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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."
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.
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.
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.
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.
Real Daleks don't climb stairs - they level the building.
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! :)
Real Daleks don't climb stairs - they level the building.
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."
.sigs: Just Say No!
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.
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.
The best education consists in immunizing people against systematic attempts at education. - Paul Feyerabend
That's Navier-Stokes
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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
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
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.
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!
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.