Cosmology 25 1the scalar fields from one minimum of its potential to another, which divides the
universe into exponentially large domains with matter in all possible states corre-
sponding to all minima of the SU(5) SUSY, including our SU(3) x SU(2) x U(1)
minimum.
These observations merged into one coherent picture after the discovery of eter-
nal inflation in the context of chaotic inflation scenario [6].11 According to this
scenario, some parts of the universe continue eternally jumping at density which
may be as high as the Planck density. Inflationary fluctuations produced in this
regime are powerful enough to jump over any barrier, and divide the universe into
exponentially large domains in which not only the scalar fields but even the type of
compactification and the effective dimension of our space-time may change [lo].
A similar regime may exist in the theories with many different local de Sitter
minima even if inflation near these minima is not of the slow-roll type [ll]: The
field may tunnel from an upper minimum to the lower minimum and back. A com-
bination of this effect and the effect discovered in [8, 3, 9, 61 provided a necessary
background for the string landscape scenario [12].
This scenario is based on the recent discovery of the mechanism of moduli sta-bilization in string theory [13], which allowed to describe inflation and the present
stage of acceleration of the universe. Once this mechanism was found, it was real-
ized that the total number of possible metastable de Sitter vacua in string theory
is enormously large, perhaps lo1'' or [14]. During inflation our universe
becomes divided into exponentially large domains of different types, which
is a perfect setup for the anthropic principle.
The large set of stringy vacua introduces an incredibly large set of discrete
parameters. However, some of the parameters of our universe are determined not
by the final values of the fields in the minima of their potential related to the string
theory landscape, but by the dynamical, time-dependent values which they were
taking at different stages of the evolution of the universe. This introduces a large
set of continuous parameters which may take different values in different parts of
the universe.
One example of a continuous parameter is the ratio n7/n~. Its observed values
is about 10-lo. In some cases, the reason why this number is so small is pretty
obvious, but in the original version of the Affleck-Dine scenario a typical value of
this parameter was 0(1) [15]. The ratio n7/ng in this scenario is determined by the
angle between two scalar fields soon after inflation. This angle is a free parameter
which may take different values in different parts of the universe due to inflationary
fluctuations of these fields [16]. It was argued in [16] that the process of galaxy
formation strongly depends on the ratio n7/nng. Therefore even if though the total
volume of the parts of the universe with n7/n~ = 0(1) is lo1' times greater than
"The regime of eternal inflation was known to exist in old inflation [7] and in new inflation
[B, 3, 91, but none of these papers except [3] mentioned the relation of this regime to the anthropic
principle.