Simulating the Whole Universe

Roland Piquepaille writes "An international group of cosmologists, the Virgo Consortium, has realized the first simulation of the entire universe, starting 380,000 years after the Big Bang and going up to now. In 'Computing the Cosmos,' IEEE Spectrum writes that the scientists used a 4.2 teraflops system at the Max Planck Society's Computing Center in Garching, Germany, to do the computations. The whole universe was simulated by ten billion particles, each having a mass a billion times that of our sun. As it was necessary to compute the gravitational interactions between each of the ten billion mass points and all the others, a task that needed 60,000 years, the computer scientists devised a couple of tricks to reduce the amount of computations. And in June 2004, the first simulation of our universe was completed. The resulting data, which represents about 20 terabytes, will be available to everyone in the months to come, at least to people with a high-bandwidth connection. Read more here about the computing aspects of the simulation, but if you're interested by cosmology, the long original article is a must-read."

Comments

Dr. Mike Johnson claims dibs on God

[Anonymous Coward]

"I always wanted to be God." said Dr. Johnson. "When they announced this project, the first words out of my mouth were 'Dibs on God!' I even have plans to introduce a son in a few billion simulated years. This is going to be exciting."

From the library reference desk

[Anonymous Coward]

Do you have a 1:1 scale map of the world I can use?

Uh yes, but it's being used right now.

Re:Obligatory question

[maxwell demon]

Does the simulation include simulated scientists simulating the universe?

From the summary:
The whole universe was simulated by ten billion particles, each having a mass a billion times that of our sun.
I somehow doubt that there are scientists which have such a large mass.

Re:Obligatory question

[Gyan]

I somehow doubt that there are scientists which have such a large mass.

How much can hot air weigh?

RTFA (Re:Umm, Paradox?)

[kirkjobsluder]

How can you accurately simulate the computer that is simulating the entire universe?

The same way you simulate anything else. You simplify the problem down to a manageable number of particles that represent larger units of whatever you are simulating. Since in looks like they are interested in mass and gravity at the galactic supercluster scale, they can use particles that weigh much more than any individual star.

So the fundamental challenge for the Virgo team is to approximate that reality in a way that is both feasible to compute and fine-grained enough to yield useful insights. The Virgo astrophysicists have tackled it by coming up with a representation of that epoch's distribution of matter using 10 billion mass points, many more than any other simulation has ever attempted to use.

THESE DIMENSIONLESS POINTS have no real physical meaning; they are just simulation elements, a way of modeling the universe's matter content. Each point is made up of normal and dark matter in proportion to the best current estimates, having a mass a billion times that of our sun, or 2000 trillion trillion trillion (239) kilograms. (The 10 billion particles together account for only 0.003 percent of the observable universe's total mass, but since the universe is homogeneous on the largest scales, the model is more than enough to be representative of the full extent of the cosmos.)

Tree / Multipole expansion

[Anonymous Coward]

The article indicates that the "tricks" these researchers used were the octree and multipole expansion--both of which have been used in gravity and potential theory for many years. They reduce the N^2 interaction problem to N or N Log(N), depending upon implementation. The story makes it sound like these researchers invented the technique; I assume the writer misunderstood the scientists, because it certainly predates them.

define "significantly"

[mangu]

what kind of useful calculations can you make when you vary that significantly from your target system.

To you and all the other (-1, Redundant) posts on how the system can't simulate every single detail in the Universe: it's a *simulation*, not the real thing, OK?

The first thing you need to do when you plan a simulation is to determine exactly what's significant or not. In this case, they decided that a set of particles with a billion times the mass of our sun would be appropriate. That's because what they are studying is mostly the long range effects of gravitation, where "long range" is defined as a sphere that contains a mass of ten billion suns.

When and if someone wants to study the workings of the Universe at a smaller scale than that, then they will have to simulate at a smaller scale. Phew, people are so dense! Next thing they will say that because a photograph didn't capture every single hair in a person's head or every single pore in their skin, that photo doesn't represent that person at all...

Re:Kind of useless?

[mangu]

I think they would've done a much better job with 1 million particles of possibly different types, simulating several other forces.

No. Of the four known forces in the universe, only gravity is important in the long range, which defines the overall structure of the universe.

The other three forces are electrical, and two nuclear forces. The nuclear ones are *very* short range, acting only in the atom nucleus. The electrical force is long range, but because there are two different electrical charges, which balance out, there isn't any perceptible electrical attraction in the long range.

At this resolution

[crisco]

that works out to 100 to 200 data points to represent our galaxy. I wonder if they will get recognizeable spiral structures, etc?

Are they modeling any of the physical (star formation, etc) interactions of matter or just the gravitational interaction. It seemed like the latter, but the article did mention the apparent non-interaction of dark matter.