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    The hyperreals exist only relative to a non-constructive ... — Carmelics
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    Challenges→An infinitesimal hyperreal exists

    The hyperreals exist only relative to a non-constructive ultrafilter whose existence depends on the Axiom of Choice, making their ontological status model-relative rather than absolute.

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    1 reason for
    1 reason against

    Reasons For

    1 perspective
    Reason for
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    • 1.Ultrafilter existence requires AC, which is unprovable in ZF, so hyperreals lack absolute foundational grounding independent of set-theoretic choices.
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    • 2.Different models of ZFC can have different ultrafilters, producing distinct hyperreal fields, demonstrating their ontological dependence on model structure.
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    • 3.Mathematical objects whose existence hinges on non-constructive principles have weaker claims to mind-independent reality than constructively definable entities.
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    Reasons Against

    1 perspective
    Reason against
    ?
    • 1.AC is a standard axiom in modern mathematics; relying on it doesn't diminish ontological status any more than relying on the axiom of infinity for naturals.
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    • 2.Model-relativity is universal in mathematics—all structures are defined relative to formal systems, so hyperreals aren't uniquely dependent or deficient.
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    • 3.Hyperreals provide rigorous infinitesimal analysis with proven applications; pragmatic indispensability suggests genuine mathematical existence regardless of axiom choice.
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    Key Terms

    Axiom of Choice(Foundations of mathematics; arises in second-order logic as the statement that every total binary relation has a choice function)
    Given a set A of non-empty pairwise disjoint sets, there exists a set B containing exactly one element from each set in A. When A is infinite, forming B requires making infinitely many simultaneous choices.
    Non-constructive(metaphysics/logic)
    Something that exists or is true on its own, rather than being built up or created from other things.
    Ontological status(in metaphysics (the study of what exists))
    What kind of thing something is considered to be or how real it exists—for example, whether something is a physical object, a concept, a property, or something else entirely.
    Ultrafilter(as used in set theory)
    A special mathematical object that picks out collections of things in a specific way; think of it as a very precise filter for organizing sets of numbers.
    hyperreals(Nonstandard analysis)
    A number system developed by Robinson that extends the standard reals and satisfies the transfer principle with respect to first-order statements about the reals
    model-relative(describing properties in logic and mathematics)
    Dependent on which particular version or interpretation of a system you're looking at; something can be true in one model but not in another.

    Connections

    2 topics

    Proof of definition segments1 linkedModality & Possibility1 linked

    Related

    AC is a standard axiom in modern mathematics; relying on it doesn't diminish ont...An infinitesimal hyperreal exists

    Details

    Type
    claim
    Perspectives
    2 (1 for, 1 against)
    Edits
    1 edit
    Different models of ZFC can have different ultrafilters, producing distinct hype...
    Hyperreals provide rigorous infinitesimal analysis with proven applications; pra...
    +3 moreShow less
    Mathematical objects whose existence hinges on non-constructive principles have ...Model-relativity is universal in mathematics—all structures are defined relative...Ultrafilter existence requires AC, which is unprovable in ZF, so hyperreals lack...