Say someone invents nano-machines which can mimic the processes of stem cells, being able to completely replicate all tissue. One of the applications of such a device might be to repair damaged tissue in the body, or even reproducing a clone.
Say we did a test on a human. The nano-machines were programmed to completely destroy each cell in the body, simultaneously replacing it with the nano-machine cell. In that process we’ve created a body made up of 100% nano-machines. The persons brain and thought processes are identical. It’s safe to assume that person is still who he/she was before their cells were replaced.
Now say the nano-machines have a process to shutdown and save-state, simulating suspended animation. During this process another set of nano-machines would completely replicate the original in another area, also in a save-state mode.
Once the clone is complete, the cells will resume function, and now there will be two of the same person. However, they are not really the same person. Even if they have all the same thoughts, or memories… if put in identical rooms when they awaken, with identical stimuli, they might behave identically until introduced to types of stimuli that are different from what the other experiences. If that’s true, the only difference difference between the two people are the space in which they exist.
The problem now arises that they are two people who share an identity. Neither knowing which one is the original, and neither willing to change their identity for the other. It is then suggested that the bodies be merged back together.
The most important thing here is the brain. So when the nano-machines are programmed they are programmed to destroy all the cells of subject A and replace them with subject B’s except when it comes to the brain tissue.
Depending on how much time has passed, the brains should still be relatively similar, but it’s clear that not all memories will stay intact. Assuming they have some sort of advanced understanding of the brain, they are able to keep some memories from both, and at the same time remove some memories from one or the other.
The question is: who is this new entity? The original? The clone? Both? Neither?