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Message: <blockquote data-quote="tarchon" data-source="post: 2097454" data-attributes="member: 5990">In Einsteinian relativity, time and the three classical spatial dimensions are treated more as  directionalities of a four-dimensional space-time. Time isn't exactly a spatial dimension but more of an observer-dependent preferred axis that the observer perceives as time. Different observers can however take different axes to be the time axis, which is how the Einsteinian construct fundamentally differs from Galilean relativity. Galilean relativity postulates time as being wholly independent of the three spatial dimensions and invariant.Extra spatial dimensions come up in a number of new theories about the underlying structure of space and matter, but they're still largely speculative, and the "spatial dimensions" in those cases are usually highly constrained, so that they don't have a macroscopically apparent extent. What they really are is something like extra modes of vibration (or mathematically analogous to vibration), and one idea is that these modes occupy some sort of vestigial spatial dimensions that aren't realized in the universe as we know it. My guess is that these theories are grabbing at straws, and someone will eventually come up with a more elegant explanation for the mathematical features they explain.</blockquote>