Sci-Fi Musings

[JNAProductions]

So, general idea:

Humanity reaches the stars, finds out they're not alone, but there's a key difference between humankind and other species.

Every other race has some level of hivemind or empathic resonance. Violence, while not entirely unknown, is incredibly rare, because if you commit a violent act on another member of your species, you feel it too. Or, for some species, they're literally only a small number of true consciousnesses, spread across many bodies.

The gist is that, because these other races work together so much better than humankind does, they didn't wipe one another out, and worked together. Humanity was viewed, before achieving galactic relevance, as one of many species doomed to failure, wiping themselves out as they grew smarter. But humankind got lucky, and started colonizing other planets. In order to prevent humans from spreading like violent, violent rabbits, other species reached out and made contact, inviting humans to galactic civilization.

That's about all I got so far.

[Mechalich]

The gist is that, because these other races work together so much better than humankind does, they didn't wipe one another out, and worked together. Humanity was viewed, before achieving galactic relevance, as one of many species doomed to failure, wiping themselves out as they grew smarter. But humankind got lucky, and started colonizing other planets. In order to prevent humans from spreading like violent, violent rabbits, other species reached out and made contact, inviting humans to galactic civilization.


I can see why humans would be extremely violent in this scenario, but why are they massively expansionistic? Post-demographic transition human societies have problems with population decline not growth. Also, certain advanced technologies make physical space broadly irrelevant, such as digital uploading (which renders the carrying capacity of Earth functionally infinite) or microgravity adaptations (which means all the rocks in the galaxy can suddenly host people, and there are so, so many of them).

[JNAProductions]

I can see why humans would be extremely violent in this scenario, but why are they massively expansionistic? Post-demographic transition human societies have problems with population decline not growth. Also, certain advanced technologies make physical space broadly irrelevant, such as digital uploading (which renders the carrying capacity of Earth functionally infinite) or microgravity adaptations (which means all the rocks in the galaxy can suddenly host people, and there are so, so many of them).

Well, digital uploading probably wouldn't exist. So there's that issue nipped in the bud.
And gravity generators could be big, clunky things-the kind of thing that needs a lot of power and space, so any small rock wouldn't work.

Plus, have you met humans? They get everywhere and are really bad at maintaining the peace! :P

[Millstone85]

Every other race has some level of hivemind or empathic resonance. Violence, while not entirely unknown, is incredibly rare, because if you commit a violent act on another member of your species, you feel it too. Or, for some species, they're literally only a small number of true consciousnesses, spread across many bodies.

The gist is that, because these other races work together so much better than humankind does, they didn't wipe one another out, and worked together.I could see it going the other way. The aliens are struggling with non-telepathic empathy, including between separate hiveminds. A starfish person would never hurt another starfish person, nor would a bee person hurt another bee person, but the starfish and bee people have been at war for centuries. Humans, being used to cooperate with someone they can't hear the thoughts of, manage to establish interspecies trade for the first time in the galaxy.

Then humans start thinking of becoming the de facto leaders of a galactic alliance. But the other species have been learning.

[LibraryOgre]

This is somewhat like the "humans as space orcs" concept... humans are the unusually robust and violent species, compared to everyone else. Our planet is a lot more dangerous, and so some things that others would consider extremely dangerous humans just say "Eh, that's just a dog. We've lived with these predators for thousands of years. Some are even the size of people!"

[NichG]

One thing to consider would be how different game theory would look in a civilization that effectively acts as an entity with a single unified shared goal, versus a civilization built to be stable against entities with wildly opposed goals coexisting. Specifically because game theory also establishes things like military thinking about 'how should we approach a totally unknown entity with unknown technological capabilities consistent with our current understanding of physics?'. For example, the novel 'The Killing Star' puts forth the idea that game theory + relativity implies that all spacefaring civilizations' best move is to hide as best they can and use relativistic weaponry to immediately wipe out any other civilization they detect, because a relativistic impactor is a weapon that cannot be detected in advance or defended against. But that has a sort of implied payout matrix arising from certain preconceptions about the nature of agents baked in to it - dominance as being the goal state, destruction of a planet as being an infinite cost, etc - which for interplanetary 'entities' with distributed consciousness would be like saying 'if I get stung by a bee, thats the worst thing ever, I must drive all bees extinct to prevent that eventuality'.

It might be funny if writings on game theory from non-linked civilizations are actually slightly taboo in the interplanetary community - not illegal necessarily, but being overly fascinated by it is sort of like being a little too interested in the writings of a genocidal military leader.

[JNAProductions]

I could see it going the other way. The aliens are struggling with non-telepathic empathy, including between separate hiveminds. A starfish person would never hurt another starfish person, nor would a bee person hurt another bee person, but the starfish and bee people have been at war for centuries. Humans, being used to cooperate with someone they can't hear the thoughts of, manage to establish interspecies trade for the first time in the galaxy.

Then humans start thinking of becoming the de facto leaders of a galactic alliance. But the other species have been learning.

