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We're not saying we're living in a simulation but someone's simulated the universe in a computer

Scientists fork reality, sorta

A team of researchers has created the largest virtual model of our universe, complete with billions of galaxies, to probe the effects of dark energy and dark matter.

The ambitious project took about three years to complete. A group of astrophysicists from the University of Zurich (UZH) developed their code, PKDGRAV3, to generate a whopping two trillion particles to form 25 billion galaxies.

To create a simulated world this big requires a beefy supercomputer. Piz Daint, at Centro Svizzero di Calcolo Scientifico, Switzerland's national supercomputing center, used over 4,000 Nvidia Tesla P100 16GB GPUs running for about 80 hours.

The results were published in the Computational Astrophysics and Cosmology journal last month.

Modelling gravity on such large scales is tricky, since its behavior isn't constant and is non-linear. N-body simulations – using two trillion particles – are used instead to simulate dark matter as a fluid.

Each body represents a large jumble of microscopic dark matter particles evolving under the effect of the mutual gravitational attraction between the particles. Just like in our own universe, the virtual one also sees the dark matter forming clumps of dark matter halos, which are key drivers to galaxy formation.

The digital galaxies aren't as big as real ones – about a tenth of the size of the Milky Way – and sit in a space as large as the observable universe.

The goal is to use this model to aid the European Space Agency's Euclid mission in exploring why the universe's rate of expansion is accelerating. It'll be used to calibrate the experiments onboard the Euclid satellite expected to be launched in 2020.

The universe is made up of about 23 per cent dark matter and 72 per cent dark energy – it's mind boggling that 95 per cent of the cosmos remains invisible and unknown.

"The nature of dark energy remains one of the main unsolved puzzles in modern science," Romain Teyssier, co-author of a paper and professor for computational astrophysics at UZH, said on Friday.

It's a puzzle that can only be solved through indirect observation. As the Euclid satellite captures the light from billions of galaxies, astronomers will be able measure the distortions of the background light to detect the distribution of dark matter.

"Euclid will perform a tomographic map of our Universe, tracing back in time more than 10 billion years of evolution in the cosmos," Joachim Stadel, co-author of the paper and researcher at the Center for Theoretical Astrophysics and Cosmology at UZH, said. It might even help physicists discover a modified version of general relativity or a new type of particle. ®

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