Take the 2-minute tour ×
Mathematics Stack Exchange is a question and answer site for people studying math at any level and professionals in related fields. It's 100% free, no registration required.

I'm not going to prove something, this is just a question. From the first day which I went to University until now I had some root problems in some basic mathematical assumptions and concepts. Please help me to solve the most important of those problems.

For example: infinity !

What is infinity? Is that real? Is infinity concept real? I mean in real world. Your answer is "Yes"? What about Zeno's paradox? I know that there are different solutions for this paradox... but I don't talk about solutions. I'm saying "this is logical" because we accept some basic assumptions. But I can not understand it and compare it with real world. This problem assumes that there are infinite numbers between two numbers OR There are infinite points between two points. But in real world there is a "smallest distance". It's about $1.6 \times 10^{-35}$ meters.

Let's talk more about my root problems: is number "$0$" real ?

What is "zero" ? You can say that "there are three apples on the desk, if you take all of them there is $0$ apple on the desk ?" I still don't see number "$0$"?

I know that they are tools which help us to solve different kind of "real world" problems (I'm a software developer and I always use $0$ and negative numbers). But I can't see it in nature!

What about empty set ? I mean this {}?

there is space between two brackets... how can it be empty? Is there any empty space in world? For example, a box which isn't any air in it! It's an empty box ! No... the element "nothing" is there! "Nothing" is a member of a set... so there is no set with size "zero". There is always a "nothing" or "null" element in there. Am I right ?

Let's talk about other things which are panics in my mind!

What about the set, $\mathbb R$ ?! (the set of real numbers)

There are millions of mathematical theorems which based on the set, $\mathbb R$ ! Somebody show me a set which is not countable in real world ? I mean in nature. (I know Cantor's theorem, but it's based on "infinity" concept! Which I can't understand ).

Again, I know that this kind of mathematics help us to solve real world problems.

I'm not talking about logical relationships between those theorems or other things. They are logical if we base them on these concepts. I'm talking about concepts. Infinity concept, "nothing" concept. etc.

I'm sorry if my question seems ridiculous to someone !

share|improve this question
27  
Where is the lie if you don't claim that any of these concepts correspond to physical reality? (By the way, writing words in capital letters may seem like a good way to emphasize words to you, but to most people it makes you look like a crank. If you expect an honest answer to this question you should make an effort to communicate in a more reasonable way.) –  Qiaochu Yuan Dec 26 '10 at 19:14
11  
@Michel: don't use the word "lies." It's inflammatory and is not making you any friends. Find some way to phrase your question that isn't accusing the people you're asking it of of lying. I'm not going to get any upvotes from christians.stackexchange.com if I ask them "is Christianity based on lies?" I am being lenient because I think you are genuinely confused and want an answer, but if you are only seeking to be provocative I will close this question as subjective and argumentative. –  Qiaochu Yuan Dec 26 '10 at 20:39
7  
I have voted up this question. I think it is legitimate and interesting. –  Matt E Dec 27 '10 at 1:23
8  
A closer question is does 1 exist? Does 2 exist? –  timur Dec 28 '10 at 14:42
14  
Contrary to some of the commenters, I think this is a lousy question predicated on a thourough misunderstanding of mathematics. Objecting to $0$ or $\infty$ on the basis that they do not "exist" (and presence of scare quotes should alert one to how flimsy this line of argumentation is) is like objecting to Shakespeare's Hamlet on the grounds that ghosts do not exist. A fundamental category error is at work here. –  G. Rodrigues May 19 '11 at 19:41
show 24 more comments

10 Answers

I think your questions and struggles with these difficult concepts are completely understandable, but your presentation is terrible. You are unnecessarily confrontational and aggressive. Having difficulties with these concepts is completely all right. Assuming that during hundreds of years mathematicians conspired to build a make-believe world makes you a crackpot. Hence the series of down-votes. I think the first thing you should do is to learn humility and present your ideas with respect. Don't assume that just because something does not make sense to you it necessarily does not make sense.

