Building the Universe Inside a Supercomputer
As my grandfather once told me, to truly understand how something works, “you need to build it yourself.” And he knew what he was talking about. As a skilled toolmaker for all his working life he actually built the tools used to build things like jet engines to automated factory machinery.
So, as I read Monday’s article about South Korean physicists building a program on one of the world’s most powerful computers to simulate the evolution of our Universe, although he wasn’t an astrophysicist himself, I knew my grandfather would instantly understand what they were hoping to achieve.
In an arXiv preprint publication submitted on Dec. 8, Juhan Kim and colleagues from the Korea Institute for Advanced Study in Seoul have completed the largest simulation of the universe ever attempted.
The simulation calculates the evolution of 374 billion cold dark matter particles in a box some 10 gigaparsecs across — this represents approximately two thirds the size of the observable Universe. This virtual universe is 8,800 times larger than the previous record holder.
These are staggering numbers and the calculations required a stupidly fast supercomputer — called Tachyon II — to process them. Tachyon II is currently the 26th fastest supercomputer in the world.
Despite the huge processing power available to it, the simulation, called “Horizon Run 3,” still took 20 days to run.
By building this cosmologically vast virtual universe, and letting it evolve using the theoretical constraints from our own Universe, Kim and his team have created some of the largest scale structures thought to form to a high degree of accuracy.
Much of the analysis still needs to be done, but already the researchers have recreated some eerily similar dark matter structures observed in our Cosmos, such as the “cosmic web” pattern of cold dark matter:
In this tiny cutout of the simulation (above), it can be seen that the simulated particles have arranged themselves in a web-like pattern, connected through filaments, separated by voids.
“Halos” of dark matter form, creating the filaments in this large-scale structure, pulling in normal (baryonic) matter to form the galaxies we see throughout the Universe today. Dark matter halos cannot be directly observed, but their presence can be inferred by their gravitational effects on the stars and interstellar dust within galaxies.
In addition to this, theoretical acoustic baryon oscillations could be glimpsed for the first time. As explained by KFC on the arXiv blog, “these are essentially the leftovers of waves in the plasma that existed in the very early universe which became frozen in place as they cooled.”
Up until now, the large scale structure of cold dark matter and acoustic baryon oscillations have been tough to simulate as the powerful supercomputers required to run the simulations have not been available.
But now, as Kim’s team is proving, the powerful number-crunching tools are becoming a reality, and they are starting to reveal some answers to the large-scale mysteries of how our Universe evolved.
For more on Horizon Run 3, see the project website, where further images and movies of the simulation will be posted.
Image (top): Our virtual universe — with the Earth in the middle. The further away from the center you move, the further you look back in time, and the higher the red-shift (Kim et al., 2011)