Talk:Infinity

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"Unboundedness" listed at Redirects for discussion

A discussion is taking place to address the redirect Unboundedness. The discussion will occur at Wikipedia:Redirects for discussion/Log/2021 February 25#Unboundedness until a consensus is reached, and readers of this page are welcome to contribute to the discussion. 𝟙𝟤𝟯𝟺𝐪𝑤𝒆𝓇𝟷𝟮𝟥𝟜𝓺𝔴𝕖𝖗𝟰 (𝗍𝗮𝘭𝙠) 21:39, 25 February 2021 (UTC)

"Subsequent thinkers, finding this solution unacceptable, struggled for over two millennia to find other weaknesses in the argument."

@D.Lazard: I think that this passage, with regard to Zeno's paradox, is written poorly. Specifically, it implies that thinkers spent two thousand years unable to comprehend the fact that men could run faster than tortoises. The actual object of contention was the proper way to formulate a mathematical limit; it goes without saying that the physical reality of things being faster than other things was quite well-understood, even at the time. The bow and arrow was used in warfare, runners competed in athletic competitions, et cetera, without issue. While I initially changed the sentence to say "weaknesses in the mathematical argument", I am willing to amend that to "weaknesses in the philosophical argument", per your revert, but I think there should be at least some clarification. jp×g 14:02, 5 May 2021 (UTC)

It seems not useful to qualify "argument", since it is at the corner of philosophy (existence of motion), physics (velocity comparison) and mathematics (resolving the paradox by understanding properties of infinite sums). D.Lazard (talk) 14:37, 5 May 2021 (UTC)
I am the author of the sentence in dispute. Of course most people, before or after Zeno, will agree that — unless seriously disabled — men can run faster than tortoises. Some who lived after Zeno were therefore motivated to find weaknesses in the argument so as to allow for the possibility of motion, and it was a long time before Cauchy succeeded. The "actual object of contention" had nothing to do with limits, a concept that was not formulated, let alone argued over, until long after Zeno. It would have been helpful to qualify the argument as "mathematical" or "philosophical" if it were necessary to distinguish it from other, non-mathematical or non-philosophical, arguments; as there is no such need, however, the qualification gains nothing. Peter Brown (talk) 17:50, 5 May 2021 (UTC)
There was a discussion at some math article not too long ago where it was claimed that the association of Zeno with considerations of the infinite was a modern misconception, and that what Zeno was actually trying to prove was that there was no such thing as motion, maybe even no such thing as change. That strikes me as a bizarre thing to want to prove, but if that is in fact what he was getting at, then we should be careful about conflating Zeno's arguments with later considerations that looked back to Zeno. --Trovatore (talk) 22:39, 5 May 2021 (UTC)
Yes Zeno was a student of Parmenides, and his paradoxes were meant to be a defense of Parmenides belief in the impossibility of change. Paul August 00:15, 6 May 2021 (UTC)
Paul August and Peter M. Brown, the name "Zeno" still does not appear on the real number page. I have long thought that this is a very serious omission, given that Zeno's paradoxes are specifically invoked when motivating the most central property of the reals, namely completeness. I would very much like to see a good, accurate discussion of the relationship at that article. It sounds like the two of you are more familiar with Zeno's thought than I am, and even though the key consideration is perhaps not so much Zeno himself as how nineteenth-century mathematicians understood Zeno, that would still be a key component. --Trovatore (talk) 16:12, 6 May 2021 (UTC)
Trovatore, how can the Achilles paradox motivate the completeness of the reals? If the racers' speeds and the tortoise's head start are all given as rational numbers, then the time it takes Achilles to overtake the tortoise will also be rational — there seems to be no requirement, here, for irrational numbers. Peter Brown (talk) 16:52, 6 May 2021 (UTC)
Hmm, yeah, but that's sort of an accident, I'd say. The underlying reasoning is topological, not algebraic. The sequence of positions where Achilles is behind the tortoise is an increasing sequence with an upper bound. --Trovatore (talk) 18:00, 6 May 2021 (UTC)
Peter M. Brown For a good background on Zeno's Paradoxes and their so-called "Standard Solution" (which requires a continuum) see the IEP s.v. Zeno's Paradoxes. Paul August 18:24, 6 May 2021 (UTC)
The IEP article seems confused. The last paragraph of section 3.a.i. starts with the sentence
The Achilles Argument ... presumes that space and time are continuous or infinitely divisible.
Well, which? "Continuous" and "infinitely divisible" are not the same thing! The rational numbers, or the multiples of 2n for integral n, are infinitely divisible but not a continuum. I do not see how continuity figures in the "standard solution". Mere density seems to be enough.
Peter Brown (talk) 17:44, 7 May 2021 (UTC)
I also was underwhelmed by the IEP article. In particular the line By “real numbers” we do not mean actual numbers but rather decimal numbers did not especially inspire confidence.
Nevertheless I believe it is true that 19th- and 20th-century mathematicians considered the paradox to be resolved via a notion of real numbers that included all limit points of bounded subsequences. Whether you or I think that's convincing (you might say, what's wrong with Achilles sometimes being behind the tortoise and sometimes ahead, but never exactly even with it?) is not really the point; the point is the contribution to the development of the real-number concept. I would like to see this discussed in a well-sourced way at real number, in part just to learn more about it myself. --Trovatore (talk) 18:16, 8 May 2021 (UTC)
Trovatore, if you're correct that
19th- and 20th-century mathematicians considered the paradox to be resolved via a notion of real numbers that included all limit points of bounded subsequences
then yes, Zeno should be mentioned in Real number § History. Why do you think so, however? We can't mention Zeno in this connection without a reliable source on 19th- and 20th-cantury mathematics.
Peter Brown (talk) 21:31, 8 May 2021 (UTC)

