When Serena Williams stepped out on to the hard court of the US Open on Monday for what may be her last tournament, she did so in a little black (tennis) dress with long sheer sleeves, a six-layer skirt – one tier for every US Open title she has won – and a bodice sparkling with a galaxy of stars. It was a dress made for a supernova’s farewell. It is fitting, in more ways than one. If you’re not paying attention to the symbolism, you’re whiffing the point.