Analysis of COBE's microwave map of the entire sky has shows us that one side of the sky is "hot" and the other one "cold", according to the speaker. Earth is moving through the Cosmos at a pace of 600 km/s. In the Milky Way there is a lot of radiation from hot gas and dust. In this "cosmic fog bank" we are looking at the past at a distance of 40 billion light years when the Universe was only 400,000 years old.

Dr. White explained the audience what the initial conditions are for the formation of all structure. The Universe is flat. 400,000 years after the Big Bang it was nearly uniform and now it is approximately 0,2 billion years old. 70 percent of the Universe consists of dark energy, 26 percent of cold dark matter and only 4 percent of normal baryonic matter. In fact, all structure was imprinted in the first 10 to -30 seconds by quantum fluctuations of the vacuum.

Through gravitation lens effects, the dark matter in a cluster becomes visible, as was shown by Dr. White. He also explained how the evolution of the Universe can be followed on a supercomputer. To this purpose, the researchers are following the material in an expanding cube, starting 400,000 years after the Big Bang. The initial conditions are selected to match the microwave background in order to calculate forwards to the present day.

According to the speaker, it is thus possible to make a simulation of the entire visible Universe using different time parameters to show more or less details. Over the last three decades, such cosmological N-body simulations - in which N constitutes a function of time - have rapidly grown in size. This is due to the fact that according to Moore's law, computers double their speed every 18 months. In addition, N-body simulations also have doubled their size every 17 months although naÔve force calculation needs N2 operations. Recently, growth has accelerated even further. In this regard, Dr. White noted that the Millennium Run should have become possible in 2010 but that it finishes in 2004 already.

The computational challenges to perform very large cosmological simulations are enormous, according to the speaker. Researchers need to develop efficient algorithms to calculate self-consistent forces between a huge number of particles and over a large dynamic range. A conservative or simplectic time integration is needed. The calculations run across 16 x 32 Regatta processors on distributed memory machines to guarantee an efficient load balancing. The domain decomposition of the simulated volume has to be adaptable and for the researchers to estimate statistics on the fly, global data are required. 27 Tbyte of memory are needed for the output and storage of the results. The Global Virtual Observatory allows to remotely run on serial machines the post-processing pipelines which have to be globally accessible.

Dr. White told the audience that the Millennium simulation was run on the Regatta supercomputer located at the Garching Supercomputer Center. The simulation required 1 TByte of RAM, using 330,000 processor hours and took 27 days on 512 CPUs/16 nodes. In serial processing, it would have taken 38 years, which means that the Regatta system only needed about 6 percent of this annual time.

The speaker also showed the audience how telescopes function as time machines to provide us with glimpses of the past. Dr. White concluded his talk by saying that the 70 percent of dark matter is responsible for the acceleration of the Universe's expansion. All galaxies, galaxy clusters and larger structures, as well as the stars and planets formed from primordial gas through the effects of gravity. Supercomputers play an indispensible role to acquire this kind of knowledge. How otherwise should researchers be able to compare theory with reality?