Dear Eckard,
When we consider the approach of the pendulum to the plumb line, the plumb line is definitely in its future. If the plumb line and the arc of the pendulum's swing are divided into n and m parts, respectively, then we can describe the projected position of the pendulum on the plumb line in terms of x/n, as x --> n, and the actual position of the pendulum in terms of y/m, as y --> m.
I think that we can all agree that a "now" moment arrives when x = n and y = m. However, the plumb line is still in the future of the pendulum at this point, since both n and m cannot be points of no spatial extent, but only magnitudes of some extent, ad infinitum. Clearly, we cannot say that the two are coincident, until both 1/n and 1/m --> 0.
Yet, if we are to measure the diminishment of these two remaining units, we have to further sub-divide them into n and m parts, and the process starts over, ad infinitum. Hence, we see that Zeno's paradox is in full force, in this case, even though we know that x --> 0 and y --> 0, eventually.
How do we resolve this paradox? I submit that one way is to transform the remaining y unit into its inverse. Since x is wholly dependent on y, it can serve as a measure of y's transformation into its inverse. When y's transformation is complete, x = 0.
But what is the inverse of y, if not -y? and doesn't x --> 1, in the other "direction," as y --> -y? How, then, does x --> 0 and x --> 1, simultaneously? The only way to resolve this new paradox, as far as I can tell, is to admit that x too has an inverse, namely -x. Consequently, as y --> 0, -y --> 1, simultaneously, and as x --> 0, then -x --> 1, simultaneously.
Such a transformation, in both cases, involves an instant change in "direction," at all "points" along the length of the units. It is only at this boundary between the two, opposite, "directions" that we can consistently define a point of no spatial extent and an instant of no temporal duration.
The physicists describe just such a constant transformation, as the potential energy of position is transformed into its inverse, the kinetic energy of motion and vice-versa. Therefore, this approach not only seems reasonable to me, but exhibits a hint of that unreasonable effectiveness of math in the natural sciences, that Wigner points out.
Warm regards,
Doug