Why Does Our Universe Have Three Dimensions?

Why does our universe look the way it does? In particular, why do we only experience three spatial dimensions in our universe, when superstring theory, for instance, claims that there are ten dimensions -- nine spatial dimensions and a tenth dimension of time?

Japanese scientists think they may have an explanation for how a three-dimensional universe emerged from the original nine dimensions of space.

According to string theorists, there are the three full-sized spatial dimensions we experience every day, one dimension of time, and six extra dimensions crumpled up at the Planck scale like itty-bitty wads of paper. As tiny as these dimensions are, strings -- the most fundamental unit in nature, vibrating down at the Planck scale -- are even smaller.

The geometric shape of those extra dimensions helps determine the resonant patterns of string vibration. Those vibrating patterns in turn determine the kind of elementary particles that are formed, and generate the physical forces we observe around us, in much the same way that vibrating fields of electricity and magnetism give rise to the entire spectrum of light, or vibrating strings can produce different musical notes on a violin.

All matter (and all forces) are composed of these vibrations -- including gravity. And one of the ways in which strings can vibrate corresponds to a particle that mediates gravity.

Voila! General relativity has now been quantized. And that means string theory could be used to explore the infinitely tiny point of our universe's birth (or, for that matter, the singularity that lies at the center of a black hole).

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