One of the most controversial subjects to talk about in physics is the "apparent gravity shielding" experiment done by Podkletnov, but I've talked on this blog about the importance of scientists boldly seeking anomalous data, and disregarding the theoretical mainstream, and I agree with Isaac Asimov who suggested that the cue for discovery in science is not "Eureka! I have it!", but "That's strange..". It seems recently that "That's strange.." is always interpreted as "That's dubious..". It is right that scientists should be sceptical, but pure scepticism is a sterile state. Podkletnov's paper was published in a good journal: Physica C, and it may disagree with standard theory, but in science experimental data comes before theory. Of course, the experiment could be wrong, and it doesn't help that it has not been reproduced in another lab (which it must be to be accepted) but this does not mean that Podkletnov's results are not reproduceable, the published accounts of the attempts made so far say that they were not able to reproduce the experimental conditions.
The experiment was done by Podkletnov and his team in Finland (see Podkletnov, 1992, 1997). They had a half-superconducting disc with a radius of 13.5 cm. They cooled it down to 70 Kelvin (-203oC) in a cryostat, so that the upper part only was superconducting and then levitated it using a magnetic field. They then applied an AC magnetic field of high frequency (MHz) which accelerated the disc. A team member was smoking when he shouldn't have been and they noticed that the smoke was rising over the cryostat. After investigation, they noticed that when the disc was accelerating due to the AC field, but not spinning, objects above the disc lost 0.05%-0.06% of their weight. When they spun the disc at 5000 rpm they noticed a larger weight loss of 0.6-2%. The greatest weight loss occured when they slowed the disc to 3000-3300 rpm and it visibly vibrated. The effect was independent of the test mass’s composition and was not due to moving air since it persisted when the test mass was encased in glass. It was not magnetic because it remained when a metal screen was placed between the disc and the masses.
I've been cautiously fascinated by this experiment for years. I think it's important when thinking about physics not to try to "Play Mathematical Games" or "Guess the Mind of God" as many theoretical physicists do, but instead to think within the context of real experiments, and to get new physics they have to be anomalous ones. I eventually found that MiHsC predicts something like the behaviour seen by Podkletnov. Consider an object suspended above the disc. When you cool its environment, nearby accelerations reduce, the Unruh waves it sees lengthen, more are disallowed by MiHsC's Hubble-scale Casimir effect and its inertia drops. Then the AC magnetic field accelerates the disc, so the Unruh waves seen by the object become shorter, fewer are disallowed and its inertia increases. This means it becomes less responsive to gravity: an apparent loss of weight. MiHsC predicts a weight loss of 0.03% which is not far from that seen (see McCulloch, 2011, note: I made a factor of two error in the published version, the arxiv version is alright).
When the disc was spun, further vibrations occurred and these are not quantifiable in the same way, or at least I don't know how to do it, so it is unclear so far whether MiHsC could predict the larger weight losses or not. Another thing that bothers me is that the column of weight loss seen by Podkletnov seemed to extend upwards indefinately. Was he forming and firing Unruh waves upwards??
I think this experiment is worth redoing. There is a chance that it is saying that something is going on that is a bit like MiHsC and I would love to have more published results to think about.
Podkletnov, E.E, and R. Nieminen, 1992. A possibility of gravitational shielding by bulk YBa2Cu3O7-x superconductor. Physica C, 203, 441-444.
Podkletnov, E.E., 1997. Weak gravitational shielding properties of composite bulk YBa2Cu3O7-x superconductor below 70K under e.m. field. http://arxiv.org/abs/cond-mat/9701074
McCulloch, M.E., 2011. Can the Podkletnov effect be explained by quantised inertia? Physics Procedia, 20, 134-139. http://arxiv.org/abs/1108.3488