Scientists Expand Knowledge of Dark Matter

nife00 writes "BBC News is reporting that British scientists at Cambridge have expanded the current understanding of the mysterious particles known as dark matter." According to the article: "[The Cambridge Team] has at last been able to place limits on how it is packed in space and measure its "temperature". "It's the first clue of what this stuff might be," said Professor Gerry Gilmore. "For the first time ever, we're actually dealing with its physics," he told the BBC News website."

Comments

How appropriate...

[Jugalator]

I just got this when first clicking on this article...

Nothing for you to see here. Please move along.

:-p

Uncertainty

[helioquake]

Give me the sensible error bar estimate on the mass, if they want to be scientific about it.

Re:Uncertainty

[drgonzo59]

They did, but it is very dark and hard to see.

Re:Uncertainty

[LiquidCoooled]

Holly: Well, the thing about a black hole - it's main distinguishing feature - is it's black. And the thing about space, your basic space colour is black. So how are you supposed to see them?

Re:Uncertainty

[MarkChovain]

The sensible error bar estimate on the "squad" is overrated. Give me the next launch that's going somewhere less terminal?

Re:Uncertainty

[GeekyMike]

ROFL, I love Red Dwarf

Just another point of view

[erroneus]

http://science.slashdot.org/article.pl?sid=06/01/2 5/1436243 -- This article points to the idea that there is no such thing as dark matter and explains everything with gravity. Now we're back to dark matter again? I still like science and all that but there are people who don't understand that "we don't really know everything" and that science as we know it today is merely an attempt at forming an understanding of our universe, not a definite mapping.

Re:Just another point of view

[drgonzo59]

I was actually wondering, could it be the case that we might not even be able to understand and explain some phonemena simply because our brain power is not adequate. For example the math works out for QM, but I don't think anyone can understand or conceptualize what is happening during entanglement (Einstein called it "spooky action at a distance" and never quite got to accept it).

Or when someone is talking about multi-dimensional spaces, it is easy to express it in a mathemtical form (R^6 or C^6), but what does that mean in reality, how would you think about such a space?

(Speaking of the 6 dimensions, there was an article on Slashdot about how the dark matter doesn't exist but instead we see what we do because "space has 6 dimensions".here.)

The point is that, just like dogs will never be able to solve integrals with the brain power they have now, so humans likewise might not be capable of understanding certain phenomena from the physical universe we live in.

Re:Just another point of view

[Beryllium Sphere(tm)]

That article dealt with only one kind of observation, namely how fast stars orbit the center of a galaxy.

Dark matter theory would be on pretty tenuous ground if it only explained one kind of observation.

There are features of the light from the Big Bang that are tough to explain without dark matter. The relative abundance of various nuclear isotopes is a sensitive gauge of conditions during the Big Bang, and again dark matter is the closest thing we have to an explanation.

>science as we know it today is merely an attempt at forming an understanding of our universe, not a definite mapping.

Isn't that the fun of it? My wife had a professor who always looked upward when he dropped a piece of chalk. He explained that we don't have real proof that gravity will always work, just an assumption that it will work like it always has, and if the chalk ever fell upward he sure didn't want to miss the event.

Oh, and that paper about explaining orbital motions without dark matter may have been mistaken in its methods. People who know more than we at Slashdot do have pointed out what they consider fatal flaws.

Re:Just another point of view

[meringuoid]

I was actually wondering, could it be the case that we might not even be able to understand and explain some phonemena simply because our brain power is not adequate. For example the math works out for QM, but I don't think anyone can understand or conceptualize what is happening during entanglement (Einstein called it "spooky action at a distance" and never quite got to accept it). Or when someone is talking about multi-dimensional spaces, it is easy to express it in a mathemtical form (R^6 or C^6), but what does that mean in reality, how would you think about such a space?

You needn't go off with such physical exotica as QM and multidimensional spaces. Conceptually they're weird, but they're relatively simple mathematically. Indeed, that's the great value of such mathematics: it gives us the language with which to accurately describe the unimaginable.

For a problem that seems to be truly beyond human intelligence, try turbulence. The mathematics to describe laminar fluid flows are well developed and understood, have been for centuries... but nobody has got the hang of turbulent flow. Even with supercomputer numerical simulations, you can only get so far. Proper modelling of turbulence has baffled the best minds for hundreds of years, and still we're not really any closer.

Re:Just another point of view

[smitingpurpleemu]

The main problem with string theory right now is that it needs extra dimensions to make it work, but those extra dimensions can't be observed, which means that the theory can't be tested. Until the physicists somehow figure out how the extra dimensions reduce to our familiar 4-space, string theory will remain in its current state; as a somewhat fringe theory that has the potential to explain everything, but doesn't. The fact that there are N dimensions (N>4, this number is changing as more research is done) in string theory isn't our fault; it's string theory's fault, b/c we can only observe 4 dimensions, so that's all we can work with in the real world.

Re:Just another point of view

[S3D]

Proper modelling of turbulence has baffled the best minds for hundreds of years, and still we're not really any closer.

We are considerably closer. The conceptual mechanism of turbulence is more understood now - it seems that turbulence is caused by finite-dimentional strange attractors in phase space (good news because navier-stocks equations phase-space is infinetly-dimentional). The bad news is that strange attractors inherintly unstable in numeric simulations and amount of calculation grow exponentially with simulation time.

Re:Just another point of view

[jdoire]

Two days there was an article that said that "Time Has a Geometry" which seems to explain a lot of the unexplained stuff with a relatively small extention to the relativity equations. Among other things, the red shift that is used to measure distances in the universe was mis-calculated, and when the new theory is used, the dark matter and dark energy is no longer needed.

Check page 5 for a list of what among other things is affected:
http://www.stanford.edu/~afmayer/docs/Lecture2Sign ed.pdf

The main page is at:
http://science.slashdot.org/article.pl?sid=06/02/0 5/006254

If what he says proves to be correct, a lot of books will need to be re-written.

Re:Just another point of view

[killjoe]

It is said that on his deathbed Neils Bohr said "when I die, I am going ask god about relativity and turbulence. I think he can tell me something about relativity".

Re:Just another point of view

[aussie_a]

If you mean turbulence, as in what planes experience when flying, wouldn't that be a case of too many variables? We're unable to predict the weather with 100% certainty because of the too many variable problem. Wouldn't turbulence be the same? Sure there'd be less variables, but surely there'd still be too many for current maths/computers at the present?

Re:Just another point of view

[jeffs72]

Sorry to be a stickler, but you're talking about one of my relatives :)

That's Navier-Stokes

Re:Just another point of view

[TapeCutter]

"could it be the case that we might not even be able to understand and explain some phonemena simply because our brain power is not adequate."

Godel has already shown that no system of description is adequate, this is independant of of the amount of brain power on hand (or in head). People often wonder why maths is so good at describing the Universe, I belive it is because it is actually describing the model used by the brain to create the illusion of "I". ie: The simulated Universe containing the simulated self we all carry around in our heads. The "physical universe we live in" is an illusion.

A favourite quote from the above link: Although this theorem can be stated and proved in a rigorously mathematical way, what it seems to say is that rational thought can never penetrate to the final ultimate truth ... But, paradoxically, to understand Gödel's proof is to find a sort of liberation. For many logic students, the final breakthrough to full understanding of the Incompleteness Theorem is practically a conversion experience. This is partly a by-product of the potent mystique Gödel's name carries. But, more profoundly, to understand the essentially labyrinthine nature of the castle is, somehow, to be free of it.

I find the quote interesting because it relates a similar experience to religious conversion, ie: acceptance of the unknowable.

Re:Just another point of view

[character sequence]

Scientists theorised for quite a long time that light was transmitted through a medium called the "aether" which supposedly filled the "vacuum" of space. They had no actual evidence of its existence, they invented it for convenience because their theories were inadequate. I guess that's just human (scientific) nature. I suspect dark matter will one day go the way of the aether as well.

Re:Just another point of view

[Patrik_AKA_RedX]

I don't think that weatherprediction is just an issue with the number of variables. More an issue with how each of the variables influences the others. You can't really apply a divide and conquer strategy on such systems without making a significant error. Take the ideal gas law. It started with a number of laws in which two parameters of a volume of gas were considered. (the others were kept constant). These laws were brought together as a single law (ideal gas law, which approximated the behaviour of hydrogin gas at a very high temperature and very low pressure) and later this law received a number of correction factors for it to work correctly with real life gasses. I believe weather prediction would follow a similar, but much more complicated, traject. Starting with explaining the elements of weather, e.g. wind, temperature, rain, ... and then combining the theories and correcting them to hold up for real weather.

Re:Just another point of view

[awol]

I was actually wondering, could it be the case that we might not even be able to understand and explain some phonemena simply because our brain power is not adequate.

