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Topic: Skepticism, mysticism, Jewish mathematics
Replies: 115   Last Post: Aug 7, 2006 1:30 AM

 Messages: [ Previous | Next ]
 Mike Kelly Posts: 344 Registered: 3/30/06
Re: Skepticism, mysticism, Jewish mathematics
Posted: Aug 4, 2006 9:26 AM

R. Srinivasan wrote:
> Mike Kelly wrote:
> > R. Srinivasan wrote:
> > > Mike Kelly wrote:
> > > > R. Srinivasan wrote:
> > > > > Rupert wrote:
> > > > > > R. Srinivasan wrote:
> > > > > > > Rupert wrote:
> > > > > > > > R. Srinivasan wrote:
> > > > > > > > > Rupert wrote:
> > > > > > > > > > R. Srinivasan wrote:
> > > > > > > > > > > Barb Knox wrote:
> > > > > > > > > > > >
> > > > > > > > > > > > Consider that calculus too started out as a half-baked theory laden with
> > > > > > > > > > > > paradoxes, and that one of the great mathematical achievements was to
> > > > > > > > > > > > put it on a rigourous footing. And indeed, set theory was one of the
> > > > > > > > > > > > important tools in that enterprise.

> > > > > > > > > > >
> > > > > > > > > > > The presently accepted foundations of the calculus still does not
> > > > > > > > > > > resolve Zeno's paradoxes.

> > > > > > > > > >
> > > > > > > > > > Why not? What's the paradox?

> > > > > > > > >
> > > > > > > > > The paradox can be stated in two ways. Consider the example of Achilles
> > > > > > > > > chasing the tortoise along a straight line at a constant velocity
> > > > > > > > > higher than that of the tortoise's (constant velocity). The paradox is
> > > > > > > > > that Achilles has to "complete" infinitely many opertaions to catch up
> > > > > > > > > with the torotoise -- from the starting point he sees the tortoise at a
> > > > > > > > > particular location ahead, and he first has to reach that location.
> > > > > > > > > When he reaches, he sees the toroise ahead at another location, and
> > > > > > > > > Achilles has to reach there. And ad infinitum. The Greeks thought that
> > > > > > > > > this was a paradox presumably because they viewed infinity as
> > > > > > > > > "potential", i.e., the infinitely many operations required to reach the
> > > > > > > > > torotoise cannot never be completed in finite time.
> > > > > > > > >

> > > > > > > > > >From the modern point of view the paradox can be stated as follows.
> > > > > > > > > How can infinitely many finite, non-zero, non-inifnitesimal intervals
> > > > > > > > > of reals sum to a finite interval (why isn't the sum infinite)? I..e,
> > > > > > > > > suppose starting from location zero, Achilles first reaches 1/2, then
> > > > > > > > > 3/4, then 7/8,...... Then Achilles covers the distance
> > > > > > > > > 1/2+1/4+1/8.....=1, where he catches up with the tortoise. The paradox
> > > > > > > > > is -- why isn't the sum infinite, given that there are infinitely many
> > > > > > > > > finite, non-zero and non-infinitesimal intervals being summed (assume
> > > > > > > > > we are using some standard version of real analysis).
> > > > > > > > >

> > > > > > > >
> > > > > > > > Well, it just isn't. I don't see any reason why it should be. You
> > > > > > > > haven't shown a contradiction in standard real analysis.

> > > > > > >
> > > > > > >
> > > > > > > That is true. The same can be said of the Banach-Tarski paradox or many
> > > > > > > of the other paradoxes of classical measure theory. But these are
> > > > > > > paradoxes nevertheless, and highly counter-intuitive.
> > > > > > >
> > > > > > > Regards, RS

> > > > > >
> > > > > > Well, they may be counter-intuitive for some people. I agree the
> > > > > > Banach-Tarski paradox is a rather surprising result. But the fact that
> > > > > > the sum of an infinite series of positive numbers can be finite I don't
> > > > > > find counterintuitive at all, myself. Do you really claim to have a
> > > > > > formulation of analysis where this result is avoided? Can you tell me
> > > > > > what it is?

