Moore isn't swinging anybody, least not from my perspective. People who are against Bush come out of it raving against Bush, People For Bush come out Raving against Moore.
You don't swing votes with extreme views/bias, you swing votes with compromise. People interested in getting info that I know come out of 9-11 at best with a list of facts to check and veriffy. If anything finding some of the better examples of poor context is enough to turn them fairly sour on Moore but still has no effect on their opnion regarding the election.
In other words people that are actually seraching for information to be swayed by are generally smart enough to dismiss the bias and take the valid issues under consideration. The poor schlubs that can't think for themselves had their minds made up before they ever bought a ticket.
This is not an issue... or I should say that it is a non-issue in light of the overwhelming role already played by media coverage regarding politics. On the other hand not allowing it (given a willing station) is more of an issue to me as that is a potential encroachment on free speach. To me not allowing it because it might have an undue influence on the election would be no different than saying someone could not publish a book because it might have undue influence on the election.
Pretty loose deffinition of civil war. In truth it was more successfull rebellion than anything. America was not a fully integrated component of English government.. which was part of the problem. Of course given transportation of the day they COULDN'T but thats another issue entirely.
Also, calling the Boston Tea Party an act of terrorisim is pretty out there. Dumping the tea into the harbor was more symbolic than anything. And hardly in the same class as a hijacking or suicide bomber.
I am kinda torn on the issue of them being blown away being a good thing. If I were positive the response would be to build a replacement capacity ASAP it would deffiantly be a good thing. If it were not then it would be better to have something rather than nothing.
There been any news on the new Delta varient that was sitting out on the pad yet ?
Gracias. Interesting stuff. I have never really had a problem with relativity per say, just some of the logical difficulties its properties present.
Time dialtion is of course one of the biggest. I have never questioned the fact there is an effect. Like I said we have observed the effect and use technology that depends on it to function properly.
HOWEVER, Just because an observed effect that can be predicted and used to perform mathmatic opeartions does not mean we actually understand it. The best example I know of this is the Ptolemaic system of explaining the motions of the planets. It worked from the premise the earth was the center and mathmatically worked just fine, and still does for that matter. Dosn't make it any more right in the end.
Perhaps Einstien nailed it. Or perhaps he is just a damn smart guy that did what he could with what was available to him. He himself said he felt like he was a kid in a gigantic library and he had managed to decipher one page of one book. Would be nice if more people felt the same.
I'm sure all your numbers are fine and dandy but they are most assuredly by the book.
I am not saying that by the book is not good.
I am saying given a good enough reason they could expedite the process.
The thing about rules and guidelines is knowing when to break them.
The thing about costs is knowing when they matter.
Worrying about 1 million when talking about billions of invested worth irreplaceapbe euipment is being placed at risk is asinine. It is a non issue. The important thing is assessing the risks and evaluating your options.
Now. having said that its very possible that leaving them was the safest possible thing to do. IE the risk in leaving them was far less than the risk of attempting to move them hastily. But that is not the impression the stories have been giving. Perhaps they have been over dramatized but it seems there was real concern that given a cat 4 storm there wouldn't be much left.
As I said in another post... the launch infrastructure is far far far more replaceable than the orbiters.
Will do that, have run across it in bits and peieces. Don't really have the math chops to really dig into it.
Though on length contraction that only happens from the ships frame of refference does it not? Meaning (unless I am really wrong) that the length does not contract for earths frame of refference.
So what I am saying still holds. It's a case of semantics really. If I understand it right then from the ships perspective the 'mile markers' would no longer mean the same thing. They are the same distance apart but what comprises that distance for earths frame of reffference and for the ships frame of reffernce are two different things.
But you are still passing them at greater than light speed if you use the ships clock in reffernce to distance covered by earths frame of refference to determine how fast you are going.
Its not that you break c. Its the fact your using non-relativistic math.
I'm sorry but a hasty departure would be prefferable to a destroyed orbiter. They can get that thing on the plane and out of there faster than a week. Now would likely incurr a lot of extra time and effort picking up where they left off on the work though but I hate it when people take nominal operating times and assume it is the best that could be done.
Anyway you slice it you still seem to break c if you choose differnt perspectives. I very particularly said "seem to" there so don't jump on it as impossible.
distance/time = speed.
example 100 miles covered in 2 hours = 50 mph
From any single perspective you can make sure speed never breaks c. However if you mix refferences then you come back with speeds greater than c. And mixing refferences is pretty common. After all relativity affects you traveling on the highway and in the air when flying. Just at such small levels you can ignore it but your still measuring your travel based on a frame of reffernce other than your own.. IE highways with mile markers and rest stops. but technically from your frame of reffernce distance is getting shorter the faster your going and time is passing slower or faster (depending on direction of tavel) but you mark speed based on the other frame of reffernce. Speed up the car fast enough and the differnce becomes more and more pronounced until you have to come up with some other way of dealing with it.
Distance from Earth refference/ Time from the ships reffernce = a speed greater than c.
For example
7 light years covered in.7 years = 10X the speed of light.
not saying 7 years didn't pass at either end and that your only.7 years older. Just that by the combined frame of refference thats how fast you were going.
Lets return to the two earth examples and instead of a featureless trip through the void lets say its got mile markers laid down and a half way point . From your frame of reffernce on the ship your clock slows down ( not that you notice it.. seems fine to you ) Your speedometer indicates.99 c but you look out the window and the markers are flashing by at an insane rate.
Now all discussions about what looking out your window will actually be like you can't escape a very basic issue. With time dilation, at.35 years on the ships clock you pass the half way point of your trip.
Now You climb into your car for a trip that covers 100 miles and you pass the halfway marker at 1 hour of travel.. how fast are you going ?
You climb into your space ship for a trip of 7 light years and pass the halfway marker at.35 years. how fast are you going ?
Now relativity and in particular time dilation is more or less established. Anyone that uses GPS uses its principles to a fairtheewell whether they realize it or not.
