By Stuart Kauffman
It is possible that the view of consciousness that I have been exploring, that the mind-brain system is a quantum cohering-decohering-recohering system in an environment, may shed light on the mighty and still unresolved problem of what is called the famous "Measurement Problem" in Quantum Mechanics. The issue I wish to address is the fact that my perception of a quantum process, capable of interference phenomena, can destroy that interference. How can my perception even conceivably "do this?"
As a scientist, I hold what I shall say below with high skepticism, but interest, for a natural interpretation of receiving sensory information from the world on this theory, plus Shor's theorem about quantum error correction, seem to imply that perceiving a quantum event, such as photon's pathway through one of the two slits in the two slit experiment can, in physical principle, partially or even perhaps completely destroy the interference pattern detected on the photodetector screen. To Be Is To Be Perceived, I shall want to say.
A fine discussion of the measurement problem can be found at Google "John von Neumann" + "Quantum Measurement" under the heading "Measurement in Quantum Theory", the Stanford Encyclopedia of Philosophy. As I shall report from this source, more than 70 years since the Schrodinger equation, the attempts to formulate the measurement problem all seem to have inconsistencies or severe problems.
I will follow the above article in part. It points out that the background views are those of Locke and Kant. Locke, a realist, thought our sensory awareness of the world mirrored the real world "out there". By contrast, Kant, using the metaphor of spectacles, thought our perception of the world was via a veil of perception imposed by our minds and the conditions of knowing. We could never know the real, noumenal world. Niels Bohr took a position, given the two slit and other experiments in which human perception altered the outcome, of thinking in extended Kantian terms of our perception as somehow partially being "constitutive of the world out there".
This raises a mighty mystery, central to what I want to write about: How can our perceiving or knowing, alter what is "out there"? How can that perceiving or knowing be, as Bohr insisted, "constitutive of the world"?
More recently Zeh has said: "Heisenberg's original hope that the quantum system was disturbed during the measurement is not tenable. Instead, various systems (the observed one, the apparatus, the observer, and the environment) get entangled."
I gather that Zeh's view about the entanglement between the (conscious) observer and the observed one and the rest above, is a prominent one among physicists.
How can such entanglement arise? And might any such entanglement be a clue to consciousness itself?
I will propose what might be a new way to think about this.
The next, obligatory step in this discussion is to briefly outline the formalization of Quantum Mechanics and the measurement problem by brilliant John von Neumann. He imagined and formalized the measurement process in two steps. First, the Schrodinger equation propagates unitarily, ie preserving probability, of all the superpositions of wave functions that the linear Schrodinger equation states, ie S, to the measuring system, M. In interacting with the measuring system, M, S and M become quantum entangled, in some sense, one system. In his famous step two, M randomly puts all the probability which was in the superposition of all the possibilities in S, into only one possibility. This is the famous "collapse of the wave function", or quantum "jump". There is no law or cause for this jump in terms of which of the possibilities M ontologically randomly jump to, but there is a probability distribution for those jumps, the familiar quantum probabilities achieved by the Born rule, which is to square the absolute value of the amplitude of each wave to get the probability that the quantum measurement jump will "land" on that now single, possibility.
It turns out that no one can formulate this model without contradictions or paradoxes, as the cited article makes clear.
I just may have something helpful to say here, but all caution is required. In my previous posts on whether law describes the processes of decoherence and recoherence in detail, I have tried to say, using philosopher Sir Karl Popper's argument, that in a Special Relativity setting, we can consider an event A with a future and past light cone separated by a region of potential simultaneity. Then consider an event B in the future light cone of A. B's past light cone encompases all A's past light cone, and more - regions that are outside of A's past light cone, and called "space-like separated". But as Popper argued, an observer at A cannot know what lies outside of A's past light cone hence cannot have a "law" for what happens until just before B. The observer cannot have a law in the real sense that he or she cannot know the conditions and possible processes in the space-like separated regions outside the past light cone of A, and until just before B, that may affect what happens at B. I just transfer Popper's argument to a quantum decoherent setting with moving detectors to create a Special Relativity setting and conclude that no function, F, at A, maps the spacetime region around A into its future until just before B. If this is right, it seems there is no law for how decoherence to classicity, or classicity "for all practical purposes", happens in any specific case. If not, there is not a solution to this part of the problem of Measurement in the sense of a sufficient law. This is one effort to substantiate von Neumann's postulate of no law for how M collapses the wave function, the famous "quantum jump" noted above. It remains to be seen if this qualitative argument can be made rigorous beyond the above, if needed.