So, putting aside my initial discomfort with your attitude, let me try to say a few words towards resolving your issues.

1) infinity --- This is indeed something hard to grasp and there are grown mathematicians who are advocating similar views. They are a bit more sophisticated and a lot less arrogant though. As for smallest distance, it has already been pointed out that that would be a statement in physics and not in math. On the other hand, if you believe in dividing integers by integers, you must realize that there are infinitely many numbers between any two numbers or infinitely many points between any two points, just divide the distance by $n$ where $n$ runs through $\{1,2,3,\dots\}$. But of course, you could try to argue that it does not make sense to talk about arbitrarily large numbers such as $2^{2011}$ as they have no practical applications. I can't say anything to that.

2) zero --- I always thought that whoever first invented zero and the empty set had to be a genius. These are indeed difficult concepts. However, you are confusing a few things here. You say

..."nothing" is a member of a set...so there is no set with size "zero". There is always a "nothing" or "null" element in there. Am I right ?

No, you are not right. First off, what do you mean by "nothing"? The only sensible mathematical meaning of that is the empty set. So, you are talking about a set that consist of one element, which is the empty set. That's different from the empty set that has no elements at all.

You also say

You wanna tell me that "there is 3 apple on the desk, if you take all of them there is 0 apple on the desk ? " I still don't see number "0" ?

Yes, you are right! There is $0$ apple on the desk and you don't see the number $0$. There are many other things you don't see. For example you don't see the dark side of the moon, but you would not doubt that it is there. You don't see the Sun at night but you know it exists even at night.

What about negative numbers? Those don't exist either? So when you take out a loan and you owe the bank a ton of money, it is not real? If you accept negative numbers, you have to accept zero as well.

3) uncountable sets --- I guess this is a more sophisticated version of your problem with infinity. So, can we accept the existence of (non-zero ;) natural numbers? Say $1,2,3,\dots$? If so, then it is easy to show you an uncountable set: take the set that consists of all the subsets of $\{1,2,3,\dots\}$.

share|improve this answer
    
I changed my question many times. Please look at my answer and let me know if I am wrong if you can. Thanks for this good answer. Thank you. –  Michel Kogan Dec 27 '10 at 17:35
4  
Dear Michel, I see that you rephrased your question and I think it is now free of the seeming arrogance of the first version. Kudos for that. As for the content, at the moment I don't think I can add anything to my answer. I believe the issues you raise are completely understandable, but the way to solve them is to try to understand these concepts. The root of your problem is that you are trying to find mathematical ideas in the real word. Mathematics is abstract. Anything you can see is only an approximation of that. (Or if you want, mathematics provides an "abstractization" of real things.) –  Michele Kakusi Dec 27 '10 at 20:21
1  
Your interesting point in 1) about whether large numbers like $2^{2011}$ are really necessary is a view advocated by many mathematicians in the form of ultrafinitism. The outspoken Doron Zeilberger, for instance.. –  Sputnik May 19 '11 at 17:50
2  
$2^{2011}$ might be too small as an example of an useless number, as RSA public key is often that magnitude. –  sdcvvc Dec 3 '11 at 23:44
add comment

Claim: At least one of $0$, $\infty$ exists.

Proof: If $\infty$ exists, we are done. If not, the number of instances of $\infty$ is $0$.

I am actually somewhat serious. This is an adaptation of a certain philosopher's (unfortunately I cannot remember who) ontological proof of the existence of the empty set, which is itself an extraordinarily perceptive and witty riff on St. Anselm's ontological argument for the existence of God. Strangely, while theists and atheists alike tend to find St. Anselm's argument intriguing but not convincing (I seem to recall that Anselm's paper begins by apologizing -- to God -- for making the argument), when you invert it to prove the existence of nothingness, it seems quite convincing!

share|improve this answer
add comment

It's not mathematics but rather physics which is based on these "lies". In mathematics, we assume (if we're Platonists) that objects like the real numbers "really exist", just not in the physical world, and then everything makes sense. Some people pretend that when they're doing mathematics, they're just combining axioms and derivation rules to prove theorems; these people have to take as an article of faith the fact that their chosen axiom system (e.g. ZFC) is consistent, otherwise all their toil makes no sense.