Now if distance shortens from that ships perspective then its no wonder you can't exceed c becasue if you reach c all distance goes to zero and time stands still. Thus to travel at c is to travel through all points simultaneously because no matter where your traveling to or from it takes 0 time to get there and you didn't cover any distance because you didn't take time to go from point a to point b.
Now is that the case or is it just a case where you wind up with division by zero because the clock stopped? After all it would still take a radio signal from alpha centauri ~7years to get here and thats hardly instentaneously whatever the radio signal itself thinks.
In other words I am not really questioning relativity so much as our explinations of it with incompelte concepts that don't seem to apply once relativistic effects become aparant like speed/distance and time... at least do not apply as we generally understand them.
However, that understanding is key to manned deep space travel. Me I don't give a rats ass if time dilates or you can break c as either allows you to do the same thing. Go farther than you would think reasonable with newtonian physics limited by c for your speed of travel.
a 14 year round trip to alpha centauri is a difficult proposal a 1.4 year round trip to alpha centauri ( regarless of 14 years passing here ) is much more doable.
The potential exists in fusion power plants to reach
Why wouldn't they add up.. remember I am sorta suggesting that time dosn't slow down. So increase mass would lead to the longer decay time. Should add up nicely.
Course it dosn't work. After all we have the cesium clocks running GPS to atest to that. Seems they wind slower, but man its weird.
Not many internships currently that I am aware of but if your really interested look out on www.nasa.gov and go to the primary contractors and look for jobs in Huntsvile/Houston etc... ( Boeing, Lockheed ). Now is not the best time for space jobs though, I'd check back after they decide about Shuttle.
Agreed that you don't need %100 realisim for good results. However you have to maintain some relationship/corelation with reality for the information derrived here to be much use in determining the early formation process of the universe. So whats a strong enough correlation ? 90%, 50%.. 10% ? And I am not reffering to exact replication here, just correlation to realisitc application of the same forces to the chosen mass points.
The process they are using seems to have an awful lot of room for loosing statisticly significant information due to the error of the process. So in the end it seems to me the density distribution ( which is what they are after ) is going to be ruled by the error inherrent in the problem rather than the rules of gravity as we understand them and they are atempting to apply them.
That make sense ?
I will have to look more into weather simulations but my understanding is that models for them have been improoving due to the applications of chaotic principles in attempting to simulate them. The methods for this problem are pretty simple and through the years have been all about limiting the chaotic influences so it seems a bit of apples and oranges to me.
Hell, i've been out of my depth for a while. I am a poly sci grad with a comp sci minor and a serious jones for space science of any kind ( also work at MSFC in the ISS POIC... translation, marshall space flight center where they do space station payload ops.. don't ask how I still don't know myself ).
Anyway Hubble calculated a mass of the universe that is fairly widely accepted, the model is using an amount that totals up to about.0003 of that mass. Also that.0003 is split into 10 billion equal masses.. and to give you an idea of the scale it would only take a handfull of them to equal the amound of mass that is in the milkyway, some of the other posts have argued about just how many.
In other words all I said was since your starting from coarse information so you can only expect to derive similarly coarse results.
We only know so much about the origins of the universe. However in a model like this that informatin is fairly critical to creating a usefull model.
You could tweak those values untill you started seeing the results you expected.. ie density distributions that resemble what we have observed and inffer that those values have some realition ship with the real values at that point in time given your model of interaction works.
Except for the problem of the n-body problem. Just doing the basic sumation of the affect of all 9,999,999,999 particles on each other individual paticle does not allow for the chaos that is inherrent in the n-body problem. IE those interactions go to hell in a hand basket pretty quick without some pretty niffty allowances based on observation. Meaning they DON'T reflect realistic interactions over time which means you don't get realistic results when using it, coarse or otherwise.
as for the weather models...
I belive weather models face a similar problem. You can guess realistic weather based on current measurements for a few days. You can guess seasonal trends for a few years but again as you attempt to model longer periods of time instability creeps in and disacociates the results with reality.
wasn't really suggesting they are after an accurate model. ( meaning an exact replication of the creation of the universe )
The ability to solve n-body aside they are limited in accuracy to what they know about the begining conditions and the ability to account for all mass at as close to the atomic scale as possible. By using.0003 of the hubble mass divided into 10 billion points they create a limit to their accuracy right there.
My ultimate issue is they ARE using the n-body problem. As you just pointed out if you could solve it then it would be fantastic.. just plug and chug. But we can't so I don't see how this is supposed to even lead to a coarse model for understanding how the system behaves. IE if the coarse model dosn't behave roughly like the system you can't derive trends from it.... its just chaos inherrent in the method * inherrent error of the the unknown factors of the begining of the universe compounded over billions of years worth of modeling the 10 billion points interactions which equals nothing relavent to reality.
I guess another way of putting it is it seems they are trying to walk before they crawl, run before they walk etc...
Though perhaps they are not. I am trying to get a practical assesment of the longer duration sims of the solar system. They all talk about exponential chaos and repetitive aberations but not what it means in terms of where the planets go in their models... though some of the graphs look damn funky.
Thanks for taking the time to respond. Everyone who has has given me a great deal of info to digest.
I earased.. or put in another comment where I was thinking if c remains constant from both perspectives then both time and distance have to be relative... ie the shortening of the distance to keep c constant from both frames of refference.
So time and distance are relative while c remains constant.
as the rate of time goes to zero distance does as well.
Interesting.
Have to noodle on the pion experiment. That is fascinating.
freaky too.
So we know the speed of light, we know the speed we acclerate the pions to, we know the rate of decay thus you only have two options left.
1) Distance is shorter.
2) The decay rate is lower at high speeds.
How do we eliminate the possibility that elements decay rates are tied to time and not to their speed... or more specifically to their mass. After all dosn't mass increase with speed and could not greater mass have a stabilizing effect at the atomic level thus slowing the rate of decay ?
