Twenty years ago I was heading for my job at the city's social services headquarters in lower Manhattan. A typical morning. As I got closer to the office I started to hear sirens and listening to the radio heard about a small plane having hit the World Trade Center. At that point it sounded more strange than tragic.  I got my usual spot on Pearl Street and got out of my car at 9:03. How can I be so sure of the precise time? Because at that instant I heard a huge explosion and even more memorably, felt a ...