One of the challenges faced by astrophysicists is that you can’t repeat your experiments. If you observe a supernova explosion, you can’t put the star back together and watch it explode again. We can watch other stars explode, and from these combined observations we can gain a deeper understanding of just how stars explode, but a single star explodes only once. With cosmology, that poses a particular challenge because we only have one observable universe. Not only can’t we repeat the experiment, we only have one experiment to observe. What we can do, however, is simulate the universe and see how it compares to the real one.
Recently a team did just that, making the most extensive computational simulation of the universe thus far. The results were published in Nature, but you can see a summary of the simulation in the video.1 The team started with an initial state representing the universe only 12 million years old (before any stars or galaxies had formed) and 350 million light years wide. The then simulated cosmic evolution over 13 billion years. This included not only the effects of gravity, dark matter and dark energy, but also effects such as active galactic nuclei and the enrichment of elements.
The simulation produces a range of galaxy types consistent with our own universe, as well as a cosmic structure that matches our own. The simulation wasn’t perfect, and some discrepancies with our universe appeared, such as the formation of low mass galaxies earlier than is observed in our universe. Still, it is a clear demonstration that the ΛCDM cosmic model (that of a universe with matter, dark matter and dark energy) is an accurate model of our universe.
Vogelsberger, Mark, et al. “Properties of galaxies reproduced by a hydrodynamic simulation.” Nature 509.7499 (2014): 177-182. ↩︎