Ok I am just thinking out loud now....
*mumble*
* I belive you took my stapler....... I could set the building on fire*
First part was just saying that if you have an equation with a known solution ( observations of the known universe ) and a whole buch of unknowns that lead to that solution then you can just plug in what you want so long as the end result matches the known solution. Or in the case the mix of knowns and unknowns matches the same form of the known solution.
Dosn't mean any values that work are the 'right' values though.
For instance we know clusters form, we know galaxies form, we know nebulas form.... thus any simulation using values that do not lead to similar structures ( in so much as the sample size allows ) needs work.
well in that case it seems there are an infinate set of possibilities which you can manipulate at will to answer the known solution.
ie
x + y = known quantity has any number of solutions ( though in this case more like a + b.... + zz = kq )
we can narrow down the range of solutions with ranges for what we do know about the unknown variables.... ok ok I see a bit more of the big picture now.
One nit I can't resist though
"I wasn't talking about the issues of simulating them"
but this whole thing is about a simulation!!!
Thanks for the info on Sussman and Wisdom, will have to look into that more. Out of curiosity did they extrapolate backwards ? Check their accuracy by comparing to known observations of the past ? Or just predict into the future? Eh probably answer my own question.
However I have to say from reading the article it still seems to me this is not what they are doing. Could just be due to an oversimplification by the article. It seems to me they just said they were assigning a given energy level based on the amount of background radiation back at the point it started then iterating ( and using various shortcuts ) to then calculate each individual mass points affect on all 9,999,999,999 other mass points over time based on Keplers laws. In other words at its most basic it is a n-body simulation where n=10,000,000,000
Is it just over simplified ? That alone is a crapload of calculations, I would hate to have to figure out how to deal with a softening factor.
but what of when you mix the frames of reffernces ?
By the way I am not being argumentative, and not intentionally trying to be stubborn, just have never had this adequately explained and I really want to understand it. It has always seemed to me something dependent upon choosing the right frames of refference, or more specifically a single frame of refference.
So if the frame of refference of the ship is earth 2 approaching at.99 c then why am I not eating for 7 years while watching an object 7 light years away approach at.99 c ? By this explination I would watch it approach at.99 c for.7 years at which point I would be there. Again for the frame of refference of the ship you cover 7 light years in under one year. That is faster than c.
Lets go further, earth 2 also has the same orbital period. If I reach it in.7 years it stands to reason I would see it revolve around its orbit a little over 14 times to account for their frame of reffernce being 7+ years. Thus we once again exceed c and reach the issue of mixed frames of refference once again.
If I watch it revolve 14 times and yet my frame of reffernce is of.7 years duration for these 14 revolutions then it should appear speeded up, ie time is moving faster for it than for me which would also seem to imply I would percieve it approaching at faster than.99 c.
again this perception of exceeding c applies only if your frame of reffernce is for.7 years during the trip.
You would HAVE to see it orbit 14 times... you start in the hole seeing what happend 7 years ago so its already orbited 7 times that you have yet to observe and by the time you get there it will have orbtied 7 more times to account for their frame of reffernce being 7 years so you would see it orbit 14 times while apporaching at.99 c for your.7 years frame of refference for the duration of your trip. Even if your frame of refference is of 7 years you would still see 14 orbits. The question is just how long it would take you to observe them.
"Of course, we can solve solar-system dynamics. The number of particles isn't the problem. The issue is that we can measure solar system dynamics very precisely, so we have to carry out the simulation at high accuracy to match observations. We can measure the large-scale structure of the universe only coarsely, so the simulations don't have to be as precise, although they do need to have many more particles."
I think you miss my point. We can indeed make systems that model what we observe in the solar system accurately. However we cannot do so based on the interaction of gravitational atraction of the known masses in the solar system. Systems that attempt to do so invariably devlove into chaos that have no ressemblence to reality.
I keep re-iterating this point becasue this is what they are doing. Essentially they are calculating the effect of each mass point on all 9,999,999,999 other points over time given intial energy as determined by the amount of cosmic background radiation extrapolated back to 380k years after the big bang give or take 8k years. We can't make these kinds of equations reflect the observed reality of the solar system. Why would it reflect reality regarding early universe structure ?
As for what you would model with 10 billion points in the solar system ?
How about having more than one particle representing a single celestial body? Perhaps you have heard of tidal forces where one side of a body is more strongly attracted than the other ? MIght 10 billion particles split into even masses then distributed through those 100 known in proportion lead to higher acurracy in modeling gravitys effect in the solar system ? Then better understanding the interactions on a micro scale you just might be able to translate that into a better understanding of how they interact on a macro scale.
"Besides, the point of the "exercise" was to understand the formation of large-scale structure in the early universe. Studying solar-system dynamics doesn't tell us anything about that."
And yet again I stress that the forces at work in both are presumed to be identical. So equations that can model the large scale structure formation of the universe should also work for solar system dynamics. The scale is different not the equations.
If the forces at work are indeed the SAME them then the issues of simulating them are by no means orthogonal.
I Understand you can't reach LS, was just using the easiest example. But even in that case, even considering H&K's flying clocks I still ask how much food you pack for the trip.. do I pack for.7 years or 7 years?
Its a very practical concern and also holds the key to distant travel in the universe. If time approaches 0 as you approach LS then high percentages of LS could lead to travel to distant stars in human life spans. I for one am hoping it's the case but I just don't buy it.
Also it seems to me this affects the issue of speed. Speed is a measure of distance covered in an amount of time. From the refference of the two earths in my example that ship traveling a.99 c covers 7 light years in a little over 7 years. By the frame of reffernce of the ship it covers 7 light years in.7 years. How fast was the ship traveling? If you figure the speed as distance covered over time from the frame of reffernce of the ship you arrive at a value far exceeding c ( roughly 7 * c actually ) which we just agreed is impossible.
Which frame of refference wins ?
