erdős #1038 · the supremum side · teorth/erdosproblems #179

How shallow can a lemniscate stay?

Tao reformulated Erdős #1038 over discrete probability measures and asked for the supremum of |{U_μ < 0}|, conjecturing 2√2 — “this may be hard to prove completely.” For rational weights the question is about root-constrained polynomials, decidable degree by degree. This machine decided the first seven degrees: the odd ones fall strictly below the conjecture, and the even ones pin its witness to within 2.3×10⁻⁵ of optimal.

Machine-derived, per-degree theorems for rational-weight measures — Tao's conjecture itself (all measures, all denominators) remains open, and the even-degree equality case is localized, not characterized. Every number on this page is a certified outward enclosure recomputed at this build; nothing is decided in floating point. Not peer-reviewed.

tl;dr
  • The finding. For every monic polynomial of degree 3, 5, or 7 with all roots in [−1,1]: |{|q|<1}| < 2.82 < 2√2 — the whole degree falls strictly below the conjectured supremum. For degrees 4 and 6 and 8: the degree supremum lies in [2√2, 2.82845], the left end attained by (x²−1)^{N/2} — the conjectured extremizer, within 2.3×10⁻⁵ of optimal.
  • The mechanism. Rational weights with denominator N make U_μ < 0 exactly |q(x)| < 1 for a monic degree-N polynomial with roots in [−1,1]. Sublevel measures are certified by BigInt Sturm isolation of the boundary roots; a branch-and-bound over root boxes prunes with the pointwise bound |q_r(x)| ≥ Π dist(x, I_i), whose own sublevel measure is computed the same way and equals the true measure on thin boxes.
  • Check it. node tools/run-sublevel-campaign.js re-derives everything; node instruments/sublevel/battery.js re-proves the degree-3 theorem and the degree-4 localization at every run, in under a second, plus 3 red controls.
per-degree theorems
6
Degrees 3, 4, 5, 6, 7, 8 — each a branch-and-bound certificate tree over all root configurations.
the witness
2√2
x²−1: certified [2.8284271247, 2.8284271247] — the two-atom measure Tao conjectures extremal.
box certificates
66,676
Across all theorems; the cubic needed 127 boxes, the heaviest even degree carries the rest.
configurations swept
838
Certified grid champions behind the landscape story, before any theorem was attempted.
§1 · the problem

The other end of #1038

Erdős #1038 concerns how small the sublevel set of a polynomial with constrained roots can be. Its infimum side was resolved in 2026 by Darvas–Peng–Tao — this lab independently verified the computational fragment of that manuscript. In erdosproblems#179, Tao poses the other end: over discrete probability measures μ = Σ pᵢ δ_{aᵢ} on [−1,1], with logarithmic potential U_μ(x) = Σ pᵢ log|x − aᵢ|, how LARGE can |{x : U_μ(x) < 0}| be?

His conjecture: the supremum is 2√2, attained by the uniform measure on {−1, +1} — and “this may be hard to prove completely.” The thread had no answers when this campaign began.

p = k⁄N rational ⟹ U_μ(x) < 0 ⟺ |q(x)| < 1,   q(x) = Π (x − aᵢ)^{kᵢ} monic, roots in [−1,1]

So the conjecture restricted to rational weights of denominator N is a statement about degree-N polynomials — a finite-dimensional, certifiable object. That is the machine's opening.

§2 · the instrument

Sublevel measures, certified

The boundary of {|q| < 1} consists of roots of the integer polynomials A ∓ dᴺ (A the root-scaled form of q). Those are isolated and refined by the BigInt Sturm machinery of the trigmin instrument — the code calibrated on Mercer's closed forms in the λ(4) campaign — and each gap between boundary roots is decided by one exact rational comparison. The measure is summed outward: a true enclosure, never a float.

polynomialcertified measure of {|q|<1}exact value
x² − 1[2.828427124746, 2.828427124747]2√2 = 2.8284271247…
[1.999999999999, 2.000000000000]2
x[2.000000000000, 2.000000000001]2
(x−1)²[2.000000000000, 2.000000000001]2
(x²−1)²[2.828427124745, 2.828427124746]2√2 again — even powers of the witness keep it

The last row is why even degrees are different: powers of the witness keep its measure, so (x²−1)^{N/2} attains 2√2 at every even degree, and no even degree can fall strictly below the conjecture the way the odd ones do.

§3 · the landscape

An interior champion, and a cliff

2.4 2.5 2.6 2.7 2.8 2√2 0.5 0.6 0.7 0.8 0.9 1.0 the free root r (remaining roots pinned at ±1; quintic pins them double) 2√2 — the conjectured supremum cubic (x²−1)(x−r) quintic (x²−1)²(x−r)
Both curves are certified enclosures recomputed at this build (the plotted value is the upper endpoint; widths are below picture resolution). The cubic supremum is at an INTERIOR critical root — certified 2.754173 at r = 201/256 — not at a lattice point. The quintic family peaks at 2.801091 near r = 905/1024 and then falls off a cliff: a topological transition where two components of {|q|<1} merge and the measure drops by ~0.09 discontinuously. The odd-degree suprema climb toward 2√2 — approaching the two-atom witness without reaching it.
§4 · the theorems

Seven degrees, decided

degreecertified statementboxesdepthtime
N = 3every degree-3 polynomial stays below 2.82 < 2√2 — the whole degree falls strictly under the conjecture127160.0 sstrict
N = 4the degree supremum lies in [2√2, 2.82845]; (x²−1)^2 attains the left end549590.1 slocalized
N = 5every degree-5 polynomial stays below 2.82 < 2√2 — the whole degree falls strictly under the conjecture1,583370.2 sstrict
N = 6the degree supremum lies in [2√2, 2.82845]; (x²−1)^3 attains the left end4,219890.6 slocalized
N = 7every degree-7 polynomial stays below 2.82 < 2√2 — the whole degree falls strictly under the conjecture28,773638.8 sstrict
N = 8the degree supremum lies in [2√2, 2.82845]; (x²−1)^4 attains the left end31,4251185.7 slocalized

Each row quantifies over EVERY root configuration in [−1,1]ᴺ — collisions and multiplicities included — through the ordered-and-mirrored branch-and-bound: a box is closed when the certified measure of {Π dist(x, Iᵢ) < 1} falls below the threshold, and that bound equals the true measure on thin boxes (a battery check). In measure language: every discrete probability measure on [−1,1] whose weights have denominator 3, 5, or 7 satisfies |{U_μ < 0}| < 2.82; for denominators 4 and 6 and 8, the two-atom witness is within 2.3×10⁻⁵ of the best possible.

not decided

deg9: bnb: box budget exhausted — recorded as attempted and open, not silently dropped.

§5 · what remains

The honest boundary