Beta
×

Welcome to the Slashdot Beta site -- learn more here. Use the link in the footer or click here to return to the Classic version of Slashdot.

Thank you!

Before you choose to head back to the Classic look of the site, we'd appreciate it if you share your thoughts on the Beta; your feedback is what drives our ongoing development.

Beta is different and we value you taking the time to try it out. Please take a look at the changes we've made in Beta and  learn more about it. Thanks for reading, and for making the site better!

Hubble Telescope Maps Dark Matter in 3D

Zonk posted more than 7 years ago | from the do-not-go-here dept.

Space 174

dido writes "The BBC reports that the Hubble Space Telescope has been used to make a map of the dark matter distribution of the universe, providing the best evidence of the role dark matter plays in the structure and evolution of the universe. From the article: 'According to one researcher, the findings provide "beautiful confirmation" of standard theories to explain how structures in the Universe evolved over billions of years.'"

cancel ×

174 comments

Sorry! There are no comments related to the filter you selected.

And yet... (1, Funny)

clifgriffin (676199) | more than 7 years ago | (#17501612)

Pluto is still not a planet.

*bitter*

you can't stop the spin machine (5, Funny)

macadamia_harold (947445) | more than 7 years ago | (#17501644)

According to one researcher, the findings provide "beautiful confirmation" of standard theories to explain how structures in the Universe evolved over billions of years.'

... thereby proving god exists.

MOD PARENT UP (0)

Anonymous Coward | more than 7 years ago | (#17502356)

mods on crack today. am i the only one that gets the joke?

This is pretty cool. (4, Interesting)

lordvalrole (886029) | more than 7 years ago | (#17501648)

I wonder what a 3d model of dark matter around a black hole would look like? Does it share the same properties as regular matter near a black hole?

Re:This is pretty cool. (3, Funny)

Tx (96709) | more than 7 years ago | (#17501692)

I wonder what a 3d model of dark matter around a black hole would look like?

Maybe I've just been around here for too long, but the parent post reads like goatse.cx meets GNAA.

Re:This is pretty cool. (1)

Coucho (1039182) | more than 7 years ago | (#17503048)

GNAA
Shhhh.. if you don't say it, it's not real!

Does Dark Matter exist? (1)

Anonymous Coward | more than 7 years ago | (#17501670)

I'm woefully ignorant on this, but is there any evidence towards the existence of dark matter, or is it something that would be necessary in order for certain theories on the composition of the universe to work?

Re:Does Dark Matter exist? (5, Funny)

clifgriffin (676199) | more than 7 years ago | (#17501698)

Think of it this way. On slashdot you have a lot of posts. Some of them are good. But they can't all be good all the time. So it follows that there has to be bad posts. Lot's of them.

That's dark matter.

I think that should be a modifier. -1, Dark Matter

Don't be mad that you didn't think of it...

Re:Does Dark Matter exist? (0)

Plutonite (999141) | more than 7 years ago | (#17502460)

I think that should be a modifier. -1, Dark Matter

Are you kidding? It's called Over-rated, and mysterious drunken moderators use it all the time.

Re:Does Dark Matter exist? (5, Informative)

HarveyTheWonderBug (711765) | more than 7 years ago | (#17501882)

Yes, there is, but we do not have a clue yet of what it is made of.
Astronomers have ways to measure the mass of objects, like galaxies, and cluster of galaxies, using a theory of the gravitation. For galaxies, the classical newtonian theory is enough: they just measure how fast the stars and the gas orbit around the galaxy, and derive directly their mass from kepler laws. For clusters of galaxies, or large structure, they use the bending of light by mass from general relativity. These measure are getting reasonably accurate. When they compare these masses to the mass they actually can see (stars, gas, etc..), they find that they can only account for 1/6 of the total mass they measure, well above all the uncertainties of the measurments. Therefore, there must be some matter (that is, something with a mass), that we cannot see (that does not interact via electromagnetism). This is the dark matter.
For more info, there is a [wikipedia] [wikipedia.org] entry.

Re:Does Dark Matter exist? (3, Insightful)

calice (570989) | more than 7 years ago | (#17502374)

This is what I don't get about dark matter, and this is just how I see it, and no one has ever given me a decent explanation. Why is it that scientists think that dark matter exists simply because the observed galaxies don't conform to Newton's Laws? Wouldn't a simpler solution be to take a step back and consider that, maybe, Newton's Laws are flawed? I am not trying to disprove dark matter, I certainly am no cosmologist, but it just seems odd that so much attention is given to dark matter, and very little is given to competing theories, such as MOND [wikipedia.org] (Modified Newtonian Dynamics), that to me, at least, make more sense.

My basic point is, from a layman's perspective, dark matter just sounds like something physicists pulled out of thin air to explain something they don't understand. Your observations don't make sense? Well, throw in some dark matter and we're good!

Can someone explain to me why dark matter is the prevalent theory? Or perhaps why something like MOND is always ignored? As I said, I don't know what is right, but it just seems like a hack-job to me.

Re:Does Dark Matter exist? (4, Informative)

Ambitwistor (1041236) | more than 7 years ago | (#17502524)

Why is it that scientists think that dark matter exists simply because the observed galaxies don't conform to Newton's Laws? Wouldn't a simpler solution be to take a step back and consider that, maybe, Newton's Laws are flawed?
You want a solution that is simple enough to explain the facts, but no simpler. Modifying the laws of gravity runs into difficulty explaining everything that dark matter can, although you can get it to explain some things (such as galactic rotation curves).

Can someone explain to me why dark matter is the prevalent theory?
In short, because it works and none of the alternatives people have proposed over the decades work as well. I can get into details if you want, but you should probably just start at Wikipedia.

Or perhaps why something like MOND is always ignored?
MOND isn't ignored. Go to the astro-ph arXiv or the Smithsonian/NASA ADS Abstracts and search for MOND papers. You'll find them, along with criticisms of MOND. Here [preposterousuniverse.com] is a nice but somewhat outdated set of slides on how well MOND fares against the evidence, and a more recent [cosmicvariance.com] blog post by the same author discussing newer evidence that tightens the screws on MOND even further.

As I said, I don't know what is right, but it just seems like a hack-job to me.
I don't know why all the hate for dark matter. Screwing around with the laws of gravity isn't any more elegant, and there are plenty of plausible candidate particles for dark matter lying around in various extensions to the Standard Model.

Dark matter == epicycles? (2, Insightful)

alienmole (15522) | more than 7 years ago | (#17504504)

I don't know why all the hate for dark matter.

Some skepticism is certainly in order. Since we currently have no way of independently confirming the existence of dark matter, we also have no way of distinguishing between two possible cases: one case is that dark matter corresponds to some real, physical material; the other is that the theory of gravity we're using is flawed. The fact that a better theory of gravity hasn't been produced doesn't mean that the current one is correct.

There are pretty strong parallels between dark matter and the infamous epicycles [wikipedia.org] . The case for epicycles was about as strong as that for dark matter: epicycles were a construction required to make the theory work, but there was no way to independently verify their existence, and they turned out to be essentially fictitious (assuming one doesn't take the position that they could be turned into a valid way of describing the solar system's orbital motion taking the Earth as center.)

The real problem is that there are no checks and balances here: by adjusting the mass distribution of dark matter, we can get whatever result we want, and there's nothing to either prove or disprove the proposed distribution. It's the ultimate hack, since it can be adjusted to suit every individual galaxy we observe.

Screwing around with the laws of gravity isn't any more elegant,

In the absence of independent evidence of dark matter, it would be more elegant if laws of gravity were discovered which explained the observations well without dark matter.

and there are plenty of plausible candidate particles for dark matter lying around in various extensions to the Standard Model.

That's a pretty weak position. It certainly doesn't do anything to counter the accusation that objects are being invented just to make the theory work.

