Dark Matter Exists 459
olclops writes "It's a big day for astrophysics. After much speculation, scientists now have conclusive proof of dark matter. This result doesn't rule out alternate gravity theories like MOND, but it does mean those theories will have to account for exotic forms of dark matter."
Re:Dark matter and tech (Score:3, Interesting)
Age of the Universe? (Score:3, Interesting)
But if there are dark clouds that can absorb the light, could there be stars further than 13ish billion light years away, that are simply obscured?
Re:Dark Matters (Score:1, Interesting)
Though in practice, the dark matter nebula they claim to have found could simply be a much finer dust made up of former neutron star [umd.edu] particles?
Silly Musings..... (Score:3, Interesting)
Storm
olbers paradox (Score:3, Interesting)
I believe the resoluiton of this paradox is one of hte outstanding successes of the expanding universe idea discoverd by hubble
Re:MOND (Score:2, Interesting)
The MOND people (generally) aren't kooks. They're just pushing in different directions, which is a good thing. But yes, this does make it even harder for them.
Re:MOND (Score:0, Interesting)
Re:The new result, in a nutshell (Score:3, Interesting)
Do we know yet what keeps that gas at million-degree temperatures? Maybe I'm naive, but I'd expect radiation (especially X-Rays!) to cool the gas, and I can't think of any mechanisms that would heat it back up that quickly.
Re:Full Paper (Score:5, Interesting)
How exactlty does demonstrating that something cannot explain a phenomina prove that a counter argument is proven? That's like saying the spontaniuos combustion of my dog cannot be proven with an alteration of the gravitational force law, and thus proves that the majority of the matter in the system is unseen.
"To be published..." (Score:5, Interesting)
From the NASA press release: "These results are being published in an upcoming issue of The Astrophysical Journal Letters."
Two points. First, journals really hate it when press releases are made prior to the publication date. Second, this journal has an "impact factor" of ~5-6, compared to Nature, or Science, which have impact factors of ~25. Why are they publishing in some obscure journal if this is really the rock-solid proof that they claim it is?? Makes me wonder.
Re:Dark Matters (Score:1, Interesting)
Any measurements are going to have flaws whether they're as simple as forgetting to carry the one or something far more egregious that can not stand the scrutiny of peer review. Dark matter doesn't exist. These scientists know exactly what they are looking for and they're working backwards like a mystery novellist in addition to massaging their equations so they add up.
Worse, scientists are asking people to accept dark matter and string theory on faith that they are smart and know what they are doing and dealing with in their observations and calculations. Sadly the deeper, fundamental concepts behind string theory and dark matter are beyond the ken of high school graduates which are in the majority compared to post-doc astrophysicists. Einstein was able to explain his theories in plain language accessible by anyone.
These astrophysicists would be better served by investigating the acceleration phenomena affecting the Pioneer probes.
Re:I don't see any proof... (Score:3, Interesting)
So what if it's a ripple/tight spot in spacetime? How could we tell?
I imagine it like the universe being a mostly inflated balloon. Everything inside is the universe. All of the super massive things (Black holes, etc) are so large, they cause outward bulges in the ballon. If you were to be standing on the inside, you would feel the effect by having the tendency of being pulled towards the bulge (gravity). So if you took your fingers and pinched the balloon and pulled a bit, you'd cause a depression (gravity from an inside observer's POV).
What if these things are also a precursor of a black hole? They obviously attract a lot of stuff with their gravity, so eventually, they'd attract A LOT of stuff, which would eventually lead to a black hole. Maybe super massive stars nearing death aren't the only mammas to black holes?
Re:Dark Matters (Score:3, Interesting)
Anybody ever think dark matter might be like Niven's 'quantum black holes'? (read "Borderland of Sol").
The idea: a miniscule black hole formed in the high pressures during the creation of the universe. Or in supernovae. Or in some other way. The method of formation doesn't matter for this little intellectual exercise.
They can have event horizon on the atomic or even subatomic scale; as such, they would have very dense gravity gradients, but would easily fail entirely to interact with matter outside of their own gravity. A couple quadrillion of them spread out in a thin hydrogen cloud - far enough apart to not fall into each other (say, an AU^3 (not AMU) holds a couple thousand), but close enough to seem like a very large, very consistent, very weak gravity shift.
Something to think about.
