Earlier quoted context omitted.
These concerns don't apply to the claim that the set of real numbers is uncountable. Cantor's diagonal proof is constructive: given any countable set of real numbers, it tells you how to construct a real number that is not in the set. That is sufficient to show that the set of real numbers cannot be countable. Also, even though many real numbers cannot be written down with a finite set of symbols, Cantor's diagonal p…
You're assuming you've been able to construct all those real numbers in the first place, using arbitrary imaginary cauchy sequences (i.e. cauchy sequences that cannot be constructed but rather rely on some magic axiom of infinite choice).
How many real numbers exist? New proof moves closer to an answer
331–340 of 359 posts
Re: How many real numbers exist? New proof moves closer to an answer
#332Earlier quoted context omitted.
Why is that wrong? If you actually ran a Turing machine for a number of steps that is beyond any number that can be written, maybe it would halt.
By number that cannot be written, I don't mean cannot be written due to lack of paper; I mean a value that there is no notation for. You cannot run a machine for "that many" steps because such a value is unreachable by steps. Non-standard models have a set of values that begin with a copy of the actual natural numbers, followed by some ordered set of copies of the integers in the sense that any values "beyond" the in…
That's true for most real numbers in ordinary mathematics too, so if you accept the existence of those numbers, no reason why you can't do the same for the natural numbers in these non-standard models.
> You cannot run a machine for "that many" steps because such a value is unreachable by steps. Non-standard models have a set of values that begin with a copy of the actual natural numbers, followed by some ordered set of copies of the integers in the sense that any values "beyond" the initial natural numbers have an infinite number of successors and an infinite number of predecessors, like integers do. By counting in steps it is not possible to move from a value in the initial natural number fragment to one of these non-standard values, because there are an infinite number of values in between them that you would be required to step through.
Yes...
Re: How many real numbers exist? New proof moves closer to an answer
#333Earlier quoted context omitted.
The problem is that exists comes to mean something technical that doesn't match common usage. Let's take my favorite example. In graph theory, a minor of a graph is a graph you can get by removing vertices, removing edges, or by replacing an edge-vertex-edge triple with a single edge. Many categories of graphs are closed under the act of taking minors. For example planar graphs, graphs you can draw on the plane with…
In the usual sense. I don’t see a problem. Just because you don’t have a perfect knowledge of something, it doesn’t mean that the thing isn’t real. I am not sure where this idea even comes from? To be honest, this sounds completely ridiculous.
Re: How many real numbers exist? New proof moves closer to an answer
#334Re: How many real numbers exist? New proof moves closer to an answer
#335https://m.youtube.com/watch?v=RkP_OGDCLY0
Sorry, I couldn't resist.
Re: How many real numbers exist? New proof moves closer to an answer
#336The mileage of others may vary, but it has been my experience that there is no cogent solid proof of uncountability that can withstand concerted critique.[0] Being charitable one might argue that the meanings of terminology had been lost in translation over time and that perhaps Cantor was trying to create non-standard analysis, but then the diagonal argument seems to represent nothing more than the truism that finit…
The executive summary of my paper is that provably there are fatal inconsistencies in Cantor's Diagonal Argument (CDA).
They take a few forms:
(1) Application of basic classical analysis tools reveals that the contradiction sought by CDA does not hold if those tools are used.
E.g. Assume we have the table of all unique infinite length binary strings {0,1}* (where * represents the supremum of the natural numbers, e.g. the first ordinal infinity in set theoretic language).
Assume that those strings represent the fractional part of binary represetations of real numbers in the continuum interval [0,1].
Assume they start big endian, so for some string s, the value v(k) of some bit at the k-th position of s is v(k) = s(k)/2^k, for k = 1,2,3....
Let f: \N x \N -> {0,1}, be a function that accesses bits in the binary strings viewed as a matrix M(i,j).
Create the binary number z as z(k) = 1 - f(k,k).
Now deploy basic analysis.
Note that k -> \infty implies v(k) -> 0.
So no matter what the value of z(k) is, k -> \infty implies |z - f(k)| -> 0, for some suitable k.
Let f be the limit of f(k) as k -> \infty.
Then in the limit k -> \infty the number z = f, and (for all practical purposes) the diagonal z coincides with a binary number in the table f within a countable limit.
This is independent of any ordering of the table rows of M(i,j).
So the contradiction of CDA does not hold convincingly when these basic tools of analysis are used.
(2) Corollary: Platonists would need to prove that infinite digit existence somehow invalidates basic analysis in order to cling to CDA. Moreover, they would have to prove that "higher" infinite digit existence does not invalidate useful concepts of numbers and limits at all.
As far as I know, no one has done that yet.
(3) Using the same basic tools of analysis, key arguments about powersets having cardinalities that are "higher" infinities do not go through, and moreover aspects of "higher" cardinal arithmetic, as presently defined, can be shown to be self-inconsistent.
Therefore: A) When the tools of basic classical analysis are so useful, why would any pragmatic user of mathematics throw them out at some key point within CDA (and CDA only) to endorse a notion of "uncountability" that creates manifold inconsistencies further on?
