Algebraically closed char 0 fields are MA model
===============================================
Author: David Libert <dave@aptosidbox>
Date: 2012-02-09 08:05:03 EST
Table of Contents
=================
1 I will note this in Wikispaces
2 this is followup and response to quasi
3 conjecture algebraically closed char 0 fields are MA models
4 I will post here proofs conj alg closed char 0 are MA models
5 related previous background
6 define algebraically closed ring
7 every algebraically closed ring is a field
8 Proofs every algebraically closed field of char 0 is MA model
8.1 AC based proof based on AC proof algebraic numbers model MA
8.1.1 Claim 1
8.1.2 Proof of Claim 1
8.1.2.1 Special case of Claim 1 for F1, F2 with #F1 < #F2
8.1.2.2 Proof of special case of CLaim 1
8.1.2.3 Proof full case of Claim 1
8.1.2.4 QED CLaim 1
8.1.3 side note claim 1 for each characteristic individually
8.1.4 finish AC proof alg closed char 0 F is MA model
8.1.5 discuss characteristic 0 in above proof
8.2 Metamathematical elimination of AC assumption
8.3 Direct proof without AC
1 I will note this in Wikispaces
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[
http://davesscribbles.wikispaces.com/modarithalgclsdma]
2 this is followup and response to quasi
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[1]
quasi
"Re: Finite Models of the Complex Numbers"
sci.logic, sci.math
Feb 7, 2012
[
http://groups.google.com/group/sci.logic/msg/0cdcdeb41bf79423]
3 conjecture algebraically closed char 0 fields are MA models
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
On Feb 7, 3:52 pm, quasi <qu...@null.set> wrote:
> On Tue, 7 Feb 2012 11:44:21 -0800 (PST), RussellE
[...]
> >Of course, I am not the one claiming algebraically closed
> >fields are models of MA.
>
> Not all algebraically closed fields are models of MA -- just
> the ones which have characteristic zero (and in particular,
> the field of complex numbers).
4 I will post here proofs conj alg closed char 0 are MA models
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5 related previous background
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
I posted that I may have a proof that C the complex numbers are an
MA model. Later independently, quasi also posted the same
conjecture about C. Soon after, quasi also conjectured that the
algebraic numbers are also an MA model. Then quasi also soon after
conjectured every algebraically closed field is an MA model.
In
[2] [
http://davesscribbles.wikispaces.com/modarithcomplex] I gave
references for quasi's conjecture aricles above, and I also
conjectured algebraically closed fields of characteristic 0 are MA
models, and noted I could prove that from C being an MA model.
[2] went on to post my claimed proof that C is an MA model.
For references about C being an MA model, [2] above and another
article see
[3] [
http://davesscribbles.wikispaces.com/modarithcomplexmain]
I also later posted proving the algebraic numbers are an MA
model,based on the corresponing result [3] for C. That is
referenced in
[4] [
http://davesscribbles.wikispaces.com/modarithalg]
6 define algebraically closed ring
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
It could make sense to define what it means for any ring to be
algebraically closed: every non-constant polymial with coeeficients
in the ring has at leas one root.
7 every algebraically closed ring is a field
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
for a in the ring a^-1 is a root of poly a*x - 1 .
8 Proofs every algebraically closed field of char 0 is MA model
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8.1 AC based proof based on AC proof algebraic numbers model MA
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
A is defined to be the set of algebraic complex numbers.
The new proof here for all algebraically closed fields of
characteristic 0 will be based on the AC based proof that A models
MA from [4] above.
8.1.1 Claim 1
=============
all algebraically closed characteristic 0 fields have same
complete theory of their models
8.1.2 Proof of Claim 1
======================
8.1.2.1 Special case of Claim 1 for F1, F2 with #F1 < #F2
-----------------------------------------------------------
That is, for F1 and F2 algebraically closed fields of
characteristic 0, with #F1 < #F2 then they have the same
complete theory in field language
8.1.2.2 Proof of special case of CLaim 1
----------------------------------------
Let F1 and F2 be as assumed. We seek to show they have the sasme
theory.
By recent discussions, F1, F2 being algebrically closed must both
be infinite. So F2 being strictly larger must be uncountable.
The [4] proof started with the theory of field A, with contants
for all members and added continuum many new constants with axiom
schemata saying these are mutually transcendental over A.