Re:Does Dark Matter exist? (3, Insightful)

HarveyTheWonderBug (711765) | more than 7 years ago | (#17502676)

It's not completely true that MOND does not get any attention, there are very regularly publications in refereed journals about it, to prove it, disprove it, or try to make it better. Here is the problem as I see it:
  1. The current accepted theory of gravitation, general relativity, works extremely well: it's predictive power has so far never be successfully challenged. Many have tried, noone has succeeded.
  2. MOND had some success in explaining various observational puzzles, but has also some problems with others, as the wikipedia entry you link indicates.
  3. MOND is an ad-hoc theory, just like dark matter is an ad-hoc solution
  4. It is very hard to change your theoretical framework, much easier to add some stuff to the universe.
This explains to me why, right now, the current accepted paradigm is dark matter. While it is not satisfying, it is enough to explain both the rotation curves of disk galaxies, and the formation and evolution of the large scale structure of the Universe. I don't think many astronomers are satisfied with this current situation, and some are trying to resolve the issue, either explaining dark matter or getting rid of it. The others find with dark matter a framework where they can go on in exploring other scientific questions, like the evolution of galaxies, where you need to explain how their (normal) matter was assembled together, but also how this matter (gas) is made into stars, etc...

Re:Does Dark Matter exist? (3, Insightful)

NotZed (19455) | more than 7 years ago | (#17504312)

# The current accepted theory of gravitation, general relativity, works extremely well: it's predictive power has so far never be successfully challenged. Many have tried, noone has succeeded.

You mean, apart from the fact that you need to create 90+ percent more matter in the universe than what is visible to prevent galaxies from flying apart?

i.e. without dark matter (and dark energy), gravity doesn't predict much.

Re:Does Dark Matter exist? (1)

WilliamSChips (793741) | more than 7 years ago | (#17503106)

Personally I think the simplest solution is that dark matter is made up of neutrinos. Although I don't know whether that would be possible or not.

Re:Does Dark Matter exist? (3, Informative)

Ambitwistor (1041236) | more than 7 years ago | (#17503182)

No. Neutrinos aren't massive enough to be (most of the) dark matter. See here [princeton.edu] for a brief but more detailed discussion.

Re:Does Dark Matter exist? (1)

tangenterine (1048270) | more than 7 years ago | (#17503882)

There are physicists who express similar dissatisfaction with this theory. Perhaps you'd be interested in Philip Mannheim's opinion at the University of Connecticut. I won't try to paraphrase his work, since I'm only a physicist-in-training, but he teaches an astrophysics class in which he addresses this problem. My take: If the theory doesn't work witht the data, it's because the theory is wrong--you don't go invent something just to satisfy the theory. Likewise, "laws" are theories we really like while the non/existence of something is absolute (well, generally). There are various takes on the evidence for dark matter, but altogether my understanding is that it's virtually undetectable (no E&M interaction)--so it can't be disproven, only "not yet verified". see for more info

Re:Does Dark Matter exist? (0)

Anonymous Coward | more than 7 years ago | (#17503632)

Holy shit... you're smart for a car.

Re:Does Dark Matter exist? (0)

Anonymous Coward | more than 7 years ago | (#17502296)

First off, I am an astrophysicist, but my field isn't particularly related to dark matter, I do instrumentation mostly, although I do try to follow brane theory research on the side.

There's a lot of disagreement about whether "darkmatter" exists or rather why we see the things we think we see - what causes the effects? There's a lot of other potential theories which seem (give or take) similarly plausible, MOND for instance or something coming out of M or brane theory. The fact is that we just don't know, and a lot of this sort of mediahumping is driven by folk anxious for 5 minutes of fame who jump to conclusions. If this were religion rather than science, each side (the different sorts of darkmatter believers) would be calling the other "fanatics" and extremists, but most scientists aren't as good at mediaspin as religionists... yet.

Budgets and penis-size competitions are what drive a lot of astrophysics today.

Re:Does Dark Matter exist? (0)

Anonymous Coward | more than 7 years ago | (#17502358)

There's a lot of disagreement about whether "darkmatter" exists or rather why we see the things we think we see - what causes the effects?
Actually, dark matter has become pretty mainstream. The disagreement now is mostly over what it is, not whether it exists.

There's a lot of other potential theories which seem (give or take) similarly plausible, MOND for instance or something coming out of M or brane theory.
That's also not true. The stringy stuff has been relatively poorly tested, and MOND runs into trouble in several areas over the last few years, most recently and notoriously with the Bullet Cluster. MOND still isn't totally dead, but it's looking more and more like even if MOND is true, you're still going to need at least some dark matter to explain things (just not as much as with no MOND).

Re:Does Dark Matter exist? (4, Interesting)

pln2bz (449850) | more than 7 years ago | (#17503870)

The real story of how we ended up with dark matter is not widely understood or accepted.

Some time ago, a man named Hannes Alfven, who is today considered the father of plasma physics, founded the field of magnetohydrodynamics, which astrophysicists have been using to model plasma in the universe for several decades now. This field treats plasma as a fluid and assumes that currents cannot flow through the plasma because it treats plasma as an ideal conductor with no resistance. This is actually not *anything* like the way that plasma operates in the real world, and since plasma represents 99%+ of all observable matter within the universe, this massively incorrect assumption yields absurd results in astrophysics today. Plasma is in fact electrically conductive and its electrical properties interact with its mechanical motions, and vice-versa. If you've ever seen a novelty plasma globe, then you intuitively know that plasma is not like a fluid. You can tell by looking closely at a plasma globe that the plasma creates filaments and these filaments pair up and twist around one another. These twisting currents are called Birkeland Currents. As the current flow increases through them, they pinch together with increasing force and this pinching action can actually condense matter into a ball. This is a big deal because there is no good reason to believe that molecules will gravitationally collapse from a diffuse collection of matter in space; in fact, gases obviously expand in a vacuum. Contrary to the more popular beliefs propagated in astrophysics and the media today, the z-pinch effect is likely actually how planets and stars form. Astrophysicists don't understand this because of their earlier assumptions regarding plasma being a fluid with no currents. But we can see strong evidence of Birkeland Currents and Z-Pinches happening through our telescopes.

The thing is, astrophysicists will see what they want to see through the telescope. All observations today are interpreted through mainstream concepts like stellar evolution and Big Bang theory. When an anomaly pops up, it can be a very simple matter to propose a "patch" for the theory to keep it going. Astrophysicists will invoke collisions, black holes, gravitational lensing or malformed electrical theory in order to explain away anomalies. But you will notice that anomalies are discovered nearly every week these days (especially with stellar evolution), and this is a problem because things like collisions should not actually be happening as often as they are being invoked to dismiss the anomalies.

When Hannes Alfven received his nobel prize for plasma physics in the 70's, he recused himself from the field that he created (MHD) and warned astrophysicists to abandon it, and that the path they were taking would eventually dead-end. But they completely ignored him and continue to do so. So, now we have mysterious forces tugging on matter throughout the universe that we can't see. This is what we call dark matter. Dark energy is supposed to be matter that can gravitationally repel. Electrical forces can accomplish both of these feats without any mysterious matter. All you have to do is drop the earlier incorrect assumptions about plasma and accept that extremely diffuse plasma flows can and do exist. You will notice over time that the dark matter studies will reveal some details that correspond with the properties of electricity over plasma. For this particular article, it was noticed that the structure of the dark matter was in places filamentary. Filamentary structures are far easier to generate with electricity than with gravity. It was also mentioned that dark matter can exist in the absence of physical matter. This is to be expected with plasma because plasma can consist of just electrons and ions, or it can also be coexisting with or collecting dust.

