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Every Riemannian 3-sphere contains at least two distinct embedded minimal spheres.

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2026-07-10 05:03 UTC pith:XKAMOSYI

load-bearing objection First general-metric existence of a second embedded minimal sphere in S^{3}, via a carefully engineered iterative relative min-max that closes the uniqueness contradiction. the 2 major comments →

arxiv 2607.08631 v1 pith:XKAMOSYI submitted 2026-07-09 math.DG math.APmath.GT

Existence of two embedded minimal spheres in S³ with an arbitrary metric

classification math.DG math.APmath.GT MSC 53A1053C4249Q05
keywords embedded minimal spheresSimon-Smith min-maxrelative min-maxmean-convex foliationmultiplicityLusternik-Schnirelmann3-sphere
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

For more than forty years it has been known that any Riemannian metric on the three-sphere produces at least one embedded minimal two-sphere. This paper proves that there are always at least two. The argument assumes for contradiction that a single minimal sphere is unique, extends it to a mean-convex foliation of the whole three-sphere, and then builds multi-parameter families of (piecewise-smooth) spheres that approximate multiple copies of that foliation. Relative min-max theory applied to these families produces a sequence of critical values that must equal successive integer multiples of the area of the unique sphere; for a large enough number of parameters the constructed families have strictly smaller area, yielding a contradiction. The result removes the positive-Ricci or bumpy-metric hypotheses that earlier multiplicity theorems required, so the existence of a second minimal sphere is now unconditional.

Core claim

Every Riemannian three-sphere admits at least two distinct embedded minimal spheres. Under the assumption that only one such sphere exists, an iterative scheme of relative Simon–Smith min-max constructions on carefully built multi-parameter families produces min-max widths equal to successive multiples of that sphere’s area; for sufficiently many parameters the families themselves have strictly smaller total area, a contradiction.

What carries the argument

An iterative scheme of relative min-max constructions on continuous families of (smoothed) spheres over simplices, built by inserting necks of controlled radii between successive leaves of a mean-convex foliation; the resulting area upper bounds and Lusternik–Schnirelmann-type comparisons force the min-max values to equal integer multiples of the unique sphere’s area until a global contradiction appears.

Load-bearing premise

If a unique embedded minimal sphere exists, it must admit an expanding neighborhood on both sides and therefore extend to a mean-convex foliation of the whole three-sphere; every subsequent construction of the families and all area comparisons rest on that foliation.

What would settle it

An explicit Riemannian metric on the three-sphere whose only embedded minimal sphere is unique (or whose second-width min-max produces only a multiple of that sphere) would refute the claim; equivalently, a gap or non-existence in the mean-convex foliation when uniqueness is assumed would collapse the argument.

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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit.

Referee Report

2 major / 6 minor

Summary. The paper proves that every Riemannian 3-sphere (S³,g) contains at least two distinct embedded minimal 2-spheres (Theorem A / Theorem 6.3). Assuming uniqueness of a Simon–Smith sphere Σ₀, the authors reduce to the expanding-neighborhood case, obtain a mean-convex foliation {Υ_t}, and construct multi-parameter families Φ_Λ : Δ_k → E of piecewise-smooth spheres by inserting necks of radii controlled by a decay parameter Λ. After smoothing (Appendix A) and an interpolation that preserves area upper bounds, they run an iterative scheme of relative Simon–Smith min-max constructions on faces F_{1,m} of a large simplex. Under uniqueness the relative widths equal m H²(Σ₀), but for large k the constructed family has area strictly less than k H²(Σ₀), a contradiction. The argument relies on relative min-max theorems (Theorems 2.2–2.3), area estimates for necks (Lemmas 3.5–3.6, Proposition 3.7, Lemmas 4.1–4.2), a Lusternik–Schnirelmann-type topological lemma (Lemma 6.1), and a varifold-neighborhood lemma for Caccioppoli sets (Proposition 2.1).

