From: Spudboy100@aol.com
Date: Thu Dec 16 1999 - 06:04:01 MST
http://www.newscientist.com/ns/19991218/newsstory10.html
The great beyond
Our Universe could be an island marooned in five-dimensional space
SPACE may have a fifth dimension--one more than the four we are familiar
with, say two physicists. And it could be infinite, unlike the tiny extra
space dimensions that have been proposed in the past.
"Incredibly, it could have gone completely unnoticed until now," says Raman
Sundrum of Stanford University in California. Physicists take extra
dimensions seriously because superstring theory, the best candidate for a
"theory of everything", requires at least nine space dimensions.
"There are two ways the extra dimensions could conceal themselves from view,"
says Sundrum. "One is if they are rolled up far smaller than an atom. The
other is if the Universe is confined to a kind of lower-dimensional island
within higher-dimensional space." An infinitely thin two-dimensional piece of
paper would form such an island within normal 3D space.
This latter possibility has now been explored by Sundrum and his colleague
Lisa Randall of Princeton University, New Jersey. Remarkably, superstring
theory requires lower-dimensional islands, or "branes". And in superstring
theory, nature's three non-gravitational forces--the electromagnetic, weak
and strong forces--can be naturally constrained to operate only within a
brane. Gravity is a problem, however. "Gravity is intimately connected with
the dynamics of space-time and so necessarily extends into all extra
dimensions," says Sundrum.
Gravity from bodies such as the Sun should theoretically spread into this
large extra space dimension, effectively diluting it within our Universe's
brane. "It would weaken with distance far faster than the inverse-square law
decline that we observe," says Sundrum.
But Sundrum and Randall have discovered this may not be so. "The key is the
gravity of the brane itself, which is enormous," says Sundrum.
Gravity pulls on all sources of energy, including the energy contained in a
gravitational field. "Consequently, the gravity of the brane pulls on the
gravity of objects like the Sun, preventing it from extending very far beyond
the brane," says Sundrum.
Crucially, with gravity confined to the brane, the force is undiluted and
displays the familiar inverse-square law. And the mechanism for confining
gravity works no matter how big the extra space dimension.
"What's so amazing is that the theory mimics familiar four-dimensional
gravity so well that it would be very difficult to tell that there is an
extra dimension," says Randall.
Source: Physical Review Letters (vol 83, p 4690)
Marcus Chown
>From New Scientist, 18 December 1999
This archive was generated by hypermail 2.1.5 : Fri Nov 01 2002 - 15:06:06 MST