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Comment by stouset | Hacker News Reader

There’s a huge asterisk here.

IIRC, it is possible to get anywhere in the observable universe in one human lifetime assuming 1g of constant acceleration.

This does not permit you to slow down and halt at your target, which greatly increases travel times.

It is also effectively a one-way ticket for anything other than objects in our immediate stellar neighborhood. If you turned around and returned to Earth after getting to an object 1,000ly away—still well within our own arm of the galaxy—at least 2,000 years will have passed on Earth. It’s probable that no civilization you know of would still exist, nor would anyone be able to understand your language.

This isn’t even beginning to address the problem of running into stray atoms at 99.99…% of the speed of light. Or god forbid a handful of stray molecules. We also haven’t discussed the real elephant in the room which is the sheer amount of energy required to accelerate a human and human life support systems at 1g for several decades.

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For the sake of pedantry, there are things in the observable universe which are increasing in distance from us by more than 1 light year per year. This means it's impossible to reach them unless the universe's rate of expansion changes. I think the Hubble volume is the region theoretically reachable; limiting acceleration to 1g would limit you to a slightly smaller region (only a tiny bit smaller, I think).

https://en.wikipedia.org/wiki/Hubble_volume

Problem is carrying the fuel (say we mastered nuclear fusion) that lets us accelerate with 1g for a longer time would use more energy than is available in our solar system.

Also, how much fuel do you need to bring along to accelerate a human and life support system and the whole craft including fuel, for a lifetime? Is it larger than a planet?

Yeah, I added that I think around the time you replied :)

Since we're already in the realm of far out engineering, you could get the energy from a laser beam from a source orbiting the sun. Your spaceship would have some kind of array to capture the energy beam.

This gives you energy, but I'm not sure how to turn that into velocity. Presumably you'd want some kind of ion beam emitter on board to propel your craft forward. Halfway through the journey, you'd turn the ion beam around to decelerate as you approach your destination.

In the Arthur C Clarke novel Songs of Distant Earth, spacecraft pushed huge blocks of ice ahead of them to absorb stray interstellar dust.

So there is also the idea of a ramjet that uses interstellar hydrogen as fuel for fusion, which provides energy & propulsion: https://en.wikipedia.org/wiki/Bussard_ramjet

Some recent findings do give it lower feasibility though.

Another option is to visit as many massive objects as possible on the way there, doing gravitational slingshots until you're half way, and then gravitational brakes on the approach. Of course now you're taking detours, but since certain amounts of fuel make the trip impossible, any workaround at all is an improvement. What's an extra few thousand years between friends?

First, what “many objects along the way”? There are basically none. To do this requires many detours that significantly increase the distance you’re having to travel.

Second, the faster you’re going, the less useful a gravitational slingshot is because you spend less time in the object’s gravity well.

It’s a fun and useful trick within our solar system, but I don’t think the physics plays out well for interstellar travel.

Stars is what I meant. Although upon further thought I think you're right. I guess the intervening stars are unlikely to be moving at helpful velocities for such a game of pinball, metric expansion being what it is.

Slingshots require very specific conditions and configurations of orbiting bodies that won't really work in deep space - all the Kuiper Belt/Oort Cloud bodiees are far too small and too far away to be usable.

But assume for example that you don't care about how long it is going to take (you are an immortal cyborg, an upload living in the computer or a popsicle in hibernation & the AI is driving. Then you can just "island hop" between Kuiper Belt/Oort Cloud objects, never gaining any high % of the speed of light but always having the next body in your sights, not farther than a few decades or a couple hundred years of flight at most.

You reach the body, refuel, repair, maybe upgrade and then off you go, to the next one. And eventually, you might be at you destination, with a fully fueled and repaired ship. It might just take like 20000 years for start to finish, but hey, you can use it for something productive like learning to play Go or something. :)

You're right, I overlooked some important slingshot requirements. As for the longevity, I figure the ship can build a facility for growing settlers when it arrives. With no humans on board it can sustain heavier accelerations.