Absolutely. To detect something one must have a tool of finer resolution than the thing itself. By corollary to understand something must one have a tool that has a "finer" resolution? I believe that one cannot understand things like entanglement with a lump of tissue (ones brain) that does not itself have the capacity to make use of entanglement (or the like) itself. As such there are things that are beyond the resolution of our reasoning organ.

What is kind of exciting is the idea that we might build a machine that is not so limited to harvest the impact of these incomprehensible quantum events. Much like we have build machines to exceed the mechanical limits of our physical bodies (cars, cranes, planes etc). It will be weird though when we start to rely on machines that are using results that the machines cannot explain to us because our brains are inadequate.

Re:Just another point of view

[Starker_Kull]

In a sense, you are right, but It's worse than that. In all the other cases, we have models of the phenomenon that (in many cases) are partially derived from second principles (the gas laws, Navier-Stokes equations, etc.). Unfortunately, turbulence in a fluid flow is apparently unamenable to modeling with those laws - they pretend that a fluid is grainless and infinitely divisible (no atoms/molecules), and wrap up the more complex intermolecular forces under the viscosity term. Turbulence (apparently) is fundamentally related to the way individual molecules interact, and we simply don't have models that can handle this in the quantites ( > 10^10 molecules being simulated) required. In other words, we can not predict turbulence in a fluid flow from first principles (intermolecular forces - i.e. quantum interactions); we have an empirical understanding of them only.

As for the turbulence in airplanes, there is some limited prediction done, but it is based on some common sense ideas, such as when the wind direction/speed changes rapidly with a change in either vertical or lateral position, there will tend to be turbulence (such as going from the core of a jet stream to the outside of one).

Re:Just another point of view

[Starker_Kull]

Actually, Godel did no such thing - he demonstrated that in any formal system of logic sufficiently complex to encapsulate basic arithmetic, there will be unprovable statements which are nonetheless true. Note that the reason we can say these unprovable statements are true is because that if they were false, there would exist a provable counterexample to the statement (i.e. an example of the falseness), and thus the statement would not be unprovable - but this knowledge comes from outside the logical system. In other words, he demonstrated that there will be true statements in a logical system that can never be proven within that system to be true; a hypothetical example might be Goldbach's conjecture, that any even number > 4 is the sum of two (not necessarily distinct) primes. If this was, in fact, true, but was somehow "unprovable", we would be left in the uncomfortable position of seeing billions of examples where it is true, not a single example where it was false, but of course there would always be an infinity of cases we didn't check yet. This is, in fact, the present state of our knowledge - and thus why I used it as an example. Of course, some clever egg might stumble upon a proof of Goldbach's conjecture tomorrow - people used to use Fermat's Last Theorem as a potential example of something that might be true but unprovable, until Wiles proved it. This is the problem, that we have no way of knowing what is unprovable in mathematics, because if we did have such a way of "knowing" (i.e. proving that a proposition is unprovable) for a specific proposition, we would have just proven it true, and thus it would not be unprovable! So we will never know what is not provable - we will only suspect that one of Godel's unprovable but true phantasms is staring us in the face.

My point (longwindedly) is that this has little or nothing to do with the physical, mathematically modeled, problems at hand here; if you want a better idea of the type of barrier we are facing in this case, you would be better served by complexity and information theory; look up Shannon and Chaitin for more info - that is the type of problem involved in turbulence simulation, not logical issues of provability and incompleteness.

Re:Just another point of view

[NichG]

I'm following you up to 'grows exponentially with computation time'. You mean that because of the exponential divergence of initial conditions? I suppose it depends on whether you want to extract an exact future system configuration or whether you want statistical information about turbulent flows. Throwing a smaller timestep at it won't make a difference anyhow if its the errorbars in your initial condition that are diverging with the chaotic dynamics, so really for long times the best you can hope for is a statistical description - that is, map out the entire region of phase space where the turbulent flow may lie.

Re:Just another point of view

[brian0918]

Have you really understood anything if the best you can do is write down a huge, abstract equation? (and in General Relativty and Quantum Physics, these equations get very huge/abstract)

Re:Just another point of view

[Capt'n Hector]

*Ahem*. Dogs certainly do know calculus.

Re:Just another point of view

[Starker_Kull]

Well, science has also postulated the existence of the anti-electron (Dirac), electromagnetic waves (Hertz), and missing elements like Eka-aluminum aka Gallium (Mendeleev), all without actual "evidence" for their existence at the time the theories were proposed. Then, once the theories were put out there, people tried experiments to see if the theories' predicitions were true. If they were, great theory! If not? Oh well, that's how it goes. Aether was one of the "that's how it goes" ones, but it wasn't invented because the theories were "inadequate", it was invented because it explained all the evidence accumulated up to that point in a theoretical framework pretty well. One of it's predictions (that the speed of electromagnetic waves would vary depending on the motion of the earth through the aether) turned out to be wrong, (as demonstrated my Michelson and Morley), but until the experiment was done, nobody could have known that! And the implications of that were so shocking and anti-intutitive, that it took an Einstein to boldly speculate that there was no aethereal medium for light waves, but instead our conceptions of time and space were off. There was no actual evidence for mass increases with motion nor length contraction either when Einstein came up with Special Relativity - that came later, after his theory suggested people look for those phenomenia. If experimentalists DIDN'T FIND THEM WHEN THEY LOOKED, then relativity too would have gone into the dustbin. But you can't know that ahead of time.

That's how science works, if it just "explains" (condenses into a few formulae/models) that which has already been observed, it's a bit useless. It HAS to make hypotheses beyond the actual evidence if it is to have any value as a predictive tool - this is why faslfyability is so important. If you can't falsify it, you haven't predicted anything, and therefore it's kinda useless.

BTW, I tend to agree with you about dark matter - it does seem to be awfully omnipresent yet remarkably undetectable. But then again, so is the neutrino! That's the exciting part, we don't know yet. It could still go either way. Wouldn't it be boring otherwise?

Re:Just another point of view

[Starker_Kull]

It's nice to see someone else who gets the idea that science is FUN because we really don't know until we look! While it's great we've figured out quite a bunch, the interesting, fun, fascinating part is the stuff we haven't tested quite yet - that's where the excitement is, and that we can't know a priori what is a good theory and what is not until we do.

Re:Just another point of view

[Mr. Slippery]

I was actually wondering, could it be the case that we might not even be able to understand and explain some phonemena simply because our brain power is not adequate.

It sometimes strikes me that every model of the universe is an instance of lossy compression; it's small enough to fit into the human mind and gives you the gist of what's going on, but data is lost.

Re:Just another point of view

[maxwell demon]

Have you really understood anything if the best you can do is write down a huge, abstract equation?

Yes: Obviously then I've understood the math notation.

Re:Just another point of view

[Lifewish]

Does it matter if you can still derive predictions?

Re:Just another point of view

[radtea]

I find the quote interesting because it relates a similar experience to religious conversion, ie: acceptance of the unknowable.

Godel's theorem says nothing about "unknowability". It is about provability within a consistent axiomatic system.

I know any amount of stuff by means other than proving it within a consistent axiomatic system. I know my name. I know my favourite colour. I know I'm wasting my time trying to explain something on Slashdot.

Likewise, it is perfectly possible to know if a given theorem is true or false within a system of formal logic without being able to prove that theorem. It may be very hard to know in any given case, but nothing in Godel's proof puts an absolute barrier to knowability.

Only people who are confused about the nature of knowledge, and for some unaccountable reason think formal proof is the only means of knowledge (I'd like to see a formal proof of that proposition) are able to experience the "revelation" of Godel's insight. And they certainly need it.

None of this says that there are not unknowable things (there are--quantum mechanics tells us that there are things we cannot know). Just that Godel's theorem addresses only formal proof, not knowability.

Re:Just another point of view

[brian0918]

"Does it matter if you can still derive predictions?"

Predictions allow you to check an existing hypothesis, but to make more progress requires a better understanding of what is actually happening.

Re:Just another point of view

[hesiod]

> The 'too many variable problem'? Not sure I know that one. Weather cannot be predicted because of chaos.

Isn't our concept of "chaos" just a matter of "too many variables" anyway? Or at least "too many variables to be easily comprehended?"

Re:Just another point of view

[localman]

Don't you think there's an interesting little symmetry there though? We're trying to understand the complexity of the natural world, usually with formulae, but even divorced from the natural world our formulae are known to have limitations. Doesn't this imply that the very concept of description and understanding through formulae is limited? It cuts right through the idea that if we could only pin everything down to a number than it would all make sense (which seemed to be the prevailing theory before Godel, and still has a few proponents today).

