The quantum mind or quantum consciousness hypothesis proposes that classical mechanics cannot explain consciousness, while quantum mechanical phenomena, such as quantum entanglement and superposition, may play an important part in the brain's function, and could form the basis of an explanation of consciousness. There are several quite distinct quantum mind theories, and these are discussed in the sections below. This school of thought is rejected by the majority of the quantum physics community.
Contents |
David Bohm took the view that quantum theory and relativity contradicted one another, and that this contradiction implied that there existed a more fundamental level in the physical universe.[1] He claimed that both quantum theory and relativity pointed towards this deeper theory. This more fundamental level was supposed to represent an undivided wholeness and an implicate order, from which arose the explicate order of the universe as we experience it.
Bohm's implicate order applies both to matter and consciousness, and he proposed that it could explain the relationship between them. Mind and matter are here seen as projections into our explicate order from the underlying reality of the implicate order. Bohm claims that when we look at the matter in space, we can see nothing in these concepts that helps us to understand consciousness.
In trying to describe the nature of consciousness, Bohm discusses the experience of listening to music. He thinks that the feeling of movement and change that make up our experience of music derives from both the immediate past and the present both being held in the brain together, with the notes from the past seen as transformations rather than memories. The notes that were implicate in the immediate past are seen as becoming explicate in the present. Bohm views this as consciousness emerging from the implicate order.
Bohm sees the movement, change or flow and also the coherence of experiences, such as listening to music as a manifestation of the implicate order. He claims to derive evidence for this from the work of Jean Piaget[2] in studying infants. He states that these studies show that young children have to learn about time and space, because they are part of the explicate order, but have a "hard-wired" understanding of movement, because it is part of the implicate order. He compares this "hard-wiring" to Chomsky's theory that grammar is "hard-wired" into young human brains. In his writings, Bohm never proposed any specific brain mechanism by which his implicate order could emerge in a way that was relevant to consciousness.
Recent papers by physicist Gustav Bernroider have indicated that he thinks that Bohm's implicate-explicate structure can account for the relationship between neural processes and consciousness.[3] In a paper published in 2005 Bernroider elaborated his proposals for the physical basis of this process.[4] The main thrust of his paper was the argument that quantum coherence may be sustained in ion channels for long enough to be relevant for neural processes. He proposes that the channels could be entangled with surrounding lipids and proteins and with other channels in the same membrane. Ion channels regulate the electrical potential across the axon membrane, and thus play a central role in the brain's information processing.
Bernroider bases his work on recent studies of the potassium (K+) ion channel in its closed state and draws particularly on the atomic-level spectroscopy work of the MacKinnon group.[5][6][7][8][9] The ion channels have a filter region that allows in K+ ions and bars other ions. These studies show that the filter region has a framework of five sets of four oxygen atoms, which are part of the carboxyl group of amino-acid molecules in the surrounding protein. These are referred to as binding pockets. Two K+ ions are trapped in the selection filter of the closed ion channel. Each of these ions is electrostatically bound to two sets of oxygen atoms or binding pockets, involving eight oxygen atoms in total. Both ions in the channel oscillate between two configurations.
Bernroider uses this recently revealed structure to speculate about the possibility of quantum coherence in the ion channels. Bernroider and co-author Sisir Roy's calculations suggested to them that the behaviour of the ions in the K channel could only be understood at the quantum level. Taking this as their starting point, they then ask whether the structure of the ion channel can be related to logic states. Further calculations lead them to suggest that the K+ ions and the oxygen atoms of the binding pockets are two quantum-entangled sub-systems, which they then equate to a quantum computational mapping. The ions that are destined to be expelled from the channel are proposed to encode information about the state of the oxygen atoms. It is further proposed that the separate ion channels could be quantum-entangled with one another.
The philosopher David Chalmers has speculated on a number of ways in which quantum mechanics might relate to consciousness.
