Solar, by Ian McEwan; Jonathan Cape, 2010, 285 pages, $32.95. Let’s suppose it’s true, as George Orwell thought it was, that a good writer’s “emotional attitude” sets in young and is never fully escaped. What kind of kid, then, might Ian McEwan have been? He was either a very naughty little boy, or, early on, he was made to feel that he was. McEwan is a novelist obsessed with the morality of guilty men. Now sixty-one, in his twelfth novel, Solar, he gives us Michael Beard, a guilty fat man who might just save the world. Or maybe he won’t.…