When mathematics is applied to the real word, e.g. in physics, then often some approximations are made, like the fact that (at least in classical physics) a Cartesian coordinate system describes space, and the real line describes time. These approximations can be explained mathematically: taking discreteness into account in general will only slightly alter the results; but it complicates everything greatly.

Some mathematics is not like that, for example when a poll is being taken, statisticians will calculate the standard deviation - this makes sense even if you don't believe in the real numbers; they are just a theoretical construct introduced to understand discrete phenomena. At a final count, everything reduces to finitistic reasoning, whose validity however rests on some unfounded belief in the consistency of some axiom system.

Last but not least, why do you oppose zero? If you take a ruler and mark a peg every inch, then you ask yourself "how many pegs do I need to jump from 2in to 3in"? The answer is $1$. Then "how many pegs do I need to jump from 2in to 2in"? The answer is zero. You can understand negative numbers this way.

Also, zero apples is the number of apples that remain after you've eaten all of them. And there are many more examples, in fact an entire book was written on the subject.

share|improve this answer
3  
+1 for it is not mathematics, but physics! –  Aryabhata Dec 26 '10 at 20:24
    
Thanks for this answer. I changed mt question and write an answer. Is my answer right ? –  Michel Kogan Dec 27 '10 at 17:43
3  
As for zero - I don't see why you're having trouble with zero. Do you also have troubles with concepts like "justice", "compassion"? Zero is much more well-defined than these, and even better defined than "red". –  Yuval Filmus Dec 27 '10 at 20:13
    
As for infinity, e.g. the natural numbers, some people (Finitists) also think that the set of all natural numbers makes no sense since you can't capture infinite in finite means (whether it exists or not). These people can perhaps agree that numbers up to (say) $10^{300}$ really exist, but such bounds are not very handy to work with mathematically. So instead they work with weak proof systems, in which natural functions don't grow "too fast". Lots of mathematics can still be done in these weak systems. –  Yuval Filmus Dec 27 '10 at 20:15
1  
No, I don't have problem with justice or compassion. I know we can speak about those concepts too. I couldn't understand zero because I couldn't see it. I gave my brain to my eyes I think. I feel much better right now, I'm going to completely understand so many problems depends on these basic problems. I still think that we can build a mathematical structure from beginning and put all physical realities in it. For example in that structure we can change R set concept to something like the set of all electrons in the universe. It's just a thought. At this moment this question solved in my mind. –  Michel Kogan Dec 28 '10 at 8:10
show 1 more comment

It seems like your premise for mathematics being a 'lie' is that its theoretical background cannot be completely applied to the real world (e.g. having the smallest distance in the real world, but not in mathematics). If that's how you define a lie, sure, but mathematics is an abstract science and I am not sure why you think it's supposed to hold certain properties that are true in the real world -- abstraction is actually the whole point.

Solutions to Zeno's paradox have been offered, I am not sure what you mean by "but i don't talk about solutions. I'm saying "this is LOGICAL". But it's not TRUE." In fact, Zeno's paradox shows the lie of the real world, as Zeno contested that motion does not exist and is an illusion.

"You wanna tell me that "there is 3 apple on the desk, if you take all of them there is 0 apple on the desk ? " I still don't see number "0" ?" -- true, but neither you see number 3 when there are 3 apples on the desk, correct? 0 is used to denote lack of objects, and it's definition is a tad more complicated than definition of other integers, and for a reason (it can be used differently in different branches of mathematics). Also, if you want a real-life definition of zero, think of not moving, not gaining weight, not making any progress -- all of this can essentially be seen as addition of zero.