Some brave scientists and electrical engineers called Electric Universe Theorists are working on understanding the universe in terms of real plasma physics -- which makes perfect sense given that space basically *is* plasma. A lot of rather intelligent people here on Slashdot though over time have accumulated very thick skin when it comes to any sort of science that is against the mainstream. However, few of them actually understand the history or theory, and there is plenty of misinformation out there. Identifying pseudosciences can be tricky. People don't want to invest a bunch of time into learning what a theory has to say only to find out that it's not true. So, the end result is that people on Slashdot tend to accept the mainstream claims from astrophysicists about black holes, neutron stars, dark matter, dark energy, magnetic reconnections on the Sun and a bunch of other nonsense, and Electric Universe Theory (which is based upon non-idealized plasma theory) is considered to be pseudoscientific. I've spoken to a lot of people here on Slashdot about EU Theory, and it is clear to me that nobody really knows what the theory says. Many people discount it on the basis of electrostatic rules they learned in high school physics, for instance, but plasma is far more complicated than that and remains an active field. You must know electrodynamics in order to fully understand it, and to my knowledge, astrophysicists are not fully trained in electrodynamics or plasma physics.

It's a really unfortunate situation because it looks like we're going to have to wait for a bunch of people to die off before all of this dark matter nonsense disappears. Astrophysicists are so convinced that they're right that they refuse to listen to reason from anybody who hasn't been educated just like themselves. We're all paying the price for their arrogance, in a sense, because we'll probably never get to see big money going into plasma cosmology or Electric Universe Theory within our lifetimes either. But there is a large amount of literature out there that's of great quality on the subject. Don Scott's new book, "The Electric Sky", is very impressive. You can find lots of other materials at www.thunderbolts.info. You can learn much of the theory by just going through their database of picture of the day's on that site.

Be wary though in talking about EU Theory with people. There is a lot of hostility out there towards anything that is not popular in physics these days. There is some strange need amongst astrophysicists and amateur astronomers for conformity these days. It's unusual actually because the large majority of our most famous ideas in science today have come from non-conformists. A lot of people have the mistaken belief that since we have proofs for the Big Bang that that means that the Big Bang has been proven; in fact, we can generate proofs for lots of cosmologies.

Re:Does Dark Matter exist? (1)

iamstretchypanda (939837) | more than 7 years ago | (#17504242)

Taken directly from CERN [web.cern.ch]

"What is "Dark matter" made of?

Measurements in astronomy imply that up to 90% or more of the Universe is not visible (i.e. does not emit electromagnetic radiation) . Scientists call this undetectable "stuff" dark matter.

Its presence is felt through the gravitational effects on the matter we can see. Stars in galaxies, for example, appear to be moving much faster than they would if they were influenced only by the visible matter in the galaxy.

The nature of dark matter and its role in the evolution of the universe are still unknown.
Probably it is made of several components, among which are neutrinos, dust, cold gas, and special particles predicted by the grand unification theories but not yet seen, the so called "superparticles".

Physicists hope to identify some of the elementary constituents of dark matter at the LHC."

As we can all see, the experts aren't even sure of the elementary principals yet.

Anyone want to expand on "superparticles." Seems as if they are referring to neutrinos.

Blue Humor (-1, Troll)

Mr Jazzizle (896331) | more than 7 years ago | (#17501674)

Any word of Dark Matter on Uranus?

Re:Blue Humor (0)

Anonymous Coward | more than 7 years ago | (#17501998)

finger smelly?

Enlighten me (3, Interesting)

Original Replica (908688) | more than 7 years ago | (#17501684)

To those /.ers that know more of physics than I do, is Dark Matter supposed to be some actual particle, or is it a kind of natural gravitational topography? Everything I read ( quick google search/old copy of "Elegant Universe") about it seems to be rather vague and mysterious.

Re:Enlighten me (0, Troll)

LiquidCoooled (634315) | more than 7 years ago | (#17501746)

I've always been sceptical of dark matter as something mysterious.
It's fucking obvious that if there is no light illuminating an object it will be dark.
In this solar system there is loads of dark matter, unless of course people and most objects naturally glow.

Re:Enlighten me (3, Informative)

bloobloo (957543) | more than 7 years ago | (#17501792)

Anything with a temperature above absolute zero glows. You've just got to be about the temperature of a star to emit most of your light at visible (to human) wavelengths.

Re:Enlighten me (2, Interesting)

marcosdumay (620877) | more than 7 years ago | (#17502246)

Only if it interacts with light. Neutrinos, for example, don't glow (and don't absorb light either).

Re:Enlighten me (1)

LiquidCoooled (634315) | more than 7 years ago | (#17502382)

Bad choice of wording from me, but something has to glow pretty damn brightly to be seen at the distances we are discussing.

If everything was visible the night sky would be bright instead of dark.
The illumination must be bright enough that we can see it at distance - its like us trying to see the lights onboard the ISS.

Re:Enlighten me (1)

forand (530402) | more than 7 years ago | (#17503528)

Sorry this is not true. It is true on the subset of KNOWN matter that we deal with on a day to day basis. However you can get rather strange states of matter or collections of unique particles that do not, like a room full of neutrinos isn't going to radiate anything other than neutrinos.

Re:Enlighten me (0)

Anonymous Coward | more than 7 years ago | (#17501910)

What is 'fucking obvious' is that you've never read up on dark matter. As the other poster already said, all 'normal' matter made up of proton, neutrons, and electrons, 'glows' in a way if it is above absolute zero. Dark matter is supposed to be made of other stuff. I think thousands of physicists who do physics for a living thought accounted for 'stuff light isn't shining on' before some idiot on /.

They might not be right on it existing, or being what they thought, but they've at least bothered to learn the basics of the theory.

Re:Enlighten me (1)

Kagura (843695) | more than 7 years ago | (#17502976)

Don't people glow in the infrared? Remember that infrared is also light, just not visible light.

Re:Enlighten me (0)

Anonymous Coward | more than 7 years ago | (#17501754)

To those /.ers that know more of physics than I do, is Dark Matter supposed to be some actual particle, or is it a kind of natural gravitational topography?

Yes.

Re:Enlighten me (2, Funny)

syousef (465911) | more than 7 years ago | (#17501816)

Kosh, is that you?

Re:Enlighten me (4, Informative)

ceoyoyo (59147) | more than 7 years ago | (#17501846)

Nobody knows.

Some portion of it could be ordinary matter that's simply non-luminous, but I think there are observations that limit that to a small proportion.

The rest seems to be something that interacts only gravitationally... it might be a particle we haven't discovered yet. That's not as far fetched as it sounds -- neutrinos are just such a particle. They have mass so they interact gravitationally but they interact with ordinary matter extremely weakly in all other ways. Massive neutrinos were also candidates to explain some of the dark matter for a while, but I believe once their actual mass was measured it was too little to explain more than a bit of the dark matter.

Re:Enlighten me (4, Informative)

Dachannien (617929) | more than 7 years ago | (#17502098)

Some string theorists believe dark matter may be gravitons, emitted by matter on adjacent branes, that intersect our own universe's brane, resulting in a gravitational distortion that becomes huge at cosmological scales. A similar concept is used to explain why the gravity exhibited by real matter in our own universe has a strength many orders of magnitude smaller than the other forces - most of the gravitons leave our universe's brane, while the mediating particles of other forces (gluons, photons, etc.) are constrained to move within the brane.

See also http://en.wikipedia.org/wiki/Brane_cosmology [wikipedia.org] .

Re:Enlighten me (1)

ceoyoyo (59147) | more than 7 years ago | (#17502208)

Yeah, I find that one of the more interesting theories since it would give us our only way of detecting what's on adjacent branes. Whatever it turns out to be, dark matter and dark energy seem to be some of the most interesting anomalies going today. Maybe one day I'll get my faster than light yacht.

