Near Heathrow airport, I looked up to see the microwaves passing through two huge dishes atop Hillingdon hospital, a pioneering 1960s centre now suffering – like much of the NHS – from a shortfall in funding. For a rent of a few thousand pounds a year, the machinery of private finance perches on the crumbling infrastructure of the welfare state: all that money, flowing invisibly just a few metres above the patients inside. This is how a difference in visibility translates into a difference in power: those who can see, can understand – and thus shape the world to their advantage.