Talk:0.999.../Arguments

MfD Result Notice

This page was the subject of an MfD discussion closed on 12 May 2007, with a keep result. Xoloz 18:36, 12 May 2007 (UTC)

Then... there're only 3 numbers?

OK... I learned about 0.(9) being the same as 1 in high school too...

But now I have this question.

1 = 0.99999... right?

2 = 1.99999... every ok so far.

does this mean that

0.99999... = 0.999999999...888... ?

or, to put it into words, is 0.(9) the same as 0. followed by infinite 9s AND infinite 8s? is that even possible?

or, even without knowing what number it would be, one could argue the following:

Since a number, like 1, is equal to the infinitely slightly "previous" number, there are only 3 numbers: zero, an infinite positive number and an infinite negative number.

Think about it... every number has an infinitely small 'equal'. At the same time, this 'equal' should have its own infinitely small equal, and so on...

Comments? —Preceding unsigned comment added by 201.246.25.69 (talk) 05:00, 18 January 2010 (UTC)

Within the real numbers, a number with infnitely many 9s followed by infinitely many 8s is impossible. Every digit only has finitely many other digits before itself.

Your "only three numbers" line of reasoning is flawed for two reasons. On the one hand, 0.999... is not "previous" to 1, not even "infinitely slightly" (or infinitesimally). They're exactly equal. (Again, within the real numbers - there are other number systems where a number denoted as "0.999..." is less than 1, but those number systems have significant drawbacks compared to the reals and are not in general use.) On the other hand, even if 0.999... managed to be both equal to and less than 1 (which is by definition impossible), not every real number has more than one decimal representation. For example, 0.333...=1/3 has just one, and there's no "infinitely slightly previous" number for 0.333... (actually, there isn't even one for 0.999... itself). Huon (talk) 06:23, 18 January 2010 (UTC)

Infinitesimals were thought to have numerous advantages by Leibniz, Euler, Cauchy, and others. Which drawbacks are you referring to? Tkuvho (talk) 11:09, 18 January 2010 (UTC)

Leibniz, Euler and to a degree even Cauchy predate the formalization of analysis (I'd set that at the age of Dedekind and Weierstraß). The specific drawbacks of the possible number systems depend on the specific number system, of course. For example, the surreal numbers and the closely related Hackenstrings have problems with multiplication: 3 * 0.333... = 1 > 0.999..., which is counterintuitive (and if you consider just the Hackenstrings, which are more closely related to decimal (or binary) representations than the full surreals, they won't form a ring). Often there will also exist numbers which cannot be represented by decimals any more, making decimal representations a bad choice to model those number systems in the first place. The article also mentions Richman's "decimal numbers" which don't form an additive group. Among the hyperreals there's no reason to denote any specific number (except, ironically, 1) as "0.999...". In any case the existence of infinitesimals will mean that you cannot define a meaningful metric on your number set (because the definition of a metric depends on real numbers and non-infinitesimal distances - of course that could be modified), and while you probably still can define a topology, it will behave very strangely. I can't think of a case where you have a topological group, limits are unique and the sequence (0.9, 0.99, 0.999, ...) converges. Huon (talk) 15:52, 18 January 2010 (UTC)

Your comment is thoughtful but not fully informed. What complicates the situation is that there are two separate issues involved: the mathematical/foundational issue, and the educational/pedagogical issue. I am not sure which is the one you would be interested in sorting out. At any rate, mathematically speaking, keep in mind at least the following two points: (1) the surreals cannot be used as foundation for analysis, since they lack the transfer principle; (2) the distance function on the reals has a natural extension to the hyperreals by the transfer principle, and in fact it can be constructed concretely in the ultrapower construction. As far as the students are concerned, at this level they are not interested in technical details of analysis and especially not topology. The real question is, whether their conception is an erroneous one, or rather a nonstandard one. Here the latter term is not referring to a particular mathematical theory, but to the possibility that their intuitions are coherent in the sense that they can be vindicated in a suitable mathematical framework. Tkuvho (talk) 12:15, 20 January 2010 (UTC)

I am no expert in non-standard analysis and may thus err in my opinions thereof. But I don't believe the hyperreals really are an improvement over the reals for educational purposes. While the hyperreals allow us to consider numbers infinitesimally less than one and may in this regard conform to the students' intuition, I dare predict that teaching hyperreals in high school would be complicated and not more thorough than the current high school education concerning decimal representations. In effect, we'd probably just have moved the regions where student intuition and mathematical model diverge.

I'm also still not convinced that the hyperreals are a good mathematical model for the 0.999... issue. As I noted before, there's no canonical hyperreal number (except 1) to be denoted "0.999...". I'm avare of the Katz&Katz paper you added, but I believe that firstly, the choice of $0.999...=0.{\underset {[\mathbb {N} ]}{\underbrace {999\ldots } }}=1-1/10^{[\mathbb {N} ]}$ is arbitrary - there are lots of other hyperreals which might just as well be denoted "0.999...". Secondly, it's an abuse of notation because the "0.999..." notation suggests nines all the way down; it would be better to denote Katz' number as $0.{\underset {[\mathbb {N} ]}{\underbrace {999\ldots 9} }}$ to show that it does have a last nine. Thirdly, I may be mistaken but I believe $[\mathbb {N} ]$ isn't even a well-defined hyperreal but depends on the choice of ultrafilter - and giving a specific ultrafilter is a non-trivial task. For example, is $[\mathbb {N} ]$ greater or less than the hyperreal given by the sequence a_n=n+(-1)ⁿ/n? Greater if the set of odd integers is contained in the ultrafilter, less otherwise. Huon (talk) 16:23, 20 January 2010 (UTC)

Thanks for your thoughtful comments. I was hoping we would narrow down the discussion to make it more manageable, to either the educational issues, or the mathematical/foundational issues, but you seem to be interested in both, which is just as well. I would like to make several points. (1) On the educational side, note that a couple of weeks ago user 67.161.232.156 spoke about the possible existence of a number of the form .000...1 (with infinitely many zeros), at the "User:ConMan/Proof that 0.999... does not equal 1" page. The suggestion was rebuffed by Tango who pointed out that ".999...8 is just as nonsensical as .000...1." Now user 67.161.232.156 might be wondering why his .000...1 is necessarily nonsensical, but Huon's .999...9 (with infinitely many 9s) makes sense. Why is his intuition erroneous, while yours not erroneous but nonstandard? (2) On the foundational side, in your comment above, you used the definite article in describing Weierstrass's formalisation of analysis. This is a possible viewpoint, but many historians view it as "a formalisation", not "the formalisation". Postulating Weierstassian formalisation as the unique foundation for analysis, of course, pre-determines the outcome of any discussion of infinitesimals, which were eliminated from the continuum by Weierstrass. As you may be aware, there are alternative foundations analysis that do not eliminate infinitesimals. One is by Robinson as discussed; another by Lawvere in smooth infinitesimal analysis. (3) .999... as a real number is well defined, and nobody claims it equals 1-(.1)^[N]. I don't think there is any abuse of notation here. (4) your question in the context of [N] boils to down to asking whether the infinitesimal defined by the sequence < (-1)ⁿ/n >, is positive or negative (the question has nothing to do with [N] itself). You are right, this depends on the choice of an ultrafilter. I am not sure why the sign matters so much. Note that the sign of this infinitesimal determines the parity of the hypernatural [N]. You are perhaps aware that the existence of a free ultrafilter is a consequence of the axiom of choice (the same goes for existence of maximal ideals, Hahn-Banach theorem, ...) Note that in the presence of the continuum hypothesis, all hyperreal continua are isomorphic. Furthermore, there are alternative constructions not relying on choice. Tkuvho (talk) 09:26, 21 January 2010 (UTC)

Concerning formalization of analysis I meant "the age of formalization of analysis", not specifically the Weierstraß approach. As I said, I'm no expert on non-standard analysis, and I wasn't aware of the specifics of Lawvere's approach; thanks for the reading suggestion.

