The universe is a very big place. It iscrowded with billions of galaxies, an uncountable numbers of stars anda mysterious force called dark energy that is making it even bigger. Inthe last ten years, thanks to amazing images sent back by the HubbleSpace Telescope, scientists have come up with a plausible explanationof how the universe began, starting with the Big Bang 13.7 millionyears ago and expanding into the stunning cosmos that exists today. Butwe are still far from fully understanding our universe and scientistsare always looking for new tools to help them fill in the picture. Onesuch tool is a model of the universe - inside a computer - recentlycreated by scientists at the University of Durham in the U.K. Calledthe Millennium Simulation, it has been described as 'thelargest and most realistic simulation ever of the growth of cosmicstructure' and may help scientists unlock some of the elusive secretsof our universe.How was the universe formed? Inthe first few million years after the Big Bang, the universe was adark, cold place full of swirling clouds of hydrogen and helium. Butover billions of years, these gas clouds formed enormous galaxies madeup of billions of stars. From these stars came all the scores ofelements that our planet is made from - and which are also the buildingblocks of life. But how was all this complexity created? Atthe University of Durham, physicist Carlos Frenk is testing out someimportant ideas about why the universe evolved the way it did. He is amember of the international team of scientists and programmers whocreated the Millennium Simulation. In particular, Frenk was interestedin testing the role played by dark matter: a mysterious substance madefrom tiny particles that don't emit light that may make up 70% of theuniverse. Ordinarymatter, says Frenk, is made of atoms, particles that we're familiarwith on Earth, protons, electrons, neutrons... dark matter,although we don't yet know exactly what it is, we have every reason tobelieve it's a kind of elementary particle which is in essencedifferent from ordinary matter.
And that's why it doesn't shine,because it doesn't interact. It doesn't make atoms, it doesn't producelight. Photo courtesy of Carlos Frenk From the Millennium Simulation, the top image shows the galaxy distribution for a rich cluster of galaxies whereas the bottom one shows the corresponding dark matter distributions. It'slong been understood that if there was no dark matter exerting apowerful gravitational attraction, galaxies would simply fly apart likedisintegrating wheels. But did this mysterious stuff have an even moreimportant role to play in the evolution of the universe. Was it theinvisible sculptor at work? Frenkset himself a challenge. Could he programme the computers with the lawsof physics, 10 billion particles of matter, plus a very big dollop ofdark matter and get something that looked like the universe? After all,it's not possible - yet - to speed into the universe itself and set upa laboratory. The results of the experiment were a stunning success:perhaps best illustrated by the two galaxies shown here. One is 'real'- the other was made by the computer. It powerfully suggests that themodel we have of how the universe evolved is right.