This is quite nicely described in the engenerator article on Orions Arm (including possible problems): https://www.orionsarm.com/eg-article/4a3d78dc77e6f

In this setting this was first done when a bunch of immortal vyborgs was on a colony ship, about hundred years from arrival but there was a probe with a matter printer already in the destination. So their got the idea to send the probe both blueprints for a humanoid body printer as well as their mind backups. That got their colony going quite a bit faster but might have resulted in some funny/awkward moments once they met in person later. :)

Presumably you could also run this withou a mind upload and let he individual develop normally.

As you get going further and faster, this energy redshifts further and further making it less and less useful. Also there’s of course the problem of focusing a laser with that amount of energy tightly enough on an object increasingly far away.

And crucially ensuring that beam continues to run for billions of years. a few decades may pass for you, but not for the laser that's pushing you

Not sure if my interpretation here makes any sense but here it is. Due to relativity time slows down on the ship, the laser is still hitting the ship, how would the measurement of the energy received from the laser be perceived on the ship, from the ships perspective a 1000 years worth of energy arrives within a few decades. My head hurts thing about this. If you had a ship that could instantly jump to 0.5c travelling away from earth and we beamed a message using a laser at say 1Gb/s, how would the bandwidth appear to the ship?

You have it backwards. The further and faster the ship goes, the less energy is received. The energy collected over a day will be spread over a week, a month, a year, a decade, etc.

GP has it backwards too. For 1g of acceleration, none of the beam that is produced after a year will ever reach the accelerating spacecraft. You only need to run it for a year.

For 1g of acceleration, none of the light produced after 1 year will ever reach the spacecraft. You only have to operate the power source for a year, but you only get a year of source power spread across an infinity of time.

Actually, even something as primitive as a NSWR (https://en.wikipedia.org/wiki/Nuclear_salt-water_rocket) can reach a good percentage of the speed of light after basically processing a comet for fuel. From the Wikipedia article:

"The design and calculations discussed above are using 20%-enriched uranium salts. However, it would be plausible to use another design which could achieve much higher exhaust velocities (4,725 km/s) and use a 30,000-tonne ice comet along with 7,500 tonnes of highly enriched uranium salts to propel a 300-tonne spacecraft up to 7.62% of the speed of light and potentially arrive at Alpha Centauri after a 60-year journey."

Sure, not 99% the speed of light or continuous 1 g acceleration but IMHO good enough for an oversized nuclear squirt gun.

Still, this is many, many orders of magnitude short of what’s being discussed. Essentially the forefront of technology could get us to just barely speed past our nearest neighbor in one human lifespan.

That's why we need to find a globular cluster with metal-rich planets, and take a generation ship over there.

Sure, a thousand generations will live and die along the way, but once we get over there, you've got stars every 0.1 ly or so, and with very plausible future tech, you could navigate between them in a few years. You could set up a proper starfaring, interplanetary civilization, with tradeships either going back and forth between two neighboring systems, or winding on long, never-repeating routes, visiting a dozen or so star systems in a human life.

(Most globular clusters appear to be old and metal-poor, and we haven't found a lot of planets there, and this only works if you find a globular cluster where ~every star can support a colony.)

> Sure, a thousand generations will live and die along the way, but once we get over there[...]

Unless you're planning on forcing those thousand generations to live in inhumane conditions (e.g. force a static culture), that should probably be "if we get over there". I'd be very surprised if, after 1000 generations, the chance for arrival is > 50%.

It takes only one generation to decide not to go along, be that by changing course, or by not reproducing enough, or internal warfare, ...

I think it highly depends how big you make the thing &indeed what are the living conditions. If the people living on the thing can go one with their life withou much hardship they might not mind - even here on Earth most people just go on with their life and are happy.

Yeah, right we are 300 hundred years from the target but & 500 years on the way but so what ? You go for somo zero-g polo, do some cooking and pottery classes with firends, maybe learn machining so you can help with ship maintenance and so on.

It is the same on Earth - you go on with your life knowing you will propabably not live long enough to see some far future projects to be complete, like the final form of the Hagia Sophia Catthedral or Half Life 3 release. And thats mostly fine ?

Even with enough space and great living conditions, there will be greedy people who will try to gain power by gating resources. There will be factions forming, there will be conflict, and fighting. You need too many people for all to feel like one cohesive social unit for 1000 generations, humans just aren't built that way.

