Rik van Riel writes:
> A few mails back the (IMHO sensible) idea was mentioned
> that supersocieties have space as their living environment
> and only use planets to get building materials.
They probably only mine planets when more easily accessible materials have run out. There might be technomagical tricks how to crack a planet quickly, then there might be not. Obviously, there are upper limits to how much energy can be deployed on the planetary surface without destroying the mining/launch structures. Fragmentation by impact makes for a better surface/volume rate, but will probably result in lossage of volatiles, and require some cooling off period.
> If that is the case, why should they be in a hurry when
> they're travelling from one star to another?
Some of them are not in a hurry. Some of them are. These who travel and reproduce fastest will obviously very quickly overwhelm any sluggards in sheer numbers. There might be a couple of sluggard civilisations nuclei out there in the Andromeda somewhere (unless the rapid travellers have starved them out of their resources, or eaten them alive, which is the more logical conclusion), but they will be sure difficult to find.
> The obvious answers would be population expansion or the
> 'need' to expand their living quarters or get material
> for scientific tests.
They don't have living quarters, space is their native habitat (this form doesn't like anything other than hard vacuum). They may do no more sience than the Amazon jungle: some humans in some university somewhere might be doing some experiments, but the rest of the ecology _just is_.
> But that answer can be effectively countered because:
> - advanced species very probably master birth control
Advanced species almost certainly rely on evolving autoreplicators, and it is impossible to contain freely evolving autoreplicators. The intelligent forms might have no interest in harming us, but some of their symbionts/parasites will not be so docile. A mature stellar ecology might be immune to gray goo type of autoreplicators, but a virgin system as ours certainly isn't. Oops, there go the natives.
Probably the best argument against such type of aliens is that our system seems to be in pristine shape, and bits of graphene nanomachinery are not raining from the skies.
> - advances in science and building means you can do
> more with the same amount of material, so you don't
> usually need to get more and more raw materials
Advances in science and building means is that you can mine more more quickly. A civilisation that is essentially a bit pattern coded as electronically excited states can grow essentially hard at the edge of the light cone. It is not hard to imagine that easily accessible material in a stellar system can be entirely converted in the course of a few months/years. Only the kinetically less accessible materials
> - a huge ecology bubble needs a very good social system
> to start with -- and such a near-perfect society
> probably doesn't have the same urge as we have to have
> more and more possessions
Then the more expansive cultures will win.