12-31-2005, 01:40 AM
wakim,Dec 30 2005, 04:33 PM Wrote:I can recall playground arguments that ultimately devolved into meaninglessness once infinity was allowed to be treated as a number of finite magnitude: "Uh-huh." "Nuh-huh." "Uh-huh, uh-huh." "Nuh-huh, nuh-huh, nuh-huh." "Uh-huh infinity!" "Nuh-huh infinity plus one!"
Well, for cardinal numbers "infinity+1" (or even "infinity+infinity") is the same as "infinity", wheras for ordinal numbers "infinity+1" really is a bigger "infinity", so I hope they were using ordinal numbers. ;) Of course, then there's infinity+2. On the other hand, 'the largest infinity' turns out to be a self-contradictory concept, but I doubt that would stop anyone on the playground ("largest infinity plus one").
Quote:I will grant, however, that if one defines "infinity" to mean something different, then naturally different conclusions will follow from that.
I certainly grant that the word "infinity" might be used in lots of different ways. But IMO all of the non-mathematical uses -- whatever their poetic, metaphysical, or religious value -- don't lend themselves well to rational argument.
Quote:The question was, if I recall, whether a set than contains some quantity of elements, whether infinite in magnitude or not, could exist that did not contain a first element? "Thus, how if one claims a set of infinite items, can it not contain a first item?"
I came in after that, but since you ask (WARNING: feel free to read no further unless you wish)...it really depends on what you mean: The set of integers (positive or negative) has no first element -- if by that you mean a smallest element. On the other hand, you could imagine reording them as, for example, 0, -1,1,-2,2,-3,3... and then they would have a first element (0).
The set of all real numbers also has no smallest element, with its usual ordering (or even the set of real numbers 0 < x < 1). You could imagine reording them by picking one number at a time, say as
pi, sqrt{2}, -25.1010010001..., -9/7,..
until they're exhausted (an exhausting procedure requiring an uncountably infinite number of choices), and then they would have pi as a first element; furthermore every subset of the real numbers would also have a first element (e.g. - 9/7 would be the first element of the rational numbers). The assumption that you can so order any set, however big, is called the well-ordering principle, and it's rather controversial (being equivalent to the axiom of choice).
Quote: The point of contention that you drew was over "So what is infinite can be larger than what is infinite? [Isn't there] contradiction in stating that a thing may be larger than itself?" This point seems incidental to the question, and I don't see why, if contested, it may not be discarded without loss to the cogency of the argument.
It may well be discarded -- I simply couldn't stand to see such imprecision about mathematically related concepts without responding. ;)
Quote:Perhaps you'd be inclined to grant that if one accepts infinity to mean "immeasurably great, unlimited, boundless, endless" that the point of contradiction is valid? and, in general, that a thing may not be larger than itself?
I honestly don't know whether "immeasurably great, unlimited, boundless, endless" really defines a meaningful concept, or whether -- in whatever context this definition is supposed to apply ---the statement that "a thing may not be larger than itself" is tautological, true, false, or meaningless.