Irrational Number Phenomenon

cloud_sync

This has been aggravating me for years. Call it "IDP" as a placeholder name for now, if you will. How come irrational numbers keep propelling forward for particular divisions? My inquiry applies for both repeating and non-repeating irrational numbers. "Just is" or "You're thinking too much into it," are answers I have received in the past. We need to embark a new mindset in math. It is almost as if there is an untold story in physics that ties in with math. Why does uneven division exist for only particular divisions? For example, if we divide 1/2 we get 0.5, but if we divide 1/3 we get 0.333333... I am not asking for the apparent answer to this question. I am asking why our number system creates this inaccuracy for only particular divisions while other divisions come out even. Is it because we use a 10-base number system? Anyone ever question why we haven't been able to established a clean-cut, division system that overrides this phenomenon?

daveyp225

The "phenomenon" you speak of is due to our decimal base. It was a choice that was made by man to pick it as a standard. Some people use different bases. Although all bases will have a similar thing going on. 1/3 in base 3 is just 0.1. But 1/10 in base 3 is 0.00220022... repeating.

There is no such thing as an "irrational repeating number." Repeating decimals are rational.

pwsnafu

Well technically "0.5" means 0.50000... which is equal to 0.499999....

We just use the convention that if the decimal expansion terminates, there is an infinite string of zeros. We just don't write them because it gets tedious.

SteveL27

I assume you know that it's pretty easy to show that in any base, some rationals will have terminating expansions and others won't. And that the ones that terminate are related to factors of the base -- just as in base 10, any rational a/2^n or a/5^n terminates, because 2 and 5 are factors of 10.

So do you mean why? Are you looking for some underlying reason? It's really just a function of the long division algorithm and the factors of the base. It's a homework exercise in undergrad number theory; no great mystery.

Hurkyl

We have lots of ways to notate numbers. "2/3", for example, is a perfectly good notation for the number you get when you divide 2 by 3.

Decimal notation for real numbers is taught because:

• It's simple
• It fits well with decimal notation for integers
• It's very easy to trade precision for simplicity. (e.g. just write the first few digits)

Most people don't have any reason to learn notations other than a mix of algebraic expressions with decimals.

cloud_sync

If you change the base it just shifts where the INP takes place in your written notation. Nothing has been solved, so-to-speak. It is almost as if there is something in nature that won't allow for clean-cut division at particular regions/magnitudes in physics.

Let's say we have a thin strip of wood that is 1 inch and we cut it it up in 3rds. This goes back to my initial fraction. Now this is physically possible. Each of the three pieces of wood will now be 1/3rd (i.e. 0.33) in length except for one. One of the pieces received an additional 0.01 more. Regardless if your at the microscopic level or at the macro level, this phenomenon appears unavoidable, so far.

SteveL27

All physical measurements are inexact. It's not possible to cut a physical object into exactly equal halves or thirds or any other fraction.

I understand the nature of your confusion now. The real numbers do not exist in the physical world. There's a difference between math and physics, and you are confusing the two.

agentredlum

I think I understand your idea. As far as positive whole numbers are concerned, and the operation of division, you run into a problem very quickly when you try to divide 1 by 3. This appears unsatisfactory to you (and to me)

Methematicians prove that .999999... = 1

Take a number like .5 they say =.500000... but it should also =.49999...

or .42 = .4200000... = .4199999...

or .1439 = .143900000... = .14389999999...

Any decimal number you can think of that can be expressed as a quotient of 2 non zero integers now appears to have at least 3 different representations, although mathematicians prove that all different representations represent the same fraction.

Zero is interesting in this scheme. I guess one can say 0 = .000000... but what is the other representation?

micromass

You are correct, it is physically not possible to divide a strip of wood in three parts. But it is possible in the mathematical world. You can divide 1 by 3 and get 1/3 or 0.3333... This is mathematically correct. But that doesn't mean that you can do it in the real world.
In the same fashion, things like e or infinity do not exist in the real world (as far as I know), but that doesn't prevent us from working with them in mathematics...

disregardthat

The divisions 1/n which will have a repeating decimal expansion are exactly those for which n contain prime factors other than 2 and 5. This is because the prime factors of 10 is 2 and 5. Generally if a/b is a reduced fraction, it will have a repeating decimal expansion if b has any other prime factors than 2 and 5. It is just because we have chosen 10 as our base for representing real numbers.

