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Quantum Mechanics and Consciousness

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Mechanist
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« on: December 09, 2008, 18:32:26 PM »

Can quantum mechanics and consciousness be linked?

Quantum physics and Consciousness. Are they connected? The microtubule connection.

Research into the brain-body-mind problem is ongoing and one way of attempting to understand it is to try and describe consciousness in terms of material particles and fields interacting between inputs, internal states, and outputs without any intrinsic meaning. Terms such as “feeling”, “intention”, “knowing” and “choice” are thus not viewed as primary causal factors of consciousness, but a byproduct of these blind interactions.

Quantum physics has not been at the forefront to attempt to describe consciousness as the neurocomputational model of laterally connected input layers of the brain’s neurocomputational architecture is viewed as the most credible explanation for consciousness. One problem that quantum mechanics face is the effect of quantum decoherence (The Role of Decoherence in Quantum Mechanics) and failures to measure it. Essentially, quantum states are believed to be too sensitive and fragile to disruption by thermal energy to affect the macroscopic nature of proteins and other macromolecular structures.

The Penrose-Hameroff orchestrated objective reduction (orch. OR) model provides a basis to connect consciousness with quantum mechanics. Microtubules are integral in this theory.

Connecting quantum mechanics, aromatic ring pi-bonds, protein formation, microtubules and consciousness.

The “quantum physics” and “aromatic ring pi bond” connection.
An aromatic (aromaticity) compound is composed of a conjugated planar ring system with delocalized pi electron clouds. Benzene is an example of an aromatic compound (Figure 1). In benzene (and other aromatic compounds) the double bonds are shorter than the single bonds, causing the carbon atoms to be pulled and pushed between two states and thus vibrate between two states (Figure 2). The pi electrons are also delocalized above and below the carbon ring (Figure 1). Aromatic compounds are thus described to be resonating and are best described quantum mechanically.

The “aromatic ring pi bond” and “protein formation” connection.
4 amino acids contain aromatic rings: tyrosine, phenylalanine, tryptophan and histidine (Figure 3). Histidine, however has 6 delocalized electrons but not a benzene ring and is hydrophilic (more polar).

When peptide chains fold to form proteins, the structure is stabilized and dynamically regulated in the intracellular aqueous phase. Polar side groups face outwardly and react with the polar aqueous milieu, while non-polar regions face inwardly (Protein folding). Aromatic amino acids are more non-polar and thus coalesce more readily in the centre of a protein. When aromatic amino acids coalesce it allows London force van der Waals interactions between the non-polar electron clouds of the aromatic rings, causing quantum resonation of the coalesced non-polar aromatic rings (Figure 4).

« Last Edit: December 09, 2008, 23:13:16 PM by Mechanist » Logged
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« Reply #1 on: December 09, 2008, 18:34:59 PM »

Continued:

The “protein formation” and “microtubule” connection.
Microtubules are long, hollow, cylindrical, filamentous, tube-shaped protein polymers consisting of alpha and beta tubulin dimers and form part of the cytoskeleton (Figure 5, Figure 6, Figure 7). Microtubules play important roles in cell signaling, cell division and mitosis, vesicle and mitochondrial transport and play crucial roles in the development and maintenance of cells and cell shape. Microtubules are highly dynamic cytoskeletal fibres and are capable of two types of dynamics:
1) Treadmilling and
2) Dynamic instability
Microtubules polymerize (rescue/elongate) at the positive (+) end and depolymerize (catastrophe/shorten) at the negative (-) end. During treadmilling, polymerization and depolymerization occur at equal rates and thus the microtubules do not change in length but changes position 4-dimensionally.
During dynamic instability, either the (+) end polymerizes quicker than the (-) end can depolymerize resulting in total elongation of the microtubule, or the (-) end depolmerizes quicker than the (+) end can polymerize resulting in total shortening of the microtubule. In the Inner Life of the Cell video this behavior can be witnessed at time approx 1.07-1.11min (rescue) and 1.11-1-15 (catastrophe).