B) Why should any pragmatic mathematician allow the extra unconvincing machinery of higher infinities into maths?
In the absence of decent answers to those questions I am compelled towards the recommendation is that mathematicians should throw CDA out.
Edit: formatting.
Re: How many real numbers exist? New proof moves closer to an answer
#337Earlier quoted context omitted.
That depends on what you mean by "assigns uniquely", "rule" and "doesn't work", which is why this question is deeply entangled with philosophical issues that cannot be settled purely mathematically. It is obvious that all expressions in the English language can be ordered from smallest to largest and lexicographically, which makes these expressions trivially countable. We can thus assign natural numbers to real numbe…
> We can thus assign natural numbers to real numbers by assigning numbers to their expressions in a natural or formal language This doesn't work because not all real numbers have expressions in a natural or formal language. This is easily shown by an obvious variation on Cantor's diagonal proof, applied to your lexicographically ordered list of expressions in any natural or formal language.
What does "to exist" mean for number which can not be written down as some formula (in broad sense of this word) in formal language?
Re: How many real numbers exist? New proof moves closer to an answer
#338The mileage of others may vary, but it has been my experience that there is no cogent solid proof of uncountability that can withstand concerted critique.[0] Being charitable one might argue that the meanings of terminology had been lost in translation over time and that perhaps Cantor was trying to create non-standard analysis, but then the diagonal argument seems to represent nothing more than the truism that finit…
For the sake of HN archival history... The executive summary of my paper is that provably there are fatal inconsistencies in Cantor's Diagonal Argument (CDA). They take a few forms: (1) Application of basic classical analysis tools reveals that the contradiction sought by CDA does not hold if those tools are used. E.g. Assume we have the table of all unique infinite length binary strings {0,1}* (where * represents th…
Pick a k. Note that z(k) is not in rows 0 through k of M, by finite diagonalization. Now, suppose that you try taking k to "infinity" again. z(k) keeps up at every step, by primitive recursion, and M is always missing at least one entry. By what justification do you suppose that M somehow outruns v at "infinity"?
I need you to remember how to be a human for just a moment. Reread your words, "the recommendation is that mathematicians should ..." and consider the precise moral justification by which you make this recommendation. Note that your attempt at the passive voice failed to shift the moral burden, because the given proof is unconvincing (and quite unrigorous). Please consider a dram of humility and give Yanofsky's paper a serious read. It's good.
Also, if you want a better idea of such an infinite Boolean matrix, consider reading about Chu spaces: http://chu.stanford.edu/
Re: How many real numbers exist? New proof moves closer to an answer
#339Earlier quoted context omitted.
Hi, Lawvere pummelled your position into the ground a while ago: http://tac.mta.ca/tac/reprints/articles/15/tr15.pdf Your critique involves repeatedly crossing the boundary between the inside and outside of the system in question; Lawvere works entirely inside the system, and shows that the paradoxes of self-reference arise from our interpretations. https://arxiv.org/abs/math/0305282v1 explains with many examples. Hi…
I'm not seeing this yet. Perhaps you could explain it to me in plain terms.
If there exists t : Y -> Y such that t;y != y for all y : 1 -> Y then for no A does there exist a surjection A -> (A -> Y).
(He actually says something much stronger.) Note that the first half of this is saying "if there exists t such that t has no fixed points..."
Let our category be Set, the category of sets and functions; it is well-known to be Cartesian closed. Let A be the set of natural numbers and let Y be the Booleans. Then Lawvere is saying that there is no surjection N -> (N -> 2), and thus definitely no bijection, because there is a function 2 -> 2 with no fixed points: the negation function which swaps true and false has no fixed point.
It does not get much plainer without actually reading Lawvere and/or Yanofsky directly, sorry. I hope that this helps explain how inescapable this sort of theorem is.
Re: How many real numbers exist? New proof moves closer to an answer
#340The mileage of others may vary, but it has been my experience that there is no cogent solid proof of uncountability that can withstand concerted critique.[0] Being charitable one might argue that the meanings of terminology had been lost in translation over time and that perhaps Cantor was trying to create non-standard analysis, but then the diagonal argument seems to represent nothing more than the truism that finit…
Hi, Lawvere pummelled your position into the ground a while ago: http://tac.mta.ca/tac/reprints/articles/15/tr15.pdf Your critique involves repeatedly crossing the boundary between the inside and outside of the system in question; Lawvere works entirely inside the system, and shows that the paradoxes of self-reference arise from our interpretations. https://arxiv.org/abs/math/0305282v1 explains with many examples. Hi…
crucial importance of Russell's orders on propositions in
blocking the construction of monster propositions using
recursive definitions. Orders on propositions block
construction of I'mFalse, I'mNotSelfapplicable,
I'mUnprovable, and MyTheoremsAreEnumerable.
See the following video for more information:
https://www.youtube.com/watch?v=AJP1VL7shiI
for the following article: