Here's an excerpt from Anil Seth's book, "Being You: A New Science of Consciousness." I found it fascinating, even though it echoes ideas Derek Parfit wrote about in one of his books. But Seth describes this thought experiment in an intriguing way.
After the excerpt, I'll share some observations about it.
Let's begin our exploration of the self with a quick trip into the future. A century or so from now, teletransportation devices have been invented which can create exact replicas of any human being.
Just like the machines in Star Trek, they work by scanning a person in exquisite detail -- down to the arrangement of each individual molecule -- and using the information in the scan to build a second version of that person in a distant location, for example on Mars.
After some initial apprehension, people quickly become accustomed to this technology as an efficient means of transportation.
They even get used to the necessary feature that, once the replica is created, the original is immediately vaporized -- a procedure that had to be built in, in order to avoid creating an explosion of identical people.
From the point of view of a traveler, let's call her Eva, this poses no practical problem at all. After some reassurances from the operator, Eva simply feels that she has disappeared from place X (London) and reappeared in place Y (Mars) in an instant.
One day, there's a hitch.
The vaporization module in London malfunctions and Eva -- the Eva who is in London, anyway -- feels like nothing's happened and that she's still in the transportation facility. A minor inconvenience. They'll have to reboot the machine and try again, or maybe leave it until the following day.
But then a technician shuffles into the room, carrying a gun.
He mumbles something along the lines of "Don't worry, you've been safely teletransported to Mars, just like normal, it's just that the regulations say that we still need to ... and look here, you signed this consent form ..."
He slowly raises his weapon and Eva has a feeling she's never had before, that maybe this teletransportation malarkey isn't quite so straightforward after all.
The point of this thought experiment, which is called the "teletransportation paradox," is to unearth some of the biases most of us have when we think about what it means to be a self.
There are two philosophical problems raised by the teletransportation paradox. The consciousness-in-general problem is whether we can be sure that the replica will have conscious experiences, or whether it will be a perfectly functioning equivalent but without any inner universe.
I don't find this problem very interesting. If the replica is created in sufficient detail -- every molecule identical! -- then there's no reason to doubt it would be conscious, and conscious in exactly the same way as the original.
If the replica is not completely identical, then we're back to arguments about different kinds of philosophical zombie -- and there's no need to go over all that again.
The more interesting problem is that of personal identity.
Is the Eva on Mars (let's call her Eva2) the same person as Eva1 (the Eva still in London)? It's tempting to say, yes, she is: Eva2 would feel in every way as Eva1 would have felt had she actually been transported instantaneously from London to Mars.
What seems to matter for this kind of personal identity is psychological continuity, not physical continuity.
(Even without teletransportation, the cells in our body are continuously turning over, most being being replaced every ten years or so -- a biological Ship of Theseus. This doesn't seem to impact our sense of personal identity very much.)
But then, if Eva1 has not been vaporized, which is the real Eva? I think the correct -- but admittedly strange -- answer is that both are the real Eva.
That makes sense to me, both the Eva on Mars and the Eva in London being the real Eva. If there is no difference between them, with each having the same memories, personality, abilities, and such, how is it possible to say that one Eva is real and the other Eva isn't?
Sure, someone who believes in an immaterial soul could argue that the Eva who has a soul is the real Eva. However, since there is no evidence for soul, it wouldn't be possible to distinguish between the Eva who supposedly has a soul and the Eva who supposedly doesn't.
Why, then, would the Eva in London object to being killed if she is identical to the Eva on Mars?
This is a difficult to answer question. Intuitively, I feel that since living beings have a preference for life over death, which is baked into the brain by evolution, this explains why the Eva in London would fear the technician with a gun.
Also, even though the two Evas were identical at the moment of teletransportation, Seth points out that they soon would begin to differ.
Back at the teletransportation facility, Eva1 managed to avoid the technician's murderous intent, and is coming to terms with her new situation, while Eva2 remains blissfully unaware of the drama unfolding back on Earth.
Even though both Evas were objectively and subjectively identical at the point of replication, their identities have already started to diverge. As with identical twins setting out on their own life journeys, the process compounds inevitably over time.
This shows that our sense of self is closely connected with our memories -- a sense of personal history that makes us feel "this is who I am." Of course, that sense is altered as we experience new things over a lifetime.
Nonetheless, so long as we feel a psychological continuity between the person we used to be and the person we are now, that supplies us with a mostly stable sense of self. Seth writes:
The self is not an immutable entity that lurks behind the windows of the eyes, looking out into the world and controlling the body as a pilot controls a plane.
The experience of being me, or of being you, is a perception itself -- or better, a collection of perceptions -- a tightly woven bundle of neurally encoded predictions geared toward keeping your body alive. And this, I believe, is all we need to be, to be who we are.
...Let's move on to matters of personal identity and to the emergence of the "narrative" and the "social" selves. As we saw with the teletransportation paradox, it's at these levels that an entity experiences itself as continuous from one moment to the next, from one day, or week, or month to the next, and -- to some extent -- across an entire life span.
These are the levels of selfhood at which it makes sense to associate the self with a name, with memories of the past, and with plans for the future. At these levels we become aware that we have a self -- we become truly self-aware.