Anyways, I'll be looking into the information theory stuff more, but I think Godel's proof applies in a loose way to the concept of the unknowable, even in one of the most purified forms of logic: mathematics.

Cheers.

Re:Just another point of view

[Prophet of Nixon]

A few years ago I was moving some junk around on my desk and accidentally pushed my stapler off the back. About thirty seconds later I realized that I hadn't heard it hit the floor, so I pulled the desk away from the wall and looked. I never have found it. I took everything out of that room when I moved about a year ago and there was no old stapler, only the slightly shinier newer stapler that I eventually bought to replace it.

I hope its in a better place.

Re:Just another point of view

[wtansill]

The mathematics to describe laminar fluid flows are well developed and understood, have been for centuries... but nobody has got the hang of turbulent flow.

Even closer to home -- where the hell do my socks go when I wash and dry them?

Re:Just another point of view

[kurzweilfreak]

...try to explain me why stuff insist to fall (not how, why).

"Why" as a question seperate from "how" implies intelligent intention. In that case, the question makes no sense.

Re:Just another point of view

[mahmud]

In other words, no matter how many significant digits you have, it may be just so that the next digit, the one you didn't include in your 100 digit decimal fraction, may be the one that is of crucial importance and it may affect the resulting predictions (in the case of chaotic systems) greatly.

Re:Just another point of view

[drgonzo59]

Very interesting point. I never heard anyone put it that way. I'd give you +5 mod points if I had any.

Re:Just another point of view

[gardyloo]

The conceptual mechanism of turbulence is more understood now - it seems that turbulence is caused by finite-dimentional strange attractors in phase space (good news because navier-stocks equations phase-space is infinetly-dimentional).

    Damnit! I follow every link to "strange attractor", because I figure that someday one is going to show Anjelina Jolie. Leave it to slashdot to disabuse me of that notion every damned time...

Re:Just another point of view

[drgonzo59]

Speaking of turbulence, I am not an expert, but I remember reading about the problem of turbulence in Wolfram's "A New Kind Of Science" book about it. He approached the problem from a CA point of view and got some interesting results. here is the chapter on it.

At the same time, I have to say it is Wolfram, the self proclaimed pioneer and genius, who wrote a book full of proofs that start with "I am quite convinced..." or "It seems to me...". But nevertheless some of the stuff he did is quite interesting. I think fluid flow is one those things.

Re:Just another point of view

[Ibag]

Godel's theorem does not quite say what you suggest that it does. Rather, assume you have a logical system (built from axioms) which is consistent (the axioms don't contradict each other) and in which you can express enough different ideas (namely, you can formalize arithmetic in the system)). Then you can express certain ideas that cannot be proven or disproven.

A fairly canonical example of this idea is the continuum hypothesis. If you look at the counting numbers, you can put them all into one infinite list in such a way that if you pick a particular number and then start reading the list, you will eventually find that number. You can make a list of all the rational numbers too. However, if you try to make a list of all the points between 0 and 1, you can prove that whatever list you make must be incomplete. The unit interval has a higher cardinality, a larger order of infinity, than the counting numbers. It is easy enough to make sets that are of even larger cardinality than the unit interval, and it is easy to see that anything smaller than the counting numbers must be finite, but people for a long time wondered if there was anything in between the two.

As it turns out, we can assume there are no orders of infinity in the middle. Or we can assume that there are two. Or three. Or infinitely many. As long as you don't do something stupid (like put more than a lines worth of kinds of infinity less than the infinity of the line), you can make a consistent model of set theory with almost any answer to the question. The continuum hypothesis is said to be independent of the axioms of set theory.

Of course, we could take any answer we wanted as a new axiom, but we don't because we have no good reason to believe that one answer is the "right" one as it relates to the real world.

Another example, perhaps a little less abstract, is Goldbach's conjecture. Every time people try to express an even number as a sum of two odd primes, they are able to. We think that you are always able to, and if there exists a counter example, we would be able to eventually find it. However, going through all even numbers and showing that we can decompose them would take a very long time and cannot actually lead to a proof. The statement looks like it should have a definitie answer, and many smart people are looking for one, but others have suggested that we might not actually be able to prove it. In this case, however, if we could prove that the statement was unprovable one way or the other, it would in essence show that no counter example exists and that the statement was "true". This is closer to the thought that there are "true" statements that cannot be proven.

In any event, there is a difference between true and proveable and "knowable", just as there is a difference between a model, an axiomatic system, and reality. People like to throw around Godel's theorem a lot without fully appreciating its limits in scope. It is a powerful theorem of mathematical logic in that it shows that we cannot fully axiomatize the world. Still, it does not have the implications that you might suspect.

Re:Just another point of view

[drgonzo59]

Actually the problem with the Weather might not be just the number of variables, but the different local sensitivities to those variables -- it is a chaotic system. So even if you buy a billion dollar computer and account for as many variables as possible you might still not similate the weather in some part of the world, because it is very sensitive on the initial conditions. For example it is inherently harder to simulate and predict weather in England. There have always been jokes about un-predictability and errors in their forecasts, but that is not because their computing power is limited but because in their region the weather is more chaotic. As someone already mentioned it is like saying that the flapping of the wings of a butterfly in South America could change the course of a hurricane in Atlantic.

Re:Just another point of view

[drgonzo59]

Well, that was the point of my post. We are using QM to build things. The math seems to predict the phenomena. Quantum encryption works with entanglement and there has been experimental proof. But it seems that we cannot really understand it. Other phenomena are likewise. So I was wondering whether there is actually a limit as to how much our brains can understand. In other words some phenomena we will comprehend as the science progresses, but some we will never be able to wrap our head around.

This is more of a philosophical debate I guess. Some scientists have claimed that knowing the math and having the equation is all we need, there is no need for conceptual models in our head. Others claim that is not enough and they would want to understand what is really going on.

Re:Just another point of view

[Lifewish]

If you're classing quantum mechanics as something that's insufficiently understood, I'd strongly disagree - we're currently way past that to quantum field theory.

Re:Just another point of view

[Jeff1946]

But we have a selective breeding program to breed brighter humans. Our children are tested and the brightest ones and ones with sucessful parents (have $$) are placed together at time in their lives with a high probability of selecting a mate. Worked for me when I was in college.

Re:Just another point of view

[bill_mcgonigle]

QM, but I don't think anyone can understand or conceptualize what is happening during entanglement (Einstein called it "spooky action at a distance" and never quite got to accept it).

I think that's a good example. "Spooky" is a good word - things we don't understand are, historically, spooky. So, since it's spooky, we should accept that we don't understand it.

The thing is, every so often a pretty simple theory comes along that explains these things rather elegantly. And then they're not spooky anymore.

It's like the concept of what a 3D object would look like to a person living in a 2D universe - a sphere moving through the 2D universe would look like a strange rapid succession of expanding then contracting circles. Spooky if you only know 2D. You can extend this and say that a 4D universe looks like rapid succession of 3D universes. So, maybe entangled particles are just what a, say, 7D particle looks like under a certain circumstance in a 4D universe. It's not anything weird, we just don't understand it or haven't experienced it before. Maybe some big M theorist will come along and say that rather than a particle being a string anchored to a 3brane and a 7brane that an entangled particle has two anchors on a 3brane and only one anchor on a 7brane and thus the mechanism for communication between the particles is established.

Or something like that.

Re:Just another point of view

[brian0918]

"If you're classing quantum mechanics as something that's insufficiently understood, I'd strongly disagree - we're currently way past that to quantum field theory."

The phrase "quantum mechanics" refers to both non-relativistic and relativistic quantum mechanics (the latter being quantum field theory). If you can't even get the lingo straight, what's the point in replying?

Re:Just another point of view

[brian0918]

The courses I took were called "quantum mechanics" regardless of whether it was relativistic/non-relativistic.

Re:Just another point of view

[MemeRot]

I think the way he would deal with turbulence is to say that it cannot be broken down into smaller calculations, the only way to find the actual outcome of a sufficiently turbulent system is to run the calculations in the real world, i.e just see what happens. It makes sense that there are some conditions that are not reducible to smaller equations, those equations are just models, and models are inherently inaccurate to some degree. Any degree of inaccuracy in modeling turbulence throws the whole result off.

Re:Just another point of view

[wrenhunter]

we don't have real proof that gravity will always work, just an assumption that it will work like it always has

Well, that's what Hume said, but Kant had other ideas (namely that our own mental structures guarantee that natural laws will always obtain).

Still, a charming anecdote ;-)

Re:Just another point of view

[drgonzo59]

What he did, is he set up a CA on a hex grid, with a certain set of rules, to be the medium (i.e. each mollecule is approximated by a cell). Then he simulated the movement of a plate through that medium and it turns out some interesting eddies form behind the plate that look very much like turbulence. The problem of course is that the CA "eddies" look like turbulence, but that doesn't mean that they somehow model the real world turbulent flow. But it is still an interesting picture to look at. Perhaps someone is aware of a more detailed simulation or a more in depth study of this...

