Superstring theory: Encyclopedia II - Superstring theory - Number of dimensions

Superstring theory - Number of dimensions

Our physical space is observed to have only four large dimensions, and a physical theory must take this into account, but nothing prevents a theory from involving more than 4 dimensions, per se. In the case of string theory, consistency requires spacetime to have 10, 11 or 26 dimensions. The conflict between observation and theory is resolved by making the unobserved dimensions compact dimensions.

Our minds have difficulty visualizing higher dimensions because we can only move in three spatial dimensions. Even then, we only see in 2+1 dimensions; vision in 3 dimensions would allow one to see all sides of an object simultaneously. One way of dealing with this limitation is not to try to visualize higher dimensions at all, but just to think of them as extra numbers in the equations that describe the way the world works. This opens the question of whether these 'extra numbers' can be investigated directly in any experiment (which must show different results in 1, 2, or 2+1 dimensions to a human scientist). This, in turn, raises the question of whether models that rely on such abstract modelling (and potentially impossibly huge experimental apparatus) can be considered 'scientific'. 6-dimensional Calabi-Yau shapes can account for the additional dimensions required by superstring theory.

Superstring theory is not the first theory to propose extra spatial dimensions; see Kaluza-Klein theory. Modern string theory relies on the mathematics of folds, knots, and topology, which was largely developed after Kaluza and Klein, and has made physical theories relying on extra dimensions much more credible.

See also: Why does consistency require 10 dimensions?

Adapted from the Wikipedia article "Number of dimensions", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki