This question was prompted by a thread in the philosophy sub-forum concerning free will. A couple of us were discussing quantum uncertainty and the scale at which it becomes significant. I thought that contributors to this sub-forum would be able to help. So do quantum phenomena affect matter appreciably on the scale of neurons? What about the scale of molecules? Are our brain processes deterministic, random, or somewhere in between?
i would have to say that everything is affected by quantum events. all actions and reactions are quantum events, though in great numbers. the reason we view them as deterministic is because we can only see them as a collective--we are looking at the big picture because we can't see the individual photons that make up that picture.
there is no randomness, only probability and the mosaic appearance of determinism. i think free will is another abstract concept defined only in the human mind; like god and love and morality. its something that can only be explained subjectively.
Quantum uncertainty shouldn't be significant on the scale of neurons, so I'd go for deterministic. It's a good thing too - we wouldn't get very far if there were no structure to our mental processes.
Somebody please correct me if I'm wrong, but I vaguely remember reading an article about brain cells and that they have microtubules (spelling) in them that are small enough to be sensitive to quantum events. I don't remember any real details though, have to google for it.
but i think of it like this; every event--the very existence of the atoms that compose a neuron--is dependent on a quantum probability. their state at any given moment is a composite of the quantum events occuring at that specific point in space/time. so it is very significant. each quantum event is a molecule of paint on a painting. but all we see is the painting. the structure we experience is because one quantum even follows another--at least in the state of space we are in.
Individual quantum event effects disappear statistically, ie on a scale where statistical numbers of similar events turn probabilities into frequencies. I don't think free will is necessarily mutually exclusive with determinism.
Determinism usually means that if one specific starting state a transitions to another state b, then the same starting state a will transition to b in another "run", too. Can you tell I'm a computer scientist?
There is an ancient debate about whether the universe contains a basically unlimited number of future possibilities regardless of the present circumstances, or whether every future outcome is already rigidly determined and free will is impossible and is an illusion. Determinism, to many who have studied the issue, is devoid of any free will. My question is, is the rigid definition being used, or, some kind of a semi determinism?
There is a form of semi-determinism that tries to get the two sides to come together and be friends. I can't exactly remember the reasoning now, though. It did sort of make sense I think. Shame I don't have my books here :\
Hi Laika, Let me first address the issue of the brain. Many people have proposed a connection between quantum theory and the functioning of the brain. Generally these people are crackpots with little or no appreciation of the actual physical processes, and in my opinion they generally have an ulterior motive. There is no good evidence of any sensible connection. One person whom I respect very much and who has proposed such a connection is Roger Penrose. Penrose is not generally a crackpot (though I think he does have an ulterior motive), and he has thought very deeply about such things. Nevertheless, his proposal appears to be flawed for a very simple reason: the brain is not operating near 0 Kelvin. In technical language, the decoherence time for neurons is far far far too short for quantum effects to be important. Penrose and Hameroff (his collaborator) have since responded, but their arguments are unconvincing. This is not to say that the atoms and molecules are not governed by quantum theory, they are, but simply that we have found nothing in the higher functioning of the brain that requires a direct quantum mechanical mechanism. Determinism in quantum theory is another story, but I don't have time right now.
I have to agree in part with Physics Monkey, and disagree in part. The signal impulses carried along the neurons have them acting very much like metallic wires in purposes and mode, and the number of electrons involved is so large for any one signal, that it would swamp a quantum effect that might otherwise alter the on/off information of the signal being transmitted along the length of the neuron. However, at the synapses (where two neurons join together), the signal is transmitted by chemical molecules (acetylcholine and cholinesterase, as I recall) that physically 'drift' to bridge the gap between the neurons, carrying the signal forward. At that juncture, if enough molecules are affected, the signal is transmitted. If not enough molecules are affected, the signal stops. Accordingly, since there are a finite number of molecules involved, there could in rare instances be a point at which the determination as to whether the signal is transmitted (on or off conveyed forward) is determined by as little as a single molecule (the proverbial straw that breaks the camel's back). Thus, at that juncture, I could conceive that if that single molecule were just barely close enough, but maybe not quite close enough, to transmit the signal, then perhaps a quantum effect would be applicable to make such 'determination'. As to whether that has anything to do with what we perceive as 'consciousness' I have no idea. However, this reminds me of a question I once posed to a Vice Consul (Boris Lifanov) of the former Soviet Union, stationed at the USSR (CCCP) consulate in San Francisco in 1975, who was formerly an electrical engineer prior to 1975. "What property of the electron is it that allows an electron to become aware of its existence?", speaking in reference to the electrons inside of a brain.
I have to disagree; it is practically inconceivable that quantum effects could be important for the motion of even a single molecule. Acetylcholine is quite small by biological standards, but it still has a mass of 146 amu. A simple order of magnitude estimate for the thermal de Broglie wavelength puts it at about 10^-10 cm! This is much smaller than the size of a single Hydrogen atom (~ 10^-8 cm). Quantum effects are therefore completely negligible, and the motion of the molecule can be modeled perfectly well with a classical approach. Cholinesterase is massive enzyme which catalyzes hydrolysis of acetylcholine (if I recall correctly) and is even more overtly classical. It is simple estimates of this kind (plus the complete lack of any positive evidence) which speak so strongly against possible connections.