Re:"To be published..." (Score:2, Interesting)
The APJ [uchicago.edu] would have to be the premier publication for publishing astrophysical papers. It is a journal read by everybody doing astronomy related research.
Nature and Science are generalist magazines with severe space constraints. Nobody would choose to publish this sort of paper in either of those journals.
As I understand the process ... (Score:5, Interesting)
This appears to be no more a confirmation for dark matter than when the Michelson-Morley experiment (in 1881) "confirmed" the existence of ether. In the immediate aftermath of the Michelson-Morley experiment, theoreticians generated lots of mathematical "proofs" (e.g., The Ether of Space, Sir Oliver Lodge, Harper & Bros, 1909 [google.com]) that showed how a boundary layer in the ether surrounding the Earth accounted for the observed results. A series of subsequent refinements of the Michelson-Morley experiment showed that the speed of light was truly independent of direction, and Einstein's theories, which did not require the existence of ether, provided a better fit for the observed results than was a boundary layer in the ether.
Over time, the Michelson-Morley experiment was recognized to have disproved the existence of ether -- but it wasn't that way initially.
Alternative explanations include "quantum critical phase transitions [newscientist.com]", and I'm sure that there are other possibilities, that a series of observations of similar cosmological events will provide the range of data needed to select the hypothesis that best describes the observations.
Being able to fudge one theory to fit a single observation falls quite a bit short of a "conclusive proof". Maybe dark matter does exist, but it's going to take a lot more observations for it to be convincing to me.
How precisely does dark matter permit the expansion of the universe to be defined, and how precisely does the observed phenomenon fit those numbers?
Wake me up when someone has a quantum mechanical model that tells how quarks are bound together in dark matter, or when someone manages to tap into dark energy (which is supposedly all around us).
Why does dark matter only hang around solid matter (Score:2, Interesting)
this stinks (Score:3, Interesting)
I've been following the "dark" story on and off since I stopped studying physics seriously after college. The MOND system makes a whole lot of sense. My non-professional-physicist read on the MOND / DARK controversy is that several of the alternate theories (like MOND) that remove the need for dark matter are fairly convincing. Dark matter is not convincing at all - not testable, not observable, and reminds me a lot of Santa Claus. Somebody brought the presents, right? The problem is that a vast majority of cosmologists are all so far down the dark matter band wagon that if dark matter goes away... lots of careers will be lost. Destroyed. These professionals who trade solely in reputation and intellectual-ism will have their rug pulled right out from under them.
A much more plausible explanation is that some people are trying really hard to amp up the PR. Sort of like what happens when you need a distraction from a big debate, so you get all the airline travelers to throw away liquids. Anyone who tells you they have proof for something that by definition can not be observed is selling PR. For those of you who believe it without question, I've got a bridge I'll sell you.
After taking about 30 minutes and reading no less than 6 heavily biased PR pieces... I say this stinks. It's certainly not science - (yet).
So what's new, then? (Score:5, Interesting)
So from there it's that either:
1. there's a metric buttload of matter we can't observe other than through gravity, in some weird distribution all through the galaxy's disc, or 2
2. we accept that gravity isn't working like we think it does
(Or my favourite: 3. galaxies are just a rotating texture there, so _of_ _course_ they rotate like a rigid. Noone would be dumb enough to simulate the individual stars just to give us a pretty sky in this MMO we call RL
And somehow the favourite is 1, for no obvious reason than that noone wants to modify gravity theories. It's as if Galileo, upon discovering that a stone dropped from the mast doesn't lag behind the ship, would then proceed to invent some "dark wind" that pushes the stone along with the ship. Since existing wind obviously isn't strong enough to push the stone that hard, it's got to be some dark wind in there too. Just, you know, for the sake of not contradicting the existing Aristotelian system.
Anyway, all along we knew that it can't be conventional matter, because we already had plenty of galaxies in various states of illumination and they all behave the same.
So exactly how does the new one help there? It seems to me like it still can't offer conclusive proof that 1 is true and 2 is false, because it would _still_ be equally well explained by 2. What this "solves" is at most a sub-distinction inside 1, once we're dead-set on believing 1 instead of 2. It says basically that if we already decided it's 1, then, yep, it's definitely not baryon matter (rocks, gases, protons, etc), but some weird matter that interacts only with gravity.
