It Took a Pair of Top Supercomputers Three Months to Simulate the Universe

That picture you see above is the result of two of the world's fastest supercomputers—separated by an international border and hundreds of miles—and the sum of human understanding of astrophysics working in concert for three consecutive months to produce the most complete and accurate simulation of the expansion of the universe ever.

The project, called Illustris, was undertaken by researchers from MIT and Harvard, and making it happen wasn’t easy. As Michael Boylan-Kolchin, an astrophysicist at the University of Maryland, wrote about the achievement yesterday, “It turns out that simulating the universe can be a difficult endeavor.”

To make it happen, the researchers took over Germany’s SuperMUC, the 10th fastest supercomputer in the world, and Curie, the 20th fastest supercomputer in the world, for three months straight. It took 8,000 processors running in parallel to complete the work, for a combined total of 16 million CPU hours. With just one of those processors, which are still faster than what you can pick up at Best Buy, it would have taken nearly 2,000 years to run the simulation.

That’s one of the reasons why the simulation, which took into account the initial conditions of the universe and all of the laws of physics we currently understand (such as the expansion of the universe, dynamics, and radiation), was only run from the time the universe was 12 million years old to the present day. So it simulated 13.8 billion years of everything, give or take a few million years and a few ideas about black hole formation that we still don’t completely understand.

The end result is a parallel universe to our own.

“What we simulate is not our real universe, we don’t have individual galaxies—you can’t pick out the Milky Way or Andromeda,” Shy Genel, a Harvard researcher who worked on the project, told me. “We simulate a representative of a statistically similar universe. A parallel universe. We see galaxies that are similar to the Milky Way, and by that, we can infer things about the formation story of our own Milky Way.”

As Boylan-Kolchin put it, "a mock observation of Illustris set to mimic the Hubble Ultra Deep Field, the deepest picture of the cosmos ever taken, can easily pass for the real thing when the two are viewed side by side.”

People first started doing rudimentary simulations of the universe in the 1970s, but, until recently, our understanding of astrophysics and our computing power simply wasn’t good enough to get anywhere close to seeing what we see with Genel’s Illustris simulation.

Of course, that’s assuming that the universe itself isn’t a simulation being run by supercomputers from the far future or a hologram, which are theories that have been proposed by very serious scientists. Here's what one of those early simulations looked like—published in 1980 by Russian researchers.

The previous best simulation was NASA’s Bolshoi simulation, run on the administration’s Pleiades supercomputer for 18 days (Pleiades is the 16th-fastest supercomputer in the world; at the time, it was the seventh fastest).

“Basically, this has only become possible in the last few years because of the ever increasing power of computers and because the models that have been incorporated have become more and more sophisticated,” Genel said. “This allows us, for the first time, to get galaxies that actually look like observed galaxies.”

Genel says that taking over the two supercomputers—which have long wait lists for researchers hoping to make climate change models, biological models, work on new nanotechnology, and medical developments—for a three month chunk was all they could have hoped for. The simulation could have been run far into the future, but astronomers already have a good idea what it’d look like, and we almost certainly won’t be around to see what happens to confirm if we’re right or not.

“You’ll see the accelerated expansion of the universe—individual galaxies will move very very quickly further apart and become completely isolated from each other at a speed faster than light,” he said. “Each would become completely isolated and would become its own universe. That’s the prediction.”