There are a variety of competing theories for the origin of large-scale structure and the fluctuations in the cosmic microwave background radiation. These models fall into two categories: (1) causal topological defect models, such as cosmic strings and textures, or (2) inflationary scenarios.
Examples of the different cosmic microwave fluctuation patterns that they create are shown below for maps of a few degrees. The random features of inflationary models and cosmic strings are quite similar, being quite distinct from the stronger features for other defects. Experimental improvements in the study of such small scale CMBR fluctuations should lead to discriminating tests between these different models.
An example of a full sky map of fluctuations produced by cosmic strings can be seen below. The statistical properties of this map can be directly compared with the COBE maps and they show satisfactory agreement. Discerning experimental tests await studies on smaller angular scales.
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