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Re: [Phys-l] zero width?



I don't know if this is a paradox. However, I think the problem is two definitions of line. Mine is what one sees when a chalk is moved against the board; it has width. The other is the edge. It is an abstraction, like the Euclidean line, which has no width. However, unless specified as an abstraction, I "go with" those who point out the edge even at zero K (another abstraction) is ill defined. So only if one is "being mathematical", OK.

bc, willing to be corrected

p.s. I understood in a dispersive medium (all media are dispersive?) pulses can not have sharp edges.

Brian Whatcott wrote:

At 02:02 PM 10/16/2007, Moses, you wrote:

...I think there
is a real physical object with the zero-width boundary. This is a
leading edge (wave-front) of any real perturbation. According to the
Sommerfeld-Brillouin theorem, it always propagates with the invariant
speed. If we have a laser pulse that can be used as a signal,
then it has sharply-defined front with no precursor. The corresponding
wave-function is exactly zero ahead of the pulse and non-zero in the
region of the pulse. The corresponding shape must be described by a
function that is non-analytic - there has to be a discontinuity
starting from derivative of a certain order....





Moses Fayngold,
NJIT



This sounds very like the thought about modeling the magnitude of
the acceleration when an object, any object, that was stationary,
begins to move.



Brian Whatcott Altus OK Eureka!
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