Figure 8 shows the structure of the alpha- and beta-tubulin dimers and the prevalence of  aromatic amino acids (1sa0.pdb). At a higher resolution (Figure 9) it is clear that the aromatic amino acids are close enough to each other (< 2nM) to allow for London van der Waals (Figure 10) interactions. When tubulins polymerize during dynamic instability (rescue) they form tube-like structures (Figure 7). Quantum level resonance as a result of quantum level dipole oscillations (London van der Waals forces) within hydrophobic pockets result in functional protein vibrations which depend on quantum effects (Figure 11). The quantum effect on a single tubulin protein conformation is superposed and exists in both states simultaneously and acts as a qubit (as in quantum computer). Thus, the elegant formation of microtubules (Figure 7  and Figure 12) can in theory constitute  a quantum computer (more detail).

The “microtubule” and “consciousness” connection.
Microtubules extend throughout dendrites and axons (neural cells) and play crucial roles in controlling synaptic strengths responsible for learning and cognitive functions through mechanical signaling, communication as well as cytoskeletal scaffolding (cell movement).

In a nutshell, the Penrose-Hameroff orch OR model proposes that quantum effects are relayed through pi-bonds in hydrophobic pockets within microtubules to the macroscopic structure of the brain, resulting in consciousness. Microtubules are thus viewed as protein quantum computers.

Off course the detail of this model is much more in depth and the following documents and web pages illustrates it beautifully. Enjoy!!!

1) Quantum consciousness
2) The Brain Is Both Neurocomputer and Quantum Computer
3) That's life! The geometry of pi electron resonance clouds.
4) Quantum computation in brain microtubules? The Penrose-Hameroff "Orch OR" model of consciousness
5) Microtubules - Nature's Quantum Computers?
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« Reply #2 on: December 10, 2008, 10:44:06 AM »

Hello, and welcome to the forum, Mechanist.

There are several grave problems with and gaps in Roger Penrose’s ideas concerning consciousness.

Basically, he posits that wave function collapse, i.e. the generation in a quantum system of one definite state from a superposition of all possible ones (potentially infinite in number) as contained in the system’s wave function, is precipitated by a quantum gravity effect that exceeds a certain threshold, which somehow then accounts for consciousness but it is unclear how.

There are three major problems with the model.  Firstly, the question of how wave function collapse is triggered and how it proceeds physically is shrouded in mystery.  We have yet to construct a valid model for it, let alone a scientific theory thereof.  The proposed consciousness model is critically dependent on this component and since our knowledge about it is very limited, the proposed consciousness model remains questionable.

Secondly, after many decades of concerted effort, we still haven’t succeeded in tying Quantum Mechanics and General Relativity together into a coherent unified field theory.  Thus, Penrose’s proposal of a quantum gravitational effect above a certain threshold is itself at this stage pure conjecture, as is its supposed ability to bring about (spontaneous) wave function collapse.  Added to our abovementioned lack of knowledge about the wave function collapse process itself, it becomes clear that we have severely limited theoretical grounds for accepting the model as credible.  Moreover, since we are tapping in the dark about wave function collapse, it is hard to see how the model could be tested empirically, even in principle.

Thirdly, we have no adequate model of consciousness mostly because we have no clear idea of what it might be physically.  So once again the link between quantum effects and consciousness is at best tenuous.

In summary, the Penrose/Hameroff model is highly speculative and contentious, it has many problems that detract from its plausibility, and very few quantum physicists find it convincing.  That doesn’t mean that it is false (Penrose is after all a well-respected mathematician who has collaborated with Stephen Hawking, no less), only that it would be premature to accept it before the problems and gaps have been properly addressed.

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« Reply #3 on: December 10, 2008, 12:07:25 PM »

Hi Anacoluthon64,

Thank you for your comments. I agree there are problems with the model, however, whether they are grave I would argue remains to be tested.

1) From what I understand, Penrose posits that the wave function is fundamentally unstable and spontaneously collapses due to an objective (intrinsic) feature of space-time reality/geometry. The model depends on this feature, whether it is testable or even verifiable is in question (like you said). If it is a grave problem for this model remains to be seen.

