"Realistic" FTL

[Lord of the Abyss]

To hold together and remain something close to culturally unified.

Some reason why they wouldn't be?

Very slow communications, very little interactions of any kind, and very slow reaction times on the part of any governing authority.

[Havok]

As Lord of the Abyss said, you didn't come close to establishing the boundaries. Here's one you didn't answer: can you turn it on anytime and anywhere you want? If that's the case, battles are going to last just long enough for one guy to realize he's losing and jump away. Unless it's possible to somehow jam or block someone from going FTL, or it takes time to activate, or it's so delicate it's the first system to fail (though in that case, people might simply avoid battle entirely unless they have a clear advantage, in which case the OTHER guy will avoid battle). And what about where you emerge from FTL? Can that be anywhere, too? Better hope not if you're writing about interstellar empires, because under those conditions, an interstellar empire will be hopeless (unless there's planetary shields or somesuch magic, but DR wanted to limit his handwavium to FTL). And then there's the whole problem of causality. How are you going to deal with that? Most writers just ignore it, but it's still something that ought to be considered.

And where's this idea coming from that if you think through your imaginary technology, you will therefore bore your readers with technobabble? How does one follow from the other? I spent months researching real-life and plausible future space technologies, astronomical facts, PLA military ranks, space elevators, spin gravity, even common recipes for pho. 90% never shows up on the page; it's in the background, informing the characters' actions without being explicitly stated. Yes, it's possible that a writer will be tempted to show off all his hard work by putting his technobabble on the page, but why are we assuming Darth Raptor is the kind of hack who would do that? And even if he slipped up and let it happen once or twice, that's what revisions are for. You can delete technobabble with hardly a thought or a worry. If it turns out a major plot development is based on a universe-breaking ability you gave your magictech without thinking, on the other hand, then you're up shit creek.

OK. I see your point. Conceded.

[Ariphaos]

Very slow communications, very little interactions of any kind, and very slow reaction times on the part of any governing authority.

Why is there a need for a common governing authority rather than a loose code?

[rhoenix]

Along this topic, since I've been wrestling with and codifying this issue with my writing recently, I heartily recommend Michio Kaku's book Physics of the Impossible, which basically compares all scifi-ish tech in terms of just how "impossible" something would be. He rated FTL tech as harder to pull off than telepathy or invisibility, but easier than parallel universes or perpetual-motion machines.

More specifically, he mentioned two basic methods of FTL - one was the Alcubierre design (which he indicated was better suited for a jump-drive or a FTL-railway sort of design), and another design which relies on much more negative energy (about a planet's mass worth) and a black hole.

The book is certainly worth a read regardless; his explanations of the underlying theories on each topic are very helpful.

[Patrick Degan]

Very slow communications, very little interactions of any kind, and very slow reaction times on the part of any governing authority.

Why is there a need for a common governing authority rather than a loose code?

Exactly how many nation-states are there that you know of that manage to hold together under that sort of system?

[Darth Hoth]

If you treat the energy needed for FTL "realistically" you logically get a society with technology that makes the Culture look wimpy by comparison. I believe the energy needed to make an Alcubierre-Van Den Broeck warp bubble is on the order of what you'd get by smashing a solar mass of matter and antimatter together. I'm not sure about wormholes but I believe they require similarly ludicrous energy.

There is nothing to say you cannot do this in a fairly "hard" setting, if you make it extreme enough; just build thousands of Dyson Sphere equivalents and wait a few millennia . . . Of course, if you have such capabilities already FTL will seem less necessary, but there might still be uses for it (local emergencies requiring rapid responses, and so on). Though for the purposes of Raptor's fic, which I got the impression he wanted to keep fairly low-key, it will probably be better to put the "realistic" in realistic requirements in scare quotes.

[open_sketchbook]

Honestly, the hardness of sci-fi is all about how you present your information, which is to say, the longer you prattle on about something, the less realistic it becomes. In Star Trek we've heard so much bullshit about warp travel it sounds completely absurd to us. In Star Wars, it's throw lever and you go real fast; we go "hey, plausibility."

