There was a delightful conference in Copenhagen celebrating that event, and I was lucky enough to attend. The slides of my talk live here: http://herpolhode.com/rob/ugly.pdf

I flew back the next day, September 10, 2011, and it was a beautiful clear night with a stunning view of the city. We sat in the last row of the plane, and had an unobstructed view of the trade towers as we landed near midnight. We went home, fell asleep, and were woken by a phone call about 9am.

-rob

On Fri, Sep 9, 2022 at 8:29 AM Dave Horsfall <dave@horsfall.org> wrote:

https://www.timeanddate.com/on-this-day/september/9

``Unix time or Unix epoch, POSIX time or Unix timestamp, is a time system
  that measures the number of seconds since midnight UTC of January 1, 1970,
  not counting leap seconds. At 01:46:40 UTC on September 9, 2001, Unix time
  reached the billionth second timestamp.''

Hard to believe that it was that long ago...

-- Dave