X-Message-Number: 27574
Date: Sat,  4 Feb 2006 16:49:34 -0500
Subject: Mythbusting 102
From: <>


>> Unfortunately on the way it melted and all the  water spilled 
into the atlantic. I used your definition to explain to him he need 
only look out at the breakers to admire my statue. <<

Did you actually understand my definition? At some point during the 
melting of the ice sculpture, and certainly when nothing remained 
but a pool of water, the predicate 'P(x) = x is an ice sculpture of 
a Nordic beauty' ceased being true, and the statue stopped existing.

You can do better than this, Peter. I know you can.

>> c) Being in jail I found myself with time on my hands so I 
studied  physics and discovered there are no infinitely continuous 
functions  observable by humans. <<

The definition I gave used the criterion of infinite continuity 
because no one knows yet whether space is quantized (the only thing 
we know is you can't measure distances beyond a certain scale). 
It's not required but it's much cleaner than an alternative 
definition that assumes the discretness of spacetime.

>> Similarly any gas may be regarded as a quantum and molecular 
computer, consisting of quatrillions of atoms, impracticable to 
simulate. And yet Avogadro's Hypothesis enables us to simulate 
gases in calculations with a pencil and a piece of paper. <<

And if by simulating a brain, you mean predict short-term 
macroscopic observables (such as, how long it would take your brain 
to cool to room temperature if it were ripped from your skull by an 
axe-wielding Pomeranian), then yes, we can 'simulate' a brain, in 
the same way we can 'simulate' a gas.

You are engaging in prevarication and I think we both know it.

>> A convincing argument against the existence of phenomes. Plainly 
 neither you nor I exist; "we" require the interpretation of genome 
and proteome, and interpolation of that interpretation across 
billions of interacting cells. <<

We are lumps of matter. Lumps of matter don't require the 
subjective interpretation of a conscious mind to exist. We're like 
rocks, which simply exist---unlike the upside-down, bearded 
grandfather in a puff of clouds that a kid sees, who, no matter how 
realistically portrayed, exists only in the mind of the kid, and 
does not possess a factual existence of his own (what exists are 
water molecules).

In any case, you engage in two fallacies with the above analogy. I 
can't force myself to believe you don't see them. I think you 
believe you are on the right side, but are more concerned with 
persuading people reading Cryonet than actually saying something 

Believing you're right is dangerous because it means you will use 
any means (fallacious reasoning, ad hominems, etc.) to justify the 
end (converting the masses).

>> A neuron has the function of mapping signals received 
biochemically from its dendrites onto biochemical signals, via the 
axon, to the  dendrites of other cells. Neurons may have a few 
other functions too. <<

Like most people familiar with IT, you like to think of the neuron 
as having N electrical inputs, and 1 electrical output. Nothing 
could be further from the truth. A vast amount of neural 
functionality occurs not through transmission of electrical 
signals, but through biochemistry---chemical interaction between 
neural membrane glycoproteins and binding complexes, for example.

In any case, let me join you in your make-believe and pretend that 
neurons have N electrical inputs, and 1 electrical output. For the 
average neuron, N is about 2000. So in order to model a neuron, all 
we need to do is come up with a black box equation that tells us 
the output of the neuron given each of its inputs.

Sounds simple, eh? Everything does to an armchair engineer---but 
real life is infinitely less tractable.

First, there is the problem of simultaneity. This problem is easier 
understood in a concrete context, so let's take the example of 

The earth exerts a force on the moon, which affects the 
acceleration of the moon; however, the moon also exerts a force on 
the earth, which affects the acceleration of the earth. This leads 
to a problem of infinite recursion: because, for example, the 
acceleration of the moon is going to affect the acceleration of the 
earth, which is in turn going to affect the acceleration of the 
moon again, and so on.

It turns out this problem can be solved for the earth and moon. Add 
another body, however, and you're out of luck (in the general 
case). We can't solve the equations, and can only approximate them; 
with increasing numbers of bodies, our approximations become 
increasingly poor, and because these systems are fundamentally 
chaotic, with enough bodies our best approximations are worthless.

This same problem is everywhere in physics (pretty much anywhere 
you see a differential equation). It's at the lowest levels and the 
highest; quantum, molecular, electrical, astronomical. Simulations 
attempt to sidestep the problem by dividing time into discrete 
units---pretending for that unit of time, one part of the system 
exists in isolation and is not affected by any other part of the 
system. Of course, it's a big fat lie---but a necessary one, as 
without it, we would be unable to do any useful simulation 

What it means, however, is that there is an upper limit to what we 
can know about an N-body system. So even if a neuron can be modeled 
perfectly as a mathematical black box with 2000 electrical inputs, 
and 1 electrical output, we would not be able to perfectly simulate 
more than (say) two of them together. At what point our simulations 
become so grossly inaccurate as to render the result useless, I 
can't say, but until someone can demonstrate otherwise, there's no 
reason to believe that limit is anywhere near ONE TRILLION (which 
is the number of neurons you need to simulate if you want something 
like a human brain).

The second problem is the inherent complexity of mathematically 
modeling an equation with 2000 inputs. Right now we assign each 
input a weight and say the neuron fires if the weighted sum exceeds 
a threshold. If you're not laughing you should be, since the 
complexity of a neuron dwarfs the simplicity of this toy model I've 
just described.

This function with 2000 inputs depends intimately on the state of 
the neuron at that time: the number and position of the billions of 
molecules floating around in the cytoplasm; the position and 
configuration of the millions of microtubules; the genetic 
expression of the neuron; the size, shape, and length of the 
dendrites and axon. I could go on and on, describing all of the 
factors that influence the shape of the 'neural function'; pointing 
out that these are changing with time, and, as with all truly 
interesting problems, are self-dependent. But I won't.

Instead, I'll point you to one of the many available neural 
simulators available on the net (start here, if you're interested: 
http://leenissen.dk/fann/). You want to put your money where your 
mouth is? Then use one of these simulators to produce something 
more than a toy. Hundreds of thousands of researchers and software 
engineers have tried over more than three decades, and you know 
what? Neural networks are still regarded as mere curiosities. A 
blip on the history of computer science.

The burden of proof is on you. You want me to believe, in spite of 
the evidence to the contrary, that neurons can be modeled and 
simulated using neat little mathematical equations? Then knock 
yourself out. Until then, you should acknowledge the fantastical 
nature of your own beliefs (and by 'fantasy', I mean, truly from 
the pages of a fantasy book, and completely and utterly divorced 
from this thing called 'reality' that we live in).

>> If you accept that, let's go ahead and replace one of your 
with our model. Are you still yourself? <<

I have objected only to the idea that neurons can be modeled 
mathematically and simulated on computers at a level necessary to 
support the emergence of human-like intelligence. Don't read more 
into what I say than what I say. You will be wrong.

I don't doubt that it is possible to create artificial structures 
that serve the same functions as biological neurons. I am even open 
to the idea that, should such artificial neurons be based on the 
same principles of operation as biological ones, certain 
configurations of these neurons might be capable of subjective 

Going one step further and supposing artificial neurons could 
interoperate with biological neurons (which implies much more than 
electrical compatibility), I do believe it would be possible to 
upgrade my brain, with my identity preserved (this is implied in 
the definition of identity I laid out some messages ago).

But that is quite a different subject altogether.

Richard B. R.

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