The Math Forum

Search All of the Math Forum:

Views expressed in these public forums are not endorsed by NCTM or The Math Forum.

Math Forum » Discussions » sci.math.* » sci.math

Notice: We are no longer accepting new posts, but the forums will continue to be readable.

Topic: Few questions on forcing, large cardinals
Replies: 17   Last Post: Mar 30, 2013 1:21 PM

Advanced Search

Back to Topic List Back to Topic List Jump to Tree View Jump to Tree View   Messages: [ Previous | Next ]

Posts: 2,720
Registered: 2/15/09
Re: Few questions on forcing, large cardinals
Posted: Mar 16, 2013 6:44 PM
  Click to see the message monospaced in plain text Plain Text   Click to reply to this topic Reply

On Mar 10, 5:47 pm, "Ross A. Finlayson" <>
> So isn't forcing simply Dirichlet box / pigeonhole principle?  Without
> appeal to forcing, simply define arguments in symmetry then as to
> transfinite pigeonhole, what's the difference?
> How can large cardinals be defined in terms of V (the Universe) when V
> isn't a set?  How are they cardinals if they aren't of sets?
> How can forcing's model be at once model and embedded in the model?
> Wouldn't it then be irregular?
> Are there any results in recursion/computation that can't simply (or
> not so simply) be framed in asymptotics without appeal to transfinite
> cardinals?
> Are there any results not of transfinite cardinals, solely due
> transfinite cardinals?

Looking to , this is a nice resource for
looking to the day's definitions of what would be "large cardinals",
were they sets or cardinals.

A particular notion of the "large cardinals" is that they are defined
in terms of embeddings into the set-theoretic universe (and
correspondingly in set theory with classes the set and class universe,
except where the distinction or existence is ignored). Then, the
Kunen inconsistency that tops Cantor's attic is that there are no non-
trivial embeddings from the universe V to itself. Yet, identity as
trivial, sees then any pair-wise switch of elements from identity, eg
for a and b that a->b and b->a, being as well an embedding. Then, if
those are all trivial, then so is any function f: S -> S from set S to
itself, which is a rather overbroad definition of "trivial". Would
that remain elementary, in that the function preserves model
isomoprhism, it would where the theorems of the resulting structure so
modeled were the same. Then basically for groups or other features
establishing isomorphisms for all relevant theorems of the structure,
the pair-wise switch among elements identical under isomorphism, would
yield non-trivial elementary embeddings. Basically that is as to
whether, for example, the elements of Z_2, can be unique as elements
of Z_2, from a sub-theory of ZF defining only the binary: that
replacing all the 1's with 0's and 0's with 1's is structurally
indistinguishable, under that all the coded results have the same

f: x e V -> V: x -> x (trivial identity)
f: x e V -> V: x -> ~x (trivial? opposition)

Then, if each structure eg Z_2 various under isomorphism isn't a leaf
or totally uniquely typed, then all mathematical structures are of a
single unified structure, then that structure as consistent as
structure itself could be: would be complete. As there exists
ismorphisms thus elementary embeddings in those structures in vacuo,
there exist all their regular 1-1 compositions defining elementary
embeddings, in their concreteness.

The Universe would be irregular and be its own powerset. This is
known as Cantor's paradox, that there can't be a universe as a regular/
well-founded set because uncountality depends on well-foundedness (and
Regularity and Infinity are the only axioms of ZF restricting
comprehension of quantification). Now, the Universe exists, simple
and structurally from that anything exists. So, the universe is not a
well-founded set, though defined by all its elements, it's naively a
set. Large cardinals aren't set nor cardinals, of ZF.

Basically then from the upper attic of Kunen inconsistency to
Con(ZFC): "Every model of ZFC contains a model of ZFC as an element",
that models of ZFC are not standard nor well-founded, that's just a re-
phrasal of Russell's paradox, that the collection of all the well-
founded sets (which ZFC is) would contain itself: as alluded to there
it does, then there's the simple question: why doesn't that imply

I suggest you review the notion of forcing, in logic, and as to
whether structurally, that breaks things. The simplest model: is a
working, structural model. The Universe: is, what it is.


Ross Finlayson

Point your RSS reader here for a feed of the latest messages in this topic.

[Privacy Policy] [Terms of Use]

© The Math Forum at NCTM 1994-2018. All Rights Reserved.