And that's just conflict. What if an early generation decides to target a planet that's less useful re/ metals etc., but that's much better suited for human life? How can you guarantee they won't decide to change course as a gift to their descendants, without draconian measures against such ideas?

> Also as for changing course - that is in many cases impossible, at least unless you want to make it 100% certain that you will die alone in the coldness of space. Just too much energy needed to signficantly change the trajectory & starts, at least in our part of the Galaxy, being too far apart.

Sure, the later generations wouldn't have that choice, but the first few definitely would. You need to bring a ton of fuel anyway to slow down, and 1000 generations is plenty of time to increase fuel efficiency a little. So a minor change e.g. at generation 5 seems very much doable, unless you have concrete examples that prove otherwise.

> It is the same on Earth - you go on with your life knowing you will propabably not live long enough to see some far future projects to be complete, like the final form of the Hagia Sophia Catthedral or Half Life 3 release. And thats mostly fine ?

I'm not forced to live my entire life working towards the Hagia Sophia or HL3, with the choice to do otherwise being taken away from myself AND from 1000 generations of my descendants.

If I was on that ship, I'd vote to blow it up, just so those responsible won't get away with it.

Yep, that ship would be a powder keg waiting for one missed ration to go off, see [1]. Hell, if the internet(?) goes down for a week that might be enough to cause a violent uprising. Actually, even if everything goes right and everyone is happy dying on the ship for no real reason, something will go wrong, it is just human nature.

[1] https://www.imdb.com/title/tt7589524/

The Hagia Sophia or the Sagrada Família took more then a lifetime to build but they were usable for their intended purpose, long before they were finished.

Also as for changing course - that is in many cases impossible, at least unless you want to make it 100% certain that you will die alone in the coldness of space. Just too much energy needed to signficantly change the trajectory & starts, at least in our part of the Galaxy, being too far apart.

A small nudge near the outset would produce a massive ultimate change in’s trajectory, so maybe not too much energy is needed to redirect.

Yeah, but why. It's not like you could redirect it enough that you'd land somewhere in your lifetime. It'd just be changing where the ship ended up in 10, or 100, or 1000 generations.

To give your descendants a better life?

The point of sending them off to a carefully selected globular cluster would already be to give them a better life.

I'm not saying someone won't convince everyone on board that a silver future for their Nth-great-grandchildren worth derailing the golden future of their 10Nth-great-grandchildren (especially if it looks like the generation ship won't last 10N more generations), but from my POV sitting on a couch that isn't on a generation ship (well, not something traditionally defined as a generation ship), it doesn't feel like something you'd get everyone all fired up over.

You're proposing to enslave a thousand generations to ship them off to dead worlds rich in certain resources. I have no idea how you imagine their life to be once they arrive, but I can promise you that you're not giving the first 2-5k generations a better life, you're forcing them into a horrible future. It's deeply concerning that you don't seem to understand this.

Also why.

Sure there will always be some people who want to explore for exploration’s sake. But a generation ship leaving a garden of Eden we’re quite literally built for in order for our children’s grand^(1000)children to terraform a rock half a galaxy away in order to have a different mix of resources?

That’s a hard sell for the first generation, to say nothing of those who come after.

I would expect indoctrination something like what keeps alignment among devout religious practitioners would be forced to emerge. The alternative is extinction on a spaceship hurtling into the vastness of space.

I suspect education on that ship would look a lot different than it does on Earth.

That would mean we'd send them off with highly limited knowledge specifically designed to keep them docile, and an automated dictatorship that keeps the system rigid without leaving room for cultural development.

At best that's slavery, at worst it's reducing those 1000 generations to cattle.

Re: changing course, as long as your generation ship accelerates for more than one human lifespan, your future generations of involuntary colonists aren't going to have a lot of options besides going along with it. The choice wouldn't so much be "keep going or veer off and colonize a closer star system" as it would be "keep going for another 800 generations or veer off and colonize a closer star system in another 80 generations". I mean, there's probably no way to stop them from making that choice, but it's hard to see anyone caring whether their nth-great-grandchildren die with one or ten millennia left on the trip.

If the ship accelerates for the first 100 generations, the 2nd generation likely still has every chance to target a different planet. I don't know which generation would be the last, but I'd need to see actual math to believe that it's strictly only the first generation.

