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Re: Energy

At 09:38 AM 9/18/01 -0400, David Bowman wrote:

.... if the model has the property being evaluated in a non-local
manner, or if it is not continuously extensive, then that property does
*not* flow for that particular model.

I certainly agree that non-local interactions are fatal to flow!

An example of such a model is for
a classical system of N classical Newtonian particles (e.g. a planetary
system or a galactic cluster) interacting via only their mutual
Newtonian gravitation.

There is more detail here than necessary. Newton's approximate description
of gravitation involves action at a distance. It's not local. It's energy
doesn't flow. That's how you know it's unphysical.

Real physical gravitation does not involve action at a distance. The
interaction is mediated by gravitational waves. They flow, carrying
energy. So in real physics, the energy flows. No exceptions.

[much detail snipped]
For such a system the system's energy does *not* flow in any useful sense
of the word.

It's not the physical system that has lost the energy-flow property. Only
the unphysical approximation of the system has lost it.

So, in a nutshell, whether or not energy flows depends on just what the
system is and how it is modeled.

Sure, if we allow the word "system" to include unphysical systems. If we
restrict it to physical systems then it is always safe to say that the
energy flows.