> > > > >
> > > > > Another way to state the paradox is as follows. Consider the infinite
> > > > > series of nested real intervals [-1,1], [-1/2, 1/2], [-1/4,1/4],... The
> > > > > intersection of these intervals contains the single point 0, but *each*
> > > > > of these infinitely many intervals is of non-zero and non-infinitesimal
> > > > > length. So why doesn't their intersection contain infinitely many
> > > > > points?

> > > >
> > > > Because they keep getting smaller, but never "reach" 0????
> > > >

> > >
> > > None of the end-points of the nested intervals ever get "infinitely
> > > close" to 0 either. This seems to *suggest* that the intersection of
> > > these intervals should contain uncountably many points.

> >
> > But the sequence of nested intervals does get "as close as you like" to
> > zero, if you wait long enough. Any point other than zero will be
> > "passed" eventually.

>
> Note carefully the difference between your approach and mine. I am
> considering the *totality* of nested intervals (which classical
> standard real analysis permits) and saying that not one interval in
> this totality has end-points "infinitely close" to zero.

It is not necessary for any interval to have end-points "infinite
close" to zero (whatever that means) to decide what is in the
intersection. You're considering which real numbers are in every one of
the nested intervals. If you pick any real number other than zero, then
some intervals don't contain it, so they aren't in the intersection. So
zero is the only real number in the intersection.

"intersection" has nothing to do with "end-point infinitely close" to
something.

> You are considering a process in time, where you are at a particular
> interval, and then pass on to the next smaller nested interval, and so
> on. If you asked the Greeks, they would have probably told you that
> this infinite process of sub-diviision can never be "completed" and
> you will "always" be an interval's length away from zero. Whereas you
> have assumed that you can somehow complete this process, and after
> completion, only the point zero is never passed. That precisely is the

No, no I don't think I assume you can complete an infinite process. I
just said that for any real number other than zero, there is some
interval that doesn't include it. This doesn't require sequentially
consideration of, or completion of, anything.

> > > > >Again you may not find this counter-intuitive, but many do.
> > > >
> > > > How many?

> > >
> > > I have seen this paradox crop up from time to time. Probably mainstream
> > > mathematicians are no longer bothered by these kinds of issues. Maybe
> > > some philosophers and philosophically inclined logicians?

> >
> > I don't understand why this is a paradox. Not trying to be patronising
> > or belittling, I just don't understand what the root of the conceptual
> > difficulty is here.

>
> Think about what I have stated above. Hope my explanation is clear.

--
mike.

Date Subject Author
7/25/06 David Petry
7/25/06 fishfry
7/25/06 Dr. David Kirkby
7/25/06 Dr. David Kirkby
7/25/06 lloyd
7/25/06 Doug Schwarz
7/25/06 Virgil
7/26/06 Mike Kelly
7/26/06 David Petry
7/26/06 Gene Ward Smith
7/26/06 Brian Quincy Hutchings
7/26/06 dkfjdklj@yahoo.com
7/26/06 herbzet
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7/26/06 Gerry Myerson
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7/30/06 zr
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7/30/06 T.H. Ray
7/31/06 Brian Quincy Hutchings
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8/1/06 Brian Quincy Hutchings
8/1/06 David R Tribble
7/30/06 Gene Ward Smith
7/30/06 Ioannis
7/30/06 Dr. David Kirkby
7/30/06 zr
7/30/06 Dave Rusin
8/1/06 David Bernier
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8/2/06 Ioannis
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8/2/06 R. Srinivasan
8/3/06 Rupert
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8/4/06 Rupert
8/4/06 R. Srinivasan
8/4/06 Rupert
8/4/06 R. Srinivasan
8/4/06 Mike Kelly
8/4/06 R. Srinivasan
8/4/06 Mike Kelly
8/4/06 R. Srinivasan
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8/4/06 Mike Kelly
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8/4/06 herbzet@cox.net
8/4/06 R. Srinivasan
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8/4/06 Brian Quincy Hutchings
8/7/06 R. Srinivasan
8/4/06 Mike Kelly
8/5/06 R. Srinivasan
7/28/06 herbzet
7/28/06 Gene Ward Smith
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7/26/06 Gene Ward Smith
7/26/06 T.H. Ray
7/26/06 toni.lassila@gmail.com
7/26/06 Bennett Standeven
7/26/06 Brian Quincy Hutchings
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