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Time Travel Research Center
© 2005 Cetin BAL - GSM:+90 05366063183 - Turkey/Denizli
Manyfold and Pre-Bang Universes
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Superstring teory predicts the universe has ten or
eleven dimensions. Why don't we see these extra dimensions? Perhaps we
are living on a brane (short for membrane) - floating in a space of five,
six or more dimensions, like a soap bubble in the bathroom. The "manyfold
universe" theory asserts that the brane we live on could be folded over
on itself many times, accordion-fashion (see diagram). Light could
travel only on the brane, but gravity could take a shortcut by jumping
from one fold to the next. Nearby matter on other folds can be detected
gravitationally as dark matter since the light it emits takes a long
time to reach us traveling around the fold (see Figure 01). |
Figure 01 Manyfold Universe
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In 3-dimensional space the gravitational force between two mass m1
and m2 is (see Figure 02):
F = Gm1m2/(r12)2 ---------- (1)
where r12 is the separation between the two masses, and G =
6.67x10-8 cm3/sec2-gm is the gravitational
constant defined in the 3-dimensional space.
If the gravitational force spreads over to n additional dimensions, which
curl up into circles with radius R, then the force would be:
F = G'm1m2/(r12)2+n ----------
(2)
where G' is the gravitational constant corresponding to the case with n
additional dimensions.
Starting from the source, the lines of force spread apart rapidly through
all the dimensions. At distance larger than R, the force lines have filled
the extra dimensions, which then cease to exert further influence (see
Figure 03). Consequently, we can equate Eq. (1) and (2) at the distance R
and obtain:
G = G'/(R)n ---------- (3)
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which states that the value for the gravitational
constant G is the result of modifying the original value G' by a factor
1/(R)n. Since the law of gravitation has been experimentally
tested down to distances of only about a millimeter, we would be
oblivious to changes in gravity caused by extra dimensions for which R
was smaller than this size. It is found that if there is only one extra
dimension (n = 1), R must be roughly the distance between the earth and
the sun. Therefore, this case is already excluded by observation. For n
= 2, R can be in the millimeter range and G' would be large enough to
allow the production of gravitons1
copiously at energy of a few Tev. |
Figure 02 Gravitational Force
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Figure 03 Extra-dimension
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The concept of branes floating in higher dimensional
space has offered some new ideas about condition at the moment of Big
Bang and further back to the time before the event (see Figure 06).
According to general relativity, density and temperature become infinity
at the moment of Big Bang. The nonzero size and novel symmetries of
strings set upper bounds to physical quantities that increase without
limit in conventional theories, and they set lower bounds to quantities
that decrease. The string theory expects that the curvature of space-time
increase as the history of the universe is re-winded backward in time.
But instead of going all the way to infinity, it eventually hits a
maximum and shrinks once more (see Figure 04). The string theory also
proposes some hazarded guesses about the pre-bang universe. There are
two popular models floating around - the Pre-Big Bang and the Ekpyrotic
scenarios. |
Figure 04 Two Views of the Big Bang
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The Pre-Big Bang model was developed in 1991 by
combining T-duality with the symmetry of time reversal. The combination
gives rise to a cosmological model in which there was a period of
acceleration before the Big Bang and then the deceleration. The Big Bang
was simply a violent transition from on phase to another (see Figure
05). The other model is the Ekpyrotic (conflagration) scenario. It
relies on the idea that our universe is one of many D-branes floating
within a higher-dimensional space. The branes exert attractive forces on
one another and occasionally collide. The Big Bang could be the impact
of another brane into ours as shown in Figure 06. |
Figure 05 Pre-BB
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Figure 06 Ekpyrotic Model
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D- brane
1Gravitons are the messenger particles which carry the
gravitational force in quantum theory. They play a part in quantum gravity
analogous to the role of the photons in quantum electrodynamics. In the
theory of superstring gravitons are represented by tiny closed loops, which
can wander into all the dimensions because unlike most of the other
particles they have no end points anchoring to a D-brane or Dp-brane
('p' is an integer which is the number of spatial dimensions of the manifold),
which is a special class of branes called Dirichlet branes. The name derives
from the boundary conditions assigned to the endpoint (of open string) which
is fixed to move only on some manifold.
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