Cardinality of real #s

May 2015
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Arlington, VA
What is the cardinality of the real numbers, if they include all possible number magnitudes?
 
Aug 2012
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What is the cardinality of the real numbers, if they include all possible number magnitudes?
$2^{\aleph_0}$. The notation literally means the set of all functions from the natural numbers to the 2-element set {0,1}. You can think of it as a binary sequence with a binary point in front, representing a real number between 0 and 1.

Now the funny thing is that if you ask, well what number is $2^{\aleph_0}$, mathematicians have no idea. It might be $\aleph_1$ or $\aleph_2$ or $\aleph_{47}$ or some transfinite cardinal much larger than that. Nobody knows. More accurately, the answer is independent of the standard axioms of set theory, and nobody's found a plausible, universally acceptable axiom that settles the matter one way or another.
 
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May 2015
494
30
Arlington, VA
Isn't Aleph-naught a minimum of some sort? Is there a simple derivation for it?

Some great new information.
 
Aug 2012
2,464
761
Isn't Aleph-naught a minimum of some sort? Is there a simple derivation for it?
$\aleph_0$ is the cardinality of the set of natural numbers $\{0, 1, 2, 3, \dots \}$. It's provably the smallest possible infinite cardinality.
 

mathman

Forum Staff
May 2007
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$\aleph_0$ is defined as the cardinality of the set of integers.