I keep hearing about things like "quantum decoherence" and the notion that measurement doesn't need a conscious observer. However, I haven't really seen these topics discussed in any of the textbooks I've used (mostly on the level of Griffiths and higher). I haven't even seen a reference to "quantum decoherence" in a textbook, and measurement discussions don't usually seem to talk about what counts as a measurement in practise. Rather, they tend to focus on what happens when a measurement is performed. I don't know if the two concepts are even related, but where can I learn about this sort of thing? I'm guessing maybe Ballentine for the "what counts as a measurement" question, but he doesn't appear to cover decoherence. Edit: I should probably clarify, since it might seem like I'm asking for an answer to the measurement problem. I realize the measurement problem isn't really resolved, but I frequently hear people saying confidently that (at least in practise) unconscious "observers" are able to perform measurements. I'm wondering if these people are wrong, or if they've learned something that I haven't.