Re:Just another point of view

[Lifewish]

The courses I took were called "quantum mechanics" regardless of whether it was relativistic/non-relativistic.

The courses at my uni appear to distinguish between vanilla Quantum Mechanics and Quantum Field Theory. Of these I've only taken the former, so I'm aware that my lingo may not be up to scratch.

Re:Just another point of view

[TapeCutter]

"if you want a better idea of the type of barrier we are facing in this case, you would be better served by complexity and information theory....the type of problem involved in turbulence simulation, not logical issues of provability and incompleteness"

I was going way OT, I was not talking about turbulence in particular I was agreeing with the GP who suggested there are things humans will never know.

"but this knowledge comes from outside the logical system"

..and that is why I pointed to Godel.

Re:Just another point of view

[TapeCutter]

"In any event, there is a difference between true and proveable and "knowable", just as there is a difference between a model, an axiomatic system, and reality. People like to throw around Godel's theorem a lot without fully appreciating its limits in scope. It is a powerful theorem of mathematical logic in that it shows that we cannot fully axiomatize the world. Still, it does not have the implications that you might suspect."

Our mind is a model of reality, I belive (but cannot prove) that it is based on an axiomatic system whose axioms may contradict each other. You cannot show it does not imply something about philosophy in exactly the same way that I cannot show that it does. It is a belief, phycologoicaly similar in some ways to the belief in God.

Re:Just another point of view

[jthayden]

You may be right in that some things are unsolvable by the human mind, but that shouldn't stop of us from trying. It really isn't possible to know what humans as a species are capable of doing, some radical thinkers are always pushing us forward. Nobody ever got anywhere by saying "This is hard, let's go to the pub." Except for maybe drunk, which is a good place to be, but not exactly the most productive.

Re:Just another point of view

[brian0918]

"The courses at my uni appear to distinguish between vanilla Quantum Mechanics and Quantum Field Theory." I wouldn't put it past my school's administration to not bother to make that distinction.

Re:Just another point of view

[techno-vampire]

An excellent, lucid explanation of the Incompleteness Theorem with one, small but important point left out. Goedel proves that in any appropriate system there's a statement that can neither be proven nor disproven within the system. In the unlikely event that the appropriate string for arithmatic were generated, there'd be no way within arithmatic to prove it true, but there might be ways using higher math, because that would be "stepping outside" the appropriate system.

Re:Just another point of view

[TapeCutter]

"I know any amount of stuff by means other than proving it within a consistent axiomatic system. I know my name. I know my favourite colour. I know I'm wasting my time trying to explain something on Slashdot."

An axiom is nothing more than an accepted but unproven truth, ie: an assumption. I would consider the things in your list "axioms" that your mind uses to build it's world view. The question of the minds axioms being consistent and the applicability of Godel to the human mind are open until we can show (one way or another) that the brain can be described by Turing's UCM. Naturally if your mind has the axiom of a soul that is independant of the physical body none of this will make much sense because the soul is already outside the system.

"Only people who are confused about the nature of knowledge..."

You seem very certain about your own ideas on the nature of knowlage, perhaps you could show me how you know that I actually exist or perhaps you could elaborate on what you belive. Either way stop branding me a fool and realise things are not always black and white. ;-)

"but nothing in Godel's proof puts an absolute barrier to knowability"

When we describe reality what we are really doing is describing our brains model of reality. Applying Godel to the brain means we could have infinite knowlage but still not fully understand ourselves or the Universe in wich we arose. This does not mean seeking knowlage is pointless just that the knowlage is eternally doomed to be incomplete, ie: we can know anything but not everything.

Re:Just another point of view

[marcosdumay]

If so, I can explain you why quantum entanglement happens.

Re:Just another point of view

[jbengt]

Chaos is more a matter of non-linear interactions, you can get chaotic behaviour with just a couple of variables.

Re:Just another point of view

[msuarezalvarez]

There is no reason why the number of dimensions in the model we make of the physical world has to correspond to the number of dimensions of the physical world. In fact, if you think about it, the world does not have a "number of dimensions": this number 3 that people keep bringing up, or 4, when they have read some relativity and/or seen some SciFi movie, is the number of dimensions of the model of physical space we are most familiar with.

BTW, have you heard of an experiment designed to show that the world is 3- or 4-dimensional?

This is not as ridiculous as it sounds. For example, experiments can be designed to decide whether physical space (excluding time...) is odd- or even-dimensional. Indeed, detailed study of the wave equation, which models electromagnetism "exactly", shows that waves have very, very different behaviour in odd-dimensional spaces and in even-dimensional spaces (for the cognoscenti, the difference comes from the very different shapes of the supports of the fundamental solutions of the wave equation).

Re:Just another point of view

[msuarezalvarez]

As long as that "higher math" you speak of is a formal system, incompleteness persists; the statement with which you had a problem will have been resolved, maybe, but there will be others, maybe new ones that appeared because of the enlargement of the theory, that are as problematic as the old one. Read up on \omega-incompleteness.

If this "higher math" is not a formal system, well, then you stopped doing math...

Re:Just another point of view

[msuarezalvarez]

An axiom is nothing more than an accepted but unproven truth, ie: an assumption.

This is a very widely held view of what an axiom is, but it is completely different from the usage of the word in current math (and, of course, in any discipline which uses math to model its object of study)

Axioms are simply assumptions, and that is not the same thing as an accepted and unproven truth. It is just an assumption.

When the group theorists posits that "the group operation is associative", she is by no means whatsoever stating that she believes that all operations are associative but she can't prove it.

An axiom is just an assumtion. Mathematicians use axioms instead of just stating the assumption explicitely before every single statement that depends on them only because of convenience and psychological reasons. Thus, there is no difference between:

Axiom 1: Pigs fly.

Theorem 1: The sun revolves around the earth.

Proof. We leave this as an easy excercise for the reader. QED

and

Theorem 1: If pigs fly, then the sun revolves around the earth.

Proof. We leave this as an easy excercise for the reader. QED

Of course, if what you are writing is a list of 500 theorems, putting the assumptions at the top is much more convenient.

The usage of the word axiom you have in mind more or less aplies to what the Greeks had in mind, and other people that came after them. There was a change when non-euclidean geometries were discovered, when algebra became modern algebra (probably, when van den Wearden's book came out).

Cheers.

Re:Just another point of view

[msuarezalvarez]

Roger Penrose has argued (Roger Penrose, Shadows of the Mind: A Search for the Missing Science of Consciousness, Oxford University Press, 1994, ISBN 0-19-853978-9) essentially that your belief is wrong.

He argues against the notion that the description of the physical world we have now is correct, based on the fact that the description we have is (let's say, for simplicity) computable; being based on an axiomatic system, like you prefer to say, is basically equivalent to that. That our minds cannot be computable, or formal-system-based, is a quite an important point in his argument.

I am not saying Penrose is right; I have not yet been able to decide if I think his argument holds water or not. He presents a very well thought-out argument, with much more detail that what most people will take. You may want to look into it.

Re:Just another point of view

[msuarezalvarez]

Hmm, this is not insightful: it is in the very definition of "modeling" that information is lost. If you "model" something in such a way that you do not lose anything, what you do is duplicate, and, quite clearly, you have not simplified your task of understanding it a tiny bit...

I've seen people around here complaining that the models we make of reality are lossy with the same spirit that ID proponents say that evolution is "just a theory". Man that annoys me! (Not saying you were doing this, mind)

Re:Just another point of view

[techno-vampire]

Of course. I thought that was obvious, but then, I'm very familiar (in a layman's way) with the issue. Thanks for pointing it out for The Rest Of Us.

Re:Just another point of view

[msuarezalvarez]

Well, as I said, this is related to Gödel's work on omega-incompleteness. I would hardly classify it as "obvious"!

The Ministry of Silly Walks

[malia8888]

Using the biggest telescopes in the world, including the Very Large Telescope facility in Chile, the group has made detailed 3D maps of the galaxies, using the movement of their stars to "trace" the impression of the dark matter among them and weigh it very precisely.

Doesn't the name "Very Large Telescope facility" sound like it is out of a Monty Python sketch, sort of like the "Ministry of Silly Walks"?

Further, I am struck with the thought that dark matter is "Silly Putty" which has gone off a bit.

Re:The Ministry of Silly Walks

[(negative video)]

I'm personally more amused by the proposed OWL telescope, which stands for OverWhelmingly Large. It's makes you wonder what they will call the next one after that. The So Enormously Large that Gosh We're All Really Impressed Telescope?

