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mattbrowne's avatar

Fate and destiny reconsidered - How sensitive are neurons in our brain to quantum effects?

Asked by mattbrowne (31719points) February 6th, 2010

During an existing Fluther debate I ran into this issue. I discovered a question in a different forum

where Iamu asked and wrote the following:

How sensitive are neurons and chemical receptors like olfactory receptors to the chemicals that stimulate them? Can a single molecule stimulate a nerve? I ask because I’m curious as to whether or not human thought and behavior is generally sensitive to random quantum effects. If a single photon could stimulate a rod, or a single molecule of a neurotransmitter could cause a neuron to fire, then our behavior might be truly random, because it would depend on truly random quantum events, but if it takes thousands of photons or thousands of molecules of a neurotransmitter, I figure our behavior would probably be governed by more-or-less deterministic classical physics.

There are only 2 answers and here’s an excerpt:

Membrane potential is constantly fluctuating due to random openings and closing of ion channels and the like. Mini synaptic events also occur stochastically probably due to quantum fluctuations (...). Randomness is not the same as free will. I’m not sure anyone has a particularly satisfying answer as to how “free will” gets into a neural system classical or not.

Keep in mind that biological systems are very noisy and often the cell employs a variety of mechanisms to cope with that noise. Even though single photon/molecule sensitivity of sensory neurons would lead to stochastic fluctuation in the signals going to the brain, the brain may have evolved control systems to deal with those fluctuations.

I wonder what our Fluther pundits have to say about this matter. Can physics prove that fate is impossible in our universe (let’s not look at the multiverse implications for the time being)? Computers are equipped with extra redundancy to deal with quantum uncertainty. Does it work the same with with our brains?

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29 Answers

HTDC's avatar

This may be the wrong place to ask. Us jellies are smart but I don’t know many quantum physics professors here. Good question though.

talljasperman's avatar

a famous scientist once said…“God does not play dice”..I think It was Einstien

ragingloli's avatar

Either way, it is bad news for “free will”. If the influence of quantum randomness is minimal, then thought processes and thus our actions are deterministic, thus negating free will.
If the influence of quantum randomness is substantial, it introduces a level of unpredictability and more importantly, uncontrollability to the system, thus negating free will as well.

ninjacolin's avatar

^ exactly true.

random != free will.

if a single proton could stimulate a rod, then random quantum events are to blame for our behavior. not “you” or “I.”

ninjacolin's avatar

the argument against free will from quantum uncertainty is a fallacy. utterly ineloquently, here’s why:

ultimately, atomic behavior is uncertain
therefore, we have free will to do what we please.

clearly false. if atomic behavior is uncertain, then you have no certainty about whether you can do what you want since you may randomly (against your will) start wanting to do something else. hence, you have no control over “Yourself.”

mattbrowne's avatar

@ninjacolin – I agree, the free will question requires different answers, like how much control does the conscious mind have over the unconscious one which might make the decisions for us. When we refer to ourselves, do we just mean the conscious mind? Let’s take the knee-jerk reflex reacting to a hammer. Did we do it? Did our knees do it?

But our unconscious mind also depends on neurons.

FireMadeFlesh's avatar

I’m quite sure I am disagreeing with my previous posts on the matter, but this is what I think is most likely the case.

I don’t think quantum fluctuations have a significant direct effect on neurons, as it takes a cascade to activate a signal. The resting potential the average neuron is around -70mV, which obviously involves a rather large ion imbalance. When the neuron is activated, the depolarisation phase can peak at a potential of +30mV. . So for a neuron to stimulate another neuron, forgetting the interplay and summation effects that are sometimes required, a PD of around 0.1V is required. The ions involved are sodium and potassium, each with a charge of 1+, so if this occurs in one tenth of a second (I’m not sure of the space of time) then around 6.2×10^16 ions are involved in the discharge. Therefore quantum effects can do little to affect the stimulation of a neuron.

