The superconductor will levitate. It's called the Meissner effect, and it might one day lead to an ''antigravity'' machine. John H. Schnurer, director of applied sciences at Physics Engineering in Yellow Springs, Ohio, thinks he might have taken a first step in that direction last fall. Above the disk was a plastic sample hanging from one end of a homemade balance scale containing no metal parts.
Many physicists are sure antigravity is a delusion.
Even if it does exist, it can't be more than one-millionth as strong as gravity, says Eric G. Adelberger, a professor of physics at the University of Washington who studies gravity. And because gravity itself is such a weak force, tiny magnetic fields and temperature changes can cause spurious results. At least two scientists theorize that the apparent weight loss is real. It would produce an unseen tunnel above the disk, and inside it things would weigh less because exotic quantum-physics reactions would be absorbing some of gravity's pull. Ning Li, a senior research scientist at the University of Alabama's Huntsville campus, believes that under the proper conditions, the minuscule force fields of superconducting atoms can ''couple,'' compounding in strength to the point where they can produce antigravity.