"One possibility is that instead of postulating novel properties, physics might end up appealing to consciousness itself, in the way that some theorists but not all, hold that quantum mechanics does."[10]
"The collapse dynamics leaves a door wide open for an interactionist interpretation."[10]
"The most promising version of such an interpretation allows conscious states to be correlated with the total quantum state of a system, with the extra constraint that conscious states (unlike physical states) can never be superposed. In a conscious physical system such as a brain, the physical and phenomenal states of the system will be correlated in a (nonsuperposed) quantum state. Upon observation of a superposed external system, Schrödinger evolution at the moment of observation would cause the observed system to become correlated with the brain, yielding a resulting superposition of brain states and so (by psychophysical correlation) a superposition of conscious states. But such a superposition cannot occur, so one of the potential resulting conscious states is somehow selected (presumably by a nondeterministic dynamic principle at the phenomenal level). The result is that (by psychophysical correlation) a definite brain state and a definite state of the observed object are also selected."[10]
"If physics is supposed to rule out interactionism, then careful attention to the detail of physical theory is required."[10]
However, Chalmers is also sceptical about the ability of any kind of New Physics to resolve the Hard Problem of Consciousness:
"Nevertheless, quantum theories of consciousness suffer from the same difficulties as neural or computational theories. Quantum phenomena have some remarkable functional properties, such as nondeterminism and nonlocality. It is natural to speculate that these properties may play some role in the explanation of cognitive functions, such as random choice and the integration of information, and this hypothesis cannot be ruled out a priori. But when it comes to the explanation of experience, quantum processes are in the same boat as any other. The question of why these processes should give rise to experience is entirely unanswered."
"The trouble is that the basic elements of physical theories seem always to come down to two things: structure and dynamics of physical processes. . . . But from structure and dynamics, we can only get more structure and dynamics. . . conscious experience will remain untouched"
The theoretical physicist, Roger Penrose and the anaesthesiologist, Stuart Hameroff, collaborated to produce the theory known as Orchestrated Objective Reduction Orch-OR. Penrose and Hameroff initially developed their ideas separately, and only later cooperated to produce Orch-OR. Penrose came to the problem from the point of view of mathematics and in particular Gödel's theorem, while Hameroff came from a career in cancer research and anaesthesia.
Gödel's theorem is central to this theory. In 1931, Gödel proved that any theory capable of expressing elementary arithmetic cannot be both consistent and complete. Further to that, for any consistent formal theory that proves certain basic arithmetic truths there is an arithmetical statement that is true, but not provable in theory.
The theorem is not in itself controversial, but what Penrose developed from it is. In his first book on consciousness, The Emperor's New Mind (1989), Penrose argued that the theorem showed that the brain had the ability to go beyond what could be achieved by axioms or formal systems. He argued that this meant that the brain had some additional function that was not based on algorithms (a system of calculations), whereas a computer is driven solely by algorithms. Penrose asserted that the brain could perform functions that no computer could perform. He called this type of processing non-computable.
Penrose went on to consider what it was in the human brain that was not driven by algorithms. Given the algorithm-based nature of most of physics, he decided that the random choice of position etc. that occurs when a quantum wave collapses into a particle was the only possibility for a non-computable process. However, Penrose admitted that the randomness of the wave function collapse, although free from algorithms, is not a basis for any useful form of human understanding.
Penrose now proposed a second form of wave function collapse that could apply where quanta did not interact with the environment, but might collapse on their own accord. He suggests that each quantum superposition has its own piece of spacetime curvature, and when these become separated by more than the Planck length of 10−35 metres, they become unstable and collapse. Penrose called this form of collapse objective reduction.
Penrose suggested that objective reduction represented neither randomness nor the algorithm based processing of most physics, but instead a non-computable influence embedded in the fundamental level of spacetime geometry from which mathematical understanding and, by later extension of the theory, consciousness derived.
When he wrote his first book on consciousness, The Emperor's New Mind in 1989, Penrose lacked a detailed proposal for how quantum processing could be implemented in the brain. Subsequently, Hameroff read Penrose's book, and suggested that microtubules could be suitable candidates for quantum processing. The Orch-OR theory arose from the collaboration of Penrose and Hameroff in the early 1990s.