Even taking into account Chaos Theory, quantum effects only ever amount to noise, which should not have much of an effect on the system considering the huge numbers involved above. I am still a firm believer in free will, but that seems to be almost a side issue in this discussion. Thought is not random, and the human brain is not susceptible to error introduced from the inherent randomness of the universe. Natural selection would quickly take care of any organism that had a significant degree of completely random behaviour.

Free will, I believe, is a result of the network patterns within the brain. I’m not exactly sure how this would occur, but I cannot abandon the idea of freedom of choice on philosophical grounds. I’ve got Daniel Dennett’s Consciousness Explained on order – hopefully that can shed some light on the issue.

FireMadeFlesh's avatar

When we are considering free will, the important question is why it would exist. While I am not sure where the burden of proof lies on this issue (clarification please?), it seems to me that the vast majority of rules are human constructs. The universe tends to favour freedom and endless possibilities.

I like to consider a chimpanzee as a microcosm of human thought. If a chimp is hungry, it will endeavour to find food as per its instinct. If it is about to become food, then it will focus its efforts on escape and worry about finding food for itself later. These events are apparently deterministic, yet they are extremely complex. Some individuals may have the presence of mind to feign strength to win a mind game over the attacker. Others may run or fight, while still more will freeze in fear and be eaten. Natural selection cannot provide an answer to these options, because there is no answer that is consistently advantageous. The chimp must have evolved the ability to make a decision as to which approach to use. Therefore natural selection would favour the existence of free will, if it is at all possible for it to exist.

dpworkin's avatar

A photon can stimulate a rod, but not above the response threshold. That takes about 10 photons, but since the effect is cumulative if the rods are bundled, it need not be one rod. You could have one photon on each of ten rods and get signal, depending, of course, upon the ambient stimulus level. This assumes zero.

mattbrowne's avatar

@FireMadeFlesh – Thanks for your detailed and insightful answer. One question: Are you familiar with the implications of Libet’s experiments?

In short they tell us that something makes a decision for us before we know that we are making this decision. There’s also a controversy about conscious veto power overruling decisions made unconsciously.

mattbrowne's avatar

@dpworkin – Quantum uncertainly does make a difference even when several particles are involved. So it’s not always about one photon or ion doing this or that. Three ions could make a difference making the neuron fire in 1 out of 8 cases. For 10 photons all having the same effect it’s only 1 out of 1024. But given enough time this will happen eventually. Much larger numbers are required to label it virtually impossible. Like nuclear fusion at the core of our Sun requiring quantum tunneling of protons.

What is the likelihood if the Sun interrupting nuclear fusion for one second?

It’s not zero. Will this ever happen? Very unlikely during a period of only 10 billion years.

FireMadeFlesh's avatar

@mattbrowne I was not aware of these experiments. I will look at it in more detail later its 2am here and I start work in 5 hours, but it seems that the experiments mentioned miss out on a few key factors. Subjects would have decided on entering the test to carry out the instructions of researchers without question. This may eliminate at least a large portion of the decision making process. If I were to approach a stranger on the street and ask them to press a button, the stranger would likely consider this request before acting. The response may be a creased forehead, or asking why or what the button’s function was. These experiments do not seem to take into account the ability of an intelligent human to anticipate the instruction, and make a free will based decision prior to the instruction being given.

