My Math Forum > Math Which infinity for irrational numbers?

 Math General Math Forum - For general math related discussion and news

January 13th, 2016, 01:45 PM   #41
Senior Member

Joined: Aug 2012

Posts: 2,393
Thanks: 749

Quote:
 Originally Posted by studiot Thank you for your comments, I will look into them. If you are going to comment seriously on my statements, please at least address them properly. I queried an infinite sum allegedly adding to zero, and you tell me it adds to 1.
I commented on your most recent post, which quoted someone else making a claim, and you saying the claim was outrageous.

I do confess I have not read through the entire thread. And my comment was not meant to be exactly on subject; but was rather a little bit of counterspin on the entire question.

We take it as obvious that some but not all disjoint unions of a collections of dimensionless and lengthless points can have dimension and length. This is an assumption that underlies many if not all of the profound mysteries of the real numbers. There's no real explanation for it in our math or logic. It's a question that so far has eluded our rationality.

So I would say that my comment was not so much off-topic, as it was a digression into the philosophical underpinnings of the entire subject.

That's my story and I'm stickin' to it!!

Last edited by skipjack; February 29th, 2016 at 02:23 AM.

January 13th, 2016, 02:00 PM   #42
Senior Member

Joined: Dec 2015
From: France

Posts: 103
Thanks: 1

Quote:
 Originally Posted by Karma Peny Any definition containing a summation from 1 to infinity requires further clarification, because it is not at all clear how we can count from 1 to infinity. Attempts at defining real numbers include declaring them as equivalence classes of Cauchy sequences of rational numbers, Dedekind cuts, or certain infinite "decimal representations". These definitions all require the acceptance of 'infinitely many' iterations or occurrences. When we say "for n = 1 to infinity" or “infinitely many” what number type are we referring to? It can't be natural numbers or integers because these cannot "go to infinity". By definition they can only take finite values. It can't even be ‘reals’ because these do not allow infinity as a value. So presumably we must be talking about something like the Hyperreal numbers or the Surreal numbers? Note that these are extensions to the reals, which they both take as already being well-defined. So all definitions of ‘reals’ are based on the assumption that ‘reals’ are already well-defined. In short, real numbers are not well-defined at all.
Effectively, infinite sum is not the limit, but a sequence of numbers that approach the limit. THis is why Zeno's Achilles cannot catch up turtle.
1/2+1/4+...=/=1 but ->1

January 13th, 2016, 02:57 PM   #43
Senior Member

Joined: Jun 2015
From: England

Posts: 915
Thanks: 271

Quote:
 Masche But the question remains. How do you pile up a lot of zeros to get 1? Even infinitely many? How does that work?]
Because you are looking at it like Zeno and his arrow, bass ackwards.

An arrow will never reach his target because he is breaking down the path into lots of zeros instead of summing a null sequence of times.

@pengkuan

This is the trick to resolve all of Zeno type paradoxes.
Transform the argument (problem) to a domain when you are summing a null sequence.

Last edited by studiot; January 13th, 2016 at 03:04 PM.

January 13th, 2016, 04:09 PM   #44
Senior Member

Joined: Aug 2012

Posts: 2,393
Thanks: 749

Quote:
 Originally Posted by studiot Because you are looking at it like Zeno and his arrow, bass ackwards. An arrow will never reach his target because he is breaking down the path into lots of zeros instead of summing a null sequence of times.
Which interval among [0,1/2], [1/2, 3/4], [3/4], [7/8], ... do you claim is zero? That's Zeno's argument. None of these intervals are zero.

January 14th, 2016, 09:30 AM   #45
Senior Member

Joined: Jun 2015
From: England

Posts: 915
Thanks: 271

Quote:
 Originally Posted by Maschke Which interval among [0,1/2], [1/2, 3/4], [3/4], [7/8], ... do you claim is zero? That's Zeno's argument. None of these intervals are zero.
First correcting the obvious typo

$\displaystyle \left[ {0,\frac{1}{2}} \right[;\quad \left[ {\frac{1}{2},\frac{3}{4}} \right[;\quad \left[ {\frac{3}{4},\frac{7}{8}} \right[;........\quad$

and then noting that we must use half-open intervals, closed at the left-hand end.

