Researchers from the University of Zurich have simulated the formation of our entire Universe with a large supercomputer. A gigantic catalogue of about 25 billion virtual galaxies has been generated from 2 trillion digital particles. This catalogue is being used to calibrate the experiments on board the Euclid satellite, that will be launched in 2020 with the objective of investigating the nature of dark matter and dark energy.
Over a period of three years, a group of astrophysicists from the University of Zurich has developed and optimised a revolutionary code to describe with unprecedented accuracy the dynamics of dark matter and the formation of large-scale structures in the Universe. As Joachim Stadel, Douglas Potter and Romain Teyssier report in their recently published paper, the code (called PKDGRAV3) has been designed to use optimally the available memory and processing power of modern supercomputing architectures, such as the "Piz Daint" supercomputer of the Swiss National Computing Center (CSCS). The code was executed on this world-leading machine for only 80 hours, and generated a virtual universe of two trillion (i.e., two thousand billion or 2 x 1012) macro-particles representing the dark matter fluid, from which a catalogue of 25 billion virtual galaxies was extracted
Thanks to the high precision of their calculation, featuring a dark matter fluid evolving under its own gravity, the researchers have simulated the formation of small concentration of matter, called dark matter halos, in which we believe galaxies like the Milky Way form. The challenge of this simulation was to model galaxies as small as one tenth of the Milky Way, in a volume as large as our entire observable Universe. This was the requirement set by the European Euclid mission, whose main objective is to explore the dark side of the Universe.
Source: University of Zurich
Journal Reference:
Douglas Potter, Joachim Stadel, Romain Teyssier. PKDGRAV3: beyond trillion particle cosmological simulations for the next era of galaxy surveys. Computational Astrophysics and Cosmology, 2017; 4 (1) DOI: 10.1186/s40668-017-0021-1
(Score: 0, Disagree) by Anonymous Coward on Tuesday June 13 2017, @06:15AM (21 children)
Nice to have a hobby, but since dark matter doesn't really exist in the real universe, this is just as fictional as Kerbal Space Program.
(Score: 3, Informative) by Anonymous Coward on Tuesday June 13 2017, @06:34AM (10 children)
That's inaccurate.
Neptune's existance [wikipedia.org] was predicted long before it was ever knowingly seen. The reason is that expected orbit of Uranus was not was actually observed given what was known of orbital physics at the time. And obviously it could have been just a problem with the orbital physics. Or it could have been an invisible perturbing force that had not yet been discovered. Most people concluded it was the latter, and indeed it was. Dark matter has not been able to directly observed yet, but there is substantial indirect evidence for its existence beyond just 'hey we can fix orbital velocities if we add this much mass.'
On the other hand there's also the luminiferous aether. [wikipedia.org] Again the problem there was that observation didn't match science. How could what was though to be waves propagate through space without any medium? And so we get the luminiferous aether. And invisible mass throughout space enabling wave propagation. It could be that, or it could have been a failing of the physics of the time. In that case it happened to be the latter as relativity and quantum physics came to be able to explain observations in a more complex fashion, but one that did not require an invisible goo be everywhere.
So which is it in this case? It's of course going to come down to opinion, even at the highest level. I tend to think dark matter likely does exist simply because of the huge amount of indirect evidence for it. It's much more than a bandaid for observation of a mismatch in the observed vs predicted rotational velocities of galactic systems.
(Score: 0) by Anonymous Coward on Tuesday June 13 2017, @07:20AM (2 children)
Oh please. Everyone knows the universe is a skein in hyperspace and all we have to do is punch a warphole to uncover the energy grid and find an infinite supply of white chocolate cookies and basic income for all lifeforms in our post-scarcity ecomony of snack cakes and koolaid.
(Score: 0) by Anonymous Coward on Tuesday June 13 2017, @07:25AM
*Capri Sun. I hear it's stellar.
(Score: 0) by Anonymous Coward on Wednesday June 14 2017, @12:00AM
Sounds like someone doesn't like the idea that life doesn't have to be a grind. Maybe we'll finally get anti-gravity and you can actually pull yourself up by your bootstraps. Of course you would be cheating, so we'll crown you as the new king.
(Score: 2) by Gaaark on Tuesday June 13 2017, @11:00AM (2 children)
How did they get the simulated halo of dark matter to not fall to the center of the system it is 'haloing', seeing as how it is affected by gravity and gravity is strongest at the center?
Much better theory at https://physicsfromtheedge.blogspot.ca [blogspot.ca]
--- Please remind me if I haven't been civil to you: I'm channeling MDC. ---Gaaark 2.0 ---
(Score: 0) by Anonymous Coward on Tuesday June 13 2017, @04:19PM
If you are not even able to answer the trivial question
yourself, you are hardly qualified to assess the quality of this theory relative to alternatives.
