Re: [asa] Brain and Determinism (fwd)

From: Bill Powers <wjp@swcp.com>
Date: Thu Oct 01 2009 - 17:03:57 EDT

Forwarded to ASA on behalf of Merv:

I will happily reply here as best I can, exposing my own ignorance when it comes
to Planck lengths or quantum uncertainties -- and hoping that then some of the
real physicists can step in and clarify for both of us. Here goes...

Regarding ontological vs. epistemological uncertainties first: I think I
understand your confusion on this since it is the same confusion I am emerging
from. I used to think that the Heisenberg uncertainty principle was no more
than a statement of a limitation on what we could find out about a small
particle. I.e. Any instrument will affect what it is measuring -- a
thermometer slightly changes the temperature of a liquid, a volt-meter will
slightly alter the circuit in which it is connected to get its voltage reading,
etc. So that's easy! (I used to think.) The electron can still be in a precise
place, have its simultaneously precise velocity and all, and we just aren't able
to measure those things since any instrument would massively affect the
particle. So I was able to preserve my notion of ontological determinism by
thinking "*In principle* the electron does have a precise location and velocity
--even if we can never know both with infinite precision." (and come to think
of it, we could never know anything with infinite precision anyway.) But our
lack of knowledge doesn't make it not so any more than my lack of knowledge
about where you are right now would make your location be indeterminate. But
physicists come along and tell me "not so fast!" Actually, the uncertainty
principle runs deeper and informs us that the electron's simultaneous position
and velocity are indeterminate *even in reality*. I.e. there are no
simultaneously precise values to known *even in principle*! Not even by God.
This is what apparently defeats the notion of ontological determinism even
though I can't wrap my mind around it. It is philosophically a much different
and more bizarre ball game than merely saying "we can't know it."

Regarding Planck lengths, I too would love to know more about this. But from
what I've gathered it represents a "smallest possible" increment in space that
would be astronomically smaller than a proton. (Probably having to do with how
far light could travel in a Planck instant). It is apparently the smallest
"unit?" of length anything could actually have. To my already fried
imagination, this has the effect of "digitizing" space. Just as we can
recognize the digitized and pixelated graphics of an object "moving" across a
computer screen, now I imagine a pixelated space where things "lurch along" from
one Planck length to the next without being able to exist in between. How this
fits with classical Newtonian notions of momentum or inertia I would love for
somebody else to explain to me. A digitized motion where something is pausing
at a new quantized location on your screen for 1/30 of a second before it is
instantaneously relocated to the next position is not at all the same as
"continuous" motion where inertia is preserved. But if Planck lengths and times
are ontologically accurate descriptions of reality, maybe there is no such thing
as "continuous" motion? George, ... somebody? ..... help!

--Merv

Quoting Bill Powers <wjp@swcp.com>:

> Merv & David:
>
> A few comments.
>
> First, I don't understand the seemingly discontinuous comment about the
> Planck length.
>
> Second, I don't follow the argument. It seems to me that from beginning
> to end they are discussing epistemological uncertainty and not
> ontological uncertainty. In fact, it seems to me that the Heisenberg
> uncertainty can be similarly interpreted.
>
> Since I don't consider the Heisenberg uncertainty to really get at the
> matter (it can be viewed as merely the result of not attempting to
> measure an eigenvalue), consider instead something like the decay of a
> radioactive nucleus.
>
> We are told that if one were to ask why this particular nucleus decayed
> at this instance that the "appropriate" answer is that there is no
> reason. Yet, we are also told that the statistical decay of a host of
> such atoms has such a small variance that we can make extremely accurate
> atomic clocks from them.
>
> The situation is analogous to tossing an honest penny. If one were to
> try to predict whether this penny on this toss would be a head or a
> tail, our knowledge would be completely uncertain. All we could say is
> that it will be either a head or a tail. And this is why we in Bayesian
> fashion say that the result is 50-50, a measure of complete ignorance.
> Yet, were we to toss 10^23 such coins we could predict with
> extraordinary accuracy the fraction of coins that are heads and the
> fraction that are tails.
>
> In this analogical story would we say that there was no reason that the
> flip of a single coin came up heads? I don't think so. Such a story
> was well known long befor QM came along, and no one was led to argue
> that we live in a random universe. Well, maybe not no one. It was
> probably a common belief prior to the advent of modern science.
>
> I know that what I'm suggesting seems to lead to hidden variables. I've
> just never quite understood the claim that we live in a random universe,
> which appears to imply what?
>
> Is a random universe that is unpredictable? That's epistemological.
> Ontologically, it must mean something like events occur for no reason
> whatsoever, and yet they are statistically deterministic. This appears
> to me, at least, to be a paradox. Does ontological randomness entail
> that events occur without any antecedent conditions, not just
> unobservable, but none whatsoever. Even with the pennies there are
> antecedent condtions: the penny must be tossed.
>
> In summary, I don't get Polkinghorne's argument. Please, explain.
>
> thanks,
>
> bill
>
> On Thu,
> 1 Oct 2009,
> mrb22667@kansas.net wrote:
>
>> My comments injected below...
>>
>> Quoting David Clounch <david.clounch@gmail.com>:
>>
>>>
>>> Polkinghorne and Beale write about determinism and the
>>> brain1<#sdfootnote1sym>
>>>
>>>
>>> Consider a single nitrogen molecule in the air you are now breathing. On
>>> average it is traveling 450 m/s and bounces off about 7 billion other air
>>> molecules every second, thus 7,000 every microsecond. Suppose you knew
> the
>>> exact position and momentum of every one of these particles (even though
>>> this is impossible by Heisenberg's uncertainty principle), then perhaps
> you
>>> could, at least in principle, predict exactly where that nitrogen
> molecule
>>> would be one microsecond later. Of course there are all kinds of
>>> complications, such as electrostatic forces, angular momentum, and so on,
>>> but lets make it simple and pretend that these were all perfect spheres
> and
>>> Newton's laws exactly applied €“ the kind of eighteenth-century
> worldview
>>> that shaped the Enlightenment and still influences much of our thinking.
> But
>>> suppose a tiny error is introduced in the angle at which this air
> molecule
>>> is traveling, for any reason at all. A little bit of uncertainty about
> the
>>> position of an electron, say. Call this error (epsilon). After one
>>> collision, the error is 2 ; after two collisions 4 , and so forth.
>>> Each
>>> microsecond this error will increase by 2^7000, or roughly 10^2100. The
>>> situation is clearly hopeless even if the initial error corresponds to a
>>> Planck length (1.6 x 10 ^ -35 m €“ the smallest possible length, at
> which
>>> conventional physics breaks down) per meter, after just 97 collisions the
>>> uncertainty will be enough for the position of the molecule to be out by
>>> more than the diameter of a nitrogen molecule (6.2 x 10^-10m), which
> means
>>> it will miss the 98th target. This will happen in less than a 70th of a
>>> microsecond. And making the error one Planck length in the size of the
>>> observable universe (about 3 x 10 ^23 m) just means it will miss the
>>> 176thmolecule. So even with the unrealistic assumptions of a perfect
>>> Newtonian
>>> world elsewhere, exact determinism is dead.
>>
>> It isn't the error amplification (chaos theory) that kills determinism.
> Because
>> the original 18th century thought assumed up front that such knowledge was
>> impossible anyway, they had already premised their speculation as being so
> *in
>> principle* since they knew nobody could know all this. And that caveat
> allows
>> them (and us now even with Chaos theory) to reduce the initial state error
> *in
>> principle* to zero (infinitely smaller than a Planck length). So it is
> only the
>> Heisenberg uncertainty as mentioned below that actually drives the real
> stake
>> into the heart of determinism. Yet for all this, it doesn't prevent some
> from
>> still thinking deterministically about the universe as a strictly causal
> domain.
>> Since my mind can't fully fathom the nature of our ontological uncertainty,
> I
>> find myself in this deterministically minded camp at least every other
> Thursday.
>> Maybe the atoms in my brain will happen to bounce that way today.
>>
>> --Merv
>>
>>> In fact, of course, we use
>>> statistical mechanics to describe the behavior of gases and liquids and
> do
>>> not try to predict the behavior of individual small molecules. But many
>>> people think of the indeterminacy in statistical mechanics as simply a
>>> limitation on our knowledge rather than a reflection of real
> indeterminacy
>>> as in the quantum world. This kind of argument strongly suggests, to our
>>> satisfaction at least, that in cases like the movement of molecules in
> air
>>> the indeterminacy is real.
>>>
>>>
>>> They go on to describe calcium ions in te synapses in the brain, and use
> a
>>> similar analysis. They conclude:
>>>
>>>
>>> We will see later that this entirely destroys the idea that the brain is
> a
>>> fully deterministic system.
>>>
>>>
>>>
>>> 1 <#sdfootnote1anc>Questions of Truth, pp. 126-127
>>>
>>
>>
>>
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Received on Thu Oct 1 17:06:15 2009

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