Origins: The Dark Universe

96% of the universe's energy content is a mystery to us. It is composed of the dark energy and the dark matter. After a brief introduction to the big problems faced by cosmologists, I will discuss a model for the dark matter. It has been proposed by Sikivie that axionic dark matter will condense like a Bose-Einstein condensate, and the necessary thermalization will occur due to gravitational interactions. In this talk, I will give an overview of axions and Sikivie's picture. We treat axions as a quantum field theory in a curved spacetime where the background is also dynamical. I will discuss some of the interesting technical tools that we are use to solve the problem, which we expect will be readily applicable to other problems.