Structure of the Universe 12 bya

Now the structure of the Universe began to evolve quite rapidly. About 2 billion years after the creation, the force of gravity made the dark matter fragment into a network of filaments forming walls around large empty spaces.

We see that structure beginning to form in the following computer simulation.

Simulation of Universe 2 billion years after creation. Click for image credit.

In the diagram each dot represents one galaxy. For the next 12 billion years, the gas in the Universe was pulled into these galaxies, leaving almost empty space between them.