Re:Enlighten me (4, Funny)

glwtta (532858) | more than 7 years ago | (#17503214)

Some string theorists believe dark matter may be gravitons, emitted by matter on adjacent branes

Yeah, but string theorists make theoretical physicists look like scientists :)

Re:Enlighten me (1)

cold fjord (826450) | more than 7 years ago | (#17502926)

The rest seems to be something that interacts only gravitationally... it might be a particle we haven't discovered yet.

It is possible that most of the dark matter needed by current theories to explain the universe we see doesn't really exist, and that our understanding of gravity is wrong. The TeVeS theory, developed from MOND, may be able to explain the universe without requiring that most of it be made of dark matter and dark energy. See Gravity's dark side [physicsweb.org] . Also mentioned in a previous Slashdot story [slashdot.org] . To really know, TeVeS will need a lot more work done with it. That will be a challenge since the dark matter theories get the vast majority of attention, time, and funding.

Re:Enlighten me (1)

ceoyoyo (59147) | more than 7 years ago | (#17503466)

It is possible, but observations seem to be making it less and less likely. It doesn't explain these Hubble observations very well, and it doesn't explain the colliding galaxies observation.

Even without those, as you said, modifying gravity might explain most of the observations. That still leaves some others, that we'd need something else to explain. Even the modified gravity researchers are saying ou still need some dark matter to make everything work.

So, Occam's razor -- which is the simplest explanation: dark matter, or dark matter plus modified gravity?

Not to say that gravity research wouldn't pay dividends, but the reason dark matter is getting the most attention is because it's the most likely.

Re:Enlighten me (5, Informative)

radtea (464814) | more than 7 years ago | (#17503364)

Some portion of it could be ordinary matter that's simply non-luminous, but I think there are observations that limit that to a small proportion.

Big Bang nucleosynthesis limits the amount of baryonic (that is, "normal") matter to a relatively small fraction of the total observed mass of the universe. The basic idea is that we know how big the universe was when protons and neutrons (collectively known as nucleons) were being formed--at some point the cosmic fireball cooled off to the point where quarks were no longer free, so they condensed into nucleons. We also know that the lifetime of a free neutron is about 15 minutes, so there was only about an hour for nuclei more complex than hydrogen to form.

So, if the universe was VERY dense in the hour or so after nucleon formation then every single proton would have run into a neutron or two and there would be almost no plain old hydrogen in the universe--everything would be helium and deuterium. On the other hand, if the the universe were extremely diffuse during that single hour there would be hardly any helium--only the few percent made by stellar fusion and supernova in the past ten billion years. As it is, we are pretty sure based on observations and theory that about 20% of the helium in the universe was formed in the Big Bang. That, plus some more problematic numbers from deuterium and lithium and helium-3, give us a very good estimate of the total baryonic mass in the universe.

The visible mass is quite a bit smaller than the total baryonic mass, and there is some reason to believe that the flat rotation curves of spiral galaxies are due to baryonic dark matter, although it would have to be in the form of small clumps of matter like comets or dead stars or something to not do any significant scattering of light.

Dark matter on larger scales is completely unrelated to galactic dark matter--the use of the single term "dark matter" for these totally unrelated problems is unfortunate and confusing, as I point out every time this topic comes up on /.

The observation reported here, like the colliding galactic clusters observation reported a month or so ago, is amongst our first clear view of extra-galactic dark matter, which is too copious to be explained as normal baryonic matter.

The problem that cold dark matter theorists have to deal with is that the extra-galactic dark matter can't just interact gravitationally, because gravity is too weak a force to produce structures in the short time the universe has been around. To clump in the manner observed, extra-galactic dark matter has to have some mechanism for losing energy. Otherwise two pieces of dark matter (or a piece of dark matter and a peice of ordinary matter) would just pass through each other. The dark matter would never be slowed down by anything, and so would never form clumps on any scale.

So it is probable that extra-galactic dark matter is pretty exotic, or that something was sufficiently different in the early universe to make gravity sufficiently dissipative to form the observed clumps. Either way, the flood of observations using these new microlensing techniques is going to start killing off theories in droves--at least those theories that make actual predictions.

Re:Enlighten me (1)

ceoyoyo (59147) | more than 7 years ago | (#17503524)

Good explanation. Thank you.

Re:Enlighten me (1)

Carmelbuck (921788) | more than 7 years ago | (#17503742)

...there is some reason to believe that the flat rotation curves of spiral galaxies are due to baryonic dark matter, although it would have to be in the form of small clumps of matter like comets or dead stars or something to not do any significant scattering of light.

Microlensing surveys have already placed upper limits of well under half the dark matter in a typical galactic halo being baryonic.

Dark matter on larger scales is completely unrelated to galactic dark matter--the use of the single term "dark matter" for these totally unrelated problems is unfortunate and confusing, as I point out every time this topic comes up on /.

On what, exactly, are you basing this statement? It's certainly not the majority scientific view.

To clump in the manner observed, extra-galactic dark matter has to have some mechanism for losing energy.

Do you have a citation for this? To the best of my knowledge, none of the (generally quite successful) structure formation simulations include any interaction for dark matter besides gravity.

I'm not criticising (yet), but you're making what appear to be claims based on evidence, and I'm wondering what that evidence is.

Re:Enlighten me (2, Interesting)

TMB (70166) | more than 7 years ago | (#17504430)

Just one minor quibble:
The problem that cold dark matter theorists have to deal with is that the extra-galactic dark matter can't just interact gravitationally, because gravity is too weak a force to produce structures in the short time the universe has been around. To clump in the manner observed, extra-galactic dark matter has to have some mechanism for losing energy. Otherwise two pieces of dark matter (or a piece of dark matter and a peice of ordinary matter) would just pass through each other. The dark matter would never be slowed down by anything, and so would never form clumps on any scale.
Actually, gravity on its own is easily enough to produce the structure we see. The dark matter doesn't dissipate any energy to form clumps, it simply falls toward the overdense regions, which become even more overdense because of all the infalling dark matter, ad infinitum. Each individual dark matter particle may pass right through all the other dark matter particles and go out the other side, but as long as it's moving at less than the escape speed then it turns around and comes back, bouncing around inside the clump forever.

In fact, one of the main problems now is that cold dark matter produces too many small clumps compared to the observations.

[TMB]

Re:Enlighten me (1)

a.d.trick (894813) | more than 7 years ago | (#17502020)

I'm not an expert on physics but AFAIK I don't think anyone knows much at all about dark matter. It seems to me like it's just a poor excuse for why the observed facts don't fit our lovely theories.

Damned facts, always getting in the way.

Re:Enlighten me (2, Insightful)

TapeCutter (624760) | more than 7 years ago | (#17503584)

Close, dark matter is the "hack" we use to make our theories fit our obervations. If we had not observed "something" we would not need to invent the name "dark matter" to label it.

I fail to see how it is a "poor excuse" for anything, it's mearly a description of something we don't fully undersatnd but can indirectly observe and therfore label. Maybe our elegant theories will need to change to account for future observation but right now our notion of what we label as "dark matter" explains the observed anomolies better than any other concept, including the proposed modifications to gravitational theory.

For a historical perspective you just need to go back a hundered years to a time when scientists were having a similar debate about the existance and structure of atoms. Sure the model of atoms looking like "a pudding with razor blades stuck in it" fell by the wayside when it failed to explain all the observations. That is how science progresses, it's an evolution of ideas and analogies, not a static statement of "the truth".

Re:Enlighten me (4, Informative)

Anonymous Coward | more than 7 years ago | (#17502086)

The general belief is that it is an actual particle. There are other competing theories such as MOdified Newtonian Dynamics which have slight corrections to our current laws of gravity, but more and more evidence is ruling out the simplest of these models and it's pretty clear that at least some of the dark matter is actually particles. Another thing people thought dark matter could be was normal matter which doesn't produce light, things like planets and failed stars. However, extensive astronomical searches for these objects (called MACHO's) using both the fact that they should occassionally block our view of stars and their potential to cause gravitational lensing have turned up nothing. This basically leaves some sort of new particle as the dark matter canidate. The current theory is that this particle only interacts via the weak nuclear and gravitational forces. It Is is called a WIMP (weakly interacting massive particle). There are a bunch of different models of what this particle is. Basically nearly every theory of physics beyond our current Standard Model has some sort of particle that it's proponents hold up as a dark matter canidate.

