How Cosmological Supercomputers Evolve the Universe All Over Again

How long until... by bejiitas_wrath · 2012-10-02 16:09 · Score: 2, Interesting

How long will it be until we can build a supercomputer that can span the Universe and if the Universe suffers a heat death it could just remake the whole Universe as it stored the state of everything within? Therefore humanity could survive even the end of the whole Universe in 100,000,000,000,000 years time. The short story the Last Question made quite an impression on me and surely with the current evolution in technology we could create a God computer eventually that would exist outside of anything we could comprehend. That would be mind-blowing.

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liberare massarum ex ignorantia, clausa descendit molestie.

Re:How long until... by Nyder · 2012-10-02 16:16 · Score: 3, Funny

How long will it be until we can build a supercomputer that can span the Universe and if the Universe suffers a heat death it could just remake the whole Universe as it stored the state of everything within? Therefore humanity could survive even the end of the whole Universe in 100,000,000,000,000 years time. The short story the Last Question made quite an impression on me and surely with the current evolution in technology we could create a God computer eventually that would exist outside of anything we could comprehend. That would be mind-blowing.
I'm pretty sure Douglas Adams covered all that.

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Be seeing you...
Re:How long until... by Yvanhoe · 2012-10-02 16:20 · Score: 2, Insightful

There is not enough energy in the universe to store all the informations of the universe in a computer.
If you focus on some information (human minds for instance) of special interest to you, on the other hand...

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The Wise adapts himself to the world. The Fool adapts the world to himself. Therefore, all progress depends on the Fool.
Re:How long until... by Tablizer · 2012-10-02 16:39 · Score: 2

Could be worse: in one of the variants, Justin Bieber's mom had quintuplets.

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Table-ized A.I.
Re:How long until... by Black+Parrot · 2012-10-02 17:13 · Score: 2, Insightful

There is not enough energy in the universe to store all the informations of the universe in a computer.
I subscribe to the view that the universe is computing its own final state.
Or more precisely, always computing its next state; apparently there isn't going to be a final one.

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Sheesh, evil *and* a jerk. -- Jade
Re:How long until... by sFurbo · 2012-10-02 19:18 · Score: 2

If there were no dark energy, the temperature difference between a heat storage and an ever cooling universe would allow you to do infinitely many calculations, at an ever slowing rate. It seems that there is dark energy though, so the point where space-time recedes faster than c from you moves closer and closer. This is, essentially, an event horizon, so it will have Hawking radiation, meaning that the visible universe will not get arbitrarily cold, so only finitely many calculations can be done. It also becomes hard to do calculations when the electrons around a nucleus recedes from the nucleus faster than c. Dark energy is really a bummer when it comes to living forever.
Re:How long until... by maxwell+demon · 2012-10-02 19:28 · Score: 2

You should probably also read The Last Answer, also freely available online. An equally thought-provoking short story.
I believe the story you're referring to is "The Last Question" by Isaac Asimov.
https://en.wikipedia.org/wiki/The_Last_Answer

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The Tao of math: The numbers you can count are not the real numbers.
Re:How long until... by wonkey_monkey · 2012-10-02 21:24 · Score: 2

The GGP mentioned The Last Question, so I think the AC really was referring to The Last Answer.

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systemd is Roko's Basilisk.
Re:How long until... by rgbatduke · 2012-10-03 01:29 · Score: 4, Interesting

Depends on how seriously you take information theory and the information content of the Universe. If, as seems rather reasonable, the information content of the (visible) Universe is irreducible/uncompressible, it would take at supercomputer with at least as many bits of storage as there are bits of information in the specification of the Universe's state. This requires a computer that is strictly larger than (in the sense of having at least as much "stuff" devoted to storage of all of those bits) than the Universe itself. Finally, since the supercomputer is part of the Universe (at least, if we built it), it also has to be self-referential and store its own state information. If it is to have any processing capability at all, it then is in a deadly game of catch-up, adding bits to describe every elementary particle in its processors and memory and losing the race even if it requires only one elementary particle to store the bit content of another (which will never be the case).