In fact from the ships perspective you don't have to reach high percentages of LS for your speed to be determined as exceeding LS from the ships frame of refference. What is the dilation at 50% c ? No matter what the dilation effect is it will wind up in the ships frame of reffrence indicating it covered 7 light years worth of distance ( from the frame of reffernce of the earth ) before 7 years passed by the ships frame of reffernce which means it exceeded light speed by its refference. The same holds true for ANY clock running slower ( ie is accelerated) than a ( relatively ) fixed refference ( actually just slower ) clock used for defineing LS.
SO either LS is variable or distance shortens the faster you go.. IE the ship at.99 only covered.99 of.7 light years worth of distance even though from the frame of reffernce of the earth it covered 7 light years thereby not violating c from either perspective.
Of course the other possibility is that the trip took 7+ years and the twins show no difference in their ages whatever the clocks show.
"The primary goal for computer simulations such as these are to understand how and why they don't work - not to test current theories."
And yet current theory is what has to be used to set up the simulation.
Theories in use here include
Creation theory, the big bang Theory regarding the age of the universe Theory of the mass of the universe theory of interaction of masses based on gravity
If your not testing current theories then there is no point to the simulation as it won't tell you anything. IE the simulation is either going to disproove current theory or support current theory. IE its not right so how to we change it to match theory, or how to we change theory to match the results. FInally how do you change both to match observations such as was the case with creating a model that would experience field reversal.
Simulation is ultimately about testing our understanding. ie if we can't simulate it well we don't understand it well. However the ability to attempt to simulate something is inherrently limited by our understanding of what we are attempting to simulate. This goes for negative ( keep changing the simulation till it matches observation ) testing as well.
It just seems silly to me to attempt a N = 10 billion problem when we can't solve an N = ~70 ( roughly known objects in the solar system ) even though we have far better observations of the solar system to work with than we do of the universe at large.
Even presuming to pick a starting point of 340k years after the big bang is arbitrary as the exact age of the universe will likely always remain open to debate. Even the most popular theory and observations have a huge margin of error a great deal larger than 340k years.
I think this excercise would be better served by say using 10 billion points distributed in a solar system model to attempt to create a predictive model of the solar system.
After all the same forces are at work at both levels according to theory and we have much better observational abilities with regards to the solar system for tweaking the simulation till it accurately reflects reality.
I am not sure I follow you on transmitting information backwards in time. What we observe in the night sky is from the past but does not represent current time/locations for what we see ( unless you extrapolate based on your observations for how far away the object is... and your extrapolations are limited in acuracy by the N > 2 problem ).
If gravity is instentaneous then it would allow for concurrent communication even though our observations based on light transmission would indicate what we are communicating with would be in the past.
For example lets say around Alpha centauri you have a parallel earth. Identical and concurrent to our own. Being some 7 (if memory serves) light years away however all our observations would be from 7 years ago. Thus recievced radio transmisions would be from 1997. However this would not indicate the current time on the parallel earth. If we were recieving transmissions from 1997 that would indicate that it was presently 2004 due to the time it would take for the transmissions to reach us.
At the parallel earth they would in return observe us circa 1997 as our transmissions to them would experience a similar delay.
Now due to lightspeed this means any communcations would face a 7 year one way delay and a 14 year round trip delay. Not very practical to say the least. Instant communications would not be communicating with the past but instead would be communicating with the present even though all our other observations would be from 'the past'.
On a side note it is this reason I have always had trouble with the whole time dilation effect of light speed. In that same example if you left here in a ship traveling at light speed you would arrive on the parallel earth in 7 years time, or in the year 2011 on both planets. Its 2004 there now and in seven years you would be there in 2011. Many people seem to think you would get there in 2004.
If you have twins, one set here and one set there where one makes the trip then according to relativity the twin that makes the trip will be the same age as when they left thus from their perspective making the trip instantly while 7 years would pass for the twins that remained on their respective planets.
In the end the practical answer to the time dilation effect is how much food you need for the above example trip. My guess is if time dilation is correct then you don't need it, however if its wrong you had better have 7 years worth of twinkies for that trip and expect to be 7 years older when you arrive no matter what Einstien says. ( historical side note, the venerable ex-suisse patent clerk had his doubts about the dilation effect late in his life )
Also as a side effect during the trip in the parallel earth example you could watch 14 years of tv in fast forward during your 7 year trip as you would be encountering the signals at 2X LS in transit. Also another funny would be that you would arrive shortly after the anouncement of your launch as you would be keeping pace with all the other information that occurs after you leave.
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. Also there would then be no theoretical limit to our observation. Supernovas when they happen instead of when they can be observed for instance.
But its not prooven yet. If memory serves the argument against those observation has something to do with in a stable system its very hard to distinguish the difference and the only real way to test it is to induce a change at a significant distance and measure when it occurs. This is very difficult with the limitation of lightspeed communication. Could be talking out of my ass though. Has been known to happen.
I can see where just wanting to know the density distribution would be good information. Seems on a smaller scale this is critical information for figuring out how a solar system forms and on larger scales how galaxies form.
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 make generelizations. Bigger the scale gets the more accurate your generalizations can get....
However, considering the same forces are at work both in the planetary system and the universe at large why would you use the results from one method that could not also be used for the other? To me that seems to be a case of not allowing observations interfere with theory.
A perfect understanding of gravity would allow a system of equations that would predict both pieces of information equally well I should think. An imperfect understanding can only yield an imperfect answer. Nothings perfect but it seems to me there is no way currently to get this one out to any significant digits before you loose touch with reality.
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.
Last I heard there was some question as to the speed of gravitational attraction. IE if the effect of gravity is only as fast as that of light then the earth is being acted on by the gravity from the point the sun was at 8 minutes ago or some such while the sun is similarly being affected by the earths poistion from 8 minutes ago.
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.
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.
Slashdot Mirror
Moore isn't swinging anybody, least not from my perspective. People who are against Bush come out of it raving against Bush, People For Bush come out Raving against Moore.
