In his IMO excellent message "Algorithmic TOEs vs Nonalgorithmic TOEs", Schmidhuber states that "things one cannot describe, do not exist".
If I interpret correctly, Schmidhuber was aiming, in this context, at _entire_ universes one cannot describe. I agree with this, but propose to extend this reasoning to _aspects_ of universes one cannot describe: I define "my universe" as equal to "all I know about my universe". Now suppose that I (me being my mind state at this moment in time) am computable. That means that all I know about my universe is computable too, because this knowledge is part of my mind state. Therefore, if I'm computable, then so is my universe. (Forgive me if this is stupid or old.) Michiel de Jong, http://www.cwi.nl/~mbj