I'd rather have humankind be the violent ones. Not to say your ideas are bad-but not what I'm looking for.


This is somewhat like the "humans as space orcs" concept... humans are the unusually robust and violent species, compared to everyone else. Our planet is a lot more dangerous, and so some things that others would consider extremely dangerous humans just say "Eh, that's just a dog. We've lived with these predators for thousands of years. Some are even the size of people!"

Yee.


One thing to consider would be how different game theory would look in a civilization that effectively acts as an entity with a single unified shared goal, versus a civilization built to be stable against entities with wildly opposed goals coexisting. Specifically because game theory also establishes things like military thinking about 'how should we approach a totally unknown entity with unknown technological capabilities consistent with our current understanding of physics?'. For example, the novel 'The Killing Star' puts forth the idea that game theory + relativity implies that all spacefaring civilizations' best move is to hide as best they can and use relativistic weaponry to immediately wipe out any other civilization they detect, because a relativistic impactor is a weapon that cannot be detected in advance or defended against. But that has a sort of implied payout matrix arising from certain preconceptions about the nature of agents baked in to it - dominance as being the goal state, destruction of a planet as being an infinite cost, etc - which for interplanetary 'entities' with distributed consciousness would be like saying 'if I get stung by a bee, thats the worst thing ever, I must drive all bees extinct to prevent that eventuality'.

It might be funny if writings on game theory from non-linked civilizations are actually slightly taboo in the interplanetary community - not illegal necessarily, but being overly fascinated by it is sort of like being a little too interested in the writings of a genocidal military leader.

I like these ideas!

For everyone who's participating, what kind of alien forms would be cool to see in this setting?

[Millstone85]

For everyone who's participating, what kind of alien forms would be cool to see in this setting?I am thinking of a quadrupedal ungulate with both a prehensile trunk and a prehensile tail, which it uses instead of hands. The creature is bad enough at climbing that it never invented the ladder, and peaceful enough that its weaponry stopped at the bow and arrow. Has otherwise developed an advanced spacefaring civilization.

[Mechalich]

And gravity generators could be big, clunky things-the kind of thing that needs a lot of power and space, so any small rock wouldn't work.

You don't need gravity generators to settle asteroids, you just need genetic engineering of adaptations to allow large organisms to function properly in a microgravity environment.

But this is mostly a stab at a fundamental aspect of designing a space opera setting: the technologies you permit will determine constraints on resources, of which space is a significant one. For example, if gravity generation is possible at all, space is functionally limitless, since you can just build gigantic space habs using artificial gravity. Earth's surface area is ~510 million square kilometers. Larry Niven's Ringworld has three hundred million times that in surface area, which means that it could support something like 2.4 sextillion humans at current Earth population densities.

And this sort of thing matters in this scenario when considering something like containment. If the aliens are really worried about humans they can buy themselves possibly millions of years by dismantling a few Kuiper Belt objects and producing a few megastructures in our solar system.

[akma]

Since those aliens are hiveminded, would it mean that if a human kills one of them, they will naturally view all humans as responsible?
Even if they rationally know it's not really true, acknowledging it could be against their pre-conceived beliefs.


Also, certain advanced technologies make physical space broadly irrelevant, such as digital uploading (which renders the carrying capacity of Earth functionally infinite) or microgravity adaptations (which means all the rocks in the galaxy can suddenly host people, and there are so, so many of them).

Sure, people could move on to live on some random asteroid, but why would they want to do that if there are other options? Why not move to somewhere more fertile or more interesting? Most people who move away from their homeland don't go to some random spot in a far away desert.

For a society, many people uploading their consciousness digitally could be beneficial, but many individuals would be strongly averse to it, even if there were no practical issues with that idea.



For everyone who's participating, what kind of alien forms would be cool to see in this setting?

Maybe to emphasize their non-violence, all aliens are plant-like.

[Millstone85]

For a society, many people uploading their consciousness digitally could be beneficial, but many individuals would be strongly averse to it, even if there were no practical issues with that idea.I can see at least two big issues.

First, the accuracy of the digital recreation:

Is it a P-zombie? It would be difficult to confirm the jump from a convincing chatbot to an AI that is itself aware of its existence.
Does it truly think like the model species? If instead a new form of mind has been created, that would be a great achievement but a poor survival plan.
Does it truly think like the model individual? If it turns out ever so subtly different in typical moods and opinions, that would be enough to say the upload failed.

Then, the continuity of consciousness. There are going to be two minds, which will then accumulate new distinct memories, and so it would be comparable to meeting an alternate universe's version of the individual. More if the program is run multiple times in parallel.

As an aside, I could see ringworlds, Dyson spheres, and matrioshka brains, being part of the setting but as these eldritch beings with which any communication, however brief, is treated as a momentous event.


