Orch OR (Orchestrated Objective Reduction) is a theory of consciousness, which is the joint work of theoretical physicist Sir Roger Penrose and anesthesiologist Stuart Hameroff. Mainstream theories assume that consciousness emerges from the brain, and focus particularly on complex computation at connections known as synapses that allow communication between brain cells (neurons). Orch OR combines approaches to the problem of consciousness from the radically different angles of mathematics, physics and anesthesia.
Penrose and Hameroff initially developed their ideas quite separately from one another, and it was only in the 1990s that they cooperated to produce the Orch OR theory. Penrose came to the problem from the view point of mathematics and in particular Gödel’s theorem, while Hameroff approached it from a career in cancer research and anesthesia that gave him an interest in brain structures.
Contents |
Gödel's Incompleteness Theorem
In 1931, the mathematician and logician Kurt Gödel proved that with most sets of mathematical axioms, it was possible to produce a statement that was obviously true, but could not be proved by means of the axioms.
However, in his first book on consciousness, The Emperor’s New Mind (1989),[1] Penrose made Gödel's theorem the basis of what quickly became an intensely controversial claim. He argued that the theorem showed that the brain had the ability to go beyond what could be achieved by axioms or formal systems. This would mean that the mind had some additional function that was not based on algorithms (systems or rules of calculation). 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 functioning non-computable.
This core assertion was vigorously contested by numerous critics, and notably by the philosophers, Rick Grush and Patricia Churchland [2].
The quantum level
Penrose went on to consider what it was in the human brain that might not be driven by algorithms. The physical law is described by algorithms, so it was not easy for Penrose to come up with physical properties or processes that are not described by them. He was forced to look to quantum theory for a plausible candidate.
In quantum theory, the fundamental units, the quanta, are in some respects quite unlike objects that are encountered in the large scale world described by classical physics. When sufficiently isolated from the environment, they can be viewed as waves. However these are not the same as matter waves, such as waves in the sea. The quantum waves are essentially waves of probability, the varying probability of finding a particle at some specific position. (These probabilities apply to other states of the particle, such as its momentum, but for the sake of simplicity we will refer to position.) The peak of the wave indicates the location with maximum probability of a particle being found there. The different possible positions of the particle are referred to as superpositions or quantum superpositions. We are speaking here of the isolated form of the quanta. When the quanta are the subject of measurements or of interaction with the environment, the wave characteristic is lost, and a particle is found at a specific point. This change is commonly referred to as the collapse of the wave function.
When the collapse happens, the choice of position for the particle is random. This is a drastic departure from classical physics. There is no cause-and-effect process, and no system of algorithms that can describe the choice of position for the particle.
This provided Penrose with a candidate for the physical basis of the suggested non-computable process that he proposed as possibly existing in the brain. However, this was not the end of his problems. He had identified something in physics that was not based on algorithms, but at the same time, randomness was not a promising basis for mathematical understanding, the aspect of mind that Penrose particularly focused on.
Objective reduction
Penrose now proposed that existing ideas on wave function collapse might only apply to situations where the quanta are the subject of measurement or of interaction with the environment. He considered the case of quanta that are not the subject of measurements or interactions, but remain isolated from the environment, and proposed that these quanta may be subject to a different form of wave function collapse.
In this area, Penrose draws on both Einstein's general theory of relativity, and on his own notions about the possible structure of spacetime[1][3]. General relativity states that spacetime (space and time are treated as a single entity in relativity) is curved by massive objects. Penrose, in seeking to reconcile relativity and quantum theory, has suggested that at the very small scale this curved spacetime is not continuous, but constitutes a form of network.
Penrose postulates that each quantum superposition (possible position of the particle) has its own piece of spacetime curvature. According to his theory, these different bits of spacetime curvature are separated from one another, and constitute a form of blister in spacetime. Penrose further proposes a limit to the size of this spacetime blister. This is the tiny Planck scale of (10−35 m). Above this size, Penrose suggests that spacetime can be viewed as continuous, and that gravity starts to exert its force on the spacetime blister. This is suggested to become unstable above the Planck scale, and to collapse so as to choose just one of the possible locations for the particle. Penrose calls this event objective reduction (OR), reduction being another word for wave function collapse.