In the end, it is provably, mathematically impossible to build a supercomputer that stores the complete state of the Universe, where the Universe is cleanly defined to be everything with objective existence. The same proof works to prove that there can be no omniscient God, since God suffers from precisely the same issues with information content and storage. A processing system cannot even precisely specify its own encoded state unless it is a truly bizarre fully compressible self-referential system the likes of which we cannot even begin to schematize, and there are lovely theorems on the rates of production of entropy in state switching on top of any actual physical mechanism for computation, all of which make this an interesting but ultimately absurd proposition.

If you don't like information theory, then there are the limitations of physics itself, at least so far. We can only see back to (shortly after, the end of The Great Dark) the big bang, some ~14 bya. It is literally impossible for us to extract state information from outside of a sphere some 27.5 billion light years across. However, making reasonable assumptions of isotropy and continuity and the coupling of the "cosmic egg" that was the early post BB unified field state, cosmological measurements suggest that the Universe is no less than 200 times larger than this, that is, a ball some 500 billion light years across (where it is most unlikely that we are in the center of any actually compact Universe). Obviously, we cannot get any state information at all beyond indirect inference of mere existence from strictly less than 1 - (1/200)^3 of the actual Universe unless and until we have new transluminal physics. And from the first argument, even if you turned this 99.99999% of the actual Universe into a computer to fully describe only the 0.00001% visible sphere that we actually inhabit, you'd barely have enough material to create the bits needed to hold the information at current peak matter-per-bit levels (and then there is the problem of the free energy needed to drive any computation, the need for a cold reservoir into which to dump the entropy, but I digress). So it is safe to say that it is also physically impossible to build a supercomputer that can store/duplicate the information content of the entire Universe (and again, the same argument works against the existence of a God presuming only that this deity requires internal switching mechanisms on top of some sort of medium in order to store information and process it.

The only exception to both is the specific case where the Universe and/or God are one and the same entity, and its "storage" of information is the irreducible representation of the information content of mass-energy in the mass-energy itself, and the irreducible computational mechanism is the laws of physics themselves.

But of course you really do understand this, if you get outside of the willing suspension of disbelief required of science fiction (and yeah

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Even when the experts all agree, they may well be mistaken. --- Bertrand Russell.
Re:How long until... by mcgrew · 2012-10-03 03:52 · Score: 2

I'm quitting smoking
Perhaps I can help.

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Free Martian Whores!
Re:How long until... by YttriumOxide · 2012-10-03 04:50 · Score: 2

Thanks for that - I just read through it and it really did help.
I planned this months in advance. My first attempt was before my daughter was born as I REALLY wanted her to have a non-smoking Dad. After one week though, my wife told me to buy cigarettes, since my mood was so foul, she just couldn't handle it.
This time, we planned it so that my wife and daughter (now 18 months old) would be on holiday without me. I've gone cold turkey - no patches, no gum, nothing. The first three days were AGONY... physical pain in all my joints and muscles, sweating, unable to sleep. It got a bit better though and by the end of the first week, when my family came back from their little holiday, I was reasonably okay. I'm now approaching the end of week 2 (in 6 hours, it'll be 14 days since my last cigarette) and I'm still horribly moody, not thinking particularly clearly and not particularly pleasant; but the worst of it is over.
Now, every time I feel I desperately NEED a cigarette (the triggers you mentioned are all there for me, definitely...), I just think of two things - the reason I'm doing it (my wife and daughter); and the agony I went through to quit, knowing I don't ever want to have to do that again.
Tomorrow is my first day back at work and it's worth mentioning that where I live, you CAN smoke in the office at work - there'll be noone smoking in my office (you can't smoke when others in the same office room object) but I do visit other people's offices quite frequently who smoke like trains, so it'll be harder/impossible to avoid others smoking. So tomorrow's going to be a very hard day for me; but I'm totally sure I'll manage it - AND every day after it for the rest of my life.

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My book about LSD and Self-Discovery
Also on facebook as: DroppingAcidDaleBewan

the simulation can never end by catmistake · 2012-10-02 16:12 · Score: 4, Funny

It started with the state the universe was in around 13.7 billion years ago (not long after the Big Bang) and modeled the evolution of dark matter and energy up to the present day.

so... what happened when it reached the simulation of the simulation, and then eventually the simulation of the simulation of the simulation? I've long been told that it's turtles all the way down, but I'd like to see a citation.