This is because if we use closed intervals as you show then the 1/2, 3/4, etc. will be counted twice or you are saying that the arrow visits these points twice on its journey?
We start at the left-hand end because the arrow must start at 0.

Now the complete Zeno argument runs that in order to cover the whole distance the arrow must first cover half the distance and when it is half way it must cover half the distance remaining, i.e. one quarter the whole distance and so on. So however close the arrow gets to its target there is always a bit left to go.

The fallacy is in the statement always a bit left to go.

Always is a measure of time; and the times to traverse each successive interval forms a null sequence

$\displaystyle {s_n} = 1,\frac{1}{2},\frac{1}{4},\frac{1}{8}...........$

Which does not sum to always (ie is not divergent).

Actually, Zeno went on with his arrow to a more difficult paradox that does represent the partition into sets of single numbers of zero measure.
He observed that the first half distance can itself be split down into a half distance and the argument can be applied recursively, with the conclusion that the arrow can never move.

Last edited by skipjack; February 29th, 2016 at 02:28 AM.

January 14th, 2016, 11:28 AM   #46
Senior Member

Joined: Aug 2012

Posts: 2,393
Thanks: 749

Quote:
 Originally Posted by studiot First correcting the obvious typo
No typo, my notation was deliberate. A countable collection of singletons has measure zero and makes no possible difference to this discussion. The endpoints do not matter. The length of the open interval (a,b) is exactly the same as the length of the closed or half-open intervals with the same endpoints.

You went to great lengths to avoid answering the question I asked you, which was: Which interval has zero size? Clearly none of them do but you claimed some or all of them do earlier.

Quote:
 Originally Posted by studiot you are saying that the arrow visits these points twice on its journey
Those are rest stops where the arrow grabs a cup of coffee.

Earlier you wrote:

Quote:
 Originally Posted by studiot An arrow will never reach his target because he is breaking down the path into lots of zeros instead of summing a null sequence of times.
I am challenging you to tell me which of the intervals listed, whether we take them to be open, closed, or half-open/half-closed, are zero.

Last edited by Maschke; January 14th, 2016 at 11:34 AM.

January 14th, 2016, 12:24 PM   #47
Senior Member

Joined: Jun 2015
From: England

Posts: 915
Thanks: 271

Quote:
 I am challenging you to tell me which of the intervals listed, whether we take them to be open, closed, or half-open/half-closed, are zero.
Did you not agree with this then?

Quote:
 Actually Zeno went on with his arrow to a more difficult paradox that does represent the partition into sets of single numbers of zero measure. He observed that the first half distance can itself be split down into a half distance and the argument can be applied recursively, with the conclusion that the arrow can never move.

January 14th, 2016, 12:56 PM   #48
Senior Member

Joined: Aug 2012

Posts: 2,393
Thanks: 749

Quote:
 Originally Posted by studiot Did you not agree with this then?
Actually as I understand it Zeno proposed four separate paradoxes, and when people say "Zeno's paradox" without carefully stating which one they're talking about, there's some ambiguity.

I'm not personally up on the specifics of which paradox is which. If you can remind me exactly what we're talking about, that will probably be a help to everyone.

As I said earlier I jumped into the middle of a thread without reading it first, so whatever point you think I'm arguing, I'm probably not. You said something about zeros, maybe you can just say what that was in reference to.

 Tags cardinality, infinity, irrational, numbers

 Thread Tools Display Modes Linear Mode

 Similar Threads Thread Thread Starter Forum Replies Last Post Albert.Teng Algebra 4 February 12th, 2014 04:55 PM niki500 Number Theory 5 October 7th, 2012 09:10 PM elim Number Theory 1 September 22nd, 2011 12:03 PM Mighty Mouse Jr Algebra 1 October 16th, 2010 07:46 PM MattJ81 New Users 11 July 10th, 2010 07:51 PM

 Contact - Home - Forums - Cryptocurrency Forum - Top