18 - Cosmological Simulations

What is a cosmological simulation?

A representation of the universe on a computer that begins at a very early cosmic epoch and tracks the matter distribution over time, and outputs maps of the matter distribution over time

What is the universe in a box simulation?

Cube chunk of the universe, with mass represented by massive number of particles each representing a small piece of total mass and simulating the gravitational interactions between them.

Why do simulations soften gravity?

To avoid R tending to 0 and the force tending to infinity

How do simulations soften gravity?

Choose a softening length epsilon to limit the gravitational force at small distances.

What is often a single timestep in cosmological simulations?

millions of years

What would we do at the edge of the box?

Assume periodic boundaries with particles moving between boxes

How do you quantify predictions for growth given by simulations?

Correlation functions, redshift space distortions, weak lensing

What are square patchs of the sky observed by telescopes called?

Light cones

What is the idea that you run a large number of simulations and see which comes closest to the data?

SBI (Simulation-based inference)

Pro simulation argument

We experience limits, such as fundamental limits in discreteness of time given by planck time, and we cannot see beyond observable universe. We have parameters like the hubble constant and gravity.

Con simulation argument

Just because we don’t understand limits doesn’t mean there isn’t a physical explanation. Complexity increases as we descent further into the cosmos, contrary to a simulation.