Gravity has a secret side. As well as the brute force that holds us to the ground, large masses should also exert a subtle swirling influence when they rotate, a force called gravitomagnetism. It's so faint that a NASA spacecraft called Gravity Probe B has been orbiting the Earth for over two years to accrue enough evidence to have a chance of confirming this force.
Yet in a lab in Austria, Martin Tajmar and his team have already succeeded in detecting a faint signal that seems to be due to this elusive component of gravity. A reason for celebration? Not quite. Puzzlingly, the force they seem to have generated is vastly more powerful than anyone else expected.
Despite its name, gravitomagnetism has nothing to do with magnetic fields as we think of them. According to Einstein's general theory of relativity, a rotating mass such as a planet should twist the ...
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