Wow so this could be the explanation for erratic seasons of unpredictable duration in ASOIAF?
This is something he is very aware of. He will tell you that like any intriguing medieval world map, his world map also has tall tales, mysteries and stories about foreign countries, big monsters and weird men, lining the edge of the map.
How else could one be free to build a medieval fantasy world so unburdened by historical realism?
I admit aside ASOIAF I haven't read much GRRM -- his awesome Sandkings short story, and his collaboration with Lisa Tuttle, Windhaven, and I'm aware of some of his horror/fantasy fiction.
Checking on Wikipedia I don't see a lot of military scifi in the list...
It's possible that will never be interesting to us given the expense, time, and hardships involved.
We have more than enough space and resources in this solar system to support north of a trillion humans if we start building space habitats. So even if we start procreating again after our population is predicted to stabilize, we won't run out of room here very easily.
My feeling is our digital worlds will get so engrossing we will turn our attention inwards rather than outwards. I don't think that lends itself to either population growth or interstellar colonization.
If intelligent civilization is sufficiently rare, that could easily explain the Fermi paradox. They're out there, just too far away and too uninterested in expansion for us to meet.
Ultimately it's to claim matter, which is the ultimate limiting factor in how long a civilization lives. For example, you talk about engrossing digital worlds. Well, those worlds require energy and energy means matter.
To be clear we're talking on truly staggering time frames here where a trillion years is a mere blink of an eye [1][2].
Edit: I learned before that this view seems controversial to many people, but I fail to see how on these timescales “humanity” could not be just a transient spark of its own short time.
There is ample reason to believe that any prominent form of life in the galaxy would be expansionary, because otherwise it would be replaced by one that is.
There is no reason to believe that selection stops operating when we are talking about galaxy level scale.
Well, then these hypothetical alien civilizations have barely even begun to start their blink.
1) Eccentricity and Boredom: I think that with a solar system population in the trillions, you will inevitably have a sufficient population of eccentrics to eventually launch generational ships. This is especially likely if humanity survivea long enough for the lifetime our own sun to present a realistic limit on the survival of the species.
2) Eccentricity and Freedom: The major advantage of interstellar colonization is distance from dominant power structures in the solar sytem. I find it quite possible that there could be societies that view fleeing the solar system as their only path to survival as a cultural unit.
The Orions Arm collaborarive hard SF universe has very many first contacts due to this as as often two civilisations of human origin that meet each other look to each other totally alien (one can survive in liquid methane, the other near stars in hard vacuum). They did meet a few actual (and very unique) aliens but it took a lot of verification it's not just another hyper adapted modification happy ofshoot of humanity. :)
Ultimately I think my notion is quite similar to yours: that the primary exchanges would be culture (art, music, fashions, language, rites,...) so the things for which we want "communication".
Gamma ray bursts can probably take out a whole solar system. So could rogue stars or black holes. I think humanity is neat and want it and its descendents to survive until the heat death, so interstellar colonization it is.
But yeah diversification at least 100 light years around in neighboring systems would greatly increase our chances of survival any kind of random brutal event (unless one of our neighbors goes supernova). It will be more of a question of survival rather than 'do we want to colonize that other system'
The cheapest way to fully explore another stellar system is probably colonizing it, so explorers can be manufactured in situ.
And that's all it takes.
Also more source material from real world events could be useful for bootstrapping.
It seems a better plan would be to send artificial intelligence which can remain dormant for hundreds or thousands of years. A planet could be "colonized" by building a data center on it and then running a detailed simulation of a habitable planet. In fact, that would open up far more worlds to colonization, because it substantially loosens the requirements for habitability.
Or if a simulation truly isn't good enough, then an AI could at least bootstrap a biosphere.
The first is that you have to get to a significant percentage of light speed for this to manifest itself. Even at 0.95c time is only traveling at 1/3 of normal speed [1].
Second, the energy cost for this is truly mind-boggling. Doing so when you carry the fuel seems highly impractical. The best bet are laser highways [2]. But, you need to build that first.
The upper limit of laser propulsion isn't really high enough for that level of time dilation.
