The early universe is a largely unknown and dark epoch, but our only hope to illuminate it is to stay within the box. In this talk, I will show how lattice simulations, finite boxes filled with fields, allow us to explore the nonlinear dynamics of the early universe. We will focus on the nonlinear physics that shapes its earliest moments and attempt to make sense of the cosmic history from the first instants, from inflation to the onset of the thermal era. I will argue that the only way to unveil the dark fabric covering this epoch is by listening to the soft whisper of gravitational waves, which may guide us up the primordial stairway to heaven.
Rebeca Beltrán