> Mostly I wanted to share my personal theory of why we haven't encountered alien life by now. Like computers themselves, things don't get larger. They get smaller. And faster. And so does intelligent life.
The sci-fi novel Blood Music [0] (expanded from a short-story with the same title) focuses on this concept.
P.S.: Some evidence in opposition to this "shrinking" theory might be the history of life on Earth: In general, both life and intelligence have been breaking new ground via larger and more-complicated systems.
This is especially true if you relax "intelligence" into something more like "computation." For example, your immune system is in a long-running cryptographic (or at least combinatoric) struggle against most other nanobots on the planet, not just in terms of inherited traits, but also during your own lifetime.
The sci-fi novel Blood Music [0] (expanded from a short-story with the same title) focuses on this concept.
[0] https://en.wikipedia.org/wiki/Blood_Music_(novel)