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How big (radius or volume, not population) should a polity of space-going humans be?
Posted: Posted March 28th
Edited March 28th by chiarizio

How big (radius or volume, not population) should a polity of space-going humans be?
Assuming they’ve mastered interplanetary travel and are on the verge of interstellar travel;
or are old hands at interstellar travel, but not “Galactic Empire” nor intergalactic-travel-competent yet;
or are anywhere between, technologically.

I’ve recently thought most such polities should average about a billion (10^9) light-seconds in radius.
Some might be as small as a million (10^6) light-seconds radius; and/or some might be as large as a trillion (10^12) light-seconds in radius.
So if the biggest ones have a thousand times the radius of the average ones, they have a billion times the volume.
And if the smallest ones have a thousandth the radius of the average ones, they have a billionth the volume.
And if the biggest ones have a thousand times the radius of the average ones, and the smallest ones have a thousandth the radius of the average ones, then the biggest ones have a million times the radius of the smallest ones. (And a quintillion times the volume!)

Should I have said million instead of billion?
A billion seconds is 31.69 years; while a million seconds is 1.65 weeks, or 11.57 days. (A year is 31,556,952 seconds, as that song from “Rent” says.)

Should the polities’ radii be limited to a light-day or less until they achieve faster-than-light travel? (Remember I’m assuming they’re all human!)
A light-day is about 173 AU (astronomical units, the radius of the Earth’s orbit).
The Kuiper Belt is only about 30 AU (is that 4 light-hours and 40 light-minutes?) from the Sun, but the Oort Cloud starts about 100,000 AU (1.581 light years) away from the Sun. (And extends to about 3 light years from the Sun, though Proxima Centauri is about 4.24 light years away).

So in the Solar system, a light-day radius would include everything we could live on (Sedna is about 90 AU, or a bit over half a light-day, away from the Sun), and also a lot more. The central eighth of that volume might contain everything we could be interested in closer than the comets in the Oort Cloud. And the central 27th of that central eighth would contain every one of our eight planets.

But I think we might be interested in monitoring and patrolling out to a light-day radius just to be safe.

A million light-second radius is about 12 light-days. Would a unified government be possible in a space that big, without faster-than-light travel? What if they had 12 times lightspeed communication, but only up to lightspeed travel —— could they hold it together then?

What technology would they need, to govern a polity a light-year in radius? Or would they need, instead or as well, some differences in biology and things like culture? I’m assuming that, if they’re humans, they’d need to be able to get people and data from the center to the edge (and/or vice-versa) within a day or less. Is that a reasonable assumption?


There are 7 Replies

On one hand, historically, humans preferred to have settlements about 1-3 day's travel apart from each other, whatever the distance that was by the fastest means of travel. However, for the most part, that was living on a continuous plane where people could choose to live any distance away from the next town, baring a few places that were too dangerous or couldn't support a town's population.

Space on the other hand has small, sparse islands of possible habitability that are different distances away. Even then, a star system might have no planets that could even be terraformed to be human livable, even with things like the proposed "cloud cities" to colonize Venus one day.

I think a polity is going to be about synonymous with a solar system. You could communicate with the next system over, but even at the speed of light, communication would be painfully slow, and so would travel. Polities might even be on the inhabitable planet level, tbh. So, within a light day, or less would be my guess, unless there are several star systems close together.

Edited March 30th by linguistcat



Posted March 30th by I killed Mufasa
I killed Mufasa
long live the king

How long a speed-of-light delay do you think people will be willing to tolerate in a “radio” conversation?
I’m thinking about 7 light-seconds might be the maximum.
More than that, it would be better to do things like text messages or bulletin boards than like an actual 2-way conversation with turn-taking and so on.



Posted April 2nd by chiarizio

I think 7 seconds could be doable, having used a radio phone that had a lag depending on distance to the person your were talking to. Remember though that Luna is about 1 light second from Earth, so that wouldn't be far by space standards.

Posted April 2nd by linguistcat

I think once the technology is advanced enough face time between star systems would be instantaneous. Much like what you see in Star Wars when the Jedi Council uses holograms to talk to Jedi on far away planets or ships. Emails and instant messengers as well. Local problems would be the only thing causing lag.

Posted April 3rd by I killed Mufasa
I killed Mufasa
long live the king

I think 7 seconds could be doable, having used a radio phone that had a lag depending on distance to the person your were talking to. Remember though that Luna is about 1 light second from Earth, so that wouldn't be far by space standards.



Yes. I think a time-lag measurable in tenths of a second —— such as maybe 0.5 or 0.8 sec —— might be considered negligible for real-time conversations; but 20 seconds or longer wouldn’t really be tolerated.
An AU is about 500 light seconds or 8 and 1/3 light-minutes. I don’t see anyone staying for a conversation taking over 3 minutes between turns.

I think once the technology is advanced enough face time between star systems would be instantaneous. Much like what you see in Star Wars when the Jedi Council uses holograms to talk to Jedi on far away planets or ships. Emails and instant messengers as well. Local problems would be the only thing causing lag.


That’s true, I’m sure. The questions I’ve been asking have different answers depending on how fast messages and goods and passengers can travel. They might also have different answers depending on what species our main characters are. That’s why my questions specify humans not much different from us, and mostly ask about situations wherein passengers can’t go faster than light, and at least start out asking about what if signals can’t go FTL either.
But if they can go 300c I think a light-year might be reasonable? Right, maybe? Though still real-time turn-taking conversations might be easier within a light-second or so.


Edited June 9th by chiarizio

I am thinking a “civilization” would probably be a year’s message-travel in radius or diameter.
The individual governable volumes in it would probably be more like a day’s message-or-person-travel in diameter (or radius?).
At the speed of light, then, the equivalent of the U.N. or the Concert of Europe or somesuch would be a light-year across, or maybe a light-year in radius; while the equivalents of its member states or nations or “High Contracting Powers” would be about a light-day in radius (or in diameter).

The “civilization”’s volume could be 182^3 or 6,028,568 times the volume of its average member-state. (Rounding half a light-year down to 182 light-day’s.)
But most of that volume would be the equivalent of “the high seas”.*

*[edit]For instance, if it were centered on our Sun, the civilization would contain no other visible “fixed” stars. Proxima Centauri is around 4.24 light-years away.[/edit]

That’s assuming a message or circular letter or journal or magazine or the equivalent has to make it from any corner of the civilization to any other corner in a year or less, and can’t travel faster than light-speed; while a messenger or envoy or whatever-you-call a fixer or troubleshooter must make it from the center of a polity to its edge, or back, in a day, and can’t travel faster than light-speed.

This might all be more interesting in a globular cluster, where the average distance between a star and its nearest neighbor star might be shorter than half a light-year.


Edited Sunday by chiarizio
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