If Newton saw today's astronomical evidence, would he come up with a different law of gravity? A growing number of people think so, says Marcus Chown There's something wrong with our understanding of spiral galaxies such as our own Milky Way. The stars in their outer parts are being whirled around far too fast. Like children on a speeded-up roundabout, they should be flung into intergalactic space. To explain why this does not happen, astronomers have been forced to propose that the visible stars and nebulae are supplemented by at least 10 times more invisible stuff. The gravity of this...
