Physicalism and duplication

This is another post I'm inspired to write in response to Shelly Kagan's Philosophy of Death class, which is freely available online.

Last week I wrote about physicalists' problem of explaining resurrection: is a resurrected person the same person after death as before death? Or is a resurrected person a new person? Borrowing from Kagan, I gave two analogies to the problem that each suggest a different answer. The first analogy involves a bicycle that's taken apart, fixed up, and put back together. In that case, there seems to be only one bicycle throughout, both before and after the fix-up. But in the second analogy, which involves a boy's block tower that's destroyed and rebuilt by his dad, there seem to be two distinct block towers, one before the destruction and one after the reconstruction. I said I think the first analogy has it more right, that in the second analogy both towers are the same tower, but also I think both analogies miss the point.

But before I divulge how I think the analogies miss the point, I'm going to describe another problem for the physicalist view: the problem of duplication. Duplication is like resurrection but without the person first dying. Instead, two identical copies of the person's body exist simultaneously. In the block-tower example, duplication happens if the block tower isn't knocked over, but instead the dad builds an identical tower to the first while the first tower still stands. Are both towers the same tower? Or are they different towers?

But why resort to using examples of block towers? Science fiction gives us the same scenario with real people—albeit of the fictional variety. In the Star Trek TNG episode Second Chances, Commander William Riker leads an away team to the surface of the planet Nervala IV. The mission is a routine one other than how the planet has a strong distortion field that makes transporting impossible for eight years at a time, while the planet is too far from its sun. The away team has a three chances over four days to get in and out.

However, after first beaming down to the planet's surface, the team is surprised to discover the presence of another human, one who appears to be just like Commander Riker. The man says he is Riker and that he's been stranded on the planet for eight years ever since he failed to transport out in time during his last mission. The away-team Riker corrects him, saying he (the away-team Riker) was there eight years ago, but he transported out OK. But neither man's account explains how there are now two Rikers, and the away team, along with the new Riker, beam back to the ship to sort out what's going on.

It turns out the problem was due to a transporter accident. Eight years ago while Riker beamed back to his ship, part of the transporter energy beam made it to the ship, where Riker rematerialized, but part of the energy beam was deflected back to the planet's surface, where another Riker materialized. But everyone in the ship, including the successfully beamed Riker, figured the transport worked, and so the ship's crew and all the universe went on with business, unaware of the second Riker doomed to playing Robinson Crusoe on the planet below.

That raises the question: Are both Rikers the same Riker?

It's hard to see how they're the same, and indeed the show plays to that conclusion. Without giving too much away, by the episode's end the second Riker gets an assignment on a different ship and has decided to change his name from William to Thomas, his middle name. But the show also shows how Tom Riker is very much like Will Riker by way of Tom romantically rejecting Counselor Deanna Troi to instead focus on his career, just as Will Riker had rejected her eight years previously.

Back to physicalism. The problem duplication presents for physicalism is that if, as according to physicalism, a person is nothing more than a body, then there should be something purely corporeal to account for what makes the two Rikers different. The quick answer is that there is such a difference. Will Riker spent eight years normally, serving as a Star Fleet officer; meanwhile, the other Riker, Tom, spent eight years alone and abandoned on the surface of Nervala IV. It's remarkable Tom didn't go insane, given such a lengthy solitary existence, and in any event the two Rikers now have enough sufficiently different experiences to be different people—to have different thoughts, desires, goals, etc.

But that answer ignores the moment when both Rikers rematerialized, one in the ship and one on the planet's surface, back when they had the same experiences, thoughts, desires, goals, etc. Were the two Rikers the same person at that moment? Presumably the two Rikers, if they were ever the same person, forked in identity as soon as their sensory organs took in different input: different sights, different sounds, different smells, etc. From that moment on the two Rikers diverged physiologically and thus became different people. But in that one moment after the split but before differentiation, were the two Rikers the same person?

It's a fun question to ponder. But I think that it, like the two analogies I wrote about last week, misses the point.