There are a wide variety of dark matter searches being conducted which directly search for the particle. The general idea is to see their interaction through the recoil of an atom when one strikes the atom's nucleus. This is very difficult. The most common current technique is searching for the "sound" a dark matter particle interacting with cryogenically cooled germanium crystals produces.

Re:Enlighten me (1)

kiyoshilionz (977589) | more than 7 years ago | (#17502884)

Really, the evidence for "dark matter" has been made through its effects - it bends light, and makes galaxies spin at a different rate than what we're currently observing. Scientists have inferred its existance from its effects. Not a really bad practice, but as the other posts around here indicate, we've got a long way to figuring out what the hell is really going on.

dark matter does not exist (3, Insightful)

ars (79600) | more than 7 years ago | (#17501750)

"beautiful confirmation" of standard theories?????

What standard theories? Dark matter does not exist, as least not as far as anyone (except astronomers with good imaginations) knows. There is a very nice (and complete!) standard model of physics, and dark matter holds no place.

I should qualify, I'm talking about theroes of non-baryonic dark matter [wikipedia.org] and even worse dark energy [wikipedia.org] .

Regular matter, that is simply dark - i.e. cold, and not emiting light, does not bother me. But making up particles no one has ever seen just because you don't understand what you are seing is fitting facts to the data.

Scientists often discuss new theories, etc, and in that context dark matter has it's place, but to claim it exists - as this story does - without being able to actually measure anything is quite silly and premature. If you don't understand something, say so, don't invent plausable explanations that have nothing supporting them except your lack of knowledge.

Re:dark matter does not exist (1)

ars (79600) | more than 7 years ago | (#17501822)

I shouldn't have used the phrase "is fitting facts to the data", please ignore it, I misstyped. Pretend the sentence just ended in a ?

Re:dark matter does not exist (4, Insightful)

ceoyoyo (59147) | more than 7 years ago | (#17501958)

Isn't that exactly what they did? They measured mass distributions through gravitational lensing and noted the places where there was more apparent mass then there should be. You can theorize that gravity works strangely at large scales, and inconsistently too, since they found clumps, but the simplest explanation that matches the observations is that there is something with mass that we can't see. It might be normal matter, but the fact that there's an enormous amount of it and it somehow avoids rubbing together and getting hot like all the other matter we know of is problematic. When galaxies collide it also seems to just keep on going while the normal matter slows down when it hits something going the other direction. Given those two observations (dark and appears not to interact other than gravitationally), a subatomic particle isn't so bad an explanation. It's not so far fetched either -- we know of other particles that have those properties. They're called neutrinos.

Re:dark matter does not exist (1)

YttriumOxide (837412) | more than 7 years ago | (#17503544)

Picture for a moment, two universes "side by side" in a dimension we can not physically see, but effectively "overlaid" in all dimensions we can measure/see. No interactions take place between these two universes other than gravity (for reasons that are exaplainable, but beyond the scope of this post).

The influence of the gravitational pull from the one universe would certainly have the exact same features/constructs as what is described here (clumped in parts, not in others etc)

Because these two universes interact gravitationally, it would make sense that matter and "dark matter" would tend to be found in the same places as well, which is exactly what has been observed. The occasional area where they're not found together (dark matter without matter) is also not so hard to comprehend (as would be matter without dark matter if we found that as well).

For those of you who think I'm talking nonsense - this is a dramatic oversimplification of what brane theory (related to string theory/M theory) would have to say on the subject. For those of who you think it's not science because it's not provable, you're probably right... but it's an avenue that I think requires some scientific thought put in to it so that one day it may well become "true" science.

Re:dark matter does not exist (5, Informative)

HarveyTheWonderBug (711765) | more than 7 years ago | (#17501988)

"beautiful confirmation" of standard theories?????
Yes indeed. The standard paradigm for the evolution of the Universe is the widely accepted lambda-CDM model, or Cold Dark Matter with a cosmological constant (or dark energy). The recent results of WMAP, of the high-z supernovae, all point toward a set of cosmological parameters where the energy density of the universe is made of:
  • 70% of dark energy
  • 30% of matter
    • out which, stars, gas, neutrino are making at most 5%
    • so we are left with 25% of dark matter
So yes, dark matter is widely accepted. It's not satisfying because we have no clue about what it is (it clearly does not interact electromagnetically), but we can feel its gravitational pull. Coming up with a good theory on its nature is one of the hardest challenges in modern astrophysics.

Re:dark matter does not exist (2, Insightful)

yusing (216625) | more than 7 years ago | (#17502994)

70% of the universe is made of some theoretical "substance" that hasn't shown up in several decades of particle physics observations??

I smell a Thomas Kuhn moment in the making. Or at least, a phlogiston moment.

Explaining the universe is hard. But saying stuff like "it's real", even implying that it is ... when there's not even a working theory about it yet ... is dangerous to the craft. When people get religious about stuff like string theory, it endangers science.

Re:dark matter does not exist (1)

Ambitwistor (1041236) | more than 7 years ago | (#17503038)

70% of the universe is made of some theoretical "substance" that hasn't shown up in several decades of particle physics observations??
Why should it, if it's weakly interacting and massive? (Which are precisely the properties it needs to explain the astrophysical observations, by the way.)

I smell a Thomas Kuhn moment in the making. Or at least, a phlogiston moment.
The difference is that dark matter keeps on passing new and independent observational tests.

Re:dark matter does not exist (1)

Ambitwistor (1041236) | more than 7 years ago | (#17503096)

Oops, you were referring to dark energy, not dark matter. Dark energy may not be a "substance" at all; the best current explanation of dark energy (the cosmological constant) is a modification of the laws of gravity, not a new kind of particle.

Re:dark matter does not exist (1)

HarveyTheWonderBug (711765) | more than 7 years ago | (#17503188)

I was refering to the energy density of the universe. You are mixing dark energy and dark matter.

Since the famous E = mc2 we can compare the energy content of the universe (like photons) and matter (like the atoms you are made of). So yes, to explain all the current observations, we need a lot of dark energy (or call it a cosmoligical constant if you'd like). There are theories to explain it, like a scalar field, etc...

But that's not the subject of the paper and press releases. They are about dark matter. That is something with a mass, so you can actually observe it's gravitational effect on the normal luminous matter. And there are some clues as to its nature, but no definitive answers yet...

Re:dark matter does not exist (1)

Too Much Noise (755847) | more than 7 years ago | (#17502054)

But making up particles no one has ever seen just because you don't understand what you are seing is fitting facts to the data.

You do realize that science is 'just' fitting theoretical models to data, do you? And that, while a model survives by being able to fit more types of data, it usually starts by fitting one or a handful?

Scientists often discuss new theories, etc, and in that context dark matter has it's place, but to claim it exists - as this story does - without being able to actually measure anything is quite silly and premature.

You are in error here. There are observations seeing dark matter (see here [physicstoday.org] for example) - it's just that they don't provide information on what it is. And ultra-low cross-section particles are not as fantastic as you seem to make them - just because we don't know they exist we shouldn't rule them out. Or in. File it as usually under 'maybe' until further testing.

Re:dark matter does not exist (1)

sholden (12227) | more than 7 years ago | (#17502890)

It's pretty clear the phrase that was meant to be typed was "making shit up".

