Simulations of the Universe are Getting Better and Better at Matching Reality

How can you possibly use simulations to reconstruct the history of the entire universe using only a small sample of galaxy observations? Through big data, that’s how.

Theoretically, we understand a lot of the physics of the history and evolution of the universe. We know that the universe used to be a lot smaller, denser, and hotter in the past. We know that its expansion is accelerating today. We know that the universe is made of very different things, including galaxies (which we can see) and dark matter (which we can’t).

We know that the largest structures in the universe have evolved slowly over time, starting as just small seeds and building up over billions of years through gravitational attraction.

Observationally, however, all we see are a bunch of galaxies.

Galaxy surveys provide the backbone of our understanding of cosmology. By studying the positions of galaxies in the universe, we can attempt to recreate the grand story of their evolution.

But linking observations to theory is a tricky thing. You have to have an understanding of all the physics involved, and how they play out over cosmic time, to go from galaxy surveys to a larger theory of the universe. And it gets even trickier because we haven’t even begun to map out all the galaxies in the cosmos – we just have access to a small sample of them.

Enter big data, and big simulations. Computer simulations enable us to bridge the gap between theories of what the universe is made of and how it evolves to the limited observations that we can make.

We’re getting better and better at it, especially using a technique called Bayesian sampling. To make this work, researchers take the galaxy survey data and start generating mock universes based on the theory they are examining. By generating a multitude of simulations, and applying some fancy statistical techniques, the researchers can find the theory that best describes the galaxy survey.

This then allows the researchers to reconstruct the entire history of the universe given the particular galaxy survey, enabling more in-depth studies of cosmological theories and stronger connections to real observations.