The entire Level II multiverse exists in a single space, so how can the dimensionality vary within it? Well, according to the most popular string-theory models, it’s only the apparent dimensionality that varies: the true space always has nine dimensions, but we don’t notice six of them because they’re microscopically curled up in the spirit of the cylinder from Figure 2.7: if you travel a tiny distance along one of these six hidden dimensions, you find yourself back where you started. Supposedly, all nine dimensions started out curled up, and then in our patch of space, inflation stretched
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