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54
votes
Accepted
What interesting/nontrivial results in Algebraic geometry require the existence of universes?
My belief is that no result in algebraic geometry that does
not explicitly engage the universe concept will fully
require the use of universes. Indeed, I shall advance an
argument that no such results …
36
votes
Accepted
Large cardinal axioms and Grothendieck universes
A Grothendieck universe is known in set theory as the set Vκ for a (strongly) inaccessible cardinal κ. They are exactly the same thing. Thus, the existence of a Grothendieck universe is exactly equiv …
33
votes
Accepted
Ordering of large cardinals by cardinality
The usual relations to consider in the large cardinal hierarchy
are
Direct implication: every A cardinal is also a B cardinal
Consistency strength implication: if ZFC + there is an A cardinal
is con …
31
votes
Recent claim that inaccessibles are inconsistent with ZF
François has excellently addressed your question 1; allow
me to address question 2. I understand the question to be:
what will be the mathematical effects if someone were to
show that there are no (we …
30
votes
Should there be a true model of set theory?
Two weeks ago a conference was held on precisely the topic
of your question, the Workshop on Set Theory and the
Philosophy of
Mathematics
at the University of Pennsylvania in Philadelphia. The
confere …
28
votes
Ultrainfinitism, or a step beyond the transfinite
My view is that the large cardinal hierarchy already has all the
principal features of the project you are proposing.
Each of the large cardinal concepts can be regarded as
corresponding to a certain …
27
votes
Accepted
On statements independent of ZFC + V=L
There are numerous examples of such statements. Let me organize some of them into several categories.
First, there is the hierarchy of large cardinal axioms that are relatively consistent with V=L. Se …
24
votes
Accepted
Large categories vs. $\mathrm{U}$-categories: why is the loss of category-theoretic informat...
Let me try to answer as a set theorist, rather than as a category
theorist, since I think that your question concerns at bottom a
matter often considered in set theory.
Namely, the essence of your qu …
23
votes
Accepted
How badly does compactness fail in $\mathcal{L}_{\omega_1\omega}$?
I like the question very much.
First, let me mention briefly that the question has a flaw in the
quantifier order, since you have first fixed the theory $\Gamma$
and then ask for a cardinal $\kappa$ …
23
votes
What "forces" us to accept large cardinal axioms?
The line of reasoning you mention at the end of your post, firmly in support of large cardinals, was first argued forcefully in
W. N. Reinhardt, “Remarks on reflection principles, large cardinals, …
23
votes
Accepted
Why believe in the existence of large cardinals rather than just their consistency?
With regard to the title question, I believe that the main argument people would provide would be that it is the actual existence of the large cardinals that explains the consistency assertions that o …
22
votes
Reasons to believe Vopenka's principle/huge cardinals are consistent
Because of Goedel's Incompleteness Theorems, we know that
we cannot describe a complete axiomatization of
mathematics. Any proposed axiomatization $T$, if
consistent, will be unable to prove the princ …
21
votes
Accepted
Can Vopenka's principle be violated definably?
Update. My new article grows out of and extends my 2010 answer to this question. The new part is the conservativity result, showing that the Vopěnka principle has the same first-order consequences as …
19
votes
Accepted
Is there a compendium of the consistency strength between the most important formal theories?
Cantor's Attic, which I founded with Victoria Gitman, is a compendium of information on the consistency strength hierarchy in set theory,
spanning the range from ZFC (which in this context is viewed a …
19
votes
Applications of infinite Ramsey's Theorem (on N)?
Beyond the infinite Ramsey's theorem on N, there is, of course, a kind of super-infinite extension of it to the concept of Ramsey cardinals, one of many large cardinal concepts.
Most of the large ca …