Suppose there is an alien civilization somewhere out there, and they revere life. Let’s suppose, just for illustration, that they had an early philosopher-teacher like Buddha, and his teachings were so good, they crowded everything else out. The whole population thinks that “Life” is the greatest good, and they should spend their efforts propagating it. Their planet looks very different because of this belief, but the planet is not that important to the question facing them. That question is simply, how do we propagate life to other planets?
Let’s also suppose that life is characterized as has been guessed in this blog, that it is hard to originate and easy to evolve. Because the alien civilization has long ago reached asymptotic technology, where they understood all there is to know about the universe and its physical laws, they know this, and realize that there are large numbers of planets in the galaxy which could support life, if it had only originated there. But it hadn’t. They also understand evolution backwards and forwards, and realize that if they seeded life on these planets, in a few billion years there would be alien civilizations there, similar in many ways to theirs. They know this because they understand that technology has to develop in a certain set of steps, each one building on the previous one, and civilization is forced to self-organize according to the current technology. All civilizations at the pinnacle of knowledge are similar. So, that gives them a little more impetus to seed these planets.
What they want to do is put some simple cells down in favorable locations on as many planets as they can. How are they going to do it?
The first thing they need is patience. The mean distance to the nearest planets might be 10 or 20 lightyears, and other ones are even further. If they go at 0.1 lightspeed, it’s a hundred years at the least; 0.01 lightspeed, a thousand, and 0.001 lightspeed, ten thousand. Perhaps they live much longer that humans do, but this is still a long time.
If they want to go at 0.001 lightspeed, which is about 10^6 km/hr, they will have to boost their rocket very much. This is fifty times the speed needed to get to low earth orbit, and energy goes as the square of the speed. So, a rocket, if they use that, would have to have 2500 times the energy of a typical current-day Earth rocket. Each power of ten in speed raises energy requirements by 100. 0.001 lightspeed might be a very optimistic goal.
Perhaps one early question would be: is it necessary to decelerate in order to perform seeding? Deceleration requires equivalently huge amounts of energy per mass as acceleration, and the bad thing is that while the rocket is leaving their home solar system, it will have accelerate all the mass needed for the deceleration at the origin planet. So, if seeding can be done at fractional lightspeed, that would save a tremendous amount of resources, energy, cost and construction. Seeding at fly-by speed requires that the seed payload reduce its speed to initially low planetary orbit speed at the very least, so it can begin its seed operations from a good vantage point. There is no hope for it to decelerate by upper atmospheric drag. Too high in the atmosphere would have it slip right through, and a little lower, the energy of fractional lightspeed motion would turn the probe into a molten blob in an instant, and then it would simply vaporize. No cells would survive.
Fractional lightspeed is so fast that using other planets for gravitational slingshot effects produces negligible effects. There are no other tricks to use. Massive deceleration the old-fashioned way is the only thing that will shed enough kinetic energy to get the seed pod to be able to arrive unvaporized.
Deceleration by reverse thrusting has to remove the momentum of the probe, and the propellant has to be present to do this. If a long, slow deceleration is chosen, the thrust of the deceleration can be lower, meaning a lighter weight thruster. So, to minimize expense, it would be best to accelerate quickly near home planet and then start decelerating shortly thereafter. This lengthens the total travel time, but reduces mass requirements.
If that issue is settled, perhaps the next one is how to produce something that can work for ten to a hundred thousand years? The environment is not the most benign. Reliability failures are often extremely diverse, sometimes from multiple causes, and notoriously difficult to predict before the first failure. How would the alien technologists build something for, say, a hundred thousand year voyage when their civilization might not yet be that old? Would having asymptotic technology provide them with enough know-how so they could build such a seedship and be highly confident it would work all the way through the end of the mission?
The answer has to be yes. First of all, they would know the environment in which the seedship would operate, both during the acceleration phase, the deceleration phase, and while it was performing its mission at the destination planet. This is basically astrophysics, utilizing large telescopes and other observing instruments. A kilometer sized telescope could be built somewhere far from their sun, and operated to observe the destination solar system. Other sensors, perhaps huge, could also be built to gain an understanding of the interstellar space between the home planet and the destination planet. Models of the overall operation of the seedship should be completely accurate. They would know, for example, the radiation environment in any specialized package on the ship, both from cosmic radiation and from any radiation sources on the ship itself, e.g. a reactor for power.
Secondly, they would understand the activity and aging of any materials, based on a thorough understand of materials in general. Predicting how, for example, a power converter or a timer would operate over long times should be simply extrapolation of the processes that go on during shorter intervals.
Thirdly, reliability failures in their civilization would be almost non-existent, as the technological know-how would build up over centuries as to the potential root causes of failures. This means that the body of knowledge in how to build reliability into objects becomes asymptotic, just like all other science and engineering knowledge.
A different question arises: is it possible, even with asymptotic technology and access to any materials needed, and a very high level of effort and funding, to build a seedship? Is there an upper limit on reliability that the seedship would exceed?
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