The trouble with 0.000...1 and 0.999...9 is, of course, context. One needs to clarify what that last digit represents. I specified that it should mean a digit given by a (more or less) specific infinite hypernatural number, all within the realm of the hyperreals. 67.161.232.156 doesn't specify context, but his basic intuitive assumption that there should be a greatest number less than 1 is as wrong in the hyperreals as in the reals. He also seems to assume that there's some end to 0.999... (just like Katz) - something I'd say is the wrong kind of intuition (and 67.161.232.156 is a good example for common intuitive assumptions that can be wrong beyond repair, so please don't tell me that we should try and make our mathematics conform to intuition unless your number system also gives a greatest number less than 1). We wouldn't denote 1-10^-Googol by 0.999...; neither should we denote 1-10^-[N] by 0.999...

Finally, concerning the structure of the hyperreals and ambiguity of [N]: I am aware that free ultrafilters exist, and that the models of the hyperreals are isomorphic no matter what ultrafilter we use. But do these isomorphisms really map the hyperreals represented by the sequence (1, 2, 3, ...) onto each other? Can you prove that? I am willing to believe that the hyperreals represented by the sequences which eventually become constant are mapped onto each other, but anything beyond that seems dubious to me. Thus, the hyperreal represented by (1, 2, 3, ...) using one ultrafilter may not be equal to the one represented by the same sequence using another ultrafilter. In that case [N] would be ill-defined unless you also specified the ultrafilter - mere existence isn't enough. Or you end up with saying that [N] is just the class of hyperreals represented by that sequence, and not a specific hyperreal at all. Huon (talk) 12:06, 21 January 2010 (UTC)

Thanks for your thoughtful comments. I think perhaps we should narrow down the discussion to the educational issues. The foundational issues are only tangentially related to the present page. The full power of the hyperreals is not needed to handle the .999... issue. A common kernel for infinitesimal theories that can account for the ".999..."<1 phenomenon resides in primitive recursive arithmetic, in the context of the fraction field of a non-standard model of arithmetic. Such models were already constructed by Skolem thirty years before Robinson. You correctly point out that [N] will not necessarily be preserved by an automorphism. At any rate, on the educational front relevant here, I have to reserve judgment concerning your statement that user 67.161.232.156 "seems to assume that there's some end to 0.999... (just like Katz) - something I'd say is the wrong kind of intuition". We should try to listen to what education people say about this. Published work by Robert Ely shows that intuitions such as those of 67.161.232.156 are not erroneous, but rather nonstandard. If I thought they were erroneous I would not have pursued this matter on this page. Tkuvho (talk) 09:23, 22 January 2010 (UTC)

Sure

You have to be sure though when claiming that it is one, to point out that it is really (1 - .0000...1)
While the difference between .999... and 1 is infinitely nothing, it cannot be dismissed because it is everywhere.
.000...1 is the first thing there is greater than zero, and it's between every change between every two numbers all the way up to one. It's everywhere, but it's nothing. I believe that it is the graviton number, but I cannot prove it. --Neptunerover (talk) 16:31, 21 January 2010 (UTC)

I have never heard of a graviton number, but I don't think there is any useful number system (except the integers) where a "first thing greater than zero" exists. We usually want our numbers to form a ring, that is, to allow multiplication. What's 0.1 times the "first thing greater than zero"? Even worse, we also want our numbers to allow for cancellation, that is, for a≠0 we'll require that a*x=a*y implies x=y. I believe these pretty straightforward requirements alone imply that if there's a first thing greater than zero, it's one.

Consequently, the difference between 0.999... and 1 is not the smallest positive number (in all number systems I'm aware of). In the real numbers, the most widely used, it's exactly zero. In more exotic number systems, such as the hyperreals, it's possible to redefine 0.999... so that there is a non-zero infinitesimal distance between 0.999... and 1, but there still is no smallest positive number, and smaller infinitesimals exist. Huon (talk) 17:14, 21 January 2010 (UTC)

This is from the infinitesimal article: "In the 20th century, it was found that infinitesimals could also be treated rigorously. Neither formulation is wrong, and both give the same results if used correctly." My suggestion is that if both formulations work, maybe one formulation might work better for certain calculations. Using a number set that contains all infinities is better than one with no upper limit to contain anything, at least when you have to deal with infinities. In figuring out gravity, they might be better off using a set with limits, although still infinite. --Neptunerover (talk) 06:05, 22 January 2010 (UTC)

That's referring to using infinitesimals for calculus, considering things like dx to be infinitesimals rather than just shorthand for a limit. The sets used in that wouldn't have 1-0.999... being a non-zero infinitesimal. I don't know what you mean by "a set with limits", but the real numbers work perfectly well to figure out gravity, infinitesimals wouldn't help. The gravitational constant (in SI units) is really small, but it's still a perfectly normal, finite number. The only time infinities come up with gravity is with black holes and I don't think using a different number system would help there, not on its own, at least. --Tango (talk) 06:15, 22 January 2010 (UTC)

The infinities you mention with gravity are the exact ones I mean. They are the reason Quantum Mechanics cannot currently be meshed with gravity. Infinitesimals are perfectly valid for use in mathematical figuring, but the practice was mostly abandoned in the second half of the nineteenth century because somebody formalized calculus using the system of numbers it now uses. But that doesn't mean there's not another way. --Neptunerover (talk) 07:03, 22 January 2010 (UTC)

A graviton number would represent the force of gravity, which is very small. By reasoning with this number set, .999... would be the opposite of the graviton number, aka. the speed of light, which is the upper limit. If we do all our calculations within the decimals, all products should stay within the set. --Neptunerover (talk) 17:49, 21 January 2010 (UTC)

As I said, I've never heard of graviton numbers before, and I believe you made up the notion. If not, can you point me to a peer-reviewed article or a text book where I might read up on graviton numbers? Also it's not really an improvement to introduce too much physics into a pure math discussion. For example, I don't see why anything representing the force of gravity should have the dimension of a velocity, which would be necessary to compare it to the speed of light. You could also answer my original question: What's 0.1 * (1-0.999...)? Those are all decimals, so the result should still be a decimal, right? What decimal? Huon (talk) 18:08, 21 January 2010 (UTC)

I suppose it would be a very very small one. I don't think that's any weirder than any of the other weirdness that comes out the number sets that are generally used. I don't really know how the math would work within the set. Each number itself represents a velocity, from zero to max. I don't really know; can C be 1 in the E=MC(squared) equation? --Neptunerover (talk) 18:31, 21 January 2010 (UTC)

What very very small one? Write it down. "Each number itself represents a velocity, from zero to max." That makes no sense. The speed of light cannot be 1, since 1 is a dimensionless quantity and the speed of light is a speed. It can be 1 light year/year (and we often do use units where the speed of light is 1 unit since it makes the maths much easier), but that is still a speed. When you talk about graviton numbers, do you mean the gravitational constant? That is a very small number in SI units, but not infinitely small - it's about a ten-billionth. --Tango (talk) 18:37, 21 January 2010 (UTC)

I think 1 might be available for the speed of light, since time stops and space looses its meaning, so dimensionlessness may fit. --Neptunerover (talk) 19:24, 21 January 2010 (UTC)

I'm not certain how it would work. Something might get canceled. For instance, say the product of .1*(1-.999...) could remain .1 having some sort of a remainder representing the gravitational force against it at that moment. And yes, the gravitational constant is what I was referring to (thanks). The Graviton is a hypothetical particle that transmits the force. --Neptunerover (talk) 18:59, 21 January 2010 (UTC)

Neptunerover is correct regarding c: It is possible to use a system of natural units where c=1. Unfortunately for him, it is then just a small step to using units where the gravitational constant also equals 1, ie c=1=G, and G is not small compared to c: Planck units. But back to 0.999... and 1: Is 0.1 * (1-0.999...) less than 1-0.999...? If so, then 1-0.999... obviously is not the smallest positive number.

