07-08-2012, 11:49 AM
The Evolution of the Universe
Introduction
Science at the beginning of the twenty-first century can make some bold,
yet simple observations:
1) the universe has evolved;
2) we are a result of that evolution.
“We are the first generation of human beings to glimpse the full sweep
of cosmic history, from the universe's fiery origin in the Big Bang to the
silent, stately flight of galaxies through the intergalactic night.” (National
Research Council)
Order in the Universe
Cosmology is the study of the evolution of the universe from its first moments to the
present. In cosmology the most fundamental question we can ask is: Does our universe have
intelligible regularities that we can understand—is it ordered? This question lies at the heart of
the scientific revolution beginning in the sixteenth century. That revolution began with the
discoveries by Copernicus, Galileo, and Newton of order in our world. Today our scientific
understanding of nature’s order has reached a critical threshold. Only now can we begin to
piece together a coherent picture of the whole. Only now can we begin to see the deep order of
our universe.
The Big Bang “Theory”
The Big Bang is actually not a "theory" at all, but rather a scenario or model about the
early moments of our universe, for which the evidence is overwhelming.
It is a common misconception that the Big Bang was the origin of the universe. In
reality, the Big Bang scenario is completely silent about how the universe came into existence
in the first place. In fact, the closer we look to time "zero," the less certain we are about what
actually happened, because our current description of physical laws do not yet apply to such
extremes of nature. The Big Bang scenario simply assumes that space, time, and energy
already existed. But it tells us nothing about where they came from or why the universe was
born hot and dense to begin with.
But if space and everything with it is expanding now, then the universe must have been
much denser in the past. That is, all the matter and energy (such as light) that we observe in the
universe would have been compressed into a much smaller space in the past. Einstein's theory
of gravity enables us to run the "movie" of the universe backwards—i.e., to calculate the
density that the universe must have had in the past. The result: any chunk of the universe we
can observe—no matter how large—must have expanded from an infinitesimally small volume
of space.
The Early Cosmos: Out of the Darkness
Although no stars and galaxies existed just after the Big Bang, the young cosmos was
anything but dull. It was humming with activity. In the beginning, physical conditions were so
extreme that matter as we know it today did not exist.
During the early part of its existence, after one times ten to the minus 12th of a second,
our universe was so small and dense that light and matter intertwined; space was hot, dark, and
ionized—filled with a plasma of charged particles. By the time the universe was one second
old, the temperatures and densities had dropped enough for protons and neutrons to form from
quarks. Within the next few minutes, the nuclei of the light elements, hydrogen, helium, and
lithium, were created in a process called primal or Big Bang nucleosynthesis. The universe at
this point was cooling rapidly enough to shut off the process of nucleosynthesis before
elements heavier than boron could form.