This theory of objective reduction is markedly different from the traditional Copenhagen interpretation of quantum theory propounded by Niels Bohr, and also from some modern alternatives to Copenhagen, such as many worlds theory and some forms of decoherence theory.
An important feature of Penrose's objective reduction is that the time to collapse is a function of the mass/energy of the object undergoing collapse. Thus the greater the superposition, the faster it will undergo OR, and vice versa. Tiny superpositions, e.g. an electron separated from itself, if isolated from environment, would require 10 million years to reach OR threshold. An isolated one kilogram object (e.g. Schrödinger’s cat) would reach OR threshold in only 10−37 seconds. However objects somewhere between the scale of an electron and the scale of a cat could collapse within a timescale that was relevant to neural processing.
The threshold for Penrose OR is given by the indeterminacy principle E=ħ/t, where E is the gravitational self-energy or the degree of spacetime separation given by the superpositioned mass, ħ is the reduced Planck constant, and t is the time until OR occurs.
There is no existing evidence for Penrose's objective reduction, but the theory is considered to be testable, and plans are in hand to carry out a relevant experiment [4].
From the point of view of consciousness theory, an essential feature of Penrose's objective reduction is that the choice of states when objective reduction occurs is selected neither randomly, as are choices following measurement or decoherence, nor completely algorithmically. Rather, states are proposed to be selected by a 'non-computable' influence embedded in the fundamental level of spacetime geometry at the Planck scale.
Penrose claimed that such information is Platonic, representing pure mathematical truth, aesthetic and ethical values. More than two thousand years ago, the Greek philosopher Plato had proposed such pure values and forms, but in an abstract realm. Penrose placed the Platonic realm at the Planck scale. This relates to Penrose's ideas concerning the three worlds: physical, mental, and the Platonic mathematical world. In his theory, the physical world can be seen as the external reality, the mental world as information processing in the brain and the Platonic world as the encryption, measurement, or geometry of fundamental spacetime that is claimed to support non-computational understanding.
The creation of the Orch OR model
When he wrote his first consciousness book, The Emperor's New Mind in 1989, Penrose lacked a detailed proposal for how such quantum processes could be implemented in the brain. Subsequently, Hameroff read The Emperor’s New Mind and suggested to Penrose that certain structures within brain cells (neurons) were suitable candidate sites for quantum processing and ultimately for consciousness [5] The Orch OR theory arose from the cooperation of these two scientists, and were developed in Penrose's second consciousness book Shadows of the Mind (1994).
Hameroff's contribution to the theory derived from studying brain cells (neurons). His interest centred on the cytoskeleton, which provides an internal supportive structure for neurons, and particularly on the microtubules, which are the important component of the cytoskeleton. As neuroscience has progressed, the role of the cytoskeleton and microtubules has assumed greater importance. In addition to providing a supportive structure for the cell, the known functions of the microtubules include transport of molecules including neurotransmitter molecules bound for the synapses, and control of the cell's movement, growth and shape[5].
Hameroff proposed that microtubules were suitable candidates to support quantum processing[5]. Microtubules are comprised of subunits of the protein, tubulin. Proteins constitute much of the driving machinery of living organisms. Proteins contain hydrophobic (water repellent) pockets. These pockets contain atoms with electrons called π electrons, which means electrons in the reactive outer part (outer shell) of the atom that are not bonded to other atoms. The tubulin protein subunits of the microtubules have hydrophobic pockets within two nanometres of one another. Hameroff claims that this is close enough for the π electrons of the tubulin to become quantum entangled [6]. Quantum entanglement is a state in which quantum particles can alter one another's properties instantaneously and at a distance, in a way which would not be possible, if they were large scale objects obeying the laws of classical as opposed to quantum physics.
