**2.2. Inflationary Expansion: The Magic of a Shrinking Comoving Event
Horizon**

Inflation doesn't make the observable universe big. The observable
universe is as big as it is.
What inflation does is make the region from which the Universe emerged,
very small. How small? is unknown (hence the question mark in
Fig. 2), but
small enough to allow the points in opposite sides of the sky (**A**
and **B** in Fig. 4)
to be in causal contact.

The exponential expansion of inflation produces an event horizon at a constant proper distance which is equivalent to a shrinking comoving horizon. A shrinking comoving horizon is the key to the inflationary solutions of the structure, horizon and flatness problems. So let's look at these concepts carefully in Fig. 1.

The new -CDM
cosmology has an event horizon and it is this cosmology that is plotted
in Fig. 1 (the old standard
CDM cosmology did not have an event horizon).
To have an event horizon means that there will be events in the Universe
that we will never be able
to see no matter how long we wait. This is equivalent to the statement
that the expansion of the
Universe is so fast that it prevents some distant light rays, that are
propagating toward us, from ever reaching us.
In the top panel, one can see the rapid expansion of objects away from
the central observer. As time goes by,
dominates and
the event horizon approaches a constant physical distance from an
observer. Galaxies do not
remain at constant distances in an expanding universe.
Therefore distant galaxies keep leaving the horizon, i.e., with time,
they move upward and outward along the lines labeled with redshift `1'
or `3' or `10'. As time passes,
fewer and fewer objects are left within the event horizon. The ones that
are left, started out very close to
the central observer. Mathematically, the *R*(*t*) in the
denominator of Eq. 8 increases so fast
that the integral converges. As time goes by, the lower limit *t*
of the integral gets bigger, making
the integral converge on a smaller number - hence the comoving event
horizon shrinks. The middle panel shows clearly that in the future, as
increasingly
dominates the dynamics of the Universe, the
comoving event horizon will shrink. This shrinkage is happening slowly
now but during inflation it happened quickly.
The shrinking comoving horizon in the middle panel of
Fig. 1 is a slow
and drawn out version of what happened during inflation - so we can use
what is going on now to understand how inflation worked in the early
universe. In the middle panel galaxies move on vertical lines upward, while
the comoving event horizon shrinks. As time goes by we are able to see a
smaller and smaller region of
comoving space. Like using a zoom lens, or doing a PhD, we are able to
see only a tiny patch of the Universe, but in amazing detail.
Inflation gives us tunnel vision. The middle panel shows the narrowing
of the tunnel. Galaxies move up vertically and like objects falling into
black holes, from our point of view they are redshifted out of existence.

The bottom line is that accelerated expansion produces an event horizon at a given physical size and that any particular size scale, including quantum scales, expands with the Universe and quickly becomes larger than the given physical size of the event horizon.