A massive simulation of the universe is digitally recreating the lives of stars, black holes and galaxies.
Richard Bower at Durham University in the UK and his colleagues have created a computer simulation approximately 1 billion light years across, which models tens of thousands of galaxies.
The team started the simulation on Tuesday and it will run continuously for 50 days across 30,000 computer processors developed by tech firm Intel in both Durham and Paris. It is 30 times larger than a previous simulation the team ran in 2015, which led to predictions about the .
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The simulation includes the physics of both baryonic matter 鈥� all the 鈥渘ormal鈥� matter such as the atoms and molecules that make up humans and Earth 鈥� and the mysterious dark matter that makes up around 85 per cent of the universe, but which we haven鈥檛 yet been able to directly observe. It also includes the physics of star and black hole formation, as well as the conditions of the universe at the time it began.
鈥淲e set the initial conditions, represented by hundreds of billions of particles in play, and then we let the universe go,鈥� says Bower.
The simulation studies galaxies by breaking them up into blocks of about 3000 light years. One of the team鈥檚 objectives is to try to understand rare objects in the universe, such as very distant galaxies that are invisible to telescopes that gather and focus visible light.
By simulating what the universe looked like at different points in time 鈥� at half or a quarter of its present age, for example 鈥� the researchers can test theories about how galaxies are related to the growth of black holes, and what happens when they die.
Simulating individual galaxies at the right level of detail is a challenge. 鈥淚f you try to do a calculation where you have less detail in the galaxy, then you really can鈥檛 understand the rate at which stars are going to form,鈥� says Bower.
Another difficulty in simulating the internal structure of galaxies, which contain gas, dust and billions of stars, is that there are huge uncertainties about their underlying physics.
鈥淭he physics is so complicated that any small mistake could lead to a very wrong prediction,鈥� says Romain Teyssier at the University of Zurich in Switzerland, who wasn鈥檛 involved in the study. He was one of the researchers behind a that contained 25 billion galaxies, focusing solely on the physics of dark matter.
The paradox is that although we don鈥檛 know what dark matter is, its physics is simple to model. That is because it doesn鈥檛 interact with anything or itself except through gravity, which is why we don鈥檛 see it emitting light or other radiation.
In contrast, we don鈥檛 know very accurately how stars form, or how much energy is released when a supernova goes off, says Bower.
To check the accuracy of the virtual universe, the team will compare simulated features to the observed universe to check for discrepancies. Teyssier says this is like weather forecasting, in which actual weather observations are used to refine predictions.
In future, the team plans to simulate galaxies in around 100 times more detail than the model can handle currently, and also further increase the scale of the simulation.
