The Quantum Multiple Personality Problem and Self-Uniqueness

You have asked an interesting question. It is related to some extent to the quantum multiple personality problem in the many-worlds interpretation. As we experience in our daily lives, in the macro quantum system that is our body, at least one consciousness of a person, which I will call the <I>, appears at any given moment. Here, the part of the self that thinks "I am this person" is written as <I> in angle brackets. In the many-worlds interpretation, different consciousness bases can be considered for the human body as a macro quantum system. In other words, it hosts a quantum multiple personality at a single moment in time.

The fact that it cannot explain why there is only one <I>, that is, one's own consciousness, is a fundamental flaw of the many-worlds interpretation.

On the other hand, the standard Copenhagen interpretation does not attempt the reckless task of explaining everything solely from the linearity of the theory, as the many-worlds interpretation does. From the beginning, the existence of the <I> and its consciousness basis are given as axioms. From there, science begins as the activities of the <I> as the observing subject. Therefore, the quantum multiple personality problem does not exist from the start.

Regarding the "problem of self-uniqueness of consciousness," it has a history of being discussed for a long time in the field of philosophy, originally separated from quantum mechanics.

As shown in Figure 1, consider two spatially separated points, A and B, create rooms at each location that are completely isolated from the outside world, and within them, create identical human bodies from elementary particles. Everything, including the memory states in the brain and the state of the limbs, is made identical. If treated with quantum mechanics, this corresponds to making the quantum states of the two bodies completely identical.

Since they are exactly the same macro systems, even if you secretly swap the two along with their rooms, they are in principle indistinguishable.

Here, focusing on the human at point A, as shown in Figure 3, this person of course thinks that the <I> is this person, the one who is "this" person. In other words, there is only one consciousness, and one feels that this consciousness does not reside in a body in another location, such as point B.this person.

However, since the body at point B is exactly the same as the body at point A, it is possible for the human at point A to wonder, "Why am I not the human at point B?" The question you asked was why it is strange that my consciousness resides in this body at point A, rather than the body at point B, and why it is "this" body.this

To organize this first, this problem of self-uniqueness is a different problem from the quantum multiple personality problem, or the basis selection problem, which requires a solution in the many-worlds interpretation theory.

What appears in the basis selection problem is, for example, the state of a human inside one room at point A. Figure 4 represents a state where a human is in a certain location in the room.

Figure 5 is a state where the human is in a different location, and the state in Figure 4 and the state in Figure 5 are states that can be clearly distinguished even in quantum mechanics with a single measurement.

However, in the basis selection problem, a linear superposition of these two states appears. For example, a superposition of macro quantum states as shown in Figure 6 is possible in principle.

The basis selection problem is that in the many-worlds interpretation, it is not decided whether to adopt the consciousness basis of the state in Figure 6 or the consciousness basis of Figure 4 and Figure 5 for a single body.

However, in the self-uniqueness problem, we are considering multiple bodies. For example, as shown in Figure 7, we generate two identical bodies and place them in rooms isolated from the outside.

In this case, the self-uniqueness problem is: why did the consciousness residing in the Earth body not reside in the Moon body? While the quantum multiple personality problem in the many-worlds interpretation dealt with a single body, this case sets up the problem with two bodies.

This self-uniqueness problem remains unsolved in both philosophy and brain science. However, in this note, I would like to share my personal view.

First, there is a reason why I intentionally consider rooms that isolate the bodies from the outside in Figure 7. In quantum mechanics, to uniquely define the state of a macro quantum system like this body, it is necessary to completely isolate the human body from the environment. If it interacts with an environment, you cannot fully specify the state of the body without considering the entire composite system formed with that environment. Two bodies interacting with different environments will end up in different states.

However, in this isolated state, the consciousness residing in the body at point A has no way of verifying that an identical body exists at point B. Therefore, if you prepare a quantum-mechanically accurate problem setting, the question 'Why am I not the person at point B?' has no meaning in the first place. Thus, the self-uniqueness problem does not arise.

Then, what happens if we take the bodies out of their respective rooms as shown in Figure 8? Since the environments interacting with the bodies on Earth and the Moon are completely different, each body will have different experiences and generate different memory states.

In other words, the differences caused by different environments affect 'me.' Only at this stage do I realize that I am on Earth or on the Moon. And only then can I ask, 'Why does the 'me' on Earth reside in this body on Earth, rather than in the body on the Moon?' In this sense, it can be said that this difference experienced through the environment is what emerges as a 'me' that is distinct from others.

However, at this stage, the 'self-uniqueness problem' of two identical bodies is absorbed into the ordinary uniqueness problem regarding other people. The Earth and Moon bodies, which have different quantum states, are the same as the bodies of ordinary twins. The 'me' on Earth can build a rocket through interactions with other people on Earth and, as shown in Figure 9, meet the other self—the 'twin'—on the Moon.

Therefore, the specific nature of considering two people with identical bodies does not affect the essence of the self-uniqueness problem.

So, why does our 'me' reside in this body of ours rather than in the bodies of other people? It may simply be that the interaction between one's own brain and others' brains is weak. Our brains are not directly connected to other people's brains. And as shown in Figure 10, each independent brain thinks, 'I am this me.'

However, if a situation is created where one's brain and another's brain exchange signals closely using near-future technology, the interaction will become stronger. Then, the other's 'me' and one's own 'me' might be integrated into one, and as shown in Figure 11, a single 'me' might emerge as a whole. Just as the right and left hemispheres of a single body are integrated to form a single 'me.'

Here, a thought experiment is also possible where one brain is turned into a quantum computer, as shown in Figure 12.

Even in that case, there is a possibility that a single 'me' will emerge together with the quantum computer.

Also, in cases where two brains are connected, even if the spatial distance between the brains or bodies is quite large, it is possible for a single 'me' to be maintained as a whole, as shown in Figure 13.

However, since the speed of information exchange cannot exceed the speed of light, conscious activity itself must be somewhat slow.

Up until now, we have considered thought experiments where multiple 'I's are integrated into a single 'I'. Conversely, thought experiments where a single 'I' splits into multiple 'I's are also possible. Furthermore, although we experience a single 'I', it is possible, for example, that the mitochondria within each of our cells are still exchanging information closely and possess an integrated 'mitochondrial consciousness' independently within the body. Our brains may simply be unaware of it. In other words, we cannot deny the possibility that multiple 'I's with different structures exist within a single body, in a setting different from the quantum multiple personality of the many-worlds interpretation.

Human mothers carry fetuses in their wombs, but usually, birth occurs before the fetus's brain grows enough to support consciousness, and the sense of 'I' buds in the infant during growth after birth. However, in the birth of higher life forms that might exist on other planets, it is possible that brain growth proceeds rapidly within the womb and consciousness buds while still inside the mother. Unlike humans, if this life form possesses a transmission system that directly connects the parent's brain to the fetus's brain, the parent's 'I' might have the sensation of the child's 'I' branching off from their own. While I have discussed the possibility of connecting multiple brains to integrate them into one large 'I' above, I personally find it interesting that there is also the possibility of the 'I' branching out in this way.

It should be noted that even with the considerations made so far, the original problem of self-uniqueness remains unsolved. The question of 'why am I this person' during the integration or branching of the 'I' is an ill-posed problem in empirical science and is ultimately an unanswerable question. This is my position at the present time.