Imagine the same replication device described above, with a twist. Right after copying you, but before destroying the original body, it is allowed to switch an identical portion of your brains (assuming you believe you are your brain)*. It has a settings knob titled "swap percentage" that is adjustable from 0% to 100% which determines the % of brain switched. For example:
- At 0%, nothing is switched; it just copies you and destroys the original like before.
- At 10%, it cuts out the same 10%-sized chunk out of each brain and surgically swaps them perfectly before killing the original.
- At 100%, it does a full brain transplant to swap the brains before killing the original; at this point it's basically killing the copy and leaving the original intact.
Assuming this is true, if 0% results in death and 100% results in survival, then one of the following must be true for the in-between percentages between 0-100: Either at some point the answer abruptly changes from "death" to "survival", or increasing the percentage knob gradually changes the result from "death" to "survival".
- Abrupt: If the answer abruptly changed from death to survival at some point, that would mean there exists some "threshold" percentage of brain matter swapped, which when crossed would suddenly result in your original consciousness "jumping over" to the new brain, despite it being physically identical to previous scenarios with slightly lower percent. In other words, you'd be claiming that there exists some percent, e.g. 50%, whereby if we swap exactly 50% of your brain matter, you will jump into the copied brain, but at 49.9999%, you will stay in the original brain.
- Gradual: If increasing the percent of the scenario gradually makes you more and more alive, that implies that in between, it is possible for you to be in a half-alive state, with your consciousness straddling two brains. In other words, you'd be claiming that at some percent e.g. 50%, your true consciousness is half in one brain and half in the other brain, even though in this scenario both brains are exactly physically identical to before the operation, thus have no physical capability to feel any different than what they would've normally felt without any modification.
How is this possible? In short: "One true you" is an illusion. The uncanny first-person awareness exists only in the present moment, and every passing moment can be thought of as a different person inheriting the old one's memories. The physical memories in your brain are the only reason you feel like a single continuous entity throughout time.
"Isn't this just Ship of Theseus?"
Isn't this just Sorites Paradox?"
"But of course consciousness exists; how can you deny the first-person experience?"
"It's impossible to partially replace the brain and have everything be okay. The result will be brain-damaged etc."
"Maybe the part of the brain responsible for consciousness is just a tiny portion or even 1 neuron, or maybe some other part of the body is involved (e.g. muscle memory, gut bacteria)"
"Even the slightest modification of the brain results in an impostor who just thinks he's you, so you're actually dying in all the scenarios except 100% swap."
"Mind uploading is different from physical copying"
"Maybe consciousness is supernatural, beyond the brain, etc"