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[NichG]

For alien societies in which uploading doesn't make sense, give them distributed forms where a lot of their cognition and personality is actually a consequence of the places they've extended themselves into. For a culture like that, digital uploading would be like wearing a particular set of clothes - not some sort of atrocity or loss of self, but at the same time you don't want to wear the same clothes every day, and a sweater ultimately is not a swimsuit no matter how much you try.

Concretely this would be something like: I have a way to make this planet part of my mind; by doing so, the details of plate tectonics, what's going on with life on the surface, etc actually become part of my cognitive processes and give me additional cognitive abilities I would not have otherwise, relating to those things on the planet. You could certainly make a simulation with which my mind could engage, extend itself into, etc in the same way, but that simulation will actually never be that particular planet, any more than a simulated rendering system is different than a camera on a robot that lets me actually interact with the world.

[JNAProductions]

Digital uploading is not something I’d be using for this setting.

[Mechalich]

Leaving uploading aside it's still important to determine the technological backdrop of a setting like this. The central premise is dependent upon humans entering a galactic community that is otherwise comprised of aliens who are at least psychologically very different. The difficulty is that space, as it is commonly understood, is against this. Space is big, post-industrial populations expand slowly if at all, and functionally the same resources are available everywhere. Contact and conflict have to be forced into being.

The best method to do this, generally, is to manipulate whatever form of FTL you place in the setting, since FTL technologies are inherently BS from the start they can be freely contorted in a manner you see fit. For a setting of this kind, I'd suggest some kind of hub-based system one where ships, or just people walking, have to travel to some kind of hub (like an ancient megastructure or a sub-dimension or whatever) before they can proceed to whatever destination they have. This not only forces the species to interact it also creates a point of vulnerability by which the 'nasty, dangerous, humans' could potentially do real damage to the much larger and more established alien civilizations. You might even create an inciting incident along those lines if you want the humans to have to face an uphill battle for acceptance.

[Tawmis]

So, general idea:
Humanity reaches the stars, finds out they're not alone, but there's a key difference between humankind and other species.
Every other race has some level of hivemind or empathic resonance. Violence, while not entirely unknown, is incredibly rare, because if you commit a violent act on another member of your species, you feel it too. Or, for some species, they're literally only a small number of true consciousnesses, spread across many bodies.
The gist is that, because these other races work together so much better than humankind does, they didn't wipe one another out, and worked together. Humanity was viewed, before achieving galactic relevance, as one of many species doomed to failure, wiping themselves out as they grew smarter. But humankind got lucky, and started colonizing other planets. In order to prevent humans from spreading like violent, violent rabbits, other species reached out and made contact, inviting humans to galactic civilization.
That's about all I got so far.

One thing that I think would be interesting to explore...

Since humanity was expected to wipe themselves out - but through sheer luck managed galactic relevance - might see humans as a threat.
Similar to how rats can spread rapidly, they can also spread disease.
So these other alien species who have not had a need to fight with one another - now see this commonly fighting species achieve galactic relevance - and now must ponder, among the other races from which they have maintained this ongoing peace - what do they do with this new race of humanity - that they consider vermin? Should something be done? Before they bring their war to these other places? Before they bring these diseases that have never existed in these new colonies that may impact them (similar to the black plague).
Perhaps these aliens reached out to the humans, not as a peace offering, but a means of observing - and perhaps directing humans onto planets - that the others haven't explored and established - because they can assure that they can keep "directing the humans" to go where they're not around. And should the humans colonize these new worlds that the others have not, they can harvest information from the humans.
So in their efforts to keep the humans away from themselves - they direct them like rats in a maze - to specific locations.
What happens when and if these humans find out?

[brian 333]

Hive minded beings may not have wars within their own being, but they may be quite ruthless, and unaware that they are. Example: Hive A arrives on Earth, and calculates it will require the resources of Australia to grow to optimum size. Hive A routinely culls its membership of weak, sick, elderly, and superfluous individuals, believing it to be no more immoral than trimming toenails or excising inflamed tonsils. They cannot conceive of an individual as its own being. To them, the idea of killing all humans on Australia would simply be a matter of practical apportionment of available territory. After all, what are a few million individual humans to the hive of billions on Earth?

Similarly, beings which routinely download themselves into manufactured bodies may not hold the concept of body as self in high esteem. Bodies become interchangeable and disposable. Arriving at Earth, they discover what they consider mass overcrowding. They download and store the minds of seven billion humans and turn their bodies into fertilizer. In their minds, no crime has been committed, and they wonder at the reluctance of the remaining billion to time-share their bodies.

Now I have a story to write. I wonder if I'm pro or con this idea?

[LibraryOgre]

Also consider the Geth, from Mass Effect, who are a hive mind, but driven by consensus. A polarizing enough consensus can result in a split, and those that split might have very different conclusions about something.

[lightningcat]

Hive minded beings may not have wars within their own being, but they may be quite ruthless, and unaware that they are. Example: Hive A arrives on Earth, and calculates it will require the resources of Australia to grow to optimum size. Hive A routinely culls its membership of weak, sick, elderly, and superfluous individuals, believing it to be no more immoral than trimming toenails or excising inflamed tonsils. They cannot conceive of an individual as its own being. To them, the idea of killing all humans on Australia would simply be a matter of practical apportionment of available territory. After all, what are a few million individual humans to the hive of billions on Earth?