In the case of the electrons in the tubulin subunits of the microtubules, Hameroff has proposed that large numbers of these electrons can become involved in a state known as a Bose-Einstein condensate. These occur when large numbers of quantum particles become locked in phase and exist as a single quantum object. These are quantum features at a macroscopic scale, and Hameroff suggests that through a feature of this kind quantum activity, which is usually at a very tiny scale, could be boosted to be a large scale influence in the brain.
Hameroff has proposed that condensates in microtubules in one neuron can link with other neurons via gap junctions[6]. In addition to the synaptic connections between brain cells, gap junctions are a different category of connections, where the gap between the cells is sufficiently small for quantum objects to cross it by means of a process known as quantum tunnelling. Hameroff proposes that this tunnelling allows a quantum object, such as the Bose-Einstein condensates mentioned above, to cross into other neurons, and thus extend across a large area of the brain as a single quantum object.
He further postulates that the action of this large-scale quantum feature is the source of the gamma (40 Hz) synchronisation observed in the brain, and sometimes viewed as a correlate of consciousness [7]. In support of the much more limited theory that gap junctions are related to the gamma oscillation, Hameroff quotes a number of studies from recent years [7][8][9][10][11][12][13][14][15][16][17].
The Orch OR theory combines Penrose's hypothesis with respect to the Gödel theorem with Hameroff's hypothesis with respect to microtubules. Together, Penrose and Hameroff have proposed that when condensates in the brain undergo an objective reduction of their wave function, that collapse connects to non-computational decision taking/experience embedded in the geometry of fundamental spacetime.
The theory further proposes that the microtubules both influence and are influenced by the conventional activity at the synapses between neurons. The Orch in Orch OR stands for orchestrated to give the full name of the theory Orchestrated Objective Reduction. Orchestration refers to the hypothetical process by which connective proteins, known as microtubule associated proteins (MAPs) influence or orchestrate the quantum processing of the microtubules.
Objections to Orch OR
Penrose's take on Gödel's first incompleteness theorem is rejected by many philosophers, logicians and artificial intelligence (robotics) researchers.[citation needed] His proposal for objective reduction is distinct from anything else in physics, although not at all unique in the field of interpretation of quantum theory. The main objection to the Hameroff side of the theory is that any quantum feature in the environment of the brain would undergo wave function collapse (reduction) as a result of interaction with the environment, far too quickly for it to have any influence on neural processes.
The wave or superposition form of the quanta is referred to as being quantum coherent. Interaction with the environment results in decoherence otherwise known as wave function collapse. It has been questioned as to how such quantum coherence could avoid rapid decoherence in the conditions of the brain. With reference to this question, a paper by the physicist, Max Tegmark, refuting the Orch OR model and published in the journal, Physical Reviews E is widely quoted.[18] Tegmark developed a model for time to decoherence, and from this calculated that microtubule quantum states would persist for only 10−13 seconds at brain temperatures, far too brief to be relevant to neural processing.
In their reply to his paper, also published in Physical Reviews E, the physicists, Scott Hagan and Jack Tuszynski and Hameroff[19][20] claimed that Tegmark did not address the Orch OR model, but instead a model of his own construction. This involved superpositions of quanta separated by 24 nanometres (billionths of a metre) rather than the much smaller separations stipulated for Orch OR.
As a result, Hameroff's group claimed a decoherence time seven orders of magnitude greater than Tegmarks, but still well short of the 25ms required if the quantum processing in the theory was to be linked to the 40 Hz gamma synchrony, as Orch OR suggested. To bridge this gap, the group made a series of proposals.
The interiors of neurons alternate between liquid (solution: sol) states and quasi-solid (gelatinous: gel) states. In the gel state, water molecules which are electrical dipoles, are ordered, or orientated in the same direction, along the outer edge of the microtubule tubulin subunits. Hameroff et al. proposed that this ordered water could screen any quantum coherence within the tubulin of the microtubules from the environment of the rest of the brain. The tubulins also have a tail extending out from the microtubules, which is negatively charged, and therefore attracts positively charged ions. It is suggested that this could provide further screening. Further to this, there was a suggestion that the microtubules could be pumped into a coherent state by biochemical energy. Finally, it is suggested that the configuration of the microtubule lattice might be suitable for quantum error correction, a means of holding together quantum coherence in the face of environmental interaction.
