MadSci Network: Physics |
Dear Joseph, It seems to me that the concept of generating anti-gravity, or shielding from the affect of Earth's gravity, is a romantic idea in the science fiction sense. Imagine launching satellites by cancelling their weight and then gently tapping them into orbit with your finger; or a wheel chair that suspends its rider in a zero gravitational field. How about anti-gravity running shoes? Ok, thats is a point. In 1992, experiments in Finland seemed to show that the Earth's gravity could be shielded or modified with a superconductor. This experiment, by Eugene Podkletnov, at Finland's Tampere University of Technology, apparently displayed the reduction in the weight of objects placed above a levitating, rotating high superconducting disk, exposed to high frequency magnetic fields. Did his device truely shield gravity, or was it a fluke, a mistake in experiment design? Podkletnov maintains that his experiments were complete. However, he apparently did not share his findings nor the details of his apparatus with the university or his coworkers at the time, so he perhaps unwittingly, perhaps permanently, cast doubt on the accuracy of his claims. One physicist has tried to explain Podkletnov's surprising results; papers written by G. Modanese offer theories as to why this effect might occur via quantum gravitational effects: specifically, a local change to the cosmological constant. Other physicists, including Unnikrishnan and De Podesta and Bull, offer alternative, non-gravitational explanations based on normal physical effects missed by Podkletnov. Two other physicists, Li and Torr, have written papers (2 papers before Podkletnov published his results, and 1 after) that predicted rotating superconductors in an alternating magnetic field would generate gravity -- perhaps Podkletnov has detected the effect they predicted. NASA have had a program in place researching this for nearly 3 years. Many other physicists simply laugh and say it's impossible due to conservation of energy, general relativity, or the fact that gravity really isn't a force -- it's just an implication of the 4 dimensional space we live in, and leave it at that. According to known physical principles, gravity cannot be shielded or modified. No combination of electromagnetic fields of any conceivable strength (that could be generated on Earth with conventional technology), near a superconductor or not, could modify gravity in any discernable way. In fact, there are so many known ways in which strong electric and magnetic fields can exert strong forces on nearby objects, that these sorts of effects almost always dominate weight measurements over even moderate changes in gravity. Thus, the design of any experiment to test for gravity changes in the vicinity of strong magnetic and/or electric fields (as in the Podkletnov device) must always be done very carefully. Attention must be paid to all of the forces present. It is not clear at all that Podkletnov's claims of having taken care of all that is valid. It is these sorts of issues that have stymied NASA so far. Because Podkletnov's claims have such far-reaching implications, a number of different groups are conducting experiments to reproduce the effect. Best regards, Emilson P. Leite IAG/USP - Brazil
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