Re:The Ministry of Silly Walks

[fruey]

"The So Enormously Large that Gosh We're All Really Impressed Telescope" sounds like it just might be accepted, were it not for the fact that the acronym SELGWARIT is a little difficult to remember, and lacks punch or reference to an animal with good eyesight (or a large animal, perhaps).

You could however, with minor adjustments, get it sounding just nice with a good acronym to boot, viz : ELEPHANT Enormously Large Exceedingly imPressive Huge Array mind-Numbing Telescope".

Re:The Ministry of Silly Walks

[maxwell demon]

That's nothing against T.REX, the Telescope of Really EXtreme size!

Re:The Ministry of Silly Walks

[dascandy]

Go metric (Square Kilometer Array). Those from the US will think it's the biggest ever, will double its size in miles and fail horribly because somebody will have mixed up the miles with inches.

Re:The Ministry of Silly Walks

[Oligonicella]

Afterward, the U.S. could top and advertize with:

Dragonfly -
Damn Right, America's Got Optics! New'n Friggin' Largest Yet!

Ssshhhh...

[Donut2099]

"For the first time ever, we're actually dealing with its physics,"

Thats because we've secretly replaced the regular dark matter with Folger's Crystals!

Lots of it, and really damned hot?

[interiot]

The article mentions that there's quite a bit more of it than normal matter, and that it's about 10,000 degrees (... C?). Is that consistent? It just sounds odd for dark matter to have such a higher energy level than normal matter, weakly interacting or not.

Re:Lots of it, and really damned hot?

[Beryllium Sphere(tm)]

Yes, it's way odd. Expansion since the Big Bing should have chilled it to about 3 Kelvin. You could guess that something reheated it, but that is hard to do with something that doesn't like interacting with normal matter. If this is borne out (right now it's just an inference) it will be one of those "That's funny..." moments that lead to better understanding.

Re:Lots of it, and really damned hot?

[LiquidCoooled]

I wondered this as well.

Technically, shouldn't anything which doesn't emit light come under the banner Dark Matter?

The Earth and Moon don't naturally emit light so would be difficult if impossible to see with a telescope.
All of the asteriods and other rocky debris in our solar system is dark.

All of this is moving at a lot more than a few centimeters a year.

There can't be that much large fragments in the blackness of space because they would block our own view of the stars and lots more would appear to twinkle than currently are seen to? (negate atmosphere by using hubble)

Re:Lots of it, and really damned hot?

[NewsWatcher]

The Earth and Moon don't naturally emit light so would be difficult if impossible to see with a telescope.
All of the asteriods and other rocky debris in our solar system is dark.

To my understanding dark matter is not defined as something that doesn't naturally give out light, but something that emits no light or radiation. The earth does emit light; that which is reflected off it from the sun, likewise for the moon. If I understand dark matter correctly, it wouldn't reflect the light from the sun, even if it shone on it directly, because it cannot emit light or radiation.

Re:Lots of it, and really damned hot?

[aussie_a]

That doesn't mean that the dark matter can block out the sun, does it? It means that the light passes through it? Would it cause the light to slow down though (I'm pretty sure glass causes it to slow down)?

I thought the fact that dark matter has mass (and therefore substance?) was why galaxies hold together when they shouldn't. But how is that possible, if dark matter doesn't interact with normal matter in any observable way? And if it does interact with normal matter, where's it all hiding?

Re:Lots of it, and really damned hot?

[cnettel]

If something doesn't EMIT black body radiation (and doesn't absorb it), why would the temperature be related to the cosmological background radiation?

Re:Lots of it, and really damned hot?

[maxwell demon]

It interacts with normal matter through graviatation. It doesn't interact through electromagnetic interaction.

Of course, light is affected indirectly through gravitation. However, normally gravitation doesn't shield light, it just bends it (the bending of light by the sun's gravitation was one of the first successful tests of General Relativity).

And yes, light would slow down a bit, since gravitation causes a slowdown of time (e.g. seen from space, the light on earth's surface is a bit slower, even when in vacuum).

Re:Lots of it, and really damned hot?

[ockegheim]

Yes, if the dark matter is concentrated (by gravity) in the middle of galaxies it may not lose its energy as quickly as the cosmological background radiation.

Re:Lots of it, and really damned hot?

[aussie_a]

How can it only interact through gravitation? Is there ANY matter that does this, besides dark matter?

Re:Lots of it, and really damned hot?

[TMB]

What a good question!

The assumption is that at the dark matter can in principle interact with other things in the universe through non-gravitational means (most likely the weak force), so at some point in the early universe when reaction rates were much much much higher, it would have been in equilibrium with everything else (including the photons that would eventually become the cosmic microwave background (CMB)).

At some point the reaction rates would become low enough that the average dark matter particle would no longer interact with anything else, and so the dark matter would decouple from everything else and cool adiabatically. Photons decoupled at redshift 1100 and cooled adiabatically since then, and are now at 3K. If the dark matter decoupled earlier (a safe assumption), then assuming it's relativistic (ie. it would cool down at the same rate as the photons), it would be even cooler now. Non-relativistic things cool somewhat slower, but it couldn't be so hot today if it didn't start out relativistically hot.

There are a few assumptions in there, but it's surprising.

[TMB]

Re:Lots of it, and really damned hot?

[Starker_Kull]

That's the amusing part; as far as I understand it, no. The whole dark matter thing is rather touchy because of this - it describes something that only interacts via gravity. Remember that our sense of "interaction" (touching, burning, etc.) are all based on electromagnetic forces, so this dark matter could be passing through us right now and we would not notice it (much like neutrinos, which pass through us by the billions per second). Of course, at least neutrinos have the decency to OCCASIONALLY interact with normal matter, or we would have never detected them at all, only hypothesized their existence to make various important laws (like conservation of momentum and particle spin) work.

It's an intriguing idea, though. The reason ordinary matter piles up into big chunks like planets and stars is not just gravity, but the OTHER forces that keep it "stuck" together. Without that, matter would just be cruising along, looping around due to gravity, perhaps even "colliding", but without a method of storing or dissipating their kinetic energy (chemical bonds, which allow "heat" or vibrational motion energy), they will never stop moving or agglomerate or anything like that, making them more like a perfect gas without a container but with gravity. Neat stuff.

I just hope there is some way of directly detecting this dark matter (have it interact with something in a particle chamber in such a way that dark matter is required to explain the observation), or at least have it fall naturally out of the Standard Model or a successor, or it is going to have an aethereal feel (pun intended) about it.

Re:Lots of it, and really damned hot?

[maxwell demon]

Well, it might also interact with normal matter through the weak force, at least I don't know any reason why it shouldn't.
Of course, different matter takes place in different interactions (e.g. only quarks and gluons take place in the strong interaction, electrons etc. don't; gluon and neutrino don't interact electromagnetically, the gluon doesn't even interact through the weak interaction). Now there's a priori no reason why there shouldn't be a particle which only interacts through gravity. (I couldn't imagine a particle which doesn't interact by gravity, though, since unlike for the other interactions, the source of gravity is not some charge, but energy and momentum).

Re:Lots of it, and really damned hot?

[DoubleEdd]

Not all matter is cold. The gas in large clusters of galaxies is sufficiently hot that it emits X-rays, for instance. In fact, in some bits of astrophysics it's quite challenging to find ways for matter to cool down.

I don't think that temperature is necessarily inconsistent with anything, but I've not read the papers yet.

No references

[Random Walk]

I'll probably never understand why newspapers are never able to quote any references for their news. Even in the absence of a published refereed paper, I would expect that there is at least a preprint or press release from the research group... apparently BBC news is convinced that their readers will drop dead on the floor if they encounter a hyperlink leading to something more than just random blurb from a journalist.

Actually, they don't even say whether 'Professor Gerry Gilmore' is part of the group that did this research, or whether he is just someone they asked 'Hey guy, what do think about this stuff?'. I.e. they don't even identify clearly any member of this 'Institute of Astronomy, Cambridge, team'.

Re:No references

[Beryllium Sphere(tm)]

Professor Gilmore's home page links to his preprints, which don't seem to include anything that matches the BBC article.

Re:No references

[FinestLittleSpace]

The BBC news 'lack of linking' can get on my nerves a bit, but they DO hide in the right hand bar a 'related links' section whihc you can just about see....and is sometimes useful

Re:No references

[graemecoates]

His research does involve the study of local group galaxies and the like (eg astro-ph/0511759), so he is more than likely a senior member of this research group. From TFA:

The Cambridge University team expects to submit the first of its results to a leading astrophysics journal in the next few weeks.

