Imagine a person who lives in 4 spatial dimensions, watching a hypercube rotate. The 4-dimensional person has a 3-dimensional retina in each of its 2 eyes (two eyes suffice for depth perception, even in 4D). Each retina records a 3-dimensional image.
This image shows what the 4-dimensional person sees, with the extra dimension shown as a variation in colour. That is, the horizontal, vertical, and ‘colour’ directions correspond to the 3 directions on the 3-dimensional retina of the 4-dimensional person. The vertical bar to the right of the picture shows the correspondence between colour and position in the extra dimension.
This is a ‘false colour’ image, because the colour corresponds to something other than true colour. Of course our 4-dimensional friend undoubtedly sees in true colour as well...
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Updated 19 Jan 2005