The article is well done and it was a pleasure to read. It is certainly the most detailed consideration of the realities of long distance space travel, as we currently understand them, that I have seen.

My statements were primarily directed at making two basic points. The first point is that even if they are not impossible ‘in theory’, whatever that means, it is apparent that the technological requirements of even the most plausible of the cases considered in this article render long distance space travel, effectively, impossible. This will be true for quite some time and, in fact, I would expect that we must have a civilization of current or better technological prowess in place for at least a few hundred years more before such a thing were even seriously attempted. This leads into the next point; that we don’t really have a great track record as a species for making such long term plans. I dispute the claim that our high-technology society has been demonstrated to be sustainable for such a long period of time. We have many challenges; technological, socio-political, and economic that no good answers have been found for. The direst consequences of this lack of long-term planning have been held at bay with relatively cheap and abundant resources, not least importantly, energy. The assertion that global ecological concerns are not pertinent to this discussion is fallacious. It is precisely those skills of long term resource management, and due consideration of the ecological impacts of technological systems for life support and resource manufacture, that would be most relevant to a succesful expedition. The belief that the problem is somehow easier because you are dealing with a closed system which, technically speaking, you aren’t, is mistaken. If anything, the components of such an ‘ecosystem’ would be more strongly coupled together, not less.

Furthermore, the example of imperial Egypt as a model for stability seems rather beside the point. Firstly, I am sure the ancient Egyptians exploited external human populations from time to time. Most empires did, that might even be part of the definition of empire. I am looking for examples of human society that don’t do this as there will be no external human resources, or hardly any others, for a deep-space expedition to exploit. The socio-political aspect of the expedition is thus highly coupled to the technological nature of the endeavour and not to be considered in some isolated fashion.

Finally, while it is likely true that humans have existed on this planet for hundreds of thousands of years only the last hundred have been in a society which comes close to having the capability to generate, utilize, organize, and manage the resources necessary to succeed at this endeavour. That is the society that would have to be sustained on a 700 year trip. Not some pre-historic hunter-gatherer society.

The Ark is certainly a Himalaya to go, an incredibly ambitious project. While obviously I have for this project the tenderness of a mother, my purpose is not to say arrogantly: “We will do it! Of course it is possible to do it!, Etc”. What’s would be the point? It will happen in the future, and if it will happen it will be without me.

My point is purely scientific, I hope (though emotionally I put a personal price on it), the question being: if we’d go, which would be the required resources, both human and technical?

From a technical point of view I am the first scared by the big numbers. That point by itself requires already a philosophical reflection.

Initially, the Ark is the compromise between two requirements. We need to collect both large mass or high energy. Where is the optimum? Which is the energy-mass bottleneck to go live out of Earth?

* ENERGY MANAGEMENT: we must master thoroughly and massively the thermonuclear fusion of all types of fusible isotopes in the solar system. And not just to boil hot water in boilers. Mastery of thermonuclear fusion should be up to the point of ordered ejection of 4 MeV ions through magnetic nozzles. Deuterium mostly, then Helium-3 maybe. This is the only possible source for the wild power of the Arch. Humanity is currently spending power in amounts of about 16 terawatt (10^12W) in 2010. For the Ark, it must reach 4 ExaWatts (10^18W). Just to send a human civilization of 10^4-10^5 individuals at 10 light-years from earth in less than 1000 years travel. Faster solutions require more energy, if we want to send at least as many people, and also considering that worlds at less than 10 ly does not certainly allow “bare head” colonization.

* MASS GATHERING: 20 Gt, of which 8 Gt of water. About 12 Gt of walls and building structure in space. Here, faster solutions are less massive by a factor of at least 1000. But again, they require that the target planet is inhabitable, that I think unlikely in less than 100 light-years radius, and very unlikely in less than 10 light-years.

So finally I came to the conclusion that there is not much choice, and that the solution is either an arch or again the same arch. Maybe smaller or larger, but likely measured in gigatons.

From a human point of view:

* We need a strong human civilization to undertake this.
* A new independent mini-civilization shall be founded, which is viable in long-term and independent from Earth. Then we need only to describe what such a civilization need to be at its core (small size, strong historical records, policy defined by its future targets, etc.).

I just want to detail this scope, at least roughly, of what is needed to leave the Earth.

Of course whether it will be done or not is another story. I clearly hope personally that it will be done. But I make no predictions.

- Many machines could have lasted 700 years, simply they are not useful. Think of boats, carts, mills… they are NOT built to last centuries and even if they where, they are exchanged for newer, more efficient ones simply for economical reasons. Simple machines like a compass, glasses, even clocks, can last for 700 years and have done so. And consider this is a closed environment, there is no external erosion, no wind, no rain, etc.

