One of several possible theoretical
beginning moments of the universe. One of the deepest questions
in cosmology, the science that deals with the study and
origin of the universe and everything in it, relates to how the
universe came into existence. Cosmologists estimate that the
universe is 10–20 billion years old and consists of a huge
number of stars grouped in galaxies, clusters of galaxies, and
superclusters of galaxies, surrounded by vast distances of
open space. The universe is thought to be expanding because
measurements show that the most distant galaxies, quasars,
and most other objects in the universe are moving away
from each other and from the center of the universe. The Big
Bang Theory states that the expanding universe originated
10–20 billion years ago in a single explosive event in which
the entire universe suddenly exploded out of nothing, reaching
a pea-sized supercondensed state with a temperature of
10 billion million million degrees Celsius in one million-million-
million-million-million-millionth (10–36) of a second
after the Big Bang. Some of the fundamental parts of the
expanding universe models come from Albert Einstein, who
in 1915 proposed the General Theory of Relativity relating
how matter and energy warp space-time to produce gravity.
When Einstein applied his theory to the universe in 1917, he
discovered that gravity would cause the universe to be unstable
and collapse, so he proposed adding a cosmological constant
as a “fudge factor” to his equations. The cosmological
constant added a repulsive force to the General Theory, and
this force counterbalanced gravity enabling the universe to
continue expanding in his equations. William de Sitter further
applied Einstein’s General Theory of Relativity to predict
that the universe is expanding. In 1927, Georges
Lemaitre proposed that the universe originated in a giant
explosion of a primeval atom, an event we would now call
the Big Bang. In 1929, Edwin Hubble measured the movement
of distant galaxies and discovered that galaxies are
moving away from each other, expanding the universe as if
the universe is being propelled from a big bang. This idea of
expansion from an explosion negated the need for Einstein’s
cosmological constant, which he retracted, referring to it as
his biggest blunder. This retraction, however, would later
come back to haunt cosmologists.
Also in the 1920s, George Gamow worked with a group
of scientists and suggested that elements heavier than hydrogen,
specifically helium and lithium, could be produced in
thermonuclear reactions during the Big Bang. Later, in 1957,
Fred Hoyle, William Fowler, Geoff and Margaret Burbidge
showed how hydrogen and helium could be processed in
stars to produce heavier elements such as carbon, oxygen,
and iron, necessary for life.
The inflationary theory is a modification of the Big Bang
Theory and suggests that the universe underwent a period of
rapid expansion immediately after the Big Bang. This theory
was proposed in 1980 by Alan Guth, and it attempts to
explain the present distribution of galaxies, as well as the 3°K
cosmic background radiation discovered by Arno Penzias and
Robert Wilson in 1965. This uniformly distributed radiation
is thought to be a relict left over from the initial explosion of
the Big Bang. For many years after the discovery of the cosmic
background radiation, astronomers searched for answers
to the amount of mass in the universe and to determine how
fast the universe was expanding, and how much the gravitational
attraction of bodies in the universe was causing the
expansion to slow. A relatively high density of matter in the
universe would eventually cause it to decelerate and collapse
back upon itself, forming a “Big Crunch,” and perhaps a new
Big Bang. Cosmologists called this the closed universe model.
A low-density universe would expand forever, forming what
cosmologists called an open universe. In between these end
member models was a “flat” universe, that would expand
ever more slowly until it froze in place.
An alternative theory to the Big Bang is known as the
steady state theory, in which the universe is thought to exist
in a perpetual state with no beginning or end, with matter
continuously being created and destroyed. The steady state
theory does not adequately account for the cosmic background
radiation. For many years cosmologists argued,
almost religiously, whether the Big Bang Theory or the steady
state theory better explained the origin and fate of the universe.
More recently, with the introduction of new high-powered
instruments such as the Hubble Space telescope, the
Keck Mirror Array, and supercomputers, many cosmology
theories have seen a convergence of opinion. A new, so-called
standard model of the universe has been advanced and is currently
being refined to reflect this convergence of opinion.