SubZir0

You would need a number system with a Field of Elements:
Q[C] = Q + CQ
where C is aleph-one (the infinite cardinal for any point between 0 and 1, for example)


If irrational numbers grind your gears then transcendental numbers must twist you up something proper! Also fractal shapes are infinite finite objects.

micromass

What is that supposed to mean?? Do you mean the fraction field generated by [itex]\aleph_1[/itex] elements?

Also: [itex]aleph_1[/itex] is NOT the cardinality of [0,1] (in general). The cardinality of [0,1] is [itex]2^{\aleph_0}[/itex]. It is unknown whether [itex]\aleph_1=2^{\aleph_0}[/itex].

ramsey2879

The fact that 1/3 has an infinite decimal expansion in base 10 has nothing to do with whether it is possible to cut a strip of wood into 3 equal lengths in the real world. 1/5 has a finite decimal expansion but it is more difficult to cut a strip of wood into 5 equal lengths than to cut a piece of wood into 3 equal lengths. It is more likely though that a piece of wood will have a length spanned by a multiple of 3 atoms than a multiple of 5 atoms so it is more likely that a piece of wood could be cut into 3 equal lengths than into 5 equal lengths. Just because we may not have the expertise to surely cut a piece of wood into three equal lengths does not mean that it could not be done.

SteveL27

Even if you thought you'd cut a physical object exactly in three; how would you know? Any measurement could only state a range for each length.

As a thought experiment, imagine the variables you'd have to take into account to divide a object into three parts. If there's slightly more mass on one side of the universe than the other, the object's dimensions would be affected. So first, you'd have to be able to account for the mass, position, and current state of motion of every particle of matter in the universe.

Of course normally we don't need to take that into account ... we know that "on average" the mass in the rest of the universe is about the same in every direction, and anyway the effect would be negligible. So we ignore it, and end up with an approximation.

If we are to be exact, we must take all these things into account. How would you measure the length of an object? The atoms keep bouncing around. How do you define length? Can you do a measurement in one instant of time? Otherwise you'd only be measuring the average length of the bouncing atoms over a period of time. An approximation!

How do you propose to exactly divide a physical object in three?

daveyp225

Randomly spouting off thoughts here. If whatever method of measurement you are using is divisible by three (say 999999999 identical atoms), given this is just a thought experiment and practical division ignored, manually separate each atom into three separate chambers and reform them into three pieces identical to the original when placed together. If the atoms bouncing around are a cause for concern to obtain adequate length, then if held at the same temperatures/pressures/whataver, they could at least theoretically be assembled in the same conditions (maybe?) so that they have the same movement. So they should be exactly equal in length?

Galron

There is no innacuracy

At the limit of infinity both are the same thing.

There is no existing circle where pi = pi at any scale for example, but that doesn't mean that we cannot use infinite limits it just means that a real world circle approximates: [itex]A=\pi r^2[/itex]; in a perfect universe of abstraction it exactly equals [itex]A=\pi r^2[/itex].

I suppose if you used something like cantors continuum hypothesis you could say that there are infinite infinities all of differing sizes which are the same size. But then you'd disappear up your own axiom.

It might be an idea to google this: Taylor-Maclaurin series

And differential geometry rules in general.

http://upload.wikimedia.org/wikipedi...ntGraphic2.svg

SteveL27

1. Starting from the problem of creating three identical lengths, now you have to create identical pressure and temperature too? Now you have more problems than before!

2. What is temperature? It's a measure of the average motion of the molecules in a given area. It's a statistical notion. Two objects having the same temperature may have very different configurations of molecules at a given instant.

It's essential to understand that there is no exactness in the physical world. Otherwise you start thinking the real numbers are "real."