A universe with hidden dimensions
String theory also postulates that in addition to the three space dimensions we are familiar with – left-right, back-forth and up-down (think: line, square, cube) - there are also another six space dimensions which are curled up at every point in space into complicated undetectably small shapes at the Planck scale known as Calabi-Yau spaces and so small that we cannot see them. To gain an intuitive feel for what these extra dimensions may be like, imagine observing electricity power lines, or even, say, a garden hose from a distance. Both look completely one dimensional, more or less like a straight line; but up close they appear multi-dimensional, each with a curved surface which may take some little time to navigate,(if you are a worm or an ant), and another dimension, indeed another universe, within[1].
In the beginning, all the spatial dimensions of string theory were on a completely equal footing: they were completely symmetrical, all tightly curled up to their smallest possible extent into a multi-dimensional Planck sized nugget – roughly the size of a typical string in string theory – wrapped around with loops of string. Then at about the Planck time (1 x 10-43 seconds), three of the spatial dimensions were singled out for expansion, while all others retained their initial Planck size scale, far too small for experiment or observation, and a random thermal fluctuation drove the three space dimensions we are familiar with momentarily to grow larger than the others following string/anti-string pair collisions.
[1] Greene (2004), 362.
In the beginning, all the spatial dimensions of string theory were on a completely equal footing: they were completely symmetrical, all tightly curled up to their smallest possible extent into a multi-dimensional Planck sized nugget – roughly the size of a typical string in string theory – wrapped around with loops of string. Then at about the Planck time (1 x 10-43 seconds), three of the spatial dimensions were singled out for expansion, while all others retained their initial Planck size scale, far too small for experiment or observation, and a random thermal fluctuation drove the three space dimensions we are familiar with momentarily to grow larger than the others following string/anti-string pair collisions.
[1] Greene (2004), 362.