You don't swing votes with extreme views/bias, you swing votes with compromise. People interested in getting info that I know come out of 9-11 at best with a list of facts to check and veriffy. If anything finding some of the better examples of poor context is enough to turn them fairly sour on Moore but still has no effect on their opnion regarding the election.
In other words people that are actually seraching for information to be swayed by are generally smart enough to dismiss the bias and take the valid issues under consideration. The poor schlubs that can't think for themselves had their minds made up before they ever bought a ticket.
This is not an issue... or I should say that it is a non-issue in light of the overwhelming role already played by media coverage regarding politics. On the other hand not allowing it (given a willing station) is more of an issue to me as that is a potential encroachment on free speach. To me not allowing it because it might have an undue influence on the election would be no different than saying someone could not publish a book because it might have undue influence on the election.
Pretty loose deffinition of civil war. In truth it was more successfull rebellion than anything. America was not a fully integrated component of English government.. which was part of the problem. Of course given transportation of the day they COULDN'T but thats another issue entirely.
Also, calling the Boston Tea Party an act of terrorisim is pretty out there. Dumping the tea into the harbor was more symbolic than anything. And hardly in the same class as a hijacking or suicide bomber.
ROFL
I am kinda torn on the issue of them being blown away being a good thing. If I were positive the response would be to build a replacement capacity ASAP it would deffiantly be a good thing. If it were not then it would be better to have something rather than nothing.
There been any news on the new Delta varient that was sitting out on the pad yet ?
Gracias. Interesting stuff. I have never really had a problem with relativity per say, just some of the logical difficulties its properties present.
Time dialtion is of course one of the biggest. I have never questioned the fact there is an effect. Like I said we have observed the effect and use technology that depends on it to function properly.
HOWEVER, Just because an observed effect that can be predicted and used to perform mathmatic opeartions does not mean we actually understand it. The best example I know of this is the Ptolemaic system of explaining the motions of the planets. It worked from the premise the earth was the center and mathmatically worked just fine, and still does for that matter. Dosn't make it any more right in the end.
Perhaps Einstien nailed it. Or perhaps he is just a damn smart guy that did what he could with what was available to him. He himself said he felt like he was a kid in a gigantic library and he had managed to decipher one page of one book. Would be nice if more people felt the same.
I'm sure all your numbers are fine and dandy but they are most assuredly by the book.
I am not saying that by the book is not good.
I am saying given a good enough reason they could expedite the process.
The thing about rules and guidelines is knowing when to break them.
The thing about costs is knowing when they matter.
Worrying about 1 million when talking about billions of invested worth irreplaceapbe euipment is being placed at risk is asinine. It is a non issue. The important thing is assessing the risks and evaluating your options.
Now. having said that its very possible that leaving them was the safest possible thing to do. IE the risk in leaving them was far less than the risk of attempting to move them hastily. But that is not the impression the stories have been giving. Perhaps they have been over dramatized but it seems there was real concern that given a cat 4 storm there wouldn't be much left.
As I said in another post... the launch infrastructure is far far far more replaceable than the orbiters.
Will do that, have run across it in bits and peieces. Don't really have the math chops to really dig into it.
Though on length contraction that only happens from the ships frame of refference does it not? Meaning (unless I am really wrong) that the length does not contract for earths frame of refference.
So what I am saying still holds. It's a case of semantics really. If I understand it right then from the ships perspective the 'mile markers' would no longer mean the same thing. They are the same distance apart but what comprises that distance for earths frame of reffference and for the ships frame of reffernce are two different things.
But you are still passing them at greater than light speed if you use the ships clock in reffernce to distance covered by earths frame of refference to determine how fast you are going.
Its not that you break c. Its the fact your using non-relativistic math.
I'm sorry but a hasty departure would be prefferable to a destroyed orbiter. They can get that thing on the plane and out of there faster than a week. Now would likely incurr a lot of extra time and effort picking up where they left off on the work though but I hate it when people take nominal operating times and assume it is the best that could be done.
Da got that bit was just saying its weird.
.7 years = 10X the speed of light.
.7 years older. Just that by the combined frame of refference thats how fast you were going.
.99 c but you look out the window and the markers are flashing by at an insane rate.
.35 years on the ships clock you pass the half way point of your trip.
.35 years. how fast are you going ?
Anyway you slice it you still seem to break c if you choose differnt perspectives. I very particularly said "seem to" there so don't jump on it as impossible.
distance/time = speed.
example 100 miles covered in 2 hours = 50 mph
From any single perspective you can make sure speed never breaks c. However if you mix refferences then you come back with speeds greater than c. And mixing refferences is pretty common. After all relativity affects you traveling on the highway and in the air when flying. Just at such small levels you can ignore it but your still measuring your travel based on a frame of reffernce other than your own.. IE highways with mile markers and rest stops. but technically from your frame of reffernce distance is getting shorter the faster your going and time is passing slower or faster (depending on direction of tavel) but you mark speed based on the other frame of reffernce. Speed up the car fast enough and the differnce becomes more and more pronounced until you have to come up with some other way of dealing with it.
Distance from Earth refference/ Time from the ships reffernce = a speed greater than c.
For example
7 light years covered in
not saying 7 years didn't pass at either end and that your only
Lets return to the two earth examples and instead of a featureless trip through the void lets say its got mile markers laid down and a half way point . From your frame of reffernce on the ship your clock slows down ( not that you notice it.. seems fine to you ) Your speedometer indicates
Now all discussions about what looking out your window will actually be like you can't escape a very basic issue. With time dilation, at
Now You climb into your car for a trip that covers 100 miles and you pass the halfway marker at 1 hour of travel.. how fast are you going ?
You climb into your space ship for a trip of 7 light years and pass the halfway marker at
Now relativity and in particular time dilation is more or less established. Anyone that uses GPS uses its principles to a fairtheewell whether they realize it or not.
