My dear friend Wolfgang,

I woke this morning with a burning feeling--although that may have been due to the saurkraut at dinner.  Still, I have kind of an idea--not really an idea, but more of a fleeting thought.  And maybe it's half-baked.  No, I guess it's fully baked.  Or at least three-quarters baked.  Maybe I shouldn't have even written you.  Probably you're busy.  You probably don't want a letter from me.  Probably you don't even like me.
Your friend acquaintance,

Werner

On this day in 1927, physicist Werner Heisenberg
wrote a letter to his colleague Wolfgang Pauli
in which he first outlined the uncertainty principle.