Microtubules are the main component of a supportive structure within neurons known as the cytoskeleton. In addition to providing a supportive structure, the known functions of microtubules include transport of molecules including neurotransmitters bound for synapses and control of the development of the cell.
Microtubules are composed of tubulin protein dimer subunits. The tubulin dimers each have hydrophobic pockets that are 8 nm apart, and which may contain delocalised pi electrons. Tubulins have other smaller non-polar regions that contain pi electron-rich indole rings separated by only about 2 nm, and Hameroff claims that these electrons are close enough to become quantum entangled.[13]
Hameroff further proposed that these electrons could become locked in phase, forming a state known as a Bose-Einstein condensate.[14][15] Furthermore, he thought that condensates in one neuron could extend to many others via gap junctions between neurons, thus forming a macroscopic quantum feature across an extended area of the brain. When the wave function of this extended condensate collapsed, it was suggested that this could give access to non-computational influences related to mathematical understanding and ultimately conscious experience that are embedded in the geometry of spacetime.
Hameroff further postulated that the activity of these condensates is the source of gamma wave synchronisation in the brain. This synchronisation has also been viewed as a likely correlate of consciousness in conventional neuroscience, and it has been shown to be linked to the functioning of gap junctions.[16][17][18][19][20][21][22][23][24][25][26]
Another neuroscientist, Danko Georgiev, has provided a footnote to the Orch-OR theory. He accepts much of Penrose's ideas, but criticises a good part of Hameroff's scheme. He proposes that quantum coherence on the surface of the microtubules extends via presynaptic scaffold proteins to the synapses, where it both influences synaptic firing, and is transmitted across the synaptic cleft to other neurons.[27][28][29]
In 2009, Jeffrey Reimers et al. showed that coherent Fröhlich condensates, the states Hameroff and Penrose implicated as the basis of Orch OR, could not exist in biological tissue. They found that coherent Fröhlich condensates of the sort required by Orch OR would require temperatures of between several thousand to several million kelvins, an environment not possible in biological tissue. If the energy required to keep the oscillators in a coherent state for the required 500 ms came from a chemical source, it would require the energy equivalent of a C-C bond being formed or broken every picosecond. The GTP mechanism proposed by Hameroff and Penrose would require the hydrolysis to GDP of approximately 4 or 5 GTP molecules every picosecond, a phenomenon that does not appear to occur in biological systems. [30] Hameroff, however, has contested their claims at the Google Tech Talk exploring Quantum Biology.[31] In addition to this, a recent 2011 paper by Roger Penrose and Stuart Hameroff gives an updated model of their Orch-OR theory, in light of criticisms, and discusses the place of consciousness within the universe. [32]
Physically, Henry Stapp's approach is aligned with objective collapse theory, in that the deterministic evolution of the wave function, and its indeterministic collapse are seen as two real and ontologically distinct phenomena. Collapse events occurring within the brain—the mind's observation or measurement of the brain—are particularly important. Since Stapp sees collapse as a mental process and the deterministic evolution of brain states as physical, his approach is philosophically aligned with interactionist dualism. The process by which collapse selects an actuality from a set of possibilities is seen by Stapp as literally a process of choice, and not merely a random dice-throw. His approach has implications with regard to time. Since the future depends on decisions in the present, it is not pre-existing, as in the block universe theory; rather there is an evolving universe in which subjects participate, as in Whitehead's metaphysics.[33]
Stapp envisages consciousness as exercising top-level control over neural excitation in the brain. Quantum brain events are suggested to occur at the whole brain level, and are seen as being selected from the large-scale excitation of the brain. The neural excitations are viewed as a code, and each conscious experience as a selection from this code. The brain, in this theory, is proposed to be a self-programming computer with a self-sustaining input from memory, which is itself a code derived from previous experience. This process is suggested to result in a number of probabilities from which consciousness has to select. The conscious act is a selection of a piece of top-level code, which then exercises ongoing control over the flow of neural excitation. Stapp thinks that this process refers to the top levels of brain activity involved with information gathering, planning and the monitoring of the execution of plans. Conscious events are, in this theory, proposed to be capable of grasping a whole pattern of activity, thus accounting for the unity of consciousness, and providing a solution to the "binding problem".