An empty set is a set (which, again, is an abstract concept) that has no elements. Careful with the words -- it's not the case that it has 'nothing' as an element, it's rather the case that it has no elements at all. Here, it comes down to semantics of the definition, but you once again seem to be drawing parallels to real life and trying to find a corresponding entity. I do not quite see why that should be the approach -- we are talking about mathematics, not physics.

With respect to the set of Real numbers, again, same story. I do not know if you can find an uncountable set in the 'real world' (though I suppose you could contest that the set of points of any object is uncountably infinite, because as you keep zooming in you will be getting more and more particles, and it's our limitations that do not allow us to see past atoms). But that is not the point. Mathematics is based on some abstract ideas, and it's true that not all of them are necessarily reflected in nature. That does not, however, make mathematics based on 'lies.'

share|improve this answer
    
Thanks for your answer dear InterestedQuest. Please look at my answer. What do you think about it ? Am I right ? –  Michel Kogan Dec 27 '10 at 17:35
    
You could say an empty set is like an empty box. "Nothing" is inside it. –  muntoo Dec 29 '10 at 19:42
add comment

First of all please agree my apologies because of my attitude and the way I asked my question. I changed it again. I really didn't aggressive in reality just present my question in a bad way. But believe me or not, whenever I asked this kind of questions from my teachers they down voted me in real world. I should ask my question in more warily way. As Yuan commented in my question "I'm not going to get any upvotes from christians.stackexchange.com if I ask them "is Christianity based on lies?"". BTW, I didn't sleep last night and thinking about my question and these answers and comments.

I read all these 3 answers many times. And thank you. I think the real answer is combination of these 3 answer:

  1. Mathematics is different from Physics. We can't completely compare them with each other. Mathematics is an abstract science while Physics is natural science. So they are different types.

  2. We should choose an axiomatic system before talking about a theorem. ( like ZFC ).

  3. About infinity: This is a part of Mathematics not Physics. We can imagine that there is a number bigger than any number. That number is Infinity ! ... I don't know if it exists in physics or not. For example "is world infinity or not !?"... "Is there a new world inside a black hole or not!" ... But in mathematics we can imagine it. And we can work with it without much problem. In many parts we see unbelievable theorems( in physics ) when we assume infinity is exists. But they are logical. So we can accept them. Infinity is just a tool. Nothing else I think!

  4. About Zero: zero is a concept. It's not real. We can't see it. But this concept is exists. Show me the word "lie". What is a "lie" ? I can't see it. but this is a concept and exists.

  5. Empty set: I can't imagine a set which don't have any element in Physics and reality. But I can imagine it in my mind. I can imagine "nothing". it's a concept again. so we call it "empty set" in mathematics. A set that there is nothing in there. I think I just playing with words in my question. nothing is not an element. it's a word.

  6. Uncountable sets: If I can accept infinity. I can accept this too. So I have no word to say about.

I think this answer is a combination of these answers. I found my answers I think. Thank you again for helping me get out of this confusion. But please let me know if this answer is wrong !

share|improve this answer
    
Please let me know if I'm wrong. –  Michel Kogan Dec 27 '10 at 18:18
5  
Yeah, except I am not sure if treating infinity as a number is correct -- it's more of a concept. You are right, most of this is conceptual. –  InterestedGuest Dec 27 '10 at 20:17
    
Infinity is not normally considered a number (what it is depends on the context... for example, if a limit is infinity, "infinity" describes the long-term behavior of a function.) Besides this technical nitpick, you're answer is absolutely correct and should be accepted. –  Brennan Vincent Dec 29 '10 at 5:37
add comment

Concerning infinity, here is my take. When we say, for example, that there is an infinity of natural numbers, we mean only that there is no largest number. Whenever you add 1 to a number, you will get another number that is greater still. Nothing very profound there. To say otherwise would greatly complicate even basic arithmetic.