Now if distance shortens from that ships perspective then its no wonder you can't exceed c becasue if you reach c all distance goes to zero and time stands still. Thus to travel at c is to travel through all points simultaneously because no matter where your traveling to or from it takes 0 time to get there and you didn't cover any distance because you didn't take time to go from point a to point b.
Now is that the case or is it just a case where you wind up with division by zero because the clock stopped? After all it would still take a radio signal from alpha centauri ~7years to get here and thats hardly instentaneously whatever the radio signal itself thinks.
In other words I am not really questioning relativity so much as our explinations of it with incompelte concepts that don't seem to apply once relativistic effects become aparant like speed/distance and time... at least do not apply as we generally understand them.
However, that understanding is key to manned deep space travel. Me I don't give a rats ass if time dilates or you can break c as either allows you to do the same thing. Go farther than you would think reasonable with newtonian physics limited by c for your speed of travel.
a 14 year round trip to alpha centauri is a difficult proposal
a 1.4 year round trip to alpha centauri ( regarless of 14 years passing here ) is much more doable.
The potential exists in fusion power plants to reach
Thats assuming time dialation is correct.
Why wouldn't they add up.. remember I am sorta suggesting that time dosn't slow down. So increase mass would lead to the longer decay time. Should add up nicely.
Course it dosn't work. After all we have the cesium clocks running GPS to atest to that. Seems they wind slower, but man its weird.
Not many internships currently that I am aware of but if your really interested look out on www.nasa.gov and go to the primary contractors and look for jobs in Huntsvile/Houston etc... ( Boeing, Lockheed ). Now is not the best time for space jobs though, I'd check back after they decide about Shuttle.
Agreed that you don't need %100 realisim for good results. However you have to maintain some relationship/corelation with reality for the information derrived here to be much use in determining the early formation process of the universe. So whats a strong enough correlation ? 90%, 50%.. 10% ? And I am not reffering to exact replication here, just correlation to realisitc application of the same forces to the chosen mass points.
The process they are using seems to have an awful lot of room for loosing statisticly significant information due to the error of the process. So in the end it seems to me the density distribution ( which is what they are after ) is going to be ruled by the error inherrent in the problem rather than the rules of gravity as we understand them and they are atempting to apply them.
That make sense ?
I will have to look more into weather simulations but my understanding is that models for them have been improoving due to the applications of chaotic principles in attempting to simulate them. The methods for this problem are pretty simple and through the years have been all about limiting the chaotic influences so it seems a bit of apples and oranges to me.
Hell, i've been out of my depth for a while. I am a poly sci grad with a comp sci minor and a serious jones for space science of any kind ( also work at MSFC in the ISS POIC... translation, marshall space flight center where they do space station payload ops.. don't ask how I still don't know myself ).
.0003 of that mass. Also that .0003 is split into 10 billion equal masses.. and to give you an idea of the scale it would only take a handfull of them to equal the amound of mass that is in the milkyway, some of the other posts have argued about just how many.
Anyway Hubble calculated a mass of the universe that is fairly widely accepted, the model is using an amount that totals up to about
In other words all I said was since your starting from coarse information so you can only expect to derive similarly coarse results.
We only know so much about the origins of the universe. However in a model like this that informatin is fairly critical to creating a usefull model.
You could tweak those values untill you started seeing the results you expected.. ie density distributions that resemble what we have observed and inffer that those values have some realition ship with the real values at that point in time given your model of interaction works.
Except for the problem of the n-body problem. Just doing the basic sumation of the affect of all 9,999,999,999 particles on each other individual paticle does not allow for the chaos that is inherrent in the n-body problem. IE those interactions go to hell in a hand basket pretty quick without some pretty niffty allowances based on observation. Meaning they DON'T reflect realistic interactions over time which means you don't get realistic results when using it, coarse or otherwise.
as for the weather models...
I belive weather models face a similar problem. You can guess realistic weather based on current measurements for a few days. You can guess seasonal trends for a few years but again as you attempt to model longer periods of time instability creeps in and disacociates the results with reality.
wasn't really suggesting they are after an accurate model. ( meaning an exact replication of the creation of the universe )
.0003 of the hubble mass divided into 10 billion points they create a limit to their accuracy right there.
The ability to solve n-body aside they are limited in accuracy to what they know about the begining conditions and the ability to account for all mass at as close to the atomic scale as possible. By using
My ultimate issue is they ARE using the n-body problem. As you just pointed out if you could solve it then it would be fantastic.. just plug and chug. But we can't so I don't see how this is supposed to even lead to a coarse model for understanding how the system behaves. IE if the coarse model dosn't behave roughly like the system you can't derive trends from it.... its just chaos inherrent in the method * inherrent error of the the unknown factors of the begining of the universe compounded over billions of years worth of modeling the 10 billion points interactions which equals nothing relavent to reality.
I guess another way of putting it is it seems they are trying to walk before they crawl, run before they walk etc...
Though perhaps they are not. I am trying to get a practical assesment of the longer duration sims of the solar system. They all talk about exponential chaos and repetitive aberations but not what it means in terms of where the planets go in their models... though some of the graphs look damn funky.
Thanks for taking the time to respond. Everyone who has has given me a great deal of info to digest.
I earased.. or put in another comment where I was thinking if c remains constant from both perspectives then both time and distance have to be relative... ie the shortening of the distance to keep c constant from both frames of refference.
So time and distance are relative while c remains constant.
as the rate of time goes to zero distance does as well.
Interesting.
Have to noodle on the pion experiment. That is fascinating.
freaky too.
So we know the speed of light, we know the speed we acclerate the pions to, we know the rate of decay thus you only have two options left.
1) Distance is shorter.
2) The decay rate is lower at high speeds.
How do we eliminate the possibility that elements decay rates are tied to time and not to their speed... or more specifically to their mass. After all dosn't mass increase with speed and could not greater mass have a stabilizing effect at the atomic level thus slowing the rate of decay ?
