What is the current understanding of the possibility of the nature of macroscopic superpositon of possible histories of the universe? Hopefully, I've worded that unambiguously, but I'll try to clarify it. I've never seen a discussion on this and I'm not entirely sure why. We're aware of superpositon of states at the quantum level and we're aware of being able to carefully prepare superposed macroscopic states when sufficiently isolated from their environment. When we talk about this isolation, it must be entirely probablistic, instead of being anything definitive, since wave fuctions inevitably cannot be entirely contained. I think the natural intuitive understanding, or perhaps given to us from the Copenhagen interpretation, is that the universe progresses on a classical level with individual particles moving from definite state to definite state, when they interact in some what that we deem to be a measurement. As I understand it, under this model, we're unsure as to what actually constitutes a measurement and have made little progress either on a theoretical level or on an experimental level in understanding what the process of making a measurement actually is. So back to my question. We're aware of the possibilities of macroscopic superposition, but can we know anything about to what extent macroscopic superpositions exist for the history of the universe? Do we have any reason to believe that superpositions must be either very small in scale or very rare? Can we presume that the universe must largely progress according to our intuitive classical understanding or could there be effects that we find difficult to accept because they don't fit this world view? Any help on this would be great. Thanks.