Cosmology is the scientific study of the large scale properties of the Universe as a whole. It endeavors to use the scientific method to understand the origin, evolution and ultimate fate of the entire Universe. Like any field of science, cosmology involves the formation of theories or hypotheses about the universe which make specific predictions for phenomena that can be tested with observations. Depending on the outcome of the observations, the theories will need to be abandoned, revised or extended to accommodate the data. The prevailing theory about the origin and evolution of our Universe is the so-called Big Bang theory. Some of the key questions for cosmology research are:
- What types of matter and energy fill the universe? How much of each?
- How rapidly is the universe expanding today?
- How old is the universe today?
- What is the overall shape of the universe? Open, flat, closed, or otherwise?
- How is the expansion changing with time?
- What is the ultimate fate of the universe?
The Big Bang Model is a broadly accepted theory for the origin and evolution of our universe. It postulates that 12 to 14 billion years ago, the portion of the universe we can see today was only a few millimeters across. It has since expanded from this hot dense state into the vast and much cooler cosmos we currently inhabit. We can see remnants of this hot dense matter as the now very cold cosmic microwave background radiation which still pervades the universe and is visible to microwave detectors as a uniform glow across the entire sky.
The Big Bang model is not complete. For example, it does not explain why the universe is so uniform on the very largest scales or, indeed, why it is so non-uniform on smaller scales, i.e., how stars and galaxies came to be. The Big Bang model is based on the Cosmological Principle which assumes that matter in the universe is uniformly distributed on all scales - large and small. This is a very useful approximation that allows one to develop the basic Big Bang scenario, but a more complete understanding of our universe requires going beyond the Cosmological Principle. Many cosmologists suspect that inflation theory, an extension of the Big Bang theory, may provide the framework for explaining the large-scale uniformity of our universe and the origin of structure within it.
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