That is very close to what the aliens from Ender's Game believed.

[Biggus]

I can see why humans would be extremely violent in this scenario, but why are they massively expansionistic? Post-demographic transition human societies have problems with population decline not growth.

There are several possible answers to that. One is if life extension/immortality exists then even quite a low birthrate leads to population problems in the long run. Another is that on the settled planets life is more primitive, especially on newly-colonised ones, which leads to a reversal of the trend towards less children in high-tech societies. Another is that the Earth is so crowded by this point that a one or two children only policy is enforced, and so the people who leave for other planets are often part of the minority who want lots of children.

I'm sure there are other possibilities, those are just the first ones which occurred to me.

[brian 333]

There are several possible answers to that. One is if life extension/immortality exists then even quite a low birthrate leads to population problems in the long run. Another is that on the settled planets life is more primitive, especially on newly-colonised ones, which leads to a reversal of the trend towards less children in high-tech societies. Another is that the Earth is so crowded by this point that a one or two children only policy is enforced, and so the people who leave for other planets are often part of the minority who want lots of children.

I'm sure there are other possibilities, those are just the first ones which occurred to me.

The lower birthrate is not caused by an increased technological base, but by a cultural belief that the measure of success of an individual is linked to a career. There are segments of the human population which currently enjoy the same technology as everyone else but which have higher successful pregnancy rates than in pre industrial times. There is no scientific law that higher technology must produce lower birth rates, but there have been huge cultural and even legal incentives that have created a low birth rate in certain cultures.

With proper incentives, birth rates could soar, and with current technology there is nothing preventing ten or more successful prenancies. Add near future technology to a pioneering spirit and you could easily fill every world with billions of humans in a few short generations.

Assume:
A society devoted to colonization.

200 individuals, half capable of live birth, with millions of frozen sperm, egg, and embryo samples to create genetic diversity.

An average of ten live births per mother.

1st native generation = 1000
2nd native generation = 5000
3rd gen = 25,000
4th gen = 125,000
5th gen = 600,000

In less than 100 years from landing, the population is approaching a million humans from a beginning of 200 individuals.

[GlyphicEngineer]

Is humanity assumed to be operating under a united government here, or are individual nation-states reaching out towards space on their own? Or something in between, like the Super-UN concept that shows up in sci-fi so often? It would be interesting to see hiveminded organisms attempt to rationalize the idea of different nation-states within the same species; they might think that each nation is akin to a hive of its own, or they may conceive of humanity as a broken, fundamentally insane gestalt consciousness. If there is some manner of world government, that could lead to its own sorts of interesting misunderstandings, with alien hiveminds initially assuming that humanity is like them and reacting with confusion to the very idea of a "government."

[Quizatzhaderac]

Brandon Sanderson's Cytoverse novels have the interesting concept that sapient carnivores are rare, and so most other species find us ghoulish in that regard.

For your story, I think it would make the justaposition best if humans and our societies are vary varied. The everage human is non-violent and the average human polity can be trusted, but aliens have to think in terms of "what's the worst humans are going to do?"

[Millstone85]

The everage human is non-violent and the average human polity can be trusted, but aliens have to think in terms of "what's the worst humans are going to do?"Agent K's words also come to mind: "A person is smart. People are dumb, dangerous, panicky animals and you know it."

The average human may be considered equal to the average alien, but utterly wasted on the proto-superorganism called humanity.

[rel]

It's the humans as space orcs idea.
New to the scene, seen as primitive, but violent and dangerous, short lifespan, impressive ability to reproduce, seen as a 'problem' by the various holier than thou ancient races.

The unique thing here is that humans as orcs lose the usual resilience, since a hive mind is by nature more resilient than any individual, no matter how tough. So what do the humans get in return?
I say independent action.

You're average hive mind needs a crew of hundreds just to maintain self. Han Solo in his space truck with his best friend riding shotgun with a space crossbow is something they biologically cannot do. But the humans can. That's the niche humans exploit as they go out into the black and see what's out there...

[Yakk]

How soft do you want your SF to be?

For uploading:
1. Nobody has figured out how to make intelligence from scratch. Best you can do is mimic an existing intelligence.
2. Intelligence without a body - a deep sensory connection to the world - goes crazy. At least human intelligence does. So you have to build it a body and print it into a body for it to work.

This means we can have uploading, but you can't live in the digital universe. The closest you can come to it is a bunch of gene-hacked organic pod bodies with their eyes wired up to TV screens.

With that kind of technology and bio-printing and the like, you also have solved the population problem. You can duplicate humans if you want to - creating a copy of someone is not that expensive. They are two individuals afterwards.

Biotech printing also means that adaption and changing is easy. Want to be taller? Shorter? Stronger? Change genders? An extra set of arms? All doable. Which also means that the nominal copies of someone might not be all that similar, as what your face looks like is a fashion statement.

