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

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.

Re:Speed of Gravitational attraction ?

[tmortn]

I am not real sure about gravity personally. Have seen pretty convincing arguments on both sides of the coin. Until we can detect and produce gravity waves its pretty open to question I think. In this case though the point is that we don't know and it is an integral piece of knowledge to accurately simulate the interactions of 10 billion mass points over time and significant distances.

On the other I know about the increased accuracy from higher fidelity time samples but all that does is postpone the inevitable chaos in the equations. Most solar system models don't even use keplers equations. They use the information determined from solving them via a 2 body problem ( planet and the sun ) and then assume that orbital period is more or less sacrosacnt. This creates a stable model which accurately represents what we have observed... but does not allow for the chaos that creeps in when we try to replicate observed motions using Keplers laws to atempt to model all interactions. If your really interested (or already know alot about it) a fascinating subject based in reality is orbital mechanics... ie how do you accurately rendesvous with other planets when you are traveling in an N body problem where N is greater than 3 over periods of time that are too great to be able to avoid the chaos ? The simple answer is you make small corrective burns along the way based on observation to recalibrate the route. But the significance there is that you can't use Keplers equations for more than a rough estimation for navigating in space at N > 2 ( like landing the martian rovers ).

Keplers laws work almost flawlessly for 2 bodies which is why they are so powerful. However I think that is the problem. They work flawlessly for N=2 even when there is no real world true N=2 problem to solve. Essentially to solve the N = 2 problem for any planet you assume the attraction from anything other than the sun is insignificant. This works amazingly well and is what led to the discovery of the last two or three planets if memory serves.

But as accurate as that is there is no getting around the chaos of the 3 body equation no matter how fine grained your time samples are. This is not true of the 2 body problem.. IE it dosn't matter what your time sample is, the 2 body problem works. If it dosn't its because there is another source of significant gravitational attraction at work. However over a great enough time span my guess is even the 2 body equation has inherent chaos in reality.. IE a pure theoretical 2 body equation is perfect, but for the earth and the sun sooner or later what is deemed insignificant in the 2 body problem for practical purposes will become significant over a long enough time frame.

All in all it reminds me of the old parallax problem that led the Greeks to dismiss a Heliocentric model of the solar system and choose Ptolemy's view of a an earth centered model. I think our frame of refference is such that the inherrent error in Keplers laws are not readily observable just the same as the greeks frame of refference was insufficient to observe parallax.