Eratosthenes by Sagan

How in the same moment a stick in Syene (Assouan, nowadays) casts no shadow and a stick in Alexandria, 800 kilometers to the North, would cast a very substantial shadow?…

Unknown unknowns…

When I want to explain the concept of Knightian uncertainty (Frank Knight, 1921) to my students. I sometimes refer to the video filmed in March 2003 of Donald Rumsfeld, former…