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Examining the Expected Effects of Dark Matter On the Solar System

timothy posted about a year ago | from the picks-up-loose-dirt-gets-out-tough-stains dept.

Space 190

First time accepted submitter LiavK writes "Ethan Siegel recently wrote a great post for ScienceBlogs discussing the expected total mass of dark matter in the solar system. As far as we can tell, dark matter only interacts weakly, via gravity, both with itself and normal matter. So, it can't collide with itself, meaning that it has no way of getting hotter and radiating away energy and momentum. This means that it remains a diffuse mess, with a density that is ridiculously low, to the point where detecting its local effects is likely to remain... challenging for the foreseeable future."

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Dark Matter (0, Troll)

lowkster (546516) | about a year ago | (#44537381)

Dark matter, the Ether of the 21st century.

Re:Dark Matter (4, Insightful)

ceoyoyo (59147) | about a year ago | (#44537395)

As opposed to the ether of the 19th century, quantum fields, which are what we currently use to explain everything?

Re: Dark Matter (0)

Anonymous Coward | about a year ago | (#44537675)

It's amazing how much the higgs field sounds like ether.

Re: Dark Matter (3, Funny)

Teresita (982888) | about a year ago | (#44537825)

It's an energy field created by all living things. It surrounds us, penetrates us, it binds the galaxy together.

Re: Dark Matter (4, Funny)

AK Marc (707885) | about a year ago | (#44538377)

Are you describing tentacle porn?

Re: Dark Matter (0)

Anonymous Coward | about a year ago | (#44539699)

The Force is strong with this one.

Re: Dark Matter (2, Insightful)

Anonymous Coward | about a year ago | (#44537917)

Actually, it doesn't really in any way. Unless you think the only relevant property of the ether was that it permeated all space, in which case there is a bunch of stuff in science, past and present, that fits that description, anywhere from various potentials to other various fields. Might as well complain heliocentricism sounds just like geocentricism because they both involved spinning things.

Re: Dark Matter (0)

Anonymous Coward | about a year ago | (#44538029)

It's nothing like it (except in that one way it's exactly like it).

Re: Dark Matter (3, Interesting)

ceoyoyo (59147) | about a year ago | (#44538361)

Don't make the mistake of thinking there was just one ether theory. There were lots of them, many quite compatible with special relativity. Quite a few that sound like 1890s versions of quantum electrodynamics.

Re: Dark Matter (3, Insightful)

ceoyoyo (59147) | about a year ago | (#44538353)

The Higgs field is just the latest one. Quantum field theory (what people mean today when they say "quantum mechanics") includes a field for every fundamental particle. Yes, the ether won.

Relativistic space under tension? (3, Interesting)

Anonymous Coward | about a year ago | (#44537789)

Or you could say space has a property of localized time. Which means time doesn't scale or progress uniformly throughout the universe. If you've got enough gravity, it's going to make things appear even more massive then they are because of time dilation. The relationship of gravity vs. time also means c should be treated as a coefficient rather than a constant. (The effective value of c still remains fixed, but that's because relationship of distance vs. time has both parts as variables. Time effectively rescales itself at higher energies to maintain c for a given distance traveled by a particle, but if you don't account for that, the extra momentum approaching or exceeding c looks like a gain in mass.)

Somebody with better math skills than myself could probably re-jigger Special Relativity in this regard and account for missing mass. It may even show a cumulative effect with gravitational time dilation when you have a system of multiple orbiting objects. But you might also have to toss the idea of a "Big Bang" out the window. (Makes "age" of things in the universe fairly irrelevant when a localized second is defined by the gravitational or acceleration field it's being measured under. Not to mention under certain conditions the typical light-year measuring stick astronomers like to use will also look about as uniform as a funhouse mirror. The funny-sounding Dr. Who sci-fi explanation of time being "Wibbly wobbly" may have some real logic to it.)

Of course it sounds nutty, because it opens up a lot of loopholes. Probably explains why Einstein was uncomfortable with some things, even if it provided the template for a more accurate model than some later revisions.

