Some theorists envision the universe as multidimensional space-time embedding a membranous entity, called a brane, also of multiple dimensions. Diagram depicts familiar 3-dimensional space (time not shown) as a vertical line. At every point along line, one extra dimension curls around with a radius (r) of no more that about 10^�19 meter. Perpendicular to every point of the brane extends the bulk, another extra dimension. Credit: Adapted from Dienes et al., Nuclear Physics B
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