Re: Where can I find information about emergent properties?

I am not in a position to give you any very specific leads. The two areas 
to look at are:

(1) There are a lot of publications (well, a few, anyway!) in the 
specialist Philosophy of Science area. Emergent properties raise some very 
interesting philosophical issues, and there have been several attempts at 
analyzing the basis of these properties at a philosophical/metaphysical 
level.

(2) There are relevant publications in the area of 'Systems Analysis'. 
Systems Analysis seems (from my external and nodding acquaintance) to be a 
field with a bit of a split personality. A lot of it is about computer 
organization and computer networks, and is very specialized and specific. 
But there is also a much broader discipline to do with the way that 
assemblies of various sorts of components operate. It seems to be mostly 
tackled by Engineers and Mathematicians.

Apart from these two areas where emergent properties are examined and 
discussed as such, I am not aware of any general discussions of emergent 
properties, but there is a lot of stuff about individual and specific 
emergent properties. To take just one example for starters, the whole of 
statistical thermodynamics is about trying to calculate bulk properties of 
materials from the known or assumed properties of their microscopic atoms 
and molecules.

I will conclude this answer with a couple of examples to illustrate just 
what we mean by 'emergent properties' to make sure that we are on the same 
wavelength, and that third parties reading our correspondence will be in 
the picture.

Example 1: The behaviour of traffic.

Traffic is just a group of motor vehicles, operating in an environment 
consisting of a road surface, some weather conditions, and possibly some 
road rules and flow control devices. You can analyze any of these 
components as thoroughly as you want to, but you will not be able to 
predict the behaviour of a phenomenon like a traffic jam/motorway snarl/
gridlock (paying due homage to local variants of the English language) from 
the behaviour of any of the components, or even the interaction of simple 
combinations of them. The way that the traffic gets blocked and then 
possibly manages to start to clear itself again cannot easily be related to 
the way a motor or a braking system or a speed limit works. It is only by 
putting a complex simulation of a large number of vehicles and their 
operating environment together that we can get any sort of model of the 
situation.

Example 2: Metals.

There is a set of properties by which we know and recognize certain 
substances as metals. It is not a clear-cut category -- there are 
borderline cases. But there is a characteristic set of physical properties 
that goes with being a metal:
Metals are opaque, with a lustrous surface when clean.
Metals are good conductors of heat and electricity.
Solid metals are somewhat plastic -- they can be beaten into thin sheets, 
or drawn into wires.

Many metals (silver, gold, copper, lead, zinc) are simple substances, made 
up of only one type of atom. Others are alloys of different elements 
(steel, brass, bronze, pewter). So we say that gold, silver, lead, etc. are 
'metallic elements'. 

But there is no sense in which an atom of a metallic element shows any of 
the distinctive properties of the metal. The opacity and lustre of a metal 
can only be seen when at least tens of thousands of metallic atoms get 
together. Bulk conductivity of heat or electricity is not expressed until 
we have layers 50 or 100 atoms thick -- quite a different set of phenomena 
governs the transfer of heat or current over shorter distances. And you 
need a cluster of about 20 or 30 atoms to define a condensed phase, a much 
larger number to decide whether it is solid or liquid, and a larger number 
still to determine whether there is plasticity in the behaviour of the 
solid.

All of the characteristic properties of metals are emergent properties of a 
large cluster of atoms of a metallic element. They are in no sense 
properties of the metallic atoms themselves.