Simulating the Whole Universe 326
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."
Obligatory question (Score:4, Funny)
Re:Obligatory question (Score:4, Funny)
Re:Obligatory question (Score:5, Funny)
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 (Score:5, Funny)
I somehow doubt that there are scientists which have such a large mass.
How much can hot air weigh?
Re:Obligatory question (Score:2, Funny)
Quite a lot, if you get the thermal kinetic energy up into the relativistic territory... once you stop thinking in kelvin and start using teraelectronvolts, you're getting warmer.
Re:Obligatory question (Score:2)
Re:Obligatory question (Score:2)
...now, if we were talking about the weight of egos...
Re:Obligatory question (Score:2, Insightful)
Stack overflow (Score:3, Funny)
Are you living in a computer simulation? (Score:3, Informative)
This paper argues that at least one of the following propositions is true: (1) the human species is very likely to go extinct before reaching a "posthuman" stage; (2) any posthuman civilization is extremely unlikely to run a significant number of simulations of their evolutionary history (or variations thereof); (3) we are almost certainly living in a computer simulation. It follows that the belief that there is a significant chance that we will one day become posthuman
Re:Obligatory question (Score:2)
Damn, now we have to send someone to check.
Dr. Mike Johnson claims dibs on God (Score:5, Funny)
Great, so maybe. . . (Score:3, Funny)
I can search it to find out where I left my cell phone last night.
Re:Great, so maybe. . . (Score:2)
Have you tried calling it to see who answers? I've recovered mine three times that way (over the years, not in the last week!)
--
GMail invites for iPod referrals [slashdot.org]
Re:Great, so maybe. . . (Score:2)
The idea of a simulation is useful for insight into possibilities but not for specifics. We can focus the simulation into a personal world where initial conditions are meticulously gathered. This can only go so far since outside influences cannot be fully observed or predicted. Even the imposition of boundaries will skew re
bittorrent (Score:2, Funny)
Why bother? (Score:5, Funny)
Re:Why bother? (Score:3, Funny)
Re:Why bother? (Score:2)
get your 42 here! fresh 42! (Score:2, Funny)
I know eBay ads come up often, but I just find the fact that ebay bought ads for "42" (and apparently other numbers) just astounding. Do they really think a lot of people want to buy numbers on eBay? I, for one, buy my numbers down on the corner fr
Re:Why bother? (Score:2, Funny)
From the library reference desk (Score:5, Funny)
Uh yes, but it's being used right now.
LMAO (Score:2)
Oh, and the ObStevenWright: You can't have (simulate?) everything. Where would you put it?
--
GMail invites for iPod referrals [slashdot.org]
Great (Score:2, Funny)
Wait wait wait (Score:2)
The last time I checked, we didn't know a whole lot about the nature of the universe as it stands... how the hell are these guys claiming that they
a) Know how it was at the start
and
b) can compare it to whats out there already when its done?
Re:Wait wait wait (Score:3, Funny)
Re:Wait wait wait (Score:2)
Hahahah, ah my sides... okay oh great sage and eminent scholar, what shape is the universe? Fairly simple question you might think. I mean, geometrically, what shape is it? Is it spherical? Cone shaped? What was the latest one... oh yeah its shaped like a horn...
Do try to keep up with current findings, eh?
Re:Wait wait wait (Score:2)
Re:Wait wait wait (Score:2)
Re:Wait wait wait (Score:2, Informative)
a) They didn't start at the beginning; they started at 380K years--the "snapshot" of which has been developed by looking at cosmic background radiation.
b) Using telescopes, they've observed very large-scale structures in the universe (arrangements of clusters of galaxies), and they are hoping to see similar large-scale structures in their model.
Imagine? .-) (Score:3, Funny)
Re:Imagine? .-) (Score:2)
Douglas Adams !?! (Score:2)
Simulating the Universe to find answers and the number 4.2 can't be a coincidence, can it?
