In episode 40, where did they get the material to put that turtle float around The Nirvash?
Was that Charles' gun that Holland left in the Nirvash, as seen in episode 44? If so, why would Holland leave them that specific gun?
That was Charles' gun. It seemed to be very powerful (able to shoot through LFO armor on its first appearance), so perhaps Holland knew that and left it just in case. Plus, he knew that Charles and Ray meant a lot to Renton, so that could've been a factor as well.
I always wondered... everyone in this show all have mostly non-japanese names, so it makes me wonder why the natural language in the show is Japanese? You'd think they'd read english everywhere. Did Japan defeat the US or something?
Short answer: It was made for the Japanese, so the language spoken and read in the show would be Japanese. Long answer? I'm not really sure; on one hand there is no US or Japan. After the Scub took over the world and the humans came back from space to live on Earth, nothing would've been the same. I'm thinking that they kept their language and when they came back to Earth, they separated like they used to be, with certain places using certain languages, but due to spending so much time close together in space, language conventions were shared - hence, the characters' English names even though they still speak Japanese.
Another possible explanation is that it's set far enough in the future that any existing languages would have changed enough to be unrecognizable (or to have died out entirely and replaced with new ones) so for the sake of convenience writing and speech is represented by Japanese rather than whatever the lingua franca actually is. The names could simply be traditional or a translation intended to give the sense of how the names might sound to native speakers.
Just what is the "Limit of Questions"? I just watched through the whole series all over again, and I don't believe they ever gave a straight answer. The most they alluded to was that it was related to Quantum Mechanics, and that if the "Limit" was reached, it would be the end of the world as we know it.
Quantum mechanically speaking, information storage capacity is a function of system entropy. There is, in turn, a maximum entropy for any given volume, which is the entropy of a black hole enclosing that volume (equal to Boltzman's constant times the surface area divided by the Plank area (~10^-70 m^2)). In context, however, the whole premise makes no sense.
The "Limit of Questions" is a concept inspired by a Sci-Fi novel called Blood Music written by Greg Bear (who's referenced in the series through Doctor Bear), which explores the concept of reality as a function of observers, itself a part of the Anthropic principle. To put it bluntly, the Coralian 'observers' are inherently incompatible with our reality, and threaten to make it unstable and possibly even destroy it if they were to awaken all at once.
Why didn't Dewey kill himself earlier even though a good part of his plan relied on taking the bullet train to heaven?
Why did it take half the series for anybody to call Holland out on assaulting Renton? What did they think he was doing to him the first few times? Trying the kill a bug on his face?