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Irrational Number Phenomenon 
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#1
Aug1711, 09:53 PM

P: 13

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 nonrepeating 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 10base number system? Anyone ever question why we haven't been able to established a cleancut, division system that overrides this phenomenon?



#2
Aug1711, 11:26 PM

P: 88

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


#3
Aug1811, 12:16 AM

Sci Advisor
P: 820

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. 


#4
Aug1811, 01:11 AM

P: 800

Irrational Number Phenomenon
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. 


#5
Aug1811, 04:17 AM

Emeritus
Sci Advisor
PF Gold
P: 16,092

Decimal notation for real numbers is taught because:



#6
Aug1811, 11:56 AM

P: 13

If you change the base it just shifts where the INP takes place in your written notation. Nothing has been solved, sotospeak. It is almost as if there is something in nature that won't allow for cleancut 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. 


#7
Aug1811, 12:08 PM

P: 800

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. 


#8
Aug1811, 04:08 PM

P: 460

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? 


#9
Aug1811, 04:23 PM

Mentor
P: 18,061

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... 


#10
Aug1811, 08:43 PM

Sci Advisor
P: 1,742

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.



#11
Aug1811, 08:52 PM

P: 14

You would need a number system with a Field of Elements:
Q[C] = Q + CQ where C is alephone (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. 


#12
Aug1811, 08:55 PM

Mentor
P: 18,061

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]. 


#13
Aug1811, 09:06 PM

P: 894




#14
Aug1811, 09:43 PM

P: 800

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? 


#15
Aug1911, 02:45 AM

P: 88

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?



#16
Aug1911, 02:50 AM

P: 45

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: TaylorMaclaurin series And differential geometry rules in general. 


#17
Aug1911, 11:05 AM

P: 800

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." 


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