evilthecat said:
You can have the pirates of Pluto complete with space parrots and cutlasses, or the solar samurai who fold their katanas a thousand times in the heat of the sun's photosphere. Where did they come from? How do they coexist? Who cares, 40k never asks those questions.
40K does answer those questions though.
First, we know that for thousands of years, human colonization relied on sub-light craft, so given the tyranny of distance, you'd expect different cultures to emerge over time. After that, they're more united with the advent of warp engines, but then you have the Age of Strife, where humanity's empire is fragmented, and its worlds are left to fend for themselves. So, by the Great Crusade, you have cultures that have been isolated for thousands of years, and even in the Age of the Imperium itself, it's established that it can still take a long time to get from Point A to Point B. Yes, those worlds are going to have some common cultural threads (e.g. worship of the Emperor), but it's easy to see why human colonists on, say, Catachan, developed cultural traits different from, say, Fenris.
But imagine if the protomolecule never arrived in the expanse solar system. Imagine if humanity just carried on for another few hundred (or even a thousand) years without being able to leave at FTL speeds. That solar system has probably become a very big place. Mercury is probably being slowly dismantled to build a dyson swarm around the sun. Many planetoids have already been broken down by millions of autonomous robots to build countless self-sustaining orbital habitats. Artificial rings around the gas giants could exist, or be in construction. There could be many times more habitats in our solar system than there are planets in the typical interstellar science fiction civilization, and since your typical science fiction planet is a monoculture anyway, these habitats could be far more culturally diverse despite being smaller. Any weird or wonderful thing you want could live on these habitats, as they've had centuries to evolve culturally, and potentially to evolve physically as well if they choose to do so.
In theory, yes, but in the context of the Expanse itself, not so much. We've seen that by the time of the books, it isn't that hard to get around the Sol system, or at least it isn't up to Saturn (Uranus and Neptune barely feature). So in a world where the gate was never created, even if self-sustaining habitats were created throughout the system, we've seen that it's easy to stay in touch to an extent, and we can assume it would get easier over time as improvements were made to the Epstein drive.
As for the monoculture thing, it does make sense in the context of the setting. Earth's under the UN, with half its population on basic, so while we do see some cultural remnants that we'd recognise (e.g. different types of food), Earth's monocultural because that's the path it's gone down. Mars, I can also by, because you've got colonists with a shared goal in mind - terraforming the planet, and staying independent from Earth, plus a more militaristic culture that a harsher environment demands (also independence from Earth). The OPA's established to be fairly elastic though, and we see this - "OPA" is more a blanket term for various Belter factions, but even with all the differences those factions entail, we see the traits you'd expect - a creole developing, resentment of the Inners, physiological differences, and a culture that emphasizes the need to survive in space (e.g. learning to use a space suit as a child).
Now, the Expanse could have been written in a manner with more cultural diversity, but the monolithic elements you mention make sense within the setting.