By the way, physics almost exclusively uses the real numbers (or the complex numbers) where 0.999...=1 exactly. Mathematicians can construct other number systems, but they are rarely used (thus the article claims by default that 0.999...=1), and their use gets ever rarer the closer the subject is to physics. Might I suggest reading up on decimal representations? Huon (talk) 19:36, 21 January 2010 (UTC)

Hey thanks. I always hated math. I think it's very one-sided as far as the brain is concerned. --Neptunerover (talk) 19:51, 21 January 2010 (UTC)

How perfect is this? (from the planck units article)
"Planck units are often semi-humorously referred to by physicists as God's units. They eliminate anthropocentric arbitrariness from the system of units."
And then what do these silly guys do next? They apply arbitrary anthropocentric concepts of measurement to the units, and then they get confused (or confounded, rather; I'm not saying it's anyone's 'fault', as my intent is not to point out a fault, but rather to suggest something else that might work. I've done plenty of things only to slap myself in the head in retrospect).
What is 'God's straightedge', and what is 'God's clock'? I'm guessing not ours.
Consider if we, instead of arbitrarily saying that the speed of light is X units of an arbitrary distance covered per arbitrary time segment, why not just say C is one, (or .999..., since time would have to stop completely at the speed of light making it dimensionless and possibly unreachable.) What if we started at the upper limit, the speed of light, call it 1 (or 100 or 1000? Whatever it is, it's the max, and the idea is to keep it an easy number and not just random), and then we figured out what the other values are going down from there? --Neptunerover (talk) 20:31, 21 January 2010 (UTC)

Also from the Planck units article, "Referring to G = c = 1, Paul Wesson wrote that, 'Mathematically it is an acceptable trick which saves labour. Physically it represents a loss of information and can lead to confusion.'". Note specifically the loss of information bit -- if you want it to have any meaning, you've got to put the units back eventually. But we're far afield from the original discussion of .999.... — Lomn 20:41, 21 January 2010 (UTC)

That actually is what we do. For historical reasons, it's not a nice round number, though. We define the speed of light to be exactly 299,792,458 m/s. We then define the metre from that (the second is defined in terms of caesium atoms). If we had known about special relativity thousands of years ago, then it would be a nice round number, but we didn't, so we have to put up with an un-round number to maintain consistency with old units that everyone is used to using. I don't know what you mean by "arbitrary anthropocentric concepts of measurement", though... --Tango (talk) 20:44, 21 January 2010 (UTC)

I mean like a meter or an inch. These are distances arbitrarily created by man, though not without use, but I believe they lead to confusion. I do admit that it might sound radical to suggest that perhaps the numbers we generally use might be confusing us (at least in Physics, which is very much math), and so I'm sorry for making the suggestion. --Neptunerover (talk) 21:02, 21 January 2010 (UTC)

What do metres and inches have to do with Planck units? Of course, one can convert from Planck units to other units of the same dimension and those conversions are usually mentioned when the Planck units are defined (since the people reading the definition will be familiar with the other units so can get a better feel for what these Planck units are if they know the conversion), but that's all. --Tango (talk) 01:08, 22 January 2010 (UTC)

While this is far off-topic for 0.999..., just imagine a speed limit of 5*10^-8 on the roads. Does that sound simple? Isn't it confusing if I tell you I live less than a heartbeat away from you? Shall we meet in a hundred trillion trillion trillion planck times? Oh, and please bring a few dozen million Planck masses of cookies (actually, since the Planck mass is dimensionless, just bring a few dozen million cookies...); I'll supply a googol of beer (Planck masses or cubic Planck lenghs? No matter, both are equally dimensionless...), ok? Our usual dimensions are appropriate for everyday tasks - and while one might redefine lengths and it wouldn't matter much, it certainly is an advantage that our units of time are (more or less) related to day length. There are other advantages of not using Planck units. Some final remarks: Saying c=0.999... is, for mathematical reasons unrelated to physics, the same as saying c=1 (that's the actual point of this article). It's also not true that "time stops at the speed of light". What would that even mean? Consider that 1 Planck time is much less than a second - are you saying that time stopped a tiny fraction of a second after it began? It took me more than 1 Planck time to write this, I can assure you, and time didn't stop in between. Finally, calling the number 1000 "easy" is again anthropocentric. We happen to have ten fingers and thus use base ten; if we had twelve, we might use a base 12 system and would consider 1728 "easy". Or how about 1024? Huon (talk) 00:18, 22 January 2010 (UTC)

They don't know what a second is. They might think they know how to measure one, but they don't know what it is. (At least not as far as I can tell). All the cells in our bodies do stuff lightning fast in a second. What's a second to them? How long does a second for us last for them? Is it because of our great mass in comparison to them that our time should be experienced differently? The human measurement of a second should not be universally applied. How many moments are in a moment depends upon how small (or big) you are. The Bible says a day for God is 1000 years for a man. God's a big guy. Not meaning to bring up religion, that's just my example that is documented (although with all the translations... who knows what it's supposed to be saying, and who relies on the Bible as a valid factual reference anyway? Anyone?) --Neptunerover (talk) 00:29, 20 January 2010 (UTC)

And I don't think 1 could ever actually be reached to where time would "stop." I think the change into a one could be like a supernova. It would be the fusion in the center of a star where there is no empty space between anything. --Neptunerover (talk) 06:35, 22 January 2010 (UTC)

You've gone past some simple misconceptions about mathematics and are now well into the realms of pseudoscience, so I'm going to bid you farewell. --Tango (talk) 06:42, 22 January 2010 (UTC)

Adios, amigo. --Neptunerover (talk) 07:14, 22 January 2010 (UTC)

Powers of ten, I consider easy, like the metric system as opposed to the foot/yard/etc. system. The idea of a meter is arbitrarily made, so that when we figure what the planck length is, based on a meter, we come up some fraction of a meter that is really only related to an arbitrary length. But if we started with the planck length and then went up from there, longer distances would be measured in gigaplancks (or I don't even know if that would be very long). I'm not really suggesting changing all the numbers we use for everyday purposes, which are generally served pretty well by the number systems we currently use for them. But to figure out the universe, I think we should start by using relevant units. --Neptunerover (talk) 03:59, 22 January 2010 (UTC)

Scientists do use relevant units. That's why Planck units exist - a scientist (called Planck, surprisingly enough) created them so he could use them to figure out the universe. They aren't used exclusively since it is often more convenient to use more conventional units, or units created for a particular purpose (eg. electron volts and parsecs), but they are used when it makes sense to use them. I don't see how any of this is relevant to 0.999..., though... --Tango (talk) 04:21, 22 January 2010 (UTC)

I just started out saying that .999... is different from 1 by the exact same difference there is between any two consecutive decimals. In order to get a 1, something, no matter how infinitely insignificant and ultimately unidentifiable, still something gets added to .999... --Neptunerover (talk) 05:20, 22 January 2010 (UTC)

"Consecutive decimals" do not exist. Either two numbers (1 and 2, 0 and 1345, 0.999999999 and 1) are distinct, in which case there are infinitely many other distinct numbers between them, or they are not distinct (0.999... and 1, 2/4 and 3/6, x+0 and x) and are therefore exactly the same in value. Not only are there infinitely many numbers between any two distinct numbers, but there are uncountably many, an infinity itself infinitely larger than your garden-variety infinity. So please, to close out, don't try to introduce your theory into the encyclopedia at large. — Lomn 14:11, 22 January 2010 (UTC)

You are splitting hairs with words, and your assumptive challenge is taken for what it is. I'm not interested in having an argument with know-it-alls; there's no point since they already know everything. Of course those people also want to control pages like this that are merely discussion pages about a topic. If you wish to 'frame' a debate, I suggest you go into politics. To close out, keep your assumptions to yourself, and if you don't like a discussion, stay away from it. --Neptunerover (talk) 07:35, 23 January 2010 (UTC)

Okay, forget about decimals for a second; they're misleading (which is kind of the reason for the existence of this page). Look at a line, and let points on the line represent real numbers. We have a point representing 0, a point representing 1, and half-way between those two points is a point representing 0.5. Now, remember that this is a platonic exercise in visualizing an 'ideal' line, and should be unaffected by the strange principles that we encounter when we get to small enough intervals that quantum mechanical effects become significant. Lomn's assertion above says that these points are dense, which is the name we give to the property that between every pair of distinct numbers, there is another number. We define real numbers this way because we want them to behave in this manner. It is analogous to the assertion that between any 2 points on a line there is another point. This is true in our platonic realization of a line, and it is true in Euclidean geometry.

