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THE BIG BANG THEORY
Currently accepted theories hold that our universe began by a BIG BANG. At that instant, all the matter and energy of the cosmos--everything you see today--was concentrated into a speck billions of times smaller than a proton. We can't kow anything about what existed before our universe because everything was obliterated in the collapse and explosion.
How do we know that the universe began this way? There are two main lines of evidence:
1. In 1929 Edwin Hubble noticed that distant galaxies were flyng away from us, and the farther they were from us, the faster they were moving. How did he come to this conclusion? Just as sound waves seem to be lengthened as a train moves away from an observer, light waves appear to be lengthened as weel. This is called the DOPPLER EFFECT. When light waves are lengthened, they shift in colr toward the longer wavelengths in the light spectrum--the longest being red and the faster they move, the longer the wavelengths. This is called RED SHIFTING. Objects that are redder than they should be are moving away from us. Scientists can measure the intensity and wavelengths of light given off by a star to identify the elements it is made of. However, the light spectra from some stars don't match any known element but have a percent longer wavelength, or red shifting. Astronomers know that galaxies are not just moving away from us--they are moving away from each other. It follows that if all objects in the universe are moving away from each other, they much once have been all together at the same point. Thus, there must have been a BIG BANG.
2. The Reminant heat from the Big Bang explosion can be found throughout the universe as background radiation. Arno Penzias and Robert Wilson won the 1978 Nobel Prize in Physics for their discovery that instead of being absolute zero, the temperature of deep space is about 2.7(degrees)Celsius.
When was the Big Bang Exactly?
How old is the Universe? To know the age of the universe, we need to know the rate at which the universe is expanding. The rate at which the universe is defined by the HUBBLE CONSTANT which is measured in megaparsecs. To determine Hubble Constant, choose a faraway object, determine just how far away it is, and how fast it is moving. Its velocity can be determined by the amount it is redshifted. Then divide the velocity by the distance to get the Hubble Constant.
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