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## Summary:

- The first three spatial dimensions are described as straight lines extending infinitely at perpendicular angles, but additional spatial dimensions are described as being microscopic. Why would there be a limit to their extent?

## Main Question or Discussion Point

As I understand it, dimension is a way of describing direction, with the first three spatial dimensions being straight lines which extend infinitely in one direction, perpendicular to each other. In string theories, several additional dimensions are required, sometimes up to nine or 10, I believe. These dimensions are sometimes described as being "curled up" into microscopic spaces. I find this a bit confusing, because if the first three are straight lines extending forever in a given direction, why would there be dimensions which can only exist in very small spaces? I know that I'm probably misinterpreting things here, but I would like to understand whether these directions are also infinite straight lines. If not, what are they, and what does it mean that they might be confined to atomic scale spaces?