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Well done, but too "cute" sometimes. Perhaps Greene thought Einstein's explanation of special relativity using "railway carriages" seemed quaint and in need of updating. I disagree, especially since Greene's idea of updating the examples involves replacing the nameless observers of Einstein's original thought experiments with characters from the Simpsons. I can sit and read Einstein's own examples several decades after he wrote them, and they still make sense. If Greene's book is in print 50 years from now, it will have to be heavily footnoted to explain who Itchy and Scratchy are, and why they are shooting at one another on a moving train. But the digressions are just small irritations in an otherwise well-crafted book. Greene focuses mainly on the "what" instead of the "why," which can be frustrating for a reader prepared for a more technical discussion, but as an overview of the main ideas treated within, Greene's book is excellent.