Because galaxies don't rotate the way our current theory of gravity says they should, because gravitational lensing isn't working the way our current theory of gravity says it should, because of a bynch of other thing I guess, the accepted solution it to declare that 95% of the universe is made of stuff we can't directly detect, can't do experiments on, doesn't exist locally, and is completely different from the universe we do observe and interact with.

But it makes the numbers work, so it's all good.

Re:dark matter does not exist (3, Informative)

Ambitwistor (1041236) | more than 7 years ago | (#17502952)

Because galaxies don't rotate the way our current theory of gravity says they should, because gravitational lensing isn't working the way our current theory of gravity says it should, because of a bynch of other thing I guess,
You act as if having a bunch of observational evidence for dark matter is unimportant.

the accepted solution it to declare that 95% of the universe is made of stuff we can't directly detect,
Would dark matter be more palatable to you if it only made up 5% of the universe? Why does it suddenly become more implausible if it makes up most of the universe. It's because it makes up most of the universe that we can even tell it's there.

can't do experiments on,
That remains to be seen; we may be able to create such particles in accelerators, and we may also be able to detect them in the Sun, in cosmic ray experiments, etc.

That being said, even if we can't do experiments on dark matter, why does that suddenly make dark matter implausible, in the face of all the other astrophysical phenomena it explains? Is there some law of the universe that says that all matter must be easily producible and manipulable by humans?

doesn't exist locally,
That's false. It surely does exist locally.

That being said, even if it didn't exist locally, why does that suddenly make dark matter implausible, in the face of all the other astrophysical phenomena it explains? Is there some law of the universe that says that everything interesting or important in the universe has to exist nearby?

and is completely different from the universe we do observe and interact with
It's not that different. Ordinary neutrinos have most of the properties needed to be dark matter; they're just not massive enough.

That being said, ... well, you get the idea.

Re:dark matter does not exist (5, Informative)

Ambitwistor (1041236) | more than 7 years ago | (#17502282)

What standard theories?
The standard theories of large-scale structure formation in the early universe, which is mediated by non-baryonic dark matter.

Dark matter does not exist, as least not as far as anyone (except astronomers with good imaginations) knows.
Wow, that's a compelling counterargument. However, it neglects the decades worth of observational evidence in favor of dark matter in the form of galactic rotation curves, the motions of satellite dwarf galaxies, gravitational lensing, measurements of galactic gas temperatures (which depend on the local gravitational neighborhood), anisotropies in the CMBR, the rate and structure of large-scale cosmological structure formation, etc.

There is a very nice (and complete!) standard model of physics, and dark matter holds no place.
Actually, one of the leading dark matter candidates is the axion, which was introduced into the Standard Model to resolve the strong-CP problem. However, the astronomical evidence indicates that the Standard Model of particle physics is most likely not complete, and that at least one new weakly-interacting massive particle is needed.

Regular matter, that is simply dark - i.e. cold, and not emiting light, does not bother me. But making up particles no one has ever seen just because you don't understand what you are seing is fitting facts to the data.
There is nothing wrong with "making up particles no one has ever seen" in order to explain discrepancies in either theory or observation. It's rather the point of science, to frame new hypotheses. Historically, see the prediction of the positron, on the basis of theoretical consistency between quantum mechanics and relativity, or the prediction of the neutrino, on the basis of apparent non-conservation of energy.

Scientists often discuss new theories, etc, and in that context dark matter has it's place, but to claim it exists - as this story does - without being able to actually measure anything is quite silly and premature. If you don't understand something, say so, don't invent plausable explanations that have nothing supporting them except your lack of knowledge.
Dark matter is a plausible explanation precisely because it is supported so well by numerous disparate observations. There are other ways one can attempt to explain various discrepant observations (e.g., by modifying the laws of gravity), but dark matter is far and away the most successful, as it passes all known independent tests. There's no reason why an ad-hoc patch designed to explain galactic rotation curves should also end up explaining, say, cosmological expansion, or large-scale structure. And it's silly to claim that we cannot measure anything: we can measure the gravitational effects of dark matter.

Sure, everyone would love it if we could detect dark matter particles directly — and if they interact non-gravitationally, we hopefully will someday. But what's silly is to claim that we have little reason to believe that dark matter particles exist.

Standard Model Complete... With Caveats (1)

BlackGriffen (521856) | more than 7 years ago | (#17502480)

It misses one of the four fundamental forces of nature. You know, an unimportant little thing we call "gravity." Naturally, if there's a particle that only interacts gravitationally, it would also have to be missing from the standard model.

There's also the unresolved matter of actually observing a little particle that is in the Standard Model called the Higgs boson.

Trust me, the standard model is really really good, but it's far from complete.

Re:dark matter does not exist (5, Informative)

Carmelbuck (921788) | more than 7 years ago | (#17502630)

Every time an article regarding dark matter is posted on Slashdot, there are nonsense "fudge factor!!1!" postings like the above. And every time, like-thinking idiots mod them up as "Insightful" or "Interesting". And every time, I suspect, people like me get the urge to go through and respond to every single one, but have to limit ourselves.

So let's start at the beginning, shall we? Galaxy rotation curves indicate that there is more mass in galaxies than would be inferred from the luminous matter. How do we know that it's not clouds of cold gas? Because that's ruled out by 21cm observations and by studying the absorption spectra of extragalactic objects. How do know that it's not clouds of hot gas? Becasue that's ruled out by UV and X-ray observations. How do we know that it's not brown dwarfs and black holes? Because that's ruled out by microlensing surveys.

Now, studies of galaxy dispersion velocities in clusters indicates that there's more mass in galaxy clusters than than would be inferred from the galaxies themselves, plus the intracluster medium which is observed in the X-ray. This is verified to high accuracy (i.e., the estimates of the total cluster mass are in close agreement) by hydrostatic X-ray mass measurements and by weak lensing observations. How do we know that it's not clouds of cold gas? Because that couldn't coexist with the hot gas, and because the dark matter spatial distributions are clearly different from the gas distributions. How do we know that it's not clouds of hot gas? See "intracluster medium" above. How do we know that it's not brown dwarfs and black holes? Because there's no mechanism for moving large numbers of objects out of the galaxies into the ICM (there are some intracluster stars, yes, but relatively very few--and the number of those gives us hints as to the number of non-luminous objects similarly ejected). How do we know that it's not neutrinos? Because neutrinos are experimentally shown to be too light and too fast, and cosmological constraints show that too few would have been produced in the Big Bang.

Now, studies of cosmological structure formation indicate that the size and number of galaxy clusters in the universe are not consistent with what would be expected given an all-baryonic universe. How do we know that...er...well, that's that. Cold collisionless dark matter is required to make the simulations work.

How do we know that modified gravity isn't the answer? See multiple independent lines of evidence above. There are no theories of modified gravity that come even close to explaining all of the above. The MOND people cheerfully acknowledge this, even if their advocates on Slashdot don't.

Look, the history of physics is replete with things whose existence was inferred long before they could be directly observed--neutrinos, quarks, atoms themselves, and much, much more. It's simply asinine to suggest that "we haven't directly measured it" means "it doesn't exist". Heck, we only really "see" subatomic particles because of the photons given off when they interact with one thing or another--"seeing" dark matter via measurements of its gravitational effects is hardly less direct.

And we'll just ignore the nonsensical "fitting facts to the data". The bottom line is, there are multiple, independent lines of evidence that dark matter exists, and that it is non-baryonic. Uninformed posters on Slashdot can pat themselves on the back for their intelligence as much as they want, but they're only fooling themselves.

Re:dark matter does not exist (1)

HarveyTheWonderBug (711765) | more than 7 years ago | (#17502738)

mod parent up !

Re:dark matter does not exist (1)

Ambitwistor (1041236) | more than 7 years ago | (#17502794)

Seconded.