So that's probably why there's no paper yet - keep an eye on the pre-print servers in a few weeks.

papers linked to

[Falcon040]

Links here for related papers:

Gravitational solution to the Pioneer 10/11 anomaly
Galaxy Cluster Masses Without Non-Baryonic Dark Matter
Galaxy Rotation Curves Without Non-Baryonic Dark Matter


Other Interesting stuff:
The Calphysics Institute and my earlier post about the Calphysics research.

You mean now it's real?

[Zadaz]

I thought measuring the temperature of dark matter was like measuring the distance to the celestial sphere.

Or for more of a /. reference, like measuring the quantity in the bit bucket.

Popper is dead...long live predictions

[Flying pig]

Karl Popper is dead, and we know that in many sciences falsifiability is not the only option. There is prediction. If a hypothesis results in a prediction that can be tested, and it is correct, then this is evidence for the hypothesis. The new version of the dark matter theory seems actually to be resulting in predictions, and the concept that the universe may be quantised in some way at a very large scale (1000 light years) could have considerably explanatory power. Theories that claim that there is no such thing as dark matter and it will can be replaced by adjustments to the theory of gravitation will run into trouble if the proposed quantisation can be demonstrated.

If the Universe does turn out to be made of 1000LY wide bricks, I sure as Hell don't want to meet the bricklayer.

weird internal modes?

[Quadraginta]

I would have thought its temperature would have had to be much lower than that of normal matter. After all, it's only in equilibrium with the translational degrees of freedom of ordinary matter, because those are the only degrees of freedom that can couple gravitationally. I'm hard pressed to believe the average translational temperature of matter in the galaxy is that high -- it implies the average speed is at least several km/s. That seems very high.

Maybe the dark matter has some kind of weird internal degree of freedom, like the electronic degrees of freedom inside ordinary atoms, and there's a lot of energy in these. I suppose since these internal modes can't couple to ordinary matter, they wouldn't be in thermal equilibrium with ordinary matter. That would let the dark matter have a temp very different from that of ordinary matter.

But I'm just guessing wildly. Really, I'm just as...erm...in the dark here as anybody else.

Re:weird internal modes?

[Stalyn]

What the findings suggest is that dark matter isn't exotic matter but a different kind of matter all together. The hierarchy of forces according to interaction goes gravity -> electroweak -> strong. This means all matter we know of interacts with gravity, all matter (until recently) interacts with the electroweak force and a subset of matter, quarks, interacts with the strong force. Note, quarks also interact with the electroweak force since protons and neutrons have electric charge and these particles are made of quarks. However leptons, like the electron do not interact with the strong force.

Now it was possible that dark matter could interact with the electroweak force but very weakly and therefore undetectable at large scales. It was assumed that this meant they were very cold and at very low energy states. However if they are moving at 9km/s that would mean they have high energy states. Therefore if they did interact with the electroweak force, they would be absorbing or emitting photons. But they aren't.

So we have a new type of matter with that only interacts with standard matter(leptons, quarks) via the gravitational force.

Re:weird internal modes?

[maxwell demon]

Neutrinos interact with the electroweak force, but they don't absorb or emit photons (except for higher-order effects, of course). That's the reason why you don't see the huge amounts of solar neutrinos which pass through earth all the time (you need large experiments to see the effects of their rare interaction with matter). Indeed, IIRC neutrinos were one candidate for dark matter (or maybe they still are?)

Now there may be other reasons to assume that there's also no weak interaction between dark matter and normal matter, but the fact that it doesn't interact with light isn't one of them, because neither do neutrinos.

Re:weird internal modes?

[Stalyn]

Neutrinos are considered a small percentage of hot dark matter. These findings suggest what we thought was cold dark matter is actually "hot". But the speed of 9km/s is way too slow for a neutrino. I guess there is the slim possibility of a massive neutrino or something like that. But I think we would have detected such by now.

The SUSY partner of the neutrino, neutralino, is considered a WIMP and a dark matter candidate. But again this was before these findings so they might be cancelled out as well.

Re:Dark Matter Blows

[meringuoid]

Dark Matter should hook up with the cosmological constant, they'd make the perfect couple.

Already done; look up 'dark energy'. Now, if you'll excuse me, I've left my dinner in the oven and I think it's burning; I smell phlogiston. Damn, with such delays I'll never get this new suit ready for the Emperor in time...

Re:What does local universe mean?

[meringuoid]

"It now looks as though the Milky Way is the biggest galaxy in the local Universe, bigger even than Andromeda. It was thought until just a few months ago that it was the other way around."

Could someone explain what the "local universe" is? And how does this compare to the entire universe?

Our local cluster of galaxies - which IIRC consists of three giant spirals and a whole bunch of small cloudlike galaxies - is unimaginatively titled the Local Group.

Hitherto it's been thought that the Andromeda galaxy was the largest in this group, with our own Galaxy about two thirds its size. Now, it seems that's not the case... damn, my childhood astronomy books lie to me again! :)

Obligatory

[SeaFox]

So I guess you could say they're shedding some light on dark matter?

Re:Obligatory

[cciRRus]

So I guess you could say they're shedding some light on dark matter?

In this light, yes, you are right. Brilliant observation!

Re:What does local universe mean?

[joe user jr]

Probably they mean the Local Group: "the group of galaxies that includes our galaxy, the Milky Way. The group comprises over 30 galaxies, with its gravitational center located somewhere between the Milky Way and the Andromeda Galaxy. The galaxies of the Local Group cover a 10 million light year diameter (see 1 E23 m for distance comparisons). The group belongs to the Virgo Supercluster."

Dark Matter

[ben_1432]

What's so hard to understand about it? It's the heaviest, densest matter available and it powers spaceships duh. Oh yeah, and Nibbler craps it.

"Scientists Expand Knowledge of Dark Matter"

[Anonymous Coward]

... they're making dark matter smarter?

Did they forget to carry the 2?

[Calathea]

I've often wondred if the search for the elusive dark matter that will plug a whole in the equations that govern what we see could in fact be a red herring and in fact the equations themselves are wrong and someone somewhere forgot to carry a 2 Is Dark Matter just another fudge factor?

Re:Did they forget to carry the 2?

[ObsessiveMathsFreak]

Don't dismiss this idea too readily. I keep running across electromagnetism papers that have the wrong sign on terms, and that treat permittivity and permeability as constant in all cases.

If there are only a few dozen people that can understand general relitivity, then I sincerly hope they've checked all their figures. Time for more automated equation verification?

AHAH... I got it!!

[DaedalusHKX]

Dark Matter == God.

Yep... dark matter and he who cannot be seen are one and the same... see?

Now, onward to forming a new religion.

Dark Matterism.

I wonder what country we'll butcher to spread THAT religion??

Anyone??

~D

Re:AHAH... I got it!!

[meringuoid]

Dark Matterism. I wonder what country we'll butcher to spread THAT religion??

Most likely a country sitting on top of a large deposit of some very dark - indeed, quite black - matter. Preferably of the liquid, flammable variety.

I mean, why break the habit of a lifetime?

Re:AHAH... I got it!!

[maxwell demon]

Well, a dark matter god would clearly be a materialistic god, therefore I'd try in the former communistic countries.

However, beware of the followers of the dark energy god religion. They argue that only dark energy can be the real god, because unlike dark matter, it's everywhere in the universe. Also it's powerful enough to accelerate the universe as a whole, while dark matter only acts in a galactic range. Also, the fact that we can learn something about the dark matter, like its distribution, shows that it's not really god-like. However, of the dark energy we don't know anything but that it must exist and at least one of its actions, so it's clearly more god-like. And finally, the big bang, i.e. the creation of the universe, was obviously driven by an expanding force, i.e. by dark energy. Therefore dark energy obviously is the creator of the universe, so it must be god.

Of course, don't forget to go after those heretics which try to remove those dark matter/dark energy gods by just writing new theories of gravitation! :-)

Re:AHAH... I got it!!

[Anonymous Coward]

Is that what keeps the Flying Spaghetti Monster from turning into sauce?

Re:AHAH... I got it!!

[Ninjy]

see?
Uhm. Well. No?

Re:AHAH... I got it!!

[Rakshasa Taisab]

Mmmm... that's *alot* of noodles.

Re:AHAH... I got it!!

[mrsmalkav]

It's coffee, isn't it!?

FINALLY! Proof that all movement comes from coffee!!!

huh?

[goarilla]

can someone please shed light on this phrase

It now looks as though the Milky Way is the biggest galaxy in the local Universe, bigger even than Andromeda. It was thought until just a few months ago that it was the other way around

I don't understand this term calledlocal universe, is it our observable universe or something else?
Because that would mean IIRC we are part of the biggest galaxy known to man???

Re:huh?