Returning to decimals, they are a representation of real numbers, not the embodiment thereof. This representation consists of a list of digits between 0 and 9. A list of anything is characterized by a function from the natural numbers to 'anything'. So the symbol "0.999..." makes sense, because it is the mapping that associates every natural number with 9. Because there is no last natural number, the symbol "0.999...9998" makes no sense unless the 8 is in a finite place value (as Huon has pointed out below), in which case it is definitely not the 'next smallest' real number, since you could produce a number in between both by simply adding more 9's. So suggesting that 1 has a next smallest real number, which we denote "0.999...", leads us to the inevitable conclusion that 1 is somehow special in this respect, since "0.999..." certainly has no next smallest real number, and neither does any irrational number, or, for that matter, any number which cannot be represented as a rational number whose denominator is a power of 10. Why would you give such a limited class of numbers such a special class of significance, not to mention in the process destroy the property of density of the real numbers? --COVIZAPIBETEFOKY (talk) 16:31, 23 January 2010 (UTC)

I don't believe it is a limited class of numbers, at least not for the specific use I have in mind. I think of numbers as representing actual things which could be different than your average mathematician's approach. The way I'm looking at it, with the set (0,1{including all 'numbers' in between}), 1 does have a special place, because it is the top. I view the set as a ratio between emptiness and solidness. There can be nothing more solid than 1, because 1 is the absence of any 'holes' or spaces between anything. For instance, an atom is mostly empty space with a little thing in the center. That nucleus, I would consider a 1 because it consists of protons, etc. that are fused together without there being gaps between them. The atoms that make up a table each have 1 as their nucleus, but a table is not a 1 because it contains mostly empty space. The center of a star would be a 1 because even the atomic nuclei are fused together, making there be no empty space in the center of a star. Ones come in all different sizes because size is not what's important; what's important is solidness (in the number set that I use, in the way that I use it). Ones and zeros; that's computers, and I say it's the world. (Even if I can't explain it very well) --Neptunerover (talk) 18:12, 23 January 2010 (UTC)

But why should 1/10 have such special significance, where 1/3 does not? After all, 0.0999... is 'just below' 0.1, whereas no such number exists for 0.333... --COVIZAPIBETEFOKY (talk) 18:35, 23 January 2010 (UTC)

I'm not sure what you're asking me. .1 is different from 1/3 by lack of a repeating decimal. Can you expand on what you're asking me? --Neptunerover (talk) 18:55, 23 January 2010 (UTC)

Every finite decimal representation has a partner, which, according to us, is equal, and according to you, is 'just less'. No other decimal has such a partner. Why should finite decimal representations be so special in this respect? These are exactly those numbers which can be represented as a ratio of two integers where the denominator is a power of 10. Why should 10 seem to have such a mystical property that determines which numbers have infinitely close partners? After all, the particular choice of 10 is just an arbitrary one based on the number of fingers on our hands. --COVIZAPIBETEFOKY (talk) 19:36, 23 January 2010 (UTC)

I think 10 is more than just arbitrary, but you probably wouldn't agree with my reasoning (In fact I find it highly doubtful). I think it really all depends on how you want to divide up your 1. 10 'equal' parts, 12 'equal' parts... 10 is what I'm used to, and I think it is natural for us. As for generalizations, from my point of view, every decimal representation has two partners infinitely indistinct from itself, and each of those has the same. Following this line of reasoning, all numbers are ultimately indistinct from one another, making them all 1. This is that infinite density. (and if this paragraph makes sense, I'd be pretty surprised). --Neptunerover (talk) 20:04, 23 January 2010 (UTC)

Don't worry, I won't surprise you. But can you tell me which numbers are 'infinitely indistinct' from 0.333..., or 1/3, knowing that "0.333...332" is a meaningless set of symbols? And can you explain why 10 is so natural and non-arbitrary? --COVIZAPIBETEFOKY (talk) 20:14, 23 January 2010 (UTC)

/dedent

My definition of density is the opposite of yours, and exactly the same. You say between any two points there is one point; I say beside any one point there are two points. I'm talking about a peak, you're talking about a valley. It's the same difference, just opposites of each other. Can you see how arguing is futile here? We each are looking from a different direction at the same thing. (That is of course my opinion, while yours is your own and likely to be different than mine). Thank you for talking to me anyway. Sorry if it can be frustrating. --Neptunerover (talk) 07:54, 24 January 2010 (UTC)

WRONG. You got my definition wrong, and your definition makes no sense. How is a set such that every point has a first point above it and a first point below it 'dense'? Aren't the integers 'dense' under your definition? Every integer has a next integer (n+1) and a previous integer (n-1).

As for my definition, I did not say there is only one point between any two distinct points, and if you thought I meant that, you are deeply mistaken. All the definition says is that there is at least one point between any two distinct points, which implies that there are, in fact, infinitely many points between any two distinct points.

Let me explain: let a and b be distinct numbers in a system which is dense under my definition. Let c be a number between them, guaranteed to exist by density. Well, c is distinct from b (it is also distinct from a), so there is another number between those two, which we'll call d, which is, in turn, distinct from c, producing another number e, and so on. Thus there are infinitely many points between a and b. --COVIZAPIBETEFOKY (talk) 16:09, 24 January 2010 (UTC)

I understand your point of view, and I agree fully with your description of density. You're saying that there cannot be two numbers next to each other because in between them there is always room for more. My peak/valley comparison might not be very accurate now that you get me to look at it another way. I'll have to consider then what I meant.

Okay, what I'm thinking about has to do with the amount of change between any two 'adjacent' numbers, the difference between them will be some power of 10, meaning a 1 following however many zeros past the decimal point. In your example of a and b, if we take their separation as being .1, then the difference between either of them and c will be .01 or a lower power of ten. Each time the valley between two 'adjacent' numbers spreads for another number, the new difference represents a drop in magnitude. I'll see what you think of this, as I'm certain it's not complete. I don't have the right words to use here. --Neptunerover (talk) 17:00, 24 January 2010 (UTC)

I don't quite understand what you're trying to define. What is given, where do you intend to get? Do you want to start with the rational numbers (or the numbers of the form a/10ⁿ, where a and n are integers, n non-negative?) and then construct a number system where 0.999... differs from 1 (and where every number has a progenitor and a successor)? What other properties shall your desired number system possess? For example, shall it include all rational numbers? All reals? Shall it be a ring, or even a field? Or are you trying to do something completely different? Huon (talk) 18:00, 24 January 2010 (UTC)

I suppose I'm trying to figure out 'God's numbers', meaning a set of numbers that realistically represents the range of the universe (realistically to me, I cannot stress enough, because, as I've said, I find math difficult). Through the holographic principle, the 'inside' of a black hole can be considered a zero while the center of a star would be a 1. All the rest of the universe consists of the border between those two polar opposites. --Neptunerover (talk) 18:44, 24 January 2010 (UTC)

In your question though, you assert something that is seen as true by you and false by me, so I'll not be able to satisfy your question as posed. I could give you an example about 10 being natural for us, but my example would likely be viewed as nothing more than silly coincidence, and since my bet is that you consider coincidence irrelevant to reality, I think I should keep it to myself. --Neptunerover (talk) 20:26, 23 January 2010 (UTC)

/dedent

If you're not willing to share your views, how can we make sense of them to properly explain why they're incorrect? You'll notice everyone else has given up on you; that is because, as far as we can tell, you are spewing utter nonsense. Would you care to define a decimal representation? To us, it is a mapping from natural numbers to digits between 0 to 9. That is obviously not capable of representing "0.333...332", so you must have something different in mind when you use the words "decimal representation" than we do. Care to explain what your version of a decimal representation is?

