**Definition**: The braneworld is a contemporary picture of our universe, which speculates that our visible universe may be confined to a three-dimensional volume which resides in a higher-dimensional space. This picture is motivated by superstring theory and M-theory. Brane is short for ‘membrane,’ the fundamental object of a scenario of the high-energy physics of braneworld (or brane cosmology).

**More about the term: **If it’s proven right then it constitutes a major revision of our understanding of the universe. This would also be *similar* to Max Tegmark’s level three and four multiverse; however, this would belong in a bit of a different category from Tegmark. This is primarily advocated by Columbia physicist Brian Greene and is known as… Braneworld.

Here’s a relevant paper abstract:

The aim of these lectures is to give a brief introduction to brane cosmology. After introducing some basic geometrical notions, we discuss the cosmology of a brane universe with matter localized on the brane. Then we introduce an intrinsic curvature scalar term in the bulk action, and analyze the cosmology of this induced gravity. Finally we present the cosmology of a moving brane in the background of other branes, and as a particular example, we discuss the cosmological evolution of a test brane moving in a background of a Type-0 string theory.

See *The Oxford Companion to Cosmology* and Briane Greene’s *The Hidden Reality*.

August 23, 2012 at 17:17

There being posited a likely relationship between string theory dimensions and the division algebra not all possible higher dimensions are possible (the relationship pointed out by John Baez. Google John Baez and octonions).

Division Algebra only allows for only 4 stable dimensional possibilities, 1,2,4, and 8 dimensions corresponding to real, complex, quaternions and octonion fields. Stable string theory dimensions always seem to be 2 above the divisional maths, namely 3,4,6, and 10 with string theory these days focusing on octonions (so 10 dimensions).

So that means that these two extra dimensions are this ‘braneworld’. It also means that since our world is no less than 4 dimensions, there are only two possibilities for higher braneworld space, namely 8 or 10 dimensions.

Add to String theory, M-theory questions of stability and symmetry and constraint imposed by division albegra, and the notion of ‘multiverse’ starts to shrink. Ultimately, my suspicions is that multiverse will ultimately shrink down to something looking very much ‘traditional’ universe.