Stapp's version of the conscious brain is proposed to be a system that is internally determined in a way that cannot be represented outside the system, whereas for the rest of the physical universe an external representation plus a knowledge of the laws of physics allows an accurate prediction of future events.
Stapp proposes that the proof of his theory requires the identification of the neurons that provide the top-level code and also the process by which memory is turned into additional top-level code.
The ideas behind quantum brain dynamics (QBD) derived originally from the physicists, Hiroomi Umezawa,[34] and Herbert Frohlich[35] in the 1960s. In recent decades these ideas have been elaborated and given greater prominence by a later generation of physicists such as Mari Jibu,[36] Kunio Yasue[36] and Giuseppe Vitiello.[37] In QBD, the electrical dipoles of the water molecules that constitute 70% of the brain are proposed to constitute a quantum field, known here as the cortical field. The quanta of this field are described as corticons. In the theory, this field interacts with quantum coherent waves generated by biomolecules in the neurons and propagating along the neuronal network.
Frohlich is the source of the idea that quantum coherent waves could be generated in the neuronal network. Frohlich argued that it was not clear how order could be sustained in living systems given the disruptive influence of the fluctuations in biochemical processes. He viewed the electric potential across the neuron membrane as the observable feature of some form of underlying quantum order. His studies claimed to show that with an oscillating charge in a thermal bath, large numbers of quanta may condense into a single state known as a Bose condensate. This state allows long-range correlation amongst the dipoles involved. Further to this, biomolecules were proposed to line up along actin filaments (part of the cytoskeleton) and dipole oscillations propagate along the filaments as quantum coherent waves. This now has some experimental support in the form of confirmation that biomolecules with a high electric dipole moment have been shown to have a periodic oscillation.[38] Vitiello also argues that the ordered chains of chemical reactions on which biological tissues depend would collapse without some form of quantum ordering, which in QBD is described by quantum field theory rather than quantum mechanics.
Vitiello provides citations, which are claimed to support his view of biological tissue. These include studies of radiation effect on cell growth,[39] response to external stimuli,[40] non-linear tunnelling,[41] coherent nuclear motion in membrane proteins,[42] optical coherence in biological systems,[43] energy transfer via solitons and coherent excitations.[44]
QBD proposes that the cortical field not only interacts with, but also to a good extent controls the neuronal network. It suggests that biomolecular waves propagate along the actin filaments in the area of the cell membranes and dendritic spines. The waves are suggested to derive energy from ATP molecules stored in the cell membrane and control the ion channels, which in turn regulate the flow of signals to the synapses. Vitiello claims that QBD does not require quantum oscillations to last as long as the actual time to decoherence.
The proponents of QBD differ somewhat as to the exact way in which it produces consciousness. Jibu and Yasue think that the interaction between the energy quanta of the cortical field and the biomolecular waves of the neuronal network, particularly the dendritic part of the network, is what produces consciousness. On the other hand, Vitiello thinks that the quantum states involved in QBD produce two poles, a subjective representation of the external world and a self. This self opens itself to the representation of the external world. Consciousness is, in this theory, not in either the self or the external representation, but between the two in the opening of one to the other.
There have been various attempts to validate the idea of quantum states being involved in neural processing. Friedrich Beck and John C. Eccles developed a model for quantal emission process at the synaptic cleft with reasonable results. These authors also discussed in detail the problem of elementary microscopic processes in protein complexes able to survive thermal fluctuations. Evidence for quantum processing was also claimed by the physicist Evan Harris Walker (see above).
