Imagine you’re trying to make sense of the universe five hundred years ago, when astronomers believe there are just seven visible ‘planets’ wandering about the Earth: the sun and moon plus Mercury to Saturn. Intriguingly, there are also seven known metals: gold, silver, copper, iron, tin, lead, and mercury. For hundreds of years there have been just seven known ‘planets’ and seven metals. Wouldn’t you be just a little tempted to see more than a coincidence here? Take gold, for example, which ‘does not react with anything in the air or the ground, and so retains its brilliance seemingly forever’: surely its power is similar to that of the ever-shining sun?