Thesis (M.Sc.)--Chulalongkorn University, 2005

It is well known nowadays that the best candidate for the cosmological model is the inflationary model which describes the rapid expansion of the universe at the early time. This inflationary scenario is assumed to take place at a very high energy scale, at which classical general relativity is no longer valid as the quantum effects become more relevant. String theory is the most promising candidate for describing the nature of physics in this scale. The universal property of this theory is the stringy space-time uncertainty relation. The noncommutative property of space and time is the important consequence of this property. The aim of this thesis is to study the inflationary model in which the effect of noncommutative space-time is taken into account. The Cosmic Microwave Background (CMB) power spectrum is the convenient quantity that one uses to compare the result of the model with observed data. The comparison can be divided into two classes according to their vacua, which are the adiabatic vacuum and the minimized uncertainty vacuum. The result of both vacua is consistent that the noncommutative effect suppresses the spectrum at the low multipole. This result is more compatible with observation than the result of the commutative space-time.