Split in two
Split in two is a thought experiment which, although it cannot be conducted on humans, still raises interesting questions about personal identity. The experiment can be summed up as, "who is the real you if you're split in two?" but is told better with this story:
- Planarians are flatworms that, when cut in cut in half, will regrow the missing half. What's more amazing, both halves retain some of the memories of the original. Scientist Jean-Paul successfully fused his genes with the genes of a flatworm then bisected himself and each side fully regrew the missing half, including the brain. This confused Jean-Paul's friends who wanted to name one man Jean and the other Paul to avoid confusion, but each man insisted that they were the original Jean-Paul because they each retained their memories and still felt like the real Jean-Paul.
Of course, we know that brain activity and memory isn't duplicated equally in both hemispheres, so this story will remain fiction. However, we might one day create a machine that can scan your body right down to the atom and start printing duplicates, each with identical brains and memories.
If we really are just our brains and our bodies, and we are somehow split ourselves into two separate but equal people with identical memories and talents, but each has their own independent consciousness, how do we refer to these new people? Surely they can't both be the same person, because, just like with identical twins, they will start having different thoughts the moment they separate. But then, unlike twins, they each have an entire life time of memories. Have two new people have been created? Is the original dead? Imagine how you would feel if this happened to you. You would still feel like you, all your memories and experiences would still be there, and if you don't feel like a new person, why should you expect to be treated like one?
This thought experiment occurs all throughout science fiction including in Altered Carbon, Star Trek: The Next Generation, and many others. Note that this is not the same as splitting a person between their evil and good sides or other aspects of their personality. In this thought experiment, each half is 100% identical to the original.