[asa] Brain and Determinism

From: David Clounch <david.clounch@gmail.com>
Date: Wed Sep 30 2009 - 23:25:22 EDT


I am reading Polkinghorne and Beale's 51 Questions book (Title is Questions
of Truth, Fifty-one responses to Questions about God, Science, and Belief).
I almost immediately went to the Appendices first because of the way they
approach the subject. In appendix B there is a section called Clocks and
Clouds, the idea being the universe sometimes behaves like a clock, and
sometimes behaves like a cloud.
I'd like to share a bit of this:

 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
world elsewhere, exact determinism is dead. 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 Wed Sep 30 23:26:21 2009

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