Nothing seems to have been said on this topic for a "LONG" time!!!!!
However, GET Scientific American this month ()ctober 2005) GREAT STUFF!
Beauty of Branes - Liz Randalls ideas. Roughly as follows .........
Apparently one of the first serious sugestions about a 5th dimension was by Kaluz in 1919.
String theory now needs 10 dimensions.
M theory needs 11.
Branes (or membranes) are domains or swathes of several spatial dimensins within a higher dimensional space. the "everyday world "POSSIBLY" being a three brane for example and it is ANYONES GUESS what dimension brane it may be embedded in.
Apparently although not intending to Randall and Sundrum ended up using extra dimensions to offer a sollution to a so called HIERACHY PROBLEM which CAN BE FRAMED IN SEVERAL WAYS.
Why is gravity so puny , possibly many billion times weaker compared to other forces - electromagnetism, and the weak and strong nuclear forces?
Discrepancies in strength make it impossible to combine gravity with the other three forces, a unifiication THOUGHT to have existed during the early phse of the BIG BANG.
Rather than supersymmetry - a POPULAR SOLUTION that ARGUES for the existence of YET uUNDETECTED PARTNERS to all known particles.
Randal and Sundrum POSITED that gravity COULD reside on a different bane than our one seperated by a 5 dimensional space time in which the EXTRA DIMENSION is 10 to the MINUS 31 cm wide.
In the RS-1 model all forces and particles stick to our 3 brane EXCEPT gravity which is concentrated on the OTHER BRANE and is FREE TO TRAVEL BETWEEN THEM AND ACROSS SPACE TIME which is WARPED in a NEGATIVE fashion called ANTI_DE SITTER SPACE. By the time it gets to us GRAVITY IS WEAK, in the other brane it is STRONG, on a par with other forces.
STRING THEORISTS had looked at the idea of confining all forces to ONE BRANE and having GRAVITY LEAK but they DO NOT KNOW HOW?
According to Joseph Lykkam, Randall and Sundrum change peoples thinking R &S refinined the idea they realised that if the extra dimension of spacetime were WARPED in ANTI-DE SITTERT fashion it could be infinitely large and what we observe about gravity COULD still be true.
This is the so called RS-" model.
All this is counter-intuitive according to Mitchell J Duff, a surprise even to those working in extra-dimensions that even though the extra dimension is very large we would NOT BE AWARE OF IT.
Newton's Laws would still be an inverse square law, not an inverse cube law which is what you might expect !
Apparently it took a while for R&S suggestions to be appreciated but the time was ripe. Anti- De Sittert space was popping up in the models, branes were thriving.
In 1988 Arkani-Hamed, Dvali and Dimopoulos had postulated a 3 brane with two large extra dimensionsSome of recent models be they RS elaborations of ADD or others WILL be put to the test when the Cern Large Hadron Colider fires up in 2007.
"IF" there is any solution to the herarchy problem it should be revealed at energies the LHC explores, say Randall. Evidence COULD include, gravitons, supersymmetric partners and evanescent, tiny black holes.
EVEN IF WE DO NOT KNOW THE ANSWER IT SHOULD TELL US WHAT THE ANSWER IS ! says Randall
According to Randall we MAY live in a 3 brane but there are regions BEYOND the HORIZON that look really ENTIRELY DIFFERENT, and we have NOT EXPLORED YET!.
According to Karch Randall is usually correct!
Best of luck from the Grumpy Old Codger Cliff
The non amateur stuff. Hawking, black holes, that sort of thing
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