- The first level is the planets;
- the second is the solar systems;
- the third one is the level of the galaxies and
- the last one is the Universe itself.
Another example for the observer-dependent nature of scales/taxonomies is the megatrajectory theory. It is based on the evolutionary mile stones and
- the emergence of life is the first so-called megatrajectory;
- the second is the prokaryote diversification;
- then eukaryotic cells appear;
- it is followed by the rise of the multicellular life forms;
- the “invasion of the land” is the 5th and
- the rise of intelligence is the 6th megatrajectory that gave an opportunity for the invasion of every possible environment
The post biological intelligence can be interpreted as the 7th megatrajectory (Cirkovic, Dragicevic and Beric-Bjedov 2005).
This taxonomy is focuses at least partly on parochial details of earthly evolution, since its aim is to give a description of the history of life on earth: I.e. the fifth megatrajectory would never occur on a water covered planet.
We can reinterpret this megatrajectory concept focusing on those factors that are presumably universal. Freeman Dyson distinguishes three classes of phenomena which can occur in our universe: “normal physical processes”; “biological processes” and radio (or another forms of) “communication between life forms existing in different parts of the universe.”(Disturbing the Universe, 1979) These factors can be interpreted as “gigatrajectiores,” because they–opposite to megatrajectories–can be typical in any universe which is populated with intelligent observers.
- The first gigatrajectory is characterized by the domination of lifeless matter;
- the appearance of life was the second gigatrajectory and
- finally intelligence rose.
What is more, if you accept one or other form of panspermia hypothesis, then it seems to be possible that life which appeared on the surface of a planet can spread in our Galaxy. But it seems to be impossible even to the microbial life to sail to the closest galaxy, since it would take billions of years. So the spread of life is localized for ridiculously small parts of the Universe. In other word: to believe that other galaxies inhabited with intelligent beings, we should believe that both life and intelligence arose independently from us somewhere in in the Universe.
Similarly, technology seems to be provide an opportunity (theoretically, at least) to conquer not only our planet, but both our solar system and our galaxy–after all, even the Fermi Paradox is based on the presumption of its possibility (if we are able to, then they should be able to visit any stars, including the sun, as well). But notice that even the SETI is mainly about the search for alien intelligence within the Milky Way. Although we have a theoretical chance to observe a super civilization’s energy emission from another galaxy, it is impossible to visit even the M31, since it would take million years even with 0.9 c. And although the time dilatation would make slower the aging on the board of the spaceship, its construction should survive an unimaginably long period of time (notice that the Homo sapiens itself didn’t existed a million year ago). This long travel seems to be not theoretically, but technically impossible. So unless we invent a revolutionary new form of travel (i.e. a warp driver, but it is only an unfounded dream today without a chance to build it), we will never leave the Milky Way and it means that the Universe is extremely huge compared to our possibilities.
In short: the spatial structure of the Universe limits the possibilities the spread of life and intelligence. It raises a question whether it would be possible a universe which can be conquerable by its habitants.