Significance. This is a substantial advance on Yau’s problem of four embedded minimal spheres in S³. Simon–Smith (1982) produced one sphere for arbitrary metrics; subsequent work obtained two or four only under positive Ricci curvature or bumpiness (White, Haslhofer–Ketover, and the authors’ multiplicity-one theorem). The present paper is the first to construct a second embedded minimal sphere for completely general metrics, more than forty years after the first. The iterative relative min-max scheme and the carefully controlled neck construction are new technical contributions that may apply to other problems previously restricted to positive Ricci curvature. The logical skeleton is complete and the estimates are quantitative; the result is therefore of clear interest to geometric analysis and min-max theory.

major comments (2)
  1. [Section 3 / §1.1] Section 3 (opening paragraphs) and §1.1: The entire construction rests on the existence of a mean-convex foliation {Υ_t} with Υ(1/2)=Σ₀. Under uniqueness the authors invoke weak stability from [40, Thm 8.9] and dispose of the contracting-neighborhood case by Song’s cutting argument, then cite Haslhofer–Ketover [17, Thm 3.1]. These reductions should be stated as a single, self-contained lemma at the start of Section 3 (with precise references), so that a reader can see exactly which external results are used before the families Φ_Λ are defined.
  2. [Appendix A / Remark A.5 / §5] Appendix A, Remark A.5 and the passage from Φ'_Λ to ˜Φ_Λ in §5: Proposition A.4 requires a uniform lower bound θ>0 on dihedral angles along the singular circles. Remark A.5 asserts this from transversality of the deformation retract D to the leaves Υ(t). For the interpolated family H(·,t) of Lemma 4.3 and for all Λ≥Λ₂ on the retracted domain Δ^ν_{k₀}, a short quantitative argument (or a compactness citation) confirming that θ can be chosen independently of Λ and of the interpolation parameter would make the application of the mollification fully rigorous.
minor comments (6)
  1. [§2.1] Notation for the spaces E and E (with overline) is introduced in §2.1 but used heavily thereafter; a brief reminder when Φ_Λ lands in E versus E would help the reader.
  2. [Figure I] Figure I is helpful but the caption could explicitly label which pieces are the interior annuli A_i and which are the necks C_i, matching the notation of (3.3)–(3.4).
  3. [Lemma 3.6] In Lemma 3.6 the equality case is stated only for s=t=1/2 and σ=0; a parenthetical remark that this case never occurs for the actual necks of Φ_Λ (where ξ_i>0 on the interior of Δ_k) would clarify that all subsequent inequalities used in Proposition 3.7 and Lemma 4.1 are strict when needed.
  4. [Proposition 2.1] Proposition 2.1: the constant θ₀ is independent of k, which is used crucially in the induction of Proposition 6.2; this independence is proved but could be highlighted in the statement.
  5. [Introduction] Several recent preprints that rely on multiplicity-one under positive Ricci (e.g., the works cited in the introduction) are listed; a sentence on which of those arguments might extend via the present methods would be of interest to readers, though not required.
  6. [Abstract / throughout] Typographical: “an iterat ive scheme” (abstract) and occasional spacing issues around math mode (e.g., “k H2”) should be cleaned in production.

Circularity Check

1 steps flagged

No significant circularity: the iterative relative min-max construction and area estimates are self-contained; prior self-citations supply independent black-box inputs under stronger hypotheses.

specific steps
  1. self citation load bearing [§3 opening paragraph / §1.1]
    "if Σ₀ is the only embedded minimal 2-sphere in (S³, g), then by [40, Theorem 8.9] we know that Σ₀ is weakly stable; that is, the first eigenvalue λ₁(L_Σ₀) of the associated Jacobi operator L_Σ₀ vanishes … Moreover, by our previous work [40], Σ₀ has an expanding neighborhood."

    The uniqueness assumption is converted into weak stability and the expanding-neighborhood property solely by citation of the authors’ own earlier paper. The citation is not circular in the strong sense (the prior theorem is an independent statement proved under stronger curvature/bumpiness hypotheses), but it is the sole justification for the foliation that the entire subsequent construction rests upon; hence a minor self-citation flag.

