FICTIONWhat We Can KnowIan McEwanJonathan Cape, $34.99There’s no doubting how formidable Ian McEwan is. It’s many years now since he wrote The Child in Time with its ravishing strangeness and its heartbreak. It’s not even that long since On Chesil Beach, in which an ordinary unpractised couple fumble with the mysteries of sex. This happens in one of his most alluring books, Atonement, and it also happens in his new and in some ways spectacularly ambitious novel What We Can Know. It is a gift to his wife, and the poems involved are sealed in a vellum bag.