Or you could abandon this hard sci-fi junk and write a Space is an Ocean steampunk sci-fi in giant space dreadnoughts in a newtonian universe where interstellar travel requires space sails. I mean, the moment you say "FTL" the fundamental rules of the universe go out the window, so you may as well.

[open_sketchbook]

Well, yes. Being consistant about my Space is an Ocean steampunk sci-fi in giant space dreadnoughts in a newtonian universe where interstellar travel requires space sails universe is pretty difficult and took about six months of working out the physics from the ground up. But what I'm saying is that you're going to lose your status as truely hard sci-fi if you use FTL, so you may as well make it work how your story requires it/as awesomely as possible because you've already softened your sci-fi.

[Ariphaos]

Exactly how many nation-states are there that you know of that manage to hold together under that sort of system?

Exactly how many nation states are you aware of with millions of years of technological development and civil refinement behind them, guided by nigh immortal intellects?

Above and beyond the fact that I never equated them to a nation state, the argument was about cultural unification - the idea that, ya'know, if someone starts throwing around sunshine they need to be smacked right quickly. That's all.

[Patrick Degan]

Exactly how many nation-states are there that you know of that manage to hold together under that sort of system?

Exactly how many nation states are you aware of with millions of years of technological development and civil refinement behind them, guided by nigh immortal intellects?

I'm sorry, is that you pretending that's actually a relevant answer to anything?

Above and beyond the fact that I never equated them to a nation state, the argument was about cultural unification - the idea that, ya'know, if someone starts throwing around sunshine they need to be smacked right quickly. That's all.

The formulation still breaks down: peoples who are isolated from one another end up becoming alien to one another. You can't have cultural unification when two cultures are separated by communication lags of decades/centuries or longer.

[Starglider]

Honestly, the hardness of sci-fi is all about how you present your information, which is to say, the longer you prattle on about something, the less realistic it becomes.

Only if you are a typical hack writer with no real understanding of the subject matter. Greg Egan can invent an entire new version of physics, make it central to the plot of his book, and it turns out awesome; even moreso if you're scientifically literate. Stephen Baxter, somewhat less so, but that's still some pretty hard sci-fi. The problem is that most writers who try to invent physics to support their sci-fi a) don't put serious effort into it and b) go about it the same way that crank 'look at my simple yet brilliant theory of everything' internet loons go about it.

[open_sketchbook]

Thing is though, most people haven't the time to reinvent the laws of physics from the ground up for a book, or the scientific knowledge to do so correctly. I managed to for my steampunk stories because I'm a student with an established unhealthy interest in Victorian science, but I was doing it because I wanted a universe with space combat the worked just so and realized there was no way to do so with any sort of plausibility in something resembling the real world. For most authors, the mechanics of the FTL drive don't effect the story that much, FTL in most good settings is "Press button, go fast" (a gross simplification yes, it might be "Get to certain point, press button, go fast" or something like that) and while there are exceptions as you have named, the tendency is that prattling on about your FTL drive, or tractor beam, or teleporter, or whatever other impossible technology you decided the universe needed usually, though not always, makes things worse.

I love this forum, but I don't understand why every statement is interpreted as all-or-nothing. For the most part trying to explain FTL travel makes it less realistic, that's all I was saying.

In addition, doing those hard-science, super researched FTL drives tend to place limitations on your system you may not want for story purposes. Even in my harder sci-fi stories I tend to restrict use of FTL to the boundaries of the star system because it means you can't just jump in to where you want to go/jump suddenly into the fight, which is useful for dramatic purposes. It is hard as hell to rationalize/handwave that, but it often makes storytelling easier in the cases where I use it. Unless the nature of the FTL drive shapes the story, you should let the story shape the science.

[Starglider]

Thing is though, most people haven't the time to reinvent the laws of physics from the ground up for a book, or the scientific knowledge to do so correctly.

Well fine. 'Hard sci-fi takes dedication and expert knowledge to do well - don't do it if you don't have these'.

