of very small populations who colonized a world.



That said, the example settings are Foundation, Star Wars, and 40k, which each have 10's of thousands of years of time to spread out, and I can believe they are capable of sending large fractions of their population to space.



Growth rates are exponential. At a 2% annual growth rate the population multiplies by 10 every 115 years or so. Even at a .5% growth rate, it takes 460 years to grow by 10. To fill up 1 million worlds like the original world takes 6 of the above cycles. at 2%, it takes a mere 700 years. at .5%, its takes 2800. That's a long time, but its well within the time spans of the target settings. If you increase the number to 10 billion, that's an additional 4 cycles, for a total of 10. So at .5% growth rate, it takes 4,600 years to fill up 10 billion like the home world. Its a long time, about the time the great pyramid of Giza has been around, but the reference settings can accommodate that time frame fairly well, I think.


For tech level, TL 11 or 12 is probably justified, but you should look up "Tech paths" and choose an appropriate one. Radical hard SF has a good chance of all those people living in dyson swarms.



I find 1 billion and 1 quadrillion to be equally abstract and mind-boggling.

[AlexanderHowl]

At TL8, half of the nations on the Earth have negative growth rates before accounting for immigration and immigrants quickly reduce their reproduction rates after a generation. At TL10, a society might have only a 0.1% growth rate even with incentives and technology, meaning that it would take 720 years to double the population. In that case, a planet colonized 7,200 years ago with 1 million colonists might only have a population of 1 billion.

[Daigoro]

Populations are likely to follow an S-curve, being exponential in an initial growth phase, then flattening out as they fill up the available space and resources. Generally, they'd reach their capacity fairly quickly then stay stable at that level until they can expand to another world and start the expansion process again.

If you want to break that cycle, inflict various catastrophes against them.

[Black Leviathan]

There could be nearly infinite reasons why words aren't colonized to capacity. You could be at the rim of the solar system. Your belt could be nearly mined out and all of the population could have moved one except the graveyard crew. Your planet could have hazards that make it unattractive but still able to produce abundant food per acre. Your world could be ravaged by war and still recovering after the loss. And if your system is full of overpopulated garden worlds and overpopulated asteroid belts maybe folks have put together a good atmospheric dome on a nearby frozen rock and turned it into an industrial planet with a dozen or so factories that process dangerous material or manufacturing that damages the atmosphere.

[ericthered]

At the moment, we don't really know what the population growth rate in the future will be. It seems that food security and reduced infant mortality has the initial effect of sending it rocketing into the sky, but that comfortable urban living tends to make it mildly negative. Its also effected by culture and philosophy, and we don't have enough generations to tell which of these are temporary and which have associated feedback loops.

I personally think that feedback loops will kick in and population growth in industrial countries will rise eventually. Negative feedback loops eventually kill themselves. But its very much an unknown. A setting creator could plausibly choose anything below 1%.

As for wars reducing the urge to colonize, I think history provides evidence to the contrary. Wars tend to move populations around, and while they generally aren't starting new settlements, people tend to migrate to locations where they think they have more opportunity. Wars have a tendency to shake people out of their ruts, and result in loosers looking for greener pastures.


EDIT: if you're looking for a population growth number in gurps:space, the chart on page 92 would have you increasing your population by x10 every 100 years, so it seems to be close to the 2% number. That's quite high (earth's maximum in recorded history), and probably factors in immigration as much as natural growth, but if you want an official number its x10 every 100 years.

[Michael Thayne]

FWIW, Space assumes that once a colony is established, the population doubles about every 30 years, which is consistent with the average woman having four children, starting in her late 20s (combined with low infant mortality). This is very reasonable, and you can imagine it happening naturally once FTL tech opens up seemingly limitless wealth, and makes concerns about overpopulation seem silly (for a few centuries, at least). If launching a new colony is difficult, the rate of new-colony creation might be lower, I suppose.