The Accelerating Expansion of the Universe

The Accelerating Expansion of the Universe

We now discuss the most interesting development of recent astronomical observations. It came
as such a surprise that many scientists, this author included, were very reluctant to accept it. We
return to what Einstein termed as the biggest blunder of his professional career, the insertion of a
term into his equations of general relativity that had no observational basis. This term is the now
famous cosmological constant. It represents energy of the expanding space-time, quite distinct
from the energy of matter and radiation. It serves as a repulsive pressure, counteracting the
inward pull of gravity. But it has such a small influence that it cannot be observed to affect the
motion of galaxies within the local region of the universe measured prior to the late 1990’s.
However, its effects do not diminish with increasing distance as does gravity. Therefore, if it is
non-zero, regardless of how small it is, it will eventually dominate over gravity over large

enough distances. Thus if the universe grows large enough in size, the outward pressure
represented by the cosmological constant then serves to accelerate the expansion.
Since measurements made prior to the late 1990’s indicated no presence of such outward
pressure, it was assumed that the cosmological constant was identically zero, even though some
theoretical models of fundamental particles and fields predicted a non-zero value for it. A nonzero
value stems from the idea that empty space is not so empty in reality. The presence of allpervading
fields interacting with “virtual” particles is responsible for explaining many observed
phenomena of elementary particle physics. But how it might generate a non-zero cosmological
constant appears somewhat speculative. The measurements of distant supernovae made in the
late 1990’s showed clear evidence that the expansion rate of the universe is now greater than
what it had been, during the early stages of the universe [14]. This is one of the reasons why the
universe turns out to be a little older than what we originally determined based upon the local
expansion rate in the universe. Since the universe had earlier been expanding at a slower rate,
trying to extrapolate back to the original Big Bang based on the more recent expansion rate gives
too young of an age for the universe. This is one of the contributing factors to the resolution of
the age problem.
The non-zero cosmological constant implies that there is energy in the expanding space-time
universe. It is now popularly referred to as “dark energy” and its origin is as unclear as the “dark
matter” that dominates the mass density of the universe. But these unanswered questions do not
pose a legitimacy issue for the Big Bang theory. It shows us that the Big Bang theory is still
incomplete as a cosmological model of our universe. It also shows us that the initial explosion
that began the universal expansion acts only one way in time; that is, the universal expansion
will never reverse itself and become eventually a “big crunch.” The Big Bang is a one time nonreproducible
phenomenon. The beginning of the universe will be very different from the end of
the universe. As the universe continues to expand it will accelerate, and galaxies will become
more spread out. Further consequences of the non-zero cosmological constant remain to be
determined. As in many other areas of science, questions remaining imply that it is still an
ongoing enterprise, welcoming further progress by talented scientists and further observations of
our universe.
Meanwhile, the Big Bang theory has passed all of the scrutiny with flying colors. Careful
examination of each of the supposed problems has only led to a clearer understanding of how the
universe changed as it expanded, leaving behind the evidences that have allowed us to
comprehend this history today. We do not understand all of the details of the universe back to
the very beginning, but in examining the evidences left behind and interpreting them in light of
well-established laws of our universe, we have been able to understand much of the early
universe back to a very small fraction of a second removed from the moment the universal
expansion began. The field of cosmology is still a very active field of scientific research and we
should expect new developments and further scientific understanding of the very beginnings of
our universe. Scientists are recognizing that there must be a connection between religious faith
and the origin of our universe, since it is clear that small changes in any of several factors would
have resulted in a universe radically different from what we see. It appears that the earth and its
place in the space-time of our universe is precisely what it must be to support life. It is becoming
clearer that the scientific evidence suggests that a Creator carefully designed the universe. We
now examine how the biblical accounts of origins correspond to this evidence.