An end to infinite?

1. Sep 24, 2007

kurushio95

I think infinite is not real. Think about it. What is the closest positive number to zero that you can have? it would be 0.000...01, right? infinite zeros plus one. What do you guys think? I didn't know where this would belong, so I bunged it here.

2. Sep 24, 2007

Hurkyl

Staff Emeritus
Why do you think there is a closest?

That cannot a decimal number. The places in a decimal number are indexed by the integers; therefore, each place must be at a finite distance from the decimal point.

Also, your notation is poor. It suggests that you have a consecutive sequence of zeroes, which must necessarily be finite. If it were infinite, then it must consist of two or more disconnected sequences. I use a pipe (|) to denote these breaks -- it is, in fact, possible to have an infinite connected sequence of zeroes:
000...​
and it is possible to have an infinite connected sequence of zeroes followed by a 1:
000... | 1​
however, there is no number to the immediate left of the 1. If you want every place (aside from the left endpoint) to have a number to its immediate left, you can build a sequence like
000... | ...0001​
but these two components do not connect in the middle. Of course, this and the previous sequence cannot denote a decimal number.

Last edited: Sep 24, 2007
3. Sep 25, 2007

ganstaman

Ok, so you think infinite isn't real, and yet you think that you can have 0.[infinite 0s]1?? How can you have an infinite number of 0s if infinity isn't real? A self-contradictory stance that proves itself is interesting, but of little philosophical or scientific value, IMO.

4. Sep 25, 2007

Hurkyl

Staff Emeritus

What does any of this have to do with reality?

This is not what you meant. The zeroes are not infinite; it's the quantity of zeroes that is infinite. You meant to say something like "infinitely many zeroes".

In fact, zero has the opposite quality: zero is smaller than every positive real number, and is thus an infinitessimal number. (It is, of course, the only infinitessimal real number)

5. Sep 25, 2007

Hurkyl

Staff Emeritus
Disconnected is an awkward word; to use here. I think I implied what I meant, but shame on me for not explicitly defining it!

What I mean is that if you have a zero in one sequence, you cannot reach the other sequence by iteratively performing the operation "move from this zero to an adjacent zero". Maybe I should have called this "stepwise disconnected".

6. Sep 25, 2007

kurushio95

like i said, i didn't know where a question like this would go. I guess the best way i could explain it is to ask what the smallest positive number is that is not zero. I'm having a hard time phrasing my thoughts into words, in case you couldn't tell.

P.S. I'm only in high school math, so I wasn't expecting to be 100% correct in my notation. thanks for pointing it out though and showing me the correct way.

7. Sep 25, 2007

Staff: Mentor

It may be easier to think about small numbers like this with fractions. Ie, 1/10, 1/100, 1/1000, etc. No matter how many zeroes you put in there, you can always put in one more.

8. Sep 25, 2007

Hurkyl

Staff Emeritus
The problem may be that you don't realize you have made an assumption. When you ask
what is the smallest positive number that is not zero​
you have assumed that such a thing exists.

The truth is that such a thing does not exist; one of the best ways of fighting off these misguided assumptions is to try and prove them. By failing When you to prove that there really is a smallest nonzero positive number, you will begin to cast off this error that is leading you astray.

9. Sep 25, 2007

jostpuur

Part of the confusion arises from the intuitive assumption that the real numbers somehow describe our physically real space. This is probably the original motivation behind the real numbers, but once one learns about the rigorous construction of the real numbers, one inevitably understands that they are not necessarily the same thing as our space.

After learning that there is also different extensions to the real numbers, I've started to think if such extension could exist also, where the smallest positive number would exist. It couldn't be a field extension at least, but perhaps some other extension, that would still contain the field of real numbers as a subset.

kurushio95, want to proceed with you philosophy? Then get rigor!

(... although it would probably be better to first understand real numbers well)