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> 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.

Wow so this could be the explanation for erratic seasons of unpredictable duration in ASOIAF?

Everything about ASOIAF can be explained by George RR Martin's long career as a military science fiction author.

How else could one be free to build a medieval fantasy world so unburdened by historical realism?

Which long career as a military science fiction writer?

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...

Thank you, Sandkings was great!

There is no explanation for the erratic seasons. GRRM (just like any storyteller) creates mystery and interest in his world and fills in the details that are required, and not so many of those that are not.

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.

What's the point of interstellar colonization?

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.

I see two major dynamics that could drive interstellar colonization:

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.

One of the interesting consequences of interstellar colonization in a universe without FTL travel or communication (which, by all indications, appears to be our universe) is the sheer amount of cultural diversity it would create. Even adjacent systems would have communications round-trip times on the order of single-digit years, and depending how far apart desirable systems for colonization are it could even conceivably be decades of round-trip comms lag to the nearest inhabited system. Centralization becomes impossible, and star systems would have only very weak cultural impact on their neighbors.

Interstellar trade of physical goods is quite impractical without FTL. If there is interstellar travel for non-colonization purposes it seems like the primary goal would be to enable low-latency communication to compensate for semantic/cultural drift that could interfere with the efficacy of the high latency communcations.

It seems to me that interstellar trade -- with or without FTL -- is quite unlikely. I wrote some thoughts on this about a year ago, (https://one.mikro2nd.net/2021/07/interstellar/) but tl;dr: If your society is capable of marshalling the resources/energy necessary for interstellar travel in the first place, you have most likely, of necessity, solved the problem of getting more resources. War seems slightly more likely because "ideology".

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".

Not just cultural but also possibly biological/corporeal diversity as the different cultrues start to adapt to their specific local environments.

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. :)

You would find "the transcension hypothesis" very interesting, it's along similar lines to what you are discussing.

We'll run out of sun at some point, even though (most) of the time left for the energetic universe is still available.

> What's the point of interstellar colonization?

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].

[1]: https://www.youtube.com/watch?v=Qam5BkXIEhQ&t=107s

[2]: https://www.youtube.com/watch?v=Pld8wTa16Jk&t=1108s

> 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].

Well, then these hypothetical alien civilizations have barely even begun to start their blink.

Humans may change to (or get replaced by) a form of life that doesn’t grow and/or demand resources uncontrollably and inter-competitively. It is just a relic of our natural origins: eat and breed or get eaten and outbred. When biological reproduction (or life) is over, there is no need for trillions of energy. And when we are speaking billions of years, all humane/natural conceptions become pretty naive. I bet that no one could correctly fantasize about even thousands (not to mention millions) of years from now on. Almost all of our science fiction and futurism is Ford’s “faster horses” of evolution.

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.

Selection pressure operates across all timescales and distance scales.

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.

> What's the point of interstellar colonization?

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.

We have the potential for greatness. If only we could somehow tame the darker aspects of humans we would actually deserve a fate like this and probably be able to do it (or at least that's my wishful thinking).

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'

You or I won't go on this trip, but I'm sure some people are crazy/bold enough to do it.

And that's all it takes.

> What's the point of interstellar colonization?

The cheapest way to fully explore another stellar system is probably colonizing it, so explorers can be manufactured in situ.

Even digital worlds need power to run and mass for hardware to run on. Eventually there will not be enough of that in Solar System and you will have to expand.

Also more source material from real world events could be useful for bootstrapping.

It seems unlikely that we would try to colonize other star systems by sending meat there— meat doesn't keep well over the necessary time scales.

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 most likely form of non-generational inerstellar travel is finding high efficiency methods to accelerate ships to high relatavistic speeds so that time dilation reduces the on-ship time to sub-generation scales.

This sounds appealing but there are a couple of major problems.

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.

[1]: https://www.fourmilab.ch/cship/timedial.html

[2]: https://www.youtube.com/watch?v=oDR4AHYRmlk

You could get to the nearest star in a few years and to the other side of the galaxy well within a human lifetime with "just" constant 1 g acceleration. Obviously this is far from easy but it doesn't seem like it is necessarily out of reach given a few thousand more years of continued technological development.

Yes, and there are at least 76 stars (i.e. potentially interesting destinations) within 100 light years of us [0]. So, assuming you can set an arbitrary course at 0.95c, and decelerate without turning the humans inside your ship to organic goo, you can reach quite a few interesting places.

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[0]: http://www.solstation.com/stars3/100-as.htm

The quotes you put round just are doing a lot of heavy lifting. If you had a perfect photon rocket you’d only need 1000000000 kg of fuel for each kg of payload to do 1g to the centre of our galaxy and slow down again.

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.

Absolutely, there are huge problems and it may not ever be feasible. However, I find it far more likely that we will find a way to solve these concerns than that we will develop FTL travel.

The thing will also be a weapon of mass destruction of plannet cracking potential, one "parking accident" away from making planets uninhabitable.

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.)

There is an interesting book called Lockstep that explores how a civilization might work without light speed. Essentially they have perfected cryogenic sleep and the entire civilization moves in lockstep, sleeping for many years between waking up which allows for ships to move between.

The book itself is only so so but the concept is interesting non the less.

I've read a SF story like this once, woth effectively a caste of space going pilots and scientists that spend most of their time in cryosleep on board of ships going at relativistic speeds, exploring the universe and starting colonies.

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.

Send a small autonomous robot; at the destination it builds a high-bandwidth radio receiver and factories; then 'upload' the colonists by radio. Much more practical if your civilization is reasonably advanced.

Hitching a ride on a fast-moving extrasolar object passing through sounds good, though it seems like finding one going the right direction (and with enough time to get aboard) would be tricky. I suppose once you landed on it you could try and alter its course with mass drivers, but of course the more massive it was, the harder that would be.

If such a rogue planet were the result of ejection from its previous planetary system, I wouldn't expect that its speed would much exceed its previous orbital velocity in terms of order of magnitude. For reference, the orbital velocity of Mercury is about 60km/s [0], which is about 130,000 mph, or 2e-4*c.

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

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[0]: https://nssdc.gsfc.nasa.gov/planetary/factsheet/mercuryfact....

[1]: https://solarsystem.nasa.gov/solar-system/oort-cloud/overvie...

It always creeps me out when someone assumes that people will keep aging and dying in the future, including very far into the future, and would thus need "generational ships" despite all scientific advancement required to make such ships possible in the first place. Right now we're standing on the verge of ending aging. It won't be much longer until it becomes optional.

>prohibitively expensive to accelerate to interstellar speeds.

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.

There was also:

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"

I was under the (false?) impression that most physicists are on board with wormholes being a real and possible phenomenon.

It requires negative energy in current theoretical physics, which is what OP is talking about, we have no idea if that will ever actually be possible, its wishful thinking at this point.

Ok, but that isn't addressing my comment. Most people aren't qualified to evaluate the cutting edge of modern physics. I'm wondering what the experts consensus is, not anonymous internet strangers. Why should I take your word over the world's best physicists?