It is very difficult for me to articulate a description of what I perceive to be boundary, or the layered onion(s) of universes or alternate realities breaking down, in a visual sense - allowing traversal between them - and then to ponder on what the consequences of that might be.
I have seen a lot of cinema / tv doing this - but I do not believe I have read about it described in books all that often until I read Cixin Liu's Death's End / The Dark Forest (part of the Three Body saga - there it is done superbly, but here...
I think I can improve. I can always improve.