- We have not figured how to sustain our life on earth? what are you talking about? we have sustained life on earth for at least 100.000 years, probably more, and we where NOT trying to sustain it. Will we last 50 or 100 years more? I do not know, and neither you. It is an empty argument, global ecological considerations are totally out of scope here (IMO).

- Have we ever developed a sociopolitical structure that lasted 700 years? Yes, indeed!. Egyptian empire lasted 3.000 years. Probably that is not what you have in mind when you say “last”, but the fact is that there are LOTS of small communities of a few tens of thousands of people that have lasted near a millennium; this is from Nassim Nicholas Taleb’s “the black swan”: “For more than a millennium the eastern mediterranean seaboard called Syria Libanensis or Mount Lebanon, had been able to accommodate at least a dozen different sects, ethnicities and beliefs - it worked like magic”. Of course that came to a bloody and horrible end, but it lasted before that, and the reasons to its end where mostly external. There are many long-lasting, small communities that simply are not “interesting” enough to enter the history books. Also, most of instabilities are external: people inside want others’ resources, people outside want inside’s resources, people outside trying to get others’ resources must cross through the site… If you can maintain a reasonable availability of resources for everyone and there is no disruption from outsiders, there is no deterministic reason for a city to not last a few millennia. Many had.

By the way, you say “nearly every aspect of the Ark is, in fact, technologically impossible”. I do not agree, maybe you can elaborate a little more. This article is just about the Scientifical and technical aspects of the ark, and most if not all of them are possible, at least in theory. A few of them are not possible *now* with our current technical level, the same that 50 years ago was “impossible” to build a computer like the one I am using right now.

Can we get to the stars in this kind of ark any sooner than tens of millennia, is my question. Can the engines of that size keep the thrust of the ark from damaging the integritry of such large scale structures? The propulsion seems to be waaayy out of what we have in this day and age, but what bout nuclear fusion? That should be coming soon with nuclear reactors coming in use in France and other countries.

Yes, the Ark may be conceived as the “exocytosis vesicle” of the Gaia cell. A “seminosphere” (from semen, inis: seed).

The goal is not to “save humanity”, but to spread it within the Galaxy in its own human and sustainable entirety. And I do not think that humanity is in danger in short-medium term. Even, not at all. However, at bigger timescales, at scales that formidably exceeds us, the ability to propagate our being in multiple points of the universe is perhaps the only strategy that can make humanity a cosmic time phenomenon.

And “our being”, Humanity, does not only include the biological species “Homo sapiens” (which is expected to “soon” give birth to new species), but also the biosphere which gave ti birth and the incredible evolutionary success it has accumulated in its various species.

But for this, it takes a great vessel ^ _ ^. A miniature biosphere.

One way to do it big is to repeat “ad infinitum” the same pattern, repeat the same process. Ark is a thin surface (thickness / surface: 10-7) formed by hollow identical polymer strands. In the central channel (diameter: ~ 1-2 m), filled with water which also circulates nutrients (CO2 dissolved … NPK) and light. The wall is made of vegetative fibre bundles (not giving flowers or fruits), of small diameter (some mm -> some tenth of cm) with a “hair” chlorophilian root in the central channel. The thickness of the fiber walls is the same as the diameter of the central channel.

Some properties of these fibers:
* They grow on both ends towards the light source,
* They are aligned in the direction of constraints,
* They cease to grow when the stress reaches a certain threshold and then grow in diameter,
* They wrap themselves around each other when they come into contact,
* They secrete bark as a viscous and water-resistant latex.

It is “enough” to devise such a kind of vegetal being to generate the two walls of the Ark. Initially, the Ark is just a few meters in diameter but it has already its final geometry (fiber arrangemen), and the growth can achieve sizes of the order of the kilometer.

Architecture of walls:

I cheated to represent two types of walls as one: the floor of the Ark that supports the ocean’s weight is thick (50 m or 12 ~ thick strands) and without inter-wall vacuum. The vacuum is 30 m between the sidewalls, finer (2 * 3 layers), which falls on the hub.There is very little inorganic system integrated with walls: just the gateways.

In the interior, there is an ocean of 25 m depth on which float a “continental platform” in the form of a puzzle of hexagons: the human habitat is completely decoupled from the walls.

The surface soil is about 3 m.

Total ocean habitat + ~ 8 Gt

Underneath the pattern of walls there is a diagram of the solar ring of 125 GW as a tapestry of élécroluminescent LED (light output close to 1). On the day, the ring shines on the surface of the Ark. The night it is turned off and the light power is injected into the strands, to feed the chlorophyllian fibers.

