Wednesday, 8 July 2009


There are two major problems for the Big Bang model of the creation of the
Universe. They are
l the flatness problem
l the horizon problem
The flatness problem relates to the density parameter of the Universe, . Values for
can take on any number between 0.01 and 5 (lower than 0.01 and galaxies can't
form, more than 5 and the Universe is younger than the oldest rocks). The measured
value is near 0.2. This is close to an of 1, which is strange because of 1 is an
unstable point for the geometry of the Universe.

Values of Omega slightly below or above 1 in the early Universe rapidly grow to
much less than 1 or much larger than 1 as time passes (like a ball at the top of a hill).
After several billion years, Omega would have grown, or shrunk, to present-day
values of much, much more, or much, much less than 1. So the fact that the
measured value of 0.2 is so close to 1 that we expect to find that our measured value
is too low and that the Universe must have a value of exactly equal to 1 for
stability. Therefore, the flatness problem is that some mechanism is needed to
produce a value for to be exactly one (to balance the pencil). A Universe of of
1 is a flat Universe.

The horizon problem concerns the fact that the Universe is isotropic. No matter what
distant corners of the Universe you look at, the sizes and distribution of objects is
exactly the same (see the Cosmological Principle). But there is no reason to expect
this since opposite sides of the Universe are not causally connected, any information
that is be transmitted from one side would not reach the other side in the lifetime of
the Universe (limited to travel at the speed of light).

All of the Universe has an origin at the Big Bang, but time didn't exist until after the
Planck era. By the end of that epoch, the Universe was already expanding so that
opposite sides could not be causally connected.
The solution to both the flatness and horizon problems is found during a phase of the
Universe called the inflation era. During the inflation era the Universe expanded a
factor of 1054, so that our horizon now only sees a small piece of what was once the
total Universe from the Big Bang.

The cause of the inflation era was the symmetry breaking at the GUT unification
point. At this moment, spacetime and matter separated and a tremendous amount of
energy was released. This energy produced an overpressure that was applied not to
the particles of matter, but to spacetime itself. Basically, the particles stood still as
the space between them expanded at an exponential rate.

Note that this inflation was effectively at more than the speed of light, but since the
expansion was on the geometry of the Universe itself, and not the matter, then there
is no violation of special relativity. Our visible Universe, the part of the Big Bang
within our horizon, is effectively a `bubble' on the larger Universe. However, those
other bubbles are not physically real since they are outside our horizon. We can only
relate to them in an imaginary, theoretical sense. They are outside our horizon and
we will never be able to communicate with those other bubble universes.

Notice how this solves the horizon problem in that our present Universe was simply
a small piece of a larger Big Bang universe that was all in causal connection before
the inflation era. Other bubble universes might have very different constants and
evolutionary paths, but our Universe is composed of a small, isotropic slice of the
bigger Big Bang universe.
Inflation also solves the flatness problem because of the exponential growth.
Imagine a highly crumbled piece of paper. This paper represents the Big Bang
universe before inflation. Inflation is like zooming in of some very, very small
section of the paper. If we zoom in to a small enough scale, the paper will appear
flat. Our Universe must be exactly flat for the same reason, it is a very small piece of
the larger Big Bang universe.

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