Hit it, chewie! (Score:2, Funny)
Umm, Paradox? (Score:2, Interesting)
Basically, you'd end up infinitely short on processing power. The faster you make the computer, the faster you need the computer to be. It's like working out so that you can get strong enough to pick yourself up by the bootstraps. The stronger you get, the more you weigh and you make the impossible less possible.
LK
RTFA (Re:Umm, Paradox?) (Score:5, Insightful)
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.
Re:RTFA (Re:Umm, Paradox?) (Score:2)
Re:RTFA (Re:Umm, Paradox?) (Score:2)
> The basic cosmological assumption that the universe is homogenous
> has been falsified by observation.
true! everywhere it is differentiated at every level of detail.
j.
Re:Umm, Paradox? (Score:2)
Why? Read Raymond Chandler (Score:2)
("Playback", 1958)
Re:Umm, Paradox? (Score:2)
How can you draw an accurate world map? It wouldn't fit on the planet?!
The (obvious) answer is: Abstraction, my friend.
obligatory Spaceballs quote (Score:2)
Col. Sandurz: Now! You're looking at "now," sir. Everything that happens now is happening "now."
Dark Helmet: What happened to "then?"
Col. Sandurz: We passed it.
Dark Helmet: When?
Col. Sandurz: Just now. We're at now "now."
Dark Helmet: Go back to "then."
Col. Sandurz: When?
Dark Helmet: Now.
Col. Sandurz: Now?!
Dark Helmet: Now!
Col. Sandurz: I can't.
Dark Helmet: Why?
Col. Sandurz: We missed it.
Dark Helmet: When?
Col. San
Re:Umm, Paradox? (Score:2)
Pick yourself up by the bootstraps? (Score:2)
Anyone who can do chin-ups can lift their own weight..
There are other physical reasons why you cant lift yourself by the bootstraps, including the fact that you really have to push the earth downwards somehow.
Beside that, your points taken.
Re:Umm, Paradox? (Score:2)
You know, that may have been a flippant, tongue-in-cheek comment, but mix in some beer(or other "interesting" substance) and some college buddies, and you have one hell of an interesting Friday night discussion.
But did they try... (Score:2)
Did they get a giant sign million light years across floating in space, saying:
Simulating universe in a simulated universe is not going to work.
You just have to try it, didn't you?
So, (Score:2)
heh. (Score:2)
I wonder if our universe is just a simulation sometimes...
Admit it... (Score:2, Funny)
Oh...
just me...
Let's look upward instead (Score:2, Funny)
Now, where can I find the scientists working on a reality-hacking machine?
One of the tricks (Score:3, Funny)
And in other news... (Score:5, Funny)
Re:Damned if you do, damned if you don't. (Score:2)
According to this article [www.cbc.ca], Black holes produce the lowest note in the universe, at 57 octaves below middle C. It will be interesting to see what the movie of this simulation looks like.
Tree / Multipole expansion (Score:5, Informative)
Re:Tree / Multipole expansion (Score:2)
Research in Virginal Territory? (Score:2, Funny)
Apparently, this will be the physics engine... (Score:2, Funny)
threads? (Score:2)
Oh Joy! Another Roland Piquepaille post! (Score:4, Insightful)
BTW, the machine in question, the Max-Planck-Gesellschaft MPI/IPP, is currently ranked 66th [top500.org]. It looks to be a fairly ordinary cluster with none of the exoticism that Cray says we so desperately need [slashdot.org]
You are Here -- (Score:3, Funny)
MOND (Score:2, Interesting)
At this resolution (Score:5, Interesting)
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:At this resolution (Score:4, Informative)
Without hydro or cooling, all you get are ellipsoidal dark matter halos, no disks.
[TMB]
Re:At this resolution (Score:2)
Re:At this resolution (Score:2)
Speed of Gravitational attraction ? (Score:3, Interesting)
As these mass points get further and further apart this would have a huge effect on the results. Unless of course Gravity is instentaneous across any distance opening the door to some interesting possibilities. Namely the ability to communicate across large distances without delay. Perhaps even FTL travel.