Now, do you want a population boom? You can literally print out an entire colony of experts. Biological wombs mean you can grow babies without having the work or risks of pregnancy, and the idea of being backed up means that a lot of people take a lot of relatively insane risks. Sure, their consciousness ends, but an identical one from before the risk wakes up.

In any kind of hard-SF situation, industry will leave inhabited planets and move to space. The asteroids provide a lot more raw materials than we can safely extract on the planet earth, and don't have an annoying gravity well in the way of shipping it. Building safe space habitats is hard, but using the slag from asteroid mining to build radiation shields and spinning up habitats should be insanely easier than any kind of interstellar colonization. Regular backups means that in the event of disaster, everyone wakes up anyhow.

Brain computer interfaces and micro downloading means part of being good at a task is being able to accept downloads for specific problems. Know how you watch a youtube video to figure out how to fix a sink? A technician will work hard to have part of their mind capable of dealing with microdownloads, and literally replace that piece of their mind in order to become an expert at solving a specific task. This needs the framework (of the technical expertise) if you don't want to fully replace the consciousness of the person doing the work.

Speaking of which, methuselahs are mostly-frozen digital uploads that get downloaded to solve specific problems. Then either their frozen copy is updated with the new consciousness, or the branch is discarded. A methuselah could have been created 100 years ago and have only lived for a day since then, with every other spawned branch discarded, despite having 1000 years of life in that century.

...

Hard SF interstellar travel is a slow and high energy process. We are talking building a star-sized power source (possibly a star contained in a dyson swarm) and a ship taking a century to reach a nearby star. (Breaking is the hard part - there are lots of solutions, like huge mirrors and solar sails, or making much of the star wisp's mass be anti-matter). You don't have space battleships or anything else like that.

If you want to add in FTL, you are inventing new physics, and new physics changes the universe massively.

In a sense, interdimensional travel seems more likely than FTL. Like, imagine the universe is a thin 3+1 dimensional membrane in a 10+1 dimensional universe. Being able to move to universes any of 7 directions away from us seems "easier" than FTL in our 3+1 universe.

That can be a real SF setting. But one where humanity doesn't expand between stars. The inter-dimensional travel might require being in space, and look like a star gate.

Other hard-SF approaches include finding exotic remnants of the big bang in order to cheat at physics, like a magnetic monopole or a cosmic string.

Much of this is post-K2 level technology.

[brian 333]

Assume superconductors and hydrogen fusion and interstellar travel becomes fast even in hard sci Fi.

You begin with a ship that is a disc or torus, with four or more fusion engines mounted on gimbals around the exterior. Now, on top of that you stack 200 times the vessel's mass in hydrogen ice.

If my engines can produce .1 g of thrust and I decelarate at the halfway point, the time to travel 500 light years, from the point of view of the ship, is about 80 years. (From the PoV of the launch point that will be about 520 years.) But my engines will get more efficient as I use up fuel, and that estimate assumes constant thrust. When my engines can produce 1g of thrust the same trip takes about 12 years from my PoV, but still takes over 500 years from the PoV of the launch site.

Once you have asteroid colonies and the ability to accelerate to relativistic speeds, interstellar travel becomes trivially easy within the current human lifetime. Relativity is your friend!

[Mechalich]

Hard SF interstellar travel is a slow and high energy process. We are talking building a star-sized power source (possibly a star contained in a dyson swarm) and a ship taking a century to reach a nearby star. (Breaking is the hard part - there are lots of solutions, like huge mirrors and solar sails, or making much of the star wisp's mass be anti-matter). You don't have space battleships or anything else like that.

While you don't have space battleships, it's not nearly that bad. It is highly probable that some form of fusion powered rocketry can get a star-ship the size of reasonable size (like 10-100x the biggest ocean-going ships we build now) up to 0.05% of the speed of light or so and deliver a payload and maybe a tiny human crew in a module to a nearby star (yes you need life extension or cryo for that part, but that seems doable on a span of decades). Now this does mean that establishing any sort of interstellar colony requires some serious Von Neumann-style self-replication bootstrapping process - ideally an entirely automated one that gets launched well in advance of sending any people - but there's no physical laws forbidding that.

The real issue is motive. If you have a Von Neumann-style self-replicating bootstrapping process available, then there's no need to leave the solar system, ever beyond super-long-term risks like gamma ray bursts. Instead you just disassemble asteroids to build Bishop Rings or McKendree Cylinders, adding a new continent's worth of habitable territory each time, to provide all the space necessary. While exploration might send tiny numbers of people off to see the stars, there's really no reason to bother with colonization.

