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Last Updated: Wednesday, 1 June, 2005, 18:44 GMT 19:44 UK
Biggest ever cosmos simulation
Quasar candidate, Virgo Consortium

Astronomers have used supercomputers to re-create how the Universe evolved into the shape it is today.

The simulation by an international team is the biggest ever attempted and shows how structures in the Universe changed and grew over billions of years.

The Millennium Run, as it is dubbed, could help explain observations made by astronomers and shed more light on the Universe's elusive dark energy field.

Details of the study appear in the latest issue of Nature magazine.

What's unique about the simulation is its scope and the level of detail
Prof Carlos Frenk, University of Durham
"We have learned more about the Universe in the last 10 or 20 years than in the whole of human civilisation," said Carlos Frenk, Ogden professor of fundamental physics at the University of Durham, UK, and co-author on the Nature report.

"We are now able, using the biggest, fastest supercomputers in the world, to recreate the whole of cosmic history," he told the BBC News.

The international team of scientists known as the Virgo Consortium looked at how the Universe evolved under the influence of the mysterious material called dark matter.

Dark matter model

According to cosmological theory, soon after the Big Bang, cold dark matter formed the first large structures in the Universe, which then collapsed under their own weight to form vast halos.

The gravitational pull of these halos sucked in normal matter, providing a focus for the formation of galaxies.

Supercomputer, BBC/Wildcat Films
Powerful supercomputers were enlisted to create the simulation
The simulation tracked some 10 billion dark matter particles over roughly 13 billion years of cosmic evolution. It incorporated data from satellite observations of the heat left over from the Big Bang, information on the make-up of the Universe and current understanding of the laws of physics on Earth.

"What's unique about the simulation is its scope and the level of detail with which we can re-create the cosmic structures we see around us," Professor Frenk commented.

English Astronomer Royal, Professor Sir Martin Rees, told the BBC: "Now we have the Millennium Run simulations, we have the predictions of the theory in enough detail that we can see if there is a meshing together of how the world looks on the larger scale and the way we expect it should look according to our theories. It's a way to check our theories."

Energy problem

Comparisons between the results of the simulation and astronomical observations are already helping shed light on some unsolved cosmic mysteries.

Some astronomers have previously questioned how radio sources in distant galaxies called quasars could have formed so quickly after the Big Bang under the cold dark matter model.

The Millennium Run simulation demonstrates that such structures form naturally under the model in numbers consistent with data from the Sloan Digital Sky Survey, a robotic telescope project that is mapping the sky in three dimensions.

The virtual universe may also shed light on the nature of dark energy, which makes up about 73% of the known Universe, and which, Frenk says, is the "number one unsolved problem in physics today - if not science itself".

"Our simulations tell us where to go looking for clues to learn about dark energy. If we want to learn about this we need to look at galaxy clusters, which encode information about the identity of dark energy," Professor Frenk explained.

Dark energy is believed to emerge from the vacuum of empty space. It acts as an anti-gravity force that is driving galaxies apart from one another at an accelerating rate.

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