Thesis

Origin of the arrow of time of the Universe

• Call:

  PT-CERN Call 2022/2

• Academic Year:

  2022

• Domain:

  Astroparticle Physics

• Supervisor:

  Marina Cortês

• Co-Supervisor:

  Andrew Liddle

• Institution:

  FCUL (Universidade de Lisboa)

• Host Institution:

  IA - Instituto de Astrofísica e Ciências do Espaço

• Abstract:

  The Energetic Causal Set [1] (ECS) model and it's quantum counterpart [2] were pioneered by one of the current supervisors, Marina Cortês, along with Lee Smolin, in the work which won first place in the inaugural Buchalter Cosmology Prize (2014). They introduced a model for the development of space-time that is intrinsically time-asymmetric throughout the emergence of space-time. The model was however implemented in only one spatial dimension. The current masters project [3] of the student candidate for this project, Vasco Gil Gomes, under the supervision of Cortês and Liddle, extended this to two spatial dimensions successfully replicating the 1d+1 results even though there were no a priori reasons to believe such an extension would be possible. The ECS framework allows the emergence of space-time from irreversible time dynamics, and simulations on 1d+1 ECS models have been shown to lead to emergence of time reversibility [1]. In ECS models new events are created through particle collisions with reversibility tied to emergence of dynamical limit cycles [4]. To ensure collisions in 2d+1 dimensions particles have been assigned a 2d finite cross-section measure. New collisions (events) are selected via a rule that seeks to extremize the distinctions between causal past sets of events. The extension to multi-dimensions which was the largest obstacle in the development of ECS for the past decade. I was able to use algorithmic information theory to solve the numerical challenges successfully replicating the 1d+1 classical results. In this Ph.D. project, I will first extend my ECS simulations to 3+1D, and carry out an extensive parameter-space investigation of both the 2+1D and 3+1D cases, statistically quantifying the transition to emergent time reversibility. The classical version will then be linked to the Hamiltonian formulation of time-asymmetric gravity, while a quantum completion will be studied using the two state vector formalism.