Third, traveling at these speeds makes any potential impact within even a speck of dust potentially fatal.
Lastly, fun fact: such a ship actually needs to be aerodynamic. Why? Above 0.95c the drag of hydrogen atoms in the interstellar medium will start to slow you down.
On the other hand a civilisation producing such things should hopefully be technically immortal with lots of distributed backups for each individual potentially affected by such accidents & resources to fix up any affected infrastructure. So still, totally worth it, go fo it! :-)
(Less advanced neighbors might still be a bit on the edge, so please be considerate.)
Okay, maybe you can use a laser or something so you don’t have to carry the fuel with you, but you’ll still need a staggering amount of energy because the rocket equation is a harsh mistress, and the relativistic version is even worse.
---
The book itself is only so so but the concept is interesting non the less.
As long as they don't have relations with normal humans outosde the caste they live quite normal lives, meeting their friends from the caste relativity often from subjective PoV, with potentially decades or centuries going one between such encounters.
Still if you say want to settle down and have children, you won't likely wont see anyone else from the caste ever again as the next time one of your friends ventures to the system you settled in they will only encounter your descendants, possibly a couple generations after your time.
We'd certainly notice something as big as a planet coming at us when it's at around the same distance as the Oort cloud, which NASA says lies at a distance of at least 2000 AU [1], or 3e12 km. Since it would take almost 1600 years to travel 3e12 km at 60km/s, I would say we'd have a fair amount of preparation time, even if my estimate for the body's speed were off by a factor of 15. ;-)
As for choosing your course, I would say if a rogue planet is about to enter the Solar System, beggars can't be choosers.
What I find more interesting is that in order for people to live on or near such a planet, it would almost have to have enough of its own internal heat to create temperatures suitable for life. So, you're almost certainly not looking at a rocky planet with a surface. Therefore, you'd want to design your habitat to orbit or exist within the atmosphere of a gas giant. To my knowledge, there hasn't been any serious proposal for such a habitat, and I'm unaware of the sci-fi perspective on this issue.
Of course, the other issue is that at 2e-4*c, you're not going anywhere very fast. :P
---
[0]: https://nssdc.gsfc.nasa.gov/planetary/factsheet/mercuryfact....
[1]: https://solarsystem.nasa.gov/solar-system/oort-cloud/overvie...
But if it's on a hyperbolic trajectory, then it would be just as hard to get to it as to escape the solar system, no?
I wonder what the theoretical distribution of speeds (relative to Earth) of random interstellar debris would be.
https://en.wikipedia.org/wiki/A_Pail_of_Air
"they maintain a breathable atmosphere by periodically retrieving pails of frozen oxygen to thaw over a fire"
So I'm firmly in the camp that the speed of light is a hard limit in the Universe. Any talk of wormholes, FTL and space folding just seems like wishful thinking and the product of not understanding the domain of functions (eg putting negative values into mass or energy).
Additionally there's macro evidence to this speed limit because if it wasn't a limit it would make the likelihood of encountering spacefaring civilizations that much more likely.
So given this, it seems like traveling to other stars requires some form of generational ship. And that seems like a problem because the energy required is massive and that's even before you get into issues of having reaction mass. There are workarounds for this (eg space laser propulsion) but the problems seem... significant.
So, rogue planets. I wonder if the first vessel for interstellar travel will in fact be some largish rogue body that visits the Solar System. Even something 100km wide will contain a wealth of raw materials that would otherwise be prohibitively expensive to accelerate to interstellar speeds.
And sure it might take 10,000 years or more for such a body to travel to a nearby star but there's really not a lot of difference between several centuries and 10,000 years.
What's more, such travelers could likely seed other rogue bodies they encounter along the way.
Could this be the initial vector of interstellar colonization?
As an aside, George RR Martin 40+ years ago wrote a book called Dying of the Light. I really enjoyed it just for the concept. In this book there are so-called Festival worlds. These are worlds that wander between systems. When they approach stars they get sufficiently warm and thaw out and may have oceans and atmospheres in that time. People would build cities in that time knowing it was all temporary.