For any countably infinite set, there exists a bijective function which maps the countably infinite set to the set of natural numbers, even if the countably infinite set contains the natural numbers. For example, the set of rational numbers - those numbers which can be written as a quotient of integers - contains the natural numbers as a subset, but is no bigger than the set of natural numbers since the rationals are countable: There is a bijection from the naturals to the rationals. --Neptunerover (talk) 17:30, 25 January 2010 (UTC)

You suggest that people abandon this discussion out of frustration, but I suggest another possibility that perhaps each in their own turn went "ah-ha!" and subsequently went off to write their own paper in hopes of recognition and perhaps a Nobel Prize. Neptunerover (talk) 08:40, 25 January 2010 (UTC)--

Don't flatter yourself. --COVIZAPIBETEFOKY (talk) 13:38, 25 January 2010 (UTC)

I think I've already stated that I consider them to represent a ratio between 0 and 1. --Neptunerover (talk) 22:34, 23 January 2010 (UTC)

I presume you mean a ratio of two integers, in which case you refer not to real numbers, but rational numbers. Those are incomplete; for example, they miss the square root of 1/2 (note that I have not defined the word 'incomplete' for you, and will not attempt to do so as it is rather complex, but that does not mean that you can magically insert your own definition; see here for a definition, if you wish). Also, the rational numbers are dense like the reals, so there is no greatest rational number less than 1, or any other rational number for that matter. --COVIZAPIBETEFOKY (talk) 23:20, 23 January 2010 (UTC)

Do you have a definition for unknown? Rather than .000...1 having no meaning (for me), I consider its meaning to be unknown. --Neptunerover (talk) 05:28, 24 January 2010 (UTC)

I'm not talking about a complete set. This set is filled with holes, and the only number without any holes is 1. --Neptunerover (talk) 07:30, 24 January 2010 (UTC)

First you say the set is filled with holes, and then you refer to a number not having any holes. Do sets have holes or do numbers have holes? I assume that for a set to have holes in it, you must mean that there is some sense in which something is 'missing' from it. How can this same vague property be applied to a number? --COVIZAPIBETEFOKY (talk) 16:09, 24 January 2010 (UTC)

Every other number besides one consists of a ratio of zero to one, making any number less than one include some amount of a hole with it. 1 is also a ratio, but there's no zero involved, it's just 1/1. --Neptunerover (talk) 18:44, 24 January 2010 (UTC)

And if you don't know what a mapping or a function is, I don't think I'm stretching the truth when I say you have gotten yourself in way over your head here. If that is the case, you should probably let this rest for a few years until you are properly introduced to these concepts. --COVIZAPIBETEFOKY (talk) 20:37, 23 January 2010 (UTC)

Your very first sentence (after the dedent) exemplifies the reason I could have for an unwillingness to share (and I have tried). We speak different languages as far as this topic is concerned, and framing the whole discussion from one point of view doesn't help two sides to understand one another, and especially when one side views its part in the discussion as being the corrector of the other side. In my personal opinion, Math textbooks are some of the most horribly written things I've ever experienced, and it takes a good teacher to translate one to a class. I'm certain you'd feel right at home reading one though. However, just because we speak different languages, that shouldn't mean we can't attempt to understand one another. All the experiences in my life have led me to this point with my current point of view, and there's no way I could ever expect anyone else to immediately get what I'm trying to say. But just because someone may be unable to explain something adequately to one, two, or however many people, that doesn't mean they are incorrect. I had no idea this concept would be so foreign to some people. I've gotten much out of this lengthy discussion, even if no one else has. --Neptunerover (talk) 22:18, 23 January 2010 (UTC)

Then perhaps my attitude is too pessimistic; obviously you must have come up with a perfectly acceptable set of numbers, along with well-behaved definitions of addition and multiplication on those numbers, such that every decimal (whatever your definition of a decimal may be) is associated with exactly one number in your system, and every number has a 'next' number and a 'previous' number.

I'd like to see that. Or some other evidence that you have good reason to believe that all mathematicians are wrong, beyond an emotionally charged rejection of a counter-intuitive notion. --COVIZAPIBETEFOKY (talk) 23:20, 23 January 2010 (UTC)

I'm not here to argue with you, especially when you add meaning to my sentences that was never there. I've read there is a big void between mathematicians and physicists. Everyone has their own angle, and it's the right one. I'm afraid I don't find your comments congenial. --Neptunerover (talk) 04:58, 24 January 2010 (UTC)

Okay, I'm failing at making myself clear. I'll try to clarify my point once again: you came here with the suggestion that the difference between 0.999... and 1 is ".0000...1", and we disagreed with you. In the system of real numbers, not only is this patently false, ".0000...1" is a completely meaningless set of symbols. However, that on its own does not mean that you were just spewing nonsense, because you may not be talking about the real numbers.

I am giving credence to your claims. I want to understand your point. As far as I can tell, you are making wild claims with no evidence. You are refusing to define your terms, because doing so will tie you down to those definitions. However, you are willing to wave your hands, and say "there's a number just less than 0.999..., which I'll call 0.999...98", without defining what those symbols mean. If you're trying to present an alternative viewpoint to the real numbers, then for gosh sakes, present it already! If you're not trying to present an alternative viewpoint, then I have sorely misunderstood your purpose in posting here. Perhaps a clarification on your part is in order. Unless you're just trolling?

Anyway, back to asking hand-wavey questions to try and pin down your point of view, since you so jealously refuse to share it openly. Since you have said that your number system, whatever it is, includes rational numbers, let me ask you this: what set of symbols, in decimal, would you denote as just less than 2/11, the repeating decimal 0.181818...? Is it 0.1818...17, or is it 0.1818...80? What if I add .5 to that number, giving 15/22 or 0.681818...? Does that make a difference to what the 'last' decimal should be? What's the last digit of 0.4673823123123123...? Since there is more than one repeating digit, is it not arbitrary what the last digit should be, and therefore how we should represent its adjacent decimal? --COVIZAPIBETEFOKY (talk) 16:09, 24 January 2010 (UTC)

And I would ask you "who's trolling who?" --Neptunerover (talk) 08:29, 25 January 2010 (UTC)

And... that's the end of my trying to converse with you. --COVIZAPIBETEFOKY (talk) 13:38, 25 January 2010 (UTC)

Here's one for you, how do you reckon .666...? --Neptunerover (talk) 14:00, 25 January 2010 (UTC)

I'll take a wild guess that he reckons .666... is 2/3. Do you reckon it differently? (Or have a different question in mind?) Phiwum (talk) 14:23, 26 January 2010 (UTC)

'C' seemed perhaps angry, and that got me thinking of an old Iron Maiden song. --Neptunerover (talk) 14:46, 26 January 2010 (UTC)

In one way, it might mean this red guy with pointy ears and a pointy tail and a pitchfork, but it must be considered that the ones who put forth that claim are also the ones who put forth plenty of other garbage concepts on the evolution talk page and so forth. The accuracy of how fanatics portray their fantasies should be questioned rather than arguing against their delusions. --Neptunerover (talk) 15:02, 26 January 2010 (UTC)

In a word, no. Your claim is wrong, and "0.000...1" has no meaning. A careless juxtaposition of the finite and the infinite does not a theory make. — Lomn 17:17, 21 January 2010 (UTC)

I don't believe I'm juxtaposing anything. I'm just saying that everything there is can be represented in the set between zero and one. I'm only referring to this one set, where anything above one is out of the question, while zero is the absolute bottom. No numbers outside of the set are needed or used. Does that clarify my statement? I'm only referring to decimals--all of them--between 0 and 1.--Neptunerover (talk) 17:38, 21 January 2010 (UTC)