2) Do you think Loop quantum gravity and the attempt at a Hamiltonian formulation of general relativity has potential, or is String theory more plausible. My knowledge is limited with regards to the mathematical aspect, but I am willing to learn.
 
3) While there is no model for consciousness, materialistic explanations do seem to have grave problems. Some are of the opinion that consciousness is a fatal problem for materialism. This paper argues at length the strengths and weaknesses of materialistic explanations. Type-F monism and type-D dualism are compatible with the Penrose-Hamerhoff model.

The Penrose-Hamerhoff model does have some serious problems, I don't think it should be discarded though. Evidence of quantum computation through quantum coherence in photosynthetic systems have been described.

For example:
Nature;Vol 446;12 April 2007: Quantum path to photosynthesis
Quote
Elsewhere in this issue, Engel et al. (page 782) take a close look at how nature, in the form of the green sulphur bacterium Chlorobium tepidum, manages to transfer and trap light’s energy so effectively. The key might be a clever quantum computation built into the photosynthetic algorithm.

Quote
The process is analogous to Grover’s algorithm in quantum computing, which has been proved to provide the fastest possible search of an unsorted information database.


And in this article: Nature;Vol 446;12 April 2007: Evidence for wavelike energy transfer through quantum coherence in photosynthetic systems.
Quote
When viewed in this way, the system is essentially performing a single quantum computation, sensing many states simultaneously and selecting the correct answer, as indicated by the efficiency of the energy transfer.


Quantum theory as it stands is incomplete with regards to the collapse of isolated quantum superpositions. Whether the solution is compatible with this model remains to be seen I guess.
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« Reply #4 on: December 10, 2008, 14:46:16 PM »

Six questions regarding the model:
(1) Explain why no one else has as yet succeeded in constructing a viable quantum gravity/GR formulation.
Because it is a fundamental problem in contemporary physics today. Whether the solution is compatible with the model remains to be seen.

(2) Give the field equations for your quantum gravity formulation and the assumptions that led to that particular gauge field.
I can't, and doubt anyone can at present.

(3) Show how those field equations contain something that will, through application of an appropriate operator, produce effects that can reasonably be thought of as consciousness – in other words, give a physical account of the observables in your system and how they or a subset thereof can be construed as consciousness.
No one exactly knows what consciousness is or how to describe it. Field equations to describe consciousness at present do not exist.

(4) Explain why no one else properly understands either what wavefunction collapse actually is or what the physics are behind its production, and give a physical interpretation of how it is actually produced by the application of the aforesaid (Hermitian) operator(s).
The reason why no-one properly understand what wave function collapse is, is because it is still a fundamental problem in quantum physics.


(5) Give a sufficiently complete mathematical model of consciousness and show how the model coheres with your field equations and the necessary operator(s) that produce conscious states.
Consciousness needs to be understood (and clearly defined), and in order for it to be understood in the Penrose-Hamerhoff model, an understanding of the collapse of the wave-function is needed.

(6) Explain why no one else knows what consciousness actually is and why the Penrose-Hameroff orch OR model is any different from a model that goes in essence, “abracadabra, come forth ye quanta! Hey presto, consciousness!”
Is there any model at present that doesn't need an "abracadabra", and is a plausible model for consciousness? Consciousness is an open question, and no clear, coherent explanation for it exists at present.

The Penrose-Hamerhoff model is just another model.
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« Reply #5 on: December 10, 2008, 22:14:11 PM »

It seems that you are underestimating or perhaps misunderstanding the severity of the three problems I have pointed out.  Each one on its own is already an obstacle separately from the others to begin with merely because each one introduces some important unknowns on which the entire model’s validity is critically dependent.  If, for example, a valid quantum gravity theory shows that wave function collapse is not complementary to some inherent property of a quantum spacetime field, i.e. it is not consistent with Penrose’s suggestion, the model will clearly need revision from the ground up.  And so it is with each of the others too.  In combination, such failures would be devastating.  But all three will need satisfactory resolution first.

