My old friend the SINC function (sci.math)
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In article

http://groups.google.nl/group/sci.math/msg/08dff005bdbdeb07?hl=en&

Randy Poe writes:

> Real, physical quantites have uncertainties. That is 
> one of the fundamental properties of physics. And it 
> isn't just due to quantum considerations. Take an 
> average metal bar. It has no exact length, not down 
> to the precision of an atomic width or so. There are 
> temperature fluctuations and small forces from 
> Brownian motion which will cause that bar's length 
> to fluctuate. The atoms themselves are in motion which 
> is another cause of inexactness. 

As Randy describes himself, there are _fluctuations_ of all kind that
will cause x = 0, when conceived as a physical quantity, to fluctuate.
Meaning that x = 0 is actually to be _interpreted_ as x = 0 +/- delta,
where delta is the uncertainity.

But we don't need Randy's argument in order to see that there is kind
of an uncertainity in _every_ realization of the real numbers. Take a
look at the floating point quantities in a digital computer:

0.000000000000000000000000000000123597059137504570... 
|----------------------------||---------------------> oo 
        material                       ideal 

Then, inside the computer at hand, _this_ value of x cannot possibly be 
distinguished from x = 0. But suppose we buy a somewhat better computer
with "extended precision", such that: 

0.000000000000000000000000000000123597059137504570... 
|-------------------------------------||------------> oo 
                 material                  ideal 

Then suddenly the value which was supposedly equal to zero becomes just 
_close_ to 0 instead. We conclude that, in the material world, a real 0
cannot be distinguished from its (supposedly very small) environment.

Now consider an old friend of mine, the function: 

sinc(x) = sin(x)/x for x <> 0 
        = 1        for x = 0 

But NO ! We insist upon our Enduring Freedom and, as _mathematicians_, 
we like to define, instead, the following: 

S(x) = sin(x)/x for x <> 0 
     = 2        for x = 0 

So I have the question: which of the above functions, S(x) or sinc(x),
has an empirical counterpart? Is it possible that S(x) will _ever_ have
an empirical counterpart? Just answer the question, please. Yes or No.

Jean-Claude Arbaut, Jiri Lebl and Randy Poe all have been clever enough
not to give a straight answer to this simple question.

Han de Bruijn