Ok I am just thinking out loud now....
*mumble*
* I belive you took my stapler....... I could set the building on fire*
thanks for the link.
First part was just saying that if you have an equation with a known solution ( observations of the known universe ) and a whole buch of unknowns that lead to that solution then you can just plug in what you want so long as the end result matches the known solution. Or in the case the mix of knowns and unknowns matches the same form of the known solution.
Dosn't mean any values that work are the 'right' values though.
For instance we know clusters form, we know galaxies form, we know nebulas form.... thus any simulation using values that do not lead to similar structures ( in so much as the sample size allows ) needs work.
well in that case it seems there are an infinate set of possibilities which you can manipulate at will to answer the known solution.
ie
x + y = known quantity has any number of solutions ( though in this case more like a + b.... + zz = kq )
we can narrow down the range of solutions with ranges for what we do know about the unknown variables.... ok ok I see a bit more of the big picture now.
One nit I can't resist though
"I wasn't talking about the issues of simulating them"
but this whole thing is about a simulation!!!
Thanks for the info on Sussman and Wisdom, will have to look into that more. Out of curiosity did they extrapolate backwards ? Check their accuracy by comparing to known observations of the past ? Or just predict into the future? Eh probably answer my own question.
Thanks for the info.
However I have to say from reading the article it still seems to me this is not what they are doing. Could just be due to an oversimplification by the article. It seems to me they just said they were assigning a given energy level based on the amount of background radiation back at the point it started then iterating ( and using various shortcuts ) to then calculate each individual mass points affect on all 9,999,999,999 other mass points over time based on Keplers laws. In other words at its most basic it is a n-body simulation where n=10,000,000,000
Is it just over simplified ? That alone is a crapload of calculations, I would hate to have to figure out how to deal with a softening factor.
but what of when you mix the frames of reffernces ?
.99 c then why am I not eating for 7 years while watching an object 7 light years away approach at .99 c ? By this explination I would watch it approach at .99 c for .7 years at which point I would be there. Again for the frame of refference of the ship you cover 7 light years in under one year. That is faster than c.
.7 years it stands to reason I would see it revolve around its orbit a little over 14 times to account for their frame of reffernce being 7+ years. Thus we once again exceed c and reach the issue of mixed frames of refference once again.
.7 years duration for these 14 revolutions then it should appear speeded up, ie time is moving faster for it than for me which would also seem to imply I would percieve it approaching at faster than .99 c.
.7 years during the trip.
.99 c for your .7 years frame of refference for the duration of your trip. Even if your frame of refference is of 7 years you would still see 14 orbits. The question is just how long it would take you to observe them.
By the way I am not being argumentative, and not intentionally trying to be stubborn, just have never had this adequately explained and I really want to understand it. It has always seemed to me something dependent upon choosing the right frames of refference, or more specifically a single frame of refference.
So if the frame of refference of the ship is earth 2 approaching at
Lets go further, earth 2 also has the same orbital period. If I reach it in
If I watch it revolve 14 times and yet my frame of reffernce is of
again this perception of exceeding c applies only if your frame of reffernce is for
You would HAVE to see it orbit 14 times... you start in the hole seeing what happend 7 years ago so its already orbited 7 times that you have yet to observe and by the time you get there it will have orbtied 7 more times to account for their frame of reffernce being 7 years so you would see it orbit 14 times while apporaching at
"Of course, we can solve solar-system dynamics. The number of particles isn't the problem. The issue is that we can measure solar system dynamics very precisely, so we have to carry out the simulation at high accuracy to match observations. We can measure the large-scale structure of the universe only coarsely, so the simulations don't have to be as precise, although they do need to have many more particles."
I think you miss my point. We can indeed make systems that model what we observe in the solar system accurately. However we cannot do so based on the interaction of gravitational atraction of the known masses in the solar system. Systems that attempt to do so invariably devlove into chaos that have no ressemblence to reality.
I keep re-iterating this point becasue this is what they are doing. Essentially they are calculating the effect of each mass point on all 9,999,999,999 other points over time given intial energy as determined by the amount of cosmic background radiation extrapolated back to 380k years after the big bang give or take 8k years. We can't make these kinds of equations reflect the observed reality of the solar system. Why would it reflect reality regarding early universe structure ?
As for what you would model with 10 billion points in the solar system ?
How about having more than one particle representing a single celestial body? Perhaps you have heard of tidal forces where one side of a body is more strongly attracted than the other ? MIght 10 billion particles split into even masses then distributed through those 100 known in proportion lead to higher acurracy in modeling gravitys effect in the solar system ? Then better understanding the interactions on a micro scale you just might be able to translate that into a better understanding of how they interact on a macro scale.
"Besides, the point of the "exercise" was to understand the formation of large-scale structure in the early universe. Studying solar-system dynamics doesn't tell us anything about that."
And yet again I stress that the forces at work in both are presumed to be identical. So equations that can model the large scale structure formation of the universe should also work for solar system dynamics. The scale is different not the equations.
If the forces at work are indeed the SAME them then the issues of simulating them are by no means orthogonal.
I Understand you can't reach LS, was just using the easiest example. But even in that case, even considering H&K's flying clocks I still ask how much food you pack for the trip.. do I pack for .7 years or 7 years?
.99 c covers 7 light years in a little over 7 years. By the frame of reffernce of the ship it covers 7 light years in .7 years. How fast was the ship traveling? If you figure the speed as distance covered over time from the frame of reffernce of the ship you arrive at a value far exceeding c ( roughly 7 * c actually ) which we just agreed is impossible.
.99 only covered .99 of .7 light years worth of distance even though from the frame of reffernce of the earth it covered 7 light years thereby not violating c from either perspective.
Its a very practical concern and also holds the key to distant travel in the universe. If time approaches 0 as you approach LS then high percentages of LS could lead to travel to distant stars in human life spans. I for one am hoping it's the case but I just don't buy it.