[brian 333]

While you don't have space battleships, it's not nearly that bad. It is highly probable that some form of fusion powered rocketry can get a star-ship the size of reasonable size (like 10-100x the biggest ocean-going ships we build now) up to 0.05% of the speed of light or so and deliver a payload and maybe a tiny human crew in a module to a nearby star (yes you need life extension or cryo for that part, but that seems doable on a span of decades). Now this does mean that establishing any sort of interstellar colony requires some serious Von Neumann-style self-replication bootstrapping process - ideally an entirely automated one that gets launched well in advance of sending any people - but there's no physical laws forbidding that.

The real issue is motive. If you have a Von Neumann-style self-replicating bootstrapping process available, then there's no need to leave the solar system, ever beyond super-long-term risks like gamma ray bursts. Instead you just disassemble asteroids to build Bishop Rings or McKendree Cylinders, adding a new continent's worth of habitable territory each time, to provide all the space necessary. While exploration might send tiny numbers of people off to see the stars, there's really no reason to bother with colonization.

There are a lot of reasons for colonization, including scientific, spiritual, and political. My personal favorite is self-determination and personal liberty.

Absent war, pandemics, or some scary-crazy Logan's Run type euthanasia scheme, any habitat will fill up in five to ten generations. Colonization can be a kind of pressure relief valve which allows breeders to self-select for migration while those who fit in with a dense population, low birth rate lifestyle remain behind.

I remember the night they broadcast the first Moon Landing. I told my mother that in twenty years I would be on the first ship to Mars. Never forget that aspiration can shape a society even if only a very tiny percentage of that society ever gets the chance to do it.

[Yakk]

Assume superconductors and hydrogen fusion and interstellar travel becomes fast even in hard sci Fi.

You begin with a ship that is a disc or torus, with four or more fusion engines mounted on gimbals around the exterior. Now, on top of that you stack 200 times the vessel's mass in hydrogen ice.

If my engines can produce .1 g of thrust and I decelarate at the halfway point, the time to travel 500 light years, from the point of view of the ship, is about 80 years. (From the PoV of the launch point that will be about 520 years.) But my engines will get more efficient as I use up fuel, and that estimate assumes constant thrust. When my engines can produce 1g of thrust the same trip takes about 12 years from my PoV, but still takes over 500 years from the PoV of the launch site.

Once you have asteroid colonies and the ability to accelerate to relativistic speeds, interstellar travel becomes trivially easy within the current human lifetime. Relativity is your friend!

200 times the ship's mass in ice isn't enough fuel I think. 0.7% of mass converted to energy means 1.4 times the ship mass as energy. That isn't enough to reach 99% of light speed and then come to a stop even if the fusion - thrust was 100% efficient.

Assuming insanely efficient fusion-thrust conversion, we get 0.5% of mass converted to KE. That gives us our exhaust velocity (as we use the He produced by fusion as our propellant; more efficient than laser drives, and the He is a waste product). 1.005 = 1/sqrt(1-v^2) means (1-v^2)=1/1.01, or v^2=0.01, or v=0.1 (ie, at low percentages, converting X of your mass to energy gives you a velocity as a fraction of c of sqrt(2X)).

Using the rocket equation https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation dv = ve ln (m_0/m_f). Here, ve is 0.1c, so dv = c/10 ln (m_0/m_f).

As it happens, in the perspective of the rocket, if you want to know your travel time you can ignore relativity - even though you never pass c, time and length contraction means that if the target is 500 ly away, and you accellerate "as if" you would cross the speed of light in newtonian math, turn around, and decellerate, you'll actually get the correct travel time from your perspective.

So if we want to cross 500 ly in 100 ship years, we have to cross the first 250 ly in 50 ship years and turn around. To cross the first 250 ly in 50 ship years we have to have an average speed of 5c, so a top speed of 10c. With a rocket exhauste of 0.1 c this means ln(m_0/m_f) has to be 100, or m_f * e^100 = m_f.

To decellerate, we need to repeat this again, so the total amount of Hydrogen ice we need is e^200 times the payload mass.

Suppose the payload we want to deliver is 1 electron. It has a weight of about 10^-30 kg. In order to deliver that 1 electron using a hydrogen fusion rocket we need 10^56 kg of hydrogen ice, or 100 times the mass of the observable universe.

Seems impractical to deliver 1 electron. And it is tricky to imagine a fusion reactor the mass of 1 electron.

You need better energy intensity than hydrogen fusion. Possibly multi-state fusion would help, but really you need either energy delivered that you don't have to carry the fuel for (lasers and sails) or something closer to anti matter, or gonzo stuff like being able to suck energy out of the vacuum.

Interstellar travel is both hard and easy. It is hard, in that the scale of the society capable of doing it is insanely scary. They should be perfectly capable of dismantling moons for construction material, and have be well on the way to a K2 scale civilization. It is easy, in that once you are at that scale, there doesn't seem to be anything stopping you from doing it.


While you don't have space battleships, it's not nearly that bad. It is highly probable that some form of fusion powered rocketry can get a star-ship the size of reasonable size (like 10-100x the biggest ocean-going ships we build now) up to 0.05% of the speed of light or so and deliver a payload and maybe a tiny human crew in a module to a nearby star (yes you need life extension or cryo for that part, but that seems doable on a span of decades). Now this does mean that establishing any sort of interstellar colony requires some serious Von Neumann-style self-replication bootstrapping process - ideally an entirely automated one that gets launched well in advance of sending any people - but there's no physical laws forbidding that.