"0.000...1" is such a juxtaposition. "..." describes an infinite sequence of 0s, to which you have appended a finite 1. You can have either infinite 0s, or finite 0s and a 1. Not both. I'm quite clear that you're referring to the zero-to-one range (which is infinite), but "0.000...1" is still just a string of characters with no mathematical meaning. Anyway, I see this has been properly ported to the Arguments page, where it may safely languish. — Lomn 18:16, 21 January 2010 (UTC)

Consider if what our speedometer read was, 0 to 1, with one being light speed, and zero being a dead stop. When we start rolling, what is our very first speed? It's going to be the very next thing up from zero, which will essentially be zero, but not quite zero. Every increase in speed is separated from the next lower speed by what is basically nothing, but still something. Like the separation between the iterations in a fractal. --Neptunerover (talk) 19:16, 21 January 2010 (UTC)

Trying to use physics to understand maths is backwards. It doesn't work like that. If you actually want to look at real world velocities then you will find that speed has no meaning on really small scales. Quantum mechanics gets in the way. Any time period smaller than the Planck time is meaningless (or, at least, not something we currently understand), so asking how far we travel in that amount of time is also meaningless. I'm far from an expert on these things, but if there is a quantization of velocity, then the quanta are finite, not infinitesimal. --Tango (talk) 20:05, 21 January 2010 (UTC)

I would think that Physics and Math should be helpful in elucidating each other. --Neptunerover (talk) 05:29, 22 January 2010 (UTC)

Not really. Maths helps you do Physics, but not the other way around. Physics helps you decide which axioms are worth investigating the consequences of, but that's it. --Tango (talk) 05:41, 22 January 2010 (UTC)

That's fine (it's just a restatement of Zeno's paradox), but it's unrelated to the original topic. — Lomn 20:03, 21 January 2010 (UTC)

.999...9998

How does (.999...9998) differ from either (.999...) or (.999...9997)? --Neptunerover (talk) 09:22, 23 January 2010 (UTC)

What is .999...9998? The answer to your question depends on that. If the "8" (and the "7" in .999...9997) is the n-th digit for some natural number n, then the difference between 0.999...=0.999...9999999... and 0.999...9998 is 0.000...0001999...

If you've read the article's infinitesimals section (or certain parts of this page), we also discuss the (much less commonly used) hyperreal numbers, which allow a positional system where digits are numbered not only by natural numbers, but more generally by (possibly infinitely large) hypernatural numbers. But in that number system, the answer is still analogous: If the "8" is the h-th digit for some hypernatural number h, then the difference between 0.999... and 0.999...9998 (and between 0.999...9998 and 0.999...9997) is 0.000...0001999..., where the "1" is now the h-th digit and 0.000...0001999... may be an infinitesimal. But 0.999... = 0.999...999999... still has nines farther down the line and equals 1. Huon (talk) 12:46, 23 January 2010 (UTC)

I had a terrible algebra teacher one time; screwed me up bad. --Neptunerover (talk) 09:30, 25 January 2010 (UTC)

I think what we have here is a problem of different understandings of infinity. You're saying an infinite, never ending string of nines, while what I'm referring to is an infinite, never ending string of zeros which has a 1 at the end of it. Now that I consider it, I'm sure that it's the paradox that causes such difficulty in this being comprehended, but I see paradox as a very important factor in this universe of ours, and denying any possibility of its existence is comparable to an ostrich sticking it's head in the sand. In fact I think the very idea of infinity might be paradoxical.--Neptunerover (talk) 09:30, 25 January 2010 (UTC)

And here's the crux of the problem. "never ending string of zeros which has a 1 at the end". If it's never ending, where is the end? You can't have it both ways. If it's never-ending, than for ever nth digit, there's an n+1th digit that has the same value. If it has a 1 at the end, that means that there's a value for n that doesn't have an n+1, so it's not never-ending. --Maelwys (talk) 14:35, 25 January 2010 (UTC)

That's what makes it a paradox. Infinity here is between the decimal and the one. --Neptunerover (talk) 14:41, 25 January 2010 (UTC)

Yes, but the problem is that the paradox has no meaning on the common understanding of mathematics. And that's why people are having a hard time discussing this with you, because the rules of math are built to prevent this kind of paradox, so arbitrarily introducing one into your logic conflicts with common understanding, and makes it hard to discuss anything. For example: Which is a bigger number: 0.999...999 or 0.999...998? Well, obviously it would appear that the first one was bigger, because they both have the same "infinite" number of 9s, but it has one extra nine at the end where the other only has an 8. But then which of these is bigger: 0.999...999 or 0.999...9999? Again, they both have the same "infinite" number of 9s, but the second one has one EXTRA nine where the first one has no value. Does that mean it's bigger? Because it has "infinity+1" 9s? --Maelwys (talk) 15:14, 25 January 2010 (UTC)

Ah-ha, so is there any field of mathematics that deals with paradox? What about wave functions? --Neptunerover (talk) 16:14, 25 January 2010 (UTC)

The paradox doesn't need dealing with, it just needs you not to try and define inherently meaningless expressions. Why do you think wave functions would help? They have absolutely nothing to do with this... --Tango (talk) 12:37, 26 January 2010 (UTC)

My question was if paradox has meaning within the study of wave functions. The last person up told me I'm in the wrong area if I want to take paradox into account. --Neptunerover (talk) 15:07, 26 January 2010 (UTC)

Short answer: No. The mathematics of wave functions is neither ambiguous nor paradoxical. Huon (talk) 15:42, 26 January 2010 (UTC)

Lemme ask this, if I'm talking about a ratio between 1 and zero, then is what I'm talking about dividing by zero, which is perhaps the central paradox of my conundrum? (Not to mention, why it doesn't fly here) --Neptunerover (talk) 09:02, 27 January 2010 (UTC)

If you're talking of 1/0 you're indeed talking of division by zero, which is undefined in most contexts (excepting, say, certain projective spaces which neither contain infinitesimals nor are relevant to 0.999...). I don't think it's possible to construct a useful number system which allows division by zero and contains infinitesimals, and even if it were, it'd probably still be unrelated to 0.999... Huon (talk) 11:56, 27 January 2010 (UTC)

half way v. 9/10

There's the old story of "How long would it take to get to X if each day you traveled 1/2 of the remaining distance between you and X?" According to the question itself though, each day when you are through traveling, there will still be a remaining distance to the 'goal' equal to that which you just traversed that day. I don't see how this could be any different if you went 9/10 of the distance each day rather than only half way, other than getting closer faster, because the entire distance to the goal is still never spanned. I suppose that's very different than going 9.999.../10 of the distance each day. In that case the second day would be a very puzzling day. --Neptunerover (talk) 12:19, 26 January 2010 (UTC)

9.999.../10=1, so the 2nd day isn't confusing, just very relaxing since you have already arrived. --Tango (talk) 12:36, 26 January 2010 (UTC)

Neptunerover - there is no difference really. But I'm not sure what conclusion you're trying to draw? The halfway example presents a geometric series: 1/2 + 1/4 + 1/8th + 1/16th etc...and is equal to 1. Do you contest that? Because the same is true for 9/10: 9/10 + 9/100 + 9/1000.... = 1. Your specific application with walking I think is related to http://en.wikipedia.org/wiki/Zeno%27s_paradoxes but not really related to any equality or inequality with the given series.76.103.47.66 (talk) 09:11, 24 February 2010 (UTC)

Isn't this also valid?

Why is the following not valid? .9 does not equal 1; .99 does not equal 1; .999 does not equal 1; etc.

