One of the later The Culture novels.
So I came across this, shiny looking, book on the shelves of Waterstones (I think) some years ago, and bought it just because it was on the "3 for 2" offer and there were two other books on it I wanted. The science fiction section has a lot of books and because I'm very loathe to spend time reading books that turn out to be shite I have read quite a narrow selection of scifi books, so I grabbed this and thought "Well, it'll sit on my shelf and one day I'll read it and it should be good. No harm done". Well it sat on my shelf indeed and, 3 or 4 years on, I've continued to avoid it (it's very big) until now I've started hearing tantalising hints of the so-called Culture books, of which Matter is a part. I'm not quite sure how it all fits together, but I think I'll read the first one (Consider Phlebas), and possibly quite soon, before I decide what I'll do.