How much can we rely on family oral traditions? The question attracts a horde of ifs, buts and maybes.
Take the undying belief of large numbers of families in the west of Ireland that one of their ancestors was a survivor of the wreck of the Spanish Armada in 1588. As many as 24 ships were indeed wrecked on the Irish coast, but the conditions that greeted anyone who made it ashore were hardly conducive to settling down and raising a family. The English military force in Ireland, too small to fight off an invasion, compensated with savagery, slaughtering every Spaniard who couldn’t be ransomed. The native Irish did not show much hospitality either.
An envoy of Phillip II sent to Ireland in 1596 to seek out survivors could find only eight individuals.
But hold on. What about those eight? If just one of them had two surviving offspring who stayed in Ireland, who in turn each had two offspring – a very conservative survival rate – and this rate of reproduction continued in each of the 13 or so generations down to the present, that single survivor would now have 8192 descendants, plenty to provide a basis for a family tradition. Though, of course, the tradition remains impossible to prove.
That’s the difference between genealogy and academic history. Because we focus on individual stories, the strangest statistical flukes crop up again and again. The wonderfully conspicuous Balthazar McGuffin will appear nowhere in the records of the 1870s, where you expect him. But dozens of Balthazar McGuffins will then begin to crop up in the records of freed slaves, or medieval guild rolls, or at the court of Catherine the Great. “Black swan” events like these give historians attacks of the vapours, and very understandably.
As for quantum physics, so for history: at the smallest level, the normal laws of space-time do not apply.