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The force of darkness - Unexpected results pop out when you relax relativity theory

点击量:   时间:2017-04-24 04:01:10

By Marcus Chown A MYSTERIOUS second type of gravity may help choreograph the motion of matter in the Universe—and help save it from the singularities nature abhors. Physicists in Britain say the force would be felt directly only by matter with a previously unsuspected “gravitational charge”. “Such matter would interact via the new form of gravity in addition to the familiar form between massive bodies,” says Robin Tucker of the University of Lancaster. The existence of gravitational charge would have profound implications for the early Universe and for black holes. “It could prevent the formation of a singularity, a point of infinite density, at the beginning of time and possibly in the heart of a black hole,” says Tucker. Tucker and his colleagues had been revisiting Einstein’s theory of gravity, the general theory of relativity. They knew that Einstein had made a certain assumption about gravity and space-time to simplify the equations. “If you relax this arbitrary assumption, a more general form of gravitation can be contemplated,” says Tucker. One consequence of the general form is the existence of a new interaction coupled to a gravitational “charge” that may be carried by some types of matter. The charge comes in two kinds, similar to positive and negative electrical charges. The force would be carried by a particle that may be as heavy as a grain of sand, and would act over distances smaller than an atom. Normal matter does not carry this charge. But Tucker and his colleague Charles Wang speculate that it might be carried by the invisible dark matter which makes up most of the mass of the Universe. The force would have been felt in the early Universe, and in any other region of the Universe where matter is very dense. Tucker and Wang found that if the gravitational charge has one sign, it might balance the normal attraction of gravity with a repulsive force. This could avoid the problem of a singularity at the beginning of time and in black holes. Alternatively, if the gravitational charge on dark matter has the opposite sign, the normal attraction of gravity would be reinforced, producing a more pronounced singularity and affecting the expansion rate of the Universe. Either way, the presence of gravitational charge could have determined the kind of Universe we live in. Gravitational charge could also be having a more indirect effect on today’s Universe. Although the new interaction has a very short range, it can nevertheless affect the shape of space-time and this would in turn affect the motion of normal matter. “If the Sun had a small gravitational charge, it would affect the motion of the planets,