But this does not yet deal with the entanglement between the observer, the observed system, the apparatus, and the environment. This is a major part of the "measurement problem." How might the conscious observer possibly play a role and be "constitutive of the world?"
My next step is to take a theory of the mind-brain system as a quantum cohering-decohering-and-recohering system, and possibilities as ontologically real, as a serious proposition.
On this theory, what could perception be, say of a visual field? Bear in mind that we know about the classical behaviors of receptor fields, including edge detectors in the behavior of retinal ganglia and visual cortical cells, so I do not want to stray far from established neurscience.
The natural interpretation of receiving information from the outside world, say visual field, is that the quantum information being received makes the partially decoherent mind-brain system become more coherent via some analogue of Shor's error correction theorem. (This postulate mirrors the chlorophyll molecule that is excited to a quantum coherent state by absorbing a photon and remains in a coherent state, helped, we think, by its wrapper of antenna protein.)
I now come to an utterly striking next feature of Shor's error correction theorem. The theorem states that information from a "quantum environment" can enter a quantum system and, detect decoherence in some few of a more numerous entangled multi-qubit (quantum bits) encoding of those fewer qubits. The Shor process detects the decoherence in the qubits via the equivalent of a quantum measurement. Having detected decoherence in those few qubits, the algorithm can make those decohering degrees of freedom recohere. The algorithm can error correct decohering qubits by restoring their coherence. But critically, the theorem says that the decoherence in the "system" does not disappear, instead the decohrence is transferred to the quantum environment!
Now let's put the above remarkable statement into our tentative theory that to perceive, the mind-brain system becomes more quantum coherent via a physical analogue of Shor's theorem, say like the antenna protein and chlorophyll. Then the conclusion is that the outside quantum environment becomes less coherent! That is, the increased coherence of the mind-brain system would acausally make the outside quantum world decohere! But this means that for the mind-brian quantum-cohering-decohering-recohering system to perceive, the world it is perceiving can or must acausally become more or entirely classical!
The perceiving observer and the observed system can possibly, (or must), become entangled by the Shor quantum error correction algorithm used together with the hypothesis that mind-brain is a quantum cohering-decohering-recohering system.
"To Be (classical) Is, (can be), To Be Perceived".
This is the clue about which I write. It might be meaningless, beside the point, or very big. For what is implied is that perception of the pathway the photon took through the two slits, via Shor's transfer of decoherence from the mind-brain system to the photon, just might actually acausally induce decoherence of the photon and destroy interference bands!
This could be a clue to a major part of the Measurement problem.
Do I believe this? Not yet certainly. It is a long step from my perception causing decoherence in the "outside world" to that decoherence bearing on a specific incoming photon in the two slit experiment. But it is striking that Shor's theorem concerning transfer of decoherence from the system which becomes more coherent via injection of quantum "information", to the quantum environment from which the information came, causes decoherence in that environment.
The above may constitute the first clue we have about why and how conscious observer measurement in quantum mechanics could yield decoherence of the observed system and loss of the interference patterns that are the hallmark of quantum behavior.
It may also be the first clue about how "I" the observer, can be "constituitive of the world", as Bohr would want it.
I confess that the fact that this theory could even conceivably account for some of the outstanding problems with quantum measurement via conscious human observation somewhat increases my own sense that the theory of the mind-brain as a quantum cohering-decohering-recohering system may have real plausibility about it. Not only does this theory, in principle, seem to answer philosophy of mind problems about how mind can act on matter and how we can have a responsible free will that have plagued us since Descartes, it may help with conscious observer induced quantum measurement and loss of interference in the two slit experiment and others, a feature of the real world and a central mystery of Quantum Mechanics.
To tie this to neurobiology, even tentativelly, seems both too brave, but also needed. I must imagine that from photoreceptor to the central nervous system, quantum behavior can arise and be correlated. But wide spread quantum entanglement is surely not ruled out in the sensory to brain system, and may span the brain and beyond. So I do not think quantum-cohering-decohering-recohering behavior in a neural brain is ruled out by the existence of neurons and action potentials. In a previous blog I suggested looking at neurotransmitter molecules in synaptic junctions, their post synaptic receptors, and transmembrane channel proteins in dendrites for signs of quantum behavior.
Is this hypothesis impossible, given chlorophyll and the antenna protein? No. Rather, it may be a new hope.
See the first comments to this blog for further issues.