Ning Li is an American scientist known for her controversial claims about anti-gravity devices. She worked as a physicist at the Center for Space Plasma and Aeronomic Research, University of Alabama in Huntsville, in the 1990s. In 1999, she left the university to form a company, AC Gravity, LLC, to continue anti-gravity research.
In a series of papers co-authored with fellow university physicist Douglas Torr and published between 1991 and 1993, she claimed a practical way to produce anti-gravity effects. She claimed that an anti-gravity effect could be produced by rotating ions creating a gravitomagnetic field perpendicular to their spin axis. In her theory, if a large number of ions could be aligned, (in a Bose–Einstein condensate) the resulting effect would be a very strong gravitomagnetic field producing a strong repulsive force. The alignment may be possible by trapping superconductor ions in a lattice structure in a high-temperature superconducting disc. Li claimed that experimental results confirmed her theories.    Her claim of having functional anti-gravity devices was cited by the popular press and in popular science magazines with some enthusiasm at the time.   However in 1997 Li published a paper describing an experiment that showed the effect was very small, if it existed at all.  Li is reported to have left the University of Alabama in 1999 to found the company AC Gravity LLC. AC Gravity was awarded a U.S. DOD grant for $448,970 in 2001 to continue anti-gravity research. The grant period ended in 2002 but no results from this research were ever made public.  Although no evidence exists that the company ever performed any other work, as of 2014, AC Gravity still remains listed as an "existent" business. 
- Li, Ning; Torr, DG (January 15, 1991). "Effects of a gravitomagnetic field on pure superconductors". Physical Review. D43: 457–459. Bibcode:1991PhRvD..43..457L. doi:10.1103/PhysRevD.43.457. Retrieved March 6, 2014.
- Li, Ning; Torr, DG (September 1, 1992). "Gravitational effects on the magnetic attenuation of superconductors". Physical Review. B46: 5489. Bibcode:1992PhRvB..46.5489L. doi:10.1103/PhysRevB.46.5489. Retrieved March 6, 2014.
- Li, Ning; Torr, DG (August 1, 1993). "Gravito-electric coupling via superconductivity". Foundations of Physics Letters. 6 (4): 371–383. Bibcode:1993FoPhL...6..371T. doi:10.1007/BF00665654. Retrieved March 6, 2014.
- Wilson, Jim (October 1, 2000). "Taming Gravity". Popular Mechanics. HighBeam Reseatch. Retrieved January 5, 2014.
- Cain, Jeanette. "Gravity Conquered?". light-science.com. Retrieved January 5, 2014.
- N. Li; D. Noever; T. Robertson; R. Koczor; et al. (August 1997). "Static Test for a Gravitational Force Coupled to Type II YBCO Superconductors". Physica C. 281 (2-3): 260–267. Bibcode:1997PhyC..281..260L. doi:10.1016/S0921-4534(97)01462-7.
- "Annual Report on Cooperative Agreements and Other Transactions Entered into During FY2001 Under 10 USC 2371". DOD. p. 66. Retrieved March 6, 2014.
- "Business Entity Details, AC Gravity, LLC". Alabama, Secretary of State. Retrieved March 6, 2014.