The real issue is motive. If you have a Von Neumann-style self-replicating bootstrapping process available, then there's no need to leave the solar system, ever beyond super-long-term risks like gamma ray bursts. Instead you just disassemble asteroids to build Bishop Rings or McKendree Cylinders, adding a new continent's worth of habitable territory each time, to provide all the space necessary. While exploration might send tiny numbers of people off to see the stars, there's really no reason to bother with colonization.

0.05% of the speed of light for a fusion-powered ship gives us e^10 fuel ratio to speed up, and e^20 to come to a stop, or 485,165,195x the ship's rest mass in fuel.

Largest ship are 1/4 of a million tonnes. At 100x that is 25 billion tonne ship (2.5*10^10). Throw in 5*10^8 fuel ratio and we are at 10^19 tonnes of hydrogen, or 0.1% of the mass of the moon in hydrogen fuel.

Basically you have to build a pure hydrogen frozen planetoid, attach thrusters and a space craft to it, and thrust that ship up to 0.05c, turn the thrusters around and repeat. The thrusters have to be part of the payload somehow, because we will want to scale them down as the moon gets smaller.

However, I'd just conclude that fusion rockets aren't good enough for relativistic travel.

[brian 333]

200 times the ship's mass in ice isn't enough fuel I think. 0.7% of mass converted to energy means 1.4 times the ship mass as energy. That isn't enough to reach 99% of light speed and then come to a stop even if the fusion - thrust was 100% efficient.

Assuming insanely efficient fusion-thrust conversion, we get 0.5% of mass converted to KE. That gives us our exhaust velocity (as we use the He produced by fusion as our propellant; more efficient than laser drives, and the He is a waste product). 1.005 = 1/sqrt(1-v^2) means (1-v^2)=1/1.01, or v^2=0.01, or v=0.1 (ie, at low percentages, converting X of your mass to energy gives you a velocity as a fraction of c of sqrt(2X)).

Using the rocket equation https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation dv = ve ln (m_0/m_f). Here, ve is 0.1c, so dv = c/10 ln (m_0/m_f).

As it happens, in the perspective of the rocket, if you want to know your travel time you can ignore relativity - even though you never pass c, time and length contraction means that if the target is 500 ly away, and you accellerate "as if" you would cross the speed of light in newtonian math, turn around, and decellerate, you'll actually get the correct travel time from your perspective.

So if we want to cross 500 ly in 100 ship years, we have to cross the first 250 ly in 50 ship years and turn around. To cross the first 250 ly in 50 ship years we have to have an average speed of 5c, so a top speed of 10c. With a rocket exhauste of 0.1 c this means ln(m_0/m_f) has to be 100, or m_f * e^100 = m_f.

To decellerate, we need to repeat this again, so the total amount of Hydrogen ice we need is e^200 times the payload mass.

Suppose the payload we want to deliver is 1 electron. It has a weight of about 10^-30 kg. In order to deliver that 1 electron using a hydrogen fusion rocket we need 10^56 kg of hydrogen ice, or 100 times the mass of the observable universe.

Seems impractical to deliver 1 electron. And it is tricky to imagine a fusion reactor the mass of 1 electron.

You need better energy intensity than hydrogen fusion. Possibly multi-state fusion would help, but really you need either energy delivered that you don't have to carry the fuel for (lasers and sails) or something closer to anti matter, or gonzo stuff like being able to suck energy out of the vacuum.

Interstellar travel is both hard and easy. It is hard, in that the scale of the society capable of doing it is insanely scary. They should be perfectly capable of dismantling moons for construction material, and have be well on the way to a K2 scale civilization. It is easy, in that once you are at that scale, there doesn't seem to be anything stopping you from doing it.



0.05% of the speed of light for a fusion-powered ship gives us e^10 fuel ratio to speed up, and e^20 to come to a stop, or 485,165,195x the ship's rest mass in fuel.

Largest ship are 1/4 of a million tonnes. At 100x that is 25 billion tonne ship (2.5*10^10). Throw in 5*10^8 fuel ratio and we are at 10^19 tonnes of hydrogen, or 0.1% of the mass of the moon in hydrogen fuel.

Basically you have to build a pure hydrogen frozen planetoid, attach thrusters and a space craft to it, and thrust that ship up to 0.05c, turn the thrusters around and repeat. The thrusters have to be part of the payload somehow, because we will want to scale them down as the moon gets smaller.

However, I'd just conclude that fusion rockets aren't good enough for relativistic travel.

You don't need to get anywhere near .99 lightspeed for relativistic effects to kick in. However, if you could, elapsed time for a trip would be virtually instantaneous from the ship's PoV, and 1 year per light year from the PoV of the launch point.