Re:Astrophysics Psychology Science (Score:3, Interesting)
Their initial assumption (page 1 right column): "During a collision of two clusters, galaxies behave as collisionless particles, while the fluid-like X-ray emitting intracluster plasma experiences ram pressure. Therefore, in the course of a cluster collision, galaxies spatially decouple from the plasma." Since the area occupied by dense matter (stars) is more than 10^11 times smaller than that of the whole cluster, literally one or two stars might impact each other. Meanwhile, the intracluster gas is, however diffuse, GAS - it can't pass through itself, and is observed to contain ~80-90% of a cluster's visible mass.
I don't know the specifics of how this is done, but they used a gradient of the change in a background galaxy's size and related it to the curvature of space (and hence amount of mass). By plotting a lot of background galaxies, they were able to integrate the gradient to find the center of mass (warning: not 100% sure of this explanation) that was causing the lensing (green gradient lines on page 2).
When this is compared with an x-ray image of the gas which is known to comprise most of the visible mass of clusters, the two mismatch by about 6 arc seconds. On page 4, they discuss the probability of other clusters creating the apparent mass (1/10 million chance) or entire filaments of intergalactic mass creating it (1 in 100 million). The only remaining conclusion from this is that something which fits the description of dark matter (in that it has mass but no other measurable property) makes up the great majority of the cluster's mass and the two clouds of it passed through each other like the galaxies.
So, they expected the stars/dark matter and the gas of colliding clusters to separate in a collision, and this is exactly what was observed
Re:This is What Slashdot Should Be (Score:3, Interesting)
Re:Dark matter and tech (Score:1, Interesting)
I think the parent, and replies, seem to be confusing energy, mass and gravity somewhat.
Matter is energy. The mass of something is effectively a measure of how much gravity it produces. Matter has mass, energy is matter, therefore energy also has mass, and yes, technically would generate a gravitional effect.
However, remember the most famous formula ever: E=mc^2
Mass is actually one hell of a lot of energy concentrated in one place. Hence most "energy" we are familiar with would exert very little (read, unnoticable) amounts of gravitional attraction.
Once you start approaching decent sized fractions of c, however, the kinetic energy of the object does actually start contributing measurably to the mass (gravitional effect) of the object.
Technically, particles like photons are classed as "massless." At rest, they have no mass, and thus no gravitational effect. Due to their nature, however, photons are never actually at rest, and therefore have some small mass. Though since the formula for kinetic energy is mv^2 / 2 something with zero mass should never gain any kinetic energy, so I'm either missing something or remembering wrong
So ignoring that hole I just dug myself, my overall point is still valid (I hope):
Energy = Matter = Mass = Gravitional Effect
Objects don't really "have" gravity - energy distorts spacetime around it and so produces an acceleration towards itself proportional to the energy density (energy per unit volume). We term this "gravity", but any accelerating object also distorts spacetime in an indistinguishable (by a single measurement) fashion.
Something doesn't have to have mass to be affected by gravity, it just has to travel in our spacetime. If spacetime is curved, producing an energy difference betweens two locations in space, then anything passing through will move towards the position of lowest energy. For gravitational effects, that's towards the center of gravity of the object creating the effect. For acceleration, it's in the opposite direction to the acceleration.
Re:So what's new, then? (Score:1, Interesting)
That is not correct.
Rotation curves of spiral galaxies are the reason people believe in galactic dark matter, which may well be baryonic. Baryons are the stuff we are made of, and Big Bang nucleosynthesis puts strong limits on the total density of baryonic matter in the universe given we know the primoridal H/He ratio, which we do with high confidence. We know from this that there is enough baryonic matter in the universe to account for galactic rotation curves, although that does not prove baryonic matter is the cause.
On larger scales, however, other dynamical anomalies are observed that require larger amounts of matter than can be accounted for by baryons. These other dark matter problems have nothing (necessarily) to do with the galactic dark matter problem.
The measurement these guys have made probes the dark matter distribution in colliding galactic clusters, making it a problem of intergalactic dark matter, which cannot be baryonic and may not be related in any way at all to the galactic dark matter problem.
The use of the single term "dark matter" for all these problems is dreadfully confusing to laypeople and fodder for cranks, and I really wish people would never use the term "dark matter" without being explicit about which dark matter they mean.