Treballs Finals de Grau de Física, Facultat de Física, Universitat de Barcelona, Any: 2015, Tutor: Enric VerdaguerThe purpose of this paper is to study the homogeneous backreaction of non-zero mass conformally coupled scalar fields on a cosmological background, including at spacetime, at one-loop order. For this study, the semiclassical Friedmann equation is solved using a method called order reduction. For a nearly at background we get a scale factor that evolves to a stationary scale factor depending on the initial quantum state. We also prove that a de Sitter scale factor is also a mathematical solution of the semiclassical Friedmann equation, and we argue this is a runaway type solution.