We show that gravitational effects of global cosmic 3-branes can be
responsible for compactification from six to four space-time dimensions,
naturally producing the observed hierarchy between electroweak and
gravitational forces. The finite radius of the transverse dimensions follows
from Einstein's equation, and is exponentially large compared with the scales
associated with the 3-brane. The space-time ends on a mild naked singularity at
the boundary of the transverse dimensions; nevertheless unitary boundary
conditions render the singularity harmless.Comment: 11 pages. Several references adde
