scholarly journals Is the Real Number Line Something to Be Built, or Occupied?

Author(s):  
Hyman Bass
1986 ◽  
Vol 51 (1) ◽  
pp. 190-200 ◽  
Author(s):  
Chris Freiling

AbstractWe will give a simple philosophical “proof” of the negation of Cantor's continuum hypothesis (CH). (A formal proof for or against CH from the axioms of ZFC is impossible; see Cohen [1].) We will assume the axioms of ZFC together with intuitively clear axioms which are based on some intuition of Stuart Davidson and an old theorem of Sierpiński and are justified by the symmetry in a thought experiment throwing darts at the real number line. We will in fact show why there must be an infinity of cardinalities between the integers and the reals. We will also show why Martin's Axiom must be false, and we will prove the extension of Fubini's Theorem for Lebesgue measure where joint measurability is not assumed. Following the philosophy—if you reject CH you are only two steps away from rejecting the axiom of choice (AC)—we will point out along the way some extensions of our intuition which contradict AC.


2010 ◽  
Vol 41 (2) ◽  
pp. 117-146 ◽  
Author(s):  
Robert Ely

This is a case study of an undergraduate calculus student's nonstandard conceptions of the real number line. Interviews with the student reveal robust conceptions of the real number line that include infinitesimal and infinite quantities and distances. Similarities between these conceptions and those of G. W. Leibniz are discussed and illuminated by the formalization of infinitesimals in A. Robinson's nonstandard analysis. These similarities suggest that these student conceptions are not mere misconceptions, but are nonstandard conceptions, pieces of knowledge that could be built into a system of real numbers proven to be as mathematically consistent and powerful as the standard system. This provides a new perspective on students' “struggles” with the real numbers, and adds to the discussion about the relationship between student conceptions and historical conceptions by focusing on mechanisms for maintaining cognitive and mathematical consistency.


1971 ◽  
Vol 225 (2) ◽  
pp. 92-99 ◽  
Author(s):  
Lynn Arthur Steen

1986 ◽  
Vol 79 (7) ◽  
pp. 507-510
Author(s):  
David R. Johnson

How do your algebra students read the symbol −x? Common responses are “negative x,” “minus x,” “the opposite of x,” or “the additive inverse of x.” The most common response is “negative x.” But are all these responses meaningful? Definitely not! In fact, the first two responses are very misleading, if not incorrect. In many classrooms, teachers are quite careful to name a real number less than zero (or to the left of zero on the real-number line) a negative number. Students quite easily grasp the meaning of the phrase negative number. But suddenly we bring out the expression − x and read it “negative x”! Trouble begins. Students immediately assume that this symbol stands for a number less than zero simply because its verbal name contains the word negative.


Author(s):  
Juan Ramirez

We present the real number system as a natural generalization of the natural numbers. First, we prove the co-finite topology, $Cof(\mathbb N)$, is isomorphic to the natural numbers. Then, we generalize these results to describe the continuum $[0,1]$. Then we prove the power set $2^{\mathbb Z}$ contains a subset isomorphic to the non-negative real numbers, with all its defining structure of operations and order. Finally, we provide two different constructions of the entire real number line. We see that the power set $2^{\mathbb N}$ can be given the defining structure of $\mathbb R$. The constructions here provided give simple rules for calculating addition, multiplication, subtraction, division, powers and rational powers of real numbers, and logarithms. The supremum and infimum are explicitly constructed by means of a well defined algorithm that ends in denumerable steps. In section 5 we give evidence our construction of $\mathbb N$ and $\mathbb R$ are canonical; these constructions are as natural as possible. In the same section, we propose a new axiomatic basis for analysis. In the last section we provide a series of graphic representations and physical models that can be used to represent the real number system. We conclude that the system of real numbers is completely defined by the order structure of $\mathbb N$.}


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