full rationale

The paper proceeds by contradiction under the assumption of a unique embedded minimal sphere Σ₀. It invokes the authors’ prior multiplicity-one/stability result [40, Thm 8.9] only to conclude weak stability (and hence an expanding neighborhood after the contracting case is cut by Song’s argument), then imports the mean-convex foliation from the external reference Haslhofer–Ketover [17, Thm 3.1]. From that foliation the authors construct, by hand, the multi-parameter families Φ_Λ (Def. 3.2), prove the neck-area comparisons (Lems 3.5–3.6, Prop. 3.7) and the strict area upper bounds on the simplex and its faces (Lems 4.1–4.2), smooth them (App. A), and run an inductive relative Simon–Smith argument (Prop. 6.2 + topological Lem. 6.1) that forces the min-max widths to equal m·H²(Σ₀) while the large-k upper bound is strictly smaller—a genuine contradiction. None of these estimates or the topological step reduces algebraically to the cited prior theorems; the latter are used as ordinary external lemmas. There are no fitted parameters, no self-definitional identities, and no renaming of known empirical patterns. The single minor self-citation of [40] for stability under uniqueness is therefore non-load-bearing for the new construction and does not raise the score above 1.

Axiom & Free-Parameter Ledger

3 free parameters · 5 axioms · 2 invented entities

The proof rests on classical GMT and min-max foundations plus two geometric facts about a unique minimal sphere (expanding neighborhood + mean-convex foliation). Free parameters are purely existential (large Λ, large k_{0}, small η) chosen to close inequalities; no data fitting occurs. Invented objects are the multi-parameter families Φ_Λ and the relative widths W_k, which are constructed explicitly rather than postulated.

free parameters (3)
  • Λ (neck-radius decay rate)
    Chosen larger than a constant Λ_{0} depending only on the unique sphere and a fixed η; controls how fast necks open near the boundary of the simplex.
  • k_{0} (simplex dimension)
    Taken large enough so that every point of Δ_{k_{0}} forces at least one short neck of small area (Lemma 4.2).
  • η (area slack)
    Arbitrary small positive constant used to absorb neck-area errors; final contradiction is independent of its precise value.
axioms (5)
  • domain assumption Simon–Smith min-max theorem produces at least one embedded minimal sphere
    Invoked at the outset; the whole argument begins from the existence of Σ_{0}.
  • domain assumption If Σ_{0} is unique then it is weakly stable and admits an expanding neighborhood, hence a mean-convex foliation {Υ_t}
    Cited from [40, Thm 8.9] and [17, Thm 3.1]; used to build the model sweepouts.
  • standard math Smale conjecture (Diff(S^{3}) ≃ O(4))
    Used to identify the space of embedded spheres with RP^{3}, limiting ordinary sweepouts to dimension ≤3.
  • domain assumption Relative Simon–Smith min-max theorems (Theorems 2.2–2.3)
    Proved in the paper by adapting [40]; supply the lower bounds for the widths W_k.
  • standard math Regularity of almost-minimizing varifolds in 3-manifolds
    Classical (Pitts, Schoen–Simon, Colding–De Lellis); used to conclude that critical varifolds are smooth embedded spheres.
invented entities (2)
  • Multi-parameter family Φ_Λ : Δ_k → E of piecewise-smooth spheres with controlled necks no independent evidence
    purpose: Approximate the Gromov–Almgren–Pitts sweepouts by multiples of Σ_{0} while keeping area strictly below k Area(Σ_{0}) for large k
    Explicitly constructed in Definition 3.2 via the recursive radii ξ_i = e^{-Λ d_i}(1-ξ_{i-1}); not an external postulate.
  • Relative min-max widths W_k = L([Φ̃_Λ | ∂F_{1,k}; rel ∂F_{1,k}]) no independent evidence
    purpose: Produce the sequence of critical values that must equal k Area(Σ_{0}) under uniqueness, contradicting the strict area upper bound
    Defined via the relative homotopy classes in Section 6; their evaluation is the content of Proposition 6.2.

pith-pipeline@v1.1.0-grok45 · 36170 in / 2889 out tokens · 32357 ms · 2026-07-10T05:03:00.824639+00:00 · methodology

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Cite this review

Pith. "Pith review of Existence of two embedded minimal spheres in $S^3$ with an arbitrary metric." pith.science (2026). https://pith.science/paper/XKAMOSYI

@misc{pith2026260708631,
  author       = {Pith},
  title        = {Pith review of: Existence of two embedded minimal spheres in $S^3$ with an arbitrary metric},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/XKAMOSYI}},
  note         = {Machine review of arXiv:2607.08631}
}
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We prove that $S^3$ endowed with an arbitrary Riemannian metric $g$ admits at least two embedded minimal spheres. The proof is based on an iterative scheme of relative min-max constructions.

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