Theory: the most advanced life forms will not undergo stellar travel. 1/

Advancement of civilization has always been pinned to availability of resources and efficiency of the civilization as a whole. Humans are doing it completely wrong, since we're two-dimensional. 2/

There is no way for the human civilization to inhabit 3-D space. We can have sky scrapers, yes - but they are always just stacks of 2-D spaces. Similar to how a Hilbert curve, even though it can fill 3-D space, is actually one-dimensional. We're just a fractal. 3/

It's obvious but we don't actually, out of our own nature, travel up and down. We're stuck on the very interface of the infinite air above us and the vast earth below us. Even in a single room, we only ever inhabit the very bottom part of it. This is inefficient. 4/

Space is an important resource - maybe the most important for a civilization. Without space to grow, progress is stunted. Every living agent in a civilization progresses it somehow. We're throwing away nearly all the space available to us. 5/

The tallest building is 828 meters. The radius of Earth is 6371 km. Even if we built an incredibly dense civizilation that's 828 meters around the whole globe, similar to the ants in Simak's City, we would still be inhabiting less than 4% of one percent of what we could. 6/

So for this reason, we need: 1. A world that can be traversed throughout its full volume and 2. A civilization of beings who are able to do so. 7/

This leaves us with either a world of beings who are incredibly tough and can immediately move through rock, beings that are unhindered by physical obstacles, or beings that live in a world made out of fluid. 8/

I think the first kind of beings - call them class 1 - so tough they can move through their world like it's butter - is unlikely. No explanation given, just that I don't think it will happen. If you do, chime in. I won't fight you. I'd love to hear your ideas. 9/

The second kind of beings - able to traverse through obstacles - can take two forms, call them 2a and 2b. 10/

2a is a being that has a physical form that can bend around obstacles. A being made out of fluid (think T-1000), or out of parts that are so small that they can fit in cracks (eg a swarm of bacteria). I'm not sure how they would build ships. Not even sure they'd want to fly. 11/

2b is a being that is unhindered by physical objects due to lack of physical interaction. This means then that physical space likely means little to 2b, and exploration of the physical world is immaterial (sorry for the pun) 12/

3 is a being living in a fluid world - either a gas giant or a water world. This has been investigated a lot by science fiction writers. 13/

The most plausible designs involve a being made out of fluid or gas itself, which stays together under the pressures provided by e.g. a gas giant, but would disintegrate if exposed to the pressures of outer space. Spacefaring is clearly very impractical to them. 14/

Perhaps 1, 2a, and 3 would specialize for different depths - in order to withstand different ranges of pressures. But more likely, like all deep swimming sea beings we know, they can surface at will. 15/

However, each of those classes of beings would still have orders of magnitude more space to evolve than we do. For example, we inhabit 0.2% of 1% of 1% of the space available to hypothetical Jovians. That's 5 million times less space. 16/

And yes, Simak talks a lot about Jovians in City as well. I didn't even realize this when I got the idea for this thread. It just occured to me when retweeting orb pictures for @OrbFacts: "what if blue and green orb, but full ofwater?" In closing, I guess, read Simak's City. 17/