The NY Times Magazine's "A Physicist Solves the City" ends on this high note: "Cities can't be managed, and that's what keeps them so vibrant. They're just these insane masses of people, bumping into each other and maybe sharing an idea or two. It's the freedom of the city that keeps it alive."
Earlier in the piece (by Jonah Lehrer and citing the work of Geoffrey West), Jane Jacobs' insights are approvingly noted, as is West's description of life at his Santa Fe Institute, where smart folks are encouraged to seek "chance encounters."
Yes, it is all about the exchange of ideas (within and among our brains) and letting it all happen. As at the Santa Fe Institute, this means that we must find a way to stand back and let people find each other. But this is the hard part that is not addressed.
Instead the piece cites Pres Obama's White House Office of Urban Affairs and it's mission to develop a "policy agenda for urban America." Guess where that one will end up?