Here’s a fun thought experiment your students are sure to get a kick out of:
A famous ship once sailed by Greek hero Theseus sits in a museum. Over time, some of its planks begin to rot. The museum replaces the rotten planks with new planks. Later, other planks rot and they’re replaced as well. Eventually, every plank on the ship has been replaced. Is this still the famous ship once sailed by Theseus, even though every plank has been slowly replaced over time?
Imagine that, when they remove the planks, the museum carefully stores them in a way that stops the rot. Years later, through new technology, the planks are treated so that they can be displayed again without rotting. The ship is rebuilt and put on display. Is this still the famous ship once sailed by Theseus?
Combine them: what if the museum has both versions of the ship on display? Which is the real ship? The one that has been slowly replaced over time or the one that was taken apart, stored, and then reassembled?
Of course, the thinking shouldn’t stop with this specific ship. Our own bodies are constantly replacing cells. Our skin is replaced every few weeks, our liver is replaced every couple years, and our skeleton is completely replaced about once a decade1.
Does this mean that I have had three different skeletons in my lifetime!? Cool.
This paradox, by the way, is called the Ship of Theseus and here’s a whole Wikipedia page of examples!