For most authors, the mechanics of the FTL drive don't effect the story that much, FTL in most good settings is "Press button, go fast" (a gross simplification yes, it might be "Get to certain point, press button, go fast" or something like that)

Underlying mechanisms don't affect the story, but as this thread has touched on, 'mechanics' can affect it a lot. For example the tactical implications of the jump drives in BSG are quite different from those of Trek warp drives. The method of power generation can also have major implications, e.g. antimatter drives being outlawed due to the WMD potential in the Night's Dawn universe.

I love this forum, but I don't understand why every statement is interpreted as all-or-nothing.

Because precision is a virtue, and ambiguity is communication failure on your part.

In addition, doing those hard-science, super researched FTL drives tend to place limitations on your system you may not want for story purposes. Even in my harder sci-fi stories I tend to restrict use of FTL to the boundaries of the star system because it means you can't just jump in to where you want to go/jump suddenly into the fight, which is useful for dramatic purposes.

Hmm. I suppose. Why couldn't you have used a 'warp drive' that allows tracking and interception inbounds?

Unless the nature of the FTL drive shapes the story, you should let the story shape the science.

The problem is that science doesn't look like science if it's being 'shaped' to meet arbitrary ends; it looks like pseudoscience e.g. Creationism. If you try to ignore the science, then you're not really writing science fiction are you? Good authors can create a system of physical law that leads naturally to technology with roughly the capabilities they want, and if they don't fit the story exactly, they adjust the story. You're acting like the story is sacrosanct, and that produces bad science fiction.

[Junghalli]

There is nothing to say you cannot do this in a fairly "hard" setting, if you make it extreme enough; just build thousands of Dyson Sphere equivalents and wait a few millennia

Of course, that does still leave the annoying little engineering problems of getting that energy into a form dense enough to fit in the 100 meter warp bubble and having the ship not be turned into plasma from its own waste heat when you flick the switch. Both will require serious magic.

[Simon_Jester]

The trick is to stop being a pompous cockflap about how HARD or PLAUSIBLE or REALISTIC your story is. If it has FTL it's unrealistic. Just internalise that and move on. Making it 'inconvenient' isn't making it 'more plausible' - reality isn't like balancing a fucking MMO. You could have the most limited, crazy-fuelled, maths-driven FTL drive ever and it's still a pile of handwaving. So why bother aside from intellectual pride?

There's realism and then there's realism.

For example, there's internal consistency. Reality is internally consistent once you know the relevant parameters. "Realistic" stories should be likewise. If it's impossible to travel through FTL without borrowing someone's Beowulf cluster for half an hour of calculations one day, it should still impossible next Tuesday, or readers want to know the reason why.

There are aspects of engineering, logistics, and human behavior that don't go away even if we find physics-crushing technology.

People will try to design technology to fail-safe, and will build in margins of error; if there is no margin of error then someone is probably doing something wrong. On top of that, if the technology does not fail gracefully and has little or no margin of error, it's hard to explain why people would rely on it for their very lives. (see "The Cold Equations" and criticism thereof).

If FTL drives are complicated and expensive and require extremely specialized parts, only powerful entities like governments and corporations will be able to afford and maintain them. Conversely, if you've got scruffy smugglers darting around their galaxy in ships that can be operated by one or two people, it's a fair bet that FTL drives are simple, mature technology. In which case you'll see things like people trying to build their own (and succeeding).

And so on.

So the fact that you have FTL doesn't mean you've thrown realism completely out the window. It is a classic commonplace that science fiction begins when you take one impossible assumption and run with it; realistic science fiction happen when you watch where you're going while you do the running. And you can still have that even in a setting where some of the basic technology requires us to rewrite the physics textbooks.
______

Really, if you want a hard sci-fi universe, trade your days of FTL travel for days of STL travel and realistically explore just how fucking vast a single solar system can be. The need for FTL is much decreased when you consider the amount of difficulty comprehending planetary distances, let alone distances out to the outer objects like the oort cloud.

