Nobody knows of any such thing as negative mass or anti-gravity, there’s no theoretical reason to expect that it exists, and every previous suggestion that something like it had been found was very probably a hoax. But let us know if you find some mysterious rocks that fall upwards in a vacuum.
No theoretical physical models have made any testable predictions that include an anti-gravitational effect
Scientists who have since studied Brown’s devices have not found any anti-gravity effect, and have attributed the noticed motive force to the more well-understood phenomenon of ionic drift or “ion wind” from the air particles, some of which remained even when Brown put his device inside a vacuum chamber. More recent studies at NASA, held at high voltages and proper vacuum conditions, showed no generated force.
Ion thrusters are real (and neat), but they are not anti-gravity tech.
Sure, but what is gravity? :D
¯\_(ツ)_/¯