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The Admin and the Engineer

Re:the simulation can never end by olsmeister · 2012-10-02 16:21 · Score: 5, Funny

so... what happened
A stack overflow.
Re:the simulation can never end by GodfatherofSoul · 2012-10-02 16:26 · Score: 4, Funny

42

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I swear to God...I swear to God! That is NOT how you treat your human!
Re:the simulation can never end by Cryacin · 2012-10-02 16:32 · Score: 4, Funny

No, it's not turtles all the way down. Eventually you hit tortoise and a SVN repository.

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Science advances one funeral at a time- Max Planck
Re:the simulation can never end by brisk0 · 2012-10-02 18:36 · Score: 2

Not infinitesimally, each universe would probably have to be significantly simpler than the one it's already in, until the point that a universal simulation is too complex for the universe. Of course any one universe could spawn [very large number] of simulated worlds in a tree structure.
So if we assume mediocrity (and assume I'm not just spouting bull), we exist in one of the simpler universes... the original must have been nuts.
Re:the simulation can never end by ctrl-alt-canc · 2012-10-02 18:49 · Score: 4, Funny

Given the amount of floating point calculations involved in the project, the result will be 41.999999
Re:the simulation can never end by Mr0bvious · 2012-10-03 00:15 · Score: 4, Interesting

Nick Bostrom has a paper on this, the intro:
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 posthumans who run ancestor-simulations is false, unless we are currently living in a simulation. A number of other consequences of this result are also discussed

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Never happened. True story.

Let's qualify that sentence just a bit... by Empiric · 2012-10-02 16:14 · Score: 3, Informative

...astronomers are turning to supercomputers that can simulate the entire evolution of the universe.

I'm thinking the intent here is to mean this qualified "up to a certain point in time", as I'm pretty sure that to say this as a general, even theoretical, possibility is a Godelian-type logical impossibility. Since the supercomputers would be part of the universe you are simulating, you have to simulate the simulation of the supercomputer, which requires simulating the simulation of the computer simulating the computer... ad infinitum.

But then again, I may be wrong. Best simulate my thought processes to be sure.

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~ Whence do you come, slayer of men, or where are you going, conqueror of space?

Re:Let's qualify that sentence just a bit... by JWW · 2012-10-02 17:10 · Score: 2

What part of "turtles all the way down" don't you understand?
Re:Let's qualify that sentence just a bit... by Black+Parrot · 2012-10-02 17:18 · Score: 2

...astronomers are turning to supercomputers that can simulate the entire evolution of the universe.
I'm thinking the intent here is to mean this qualified "up to a certain point in time", as I'm pretty sure that to say this as a general, even theoretical, possibility is a Godelian-type logical impossibility. Since the supercomputers would be part of the universe you are simulating, you have to simulate the simulation of the supercomputer, which requires simulating the simulation of the computer simulating the computer... ad infinitum.
Almost without exception, simulations are simpler than the thing being simulated. You use simulations when the real thing would be impossible, or too dangerous or expensive.

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Sheesh, evil *and* a jerk. -- Jade
Re:Let's qualify that sentence just a bit... by Anonymous Coward · 2012-10-02 19:24 · Score: 2, Insightful

You fail to realize something. If the reality we are experiencing is in fact a simulation, then it doesn't matter if one plank-step of the simulation takes an hour or a Universe worth of time to compute -- To us within the simulation, time remains locally constant. Likewise, The super computers can simulate the entire evolution of the universe by imposing acceptable error rates (epsilon).
A very low resolution simulation would simply count down from 1.0 (max Universal energy) to 0.0 (heat death) over one universe worth of time steps, the fastest of such simulation is a single constant approximation: .42
A higher resolution simulation could produce a more detailed simulation using much more than a single time step. Interestingly, the quantum error rate can be predicted from within the simulation via observation. Heisenberg has calculated the epsilon of our Universe... Plank calculated the physics step size.
In short: One can indeed calculate an entire Universe within another if one allows a high enough "acceptable" error rate and low enough resolution. Quantum Uncertainty may be proof such corner cutting has already happened at a higher dimension.

Or we could ... by PPH · 2012-10-02 16:28 · Score: 3, Funny

... put this supercomputer to work generating all possible Slashdot logos.

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Have gnu, will travel.

Simulation Variant #85472721 by Tablizer · 2012-10-02 16:46 · Score: 3, Funny

I wonder who they say will win the election next month.