All elements of the Ark are 100% recycled (except 16 Gt of fuel, of course:)).

I’ll continue on the same later.

Could you elaborate on the nature of the Ark’s organic construction material and the internal structure of the Ark. The three diagrams in the article are captioned in French and, unfortunately for me, I am not fluent. (By the way I do greatly appreciate the fact that you are fluent in English!) How would it be “grown” into Ark proportions? integrated with the non-organic systems? Maintained with enough water, sunlight, and nutrients through the long journey?

What are your thoughts on terraforming? Mars, for example, sounds like a decent candidate for this process in our immediate solar system. Each case would of course have different variables, but it seems we could apply basic principles we might learn about the process in attempting to terraform Mars to bodies in other star systems.

I do feel that humanity will and should focus on colonizing our immediate neighborhood to a reasonable extent (orbital stations, Moon, Mars at the very least, perhaps Mercury, Venus, asteroids, and a few of the outer system moons) before venturing to “nearby” stars, and regardless of what transhumanistic developments occur in the next few centuries. Learning to crawl before we try to run and all that.

Convincing enough people that space settlement is an inevitable part of humanities future and should be pursued wholeheartedly is another matter.

Not to mention making sure that space is a demilitarized zone of human operation. This will take an awful lot of sociopolitical cooperation at an international level to pressure the warmongering hawks enough to make peaceful coexistence a reality for space.

What do you think about the “space elevator” (you may know it by other names) idea to decrease to cost of payloads exponentially? Once they perfect the carbon nanotube technology it seems this could be a reality in the next 10 to 20 years or so.

Thanks for responding so promptly and thoroughly to my last post!

I have no particular prejudices against the transhumanist movement, it is an idea to be researched, but philosophically, I think that the human phenomenon is an inseparable whole:

* A biology: in biology, I put also the spirit (anima, awareness …), which is like Spinoza said “the idea of the body.” The man-organism capable of thought.
* A society: the man-organism is characterised by a hyper-sociability and only develops in interaction with others.
* A natural environment: the men in society have given birth to the so-called humanity, interacting with a biotic and abiotic environments (the starry sky for example).

With these three elements, we can reconstruct what we call humanity in its essential aspects, even if its entire memory has been obliterated in the past.

While a single thinking machine (even aware of itself and of the world) is not an humanity and can not reproduce. Even bearing in mind all that man has done in terms of knowledge and memories. And the same, in my opinion, applies to a machine without a body, without this particular interaction with a natural environment.

Of course, this is not because the spirit “in silico” is a sub-mind. But it is no humanity, is something else to explore. The ark is a “minimum Humanity”: this is the concept. (Whether technically it can be reached with the Ark of the article, it is another story…). It is a fully human entity requiring the minimum energy expenditure.

Otherwise, of course, we can add the idea that the Ark also boards an hypothetical “silicium soul” (or whatever …), or “hibernants” embryos, why not?

Returning to more “down to earth” consideration How is it possible to “land” from the Ark?

The Ark is not abandoned once arriving in the target planetary system. It remains the living environment of reference. So this is a place to live virtually forever (as a planet). Its walls are renewed permanently. The target stellar system is a largely hostile environment.

To get on this “planet”, I imagine a dozen shuttles containing some dozen of people (say 100 tons of payload) powered by fusion propulsion. These shuttles would be used initially to carry out missions in the solar system. During the last centuries of the travel, the arkonauts could of course improve or rebuild them. The ark has a significant technological capacity.

a+

I love the idea of a plant based structure for the ship.

I’ll have to go back and read my Kurzweil book to really have much to say about the feasibility of uploading the mind. My personal belief is that we are made up of three basic parts, body, mind, and spirit, working in unison to create human consciousness. It seems to me it will be quite some time, if ever, for us to be able to technologically transfer the spirit element into an artificial host.

What would the process of disembarking from the ship and setting up a colony once it arrives at its destination look like? Wouldn’t they need some sort of smaller vessels along, or the ability to construct them, to ferry raw materials and people around?

Aren’t there documented cases of certain yogis being buried alive for extended periods of time without food, water, and with limited air? Could these types of techniques be applied to a hibernation strategy?

Why couldn’t a single ship incorporate the several different strategies (generations, Methusalah (sp?), hibernation/cryo, embryonic, cybernetic etc.) into one amalgamated scenario?

I realize the last post was quite a while ago, but these are things I’ve been thinking about as I’ve been reading. I’ll have to see if I can find the Wiki page….

Take care and keep dreaming!