One more consideration is targeting data. Do you even have another target or the sensors to find one ? The means of detection for a suitable planet or even just a good solar system, where you build a bunch of habitats might require huge telescope arrays or even something like a special telescope that uses the Sun as a gravity lens source.

Might be out of reach for even a massive generation ship.

Then you have a natural upper bound on the amount of amenities etc, because if you provide too much, 1000 generations can probably use it to try and find another target.

I'm sure you can keep making the situation more and more specific, but that's not going to increase your chances, or make the whole thing morally acceptable.

Well if the goal is to settle a new planet or solar system then I guess it is working fine ?

I have no idea how to interpret this answer in the light of the arguments I've been bringing up, it doesn't feel like you're engaging with my words.

The goal is not to settle any random new planet or solar system, so no, it's not working fine.

Human lifespan is another important variable to work on not just for this reason.

Imagine such a complex machine working without fail for 60 years. It's just not plausible in my view.

The Voyager probes have been running since the 1970s, so we have some precedent.

Less if we just send some eggs and sperm and spin up a human on arrival. We can construct a larger life support system out of things we find at the destination.

Or better yet, send some cancer cells so they can replicate during the journey, then switch from cancer mode to gamete mode for the final generation. That way they're fresh when you need them. You're gonna want DNA repair happening continuously, rather than all at once upon a thaw.

If I recall correctly, it's about the size of a large asteroid (assuming 100% conversion to energy). It's a long time since I worked the problem, though, so I could remember wrong.

What to send is DNA along with some sort of robot that can grow it into a man upon arrival.

Maybe better to start with a woman...

Not necessary. A cell (with a nucleus) has all the DNA required. You just need to have a viable system to build up a human from it. I think right now this is not possible, but this will be solved eventually. The question is, though: do future humans really want to do that?

Don’t be so sure. I hate to draw the comparison but raising a child in an artificial womb is probably at least as difficult as growing chicken wings in a sterile environment. A startup founder that wanted to grow meat pivoted to lab grown egg whites, in his words in order to grow a cube of solid meat any bigger than a centimeter cubed, you could not keep it sterile, it is too attractive of a growth medium. In the case of a chicken, it’s like the rest of the bird is needed to provide an immune system so the meat doesn’t spoil.

Mothers provide more than a growth vat to their children, not to mention the immunities passed on in breast milk.

To birth a child in a sterile vat, they would likely need to be kept in a bubble the rest of their lives too.

> nor would anyone be able to understand your language.

Greek and Latin are still understood. I don't know if the Chinese spoken today resembles Chinese from 2000 years ago, but maybe some of the written language would be understandable. Both Hebrew and Tamil are comprehensible that far back, and farther. Arabic goes nearly that far back.

Of course, that's six languages out of... how many do we speak?

> Greek and Latin are still understood.

Nerds specifically kept the archaic forms alive, but they'd also tell you that Latin and ancient Greek were not static for their whole existence (Attic != Homeric != Koine), and modern Greek is somewhat different from what is taught as "ancient" Greek.

Treat Latin and (ancient) Greek like you would Quenya or Esperanto.

If this were to happen with English, I'd expect us to keep Chaucer, Shakespeare, and enough to understand Victorian literature, but it's anyone's guess if modern English would survive at all.

Arabic… kinda? It has an international standard form, but from what I've been told the language also comes with local dialects which can be difficult to mutually comprehend (though this is also the same with English just by going from central London to Sheffield).

> IIRC, it is possible to get anywhere in the observable universe in one human lifetime assuming 1g of constant acceleration.

Huh? You can’t go faster than light speed, and the observable universe is way larger than ~100 light years.

This is using the fact that at 1g acceleration, one will quickly approach the speed of light relative to its starting rest frame and time dilation will give the astronaut a _very long_ life relative to that frame.

Ahh fair enough. Guess I wasn’t measuring the length of the observable universe in the frame of the astronaut…

The closer to lightspeed you get the more shit you would collide with. I think you would reach an equilibrium speed where drag balances thrust?

And hitting a microscopic speck of space dust would be like a nuclear explosion.

Time experienced will be slowed down for the person in spaceship as you near lightspeed

> nor would anyone be able to understand your language.

Huh? We already have machines that can understand any language from a sample.

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