What is the Origin of the Universe
and its Destiny?
The Big Bang Theory is that the observable universe began as an expanding
point, approximately fifteen billion years ago. Since then, the universe
has continued to expand, gradually increasing the distance between our
Galaxy and external galaxies. We observe this effect. Will this expansion
continue forever, causing the universe to become ever colder and darker?
Or will the expansion eventually halt and, perhaps, reverse leading to
a "Big Crunch"? What came before the initial expanding point?
The gravitational pull of matter in the universe slows the expansion.
If the matter is dense enough, the expansion will eventually reverse -
gravity will win - and the universe will recollapse. If it is not, the
expansion will continue forever. The density of matter in the universe
will determine the ultimate fate of the universe. The minimum density required
to halt the expansion is called the "critical density". What
is the density of matter in the universe? We don't know the density of
the universe yet, but we know what observations and what space missions
we need to find out.
The density of the universe also determines its shape. If the density
of the universe exceeds the critical density, space is finite and curved
like the surface of a sphere. This implies that light rays could traverse
the circumference of the universe and return to their point of origin.
If the density of the universe is less than the critical density, space
is infinite and curved like the surface of a saddle. If the density of
the universe exactly equals the critical density, the universe is infinite
and flat like a sheet of paper.
The simplest version of the "inflationary theory", an extension
of the Big Bang theory that draws on developments in modern particle physics,
predicts that there was a very brief period of extreme expansion shortly
after the Big Bang. If true, this exceptional growth caused the universe
to become so large that any original curvature would be effectively unobservable
in the region of the universe we can see from Earth. (This is equivalent
to the fact that our small local view of Earth appears flat to us even
though the Earth is really round.) Thus inflation predicts that the shape
of the "local" universe is flat, like a sheet of paper.
New space missions can answer the fundamental questions about the shape,
origin, and destiny of the universe. Following up on the spectacular results
from the COBE mission, new windows on the cosmic microwave background (the
afterglow radiation from the Big Bang) are needed.