You misinterpret my hypothesis. First, you are correct that those are both large molecules, and the one is the enzyme (cholinesterase) that converts the other back and forth. If the on/off signal is being transferred by that last molecule of acetylcholine (the 'close-case'), at it has reached its point of being catalyzed, whether it actually gets catalyzed (and transmits the signal) is a chemical reaction involving the outermost electron orbitals of both molecules. The only point I'm making is that sometimes it could go either way, and that that is the 'quantum effect' that could conceivably be at play. Like I said, whether that has anything to do with 'consciousness' is anyones guess. Others have pondered on this in greater depth than I, and that is where they came up with the microtubules theory referenced by Maast, brifely mentioned below. I checked a web site of an anethesiologist from Arizona (they like studying consciousness, of course), and he indicated that Masst is correct, namely that there are microtubules involved in neurological signals, and that conceivably in the interior of such 'nanotubes' a quantum-effect might also take place. I don't know enough about that to weigh in on it, but at least Maast had a good memory on the topic! I googled on arizona, anesthesiology, and microtubules, and got his web site again at: www.quantumconsciousness.
Certainly the chemical properties of molecules are quantum mechanical in origin. Nevertheless, one simply models the changes in concentrations of molecules with differential equations. This is the sort of thing one learns in basic chemistry. If the concentrations are low then stochastic differential equations may be employed. If the well stirred approximation fails then one may combine diffusion equations with rate equations, and so on and so forth. There is nothing quantum mechanical about this description, and furthermore, this is not the sort of thing that Penrose and Hameroff have in mind anyway. What they is want is quantum mechanical superposition in various biological structures in order that the brain may be regarded as a quantum computer. The website you linked to is none other than Hameroff's site, and it should be viewed with due caution. It's quite the clear that the website is meant to be propaganda. For example, Hameroff says, "However computation alone cannot explain why we have feelings and awareness, an "inner life."," but he has no idea if this is true! Further down he claims the laws of quantum mechanics are paradoxical which is absolutely false. They may be classically counter-intuitive, but they are not paradoxical. Furthermore, quantum mechanics does not claim that particles can be in two places at once, and it does not say time does not exist! His comment about particles being "connected over distance" is at best a misrepresentation of EPR type experiments. My original criticism stands: where is the evidence? The Orch OR model was found to be physically nonsensical by Tegmark Phys. Rev. E 61, 4194 (2000). Hameroff's response is totally unconvincing. We are talking about science here, so the only real reason why Hameroff's idea is nonsense is simply because there is no evidence for it and substantial evidence against it.
I agree that Hameroff does not make his case in his web site. I posted it primarily to show that Maast had a good memory in having read something about 'microtubules', which is the theory expounded upon by Hameroff. However, not making one's case, and not providing evidence to support one's supposition is not exactly the same thing as nonsense. Hameroff does have some of his statements regarding quantum physics wrong, as noted by Physics Monkey, so yes, his site is certainly not a reliable 'proof' and referring to it as 'propaganda' is probably not an exaggeration. He's likely simply posting his web page to stimulate thought and discussion along certain lines and to promote a certain 'cause', which is what propaganda does. Obviously the topic has some interest for Physics Monkey, as he's been reading more extensivley in the area (Tegmark, Phys. Rev. E. 61, 4194, year 2000) than have I. As to using equations developed for systems of molecules on the order of 1E20, when one is working with a much smaller system on the order of 1E2 molecules, as suggested by Physics Monkey, is likely going to result in problems. That's where we disagree, apparently. I'm simply suggesting that if one has only a few molecules drifting across a synapse to trigger the continuation of a signal, there might come a time when it is so close that the statistical likelihood of swamping the quantum effect, as when dealing with large numbers of electrons transmitting the signal along the neuron, could result in a situation in which it's literally the proverbial 'toss of a coin' as to whether or not the signal is transmitted. At that juncture, the quantum effect could come into play. But again, whether or not it does is currently anyone's conjecture, and I see no easy way to prove it, or to assert that it has anything to do with 'consciousness', 'soul', or any of the other esoteric terms people use to describe humans and their behaviour.
My thanks to everybody for your input. Zephyr, No! Randomness does not equate to free will (in my humble opinion, of course). Magic Chicken, I'm interested to hear how you believe you can reconcile free will with determinism (though perhaps not in the physics & math forum). Physics Monkey and Walter L. Wagner, I've enjoyed following your dialogue very much. So... the fact that the fundamental 'units' of thought, having such insignificant de Broglie wavelengths, are effectively beyond the influence of quantum effects seems to suggest that our brains are deterministic after all. Is that fair to say? Roger Penrose's view has never seemed very much like science to me (not that I'm particularly well versed in the details, mind you). I think even 'speculation' might be too kind a term. Rather, it seems more like a weak justification of a belief. I'm sure I'm being unfair, however. The question of how subjective consciousness arises from dumb matter is, of course, a huge one (as Duendy loves to remind us - "the Hard Problem!"). I won't attempt to address is here.
