One of the nicest things about physics is that it has remained unchanging throughout all of time. Evolutionary biologists and astronomers alike have to spend their time painstakingly collecting data about the actual reality of the world, and to see into the past they have to find fossil evidence — whether the fossil is made of bone, or of light. However physicists have the luxury of being able to look into the past though the lens of mathematics. They can analyze the trends of today, then run those trends backward virtually as far as they like. Such simulations have helped predict everything from the distribution of stars to the likelihood of an earthquake.
Now that concept has been taken to its ultimate extreme with a simulation of the very beginnings of the universe. Such simulations have been made before, but they’ve focused either on the large scale with little detail, or on the small scale with plenty of shading. This one, called Illustris, uses a complex new program the international research team spent the past five years developing. It can not only track and render some 12 billion voxels, each with its own physical state, properties, and effects, but it can account for the formation and action of oddities like super-massive black holes.
The result is that Illustris can simulate and render something like an accurate history of the universe. It starts from about 500 million years after the Big Bang — before that, their backward extrapolations begin to lose legitimacy due to sheer proximity to the greatest singularity of all time (or perhaps before time, technically?) View a super-speed video of the simulation below.
This run of the simulation renders a box roughly 350 million light years to a side — big enough to say that we’re rendering out “the universe.” The 12-billion voxel resolution means they still can’t render the formation of individual stars, but it can look at the larger-scale changes in some detail. Huge masses of formless matter become smaller clumps, which begin to organize into super-clusters of small units that will soon become galaxies. It illustrates the sheer size of the universe, that this most detailed model has units the size of the Milky Way.
That might sound unimpressive, but it’s an enormous feat of computational effort. An average desktop PC would take a few thousand years to run a simulation of this complexity, modelling the gravitational impact of 12 billion objects, all in motion and affecting one another. The server farm they actually used had over 8,000 processors humming away steadily for several months.
Illustris takes things like matter, dark matter, and dark energy into account in its model. It is the first to successfully bridge this gap, and thus the first to be able to accurately run from starting conditions to the general universal layout we observe today. In the video below, you can watch the researchers switch between different rendering filters, showing how different constituents of our universe are disbursed. Dark matter and dark energy only interact with regular matter via gravity, so to ignore their impact (especially dark energy) is to have wildly incorrect predictions about the locations of super-clusters and super-voids of galaxies.
The simulation takes some very nuanced forces into account, from the “wind” given off by large numbers of newly forming stars, to the heat-transfer that happens when a black hole is born. The swirling impact of a super-massive black hole, thought to be at the center of most if not all galaxies, can be predicted through simple particle simulation — that’s pretty amazing.
The team wants to continue improving the model, of course. Increasing the sheer number of voxels will be priority number one, a process they’ve had great success with, thus far. Additionally, while their model did come out with a largely correct prediction of the modern universe, it was off in certain ways; for instance, the ages of stars in smaller galaxies are incorrect, and the real universe seems to delay their formation more than the model predicts, though we don’t know why this might be. It will take fundamental improvements to the model to fix these problems.
The next incarnation of Illustris will hopefully allow more extreme levels of zoom, well past the galactic scale; once you’re done watching the formation of galaxy-clouds, move in closer to watch the formation of the Milky Way and its subunits. That’s a long way off in terms of both physics and computing power, but this team is already work hard at improving both.