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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 …
Joel David Hamkins's user avatar
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 …
Joel David Hamkins's user avatar
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 …
Joel David Hamkins's user avatar
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 …
Joel David Hamkins's user avatar
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 …
Joel David Hamkins's user avatar
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 …
Joel David Hamkins's user avatar
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 …
Joel David Hamkins's user avatar
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 …
Joel David Hamkins's user avatar
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 $\kappa$ …
Joel David Hamkins's user avatar
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, …
Joel David Hamkins's user avatar
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 …
Joel David Hamkins's user avatar
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 …
Joel David Hamkins's user avatar
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 …
Joel David Hamkins's user avatar
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 …
Joel David Hamkins's user avatar
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 …
Joel David Hamkins's user avatar

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