[Myrano]

I'd guess they just mean the local cluster of galaxies, that is, the group of galaxies around us that we are gravitationally bound to. It's been known for a while that the Milky Way is larger than average, but Andromeda (which we are on a collision course with) was thought to be larger than us. I'm skeptical, myself, but it would be awesome if we did turn out to be bigger. 'Cause that kind of thing is cool.

Re:huh?

[Anonymous Coward]

I expect that article is talking about the local group. I can't say for sure, 'cause I can't get to the article. The local group is a group of over 30 galaxies within about a 100 light year diameter that are bound to each other with gravitational forces. Andromeda and the Milky Way are (by far) the two largest members of the local group, with the Milky way being quite a bit larger than Andromeda. The local group, in turn, is a member of the Virgo supercluster. And we can still see outside of the Virgo supercluster, so the article's definitely not talking about the observable universe.

Re:huh?

[SlowMovingTarget]

I did a quick Google search on the term and the closest thing to a direct definition I'm able to find is from contextual clues. It seems the term "local universe" is usually used to describe the observable universe, that is, that portion of spacetime that lies within our particle horizon.

If current observations suggest that our Milky Way galaxy is the largest we can see, this may perhaps mean that we're comparing images of our galaxy at a few tens of thousands of years old, to images of galaxies a few hundred million years old. What would you call that... Temporal parallax? You wouldn't think there should be so much of a difference on a cosmological scale.

OTOH, maybe we are at the center of the universe [grin].

Re:huh?

[SlowMovingTarget]

Thank you for the correction.

Re:huh?

[Explo]

Um, I assume that instead of 100 light years you mean something like slightly less than 10 million light years..? :) (NGC 404 is assumed to be just far enough to be not gravitationally bound to the local group, and it's about 8 million light years away.)

"its physics"?

[layer3switch]

So what do we call this physics? _fill_in_the_blank_ physics?

Re:"its physics"?

[maxwell demon]

Dark side of the force physics!
Or maybe simply dark physics? :-)

Still assumes the answer

[AlecC]

I was hoping that this would provide some real evidence for Dark Matter. I have a problem with something so massive which, as far as I can see, is invented to explain a single fact: the anomalously fast rotation of galaxies.

But this article doesn't do that. It says, as I understand it, if the rotation of galaxies is caused by dark matter then dark matter has these properties. If the unexpected rotation is caused by something else, then this is just a curious kind of meta-measurement,

It is a bit like the phlogiston theory. If fire were caused by the release of phlogiston, you could measure the mass of phlogiston - and come out with a negative mass. Which is perfectly logical, but counter-intuitive. Further investigation then makes the phlogiston theory even less attractive - but in the short term, the theory can be patched to work.

Re:Still assumes the answer

[rknop]

I was hoping that this would provide some real evidence for Dark Matter. I have a problem with something so massive which, as far as I can see, is invented to explain a single fact: the anomalously fast rotation of galaxies. ...and the anomolously high velocity dispersion of clusters, and matter evolution models that go from the observed fluctuations in the Cosmic Microwave Background to the observed distribution of matter today, and the anomalous amount of gravitational lensing seen in various cluters...

The galaxy rotation curves are the cleanest and best piece of evidence, but there's a lot of evidence for dark matter. It's a major paradigm in astronomy, without which quite a number of things would be lacking an explanation.

-Rob

Re:Still assumes the answer

[amnesiaWind]

I was hoping that this would provide some real evidence for Dark Matter. I have a problem with something so massive which, as far as I can see, is invented to explain a single fact: the anomalously fast rotation of galaxies.

Actually the galaxies are rotating just as they should - dark matter was invented to explain anomolies in our mathematics.

Re:Still assumes the answer

[bill_mcgonigle]

It is a bit like the phlogiston theory.

I like your analogy. I fear it's correct.

The dark matter that you can see...

[kale77in]

"The dark-matter that you can see is clearly not the TRUE dark-matter."

-- Serious Black (attrib.)

In other news...

[jettoki]

British scientists at Cambridge have also placed limitations on the possible properties of the luminiferous aether. "We're pretty sure it's not yellow," says one researcher, "and we've also ruled out blue and pink. It's nice to know that we'll soon have figured out both this dark matter stuff and the luminiferous aether. Then we can start puzzling out those epicycles again."

Re:In other news...

[PermanentMarker]

Dazling... Let me think dark matter, it might be black..

Re:In other news...

[maxwell demon]

Of course, dark matter and luminiferous aether are one and the same. Isn't that obvious? This explains immediatly why we cannot see it: It's not something in the way of light, but it's the medium of light itself!
BTW, the dark energy is also solved. It's phlogiston. You know, phlogiston has negative weight, therefore it causes anti-gravitiaion. This neatly explains why dark energy causes acceleration of the universe expansion.
The epicycle problem isn't yet completely solved, but it's likely that the enormous heat of the dark matter comes from the friction of the planetary machinery.

Re:I say dupe...

[maxwell demon]

I guess you meant shed, not shred (maybe a freudian slip because you wanted to shred this article? :-))

Now, you cannot really shed light on dark matter anyway, because the light will just go through it.

Re:What does local universe mean?

[david.given]

Our local cluster of galaxies - which IIRC consists of three giant spirals and a whole bunch of small cloudlike galaxies - is unimaginatively titled the Local Group.

Ah, bring back the days of the ancient Arabian astronomers who could come up with poetic names like Mintaka, Bellatrix, Deneb, Sirius... the Local Group contains galaxies with names like:

• Milky Way (I mean, what is that?)
• Wolf-Lundmark-Melotte
• Pisces Dwarf
• SagDIG
• SagDEG (Huh?)
• Andromeda
• Andromeda I
• Andromeda II (and so on, up to V)
• Fornax Dwarf (sounds obscene)
• Ursa Major Dwarf
• Original Ursa Major Dwarf
• IC 10 (my computer's got one of those!)
• NGC 6822 (wasn't that one of the ships from Star Trek)?
• UKS 2323-326 (yes, you can find this galaxy on the back of your hi-fi)

And don't forget the incredibly poetic 2318-42. I mean, that name doesn't even have any friggin' letters in it. Astronomers these days have no soul.

Don't believe me? The full list's on Wikipedia.

Interesting research...

[Vo0k]

IF dark matter exists, then it's like this...

Reminds me Homer, author of Illiad and Odyssey. We don't know if he existed, but we know he was blind.

Re:Dark Matter Blows

[rknop]

It's always fun to watch people on Slashdot without a clue what they're talking about dismiss so much of our current understanding of cosmology with such an unjustified supercilious attitude.

-Rob

Here's what makes me unhappy

[rknop]

Here's what makes me unhappy:

The Cambridge University team expects to submit the first of its results to a leading astrophysics journal in the next few weeks.

I don't like this "press release before publication" mode of doing science. It's all about making sure that you get the attention and public recognition, and not about propery distributing the results so that others can understand and evaluate what you've done. Alas, it seems that Marketing Is All in the modern world, and not just in the USA any more. You can be sure that the institutions who house these scientists love to get the attention and so forth.

I'd be happier if the paper had already been accepted by some real journal, with a preprint available on www.arxiv.org. As it is... we have a press release and a pop-sci article about an intersting result that's hard to truly evaluate. The article is mostly good and sounds reliable, but in my experience these pop-sci articles usually get something wrong. (For instance, even though 10,000 degrees sounds "hot", given the likely mass of the Dark Matter particle, it still is "cold" in the cosmological sense of "cold dark matter", which really means "nonrelativistic dark matter". I'm not sure how much of a surprise that temperature is, but it's probably not enough to make CDM wrong.)

-Rob

They always forget to mention...

[dysfunction]

In these articles they always talk about dark matter being more than 90% of the universe. However, they never mention that based on galaxy rotation alone, dark matter is not required to account for any more than 90% of the universe's mass. However, for many reasons, mostly aesthetic ones, cosmologists long for omega to be one, requiring the universe to be around 99% dark matter.

Re:They always forget to mention...

[PiMuNu]

However, for many reasons, mostly aesthetic ones,

... oh, and the fact that omega is measured by several techniques to be 1 ...

Re:What does local universe mean?

[maxwell demon]

And don't forget the incredibly poetic 2318-42.

Let's see ...
23: the number of the Illuminati.
18: used by some groups as code for "Adolf Hitler" (A=1, H=8). Also the sum of digits of 666, the number of the beast.
-: Subtraction sign.
42: The answer to life, the universe and everything

I'm sure this galaxy name is meant to tell us something ... :-)

I mean, that name doesn't even have any friggin' letters in it.

1337!

Inflation explained?

[grimJester]

If there is a "magic volume" of space a given amount of dark matter occupies, would this inflate the early universe until the dark matter fits?

Re:What are British Scientists doing .....

[beef3k]

In any case I'm willing to bet you don't work at either of the two.

