The Millennium Run is the name of a simulation created to investigate how the Universe evolved over time, and is used by scientists working in physical cosmology to compare observations with theoretical predictions.
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Overview
A basic scientific tool to test theories in cosmology is to evaluate their consequences for the observable parts of the Universe. This includes, among other things, the distribution of matter (galaxies and intergalactic gas) as it is seen, now. Since looking further into the distance also means looking back in time, a meaningful test of the evolution of that distribution over time is possible. The Millennium Run simulation starts with the initial state of the Universe, where the Cosmic background radiation was created. Its properties are well known by satellite experiments and serve as the starting point for the corresponding matter distribution. Using the physical laws of the currently known cosmologies, the evolution of matter as galaxies and black holes is simulated and recorded. This simulation was created and executed for the first time in 2005 by the Virgo consortium, an international group of astrophysicists from Germany, the UK, Canada, Japan and the USA.
Size of the simulation
For the first scientific results, published on June 2, 2005, the Millennium Run traced more than 10 billion "particles". The region of space simulated was a cube with about 2 billion light years as its length. This volume was populated by about 20 million "galaxies". A super computer, located in Garching, Germany, was executing the simulation code for more than a month. The output of the simulation needed about 25 Terabytes for storage.
First results
The Sloan Digital Sky Survey had challenged the current understanding of cosmology by finding black hole candidates in very bright quasars at large distances. This meant that they were created much earlier than initially expected. The Millennium Run demonstrated that these objects can indeed be explained, and do not contradict our models of the evolution of the Universe.
Other large scale universe simulations
The 2007 Horizon simulation project features the largest N body simulation ever performed: 70 billions particles were evolved.
For the first time, we have performed a simulation of half the observable universe, with enough resolution to describe a Milky Way-like galaxy with more than 100 dark matter particles.