Re:dark matter does not exist (1)

NeoSkink (737843) | more than 7 years ago | (#17502920)

Indeed! Carmelbuck covered the reasons Dark Matter is part of the standard cosmological model very well. His comment really should be the highest moded, not the above uninformed "Dark Matter is just made up!" rants.

Re:dark matter does not exist (1)

fermion (181285) | more than 7 years ago | (#17502730)

On one level, I consider dark matter to have the same credibility as the æther. An interesting concept, but largely created as hack to the model. The æther is shown not to exist and we have a more robust theory for the propagation of light. I suspect that the same will be true dark matter, and it will lead to a more robust theory of gravity.

That said, as the universe is explored in more detail, we increasingly see that the standard model is robust but has some issues, in the same way that more detailed analysis of the solar system validated Newtonian mechanics with caveats. Many things behave as they should. The Hubble recently detected dark matter behaving as predicted. Certain unexplained acceleration in the cosmos has renwed interest in the Einstein cosmological constant, which if it exists, renews the presence of the æther, albeit in a different form.

The evolutionary shifts in our understanding of the universe cannot be predicted. Dismissing a concept simply because it is a mathematical hack is a mistake. In reality we use mathematics because it is a precise language that will often lead us to an unobserved reality. Recall that quantum mechanics is based on Plank proposing the ludicrous mathematical hack that energy cannot be any arbitrary value. Recall that special relativity is based on Einstein's assertion that equations should be symmetric. And, for the record, we must also admit that there is no evidence for a particle of magnetic or gravitation force.

In any case, the search for the implausible particle that only interacts with the universe through gravity, and is unaffected by all other forces, will continue. What is for sure is the no matter what happens, the future likely holds a much stranger picture anything we might imagine today.

Re:dark matter does not exist (2, Informative)

Ambitwistor (1041236) | more than 7 years ago | (#17502834)

On one level, I consider dark matter to have the same credibility as the æther. An interesting concept, but largely created as hack to the model.
Aether theories didn't make any predictions that correctly explained any new observations. Dark matter does.

Certain unexplained acceleration in the cosmos has renwed interest in the Einstein cosmological constant, which if it exists, renews the presence of the æther, albeit in a different form.
The cosmological constant is a modification of the laws of gravitation, not anything like what was historically referred to as the aether.

Dismissing a concept simply because it is a mathematical hack is a mistake. In reality we use mathematics because it is a precise language that will often lead us to an unobserved reality.
This point is well taken. However,

Recall that special relativity is based on Einstein's assertion that equations should be symmetric.
That wasn't Einstein's motivation for introducing special relativity. (On the other hand, the complete form of Maxwell's equations of electromagnetism were based on Maxwell's assertion that the equations should be symmetric.)

And, for the record, we must also admit that there is no evidence for a particle of magnetic or gravitation force.
The electromagnetic force is mediated by the photon, for which there is abundance evidence. Gravitons, as you say, currently have no experimental evidence in their favor.

Re:dark matter does not exist (1)

yusing (216625) | more than 7 years ago | (#17503100)

Dismissing a concept simply because it is a mathematical hack is a mistake.

But talking about hypotheses as if they were solidly established theoretical constructs, dovetailing with the framework of well-established physics, does, IMHO, a disservice to science. For one thing, it tends to make it hard to see alternatives by freezing an attitude and blinkering the imagination needed to see alternatives. For another, it tends to make some laymen skeptical about *any* claims of science.

IIW, a hypothesis repeated with too much zealousy becomes an icon.

Re:dark matter does not exist (1)

Ambitwistor (1041236) | more than 7 years ago | (#17503166)

But talking about hypotheses as if they were solidly established theoretical constructs, dovetailing with the framework of well-established physics, does, IMHO, a disservice to science.
Dark matter is a solidly established theoretical construct. It hasn't risen to the level of "proven" (insofar as anything can be "proven" in science), but there is a hell of a lot of evidence in its favor.

For one thing, it tends to make it hard to see alternatives by freezing an attitude and blinkering the imagination needed to see alternatives.
There are alternatives to dark matter. They're not faring too well compared to dark matter when it comes to explanatory power, but they exist. I know you'd like to play amateur psychologist to the astrophysics community, but alternatives are considered. It's just becoming harder and harder to come up with alternatives that work, since observations have excluded so many of them. That's the reason why dark matter has become the mainstream explanation. Not because of "blinkered imagination", but because it works and the alternatives just don't. Alternatives that have at least some success do get attention, in proportion to the number of tests they pass.

For another, it tends to make some laymen skeptical about *any* claims of science.
Possibly because said layman are unaware of the decades of extensive testing the theory has undergone and all of the alternatives that have failed to measure up.

Re:dark matter does not exist (1)

radtea (464814) | more than 7 years ago | (#17503482)

Scientists often discuss new theories, etc, and in that context dark matter has it's place, but to claim it exists - as this story does - without being able to actually measure anything is quite silly and premature.

The whole point of these observations is that they are an entirely new probe of extra-galactic dark matter, and they are consistent with dynamical estimates of extra-galactic dark matter distributions.

Ergo, they consistute compelling evidence that extra-galactic dark matter is not just a mistake fix for an error in our understanding of the dynamics of the universe on a large scale, but rather a real, observable component of the universe that has multiple unrelated effects.

The new lensing and colliding-cluster measurements are precisely "measuring something" that compels anyone who does not have a faith-based epistemology to believe that extra-galactic, non-baryonic dark matter exists, in the ordinary and always somewhat uncertain meaning of the term "exists".

Previously, dark matter was plausible but unconvincing. Now it would be surprising as hell if anything else turned out to be the correct explanation for the dynamical anaomalies that gave rise to the hypothesis in the first place.

this is fun and scientific! (-1, Offtopic)

Anonymous Coward | more than 7 years ago | (#17501802)

Anus bnus cnus dnus enus fnus gnus hnus inus jnus knus lnus mnus nnus onus pnus, qnus rnus snus tnus unus vnus wnus xnus ynus znus!

LOL!

"There's something out there" (0)

Anonymous Coward | more than 7 years ago | (#17501808)

Why is it easier for Slashdotters to believe in dark matter than it is to accept another's believe in a God? Dark matter is an unproven theory.. all scientists really know is that there is something out there that may or may not be exherting somekind of magical force that may or may not explain away some unbalanced numbers (42).

Re:"There's something out there" (3, Funny)

thryllkill (52874) | more than 7 years ago | (#17502226)

Maybe because Dark matter doesn't damn you to hell for wanting to have sex? Or because it is not based on campfire tales of desert nomads from thousands of years ago, but rather mathematical equations, observations, you know, scientific stuff.

Re:"There's something out there" (0)

Anonymous Coward | more than 7 years ago | (#17502584)

Treating theories as fact and a foundation for further research hardly seems "scientific." Another that comes to mind is the _theory_ of evolution... why is this taught in the public schools as if it were any more proven than some theory of a supreme being?

Re:"There's something out there" (2, Funny)

chazwurth (664949) | more than 7 years ago | (#17502986)

Next time you get an infection, please do us all a favor and take the ID challenge: http://www.doonesbury.com/strip/dailydose/index.ht ml?uc_full_date=20060702 [doonesbury.com]

Re:"There's something out there" (0)

Anonymous Coward | more than 7 years ago | (#17503206)

hmm... "evolved"? I'd say more like "adapted." When the cold bug natually mutates enough to no longer be a cold bug let me know.

Re:"There's something out there" (1)

chazwurth (664949) | more than 7 years ago | (#17503868)

Have you read Darwin? You do understand that according to the theory, speciation occurs over vast periods of time, and in the short term, this occurs through adaptation, right? If you get that much, you must understand that your gripe boils down to this: we can't have adequate evidence that something occurs without watching the process from beginning to end, and thus observation of adaptation plus the fossil record plus common genes shared between distinct species isn't good evidence.