The drawback is that if our solar system is any guide, while there may be many places in a star system that are very far apart, there aren't a lot of good reasons to go to most of them. You can substitute "three months by hyperdrive to Zabriska III" with "three months by rocket to Mars," but then you have to explain why anyone wants to go to Mars. Right now, no one seems very motivated to do so, and not without reason. There honestly isn't that much to interest your average adventure hero on Mars, because the entire planet is covered with variations on the themes of rocks, sand, and airlessness.

You can start talking about mass terraforming (the Firefly solution), but when you do that you're in danger of leaving the realism zone just as thoroughly as you would with an FTL drive. How many places will there be in one star system that can be made into places to live that would make you want to go there? Remember, that doesn't just mean "I can breathe and live on algae grown in tanks." That means "the living conditions are comparable to what I can get where I already live." People do not volunteer to travel long distances if they expect drastic cuts in their quality of life.
________

Very slow communications, very little interactions of any kind, and very slow reaction times on the part of any governing authority.

Why is there a need for a common governing authority rather than a loose code?

In the strict sense, you don't. But if you want cultural continuity, you do. Look at how many places on Earth you have where two quite different cultures exist within distances that can be covered by walking for a few weeks. Why would you see more continuity and not less over distances that can't possibly be traversed in anything less than decades?

Cultural uniformity only arises when two societies are in close enough contact that people from group A knowingly adopt the culture of group B, either because they honestly prefer it or because they are forced to do so against their will. Otherwise, it is unstable over any time scale longer than decades.
__________

Honestly, the hardness of sci-fi is all about how you present your information, which is to say, the longer you prattle on about something, the less realistic it becomes. In Star Trek we've heard so much bullshit about warp travel it sounds completely absurd to us. In Star Wars, it's throw lever and you go real fast; we go "hey, plausibility."

Or you could abandon this hard sci-fi junk and write a Space is an Ocean steampunk sci-fi in giant space dreadnoughts in a newtonian universe where interstellar travel requires space sails. I mean, the moment you say "FTL" the fundamental rules of the universe go out the window, so you may as well.

There's one catch.

We usually prefer to imagine that science fiction could exist in our future. Even if we specify that it happened "a long time ago, in a galaxy far, far away," we still tend to think "this is what the future looks like." If you postulate giant space dreadnoughts in a Newtonian universe, you've made it clear that wherever all this is going on, it isn't our future or our past. At which point it becomes a story about a thing which never was, is not, and never will be... which is more the domain of the fantasy genre. That doesn't mean it's automatically bad fiction, but it does make affect the way your audience will read your story.
______

But what I'm saying is that you're going to lose your status as truely hard sci-fi if you use FTL, so you may as well make it work how your story requires it/as awesomely as possible because you've already softened your sci-fi.

But "hard sci-fi" isn't a binary condition. There are multiple senses in which we can talk about a thing being realistic. There are varying degrees of "consistent with the rules we know." It's not as if once a story deviates from absolute adamantine "hardness" it immediately loses some essential virtue and might as well go wild with abandon, dropping all rules of logic or all principles of science at once.

[Ariphaos]

I'm sorry, is that you pretending that's actually a relevant answer to anything?

Yes.

In an interstellar civilization:
1) The civilizations began with contact with each other, with the same cultural roots.
2) Contact between the civilizations was never interrupted.
3) Many of the sapient beings that originated the respective neighboring civilizations knew each other personally in a rapid communication context.
4) The most powerful members of different star systems are the most likely to be the eldest, and thus at one point, close personal friends with each other.
5) Given the above, and lifespans comparable to that of stars, it is not infeasible to imagine that the rate of meaningful moral drift is exceedingly slow.
6) Sapient beings in such a civilization would have want for rather little, at least the ones in control of their star.
7) Sapient beings in such positions would have plans spanning thousands to millions of years. A twenty year communications trip is nothing in comparison.
And for all of the above, even though it may take decades to centuries, moving from star to star is still possible.

Sure, at some point, nastiness could break out every now and then between star systems - that's the purpose of storytelling after all - but a loose confederation is perfectly feasible. We have no modern analogue to such a civilization, so comparing Earth society is inherently fallacious - the best you can do is pick out individual trends and apply those.

[Formless]

4) The most powerful members of different star systems are the most likely to be the eldest, and thus at one point, close personal friends with each other.

Please explain how this is possible with STL communication.

5) Given the above, and lifespans comparable to that of stars, it is not infeasible to imagine that the rate of meaningful moral drift is exceedingly slow.

Please justify this assumption.

[Patrick Degan]

I'm sorry, is that you pretending that's actually a relevant answer to anything?

Yes.

In an interstellar civilization:
1) The civilizations began with contact with each other, with the same cultural roots.
2) Contact between the civilizations was never interrupted.
3) Many of the sapient beings that originated the respective neighboring civilizations knew each other personally in a rapid communication context.
4) The most powerful members of different star systems are the most likely to be the eldest, and thus at one point, close personal friends with each other.
5) Given the above, and lifespans comparable to that of stars, it is not infeasible to imagine that the rate of meaningful moral drift is exceedingly slow.
6) Sapient beings in such a civilization would have want for rather little, at least the ones in control of their star.
7) Sapient beings in such positions would have plans spanning thousands to millions of years. A twenty year communications trip is nothing in comparison.
8 ) And for all of the above, even though it may take decades to centuries, moving from star to star is still possible.

Sure, at some point, nastiness could break out every now and then between star systems - that's the purpose of storytelling after all - but a loose confederation is perfectly feasible. We have no modern analogue to such a civilization, so comparing Earth society is inherently fallacious - the best you can do is pick out individual trends and apply those.

Do you really not see the inherent practical problem with trying to maintain cultural unity between planets which are separated by lightyears in the distance, with communication lags of decades if not centuries? You just keep assuming, a priori, that this is feasible or that the inhabitants of either star system would even think it imperative to their own civilisation when that is not a given.

[Ford Prefect]

But what I'm saying is that you're going to lose your status as truely hard sci-fi if you use FTL, so you may as well make it work how your story requires it/as awesomely as possible because you've already softened your sci-fi.

This seems rather all or nothing, and doesn't really make much sense. Is a series which has faster than light travel spectacularly less 'hard' than one with 100 gee fusion drives? Is Revelation Space harder sci-fi than 2OOI, because 2OOI has FTL, despite Revelation Space having stuff like cryoathrithmetic engines and hypometric weapons?

[open_sketchbook]

What a strange conclusion to jump to. Of course if I say that FTL drives reduce the hardness of sci-fi, it makes it softer than all non-FTL universes. Of course this isn't putting words in my mouth at all.

If you actually read my statement you'd find that it isn't as all or nothing as you think. Having FTL drops you out of the hardest of hard sci-fi, yes; once you've made that leap, you are no longer writing a realistic story and must now settle for plausible, which gives you more wiggle room if you choose to take advantage of it. If you throw unrealistically powerful STL engines into a non-FTL universe, it may be harder of softer than a given FTL-capable universe on a case-by-case basis, but in either universe the stories have ceased to become realistic science fiction because physical laws of the universe have been violated. The moment magic handwavium becomes involved, your story starts to drift towards fantasy, no matter how consistent you make it.

What gets me is people who go "I want to write a totally hard sci-fi story... with FTL/teleporters/whatever!" You shouldn't have to be afraid of softening your universe for the sake of your story because sometimes imagination doesn't fit inside the laws of the universe we live in. I want to read stories, good stories with good pacing and characters and drama and whatever else and if a preoccupation with scientific accuracy is getting in the way of a good story than the science should shift before the story does. As long as it's reasonably consistent then it'll feel right and at the end of the day that's what really matters. fiction, after all, means it's not real. This isn't to say there isn't a place for super-hard sci-fi, of course there is, but those people are reading it because its absurdly hard sci-fi and you're going to lose their interest with a pinch of handwavium or a dumptruck full, so make the choice that feels right for the story you want to tell.

[Ariphaos]

Do you really not see the inherent practical problem with trying to maintain cultural unity between planets which are separated by lightyears in the distance, with communication lags of decades if not centuries? You just keep assuming,

This is speculative fiction. The idea is that we make either make assumptions and see where they go, or see where we want to be and figure out the path to get there.

a priori, that this is feasible or that the inhabitants of either star system would even think it imperative to their own civilisation when that is not a given.

