Throughout history, scientists, philosophers, mathematicians and PhD students lacking funding for actual research have turned to the thought experiment in hopes of discovering something publishable, thereby retaining tenure and/or attracting the admiration of comely undergraduates.

The best thought experiments throw light into dark corners of the universe and also provide other scientists, philosophers, mathematicians and destitute Phd students a way to kill time while waiting for the bus.

Below is a classic thought experiment, pillaged from my book The Geeks' Guide to World Domination (Be Afraid, Beautiful People). I'll post a new thought experiment each day this week.

Ship of Theseus

The Greek historian Plutarch described the following dilemma: “The ship wherein Theseus and the youth of Athens returned was preserved by the Athenians down even to the time of Demetrius Phalereus, for they took away the old planks as they decayed, putting in new and stronger timber in their place.”

By the time of Demetrius Phalereus, which was at least 200 years after Theseus’ return from Crete, so many planks and timbers had been replaced that none of his ship’s original wood remained.

The question is—was it still Theseus’ ship? More generally, what creates identity? If all the molecules of a thing (or person) are identical to the molecules of another thing (or person) are the two the same? If they are different, what makes them so? If a person were teleported by a machine that disintegrated their molecules and then reassembled them in an exact copy, would it be the same person?

What d'you think?