Albert Einstein, although believing in the former, formulated the theory of relatively which proved the latter. He just couldn’t bring himself to believe that the universe had a beginning. Furthemore, the leading scientists of the day distanced themselves from the then derisively-called Big Bang theory because of the religious connotations.
Finally, the discovery of cosmic background microwave in 1964 confirmed that yes, the universe had a start point, and the microwave was the repercussion of that start, which was a humongazoidal bang. As MSN Encarta says it -
"According to the big bang theory, the universe expanded rapidly in its first microseconds. A single force existed at the beginning of the universe, and as the universe expanded and cooled, this force separated into those we know today: gravity, electromagnetism, the strong nuclear force, and the weak nuclear force...
One widely accepted version of big bang theory includes the idea of inflation. In this model, the universe expanded much more rapidly at first, to about 1050 times its original size in the first 10-32 second, then slowed its expansion …
The universe cooled as it expanded. After about one second, protons formed. In the following few minutes—often referred to as the “first three minutes”—combinations of protons and neutrons formed the isotope of hydrogen known as deuterium as well as some of the other light elements, principally helium, as well as some lithium, beryllium, and boron. The study of the distribution of deuterium, helium, and the other light elements is now a major field of research. The uniformity of the helium abundance around the universe supports the big bang theory and the abundance of deuterium can be used to estimate the density of matter in the universe.
From about 380,000 to about 1 million years after the big bang, the universe cooled to about 3000°C (about 5000°F) and protons and electrons combined to make hydrogen atoms. Hydrogen atoms can only absorb and emit specific colors, or wavelengths, of light. The formation of atoms allowed many other wavelengths of light, wavelengths that had been interfering with the free electrons prior to the cooling of the universe, to travel much farther than before. This change set free radiation that we can detect today. After billions of years of cooling, this cosmic background radiation is at about 3 K (-270°C/-454°F)…
The Cosmic Background Explorer (COBE) spacecraft, a project of the National Aeronautics and Space Administration (NASA), mapped the cosmic background radiation between 1989 and 1993. It verified that the distribution of intensity of the background radiation precisely matched that of matter that emits radiation because of its temperature, as predicted for the big bang theory. It also showed that cosmic background radiation is not uniform, that it varies slightly. These variations are thought to be the seeds from which galaxies and other structures in the universe grew.
"Big Bang Theory," Microsoft® Encarta® Online Encyclopedia 2008.
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Next time you have the chance, do catch the documentary on the History Channel - it will really show how small we are in the grand scheme of things.