A Bang or a Whimper?

Article excerpt

COSMOLOGY AT THE BEGINNING OF A NEW MILLENNIUM

WHERE DID IT ALL COMB FROM? Religions have been invented in part to answer this question, but today we use science to discover the truth about the world. In recent times, science has discovered a great deal about the origin of the universe but many questions remain unanswered. This article will discuss some of the rapidly changing discoveries in this field which often change the way we view our theories.

THE BIG BANG WINS OVER ITS COMPETITORS

In the mid-20th century there were several competing theories for the origin and evolution of the universe. The Big Bang theory was based on three key observations. The most basic was that the universe was expanding. Spectral light of distant galaxies showed a shift of key features toward the longer, red end of the spectrum when compared to the spectral light of elements generated in a laboratory. The consensus was and still is that the movement of distant galaxies away from the earth causes this redshift. This is similar to the change in pitch heard as a whistle-blowing train passes--the Doppler shift. What's more, for galaxies that were apparently twice as far away as measured by their brightness, the redshift was twice as great. The discovery of this remarkable linear relationship, now known as Hubble's law, was evidence of an expanding universe. In such a universe, every galaxy, or group of gravitationally bound galaxies, moves away from every other. If we project such a universe back in time, it was sign ificantly hotter and denser than it is now.

This realization led to two other predictions. Early in its history the universe must have been hot enough for a burst of nuclear reactions to occur. The proportion of light elements and their isotopes that would have been formed in this nucleosynthesis era were calculated and later verified by observations. It was also realized that the early universe would have been so hot that matter would have been ionized--free electrons, protons, and bare atomic nuclei would have been present. Photons, particles of light, would not have been able to travel far before colliding into other particles. (in fact the photons and free charged particles--ions-formed a sort of fluid.)

The universe at this time was opaque, similar to the surface of the sun today. But as the universe expanded over time, it cooled. It was calculated that about 300,000 years after the beginning, the temperature dropped low enough for the ions to combine into atoms. This caused a drastic drop in charged particles, allowing photons to travel reasonably long distances before they collided with ions. The universe became transparent. The light that was released expanded along with the continued expansion of the universe, and cooled. Today this radiation should be present in the microwave region of the radio spectrum. We have detected this radiation and we now call it the cosmic microwave background radiation (CMB).

The redshifts of galaxies, the proportions of light elements, and the CMB are the three key pieces of evidence that validate the Big Bang. But the Big Bang has had its detractors. The two main competitors were the Steady State theory (its proponents later modified it and called it the quasi-Steady State theory) and plasma cosmology. In its original form, the Steady State model proposed that the universe was not only isotropic (the same in all directions) and homogenous in space, but unchanging as well. A Steady State universe has no beginning or end. It is infinitely old, and as it expands a continuous creation of matter is required to maintain the average density of the universe that we see today. Its proponents claimed that nucleosynthesis took place in stars rather than in the early hot, dense universe. But with this mechanism, the calculated proportion of helium is different What's more, the Steady State universe does not predict a background radiation and distant parts should look the same as nearby par ts. …