Cruiser's avatar

Interesting thought Matt, but a single molecule, atom or whatever pinging your brain may have some effect but IMO no more so than a pebble hitting your windshield when you are driving on the highway. Too much going on in the brain for a single anything as a random event to have much of an overriding affect or influence on what your brain has already got going on, plus the brain and the rest of our bodies are already well adapted to the constant bombardment of particles every millisecond of the day.

dpworkin's avatar

Besides, as I mentioned before, you have the threshold problem. Everything below threshold is interpreted as noise, and never gets processed.

mattbrowne's avatar

Do you accept the single neuron trigger?

ninjacolin's avatar

oops, i meant the argument against determinism from uncertainty is a fallacy

ninjacolin's avatar

the burden of proof lies with free will.
it’s basic to imagine that before there was life, everything was deterministic from the formation of planets and solar systems to tectonics and everything else. so, why would life’s forming not also be determinisitic? if all the animals are determinisitic, why wouldn’t humans be also?

free will presupposes that man is more special than the rest of the universe in our ability to choose. but there’s no reason to believe that we have this ability.

dpworkin's avatar

Single or multiple, the stimulus has to be above threshold or the neuron doesn’t fire.

FireMadeFlesh's avatar

@ninjacolin What makes you think the formation of planets etc. is deterministic? Doesn’t Chaos Theory preclude that option?

ragingloli's avatar

No. Chaos Theory is about deterministic systems that are so complex and sensitive to initial conditions that it becomes almost impossible for us to predict outcomes. This is also known as the butterfly effect. It has nothing to do with randomness.

dpworkin's avatar

In fact, without Chaos there would be no Emergence, and emergence is rather orderly.

ninjacolin's avatar

@FireMadeFlesh, True chaos does not exist.

If there was True Chaos nothing would be able to form. You would try to build a house and it would turn into a Lemur. You would try to tell your boss, but your legs would turn into water. And when your boss got mad about things not going his way, he would drown the night sky with carrots.

That’s what chaos would be like. We don’t experience that. Instead, we have a pretty stable universe that goes about whatever it’s doing in a very orderly way.

Chaos theory, as has been said, speaks only to our limitations as human observers.

FireMadeFlesh's avatar

Chaos theory is, as @ragingloli pointed out, about systems that are so complex and sensitive to initial conditions that predictions have a very small limit of accuracy. It does not introduce any random factors of its own, but it does greatly magnify the effect of existing sources of probability. Since quantum fluctuations were far more influential in the past, and are responsible for the non-uniformity of the universe following the Big Bang, is it really fair to assume that the formation of planets a few hundred million years later was totally immune to the effects of these?

ninjacolin's avatar

immune? why would they be immune? they are the products of.

ragingloli's avatar

Because quantum randomness does not necessarily translate from the quantum scale to the subatomic or atomic scale.
When we have a stable hydrogen atom we can reasonably predict based on the laws of physics that it still will be a stable hydrogen atom 5 minutes , 5 hours, or 5 years from now. It does not suddenly turn into a subatomic cloud of quarks without any cohesion.
In the same way we can expect gravity to apply all throughout history, that hydrogen clouds become denser because of gravity and pull in more hydrogen and eventually become stars, which then proceed to create the heavier elements which are then accumulated into planets, asteroids, comets, etc. We can predict this to happen in that way, and we have not seen any thing else, because the universe, throughout its history, apparently was immune to, or rather unhindered by these quantum randomness effects.

FireMadeFlesh's avatar

@ragingloli I never suggested that a hydrogen atom would suddenly disintegrate into a subatomic cloud of quarks. A hydrogen atom, as with all matter on the quantum scale, is never at a precise point in space. Rather, it is spread out in a probability wave. Therefore quantum probability introduces a certain amount of randomness into the location of the atom, which when amplified by Chaos Theory could determine the location of the bodies that form from the gravitational collapse of the matter. The location of these bodies would then influence their features, such as temperature and rate of geological change. The matter would always condense into stars and planets, but it did not have to form the exact stars and planets that it did with the exact composition that it did.

ninjacolin's avatar

“The matter would always condense into stars and planets, but it did not have to form the exact stars and planets that it did with the exact composition that it did.”

according to the evidence, this statement is false.

FireMadeFlesh's avatar

@ninjacolin Can you please provide a link?

ninjacolin's avatar

certainly, have a peek: link

you’ll notice that to the best of our knowledge, it couldn’t be any other way. ;)

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