Inflation and String Theory
A significant advance in this area was obtained when the theory of inflationary multiverse was implemented in the context of string theory. In 2000, Bousso and Polchinski proposed to use the regime of eternal inflation and transitions between many different vacua in string theory for solving the cosmological constant problem. At that time, no stable or metastable vacua of string theory were actually known. A possible mechanism of string theory vacuum stabilization was proposed in 2003 by Kachru, Kallosh, Linde, and Trivedi, who also found that all of these vacua describing expanding universe are metastable, i.e. they must eventually decay. Then Douglas and his collaborators estimated that the total number of different stringy vacua can be as large as 10500, or even more, and Susskind developed the string theory landscape scenario based on investigation of cosmological phase transitions between different string theory vacua.
One of the main challenges of this theory is to find the probability to live in each of these different parts of the universe. However, once string theory is invoked, it is extremely difficult to return to the previous picture of a single universe. In order to do so, one would need to prove that only one of the many vacua of string theory is actually possible, and to propose an alternative solution of the many problems which can be solved by using the anthropic cosmological principle in the context of the theory of inflationary multiverse.
At present Linde is continuing his work on the theory of inflationary multiverse. He is also working on the development of advanced versions of inflationary theory based on string theory and supergravity, which should be flexible enough to properly describe a vast amount of new and upcoming cosmological observational data.
Read more about this topic: Andrei Linde
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