Achilles v. Tortoise race duration

@D.Lazard: We are in agreement that Achilles takes ${\displaystyle {\frac {10}{0.99}}}$ seconds to overtake the tortoise. As a repeating decimal, that's 10.101010... seconds. You claim that this is ${\displaystyle 10{\frac {100}{99}}}$ seconds, but that works out to 11.010101... seconds. My replacement, ${\displaystyle 10{\frac {10}{99}}}$ yields 10.101010..., which is what we want.

Peter Brown (talk) 02:23, 23 July 2021 (UTC)

${\displaystyle 10{\frac {10}{99}}={\frac {100}{99}}=1.010101...}$ not ${\displaystyle 10.101010...}$ Oh, you do not mean a multiplication, but the vulgar fraction ${\displaystyle 10{\tfrac {10}{99}}}$. IMO, even correctly formatted, this must be avoided, as vulgar fractions are not commonly used in many countries. I'll add a multiplication sign. D.Lazard (talk) 08:20, 23 July 2021 (UTC)

Yes, I was interpreting ${\displaystyle 10{\tfrac {10}{99}}}$ as a mixed number. Now, it isn't obvious to me, or probably to the general reader, why ${\displaystyle {\frac {10}{1-0.01}}}$ should be equal to ${\displaystyle 10\times {\frac {100}{99}}}$ or why anyone should care. I am accordingly omitting this step. Peter Brown (talk) 18:15, 23 July 2021 (UTC)

"Unendlichkeit" listed at Redirects for discussion

An editor has identified a potential problem with the redirect Unendlichkeit and has thus listed it for discussion. This discussion will occur at Wikipedia:Redirects for discussion/Log/2022 February 12#Unendlichkeit until a consensus is reached, and readers of this page are welcome to contribute to the discussion. ~~~~
02:05, 12 February 2022 (UTC)

History section - Dubious Tag Discussion

In the pages History section the Brihadaranyaka Upanishad is cited as showing how ancient Indians understood the concept of mathematical infinity. I found no such support for this claim given in the English translation for this and instead it only refers to infinite from a spiritual sense, not specifically within the context of an abstract mathematical or philosophical concept. I don’t claim to be familiar with this source but if we do keep this source it would follow we must also discuss all other ancient cultures who made reference to the idea of the eternal or everlasting as equally being aware of the idea of infinity.

Perhaps we need to better define whether we are covering the history of mathematical infinity or infinity in a broader perhaps more spiritual sense. This way we can narrow down what should and should not be included in this section. 121.98.205.163 (talk) 06:34, 14 September 2022 (UTC)

I thought that looked familiar. That section is very similar to what was discussed here, which ultimately (IMO as a participant in that discussion) ended in a consensus to not include the text, and with the OP receiving an indefinite block which is still in place. Looks like it was re-added in February, but with no better sourcing than before, so I've re-removed it. Writ Keeper  13:59, 14 September 2022 (UTC)