NetNews Usenet Archive 1992 #16/NN_1992_16.iso/spool/sci/physics/11727

Internet Message Format | 1992-07-27 | 1.9 KB

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From: [e-mail] (Victor V. Gurarie)
Newsgroups: sci.physics
Subject: Re: The Modern Physicist in Calculus I
Message-ID: <[e-mail]>
Date: 27 Jul 92 16:39:35 GMT
References: <[e-mail]>
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In article <[e-mail]> [e-mail] (Mcinnes B T (Dr)) writes:
>TA: And here we have the graph of y = 1/x, x>0. As you can readily
>verify, this is a perfectly well-behaved, continuous, indeed, infinitely
>differentiable function on the open set (0, infinity).
>Modern Physicist [excitedly] Clearly, we have here a SINGULARITY!
>y=infinity at x=0. This is totally unacceptable!
>TA: As I said, the domain is an open set. x=0 is excluded. There is
>nothing remarkable about that.
>MP: Nonsense! Next thing you'll be saying that there is nothing
>remarkable about the SINGULARITY at the beginning of the Universe! Then
>you will try to tell us that time is defined on an open set, and that
>there is nothing remarkable about that either!
>TA: Quite.
>MP: No! Everybody knows that the prediction about the singularity shows
>that "GR contains the seeds of its own destruction" [tm]. And now I
>begin to suspect that the graph of y = 1/x proves that freshman calculus
>also contains the seeds of its own destruction......
>
>Moral: Time is defined on an open set. Spacetime has no singularities.


   What a nonsense all that is! Look at this: if y=1/x, x belongs to
(0,infinity), then for any M there exist epsilon such that for all x
less than epsilon (and still belonging to the set) y(x)>M. This is a
singularity. The writer of the posting above should refresh his knowledge
of freshman calculus!