- A requirement:
inflation must have occurred for long enough to create the observable
universe from a single Hubble volume. This is satisfied only if
expansion occurred at least a factor of 10^26.
- The Early Universe. Edward Kolb and Michael Turner. Westview Press, 1994.
- A problem:
Theoretical circumstances must be adjusted slightly. Slow-roll
conditions, which say that inflation potential must be flat and
inflation particles must be of a small mass, must be satisfied. Thus,
the universe must have a scalar field with flat potential and unique
special conditions.
- Cosmological Inflation and Large-Scale Structure. Andrew Liddle and David Lyth. Cambridge University Press, April 2000.
- An alternative:
String theory provides for extra dimensions that are curled up. Why
did some dimensions expand and some remain small and compact? String
gas cosmology, proposed by Robert Brandenburger and Cumrun Vafa, is a
theory that argues that a dimension can only expand if the strings
winding around it destroy each other. The largest number of dimensions
in which two strings will intersect is three, providing for the
likelihood of expansion of three dimensions.
- Review of Modern Physics, 78. String Gas Cosmology. Thorsten Battefeld and Scott Watson. 2006.