As opposed to FTL being feasible, the idea of an immortal race deciding to use an insignificant amount of energy to keep in touch with far-flung friends and lovers is infeasible? Pardon if I'm skeptical of your conclusion.

This, of course, is about fiction - a possibility entertained by one mind to entertain others. Fiction does not need to play out in reality. Ideally, it just needs to be somewhat plausible. You are making claims involving millions of years of social and technological development based on your understanding of the past ten thousand years. There is nothing physically wrong with the STL civilization I paint.

Your declaration of impossibility is fine - others read what I write. Feel free not to - trust me, I am not bothered.

[Formless]

Xeriar, your argument only works if:

1) colonization takes place after civilization has reached the point where individuals can have "lifespans comparable to that of stars." ()

and following from that

2) the colonizers are motivated to try and stay in touch with the mother civilization.

To the first, while it is infinitely more plausible than FTL, it is not a given; I don't know about you, but its seems to me to be a whole lot easier to just construct a seeder ship(s) (especially if we throw in Von Neumann self replication ) and start spreading humanity. But I could be wrong on that point, so lets assume for the sake of argument that you have already created a transhumanist utopia that gets around those pesky little things like mortality using, say, genetic engineering, robotic bodies, or good old minds on a chip. Does that mean that the colonizers are necessarily going to want to stay in contact with their parent civilization?

No.

In fact, it would be rather detrimental to your argument because both of the two approaches for drastically extending lifespan (extending the life of the body with gene tech or robot bodies or flat out uploading peoples minds to a computer) eliminate one or another of the historical factors for colonization; specifically, population growth and population density * .

Now, in a civilization where your physical body can live for tens of thousands of years or is otherwise functionally immortal, then its a safe bet this civilization has already mastered the art of population control. The only conceivable reason people in such a civilization would have for leaving their home system is if they want to get away from their mother civilization for whatever reason (civil unrest, war, discontent of some kind-- possibly with the population controls themselves ). Which means a cultural divide is already there, and the colonization would be a symptom of (or at least an outlet for) it. Plus, any colony that gets started will probably experience relatively large growth compared to its parent civilization due to the ready availability of space and resources. This growth will mean that pretty soon, the majority of the population isn't going to have any connection to the parent civilization at all.

Think about how different the U.S. and the U.K. are. Now imagine how different they would be if communication never improved past snail mail.

Furthermore, if you go for the mind in a chip approach, you have now effectively eliminated population density from the equation. The efficiency with which this civilization can use the space it has to house people will go up by so many magnitudes as to render colonization a pointless exercise except as a way of creating a back up copy for disaster insurance. If they even go through with it, then there is no need to keep in contact with friends back home-- you can just bring along copies of them and you will never know the difference. Freaky, but that's how that kind of civilization works.

And of course, if you use the classic setting with humans colonizing worlds and living lifespans no longer than modern Earth, cultural unity is a lost cause. But you knew that.

* well, historically the third factor would be greed... but considering how ungodly expensive it is to move materials interstellar distances, I think we can agree that this isn't going to be much of an issue anyway. Not without inventing some really, really contrived bit of handwavium.

[Ariphaos]

Xeriar, your argument only works if:

1) colonization takes place after civilization has reached the point where individuals can have "lifespans comparable to that of stars." ()

To the first, while it is infinitely more plausible than FTL, it is not a given; I don't know about you, but its seems to me to be a whole lot easier to just construct a seeder ship(s) (especially if we throw in Von Neumann self replication ) and start spreading humanity. But I could be wrong on that point, so lets assume for the sake of argument that you have already created a transhumanist utopia that gets around those pesky little things like mortality using, say, genetic engineering, robotic bodies, or good old minds on a chip.

It doesn't need to be a utopia for everyone, just the people that matter for our purposes. Anyway...