Between 2003 and 2009, Elio Conte, Andrei Yuri Khrennikov, Orlando Todarello, Antonio Federici, Joseph P. Zbilut, performed a number of experiments reaching evidence on possible existence of quantum interference effects on mental states during human perception and cognition of ambiguous figures. See further reading.[13, 14, 15, 16] These authors have also realised theoretical contributions on the analysis of quantum interference effects in mental states, and on time dynamics of cognitive entities.[13, 14, 15, 16]
Studies in the last few years have demonstrated the existence of functional quantum coherence in photosynthetic protein. Engel et al. (2007) was the definitive paper in this field, while Collini et al. (2010) showed that this type of coherence in protein could exist at room temperatures. These systems use times to decoherence that are within the timescales calculated for brain protein.[45][46]
Physicists at the University of California, Berkeley believe they have discovered that green plants perform quantum computation in order to capture the sun's light through photosynthesis—evidence of quantum coherence in a living system.[47]
A 2011 paper in Physical Review letters argues that the extraordinary sensitivity of European robins to small changes in the prevailing magnetic field is evidence that "superposition and entanglement are sustained in this living system for at least tens of microseconds, exceeding the durations achieved in the best comparable man-made molecular systems", and the authors produce a simple model to this effect.[48][49][50]
"No serious researcher I know believes in an electromagnetic theory of consciousness,"[51] Bernard Baars wrote in an e-mail. Baars is a neurobiologist and co-editor of Consciousness & Cognition, another scientific journal in the field. "It's not really worth talking about scientifically,"[51] he was quoted as saying.
The field theories of consciousness do not appear to have been as widely discussed as other quantum consciousness theories, such as those of Penrose, Stapp or Bohm. However, David Chalmers[52] argues that quantum theories of consciousness suffer from the same weakness as more conventional theories. Just as he argues that there is no particular reason why particular macroscopic physical features in the brain should give rise to consciousness, he also thinks that there is no particular reason why a particular quantum feature, such as the EM field in the brain, should give rise to consciousness either. While at least one researcher claims otherwise, Jeffrey Gray states in his book Consciousness: Creeping up on the Hard Problem, that tests looking for the influence of electromagnetic fields on brain function have been universally negative in their result.[53]
The main argument against the quantum mind proposition is that quantum states in the brain would decohere before they reached a spatial or temporal scale, at which they could be useful for neural processing. Michael Price, for example, says that quantum effects rarely or never affect human decisions and that classical physics determines the behaviour of neurons.
In quantum terms each neuron is an essentially classical object. Consequently quantum noise in the brain is at such a low level that it probably doesn't often alter, except very rarely, the critical mechanistic behaviour of sufficient neurons to cause a decision to be different than we might otherwise expect...—Michael Clive Price [1]
Price's position does not necessarily imply that classical mechanics can explain consciousness, but that quantum effects including superposition and entanglement are insignificant.
An arguably more formidable opponent of quantum mind theories is the physicist, Max Tegmark. Based on his calculations, Tegmark concluded that quantum systems in the brain decohere quickly and cannot control brain function, "This conclusion disagrees with suggestions by Penrose and others that the brain acts as a quantum computer, and that quantum coherence is related to consciousness in a fundamental way".[54][55]
Proponents of quantum consciousness theories have sought to defend them against Tegmark's criticism. In respect of QBD, Vitiello has argued that Tegmark's work applies to theories based on quantum mechanics, but not to those such as QBD that are based on quantum field theory. In respect of Penrose and Hameroff's Orch-OR theory, Hameroff along with Hagan and Tuszynski replied to Tegmark.[56] They claimed that Tegmark based his calculations on a model that was different from Orch-OR. It is argued that in the Orch-OR model, the microtubules are shielded from decoherence by ordered water. Energy pumping as a result of thermal disequilibrium, Debye layer screening and quantum error correction, deriving from the geometry of the microtubule lattice are also proposed as possible sources of shielding. Similarly, in his extension of Bohm's ideas, Bernroider has claimed that the binding pockets in the ion selection filters could protect against decoherence.[4] So far, however, there has been no experimental confirmation of the ability of the features mentioned above to protect against decoherence.