Mitt Obamney: He taxes the rich to pay for birth certificate forgeries and dog racks on top of all GM cars. He told the UK Olympians that their skeet shooters are bitter gun clingers.

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Table-ized A.I.

Re:Simulation Variant #85472721 by Black+Parrot · 2012-10-02 17:16 · Score: 2

Mitt O['B]amney
Not a Kenyan, not a Mormon, but an Irishman!

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Sheesh, evil *and* a jerk. -- Jade

Any Cosmologists Here? by steppedleader · 2012-10-02 16:46 · Score: 2

First off, "entire evolution of the universe" should obviously be qualified with "on cosmological scales", unless they've built the matrix. That said, how big is the domain? Is it just set to match the observable universe? 2048 grid points across the entire universe (or just the observable universe) seems rather... low-res. The TFA mentions an adaptive grid, but fails to mention what factor that can increase the local resolution by.

Also, how exactly do we model dark matter when we don't really know WTF it is beyond the fact that it has gravitational mass? Does it work because gravitational effects are the only thing that really matters on cosmological scales?

I must say I like the use of periodic boundary conditions, though, simply because it makes their simulated universe conform to the Modest Mouse lyric "The universe is shaped exactly like the earth, if you go straight long enough you end up where you were".

Re:Any Cosmologists Here? by mendelrat · 2012-10-02 18:23 · Score: 5, Informative

I'm not a cosmologist, but I am an astronomer. Most of the questions you ask are in the papers associated with Bolshoi, but science writers just leave them out because the numbers are so huge and hard to relate with -- I'm going to use megaparsecs for distances; 1 megaparsec = 1 million parsecs = 3.26 million light years = 200 billion astronomical units. 1 astronomical unit is ~93 million miles, the distance from the Earth to the Sun.

First off, "entire evolution of the universe" should obviously be qualified with "on cosmological scales", unless they've built the matrix. That said, how big is the domain? Is it just set to match the observable universe? 2048 grid points across the entire universe (or just the observable universe) seems rather... low-res. The TFA mentions an adaptive grid, but fails to mention what factor that can increase the local resolution by.
As you point out, the 'entire evolution ...' phrase is a bad way of saying that the simulated volume and mass is large enough to be statistically representative of the large scale structure and evolution of the entire universe. It's 2048^3 particles total, which is a heck of a lot. 8,589,934,592 particles total, each pushing and pulling on each other simultaneously. It's an enormous computational problem. The particles are put into a box ~250 megaparsecs on a side; the Milky Way is ~0.03 megaparsecs in diameter, and it's ~0.8 megaparsecs from here to the Andromeda galaxy, our nearest large galaxy. 250 megaparsecs is a huge slice and more than enough to ensure that local variations (galaxies) won't dominate the statistics. The ART code starts with a grid covering 256^3 points, but can subdivide to higher resolutions if some threshold is passed up to 10 times if I remember correctly, giving a limit of around 0.001 megaparsecs. My memory is hazy, and the distances are scaled according to the hubble constant at any given point, but they're in the ballpark I think.

Also, how exactly do we model dark matter when we don't really know WTF it is beyond the fact that it has gravitational mass? Does it work because gravitational effects are the only thing that really matters on cosmological scales?
Essentially, yes; gravity absolutely dominates at these scales compared to all other forces considered. The role of stellar and galactic feedback into their environment when forming (and as they evolve) changes lots of important things, but simulations like Bolshoi seek to simulate the largest scale structures in the universe. Smaller subsections of the simulation can be picked out to run detailed N-body simulations of Milky Way type galaxies, or to statically match the dark matter clumps (which will form galaxies) to huge databases like the Sloan Digital Sky Survey. Both of those are pretty active things-to-do in cosmology now.

Re:Did it find out who killed JFK? by Tablizer · 2012-10-02 16:50 · Score: 2

We all did, in at least one variant. My avatar slipped on Marilyn Monroe's used tampon in a grassy knoll, setting off a guard's gun. Sorry 'bout that.

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Table-ized A.I.

Reminds me of that old joke by khelms · 2012-10-02 16:50 · Score: 2

Scientists build the ultimate computer. The first thing they ask it is, "is there a god?". The computer answers "there is now!"

