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# Introduction

Welcome to this free course, Unsolved problems in cosmology. If you have read any other books or articles about cosmology, or seen TV programmes on the subject, you will probably be aware that cosmological theory has been very successful in explaining a wide range of observational evidence about the Universe. This includes phenomena such as the detailed properties of the cosmic microwave background (CMB) radiation, the distributions of galaxies, and the abundances of the light elements in astrophysical environments. However, you may have also become aware that there are several major unknowns in cosmological theory. These knowledge gaps are frustrating for cosmologists, students, and members of the public who would like to understand the nature of the Universe.

This course will discuss the three most crucial unresolved problems in modern cosmology:

- the nature of dark matter, which is suggested to explain the motion of stars in the outer regions of galaxies and the motion of galaxies in clusters
- the nature of dark energy, which is postulated as an explanation for the present-day acceleration of the expansion of the Universe
- the need for an early period of inflation, soon after the big bang.

You will explore these ideas by examining a set of articles and videos. In the case of the articles, you only need to read at a depth that allows you to follow the arguments being presented. There is no need, for example, to undertake secondary reading of any sources that are cited within the article (unless you are particularly interested in reading more about the subject in question).

There are exercises associated with the articles and videos, with questions to help guide you through the main ideas presented. You should be able to answer each exercise in a few sentences or, at most, a short paragraph. Discussions are provided to accompany the exercises, but you should try to note down your own answers before accessing these. There is also a short quiz at the end of the course.

This OpenLearn course is an adapted extract from the Open University course S385 Cosmology and the distant Universe.

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OpenLearn - Unsolved problems in cosmology
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