While I find this excercise interesting I also find it a tad ridiculose. So many simplifications have to be made to even attempt it and the whole thing is based on some assumptions that are not necesarrily cold hard fact... such as the mass of the universe. Theory says one thing, observation says another. Dark matter was invented to close the gap. Don't get me wrong, there are a lot of smart people that have come up with an awful lot of observation which seems to confirm its existence, but it could be that our point of veiw is insufficient. After all by all observations the Ptolemaic model of the movement of the heavens was accurate and it had all sorts of added rules for handling what was observed.
Also there is the issue of the N body problem where N is greater than 2. Did you know we cannot accurately model our solar system just using keplers laws ? We have to create stabilising factors in the system to keep the planets paths from becoming unstable in their orbits. And yet here they are attempting to simulate an N body problem where N = 10 billion.
http://www.lactamme.polytechnique.fr/Mosaic/image
That link shows what happens with a pure Keplerian system of equations for 9 bodies.
Thus introducing such things as mass simplification for objects farther away ( creating groupings etc ) and the tree approach for close objects all creates an introduction of error into the equation. Further more they have to use some means of stabilizing the equations similar to solar system models which is a value based on observation but with no understanding for what really controls it ( if they don't do this then the system of equations can't model our own solar system much less 10 billion mass points expanding since 380k years after the big bang ). This is all chance for more error to creep into the equation. Then with all of this they run a simulation for a simplified mass points using simplified interactions with an unkown stabilizing force over the course of billions of years and then expect people to believe that what they wind up with has any significant correlation to reality.
Do not be decieved by impressive things like 4 teraflops and 20 terabytes of information. To me this seems an interesting intellectual excercise, but the chances of the results being meaningful are pretty slim.
Re:Speed of Gravitational attraction ? (Score:2, Interesting)
Re:Speed of Gravitational attraction ? (Score:5, Interesting)
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.
Re:Speed of Gravitational attraction ? (Score:2)
Experiment for detecting the speed of gravity (Score:2)
If you were to do something like that and take into account the change in distance from the sun and tidal effects, you could compare the force data to the observed relative position of the sun, find the amount of delay, and then calculate the
Re:Speed of Gravitational attraction ? (Score:2)
Actually, it doesn't work that way... we really don't care where each individual particle ends up, just what the overall phase space density is. The best
Re:Speed of Gravitational attraction ? (Score:2)
It seems to me your saying this should create a system that acts similar to the universe while it is not supposed to be an exact model. Sort of like the chaos anaology with the drop of water.. no matter how precisely you drop it there is no real predicting how it will fall but you can m
Re:Speed of Gravitational attraction ? (Score:4, Insightful)
The primary goal for computer simulations such as these are to understand how and why they don't work - not to test current theories.
For instance, many different attempts had be conducted before an computer model of Earth's magnetic field exibited magnetic field reversal - and even then, it wasn't exactly like how the geological evidence shows. However, it suggests a basic model that can be adjusted to more accurately describe our planet's core.
It is the same with this attempt to simulate a Universe. The goal is to understand how things interact, how the simulated universe differs from our Universe, and why it differed. Some things would be due to problems running computer simulations with a Von Neuman Machine (such as the "three body problem"). Other errors will be caused by problems with our current model. If the two effect can be seperated and analysed, then advancements could be done in both computer science (e.g. weather forcasting) and cosmology. That's the point of this excersize.
Re:Speed of Gravitational attraction ? (Score:2)
Re:Speed of Gravitational attraction ? (Score:2)
This discussion thread looks like if newton's law is the last theory there is about gravity. But Einstein has invented/discovered general relativity now nearly 90 years ago.
And yes, gravitational waves have been at least indirectly observed (there was a nobel prize for that discovery!).
So, general relativity has some experimental/observational data which supports it. It's probably not the last word about gravity, but it is a significant refinement of newton's theory.