Note the difference in ship PoV elapsed time using different thrust. That's because the ship is achieving a higher percentage of light speed. The trip duration from the launch point PoV is only marginally different. Basically, 1 year per light year plus time to get up to fractional light speed.

[Yakk]

You don't need to get anywhere near .99 lightspeed for relativistic effects to kick in. However, if you could, elapsed time for a trip would be virtually instantaneous from the ship's PoV, and 1 year per light year from the PoV of the launch point.

Note the difference in ship PoV elapsed time using different thrust. That's because the ship is achieving a higher percentage of light speed. The trip duration from the launch point PoV is only marginally different. Basically, 1 year per light year plus time to get up to fractional light speed.

There is a mathematical shortcut to doing all of the relativistic math. It happens that if you have a 500 ly journey and you want to travel it in 12 years ship-time using a uniform acceleration ship you can solve for the thrust required while ignoring relativity.

The result matches up with the relativistic result. You don't actually hit the super-luminal speeds, but the thrust time and ship-time match up. Time dilation and space contraction from relativity cancel out.

So to go 500 ly, you just work out the uniform accelleration required to go 250 ly in 6 years. This is easy to work out - d = 1/2 at^2, 250 ly = 1/2 a (6 years)^2, 500 ly / (6 years)^2 = a, a =~ 132 m / s^2, or about 13 gravities.

132 m/s^2 times 6 years gives a "no relativity" speed of 83 times the speed of light. That doesn't actually happen, of course, because relativity kicks in. Time dilation factor is 1/sqrt(1-v^2/c^2)

50% speed of light: 15% time dilation (x1.15)
75% speed of light: 50% time dilation (x1.5)
90% speed of light: 130% time dilation (x2.3)
95% speed of light: 3.2x time dilation
99% speed of light: 7.1x time dilation
99.9% speed of light: 22.4x time dilation

with distance being contracted (by the travelers) by an identical factor.

"Near instant" travel requires speeds very close to c, which are both energy intensive and basically impossible for macroscopic objects in the current epoch of the universe (the interstellar medium is too thick).

The energy budget of a perfectly efficient drive happens to match the time dilation factor - if you want to hit 50% of the speed of light, your perfectly efficient energy budget is 15% of your rest mass converted to energy. And no drive system is perfectly efficient (as the exhaust is going to contain energy); the SF 'perfect' drive is one that grabs the entire universe and pushes it backwards (in the limit as the mass of your exhaust reaches infinity, the efficiency of your drive approaches perfection).

In short: you aren't going to have short interstellar trips without converting the mass of planetoids into energy, even from the perspective of the people on the ship.

But hitting 0.005c is plausible in a hard-SF universe. At 0.005c you could have an ship the mass of an asteroid decelerate and deliver a payload the size of a pop can, and accelerate using laser sails that use a fraction of the launching star's output during launch. That pop can would then bootstrap production in the target system as a self-replicating probe. When the target system industrializes it can then build a catcher's mitt (a laser braking system) and you can get far, far larger payloads (like, the size of a car) loaded with data, which you can then print out in the destination system.

(If it takes 10,000 years for a system to industrialize and be able to launch 1 probe every 1000 years for an average of 10 cycles, the probes have a 25% success rate, they travel at 0.005c, that means number of probes double every 15k years or so. There are 100,000,000,000 stars in the milky way, so that is 37 doublings or 555,000 years to have as many probes as stars. The milky way is 100,000 ly in diameter, so crossing it takes 20 million years at 0.005c; so colonizing the entire milky way this way requires on the order of 20 million years, as after a small fraction of that every local star will be industrialized, and a wave of probes traveling at 0.005c will build up heading to new uncolonized stars with multiple redundancy. The milky way is 13 billion years old, so this could complete in 0.15% of the milky way's age (an eyeblink).)

This also means that if there is more than 1 intelligent species reaching the stars at the same time in our galaxy it has to be because of an external effect; a single species could colonize the entire galaxy with a modest initial investment in a period much shorter than the galaxy has existed. A simple solution to this is that it indeed happened, and humanity (and other intelligent species) are actually the colonists; the alien species sent probes that engaged in uplift, turning life into intelligent technological life.

Humans start being unique in the geological record on the order of 10,000 to 1 million years ago with our tool use. So you could imagine a galactic 'seeding' event, where systems with life where uplifted using probes, and other systems where used to launch more probes, before the galactic colonization system skuttled itself.

It still doesn't explain how intelligent life interacts much over interstellar distances, or gives you anything like space battleships.

[NichG]

Really the answer to interstellar travel in hard scifi is to just get everyone in the civilization to slow their brains (and the rest of their biology) down by a factor of 1000 or more. Now a trip that would take 1000 years and be enough time for nations to rise and fall is just one perceptual year.

Granted, this is going to cause some problems for diplomats, sports fans, ...

I guess you'd have to live in very cold, low gravity (or buoyant) environments where very slow motions would still be sufficient to move around and interact and do things.