The Universe

Origin of the Universe

Why is the inflationary model important in the modern Big Bang theory?

The inflationary model was proposed in the early 1970s to explain two key observations about the universe. First, the matter and energy in the universe appears to be statistically the same in every direction, as far as astronomers are able to observe. This means that parts of the universe that do not share a cosmic horizon today—that is, parts that should not have to be the same—somehow shared a cosmic horizon long ago in the past. (This is called the “horizon problem.”) Second, the universe has a “flat” geometry; this is a unique and very specific geometric structure, and there is no simple reason why the universe should be shaped this way. (This is called the “flatness problem.”)

As it is currently modeled, the inflationary period in the early universe addresses both the horizon problem and the flatness problem. The hyperinflation was so fast that it carried parts of space that used to share a cosmic horizon away from each other, so that in the present universe they would be statistically identical, even though they were no longer close enough to achieve balance with one another. In addition, the hyperinflation happened in such a way that it forced all of space to become a “flat” geometric structure. Although the model seems to explain what has been observed about the universe, it does not explain why it happened, nor exactly how much larger the universe grew during that time.


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