The identity of the Ship of Theseus has been a pseudo philosophical paradox for a couple of dozen centuries. Plutarch’s version goes like this:

The ship in which Theseus and the youth of Athens returned from Crete had thirty oars and was preserved by the Athenians. They took away the old planks as they decayed and replaced them with new and stronger timber. This ship became a standing example among the philosophers, for the logical question of things that grow; one side holding that the ship remained the same, and the other contending that it was not the same.

This is not at all a paradox for the metaphysician. The Ship has no being because it has no unity in itself. Its unity is given to it by the builders. Hence, it is an object of thought and is called a ship by convention. In other words, there is no divine idea of the ship that allows it to be known.

A similar, and more compelling example, is a sports team.  The Juventus football club in Turin, Italy was founded in 1897. Over the past 124 years it has undergone name changes, the owners have changed, the players changed, where they play matches has changed, and so on. Nevertheless, there is a continuity of thought that identifies the club as “Juventus” even though no material elements from 1897 still exist today.

Natural Things

The Ship of Theseus and the Juventus F.C. are artifacts because they are human constructions. Natural things have unity within themselves and are not constructed. For example, I can give you instructions about how to build an artifact like a mousetrap. However, I cannot give you a blueprint to build a mouse. Even if you had all the elements and compounds and a detailed design document, you cannot create a mouse. You will have to grow a mouse. That is because a mouse has its own inner unity and is therefore real.

Human Beings

The same applies a fortiori to human beings. A human being has a Self that gives it identity. Therefore, a human being is more than its material composition. It seems to me – at least I have not yet found a counterexample — that even the most ardent does not deny his own continuous identity over time. But what holds all the atoms together? After all, there is no physics of the human being. If you start at the Big Bang and you know quantum and relativity theory, you still cannot possibly derive the existence of human beings at some future date.

In the Many Worlds theory, at every moment a new copy of “you” appears in a different universe, who is your “counterpart”. But why do your body parts all hold together? If your identity lies in consciousness, does your counterpart share the same Self? Metaphysically, the Self cannot be in the same state twice. Specifically, if it is in the human state in one universe, it cannot possibly be in the human state as a counterpart in a different universe. It would have to be a different being in the second universe. However, it cannot be “built”, it must grow, and there is no time for that to happen.

Ideas of Things

Aristotle had competing, but not necessarily incompatible, theories about the ideas of things. Plato believed that the ideas existed in the world of thought, independent of the world of the senses. Aristotle believed that the ideas inhere in the things. Both theories are objective in the sense that the ideas are independent of any physical manifestation.

The alternative is to believe that all ideas are human constructs. Hence, we call a thing a “mouse” because it has qualities similar to other mousy things. This theory is called “nominalism” because the ideas are only names, without independent and objective existence. This is unsatisfying because we like to believe that the classification of mousiness is objectively true. Otherwise, the standard model of physics, the periodic table of chemistry, and biological taxonomy would make no sense.

Quantum Darwinism

The secret teaching of quantum theory is that there is no explanation for the existence of things in the world, i.e., things that we can see, touch, hear, etc. There is no explanation for stars. Do stars have their own unity or are they stars solely by convention? What then is a galaxy in terms of physics? The is the so-called measurement problem: to wit, if the world is just a grand quantum state, then how do individual things appear.

A recent theory is based on the concept of entanglement. In the simple case, it means that the quantum states of two entangled particles are not independent of each other. Moreover, entanglement can be extended to multiple particles so that entangled particles seem to act together as a unified being. In this view, then, a mouse is a collection of entangled particles that together create mousiness.

Assuming entanglement can involve such a large number of particles, it is worth exploring. But, like the Ship or Theseus, how does that explain the identity of a thing over time. A human being, for example, grows and changes, so that probably close to none of the particles of a human being at age 4 still exist at age 44. So how can one set of entangled particles be replaced by another set years later, while the human being maintains the same identity over time?

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