We similarly form the theory of F1 with constants for all F1
members, and add #F2 many new constants and axioms saying there
are mutually transcendental over F1.
As in [4], argue this theory is consistent. As in [4], find M a
model of it, extending F1 and with the same thoery. As in [4],
take N a elementary substructure of M, now of size #F2.
N is an algebrically closed field with #F2 many mutually
tanscendental elements over F1, and with N of total
cardinality #F2.
With AC, N has a #F2 sized transcenednce basis.
[
http://en.wikipedia.org/wiki/Transcendence\_basis] (
http://en.wikipedia.org/wiki/Transcendence_basis)
F2 was algebrically closed with #F2 uncountable, so F2 also has
an #F2 cardinality trancendence basis.
So F2 and N must be isomorphic, so they have the same theory. But
N had the same theory as F1
QED Special case of Claim 1
8.1.2.3 Proof full case of Claim 1
----------------------------------
Suppose F1 and F2 are algebraically closed characteristic 0
fields. We seek to show F1 and F2 have the same theory.
By upward Lowenhiem Skolem, there is F3 an algebraically closed
field of characteristic 0 with #F3 > #F1 and #F3 > F2.
By 2 applications of the special case of Claim 1, F1 has the same
full theory as F3 and F2 has trhe same full theory as F3.
So F1 and F2 have the same full theory
QED full case CLaim 1
8.1.2.4 QED CLaim 1
-------------------
8.1.3 side note claim 1 for each characteristic individually
=============================================================
Fields of different characteristic from each other have different
full theories.
But for each characteristic p, p = 0 or p a prime, all
algebraically closed fields of characteristic p have the same
theory as each other.
This was proven above for case p = 0.
The same proof works for each prime p. Namely the characteric 0
proof above used that F1, F2 are both infinite. But this is also
true in characteristic p since both are algebraically closed.
The proof from [4] used the field was infinite, but as noted we
have that still.
Below though, I will just need the original Claim 1 for
characteristic 0.
8.1.4 finish AC proof alg closed char 0 F is MA model
======================================================
Suppose F is algebrically closed and characterisic 0. We want to
show F is an MA model.
C is complex numbers are algebrasiclaly closed and
characterisit 0. So by Claim 1, F and C have the same full theory
of their models in field language.
But C is an MA model, from [2] above.
So F is an MA model
QED AC basied proof
8.1.5 discuss characteristic 0 in above proof
=============================================
The proof above used Claim 1. As from the disccusion above, Claim
1 holds individually in each other charateristic.
But the proof went on to use Claim 1 to relate an arbitrary
algebraially closed charactertic 0 field to C.
That comparison using Claim 1 would have worked in other
characteristics p to cpmaore an arbitrary charateristic p field F to some other
field of characteristic p.
The proof above used the [2] result about C. And that is where
characteristic 0 was used. The [2] proof used C has characteristic
0, namely to get some finite succssor chain above 0 and below x
are each outside of fionte set F.
For a field F of characteristic p =~ 0, we can't used the p
version of Calim 1 to compare F to C. Instead we have to compare
F to some other field D of characteristic p. And for such D the
[2] proof would have a gap to copy to D.
8.2 Metamathematical elimination of AC assumption
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Above proved in ZFC that all algebraically closed fields of
charactirstic 0 model MA.
So by Godel's completeness, it shows the theory of algebrically
closed fields of characteristic 0, a recursivelyt axiomatized
theory, proves the shchmeata of MA axioms.
But this claim about a reucrisely axiomized first otrder theoy
proving a recursive set of axioms, is itself a purely arithmetical
claim.
So by Godel's L construction, if ZFC proves then then ZF does.
Paul Cohen discusses this in
_Set Theory and the Continuum Hypothesis_.
There is also Shoenfield's Absolutness Lemma, a stronger form of this.
8.3 Direct proof without AC
~~~~~~~~~~~~~~~~~~~~~~~~~~~
This all traces back to the elimination of quantifiers argument for
C from [2]. As I remarked before, all this argument used about C
was that C extends the inegers and is algebraically closed.
So directly run the argument from [2] with F algebrally closed of
charactoeristic 0 (hence exnteding integers) replacing C, to
directly get F satisfies induction. That argument from [2] did not
use AC.
--
David Libert
ah...@FreeNet.Carleton.CA