The subsequent post with your list of six questions actually makes the point.  Those questions encapsulate the most immediate problems with the model and in each case one must presently confess a lack of knowledge.  Nor is it clear that solving them will sustain the model.  Your conclusion that the “Penrose-Hamerhoff model is just another model” is fairly accurate but I feel that it overstates the case somewhat because there’s a tendency to pin more hope on it than is warranted, given the extent and severity of its unresolved difficulties.  When something says “quantum” many people pay attention simply because the term excites their sense of mystery and the unknown, not because it really clears anything up for them.

As for string theory, I’m reasonably sure that it has just about run its course.  It has been quite unsuccessful and much of a dead end but that’s how science often advances.  Something new is required, probably a deeper insight or a different take.  I’m sure you’ll be aware of how intensely the problem is being worked on.

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« Reply #6 on: December 13, 2008, 02:03:15 AM »

This is an interesting discussion.  I personally don't think that our understanding of consciousness requires quantum mechanics (for the sake of filling the gap in our knowledge).  But before I go any further, I don't know if we are all talking about consciousness in the same sense (unless I am misunderstanding the posts).  Consciousness has varied meanings in specific situations - intuitively I get what you're trying to say but it is in the ambiguity that explanations can dodge closer scrutiny.  I can't remember where I read it, but the various views of consciousness were explained as follows:

  • not knocked-out, as in "he regained consciousness in the ICU" - I am sure we are not talking about this aspect of the word, but I had to mention it.
  • the internal dialogue of "conscious thoughts" - the thoughts that run through your head, even the thoughts you experience as you read this, are experienced as language
  • the sense of me being "conscious of the world" - the controller in the control room interacting with the world
  • the non-automatic thoughts where I "consciously contemplate the way to solve the problem" - we actively think about what we must buy from the shop on the way home but we do not actively think about the muscle manipulation required to unlock a door or to climb a flight of stairs

You may say that the last three are all piecemeal descriptions of the same thing, the same consciousness we are talking about, but I think that they are all separate and have been confused by our familiarity with the word we use for all four different experiences.

But why do I mention this?  Just to confuse the discussion?  No.  I think that our understanding of consciousness will come from the various breakthroughs that psychologists have made in describing the necessary components which form part of the four aspects above (individually). 

For example: Cognitive Linguistics is a field in psychology (that I take great interest in) that describes the mental cognitions involved with all aspects of language, like grammar, the mental lexicon, linguistic categorisation and so on.  One concept in Cognitive Linguistics posits that once language is acquired by a being, mental thoughts in that language naturally follow.  The sense of self that we naturally talk to becomes more "complete" as more language is acquired.

As for the sense of me who is acting as a controller in a control room, monitoring the world and deciding on a next move, it is largely an illusion anyway, more a case of us watching a constant instant replay rather than experiencing the world and making decisions.  How do we construct the whole complete image?  Well, if we look at it this way perhaps we get a better answer ... How could any organism live without such a coordinated sensory perception?  If we could only hear or see at any one time without being able to do both we would be at a disadvantage.  A coordinated view is a survival trait and a more accurate coordinated view is an even better survival trait.  Our view of the world is not perfect and can easily be fooled (optical illusions, etcetera) so using this as part of a description of the consciousness we are discussing introduces new problems.

What I'm really trying to get at is if consciousness (as a unification of all the pieces of consciousness) is real at all or a naturally emergent property of the delusions our mind creates.

So where do I think consciousness (the pieces) come from ultimately?  How can the firing of neurons make me think I'm an individual?  To me it's an example of Langton's Ant at work.  Yes, I know, you can explain almost anything with the Ant if you think about it, but really, in this case I think that the analogy is very helpful to our understanding.

What is Langton's Ant?
Langton's Ant is a demonstration that simple algorithms can have unpredictable results.  Imagine a world which consists of nothing but white squares; there is one white square and on all sides white squares extend on towards infinity.  A really boring, really massive chess board.  In this square at the source (there is no middle for an infinitely large chessboard, that's why I mentioned a single white square at the beginning) there is a programmed ant.  This programmed ant has a simple list of instructions:
1) Move forward to the square in front of you
2) If you arrive at a white square, turn right
3) If you arrive at a black square, turn left
4) Change the colour of the square you are in from black to white or vice versa
5) Go to step 1.

The instructions are extremely basic.  Looking at them we imagine that the ant will turn a circle and arrive at the source and turn a circle in the opposite direction and head back towards the source and continue to make symmetrical patterns of this sort.  But when we run the simulation, that is not what happens.  After about 470 steps it seems to stop making symmetrical patterns and start making random-looking patterns and most bizarrely, after about ten thousand steps it builds a "highway", a long wide repeating pattern which (it is presumed) continues on to infinity.  But why?  Why does it do these weird things especially seeing as we did not program the ant to do anything like that?  Even more bizarrely, you can't stop the ant from making a highway.  You can put three, eight or even fifty ants at random locations and even though they run into each other while following their instructions (they come to a black square that should have been white) they will eventually build the highway but it will take more steps to get there (only very few configurations end in stalemate where two ants build a pattern, hit each other coming the other way and go back and delete the entire pattern, reach the start and then build the same pattern, then delete it and so on). Even if you "pollute" the universe, place hundreds of randomly placed black squares, the ant cannot be stopped, it will still build a highway (in a different place).

If neurons are given simple reactionary instructions to follow, how can they build a consciousness?

But beware, this is not a kind of "I'll throw my hands up and say; 'That's a good enough explanation'" mentality that I'm promoting, it is rather that the emergent properties are not always predictable at the lowest level.  I would love to learn more about consciousness, I just don't think replacing one unknown for another unknown will be an adequate solution.

James
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« Reply #7 on: July 01, 2009, 22:17:53 PM »

It seems that you are underestimating or perhaps misunderstanding the severity of the three problems I have pointed out.  Each one on its own is already an obstacle separately from the others to begin with merely because each one introduces some important unknowns on which the entire model’s validity is critically dependent.  If, for example, a valid quantum gravity theory shows that wave function collapse is not complementary to some inherent property of a quantum spacetime field, i.e. it is not consistent with Penrose’s suggestion, the model will clearly need revision from the ground up.  And so it is with each of the others too.  In combination, such failures would be devastating.  But all three will need satisfactory resolution first.
Even if so, these arguments pose no fatal problem for the model, and at present are nothing more than arguments from ignorance.

A few recent findings and articles of interest.
The “conscious pilot”—dendritic synchrony moves through the brain to mediate consciousness
Abstract:
Quote
Cognitive brain functions including sensory processing and control of behavior are understood as “neurocomputation” in axonal–dendritic synaptic networks of “integrate-and-fire” neurons. Cognitive neurocomputation with consciousness is accompanied by 30- to 90-Hz gamma synchrony electroencephalography (EEG), and non-conscious neurocomputation is not. Gamma synchrony EEG derives largely from neuronal groups linked by dendritic–dendritic gap junctions, forming transient syncytia (“dendritic webs”) in input/integration layers oriented sideways to axonal–dendritic neurocomputational flow. As gap junctions open and close, a gamma-synchronized dendritic web can rapidly change topology and move through the brain as a spatiotemporal envelope performing collective integration and volitional choices correlating with consciousness. The “conscious pilot” is a metaphorical description for a mobile gamma-synchronized dendritic web as vehicle for a conscious agent/pilot which experiences and assumes control of otherwise non-conscious auto-pilot neurocomputation.

Good explanation (ppt file)

Are quantum states too sensitive and fragile to disruption by thermal energy to affect the macroscopic nature of proteins and other macromolecular structures.

Maybe not:
Coherent Intrachain Energy Migration in a Conjugated Polymer at Room Temperature
Quote
Our results show that quantum transport effects occur at ambient temperature along conjugated polymer chains. We conclude that chemical bonds connecting chromophores, such as in polymers, macromolecules, and supramolecular systems, play an important role in introducing quantum effects in EET dynamics. This observation extends the paradigm of protein-protected coherences proposed by Fleming and co-workers to chemically bonded chromophores in nanoscale materials at ambient temperatures. In the case of conjugated polymers, this phenomenon may assist formation of the semiconductor band character of the electronic states.


