🚀 go-pugleaf

On Sun, 26 Feb 1995, Peter Schmurr wrote:

>  Is the fact that a book rests on a desktop due to electronic repulsion?
>
> Peter

You might have asked another question, preserving the symmetry:

Is the fact that a wire resists stretching due to electronic attraction?

The answer: Yes, and no. It is due to electronic (better, electrostatic)
forces, but not simply repulsion, nor simply attraction, but a combination
of both.

The origin of elastic forces in both situations is due to those
electrostatic forces which hold the atoms of the solid together in
equilibrium, both attraction and repulsion in a neat balance. Disturb the
balance by distorting part of the solid, and the charge disributions
change in such a way as to oppose the force causing the disruption. This
can be done up to a point, then permanent deformation can result.

I recall J. R. Pierce in his book "Symbols, Signals and Noise" making the
point that *if* all the forces involved were linear, matter could
interpenetrate, just as two messages down a transmission line can pass
through the same wire or fiber without disturbing one another. Or two
beams of light can pass through the same region of space without
disturbing each other, even if the space is filled with a linear (to
light) medium. But if the medium is non-linear, or the light intense
enough to force the medium into non-linear response, the signals can be
distorted, and harmonics and beats will appear.

Your subject line, "Why can't matter interpenetrate?" reminds me of
my high school physics book which 'defined' matter as "That which fills
space." Elsewhere in the book space was defined as 'The absence of
matter." That was my first inkling that many high school physics books are
written by idiots. Of course those were the only answers which would be
counted correct on the exams, as I found out.

        -- Donald