Editing String theory (section)

=== Cosmology ===
{{main|String cosmology}}

[[File:WMAP 2012.png|thumb|upright=1.4|A map of the [[cosmic microwave background]] produced by the [[Wilkinson Microwave Anisotropy Probe]]]]

The Big Bang theory is the prevailing [[physical cosmology|cosmological]] model for the universe from the earliest known periods through its subsequent large-scale evolution. Despite its success in explaining many observed features of the universe including galactic [[redshift]]s, the relative abundance of light elements such as [[hydrogen]] and [[helium]], and the existence of a [[cosmic microwave background]], there are several questions that remain unanswered. For example, the standard Big Bang model does not explain why the universe appears to be the same in all directions, why it appears flat on very large distance scales, or why certain hypothesized particles such as [[magnetic monopoles]] are not observed in experiments.<ref>[[#Becker|Becker, Becker and Schwarz]], pp. 530–531</ref>

Currently, the leading candidate for a theory going beyond the Big Bang is the theory of cosmic inflation. Developed by [[Alan Guth]] and others in the 1980s, inflation postulates a period of extremely rapid accelerated expansion of the universe prior to the expansion described by the standard Big Bang theory. The theory of cosmic inflation preserves the successes of the Big Bang while providing a natural explanation for some of the mysterious features of the universe.<ref>[[#Becker|Becker, Becker and Schwarz]], p. 531</ref> The theory has also received striking support from observations of the cosmic microwave background, the radiation that has filled the sky since around 380,000 years after the Big Bang.<ref>[[#Becker|Becker, Becker and Schwarz]], p. 538</ref>

In the theory of inflation, the rapid initial expansion of the universe is caused by a hypothetical particle called the [[inflaton]]. The exact properties of this particle are not fixed by the theory but should ultimately be derived from a more fundamental theory such as string theory.<ref>[[#Becker|Becker, Becker and Schwarz]], p. 533</ref> Indeed, there have been a number of attempts to identify an inflaton within the spectrum of particles described by string theory and to study inflation using string theory. While these approaches might eventually find support in observational data such as measurements of the cosmic microwave background, the application of string theory to cosmology is still in its early stages.<ref>[[#Becker|Becker, Becker and Schwarz]], pp. 539–543</ref>