I make a point of re-reading this each year on or around the anniversary of Gettysburg, and of recommending it to friends who don't understand the American/Southern obsession with the Civil War. There's really no better one-book introduction to the actual people involved, and their motivations.
Waiting to see how this turns out before I post any further annotations; I'm deep into spoiler territory now.
Arsibalt's explanation of "Sconic thought" is a decent enough summary of some of the problems explored by Kant in the Critique of Pure Reason, regarding both the fact that we cannot directly access knowledge concerning the world outside our heads, and the fact that certain questions are, by their nature, unanswerable by human reason.
This also ties in once again to twentieth-century work related to the demarcation problem, which attempted to put all such metaphysical questions "out of bounds".
Arsibalt's lecture here brings to mind philosophical debates about the metaphysics of propositions namely whether they can be said to exist regardless of the tokens (words, symbols, etc.) used to express them.
Which returns to the problem of universals, and the symbol/symbolized distinction.
Of related interest is the field of exolinguistics and the problems arising from our attempts to create things which could be understood by extraterrestrials.
And we get into spoiler territory again: this sort of thing has actually been theorized about, as part of the first and now-defunct Project Orion.
Familiar ground; Stephenson is wandering near to a lot of material I covered when I was doing my thesis. Since I could talk for days about this stuff, I'll compensate by keeping my notes here extremely short.
The arguments for and against "design" in the universe have recently been picked up by physicists and cosmologers, and Jesry's explanation based on a many-worlds interpretation (see previous note) touches, in a nutshell, some of those arguments, specifically those centered around the anthropic principle.
The many-worlds interpretation of quantum mechanics posits that there is essentially a huge number of "universes", one for each possible outcome of each collapse of each quantum waveform throughout history (more colloquially expressed as the idea that "everything which can happen, does happen, somewhere").
In the twentieth century, the branch known as philosophy of science became increasingly concerned with the problem of demarcation, separating things which were science from things which were not. Mainstream English-speaking philosophy picked up on this as well, and a movement arose to cast out metaphysics from philosophical discussion on the grounds that such questions could not be meaningfully tested, nor could their answers be meaningfully verified.