Quite when the concept of coolness became a thing is uncertain, even to etymologists. As early as 1884, an academic paper noted the expression ‘Dat’s cool!’ among African-Americans. But it’s about 100 years since ‘cool’ entered the lexicon as an unambiguous description of something to aspire to (via jazz, inevitably), and it’s still a crucial concept in the world of pop: it’s being cool that meant the Strokes could attract 50,000 or so people to east London, even though most of those present were at primary school when the band released their two first two albums, which are the two...