If that's your position, please let me know the next time God shows up at your house; I have some complaints I'd like to make.

Re:"There's something out there" (1)

wrf3 (314267) | more than 7 years ago | (#17502522)

Why is it easier for Slashdotters to believe in dark matter than it is to accept another's believe in a God?

Dark matter doesn't make a claim on one's life. The other replier who said, "dark matter doesn't damn you to hell for wanting to have sex", while wrong, illustrates this point. "If God doesn't want what I want then screw Him/Her/It/Them".

Re:"There's something out there" (1)

Maekrix (1025087) | more than 7 years ago | (#17503612)

Well, while I don't have the time to explain the complex equations, dark matter is simply the substance that makes up the Flying Spaghetti Monster's two delicious meat balls. Praise His Noodliness. And don't worry, Pastafarians have flimsy moral standards. FSM doesn't care if you have sex- evidence? Heaven has a Beer Volcano and Stripper Factories..

Hmmm... (1)

kitsunewarlock (971818) | more than 7 years ago | (#17501812)

The map streches back to half the life-span of this universe. That means that if a single unit of a radioactive atom exists in the universe with just the right value...
Uh-oh! It just reached half-life! Nasa better hurry up and find this long lasting nuclear element before its lost forever. We wasted the first half of this universe's existance, lets not waste the second.
Oh wait...this statement would only be true if the universe was ending at exactly this moment and the hubble did this scan half-a-universe's-life-span ago.

I had a great shag last night... (-1, Offtopic)

Anonymous Coward | more than 7 years ago | (#17501818)

... with your mum [twofo.co.uk] lameness filter encountered. Post aborted with a rusty coathanger.

RTFA (2, Insightful)

Swimport (1034164) | more than 7 years ago | (#17501832)

"We understand statistically what those galaxies are supposed to look like,"
 
So this map is based on what they assume the universe should look like. Then they use how its different to find where the dark matter might be. Doesnt sound 100% certain by any means, but its a nice picture.

Re:RTFA (2, Insightful)

HarveyTheWonderBug (711765) | more than 7 years ago | (#17502190)

Actually astronomers do :). Most galaxies are "disk galaxies", i.e. lenticulars and spirals. Face-on (viewed from above), they look like a disk. So they should look like ellipsoids when viewed on the sky, due to their inclination. But this basic shape gets distorted when viewed through a lens (in this case, the lens is a massive object in front). The distortions are very small, so what astronomers do is that they measure the shape of as many galaxies as possible in a given region, and look for a statistical departure from the expected one.
There is no assumption on the Universe is supposed to look like in this map. The only assumption is that the General Relativity of gravitation is correct. So far, it has not been disproved.

Re:RTFA (1)

TMB (70166) | more than 7 years ago | (#17502934)

It's not so much that they assume what the universe should look like, as that they assume a particular property of the universe - that it's isotropic on large scales. Therefore, on average we view galaxies from a random angle and so the orientation of their images on the sky is random. You then look for statistical deviations in the orientations of the images due to lensing of the light by matter along the line of sight.

Isotropy is an assumption, but we have never detected a significant deviation from isotropy on large scales except for that due to effects that we expect - like the gravitational lensing that's used in this study.

[TMB]

Density Issues affecting the shape? (1)

popo (107611) | more than 7 years ago | (#17501860)

Are all the "solid" areas of the 3d shape a roughly similar density of dark matter?

Seems to me there would be a wide range of density distributions. If so there must have been a human decision to decide
which level of density constitutes matter vs. empty space in this 3d depiction. I wonder how the 3d shape would change
if we arbitrarily moved this balance point of requisite density up or down the scale.

A Cool-Blue Model (1)

css-hack (1038154) | more than 7 years ago | (#17501924)

I don't know how much weight this "dark matter" theory holds (pun intended). But I was immediately interested when I saw their translucent blue 3d render of the stuff.

I wonder how many other people that works for...

Politically incorrect (2, Funny)

AlphaLop (930759) | more than 7 years ago | (#17501932)

You should call it "Light Challenged" matter in this age of political correctness. Be more sensitive to other matter people!

HubbleSite.org press release (1)

grimJester (890090) | more than 7 years ago | (#17502058)

Here. [hubblesite.org]

I've tried to find something about whether this tells us something new about the properties of dark matter, but so far no luck. Anyone have a link to something more informative?

Fermi paradox (0)

Anonymous Coward | more than 7 years ago | (#17502392)

It's life, dammit. That's where everybody is.

More Theories (0)

Anonymous Coward | more than 7 years ago | (#17502502)

'According to one researcher, the findings provide "beautiful confirmation" of standard theories to explain how structures in the Universe evolved over billions of years.'

More 'theories' with supposed scientific evidence propagated my the liberal media. Evolution, dark matter, next thing you know they'll have a 'theory' as to why we don't float off into space. Thank God that the force of his holy bowel movements keep us bound to this 3,000 year old center of the entire universe called Earth.

wtf is "dido"? (1)

r_jensen11 (598210) | more than 7 years ago | (#17502532)

and why is it a related link? Is there something special about dido@@@imperium...ph [mailto] ?

What's It Like, Other Than Dark? (1)

Doc Ruby (173196) | more than 7 years ago | (#17502594)

Dark matter is becoming as household a term as "black hole". But what makes it dark? It's matter that doesn't interact with electromagnetism, so we can't see it - though its gravitation makes it detectable by other means. But what kind of matter doesn't interact with electromagnetics? Have we ever physically obtained any? Synthesized any? And supposedly something like 70% of the dark "matter" is energy. How does non-dark energy interact with electromagnetism, where the dark "stuff" does not?

Re:What's It Like, Other Than Dark? (1)

Ambitwistor (1041236) | more than 7 years ago | (#17502624)

But what kind of matter doesn't interact with electromagnetics?
Any elementary particle that is electrically neutral.

Have we ever physically obtained any? Synthesized any?
If by "any" you mean "electromagnetically non-interacting", then there are neutrinos. If you mean "the kind of dark matter that is needed to account for astronomical observations", then no, we haven't.

 

And supposedly something like 70% of the dark "matter" is energy. How does non-dark energy interact with electromagnetism, where the dark "stuff" does not?
What is "non-dark energy"? Photons? I don't understand the question.

Re:What's It Like, Other Than Dark? (1)

Doc Ruby (173196) | more than 7 years ago | (#17503854)

AFAIK, the Standard Model doesn't call for 70% of the mass of the universe to reside in neutrinos, or even 10%. Does the standard model describe the majority of mass as non-electromagnetic?

Photons aren't energy, they're matter with an energy equivalence proportional to their frequency. Maybe the descriptions of "dark energy" are inaccurate - they're describing dark matter at high energy. Perhaps neutrinos, or some other non-interacting particle in motion. But dark energy [wikipedia.org] is described as different from familiar energy: negative pressure, something like "antigravity".

It just seems strange that we've never directly experienced dark matter/energy on or near Earth, when it's the large majority. Not that we should have it on our unique planet (in Feynman's terms - because we're on it, it's unique) - but can't we synthesize it, to study it? Especially if it's got nearly magical properties of undetectability and/or antigravity.

Aliens (1)

jrmiller84 (927224) | more than 7 years ago | (#17503144)

This dark material bends light in much the same way as light is bent when travelling through a lens.

Anyone else read this as... This dark material bends light in much the same way as light is bent when travelling through aliens.

But I thought... (1)

Conspiracy_Of_Doves (236787) | more than 7 years ago | (#17503558)

I thought that we weren't 100% certain that dark matter even exists

Hubble spys on Litter Tray (1)

RavensDark (321683) | more than 7 years ago | (#17504202)

Why are we using the hubble to spy on Nibbler using the litter box.
Load More Comments
Slashdot Login

Need an Account?

Forgot your password?