Hameroff has proposed 20 different ways in which Orch OR might be tested. One of these is the test for objective reduction mentioned above, and the other 19 refer to features that might be observed in the brain [21].
See also
- Electromagnetic theories of consciousness
- Holonomic brain theory
- Many-minds interpretation
- Quantum Aspects of Life (book)
- Quantum mind
- Space-time theories of consciousness
- Discussion in psyche journal [9]
- Online talk by Penrose with Q&A session [10]
- Quantum-Mind
References
- ^ a b Penrose, R. (1989), Emperor's New Mind. Oxford University Press
- ^ Grush, R. & Churchland, P., Journal of Consciousness Studies, 2, No. 1, (1995), pp. 10-29
- ^ Penrose, R. (1994), Shadows of the Mind. Oxford University Press
- ^ Marshall, W.,Simon,C. Penrose, R., Bouwmeester, D. (2003), Physical Reviews Letters, 91:13
- ^ a b c Hameroff, S. (1987), Ultimate Computing. Elsevier [1]
- ^ a b Hameroff, S.[2]
- ^ a b Bennett, M. & Zukin, R. (2004), Neuron 41,4:495–511 [3]
- ^ Buhl, D. et al. (2003), Journal of Neuroscience 23,3:1013–18
- ^ Dermietzel, R. (1998), Brain Research Reviews 26,2–3:176–83 [4]
- ^ Draguhn, A. et al. (1998), Nature 394:189–92 [5]
- ^ Fries et al. (2002), Journal of Neuroscience 22,9:3739–54
- ^ Galaretta, M. & Hestrin, S. (1999), Nature 402;72–75 [6]
- ^ Gibson, J. et al. (1999), Nature 402:75–79
- ^ Hormuzdi, S. et al. (2004), Biochimica Biophysica Acta. 1662,1–2:113 [7]
- ^ LeBeau, F. et al. (2003), Brain Research Bulletin 62,1:3–13
- ^ Perez Velasquez, J. (2000), Trends in Neurosciences 23,2:68–74 [8]
- ^ Rozental, R. (2000), Brain Research Reviews 32,1:11
- ^ Tegmark, M. (2000), "Importance of quantum coherence in brain processes", Physical Review E 61:4194–206
- ^ Hagan, S., Hameroff, S., & Tuszyński, J., (2002), "Quantum Computation in Brain Microtubules? Decoherence and Biological Feasibility", Physical Reviews E 65:061901.
- ^ Hameroff, S.(2006), Consciousness, Neurobiology and Quantum Mechanics, In: The Emerging Physics of Consciousness, Ed. Tuszynski, J., Springer
- ^ Hameroff S.R., & Watt R.C. (1982), Journal of Theoretical Biology 98:549–61 and "Information processing in microtubules"
Other Relevant Papers
- Kanade, T. (1980), Artificial Intelligence 13:279
- Kanade, T. (1981). Artificial Intelligence 17:409
- Bialek, W. (1987), Physical Review Letters 58:741
- Bialek, W. & Sweitzer, A. (1986), Physical Review Letters 54:725
- Tejeda, J. et al. (1996), Quantum coherence in the brain". Science 272:424
- Warren, W. et al. (1998), Quantum coherence in the brain". Science 281:247
- Rizi, R. (2000), "Quantum coherence". Magnetic Resonance Med. 43:627
- Richter, W. et al. (2000), "Quantum coherence". Magnetic Resonance Imaging 18:489
- Prokhorenco, V. (2006). Science 313, No.5791:1257–61
- Binhi, V. & Savin, A. (2002), "Molecular gyroscopes and biological effects of very low frequency magnetic fields". Physical Review E 65:051912
This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)
