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If every cell in a creature's body were replaced (as in Theseus's Ship), would the creature still have its consciousness? E.g. a white blood cell would be destroyed and replaced by a nanobot that flows around the bloodstream, killing foreign substances; an interneuron would be replaced by a nanobot that sends an electrical impulse when it detects acetylcholine, etc.
Reality-checking Phyresis from Magic the Gathering here.
Truth is - No one knows.
We are so far from perfectly replicating single neuron, and so far from understanding what consciousness is, that no one can tell.
Good thing is - both "yes" and "no" are believable answers in the (lack of) light of current science, so use whichever you need.
Yes, by definition
If you're replace something with something that is functionally identical then by definition it must be functionally indistinguishable from the thing it replaces. If replacing the cells with nanobots doesn't reproduce consciousness then they're not functionally identical.
The more interesting question is whether it is possible to replace the cells with nanobots and preserve function.
That depends. Do you believe that consciousness is a consequence of having a soul? If not, then if the nanobots faithfully simulate all cell activity, there is every reason to believe that consciousness would be preserved. In this view, consciousness is an emergent property of neural function given the organizational constraints which derive from our brain structure.
If you want something more mystical and less prosaic, then the existence of a soul would presumably not be supported by mere machinery. As to the point of replacement/failure of consciousness, that is not answerable until someone can quantify/qualify consciousness. And that does not seem to be likely any time soon.
Most of the body would not matter one bit. Is a man with a wodden leg still concious? You could change the limbs, bone, blood, intestines, etc. without having any effect on his mind.
As for the brain, replacing a brain cell with a nanomachine that works in exactly the same way would do the trick. It would have to connect to other cells in the same way and have the same behavior. A living cell is a complex nanomachine. So consider replacing the cell with another exactly like it.
Everything we know informs us that consciousness arises from the physics of the atoms making up the brain. (See this question to explore otherwise; and comments and references concerning this fact.) So if a brain cell were replaced with a different nanomachine that was in fact behaviorally identical, it would make to difference.
You are talking about replacing every single cell in a body, which means nothing original would be left. In that case, how is it different from creating a new clone?
If you create a new clone, you would probably have a new human there. The new human would probably be considered conscious, because it moves, but the old human doesn't get unconscious either, if it is a good clone that doesn't affect the original body. So the problem is, is it just the same consciousness, or a new one?
Meanwhile, you can't say that the person becomes unconscious. Consider a person whose neurones are all replaced except the last one. Each other cell is perfectly cloned. As a cell unit, the last cell is still conscious.
If the person is perfectly cloned, to other people it seems that he is still conscious, because he will act like what he was before. But what about the original consciousness? Well, that's the same question as what happens after a person dies ‐ nobody knows.
If you believe in souls, you can mention that neurones are just a physical carrier of a soul, and that nanobots can or cannot carry a soul, depending on your requirements. Does the soul get surgically removed when the brain cells are surgically removed? This is up to you as well. It might even get torn apart by the surgery. Someone has once hypothesized that a cloned human would have the physiological capabilities like an animal, but not the wisdom of a human. Nevertheless, considering the hypothesis that intelligence memory is probably stored in the brain, this might not be true as well.
Consciousness is the result of the brain, a mixture of senses,memories and a complex communication between the neurons.
To make an example see neurons as people, having 10 people there doesn't do anything.
But if you give those 10 people something to talk about they will create a conversation, this conversation is the consciousness of the group.
If one of the ten people dies and gets replaced the conversation and so the consciousness will change and lose or gain new qualities.
Over time these 10 people will die and be replaced causing the conversation to deviate completely from the original group.
In short, we all die slowly over time until there's nothing left of what we used to be.
Replacing the neurons of a person with nanobots would be exactly like killing that person and having someone replace them that thinks to be them.
another Example:
1-Jimmy is alive and knows it.
2-Every single cell in jimmy's body gets replaced by nanobots.
3-Jimmy is killed by the nanobots.
4-The nanobots give life to Jimmy-bot.
5-Jimmy-bot is alive and knows it.
6-Jimmy-bot doesn't remember about the existence of the original Jimmy therefore now Jimmy-bot became the true original Jimmy leaving the old one in the oblivion.
This is essentially a new take on an ancient (and I do mean ancient) thought experiment.
The Ship of Theseus. Discussed by Plato and other ancient philosophers.
If you have a ship/boat, and every single component is replaced with an identical replacement (no upgrades). Is it still the same boat?
There are other variations, such as the grandfather axe, where both the axe handle and axe head are replaced.
Your question asks about whether the nanobot body would still be conscious. I think another very important thing to take into account is, is it even the same consciousness?!
Technically, your body does this every ~1 year. And do you lose consciousness every year?
Depends on your definition of consciousness.
If you define consciousness as a state of matter (materialist way), then yes. However from that point of view, consciousness itself is meaningless word and everything can be said to have it, even rocks.
However if you believe there is some unique spiritual value bound to consciousness (eg. soul) then no, because method you propose allows (or would allow) for duplication of this entity and we said it's unique.
Assume you retain no consciousness after the process, since you interact with the world using your human interface (you know hands, feet, eyes etc.) and you already stated that cells keeps their functionality, then replacing each cell by keeping the same functionality keeps the interface functioning with the rest of the world, then you appear to be conscious even if you are not.
So I could ask about your conciousness and you would still answer like if you were conscious making that not distinguishable.
Conclusion: Either you are not conscious already or you will remain conscious after the replacement.
I think there is a fundamental flaw in your question, and that is that each cell is replaced by one nanobot. While that might (might) work for a red blood cell, or a WBC, or a muscle cell, there are no cells in the body with as many interconnections as neurons.
Each neuron may be connected to up to 10,000 other neurons. One nanobot cannot possibly perform the same as a biological neuron.
So no, there would be no mind or consciousness above the level of primitive organisms.
