You might think simulating the entire Universe is difficult, and it is, but not for the reasons you would think. The Physics is actually somewhat straightforward. We know the math behind star formation, Gravity, and fluid dynamics, and throwing in a few other effects is not too bad. The hard part is finding a computer powerful enough to do the calculations in a reasonable amount of time.
Think about it. Imagine having a universe of 100 Billion ‘particles’ used for a simulation. Each particle has a starting point, and that it pretty easy to do. But then for every single time step forward, whether it is 100 years or 100,000 years, you have to calculate the new position and state of each of your 100 Billion particles using the Physics you input.
Essentially more particles + more Physics concepts + smaller time steps = way way more computer time.
Scientists can come up with beautiful simulations that would allow them to study the Universe in incredible detail, but if it takes 10,000 years of computer time to run the simulation, then what’s the point?
The Millennium simulation, finished in 2005 and pictured above, used 10 Billion ‘particles,’ where each particle was representative of 1 Billion Solar Masses of Dark Matter. The simulation ran for a month on a German supercomputer and required 25 Terabytes of storage.
And then it was done again in 2010, with the Millenium XXL simulation using 12,000 CPU cores for an equivalent CPU time of 300 years. It also used 30 Terabytes of RAM and 100 Terabytes of storage.
So we can see that the simulations can use an incredible amount of resources. However, computing technology is still moving forward rapidly and its only a matter of time until the next mind blowing simulation is realized.
Well now we have reached the next step with an international team of Astronomers simulating the entire Universe of Galaxies over the ~14 Billion year history of the Cosmos. Their model has allowed them to simulate real Galaxies that match what we actually see in the Universe.
The Eagle (Evolution and Assembly of GaLaxies and their Environments) project is the answer to previous simulations that failed to accurately model real galaxies. The simulations would often produce galaxies that were too massive, small, old, and spherical. The Eagle simulation took several months to run on two European supercomputers, and has produced beautiful accurate galaxies the way we see them in the real Universe.
The difference is that the Eagle simulation implemented strong galactic winds, fuelled by Stars, Supernovae, and Black Holes. These winds blow away the gas supply that galaxies need for star formation, causing stars to form later and less often, resulting in younger, less-massive galaxies.
This simulation will allow Astronomers to study the fine details of how Galaxies have formed over the entire history of the Universe, and even how they could evolve in the future.