Posted by
Russell Standish on
URL: http://friam.383.s1.nabble.com/Emergence-and-explanation-tp3187993p3245111.html
On Thu, Jul 09, 2009 at 09:11:28AM -0700, glen e. p. ropella wrote:
> Thus spake russell standish circa 07/08/2009 05:33 PM:
> > On Wed, Jul 08, 2009 at 10:16:55AM -0700, glen e. p. ropella wrote:
> >> Well, since my post consisted of questions, I could hardly be wrong. ;-)
> >>
> >> The question was: Is there any identifiable property of a system that is
> >> NOT an emergent property, regardless of how one defines "system"? If
> >> anyone knows of one, please name it!
> >
> > Absolutely! The positions of the particles in a Newtonian n-body system
> > are not emergent. Of course there are other properties of these
> > systems that are emergent, but position & momenta of the particles are
> > not amongst them, being part of the basic vocabulary of the model.
>
> Excellent! Thanks Russell.
>
> However, I claim that the positions and momenta (note the plural) of the
> individual components are not properties of the _system_. Those are
> properties of the individual components. A systemic property related to
> those component properties might be a centroid or cumulative (averaged,
> summed, etc.) momentum for the system as a whole.
Is not the vector of positions and momenta a systemic property? It
precisely defines the state of the system.
>
> Of course, the position or momentum of an individual particle is a
> systemic property of the system that constitutes that single particle (a
> system of quarks, say).
>
> The question then becomes, is a centroid or cumulative measure of a
> system of particles "emergent"? Or are the position and momentum of a
> system of quarks "emergent"?
>
I would agree with you that the centre of mass, and the summed momenta
are emergent properties, however - they are what Bedau calls "resultant
emergent", the very weakest, and least interesting of emergent phenomena.
WRT quarks - in the Standard Model, protons and neutrons _are_
emergent, and properties such as their positions and momenta are
emergent.
But in something like Bohr's hydrogen model, the nucleus is a point
particle, so the position of the nucleus is not an emergent property.
Maybe you're wondering why I keep banging on about models - the point
is that emergence is always relative to a model. It has nothing to do
with real systems (except in as much as the models are good
descriptions of the system). In fact I would tend to go further an
claim that the concept of a "real system" is actually flawed, but that
is a whole other debate, as emergence has nothing to do with "real
systems", whether or not real systems really exist.
> --
> glen e. p. ropella, 971-222-9095,
http://agent-based-modeling.com>
>
>
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