Ning Li and Douglas Torr proposed in 1991 that rotating ions in a Type-II superconductor could generate a gravitomagnetic antigravity effect

Physicist Ning Li (1943–2021), then at the University of Alabama in Huntsville, proposed with Douglas Torr in 1991 that rotating ions inside a Type-II superconductor could generate a "gravitomagnetic field" strong enough to produce measurable antigravity effects. The proposal borrowed the vocabulary of a real general-relativistic phenomenon — frame-dragging, the twisting of spacetime by a rotating mass — but asserted a laboratory-scale, useful magnitude that the real effect does not approach. The work sat inside NASA Marshall's speculative-propulsion orbit before migrating into a privately funded venture, AC Gravity LLC.

[unverified — the existence, date, and content of the 1991 Li–Torr proposal are recorded here from Tier-4 Wikipedia, not the primary paper. As a surprising and load-bearing physics claim it does not clear the sourcing floor for Tier 3–4; the primary (a Li & Torr paper, reportedly circa 1991–1992) must be located and read. See [[question-verify-ning-li-antigravity-primaries]].]

The claim belongs to the vault's cluster on how scientific error is — or is not — formally closed. Unlike the fabricated data that Jorge Hirsch helped expose in Ranga Dias's superconductivity work, Li's proposal was never retracted or refuted in the literature so much as quietly abandoned: it simply failed to replicate and drifted out of active research, much like the yellow-rain case where a decisive refutation never reached the official record. An unreplicated claim with no formal closure is exactly the kind of loose end that, decades later, can be re-read as significance rather than dead end.