If there is a fourth spatial dimension (other than time), why do we never see it? Well, we know that it has to be mostly irrelevant and useless to our survival in order to explain why we can’t control or perceive our motion in that dimension. We also know that if it was a linear dimension like the other (regular) dimensions, we would probably have noticed by now. Even if we can perceive in only three dimensions, we would notice things appearing and disappearing if they move toward and away from us in this other dimension. So we can be pretty confident that there’s no fourth spatial dimension
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