First Evidence of Entanglement in Photosynthesis
Quote
Room-temperature entanglement seems to be a by-product of the process of harvesting light. Physicists are fascinated with entanglement, the strange quantum phenomenon in which distinct objects share the same existence, regardless of the distance between them. But in their quest to study and exploit entanglement for information processing, physicists have found it fragile and easily destroyed. This fragility seems to severely limits how entanglement might ever be used.

But a new, more robust face of entanglement is beginning to emerge from other types of experiment. For example, physicists have recently found the signature of entanglement in the thermal states of bulk materials at low temperatures. This has huge implications for biological systems: if entanglement is more robust than we thought, what role might it play in living things?

Now we're beginning to find out. In the first rigorous quantification of entanglement in a biological system, an answer is beginning to emerge. Researchers from various institutions in Berkeley California have shown that molecules taking part in photosynthesis can remain entangled even at ordinary atmospheric temperatures.

The evidence comes from detailed study of light sensitive molecules called chromophore that harvest light in photosynthesis.

Various studies have shown that in light harvesting complexes, chromophores can share coherently delocalised electronic states. K. Birgitta Whaley at the Berkeley Center for Quantum Information and Computation and pals say this can only happen if the chromophores are entangled.

They point out that these molecules do not seem to exploit entanglement. Instead, its presence is just a consequence of the electronic coherence.

This is a big claim that relies somewhat on circumstantial evidence. It'll be important to get confirmation of these idea before they can become mainstream.

Nevertheless, if correct, the discovery has huge implications. For a start, biologists could tap into this entanglement to make much more accurate measurement of what goes on inside molecules during photosynthesis using to the various techniques of quantum metrology that physicists have developed.

More exciting still, is the possibility that these molecules could be used for quantum information processing at room temperature. Imagine photosynthetic quantum computers!

And beyond that is the question that Whaley and co avoid altogether. If entanglement plays a role in photosynthesis, then why not in other important biological organs too? Anybody think of an organ where entanglement might be useful?

Ref: arxiv.org/abs/0905.3787: Quantum Entanglement in Photosynthetic Light Harvesting Complexes


And another interesting article:
A quantum mechanical model of adaptive mutation
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« Reply #8 on: July 02, 2009, 20:53:58 PM »

Even if so, these arguments pose no fatal problem for the model…
It seems you don’t understand the severity of the objections.  Yes, each one on its own very much could be fatal.  Have you any idea how many papers in number theory begin with the phrase, “Assuming the Riemann Hypothesis to be true, …” or some variant thereof?  If tomorrow someone finds just one counterexample to the Riemann Hypothesis, most of these papers will become instantly pretty much worthless, and the possibility of a counterexample cannot be ruled out.  Many of those papers are deeply intriguing – but no less speculative for it.

… and at present are nothing more than arguments from ignorance.
The whole quantum-consciousness model is one big argument from ignorance!  That’s the point.  It cannot even be called an “hypothesis” yet because it lacks any rigorous formulation.  We don’t have a quantum gravity model, let alone any coherent account of consciousness, and therefore we can’t even begin to speak of testable consequences.  At present, it is no more than an interesting bauble, and to base any kind of scientific explanation on it is severely to overstep what the scientific method permits.

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« Reply #9 on: August 19, 2009, 09:41:50 AM »

Some apologists think there is a way God could intervene in the world by manipulating quantum events; others think quantum mechanics can explain free will and consciousness, allow for a unified cosmic consciousness, and even allow us to create our own reality. Stenger shows that such speculations are based on wildly inaccurate misappropriations and misunderstandings of the concepts of advanced physics.
(My emphasis.)