And, if you consider spe
Re:Speed of Gravitational attraction ? (Score:2)
I find it interesting because this means at great distances you could predict changes by detecting changes in gravitational forces. Also if you could manipulate gravity waves you could then instentaneously communicate over any distance.
Further more if you could distinguish gravitational influences of very distant objects you could make current observations about it rather than observations that are years (millions of years in many cases) old based on the transmission of light.
Hari Seldon (Score:2)
Re:Hari Seldon (Score:2)
Warez Request (Score:3, Funny)
thx
Re:Warez Request (Score:2)
-
And the answer of the computer was: (Score:2)
but (Score:2)
Lots and lots of particles (Score:5, Insightful)
It doesn't quite come out in the article, but what's really groundbreaking about this work is the number of particles they're using. When you make models like these, you always have to prioritize how large a volume you want to simulate (the more volume you have, the more representative a fraction of the universe you have and the larger number of structures you can analyze) vs how massive the particles are (the smaller the particles, the smaller structures you can analyze).
The more total particles you have, the less you need to compromise your volume or particle mass. Until now, simulating such a large a fraction of the universe (NOTE: unlike what the submitter said, this is not the full universe; as the article itself says, it's about 0.003 of the Hubble volume) required such large particles that it was impossible to say anything about individual galaxies.
However, with 10^10 particles, the mass of their particles is only about 10^9 solar masses, so they can reliably resolve structures of 10^11 solar masses. For reference, the mass of the Milky Way is roughly 10^12 solar masses. This is a fantastic leap forward - most other modern simulations have 10^8 - 10^9 particles, and so either can only simulate a much smaller fraction of the universe (like the simulations I study), or cannot say anything about galaxies, only massive galaxy clusters.
[TMB]
Re:Lots and lots of particles (Score:2)
"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 (2^39) kilograms."
Actually, there appears to be an error in the article, with the author leaving out a "*10^". 2^39 is supposed to be 2x10^39 and that is the number of zeros used in one of the excerpts(sp?). That works out to only 1E19 solar masses, significantly more than the mass of our galaxy by, oh, seven or
Zaphod's Shortcut (Score:2)
I knew it (Score:2, Funny)
Curse the slow connections of us mere mortals (Score:2)
Indeed.
Simulating the "universe" (Score:2)
Just in terms of mass, each particle in the "universe" simulation must represent between 10 and 100 galaxies.
So the simulation actually represents the gravitational interactions of groups of early galaxies, not really the whole "universe".
Sounds like a job for... (Score:2, Offtopic)
*duh duh duh-duh!*
BitTorrent!
That would be beautiful, thousands of HUGE files posted to one massive bittorrent tracker!
Whew! (Score:3, Interesting)
Well, at least we know that we will be around for a few months. Do we have to download the whole bloody thing to find out when the world ends?
Re:How about Boinc? (Score:2)
Re:Kind of useless? (Score:3, Interesting)
They learn how large-scale structures formed in the universe ... galaxies, galaxy clusters, etc.
It is, if you don't care about how the universe as we see it came to be. If you do, it isn't.
Re:Kind of useless? (Score:5, Informative)
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.
Re: (Score:2)
define "significantly" (Score:5, Insightful)
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:define "significantly" (Score:2)
Re:Shortcuts (Score:2)
Re:Shortcuts (Score:2)
If theres a certain type and amount of gravitational interaction in one half of the universe, its safe to assume the sames happening in the other half. Because the universe started from such a tiny point, its very much rotationally symmetrical on a larger scale.
Secondly, random quantum events early during the boom caused the varied stars, galaxies, black holes etc. So t
Re:Shortcuts (Score:2)
If there's a certain type and amount of gravitational interaction in one half of the universe, its safe to assume the same is happening in the other half.
Your comment can be condensed the above except I took, and I will make my comment on that. It's worth reminding ourselves that nothing can be assumed in the realm of the fringes of physics (Einstein had a quote about throwing all assumptions and common sense out the window). Granted, it's intended for the subatomic world (and rightfully so), but there
Re:Misleading title (Score:2)