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# 5 Inflation

Inflation is a process by which the scale factor increased by a factor of at least 20–30 orders of magnitude over a tiny fraction of a second, about seconds after the big bang. The theory was developed in the 1970s and 80s by physicists including Alan Guth, Alexei Starobinsky and Andrei Linde, in order to address several problems with standard cosmological models. It is now well accepted as part of the cosmological model, but it is difficult to test observationally and presents some challenges for particle physics.

The three main problems solved by inflation are the horizon problem, the flatness problem and the monopole problem, which will now be summarised in turn. Then, in the final section of this course, you will learn more about how inflation works, and the state of current theory and observational tests.

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OpenLearn - Unsolved problems in cosmology
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