In the standard model for the universe, the Big Bang
occurred 14 billion years ago and marked the beginning of
the universe. The cause and reasons for the Big Bang are not
part of the theory but are left for the fields of religion and
philosophy. Dr. William Percival of the University of Edinburgh
leads a group of standard model cosmologists, and
they calculate that the Big Bang occurred 13.89 billion years
ago, plus or minus half a billion years. Most of the matter of
the universe is proposed to reside in huge invisible clouds of
dark matter, thought to contain elementary particles left over
from the Big Bang. Galaxies and stars reside in these huge
clouds of matter and comprise a mere 4.8 percent of the matter
in the universe. The dark matter forms 22.7 percent of the
universe, leaving another 72.5 percent of the universe as nonmatter.
At the time of the proposal of the standard model,
this ambiguous dark matter had yet to be conclusively detected
or identified. In 2002 the first-ever atoms of antimatter
were captured and analyzed by scientific teams from CERN,
the European Organization for Nuclear Research.
Detailed observations of the cosmic background radiation
by space-borne platforms such as NASA’s COBE (Cosmic
Background Explorer) in 1992 revealed faint variations
and structure in the background radiation, consistent with an
inflationary expanding universe. Blotches and patterns in the
background radiation reveal areas that may have been the
seeds or spawning grounds for the origin of galaxies and
clusters. Detailed measurements of this background radiation
have revealed that the universe is best thought of as flat—
however, the lack of sufficient observable matter to have a
flat universe requires the existence of some invisible dark
matter. These observations were further expanded in 2002,
when teams working with the DASI (Degree Angular Scale
Interferometer) experiment reported directional differences
(called polarizations) in the cosmic microwave background
radiation dating from 450,000 years after the Big Bang. The
astronomers were able to relate these directional differences
to forces that led to the formation of galaxies and the overall
structure of the universe today. These density differences are
quantum effects that effectively seeded the early universe with
protogalaxies during the early inflation period, and their
observation provides strong support for the standard model
for the universe.
Recent measurements have shown that the rate of expansion
of the universe seems to be increasing, which has led cosmologists
to propose the presence of a dark energy that is
presently largely unknown. This dark energy is thought to
comprise the remaining 72.5 percent of the universe, and it is
analogous to a repulsive force or antimatter. Recognition in
1998 that the universe is expanding at ever increasing rates
has toppled questions about open versus closed universe
models and has drastically changed perceptions of the fate of
the universe. Amazingly, the rate of acceleration of expansion
is remarkably consistent with Einstein’s abandoned cosmological
constant. The expansion seems to be accelerating so
fast that eventually the galaxies will be moving apart so fast,
they will not be able to see each other and the universe will
become dark. Other cosmologists argue that so little is
known of dark matter and dark energy that it is difficult to
predict how it will act in the future, and the fate of the universe
is not determinable from our present observations.
Alan Guth and coworkers have recently proposed modifications
of the inflationary universe model. They propose
that the initial inflation of the universe, in its first few
microseconds, can happen over and over again, forming an
endless chain of universes, called multiverses by Dr. Martin
Rees of Cambridge University. With these ideas, our 14-billion-
year-old universe may be just one of many, with Big
Bangs causing inflations of the perhaps infinite other universes.
According to the theories of particle physics it takes only
about one ounce of primordial starting material to inflate to
a universe like our own. The process of growing chains of
bubble-like universes through multiple Big Bangs and inflationary
events has been termed eternal inflation by Dr. Andrei
Linde of Stanford University.
Cosmologists, astronomers, and physicists are searching
for a grand unifying theory that is able to link Einstein’s General
Theory of Relativity with quantum mechanics and new
observations of our universe. One attempt at a grand unifying
theory is the string theory, in which elementary particles
are thought to be analogous to notes being played on strings
vibrating in 10- or 11-dimensional space. A newer theory
emerging is called M-theory, or Matrix theory, in which various
dimensional membranes including universes can interact
and collide, setting off Big Bangs and expansions that could
continue or alternate indefinitely.
Cosmology and the fate of theories like the Big Bang are
undergoing rapid and fundamental changes in understanding,
induced by new technologies, computing abilities, philosophy,
and from the asking of new questions about creation of
the universe. Although it is tempting to think of current theories
as complete, perhaps with a few unanswered questions,
history tells us that much can change with a few new observations,
questions, or understanding.
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