It may even be possible to do away with the use of the word "infinity" (or any equivalent notion) in most if not all of mathematics. It may be nothing more than a convenient shorthand. When we say, for example, the limit of some expression as x tends to infinity, we could as easily have said, the limit as x increases without bound. The latter would have the advantage that there would be no confusion about there being some kind of endpoint called "infinity."

share|improve this answer
1  
However, when we say that there are $\omega$ natural numbers, we are saying much more than that there is no largest natural number. And though there is a largest negative integer, the set of negative integers is nevertheless infinite. –  Brian M. Scott Feb 18 '12 at 1:01
1  
Good point. When we say that there is an infinity of negative integers, we mean there is no smallest negative integer. Whenever you subtract 1 from a negative integer, you get another number is the SMALLER still. The successor relation you pick depends on the set in question. The point is, it never terminates and never comes back to the same point. –  Dan Christensen Feb 19 '12 at 3:50
add comment

As an indirect way of answering this question, I'd like to bring up an example from wave mechanics that I was told earlier this semester. Physically, when an electromagnetic wave hits a perfect conductor, say from the left, the wave disappears to the right of the conductor. What happens mathematically is the following: the charges emit a wave that is the exact mirror of the original one, cancelling it for all time and space to the right of the conductor. Now, a natural question in this scenario is, are the two waves to the right of the conductor real, actually extending infinitely, or is there really no wave there any more?

The answer to this question is: the question does not make physical sense. Physics is concerned with measurable quantities; you can ask "what is the electric field to the right", and both interpretations of what's 'really' happening will give you the same (correct) answer.

In the same way, mathematics is built on abstractions. The question of these abstractions being 'real' or not is not mathematical (nor logical), but philosophical; mathematics is the foundation of our technological society, which works quite well, which is the proof that mathematics is valid in the real world.

share|improve this answer
add comment

In reading through these answers, I'm pretty sure that most everything has been answered - except for the treatment of the empty set. By now, I think that we can say that $\infty$ is not a number, but instead a convenient convention referring to an unbounded convention. $0$ is a number and it refers to a very concrete thing - but no one (I think) has yet said anything of how number systems came into being. While I think that many people know that our current positional number systems (like binary or hex for programmers, decimal for day-to-day life) are relatively recent developments. But many number systems do not have a symbol for 'zero.' Why would they? We use it in our positional system all the time - when we write 102, we refer to 1 100, 0 10's, and 2 1's. We rely on zero all the time. But without relying on a positional number system, the only time one would need zero would be when referring to... nothing. There are no apples on the desk and there are zero apples on the desk. Does that deserve its own number?

We think it does, and it's useful for it.

But this is very different than the empty set. We think of sets of things all the time, even if we don't explicitly call it a set. We have a box of chocolates, for example. This is like saying that we have a set of chocolates, or maybe we have a set of boxes that can contain chocolates with exactly one element. What happens when we eat all the chocolates (or as happens upon occasion, the chocolates are not tasty, and so we throw them away)? Then now or 'set of chocolates' collection is empty. But until we throw away the box, our 'set of boxes' still has one thing.

I think that maybe the problem you're identifying with the empty set is related to the concept of vacuously true statements. For example, the set of flying pink elephants that contributed to both Nephireti's and Hitler's rule is empty. And all such elements are right in front of me. All such elephants are also versed in calculus. And so on. The problem with vacuous things is that there is no substance to them - there can be no counter examples found within the set if it's empty. It's very troublesome.

But just like the number zero, the empty set is useful. We use it all the time - it's a useful idea. This is similar to the number 7 - it's a useful idea that may not be entirely obvious. For a while, people had trouble distinguishing between a number and a number of objects. For example, is the '7' in '7 sheep' somehow different than the '7' in '7 cows?' Does it make sense to talk of this '7' apart from some sort of counting reference? We do it all the time, but it's not so obvious to do so.

That's my take on the subject, anyway.

share|improve this answer
    
@Michel: I also add that there are many instances of real world examples that are not countable. As soon as we talk of possibilities, for example, it comes up all the time. Say we toss a baseball into an empty baseball diamond. How many places could it land? There is a continuum of places where it could land, so it's not countable. –  mixedmath May 19 '11 at 20:04
add comment

(Disclaimer: I am neither a trained linguist nor a psychologist, so take my claims with a grain of salt)

Part of your concern is not about mathematics, or of physics, but actually of the English language. There is a famous idea that "language constrains thought".