I think there is a paradox here. Proofs to the contrary do not make the proof above invalid. Why is this intuition not acceptable?Tristan Tondino (talk) 02:01, 5 February 2010 (UTC)

It is indeed a paradox. No number in the sequence is equal to 1, yet the limit is 1. Likewise, in the sequence 1, 1/2, 1/3, 1/4, ..., no number is equal to zero; yet the limit is zero. But you don't have a proof: Your argument has no bearing on the limit, only on the terms. Limits exist on the continuous real number line, not for discrete truth values.--Nø (talk) 08:24, 5 February 2010 (UTC)

If that line of reasoning were valid and implied that 0.999... didn't equal 1, we could also argue:

.9 does not equal 0.999...;

.99 does not equal 0.999...;

.999 does not equal 0.999...;

etc., and we'd have shown that 0.999... does not equal itself. Thus, the intuitive approach leads to self-contradiction. Huon (talk) 10:47, 5 February 2010 (UTC)

I confess that I don't understand why Nø claims that this is "indeed a paradox". There is simply no paradox to be found here. A simple reflection on the definition of limit will confirm that, for some sequences x_n, we have

for all n, x_n < lim x_n.

Tristan's observation is no deeper than that. Phiwum (talk) 15:49, 5 February 2010 (UTC)

Insertion: A paradox is when two lines of reasoning collide. Here, a "common sense" argument that might convince some non-mathemaricians collides with the strict logic of mathematics.--Nø (talk) 09:08, 6 February 2010 (UTC)

Reply: that is a much weaker notion of paradox than I've ever seen. Especially since one of the lines of reasoning here is simply invalid. The fact that a correctly understood conclusion differs from an invalid bit of reasoning to the contrary does not make a paradox in my book! (But our difference here is merely semantic, of course.) Phiwum (talk) 10:07, 6 February 2010 (UTC)

I think there is a mistake in your argument Huon: .9 does not equal 0.999... or maybe I have misread it. -- Phiwum, my sense is that these are different kinds of proofs -- the expression in question is "as the limit approaches zero." Is my "pseudo-proof"... logical and the other proof mathematical? Is this an acceptable distinction? Can we be certain there is no paradox without being committed to disunification? Or, in other words, do you mean (in layman's terms... i.e. mine) the language of the first pseudo-proof is meaningless (illformed) in mathematics?Tristan Tondino (talk) 22:53, 5 February 2010 (UTC)

Insertion: Your argument is not logic; it is maybe common sense. The mathematical argument is strictly logical.--Nø (talk) 09:08, 6 February 2010 (UTC)

I believe you misread my argument. We agree that 0.9 does not equal 0.999..., just as 0.9 does not equal 1. I repeated your argument and substituted "0.999..." for every occurence of "1". I believe you intended to argue that since all of 0.9, 0.99, 0.999 and so on are less than 1, so is 0.999... If that were valid I'd argue that since all of 0.9, 0.99, 0.999 and so on are less than 0.999..., so is again 0.999... - which cannot be true. Thus, just because something holds for all of 0.9, 0.99, 0.999 and so on, it needn't hold for 0.999... - and "not being equal to 1" is such a property just as well as "not being equal to 0.999...". Thus, your pseudo-proof is indeed wrong mathematically (and logically too, I'd say). Huon (talk) 23:32, 5 February 2010 (UTC)

Wow, so if I understand correctly, my non-proof is based on one concept "is less than" which cannot hold as we approach infinity... otherwise I would have to accept that 0.999... is less than 0.999... But... is there a proof for 0.999... equals 0.999... or is this an intuition?

Since, 0.9 does not equal 0.99; and 0.99 does not equal 0.999 etc.Tristan Tondino (talk) 00:05, 6 February 2010 (UTC)

Wow, I just read the talk page!?Tristan Tondino (talk) 00:31, 6 February 2010 (UTC)

"is there a proof for 0.999... equals 0.999... or is this an intuition?" It's not much of a proof, but since equality is supposed to be a reflection of 'sameness', we expect it to be reflexive (actually, we expect it to satisfy all the properties of an equivalence relation, which includes reflexivity). That is, x=x because x is certainly the same as x. --COVIZAPIBETEFOKY (talk) 01:06, 6 February 2010 (UTC)

But, "identity" is a complicated issue. There are many cases where x may not equal x - though this seems counter-intuitive and illogical -- at present the proof for 0.999.... equaling 1 seems to rely on an intuition as did the intuitive proofs above -- that mathematics cannot contain contradictions, but this is not established... At least on one reading of Godel's incompleteness theorem. Any thoughts? Tristan Tondino (talk) 01:57, 6 February 2010 (UTC)

Can you provide an example of x not equaling x (besides the obvious x being defined in one context to be 1 and in another context to be 2, and the x's in different contexts being unequal)? I'm really not sure what you have in mind there. --COVIZAPIBETEFOKY (talk) 02:23, 6 February 2010 (UTC)

a =√4 a=2 a=-2 2a=-2a a=-a This may be contextual of course, or just wrong.Tristan Tondino (talk) 02:35, 6 February 2010 (UTC)

Contextual? No. Just wrong? Bingo!

√(x) is defined for non-negative real x to be the unique non-negative real number y satisfying y*y=x. Of course, -y also satisfies the property (-y)*(-y)=x, but √(x) is the non-negative solution. So a=2, and a≠ -2. --COVIZAPIBETEFOKY (talk) 02:42, 6 February 2010 (UTC)

This is being explained to Tristan also at Talk:Square root. --jpgordon^{::==( o )} 07:05, 6 February 2010 (UTC)

Getting back to the problem. There is a fallacious argument in each of the article's proofs. If we cannot assume 0.999... = 1, since it is what we are trying to prove... we also cannot assume 1/3 = 0.333... since it begs the same question as the first proposition. In other words, the pseudo-proofs in the article do not succeed in anything more than hiding the problem. Tristan Tondino (talk) 15:09, 8 February 2010 (UTC)

First, there isn't a problem. But - you are right - some of the proofs are "pseudo-proofs", and the article does not try to hide that. Most students know and accept that 1/3 = 0.333..., and therefore they find arguments like "3 x 0.333... = 0.999... = 1" convincing, but in order to PROVE either of the statements "1/3 = 0.333..." and "1 = 0.999..." formally, you need to understand limits first.--Nø (talk) 15:25, 8 February 2010 (UTC)

I did do some calculus; but what we may be discussing are definitions of 1. 1 is not as simple as it looks. It is as unbounded as 0.999...; 1 could mean the infinite set of all calculations equaling 1. e.g. (2-1,3-2,0.999...) Tristan Tondino (talk) 15:59, 8 February 2010 (UTC)

Those are indeed all representations of 1. Unfortunately many people have trouble seeing that 0.999... is another representation of 1; hence the article. Concerning the 3*0.333... proof: The idea is that one can "show" 1/3=0.333... by long division (where one effectively hides all the limits out of sight); then one can conclude that 0.999... = 3*0.333... = 3*(1/3) = 1 without circular reasoning. Huon (talk) 16:11, 8 February 2010 (UTC)

The article makes it clear (or at least did so last time I read it) that in this context, "1" is a real number, and the definition is pretty unambiguous. I think your problem is not about the definition of "1", but about equality - but the answer to that is that two notations are equal if they represent the same real number.--Nø (talk) 16:16, 8 February 2010 (UTC)

"Sameness"... "equality"... "identity" are curious and generally very ambiguous to me. Even in a Mathematical context. So Nø, your observation is fair.Tristan Tondino (talk) 17:46, 8 February 2010 (UTC)

The terms are ambiguous on their own. What "equal" means depends on the objects you are talking about. You have to define it. Maths is most often phrased in terms of set theory, so all objects are sets and we define two sets to be equal if the each contain the other. We can define the real number, 1, as an equivalence class of Cauchy sequences of rational numbers. For that, we need to define an equivalence relation on those sequences, which we do (roughly speaking) by saying two sequences are equivalent if they get closer and closer to each other as you go further and further along the sequences. Decimal expressions don't actually correspond to real numbers, they correspond to Cauchy sequences of rational numbers (not all such sequences correspond to a decimal expression, though). We say two decimal expressions represent the same number if their corresponding decimal expressions are equivalent. 0.999... corresponds to (0.9,0.99,0.999,0.9999,...) and 1 corresponds to (1,1,1,1,1,1,1,1,1,...). If you examine those sequences you will see that they get closer and closer to each other (ie. for any positive rational number the difference between the nth terms of the sequences is less than that number for a large enough n), so they are equivalent and thus are part of the same real number. (All of this assumes you already have a working definition of rational numbers, which are the field of fractions of the integers, which are defined in terms of the Peano axioms.) --Tango (talk) 12:53, 11 February 2010 (UTC)

