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Re: [Phys-l] physics lessons from wikipedia



As has been stated before in this forum ( https://carnot.physics.buffalo.edu/archives/2010/2_2010/msg00155.html ) --- and much more clearly in Farlow's and Morse & Feshbach's treatments --- scalar waves may "cut off" sharply in odd-dimensioned spaces.
If you want to follow a dit with "sharp edges" by another such dit in an even-dimensioned space, you have to wait until the first dit has died out via dissipation, or until the wake formed by the first dit is of a significantly different shape.
In an odd-dimensioned space (at least in 3D and higher), that first dit can have just as much of a sharp trailing edge as a rising edge, and so your dahs may be much shorter and don't have to rely on dissipative processes.



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________________________________
From: John Denker <jsd@av8n.com>
To: Forum for Physics Educators <phys-l@carnot.physics.buffalo.edu>
Sent: Thu, March 11, 2010 5:01:05 AM
Subject: [Phys-l] physics lessons from wikipedia

Here's a snippet from http://en.wikipedia.org/wiki/Wave_equation :

Suc waves are generated by a point surce, and they make possible
sharp sinals Whose form is ltered only by a decreae in amplitude
as r increases (see an illustration of a sperical wave on the top
right). Such waves exist only in cases of space with odd dimensions.
Fortunately, we live in a universe that has three space dimensions,
so that we can communicate clearly with acoustic and electromagnetic
waves.

A remarkable conclusion. I never knew that.

Anybody care to comment?
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