String theory has to confront this same problem. We have to curl up these unwanted higher dimensions into a tiny ball (a process called compactification). According to string theory, the universe was originally ten-dimensional, with all the forces unified by the string. However, ten-dimensional hyperspace was unstable, and six of the ten dimensions began to curl up into a tiny ball, leaving the other four dimensions to expand outward in a big bang. The reason we can’t see these other dimensions is that they are much smaller than an atom, and hence nothing can get inside them. (For example, a
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