christopher hall

I have been reading Brian Green's new book "The Fabric of the Cosmos"
and I have some musings/questions on the three
Brane Scenario.
Although my Physics knowledge is weak, I do know some Mathematics. Let
me make some assertions that seem to
approximate the reality of the three Brane scenario.
The universe is R3 direct sum M(Where M is a compact seven dimensional
manifold and direct sum is geometric.). We
only experience the R3 directly. With the exception of gravity, all forces
are transmitted along the three brane.
The first speculation is on the nature of dark matter. Couldn't it be
ordinary matter contained on 3-branes "parallel" to
our own. Since gravity is transmitted beyond our brane, clumping on
parallel branes would mirror clumping on our own.
The second speculation is on the relation of the size of hidden
dimensions to the feebleness of gravity. Consider two
universes U1 and U2. The difference between them is the M in the direct
sum. M1 is geometrically similar to M2, with
every distance in M1 being half of it's counterpart in M2. Clearly, the
seven volume of M2 is 128 times the seven volume
of M1. Given the dilution of gravity in the M coordinates, gravity is
clearly 128 times as strong in U1 as in U2 at reasonable
distances. Playing with these facts(and some others that I don't know how
to compute), we should be able to make some
statements about the minimal size of the largest extra dimension.