A duplicate universe, trapped in a computer
Consortium of scientists simulates 'cube of creation'
Tim Radford, science editor Thursday June 2, 2005 The Guardian
Scientists have recreated a vast segment of the universe inside a computer and written a brief history of time, black holes and galaxy formation.
The Millennium Simulation - the biggest exercise of its kind - required 25 million megabytes of memory. But it tracked the 14bn-year history of creation in months and now offers a tool to explore mysterious events in galaxies far away and long ago.
"It is the biggest thing we have ever done," said Carlos Frenk of the University of Durham. "It is probably the biggest thing ever in computational physics. For the first time we have a replica universe which looks just like the real one. So we can now for the first time begin to experiment with the universe.
"Unlike people who study human behaviour, who can study many humans, cosmologists have been stuck with only the one universe. Well, from today we have more than one."
The British, German, US and Canadian astrophysicists in the Virgo consortium, led by Volker Springel of the Max Planck Institute in Germany, report in Nature today that they already knew the so-called "initial conditions" of the universe.
These were imprinted in the cosmic microwave background radiation, the embers of the Big Bang, when the universe was only 400,000 years old.
In the last few years, they have been able to determine that all the stars, galaxies, black holes and their radiation add up to a trifling 5% of the universe. Around a quarter of creation is mysterious stuff called cold dark matter. The other 70% is now known to be the even more baffling "dark energy", a kind of antigravity that is pushing the universe apart.
Prof Frenk said: "We programmed the biggest computer in Europe with these ingredients and the laws of physics and we just let it compute a universe. We let it churn away - in fact we shut down all science in Germany, we excluded all German science for a month while this very large machine ground away - and at the end we got this beautiful universe, which for all intents and purposes looks like the real thing.
"We are now going to study it in detail. What we are going to do now is ask all the questions we wanted to ask about the real universe, but we have no way to tell.
"For example, we now understand that black holes are crucial in determining the properties of galaxies. In real universes, it is very difficult to ask any detailed questions, but in the simulation we can ask where do the black holes form? When? How big are they? What do they do to galaxies?"
The simulated universe represents a cube of creation with sides that measure 2bn light years. It is home to 20m galaxies, large and small. It has been designed to answer questions about the past, but it offers the tantalising opportunity to fast-forward in time to the slow death of the galaxies, billions of years from now.
But the first challenge was to understand the role of black holes in the formation of galaxies. At the heart of the Milky Way - the collection of 100bn stars that is home to the sun and the Earth - is a black hole with the mass of 100m suns. It occupies a tiny space, no bigger than the solar system.
"And yet, it's amazing that the existence of this little monster in the centre determines how big a galaxy can grow. It eats material and it spews out energy and it seems to control, essentially, the evolution of galaxies. We are now beginning to understand, through the simulation, the role that quasars and black holes play in galaxy formation," Prof Frenk said.
"We asked the question: when did the first black holes form? The answer is: they formed when the universe was only about 1m years old. We now know it is about 14bn years old.
"If we wanted to go and find the first black hole today, where should we look? We now know if we want to find the earliest black holes, we need to look into the very centres of collections of galaxies called galaxy clusters: they are the biggest beacons in the universe, these collections of thousands of very bright galaxies very tightly packed together."