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From: meron@cars3.uchicago.edu
Subject: Re: Stapp, PK & Physics Today
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Date: Mon, 14 Aug 1995 21:59:15 GMT
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In article <NEWTNews.808441114.14349.richard.caldwell@oufan.oklaosf.state.ok.us>, Richard Caldwell <richard.caldwell@mhs.oklaosf.state.ok.us> writes:
>
>In article <40o0dn$ki5@csnews.cs.colorado.edu>, <juola@suod.cs.colorado.edu> 
>writes:
> 
>> Standards of evidence of course vary from person to person -- in hard
>> sciences as well as the softer versions.... There's a research group
>> here at CU that's trying to determine whether gravity really does
>> fall off as 1/r^2 and have confirmed that the 2 is accurate to about
>> one part in a billion.  Most of the rest of us use the 2 as though it
>> were completely accurate.
>
>What a joke!  The inverse square law has nothing to do with gravity in 
>particular.  It is a result of the geometry of anything that radiates 
>spherically from a point source.  The surface area of a sphere increases with 
>the square of the radius, so the flux density of anything radiating uniformly 
>from a point source must decrease with the square of the distance from the 
>source.
>
>The only way this could not be true is if something (like gravity) doesn't 
>radiate uniformly in all directions.  This is true when you're very close to a 
>large body of irregular shape and irregular density.  That's why they can use 
>variations in gravimetric readings to predict vocanic eruptions.
>
>Richard

That's not quite that simple.  If you've a force propagated by massive bosons
(i.e. particles with a finite lifetime) the force drops faster than inverse
square, in spite of spherical symmetry.  If you prefer to think in terms of 
field lines and flux, think about a situation in which each field line, instead
of extending indefinitely, has a finite probability per unit length to be
terminated.  Clearly Gauss' Law isn't exactly fulfilled under this 
circumstances.  Better yet, imagine light radiated by a point source in an
absorbing medium.  At any given distance the distribution is spherically
symmetric.  Nevertheless, the intensity drop is faster than inverse square.

Beyond this, I think that the previous poster also has a small misunderstanding.
The statement "the power is 2 to within one part in a billion" doesn't mean "it
is not really 2, but it is close".  What it does mean is "to within the 
accuracy to which we can measure (which happens to be one part in a billion),
we see no contradiction to the claim that the power is 2".  Therefore, it is
misleading to say "Most of the rest of us use the 2 as though it were 
completely accurate".  It is completely accurate, at the moment, to the level to
which we can measure, and that's the most one can ever say about the accuracy
of a physical value.


Mati Meron			| "When you argue with a fool,
meron@cars3.uchicago.edu	|  chances are he is doing just the same"