Actually it makes sense

[brian0918]

For something to lose energy, it needs to bump into a lot of stuff. If dark matter really is weakly interacting, then you would expect it to have a higher temperature than more interactive stuff at the same number density. As for why it is hotter to begin with, who knows...

BBC doesn't have fact checkers?

[amnesiaWind]

"Such observations have established that dark matter makes up about 85% of all the mass in the Universe."

Actually dark matter is only responsible for about 25% of the mass of the universe, with dark energy being responsible for the majority (about 70%). The remaining 5% is about 4.5% normal matter and 0.5% neutrinos.

Re:BBC doesn't have fact checkers?

[Xantharus]

But you said it yourself, about 70% of the universe is comprised of Dark 'Energy'. This is not considered mass because it doesn't interact gravitationally. Dark Energy is currently more of a wild card than dark matter. It is something that seems to be the driving factor in the expansion of the universe... but no one is really sure what it "is".

But in short, the BBC is correct, about 85% of matter is Dark Matter, eventhough matter only comprises 30% of the total energy budget of the universe.

Re:BBC doesn't have fact checkers?

[Xantharus]

Fair Enough... I was wrong, Dark Energy does interact gravitationally. I was just hoping to skirt the fact that something that interacts gravitationally actually results in a 'negative pressure' effect on the universe. I didnt want to go into all of that...

Re:BBC doesn't have fact checkers?

[Use Psychology]

I didnt want to go into all of that...

sure, because you sound like you really know what you're talking about

Local Group

[TakaIta]

Local Group

We don't assume Omega=1...

[jpflip]

Dark matter is thought to make up >80% of the matter (slow-moving stuff which clumps under the influence of gravity) in the universe. There are lots of reasons for thinking that this stuff is out there:

• galaxy rotation curves (you're right that this alone doesn't tell us about the universe's energy budget, just that of galaxies)
• gravitational lensing (a surprisingly independent measure of the stuff in galaxies and galaxy clusters)
• structure formation (you need more matter than the visible amount for the structure we see to form quickly enough)
• the cosmic microwave background (the shape of the first two peaks of its spectrum tells us about matter and dark matter densities)

Dark energy seems to make up the remaining 70% (25% dark matter, 5% ordinary matter). The evidence for this comes from the acceleration of the universe's expansion, which is a fairly amazing thing.

You don't actually need to assume that Omega=1 (the universe is flat), because these different lines of evidence pick out a unique consistent solution. There's a great plot at LBL showing this. We don't need an ad-hoc assumption that Omega=1 anymore!

DUH

[Loquax]

If they'd used an alethiometer to begin with we wouldn't be having such an issue with this stuff. BTW my daemond is a slug.

Re:Dark Matter Blows

[localman]

It is fun, which is why I keep coming back :)

But you must admit -- dark matter theory has that ring to it of something stuck in there to explain what we don't quite understand yet. Maybe it'll turn out to be true... but right now it sure seems like the remainder to an imperfect equation.

Cheers.

All Before . . .

[Dausha]

"'It now looks as though the Milky Way is the biggest galaxy in the local Universe, bigger even than Andromeda. It was thought until just a few months ago that it was the other way around.'"

Yeah, but it's like I was telling the Old Lady just the other night. It's really not so much the size, as how its used. I think Andromeda gets a whole lot more use out of itself than we do with the Milky Way. And, I find a hard time calling our galazy the Milky Way. I mean, Milky Ways have no nuts in them--and our galaxy has more nuts than I care to count. Maybe we should rename it "Snickers?"

Re:So um

[maraist]

Is it possible that dark matter isn't additional matter at all, it's just a fourth force?

I suppose it could, but that wold be kind of like formulating geometry for the first time based entirely on a blurry photograph. I meant we have these huge super colliders which have given us pretty accurate measuements of the currently known forces. We've even fund that he weak and electro-magnetic fields perfectly align at certain temperatures. So without a way of testing, it still serves us best to fiddle with new theories. That is unless we can ever solve any of these damn string theory equatons.

Here is a thought

[alricsca]

Since I consider highly unlikely that our galaxy happens to be the largest in the region as the article suggest it appears to be. I am of the opinion there is some sort of observational bias effecting the results. One thought that comes to my mind that might account for the fact that these galaxies appear to be rotating faster than they should be for their given visible mass, that might account for various odd super structures in space, and might even explain dark matter is that the flow of time is not consistent across vast regions of space. If for example a small galaxy was moving faster through time relative to us, it would appear to be rotating very fast due to this temporal bias. If these fields pervade the local space around our and other galaxies it might simply mean that at the current time relative to flows of time in the other galaxies in the local area ours is going slower which is also odd but it explains the visible effects without dark matter. There is however another possibility in this theory which eliminates the observational oddity at least at the galactic level, we could be observing these galaxies through several distortions between Earth and them that happen to create this type of visual effect from our point of view. This would limit the issue to a more localized point of view argument. Another words at the moment Earth is in a observational position relative to several large objects in space that make it look this way. Interestingly enough, this only requires better understanding of the structure of space and time but does not require a whole new physics to account for some strange form of matter and if these fields are common then Earth would simply be one of many places where this would appear to be the case. It might even be that Galactic masses have a stable time fields around them but that the space between then is less stable or has variations on a universal scale. That would mean that in a given galaxy everything would appear stable and so would any observations of other galaxies. We would see speed or slowness but it would not confirm the cause. What might be interesting to look for would be a galaxy that has a time variation between us and it that only partially intersects it. That would create an apparent visual anomalies we could recognize.

Just my own theory,
Alricsca

possibly related current publications

[ankhank]

http://www.aas.org/publications/baas/v37n4/aas207/ 765.htm

"... radial velocity measurements of red giants in the Galactic dwarf spheroidal (dSph) galaxy Leo I based on data taken with Gemini's Multiobject Spectrograph GMOS. These data, reaching out to the galaxy's nominal tidal radius, permit us to trace its velocity dispersion profile across the whole area of Leo I. By means of detailed dynamical modelling we discuss the implications on this dSph's dark matter halo and mass profile."

not consistent with observation

[idlake]

Since there have been observations of galaxies consisting almost entirely of dark matter, it doesn't seem like a modification of the gravitational law is sufficient to account for the observations.

Telescopes of Unusual Size?

[billstewart]

I don't believe they exist....

Re:What does local universe mean?

[vandon]

42: The answer to life, the universe and everything

Actually, 42 was just the ultimate answer. No one can know what it is the ultimate answer for; as it is impossible for both the ultimate answer and the ultimate question to be known about the same universe.
However, the ultimate question may be 'Think of a number'

Re:What does local universe mean?

[wrenhunter]

It now looks as though the Milky Way is the biggest galaxy in the local Universe, bigger even than Andromeda. It was thought until just a few months ago that it was the other way around.

Anyone want to bet that this measurement will end up being observer-dependent in some way, i.e. everyone will think theirs is the biggest?

Re:What does local universe mean?

[erice]

"It now looks as though the Milky Way is the biggest galaxy in the local Universe, bigger even than Andromeda. It was thought until just a few months ago that it was the other way around"

Might this conclusion be a little premature? They measured the mass of Milky Way using a new method and found it was bigger than they thought. But, have they measured the mass Andromeda using the same methods? Perhaps Andromeda is also bigger than previously thought and still bigger than the Milky Way.

Re:What does local universe mean?

[techno-vampire]

Wolf-Lundmark-Melotte

Ah, yes, Lundmark's Nebula, later known as "Second Galaxy." Home to Boskone until the Lensmen wiped it out.

Spot The Reference, and win a Know Prize!

Re:What does local universe mean?

[maxwell demon]

Deep Thought disagrees (emphasis by me):

"Alright," said Deep Thought. "The Answer to the Great Question..."

"Yes...!"

"Of Life, the Universe and Everything..." said Deep Thought.

"Yes...!"

"Is." said Deep Thought, and paused.

"Yes...!"

"Is."

"Yes...!!!...?"

"Forty-two," said Deep Thought, with infinite majesty and calm.

(Actually quoted from http://sv-fortytwo.com/hhgttg42.html though)

And of course everyone knows what it is the ultimate question for (you can actually read it above). What know one knows is the question itself.

Ah, and did you look at the title of the Wikipedia page you just linked to?

What is the opposite of matter?

[Phist]

When a photon (a piece of light) is destroyed, it divides into two parts - matter and its opposite. This opposite matter reacts opposite of matter in every way. For example, anti-gravity. It cannot be directly observed by us because we are looking for matter. Look for the opposite of matter and you will find your "dark" matter.

Re:What does local universe mean?

[Grahad]

I can't help but think that dark matter screams of the historical theory of the Ether. That these phenomena could be explained if this ether / subatomic mass was factored into the equations.