alexwlchan favourites all posts talks Falsehoods programmers believe about Unix time Posted 15 May 2019 Posted in Programming and code With apologies to Patrick McKenzie . Danny was asking us about our favourite facts about Unix time in the Wellcome Slack yesterday, and I was reminded of the way that it behaves in some completely counter-intuitive ways. These three facts all seem eminently sensible and reasonable, right? Unix time is the number of seconds since 1 January 1970 00:00:00 UTC If I wait exactly one second, Unix time advances by exactly one second Unix time can never go backwards False, false, false. But it’s unsatisfying to say “this is false” without explaining why , so I’ll explain that below. If you’d like to think about it first and make your own guess, don’t scroll past the picture of the clock! A bracket clock. Construction and assembly by ...