No! Equality is not ambiguous and its meaning does not depend on context. a = b iff they are (or denote) the same thing. The axiom of extensionality does not define equality on sets, but rather spells out an important feature of sets: sets with the same elements are equal.Phiwum (talk) 13:01, 11 February 2010 (UTC)

But 0.999... and 1 clearly aren't the same thing - they look different. In the context of real numbers, they are equal, in the context of strings, they aren't. Whether the axiom of extensionality defines equality on sets of just describes it is a question for mathematical philosophers, which I am not and have no desire to be. --Tango (talk) 13:24, 11 February 2010 (UTC)

Of course the syntactic objects 0.999... and 1 are not the same thing. But when we write 0.999... = 1, what we mean is that the object denoted by the two syntactic objects are identical. They are, of course, since both denote the real number one. The issue, then, is not that equality is context dependent, but rather that the interpretation of terms (what each non-logical syntactic object denotes) is context dependent. I suppose my complaint is a bit pedantic, but it seems important to me. Phiwum (talk) 14:36, 11 February 2010 (UTC)

Floor Function?

I'm sorry if this has already been discussed, but can't we just say that 0.999... does not equal one because of this function? I'm not arguing anything, just asking a question.

Floor m.n where m and n are strings of digits, is always m. So doesn't that mean floor (0.999...) = 0? Floor (1) = 1. —Preceding unsigned comment added by Goldkingtut5 (talk • contribs) 06:49, 11 February 2010 (UTC)

Your floor function is defined on decimal representations (or on pairs of strings of digits), not on (real) numbers. Of course "0.999..." is a different decimal representation of a number than "1", but they both represent the same number. For an analogy consider the map E on fractions given by E(p/q) := p. Then we have E(1/2)=1, E(2/4)=2, but still 1/2 = 2/4.

The article already discusses the "decimal numbers" which are in a 1-to-1 correspondence with decimal representations; they suffer from a lack of subtraction because 1-0.999... can't be defined in a satisfactory way. Huon (talk) 12:21, 11 February 2010 (UTC)

The floor function isn't usually defined like that. It is defined as the largest integer than is not larger than the number. The largest integer not larger than 0.999... is 1, since 1 is an integer and 0.999...=1. --Tango (talk) 12:38, 11 February 2010 (UTC)

I see. Thanks for clearing this up. Me, GKT5 15:10, 11 February 2010 (UTC)

And, it's me again, but consider real space. Pick a random point in space. The probability of choosing any one point that is not this picked point would be 1, then, right?Me, GKT5 04:59, 6 March 2010 (UTC)

You don't quite make sense, but I think you are talking about the concept of almost surely. That article should help you out. --Tango (talk) 05:54, 6 March 2010 (UTC)

Ahh, thanks!Me, GKT5 05:46, 7 March 2010 (UTC) —Preceding unsigned comment added by Goldkingtut5 (talk • contribs)

Another way

Here's another way. Since 1/0 equals infinity, then 1 = 0*infinity, and 1/infinity = 0. 0.999... plus 1/infinity = 1, then 0.999... plus 0 equals 1, and 0.999... = 1. 24.1.201.172 (talk) 01:56, 21 May 2010 (UTC)

The reason why it is like this is because i don't know how to format with actual math symbols since they introduced this new setup. 24.1.201.172 (talk) 01:59, 21 May 2010 (UTC)

Yeah, but 1/infinity = 0, that just proves that 1=0 (multiply each side by infinity, duh), so it won't work. 68071 (talk, contributations, something random)

ipart formula from calculator

I have a TI-34 II calculator at home and it has the ipart function and the fpart function. The ipart stands for integral part, and if 0.999... was inputed into the calculator with the ipart function thingamajig (like this: ipart(0.999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999...)), it will still be 0. If you do 1, it will come up as 1. Therefore, they aren't the same. 24.1.201.172 (talk) 02:07, 21 May 2010 (UTC)

I doubt that you really entered an infinite number of 9s. If not, then the calculator was, of course, right. The integral part (i.e., the floor) of 0.999...9 is 0 for any finite number of 9s.

It does not follow that 0.999... < 1 (where 0.999... has infinitely many 9s).

Tell you what: try it again, but this time, enter an infinite number of 9s. We'll wait for it. Phiwum (talk) 02:35, 21 May 2010 (UTC)

First of all, I agree with you. The person (my brother) who wrote the thing up there didn't punch in infinity digits of 9s, because it is impossible. The Sinebot thingy didn't know that was my brother (duh, it is a bot). Sixeightyseventyone (talk) 21:16, 21 May 2010 (UTC)

I give reason against my brother that 0.999... is equal to 1. The reason why is because:

0.999... = the infinite series 9/10 + 9/100 + 9/1000 + 9/10000 + ... , which converges to 1. Sixeightyseventyone (talk) 01:52, 22 May 2010 (UTC)

Understanding why 0.999... = 1 in simple terms

The facts I presented violated the terms of Wikipedia according to some people - So I removed my piece on explaining it in simple terms. If you have no mathematical background, then sorry, I guess understanding this is not in the cards for you, because presenting the facts of this for you violates wikipedia. I suppose they want you to go take 5 years of math and then understand the proofs.

Would you care to summarize your main points? Tkuvho (talk) 08:56, 26 May 2010 (UTC)

No. Because this isn't so easy for people to understand, and I feel it should be perfectly clear for anyone who is having a hard time. If you think it is too long to read, then you can surely find many many people who explain it very quickly, using precise mathematical proofs. If you do not understand those definitions and proofs, then you need this laid out in this fashion. I wrote this for people who have virtually no background in math other than maybe Elem and Middle School. In that sense, all the points are "main points" and if you just want a summary because you are too lazy to read it or you dont feel like trying then I can't help you. I am NOT trying to be rude, it is just true - and if you found this too complicated to understand than you will have to find someone else because I don't think I could explain it any simpler but I can almost guarantee you that someone could offer an even more simplified version. But If you still don't understand I would be happy to offer you an alternative point of view on the matter, however, if you want less reading, you will get more math, if you want less math, then you will get more reading. 108.2.103.208 (talk) 16:57, 26 May 2010 (UTC)

What's the other point of view on the matter? Tkuvho (talk) 09:28, 27 May 2010 (UTC)

I suspect that you have missed Tkuvho's point. While you're mulling it over, you might want to review WP:SOAP. --Trovatore (talk) 21:27, 26 May 2010 (UTC)

What are you talking about? That wasnt any self-promotion, or opinion piece, it was an explanation of why 0.999...= 1 Without complicated proofs so that people who are not math experts can understand. I can offer any number of proofs for you, but unless you have a background in Mathematics you will not have a clue what I am talking about. I noticed a lot of people were confused and bothered by this fact, so I took time out of my day to help all those people who never went far beyond arithmetic or basic algebra to at least have some sense of understanding. How are the facts that 0.3 is 3/10 and 0.333... is 3/9 ect.. opinions or self promotion? that is ridiculus and uncalled for to accuse me of this. I simply stated FACTS. And then I followed up with a brief explanation of why it seems like it violates common sense and why these things pop up to begin with, by explaining that the number system was our invention that was originally needed for counting, and we kept taking more and more steps.

Those are not opinions. This is an argument page anyways, so isn't this a place to make your arguements based on 0.999... being equal to 1? Well that is what I did. And Tkuvho didnt have any point, how could I miss it?? He said "can you summarize" and I said no, not without adding proofs that people won't understand. However Trovatore if you think I am violating Wikipedias terms than I am removing this entry - now no one will get an easy explaination, they can go take 5 years of math and understand the proofs. And from now, I won't add anything that is 100% factual based, which is .... everything I would write. 173.62.181.145 (talk) 04:32, 1 June 2010 (UTC)