More: Seven things that don’t make sense about gravity
Though the notion of building a gravity shield has a long history, no one has yet managed to do it. Perhaps the most famous attempt was by Russian émigré scientist Evgeny Podkletnov.
In 1992, Podkletnov published a paper in which he claimed to have detected a 2 per cent weight reduction around a spinning disc made out of a ceramic superconductor.
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Martin Tajmar, a researcher at the company Austrian Research Centers, published a similar claim in 2003 and was able to pursue the research further with funding from the European Space Agency. Three years later Tajmar and ESA announced they had measured an effect in a spinning superconductor that might, with further development, be harnessed to affect gravity. Others have tried and failed to replicate this effect.
Why does anyone think it might even be possible? Because relativity does not rule out the possibility that the bent space-time that gives rise to gravity’s pull can be “unbent”. “By appropriate arrangements, it should be possible to diminish – or enhance – the influence of gravity,” says physicist Bahram Mashhoon at the University of Missouri.
Tajmar invokes an effect called “gravito-magnetism” as a way of doing this. According to general relativity, the mass of a rotating body will drag space-time around with it, putting a twist into it. Just as a spinning charge creates a magnetic field, a spinning mass creates a gravito-magnetic field.
This should have real-world effects – the Earth’s spin, for instance, should cause satellite orbits to precess – but you won’t be surprised to hear there are practical issues with using the idea to reduce gravity. “The relativistic effects are extremely small in practice,” Mashhoon points out.
Though it’s not even clear that a spinning superconductor has any gravito-magnetic influence, people should not be ridiculed for continuing to research in this area, Mashhoon says. It might just turn out to be the only way we can achieve interstellar travel. Some researchers have suggested that above a certain critical speed, relativity can give repulsive gravitational effects that could be used for propulsion as well as gravity shielding. “With present technology, it would take us about a million years or so to go to the nearest neighbouring star,” Mashhoon says. “It is hard to blame people for looking into these things.”
More: Seven things that don’t make sense about gravity