(Score: 0) by Anonymous Coward on Wednesday June 14 2017, @01:44AM
It doesn't all fall into the gravitational center for the same reason conventional matter doesn't. Namely conservation of (angular) momentum. Just because it doesn't appear to interact with conventional matter via electroweak or strong nuclear forces doesn't exclude it from the laws of motion, given dark matter has an observed mass.
I have read about MIHSC, it doesn't explain observations of the Bullet Galaxy (the smoking gun if you will for the existence of dark matter) and makes some rather extraordinary claims (like photons having relativistic mass).
(Score: 0) by Anonymous Coward on Tuesday June 13 2017, @03:39PM (3 children)
Neptune was discovered like 3 years after the predictions (ie pretty much right away since the predictions were useful and accurate). We are coming up on 100 years for dark matter...
(Score: 1, Insightful) by Anonymous Coward on Tuesday June 13 2017, @06:23PM (2 children)
That's because the technology to see what was already predicted was already there and widely available. The Higg's Boson was not able to be 'observed' for 50 years after its prediction. Relativity, the explosive growth of the standard model, quantum mechanics and more are showing that our universe is an incredibly bizarre place. And trying to experimentally dig into the universe is getting ever more costly. Both technologically and economically. An issue that is likely to only become worse over time.
(Score: 0) by Anonymous Coward on Tuesday June 13 2017, @06:33PM (1 child)
So the theories are making less and less useful predictions that get ever more expensive to check. This sounds more like a self-perpetuating bureaucracy than progressing science.
(Score: 0) by Anonymous Coward on Wednesday June 14 2017, @10:22AM
Science is about knowledge, not about usefulness. Usefulness of many scientific discoveries is more of a happy coincidence, and often only discovered long after the fact.
When Kepler determined his laws for the movement of planets, he couldn't know that those laws, and others which were derived in order to explain them, might one day be useful for enabling worldwide communication, navigation and weather forecast.
(Score: 1, Funny) by Anonymous Coward on Tuesday June 13 2017, @07:18AM
Having said that, why didn't they simulate this, then put jump gates in it and fund future research by using it as an Eve expansion cluster? :)
(Score: 1) by khallow on Tuesday June 13 2017, @10:59AM
Unless it does exist. And let us note here that dark matter does exist. Earth is dark matter, for example (it doesn't strongly radiate EM waves, unlike the Sun). We also know about neutrinos which definitely are dark matter. The question isn't whether dark matter exists, but whether it's massive enough to throw our models of cosmology. Evidence indicates it is.
(Score: 0) by Anonymous Coward on Tuesday June 13 2017, @12:11PM (5 children)
Great to have such an authority on astrophysics here. Why oh why do we waste money on confirming or denying the theories proposed by all those professional researchers when an AC has all the answers?
Joking aside, we don't know if the dark matter exists or not, which is why we keep looking for it. If scientists were hundred percent sure it does exist, why would they be trying to find it? They could use the money and time on other endeavors. There's enough other unsolved problems around.
But they're not sure, they assume it may exist because that seems the best fit. If they find the evidence on the contrary, dark matter will go the way of ether. So they run the simulation that assumes a certain model of dark matter, check with observations to see if the results fit or not, refine or reject the model. In other words, Science!
(Score: 0) by Anonymous Coward on Tuesday June 13 2017, @01:18PM
Stop introducing subtlety and nuance! Nothing that wasn't taught in my 6th grade science class exists! And they only taught me global warming because it's a liberal conspiracy! Dark matter doesn't exist! Climate change doesn't exist! Ideas that make me uncomfortable don't exist!
(And the world is flat, 6,000 years old, and the planets are affixed to perfectly circular epicycles in the heavens, because anything else makes me uncomfortable and therefore is wrong!)
Now stop getting in the way of warp drives with your relativity faggot crap! Warp drives were used on a TV show I watched as a kid, so it must be possible! If not for you liberal scientists!
(Score: 0) by Anonymous Coward on Tuesday June 13 2017, @03:34PM (3 children)
Most people who defend dark matter really don't realize the ridiculousness of it. Do you realize that the way it works is they put invisible stuff wherever it is needed so the model makes the right prediction? This amounts to arbitrary spheroids around each galaxy of arbitrary mass and shape.
Meanwhile the amount needed is perfectly predicted from the amount of visible matter at any location. Ie they place it arbitrarily when that is clearly not the case.
(Score: 0) by Anonymous Coward on Tuesday June 13 2017, @04:24PM (2 children)
The simulation this story is about did explicitly not put the dark matter where it was needed to make the models make the right prediction.
(Score: 0) by Anonymous Coward on Tuesday June 13 2017, @04:40PM (1 child)
This simulation cannot predict anything about stuff smaller than 10^9 solar masses.
(Score: 0) by Anonymous Coward on Wednesday June 14 2017, @10:27AM
The mass of the milky way is about 1012 solar masses, about three orders of magnitude larger than that granularity.
(Score: 2) by KGIII on Wednesday June 14 2017, @12:59AM (1 child)
Hi.
Let me preface this by saying that I am not a physicist. I am, however, a mathematician. Yup... Those crazy bastards even gave me a Ph.D.!