Ignoring the fiction license for the moment, the issue here is when we would actually launch an interstellar colonization effort. Put a man on Mars by 2030, set up a colony by the end of the century and begin terraforming - that's a century of progress when we are already beginning to find rather clever means of peering into the mind, genetic therapy, whatever.

Seeder ships actually become rather inefficient in such a scenario, and rely far too much on finding a habitable biosphere. There is no true need for such other than the desire for humans to look and be 'human'.

and following from that

2) the colonizers are motivated to try and stay in touch with the mother civilization.

Does that mean that the colonizers are necessarily going to want to stay in contact with their parent civilization?

No.

In fact, it would be rather detrimental to your argument because both of the two approaches for drastically extending lifespan (extending the life of the body with gene tech or robot bodies or flat out uploading peoples minds to a computer) eliminate one or another of the historical factors for colonization; specifically, population growth and population density * .

Now, in a civilization where your physical body can live for tens of thousands of years or is otherwise functionally immortal, then its a safe bet this civilization has already mastered the art of population control.

Considering the quantity of resources in a star system, no. There's no absolute reason to, for one.

The only conceivable reason people in such a civilization would have for leaving their home system is if they want to get away from their mother civilization for whatever reason (civil unrest, war, discontent of some kind-- possibly with the population controls themselves ).

Wanderlust? A desire to discover? Literally speaking, seeking out new life and new civilizations?

Which means a cultural divide is already there, and the colonization would be a symptom of (or at least an outlet for) it. Plus, any colony that gets started will probably experience relatively large growth compared to its parent civilization due to the ready availability of space and resources. This growth will mean that pretty soon, the majority of the population isn't going to have any connection to the parent civilization at all.

Think about how different the U.S. and the U.K. are. Now imagine how different they would be if communication never improved past snail mail.

You are comparing a pair of ancient civilizations with a race in which the entirety of human history and science is available with immediate recall. I find the claim that the results will be similar rather spurious - they may be, but there's no absolute need for me to write that way.

Furthermore, if you go for the mind in a chip approach, you have now effectively eliminated population density from the equation. The efficiency with which this civilization can use the space it has to house people will go up by so many magnitudes as to render colonization a pointless exercise except as a way of creating a back up copy for disaster insurance. If they even go through with it, then there is no need to keep in contact with friends back home-- you can just bring along copies of them and you will never know the difference. Freaky, but that's how that kind of civilization works.

That's only assuming people may want to be copied or have no protections against doing so. If you want to write it that way, great, but no reason for me to do so.

And of course, if you use the classic setting with humans colonizing worlds and living lifespans no longer than modern Earth, cultural unity is a lost cause. But you knew that.

* well, historically the third factor would be greed... but considering how ungodly expensive it is to move materials interstellar distances, I think we can agree that this isn't going to be much of an issue anyway. Not without inventing some really, really contrived bit of handwavium.

Or light sails using a miniscule fraction of their parent star's output.

One short story I never got around to finishing was about a light sail network spanning the Galaxy, with various far-flung 'peoples' making million-year pilgrimages to Earth.

Because they can.

[Junghalli]

Longer lifespans are likely to slow down cultural change for the simple reason that the older generations hang around a lot longer and keep influencing the culture. Imagine, say, the effect on our culture if people from the 1800s were still alive and many of them still occupied positions of power and influence. And if population stabilizes a population where accidents and suicides are the only cause of death that's stable will have a very low birth rate, which will dramatically enhance the effect. Not only do the old people hang around much longer, but much fewer new people are being created in a given year, decade, or century.

I don't really see why a high degree of cultural conformity between different worlds is all that important anyway. As long as their governments agree on certain common goals you have your "empire". And I would think from a storytelling perspective cultural divergence is cool - lots of different worlds for the author to explore.

[Ariphaos]

Exactly. The main idea is that you need to be on at least cordial terms with your neighbors. You don't need to be building the same sorts of VRs or whatever, but you do need to agree that if someone starts going nuts with sunshine and happiness, they need their butt kicked.

Having a lightsail transfer arrangement between neighboring star systems would also be nifty, especially as many would be suspicious about beaming their awareness to someone else's receiver.