When we observe the universe around us, beyond our own galaxy - the Milky Way - we see that it is filled with billions of other galaxies.
These galaxies are very diverse: some are up to thousands of times larger than our own. Others are much smaller. They are spherical and spiral, and of multiple colours, depending on the ages of the stars that make them up.
These galaxies are not randomly distributed in the cosmos, but are part of a great "cosmic web", in which there are vast regions of space that are almost empty and others where galaxies are concentrated.
Why is the universe the way it is and not some other way? Computational cosmology creates universes on computers to try to understand the universe around us: its origin and future, and also the laws of nature that govern it.
The galaxies we observe are only a small fraction of the matter in the universe. Most of it is invisible and we call it "dark matter".
While we can't observe it directly, we do measure the effect of its gravity on galaxies, stars, and the light around them.
We are now flying at more than 100 million light years per second through dark matter in a simulated universe.
This virtual universe was created on one of the world's largest supercomputers and required the equivalent of 30 years of calculations on a normal desktop computer.
These simulations show us that galaxies form and develop in areas where dark matter is densest, and that their characteristics also depend on the dark matter surrounding them.
In simulated universes, we can predict the current state of the universe and also observe virtually what its origins were like.
Shortly after the Big Bang, dark matter was more or less homogeneously distributed in the universe.
However, over hundreds of millions of years, small dark matter structures were attracted to each other by the force of gravity. Thus, dark matter became concentrated in denser and denser areas where the first galaxies began to form.
As time went on, these dark matter structures merged with each other, growing steadily and eventually becoming home to thousands of galaxies.
But what is dark matter? We don't know yet, but cosmological simulations help us test different theories.
In a simulation we can change the law of gravity, or the type of dark matter, and visualise how this would affect the distribution of galaxies in the universe.
For example, at the top of the video we see a scenario where the dark matter corresponds to a very heavy type of particle. At the bottom, another scenario where the dark matter is very light. With these predictions in hand, we can compare the virtual universe with observations of the real universe and determine which alternative is correct.
By combining observations and supercomputers, we try to decipher the nature of the universe, its origin and evolution, and ultimately understand our place in the cosmos a little better.