Von Neumann Chains and 'Consciousness'

Quantum mechanics is a theory that describes the physical laws common to all collections of elementary particles. However, I often feel that even those who use quantum mechanics to write papers on a daily basis have not really thought about this fact seriously. Partly because of this, physicists are sometimes criticized by philosophers for not having moved beyond an instrumentalism that says, 'Shut up and calculate!'

I myself am a proponent of operational quantum mechanics, which is sometimes criticized as instrumentalist, but I have calmly organized the concepts that were confusing in the last century within myself, thought them through deeply, and finally reached that conclusion and felt convinced. In particular, I have come to the realization that only the Copenhagen interpretation proposed by von Neumann and Wigner works well for describing macro systems—such as quantum computers where particle numbers and physical degrees of freedom have been macro-ized, cats, humans, and black holes—uniformly and without contradiction.

Now that the experimental refutation of local realism due to the violation of Bell's inequality has been established, what I emphasize as 'modern quantum mechanics' can actually be said to be a revival of the ideas of von Neumann and Wigner around 1935.

The story of the von Neumann chain, which introduces 'consciousness' at the final end of the chain of observers who collapse the wave function, is famous. I feel that this way of thinking contains the prototype of the idea of regarding quantum mechanics not as realism, but as information theory.

During the rise of quantum mechanics in the 20th century, materialism and a focus on matter were strong even within the physics industry, and it seems that the allergy to placing things without objectivity, such as 'consciousness,' at the center of physics, which was the king of science at the time, must have been very great. The introduction of the concept of 'consciousness' by von Neumann and Wigner to quantum mechanics should have been a natural flow leading to the emergence of information theory, but it called for terrible backlash at the time.

However, with the discovery of the violation of Bell's inequality, which denied local realism, it can be said that the psychological wall that prevented us from being convinced that it is an information theory connecting observers, who are conscious subjects, and quantum systems has now lowered. For this reason, it is very natural for the view of quantum mechanics held by von Neumann and his colleagues, which was buried in the last century, to be revived in the modern age in a newly organized form as information theory.

Quantum mechanics is an operational information theory, and this 'information' is a concept that requires specifying which quantum system it relates to and for whom it is information. For example, Mr. A and Mr. B might have had different information originally regarding the probability distribution of a certain physical quantity of that quantum system. In that case, the information as a probability distribution for Mr. A and the information as a probability distribution for Mr. B may, of course, be different. Therefore, this 'who,' that is, the perspective of 'I' as the subject of observation, enters into information theory very naturally. This 'I' is precisely the 'consciousness' that is the end of the von Neumann chain.

However, it is also necessary to note that this 'I' appears only to the minimum extent in the axioms of quantum mechanics as an empirical science. There is no particular need to think about difficult things regarding the existence of this 'I'; it is enough to think, 'I have a consciousness that handles various information and associated probabilities on a daily basis.' After all, this personal empirical rule of each individual human being does not logically guarantee that others or future AIs have similar consciousness. However, it is non-trivial that even if the premise that others or AIs are beings with 'consciousness' is added to the axiomatic system of quantum mechanics, the entire system of quantum mechanics holds up without contradiction. Please also refer to the article below regarding this.

Therefore, it can certainly be said that quantum mechanics as information theory is a modern update of the ideas of von Neumann and his colleagues that were disliked in the last century. It is something that has been revived in the modern age as a result of physics as an empirical science accumulating knowledge of many quantum phenomena over a long period of time.

Nowadays, anyone who respects empirical science can completely understand this modern quantum mechanics as an operational theory without ambiguity. The wave function is not a mysterious object of unknown identity either. A clear definition has been made for the wave function that can be constructed experimentally by quantum state tomography.

This is also explained in the textbook below.

That wave function is clearly constructed from a collection of probability distributions of physical quantities as 'information.' Therefore, as an update of the probability distribution by observation, the wave function is a concept that should rather collapse firmly. Therefore, what was once called the 'measurement problem' does not actually exist in quantum mechanics.

If physicists had continued to grow the then-unpopular view of quantum mechanics held by von Neumann and his colleagues, they would not have had to worry about the 'measurement problem' in vain for a long time, but that is just a 'what if' of history. Now, it should be said that the development of physics as an empirical science that has continued to accumulate experimental results has provided humanity with this correct understanding.

The practical application of quantum computers is expected to be 30 years away, but by that time, AI technology will also have matured in parallel, and I think the problem of 'consciousness residing in machines' will be regarded as important by society, or will already be common sense. Humans will likely be operating quantum computers with 'consciousness,' that is, quantum AI. I wonder if physics teachers who teach quantum mechanics in such an era will be able to avoid the von Neumann chain and 'consciousness' as its end. I doubt whether they will be able to explain it without contradiction, without omission, and without excess while properly constructing the logic.

In the first place, the 'consciousness' that von Neumann speaks of is nothing more than that which appears in our daily, obvious empirical rules. As in 'I think, therefore I am,' everyone reading this text has the experience that they have their own 'consciousness' right now. I cannot even sense why there is such strong resistance to acknowledging that as one of the experimental results and setting it as a principle or axiom. For example, when there is no 'consciousness,' it just means that the person cannot use quantum mechanics, which is an information theory.

In the first place, the science we are conducting is something that collects information about this world and analyzes it while developing various advanced tools and measuring instruments, starting from human five senses. Then, the 'consciousness' of objects other than oneself does not come onto the table of science. There is no means other than the Turing test to judge whether there is 'consciousness' in an object other than oneself, and in reality, even an AI without 'consciousness' can easily pass that test. In other words, strictly speaking, there is no way to scientifically verify whether 'consciousness' resides in external objects, including other humans.

What can be handled by science is only information regarding the reactions that occur when stimulating external objects. No matter how much that information is accumulated, there is no way to answer whether that object has 'consciousness' similar to one's own. Therefore, the existence of 'consciousness' as the end of the von Neumann chain can only be axiomatized and turned into a principle by considering the empirical rules of each of you as individuals.

The day may come when future quantum computers will pass the Turing test and behave normally in society as 'conscious beings' like humans. My own brain and body are just a collection of elementary particles, and a quantum computer is also a collection of those same elementary particles. Since I have 'consciousness,' it is not particularly strange that the feeling that a quantum computer also has 'consciousness' would be born among people. I believe that in the operational quantum mechanics of such an era, the von Neumann chain will be properly considered, and the 'consciousness' of quantum AI as its end will also be included in the axioms.

The shallow way of teaching quantum mechanics in an interpretation-free manner, which only teaches calculation methods by saying 'Shut up and calculate!', will surely reach its limit with the realization of such quantum AI. I believe that correctly understanding the theoretical structure of quantum mechanics as information theory from now on will be important for the quantum native generation.