Re:GIGO by steppedleader · 2012-10-02 17:08 · Score: 2

It appears that the model reproduces some large scale statistical properties of the universe with reasonable accuracy. That seems reasonable. It's a far cry from being able to say "the model reproduced the Milky Way", but the statistical information by itself could very well be useful as a tool for developing new hypotheses. Of course, if the model is all wrong those hypotheses will be useless, but let's see what they can do with the data before we make that conclusion.

Epistemological Weakness by Required+Snark · 2012-10-02 17:56 · Score: 4, Interesting

This is clearly good work, but I believe that the article glosses over real problems with these kinds of simulations. The short version of the problem is that the agreement between the model and the observations doesn't provide a huge degree of confidence in the model being tested. It appears that both the model and the starting setup are per-disposed to produce results that match observations.

There has been no perturbation testing of the model. It does not seem that they did any runs that were intended to produce a result that did not match observations. They have no idea what range of input or modeling change produce a result that matches observations.

The greatest utility of these simulations is when they don't match observations. This opens the possibility that the current ideas are incorrect, and that new ideas are needed.

I also wonder about scaling issues. The three simulations at different scales are unconnected. There is no way to see how events at one scale effect events at other scales.

The author also said one specific thing that bothered me:

Astrophysicists can model the growth of density fluctuations at these early times easily enough using simple linear equations to approximate the relevant gravitational effects.

I am not a physicist or cosmologist, but that seems to be a huge assumption. We have no idea what dark energy or dark matter are, but they can be modeled by "simple linear equations."

I know that the shear cost and complexity of these computational experiments means that they are hard to accomplish. Even so, I will be less skeptical about their value when they are done in ways that test how the simulations fail, as well as how they verify current ideas.

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Why is Snark Required?

Re:Epistemological Weakness by Anonymous Coward · 2012-10-02 19:26 · Score: 2, Insightful

Yes, Bolshoi's initial conditions were in some sense designed to match observations. Specifically, the five main parameters which describe cosmology (including the abundance of dark energy and dark matter) were derived from observations of the cosmic microwave background, supernovae, and galaxy clustering. These five numbers were used to generate the initial conditions for Bolshoi; a supercomputer spent the time to figure out how the universe should evolve from several million years after the Big Bang to the present day. Thus, Bolshoi serves as a giant consistency check of the model: i.e., it tests whether the five parameters are enough to explain everything we observe about the evolution of the universe, as well as whether observers calculated them correctly.
However, the fact that Bolshoi matches observations now is no guarantee that a future observation won't come along and break things. The previous large simulation (the Millennium Simulation), which was run in 2005, was also designed to match all observations up to that point. However, since then, we've made observations which contradicted results from that previous simulation, which have indeed taught us new things.
Finally, to address the specific point that you raise: we don't know what dark matter and dark energy are, but to our knowledge, gravity doesn't care about the type of matter/energy involved. This assumption could be wrong, of course. So far, however, making that assumption has led to predictions which seem to match observations. (So it would definitely be interesting if someone made an observation that proved otherwise!) The "linear equations" the author is referring to are simply Taylor expansions of the gravitational potential. Since the density fluctuations in the early universe are tiny (variations of +/- 0.001% even 300,000 years after the Big Bang), using a linear approximation doesn't introduce significant errors. However, once the density fluctuations grow to +/- 10% or so, then the linear approximation is no longer as useful; that's when the supercomputer takes over to do more accurate computations of gravity.

Re:Pretty sure their model didn't come close by ledow · 2012-10-02 23:15 · Score: 2

As centuries of relying on Newtonian physics demonstrate:

It doesn't need to be accurate. It just needs to be close enough when looking at the parts you're interested in.

Nobody claims to be simulating a universe down to the sub-atomic level. They are just claiming that: the best they can simulate their own ideas of how it formed correlate with roughly what we see when we peek at the sky.

It's like saying that there's no point in simulating a rocket launch if you can't model every atom. There is. And it saves us a lot of work and tells us when something is (probably) wrong with our design.

Newtonian physics was THE most accurate method for centuries, correlated to millions of independent experiments to be correct. The fact that it's nowhere NEAR the full story of how things operate is neither here nor there, and we still teach it in schools because it's still accurate ENOUGH.

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How Cosmological Supercomputers Evolve the Universe All Over Again

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