Also it seems to me this affects the issue of speed. Speed is a measure of distance covered in an amount of time. From the refference of the two earths in my example that ship traveling a
Which frame of refference wins ?
In fact from the ships perspective you don't have to reach high percentages of LS for your speed to be determined as exceeding LS from the ships frame of refference. What is the dilation at 50% c ? No matter what the dilation effect is it will wind up in the ships frame of reffrence indicating it covered 7 light years worth of distance ( from the frame of reffernce of the earth ) before 7 years passed by the ships frame of reffernce which means it exceeded light speed by its refference. The same holds true for ANY clock running slower ( ie is accelerated) than a ( relatively ) fixed refference ( actually just slower ) clock used for defineing LS.
SO either LS is variable or distance shortens the faster you go.. IE the ship at
Of course the other possibility is that the trip took 7+ years and the twins show no difference in their ages whatever the clocks show.
"The primary goal for computer simulations such as these are to understand how and why they don't work - not to test current theories."
And yet current theory is what has to be used to set up the simulation.
Theories in use here include
Creation theory, the big bang
Theory regarding the age of the universe
Theory of the mass of the universe
theory of interaction of masses based on gravity
If your not testing current theories then there is no point to the simulation as it won't tell you anything. IE the simulation is either going to disproove current theory or support current theory. IE its not right so how to we change it to match theory, or how to we change theory to match the results. FInally how do you change both to match observations such as was the case with creating a model that would experience field reversal.
Simulation is ultimately about testing our understanding. ie if we can't simulate it well we don't understand it well. However the ability to attempt to simulate something is inherrently limited by our understanding of what we are attempting to simulate. This goes for negative ( keep changing the simulation till it matches observation ) testing as well.
It just seems silly to me to attempt a N = 10 billion problem when we can't solve an N = ~70 ( roughly known objects in the solar system ) even though we have far better observations of the solar system to work with than we do of the universe at large.
Even presuming to pick a starting point of 340k years after the big bang is arbitrary as the exact age of the universe will likely always remain open to debate. Even the most popular theory and observations have a huge margin of error a great deal larger than 340k years.
I think this excercise would be better served by say using 10 billion points distributed in a solar system model to attempt to create a predictive model of the solar system.
After all the same forces are at work at both levels according to theory and we have much better observational abilities with regards to the solar system for tweaking the simulation till it accurately reflects reality.
I am not sure I follow you on transmitting information backwards in time. What we observe in the night sky is from the past but does not represent current time/locations for what we see ( unless you extrapolate based on your observations for how far away the object is... and your extrapolations are limited in acuracy by the N > 2 problem ).
If gravity is instentaneous then it would allow for concurrent communication even though our observations based on light transmission would indicate what we are communicating with would be in the past.
For example lets say around Alpha centauri you have a parallel earth. Identical and concurrent to our own. Being some 7 (if memory serves) light years away however all our observations would be from 7 years ago. Thus recievced radio transmisions would be from 1997. However this would not indicate the current time on the parallel earth. If we were recieving transmissions from 1997 that would indicate that it was presently 2004 due to the time it would take for the transmissions to reach us.
At the parallel earth they would in return observe us circa 1997 as our transmissions to them would experience a similar delay.
Now due to lightspeed this means any communcations would face a 7 year one way delay and a 14 year round trip delay. Not very practical to say the least. Instant communications would not be communicating with the past but instead would be communicating with the present even though all our other observations would be from 'the past'.
On a side note it is this reason I have always had trouble with the whole time dilation effect of light speed. In that same example if you left here in a ship traveling at light speed you would arrive on the parallel earth in 7 years time, or in the year 2011 on both planets. Its 2004 there now and in seven years you would be there in 2011. Many people seem to think you would get there in 2004.
If you have twins, one set here and one set there where one makes the trip then according to relativity the twin that makes the trip will be the same age as when they left thus from their perspective making the trip instantly while 7 years would pass for the twins that remained on their respective planets.
In the end the practical answer to the time dilation effect is how much food you need for the above example trip. My guess is if time dilation is correct then you don't need it, however if its wrong you had better have 7 years worth of twinkies for that trip and expect to be 7 years older when you arrive no matter what Einstien says. ( historical side note, the venerable ex-suisse patent clerk had his doubts about the dilation effect late in his life )
Also as a side effect during the trip in the parallel earth example you could watch 14 years of tv in fast forward during your 7 year trip as you would be encountering the signals at 2X LS in transit. Also another funny would be that you would arrive shortly after the anouncement of your launch as you would be keeping pace with all the other information that occurs after you leave.
I have heard of that as well.
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. Also there would then be no theoretical limit to our observation. Supernovas when they happen instead of when they can be observed for instance.
But its not prooven yet. If memory serves the argument against those observation has something to do with in a stable system its very hard to distinguish the difference and the only real way to test it is to induce a change at a significant distance and measure when it occurs. This is very difficult with the limitation of lightspeed communication. Could be talking out of my ass though. Has been known to happen.
I can see where just wanting to know the density distribution would be good information. Seems on a smaller scale this is critical information for figuring out how a solar system forms and on larger scales how galaxies form.
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 make generelizations. Bigger the scale gets the more accurate your generalizations can get....
However, considering the same forces are at work both in the planetary system and the universe at large why would you use the results from one method that could not also be used for the other? To me that seems to be a case of not allowing observations interfere with theory.
A perfect understanding of gravity would allow a system of equations that would predict both pieces of information equally well I should think. An imperfect understanding can only yield an imperfect answer. Nothings perfect but it seems to me there is no way currently to get this one out to any significant digits before you loose touch with reality.
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.
Last I heard there was some question as to the speed of gravitational attraction. IE if the effect of gravity is only as fast as that of light then the earth is being acted on by the gravity from the point the sun was at 8 minutes ago or some such while the sun is similarly being affected by the earths poistion from 8 minutes ago.
s /NCOR.11.16.D/display.html
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.