There's hardly a problem that physicists haven't tried to solve by adding extra dimensions to our everyday three of space and one of time: whether with scrunched up dimensions too small to see, or the idea that our 4D world exists on a "brane" floating in an inaccessible higher dimensional world.
How to envisage such things? Physicist Carlo Rovelli of the University of Marseilles, France, doesn't personally have much truck with more than three spatial dimensions – "I do not think they exist," he says – but he finds extra dimensions easy enough to picture. "It is just a space where you can go up-down, left-right, ahead-back, but also in one other dimension, something like leftB-rightB," he says. "It is a bit like having many arms, like an Indian god."
Others are more circumspect. "Visualising higher dimensions is certainly harder," says Don Marolf ...
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