One example of this is the notion of degeneracy. In English, one can say

There is/are <quantity> apple(s) on the desk.

where is a positive integer. But in natural English, one cannot say

There are zero apples on the desk.

Instead, one expresses this degenerate case with a different linguistic construct, e.g.

There are not any apples on the desk.

("there are no apples" is an abbreviation of this: see here). In this situation, one does not answer the question "how many apples are on the desk?" but instead rejects the premise that there are any apples at all.

Because language treats the cases fundamentally differently, this shapes peoples' thought about quantity and makes it difficult for them to think of "zero" as an answer to a "how many" type of question.

This gets confounded further with words like "nothing". When the phrase

There is no thing on the desk.

is shortened to

There is nothing on the desk.

people still think of the latter being the same as the former: a rejection of the claim that there are any things on the desk. The danger is when one gets the idea that we can use a word like "nothing" to answer the question "what is on the desk?", but is still believes answering the question without rejecting it means accepting the implicit premise that there is something on the desk.

Such a person then has an incredible amount of trouble sorting through all of the classic "nothing is something" wordplay.

share|improve this answer
    
"I have no idea" -> so I have an idea about having no idea.... If i'm talking about an "empty" box, there is "nothing" inside that box. So, its not empty. its contain "nothing". for sure there were philosophers that struggled with these concepts. –  Michel Kogan Jun 17 '12 at 15:45
add comment

The empty set and 0 are easy. The empty set is a set which has no proper subsets and its cardinality is 0. The important concept here is that if you have 0 apples on your desk I can not take an apple from your desk, and I shall be able to see that.

If you had 5 apples on your desk there would be a 1 to 1 mapping between the set of digits on my hand and the set of apples on your desk, with 0 elements left in either set. These sets would both have cardinality 5. You can define <, =, and > by considering which, if either, set has elements left over after mapping. I can now take an apple from your desk and when you map the proper subset I leave against your hand you will see you are missing an apple (or you have grown an extra digit).

Infinity is trickier. The set of even integers is a proper subset of the set of integers and there is a 1 to 1 mapping between the set of integers and the set of even integers, both sets have the same cardinality. This property defines infinite, and in this case both are countable.

There is a 1 to 1 mapping between the set of integers and: the set of rational numbers; the set of irrational numbers which are the root of an integer polynomial, so these are also countable.

The set of transcendental numbers is much larger than any of these sets and is called uncountable (i.e. there is not a 1 to 1 mapping between the set of integers and the set of transcendental numbers, there are transcendental numbers left over when the set of integers is exhausted). The set of real numbers is made up of the sets of integers, rational numbers, irrational numbers which are the root of an integer polynomial , and transcendental numbers and so it is uncountable.

The next known larger infinity is the set of all single value functions (see http://www.math.utah.edu/~pa/math/sets/FgtR.html).

share|improve this answer
    
I have never seen a definition where $\text{irrational}\not\supset\text{transcendental}$ like you're implying. –  Karl Kronenfeld Aug 12 '13 at 12:07
    
You seem to be claiming a bijection between the integers and the irrationals. But it might just be an odd notation, using a ; there. –  Tobias Kildetoft Aug 12 '13 at 15:28
    
The last sentence is completely incomprehensible, and I suspect that it's false (if I understand it correctly) just as well. –  Asaf Karagila Aug 12 '13 at 15:34
    
Yes. The last sentence is false. –  Asaf Karagila Aug 13 '13 at 13:44
add comment

protected by Qiaochu Yuan Jul 23 '11 at 18:00

Thank you for your interest in this question. Because it has attracted low-quality answers, posting an answer now requires 10 reputation on this site.

Would you like to answer one of these unanswered questions instead?

Not the answer you're looking for? Browse other questions tagged or ask your own question.