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« Reply #10 on: September 07, 2009, 00:29:11 AM »

Terms such as “feeling”, “intention”, “knowing” and “choice” are thus not viewed as primary causal factors of consciousness, but a byproduct of these blind interactions.
Since this sentence was generated by your consciousness is the sentence itself thus a product of blind interactions? And if so why should we then believe the sentence.
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« Reply #11 on: September 07, 2009, 14:31:12 PM »

Why are we proposing Quantum computing when the ordinary kind does the trick?
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« Reply #12 on: September 07, 2009, 15:46:49 PM »

Why are we proposing Quantum computing when the ordinary kind does the trick?
Because certain instances of a special class of computational problems called “BQP” lend themselves to what is in effect massively parallel, non-deterministic processing.  Put simply, that’s like letting billions of blindingly fast networked computers loose at the same time on a particular problem — except that there’s a price to pay for the number and speed of those computers: each of them only produces a correct result with a certain probability (hence “non-deterministic”), sometimes spitting out garbage.  By comparing the results of all of these individual “dodgy” computers, the correct answer can be found very quickly and with a high degree of certainty.

(More here.)

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« Reply #13 on: September 08, 2009, 12:38:02 PM »

Why are we proposing Quantum computing when the ordinary kind does the trick?
Because certain instances of a special class of computational problems called “BQP” lend themselves to what is in effect massively parallel, non-deterministic processing.  Put simply, that’s like letting billions of blindingly fast networked computers loose at the same time on a particular problem — except that there’s a price to pay for the number and speed of those computers: each of them only produces a correct result with a certain probability (hence “non-deterministic”), sometimes spitting out garbage.  By comparing the results of all of these individual “dodgy” computers, the correct answer can be found very quickly and with a high degree of certainty.

(More here.)

'Luthon64


I wouldn't argue that human brains don't have a tendency to sometimes spit out garbage, but how quickly and accurately do we actually solve these BQP problems? Wouldn't ordinary deterministic computing provide sufficient explanation for our somewhat limited abilities? Does proposing a quantum brain offer any explanatory value?
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« Reply #14 on: September 08, 2009, 18:31:44 PM »

I wouldn't argue that human brains don't have a tendency to sometimes spit out garbage…
True enough, but quantum computing is more akin to individual neurons occasionally firing haphazardly, rather than the whole brain going off the rails.  As long as some majority (above a certain threshold) of the neurons fire in concert, the brain will produce a definite answer (or so neuroscientists are currently inclined to believe).  The correctness of the answer will depend on several other factors which can be loosely grouped under the heading “inputs.”

… but how quickly and accurately do we actually solve these BQP problems?
Theoretically, a quantum computer would solve certain general instances (NB! not all of them) of BQP (and P) problems very, very fast – much faster than even the most powerful modern supercomputers and superclusters that presently are capable of speeds in the order of ten teraflops.  However, there are some tricky technical problems to overcome first before quantum computing becomes a reality.  Execution time on a quantum computer will grow sub-linearly with desired accuracy.

Wouldn't ordinary deterministic computing provide sufficient explanation for our somewhat limited abilities?
It seems unlikely.  If it was so, we would probably be able to simulate a human brain fairly decently, which is something we still cannot do.  Moreover, the brain can exhibit problem solving behaviour that is outside the P complexity class.  For example, often when you solve a crossword and are looking for the answer to a particularly vexing clue, you don’t systematically run through all the possibilities, although naturally you’ll try a few.  The answer, when it comes, suddenly pops clearly into your head and is almost instantly recognised.

Does proposing a quantum brain offer any explanatory value?
Not at present but it may do one day, although it does seem rather unlikely.  Consciousness is an essential dimension of a functioning human brain but nobody knows what consciousness is.  The squabble in this thread is over just this crucial issue:  the complete QM-consciousness model is still a wild guess because it is missing several key ingredients.  It is scientific only insofar that some aspects of it can be tested, at least theoretically, but the essential difficulty of how QM effects produce brain activity (and/or consciousness) remains entirely obscure and a matter of considerable speculation.  Also, a large part of the problem is that “quantum” has in many quarters (especially in New Age ones) become the next Supremely Transcendent Universal Principle of Ignorant Deduction (STUPID), much like god/gods was/were in the past: “I don’t quite know how this works, so it must be quantum.  Hallelujah!”

'Luthon64
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