As I write this I am trav­el­ing. While trav­el­ing, I notice markers—mile mark­ers along the side of the road—that tell where I am and how far I have come. Mile mark­ers were once called “mile­stones.” Now we think of a mile­stone, not as a mea­sure­ment of phys­i­cal dis­tance, but as a marker of a sig­nif­i­cant […]