Caption: This computer simulation illustrates the formation of the large-scale structure of the universe.

Features:

1. The structures in the simulation are all actually the dark matter gravitational wells in which the visible structures form.

2. The simulation just follows the evolution of clumps of dark matter---which are bright simulation particles in the animation.

3. Dark matter is made up of hypothetical exotic particles that interact very weakly with other matter and with each other, except by gravity.

   Dark matter makes up 84.5 % of all matter according to best modern measurements (see Wikipedia: Dark matter: Overview).

   Dark matter forms gravitational wells in which the ordinary matter clumps and forms visible structures form.

   The galaxies form in what are called dark halos.

   So there NO stars or galaxies in the simulation.

   But you can imagine where they are from the clumping of the bright simulation particles.

4. The visible structures (which are NOT not seen in the simulation) include dark halosgalaxy clusters, galaxy superclusters, galaxy filaments, galaxy walls, and voids.

5. Nowadays some people call this structure the cosmic web, but it seems more like the cosmic foam to yours truly.

6. The simulation illustrates gravitational collapses.

   Regions that are initially denser have runaway growth pulling in dark matter.

   Regions that initially less dense lose dark matter and become voids.

   In other words, "The rich get richer and the poor get poorer."

   And that's how the cosmic web forms.

7. The computer simulation is done in a box with sides of 43 Mpc (140 Mly) in (cosmological) comoving distance.

   This means that (cosmological) proper distance size (true physical size) of the box increases with cosmic time due to the expansion of the universe, but that growth is "divided" out of the animation.

   But it really happens in simulation.

8. The evolution of the simulation is from cosmological redshift z = 30 to z = 0 (which corresponds to the present in cosmic time).

9. The cosmic scale factor a(t) is related to z by the formula:

             a(t)/a_0 = 1/(1+z) , 
             

   where a_0 = a(t=present) = 1 by convention.

   Since z goes from 30 to 0, cosmic scale factor a(t) a(t) increases from 1/31 ≅ 0.032258 ... to 1 or by a factor of 31.

10. The caption with the simulation does NOT specify the underlying cosmological model used, but the simulation is supposed to be similar to an Illustris project simulation, but probably a lot simpler.

    Thus, the underlying cosmological model is probably the concordance model which is favored modern cosmological model.

11. Given that the underlying cosmological model is the concordance model, cosmic time increases in the simulation from ≤ ∼ 1 Gyr to the present.

    The age of the universe according to the concordance model is 13.8 Gyr, and so the simulation probably starts within 1 Gyr of the Big Bang.

    Probably, the simulation is met to represent structure formation starting from primordial density fluctuations.

12. The most advanced computer simulations (which are immensely complex are require very long runtimes on supercomputers) do a fairly good job of reproducing the observed large scale structure.

    This suggests that they are doing many things correctly.

    However, significant disagreements or tensions between simulations and observations exist.

    These might removed by improvements in the realism of the simulations.

    However, it may be that key ingredients are missing from the simulations or that the concordance model is not the correct cosmological model of the observable universe.

    Hopefully, the simulations will improve and give us more answers about the observable universe and the universe as whole which may be the multiverse.