Brane cosmology: Encyclopedia - Brane cosmology

Brane cosmology

Brane cosmology is a protoscience motivated by, but not rigorously derived from, superstring theory and M-theory. The idea is to solve problems in cosmology using speculative particle physics theories and in turn use cosmological observations to motivate ideas in string theory.

The central idea is that our visible, four-dimensional universe is entirely restricted to a brane inside a higher-dimensional space, called the bulk. The additional dimensions may be taken to be compact, in which case the observed universe contains the extra dimensions, and then no reference to the bulk is appropriate in this context. In the bulk model, other branes may be moving through this bulk. Interactions with the bulk, and possibly with other branes, can influence our brane and thus introduce effects not seen in more standard cosmological models.

As one of its attractive features, the model can "explain" the weakness of gravity relative to the other fundamental forces of nature. In the brane picture, the other three forces (electromagnetism and the weak and strong nuclear forces) are localised on the brane, but gravity has no such constraint and so much of its attractive power "leaks" into the bulk. As a consequence, the force of gravity should appear significantly stronger on small (sub-millimetre) scales, where less gravitational force has "leaked". Various experiments are currently underway to test this. For example, in a particle accelerator, if a graviton were to be discovered and then observed to suddenly disappear, it might be assumed that the graviton "leaked" into the bulk.

The Randall-Sundrum, pre-big bang, ekpyrotic and cyclic scenarios are particular models of brane cosmology which have attracted a considerable amount of attention.

The theory hypothesises that the origin of the big bang could have occurred when two parallel branes touched.

See also

• Cosmology
• Kaluza-Klein theory
• M-theory
• String theory

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