Now, before we go too much further, what is it that you think they mean when they say 'dark matter?'
If we know what you're thinking, we might just be able to clear this up. Frankly, I am horrified by the name. It's probable better than Fucked If We Know Matter, though that might be more accurate.
See, dark matter does exist. We can observe it. We can even make predictions based on it, and then test to confirm them. What is it? No clue. Anyone who tells you that they know what it is, is a dirty rotten liar. However, it does exist.
I think the problem comes from the name. I think that's why people have all sorts of strange opinions on it. Consider the name to be a placeholder, if you want, meaning, 'Shit we ain't figured out just yet,' It really doesn't mean much more than that. But, we know *something* is causing these effects and we can even predict the effect it will have on particles of light that have traveled over enormously large distances.
So, something is causing this effect. Buggered if we KNOW what it is, but there are some ideas. It really is a horrible name. It also doesn't help that pop science and journalists have muddied the waters with myriad crackpot theories backed by bad science and borderline insanity.
Again, I'm a mathematician and not a physicist. We share much of a common language, and there's a goodly amount of overlap in the disciplines. If it helps, I sometimes think they are crazy, as well. Other times, I'm pretty sure they are just making shit up. However, in this case, we can confirm the effect - we just haven't a clue as to the cause. Whatever that cause is, that is dark matter.
Anyhow, if you'll tell us what you think is causing this, I'm all ears. I guess you could deny the effects, but they're pretty well repeated, observed, and documented. I'd still be willing to hear you out.
"So long and thanks for all the fish."
(Score: 2) by KGIII on Wednesday June 14 2017, @01:04AM
I take that back, in part. We can not observe it. We can observe the effects. I should have hit the preview.
"So long and thanks for all the fish."
(Score: 0) by Anonymous Coward on Tuesday June 13 2017, @06:36AM (7 children)
Would a 1 exaflops supercomputer be able to simulate 200 trillion "macro-particles"?
(Score: 2) by c0lo on Tuesday June 13 2017, @09:13AM (6 children)
Very probable, the complexity is over O(N). I feel the best case could be O(NlogN), but I doubt it.
Keep in mind that the simulation need to consider spacetime dimensionality.
https://www.youtube.com/watch?v=aoFiw2jMy-0
(Score: 0) by Anonymous Coward on Tuesday June 13 2017, @10:26AM (5 children)
I just checked, and their algorithm is O(N). They're using a "fast multipole method", whatever that is... I assume it's some form of mean-field approximation for interactions at large distances.
Note that I think their algorithm is O(N) asymptotically as N becomes larger and larger, probably true for the trillions of particles they are talking about.
(Score: 1) by khallow on Tuesday June 13 2017, @10:54AM (3 children)
(Score: 1) by shrewdsheep on Tuesday June 13 2017, @12:53PM (1 child)
If their algorithm is O(N) asymptotically, then by definition it is O(N). Big O is asymptotic by definition.
OTOH nothing wrong with the statement of GP (maybe somewhat tautological). What he meant: If the (time-complexity of) their algorithm can be bound by a constant times N, asymptotically, then ...
(Score: 1) by khallow on Tuesday June 13 2017, @11:17PM
(Score: 0) by Anonymous Coward on Tuesday June 13 2017, @02:38PM
I guess you're right. For some reason, I always assumed in algorithm complexity discussions the big O signified "let's ignore constant proportionality factors", not "when N becomes very big".
In which case I should clarify: the number of operations is bounded from below by something proportional to N, but it does get close to that bound as N increases.
(Score: 0) by Anonymous Coward on Tuesday June 13 2017, @04:28PM
Couldn't they do a charitable-field approximation instead? I think that would give a much more friendly universe. ;-)
(Score: 2) by c0lo on Tuesday June 13 2017, @06:39AM
The dark side of gravitation spawned dark chocolate cookies.
A mean size of just 1000 dark midi-chlorians/galaxy but, boy, are those particles mean or what?
https://www.youtube.com/watch?v=aoFiw2jMy-0
(Score: 2) by opinionated_science on Tuesday June 13 2017, @11:33AM
hyperdrive. I've not played "Elite Dangerous" , though there is a clone on my desktop.
I seem to recall, even hyperspace hops are a little dainty...
(Score: 0, Disagree) by Anonymous Coward on Tuesday June 13 2017, @11:45AM (2 children)
You are unable to account for 90% of all matter, and then you gush about the awesomeness of your what-if simulation? Excuse me while I puke.
(Score: 0) by Anonymous Coward on Tuesday June 13 2017, @04:32PM (1 child)
No, I don't excuse you. A what-if simulation is exactly the way to find out whether the hypothesis is right or wrong.
(Score: 0) by Anonymous Coward on Tuesday June 13 2017, @06:25PM
To find out whether it's wrong at least. Failure to falsify is a far cry from a proof!
(Score: 0) by Anonymous Coward on Wednesday June 14 2017, @05:35AM
also in that universe?