Probability and astonishment

     A small poem by Lia Purpura in the January 29, 2015 issue of The New Yorker delights even as it highlights the errors that many of us make in supposing that coincidences -- such as meeting some home town friend in a distant vacation spot -- are rare rather than probable.  

       Probability     by Lia Purpura

       Most coincidences are not
       miraculous, but way more
       common than we think--
       it's the shiver
       of noticing being
       central in a sequence 
       of events
       that makes so much
       seem wild and rare--
       because what if it wasn't?
       Astonishment's nothing
       without your consent.

For more about Lia Purpura, follow this link to her website.  

     One of the possible coincidences that surfaces frequently is the so-called birthday paradox -- the fact that if there are more than 23 people in a room the likelihood is greater than 50-50 that two of them share the same birthday (day, but not year).  Here is a link to one of many online discussions of this problem/paradox. 
     For Isaac Asimov's reflections on coincidences (and a first mention of Purpura's poem and the birthday problem), follow this link to my January 2015 posting," Probabilty and Coincidence."  That posting mentions Fluke:  The Math and Myth of Coincidence by Joseph Mazur, which has now been published and is available here.