Do we live in 11 Dimensions?  

The three space dimensions that we see are expanding,
and were once small and highly curved. It may be that
there are additional directions, perpendicular to all that
we see, that remain small and highly curved. If these are
small enough they would not have been detected yet,
but their existence has important indirect effects.

In particular, it is a powerful unifying idea: what look
like different particles to us might be the same kind of
particle, but in different states of motion or polarization
in the extra dimensions.

In fact, this idea is part of string theory: the mathematical
structure of string theory seems to require nine space
dimensions, in addition to time. Further, the more complete
understanding that came with M theory revealed a tenth
space dimension. Recent ideas have also suggested new ways in which these dimensions might be
detected, in measurements of the gravitational force at short distances and in processes where particles scatter into the extra dimensions and seem to disappear--- either in particle accelerators, or in supernova explosions.

These ideas were explored most recently in the Braneworld miniprogram in January 2002.