Re:Relativistic space under tension? (1)

ceoyoyo (59147) | about a year ago | (#44538327)

Sure, you can make all sorts of complex theories to explain anything you want. The reason cold dark matter is so popular is because one simple, very plausible hypothesis, the existence of a heavy, weakly interacting particle, explains a great deal.

Don't think a heavy, weakly interacting particle is plausible? Right, because it's not like we've observed any light weakly interacting particles [wikipedia.org] already.

Re:Relativistic space under tension? (0)

Anonymous Coward | about a year ago | (#44540129)

The problem is that all other particles that exists abundantly also exists everywhere.
In the dark matter theory the idea is that exists abundant amounts of one specific type of matter that doesn't exist in other places.
For the dark matter theory to be plausible it also need to explain why we don't have dark matter in this solar system when all other types of matter can be found.

Re:Relativistic space under tension? (1)

Bengie (1121981) | about a year ago | (#44539231)

Time-dilation caused by gravity is more of an issue near the surface of objects than that of objects moving through space. While an individual object, like a star within a galaxy, may have high dilation, it's motion through the galaxy will be relatively unaffected. Which is why black-holes orbit similar to any other object, even though "time has stopped" for them.

The only real distortion of space that matters is that caused by the average distortion caused too all space within the galaxy, which is quite weak.

I am not a scientist

Re:Relativistic space under tension? (0)

Anonymous Coward | about a year ago | (#44539361)

Somebody with better math skills than myself could probably re-jigger Special Relativity in this regard and account for missing mass. It may even show a cumulative effect with gravitational time dilation when you have a system of multiple orbiting objects. But you might also have to toss the idea of a "Big Bang" out the window. (Makes "age" of things in the universe fairly irrelevant when a localized second is defined by the gravitational or acceleration field it's being measured under

It is called General Relativity, and while it can add a few caveats to things like "age of the universe" it doesn't make it anywhere near irrelevant. These effects are already taken into consideration as part of the most basic level of cosmology theories.

Just the opposite (4, Insightful)

Beryllium Sphere(tm) (193358) | about a year ago | (#44537403)

Michelson and Morley found that the hypothetical ether had no detectable effects.

In contrast, scientists started by measuring orbital velocities and could only explain them with dark matter.

Re:Just the opposite (-1)

Anonymous Coward | about a year ago | (#44537441)

Michelson and Morley found that the hypothetical ether had no detectable effects.

In contrast, scientists started by measuring orbital velocities and could only explain them with dark matter.

Michelson and Morley found nothing, they were full of shit.

Re:Just the opposite (4, Funny)

tqk (413719) | about a year ago | (#44537495)

Michelson and Morley found nothing, they were full of shit.

Yeah, experimenting to prove something beyond a shadow of a doubt is always just a waste of time and effort. I hear Kepler was disappointed to learn of elliptical orbits too.

Re:Just the opposite (4, Informative)

paiute (550198) | about a year ago | (#44537735)

Michelson and Morley found nothing, they were full of shit.

They found nothing, and that was their great discovery. http://en.wikipedia.org/wiki/Null_hypothesis [wikipedia.org]

Re:Just the opposite (0)

Anonymous Coward | about a year ago | (#44539977)

Michelson and Morley found nothing, they were full of shit.

They found nothing, and that was their great discovery.

http://en.wikipedia.org/wiki/Null_hypothesis [wikipedia.org]

Their "proof" was based on old science and didn't prove what they said it proved. People who keep using their work as a basis for ether not existing, and yet support quantum field theories should be very ashamed of themselves. And they say that 'Institutional Science' isn't a religion... At the very least it is chock full of hubris and faith based assumptions.

Re:Just the opposite (1, Funny)

Tonko Boekhoud (3007661) | about a year ago | (#44537995)

Well, I sometimes want to see my dark matter explained. But most times, it's just flushed away...

Slight change in perspective (1)

Livius (318358) | about a year ago | (#44538665)

They found that that the effects predicted on the basis of analogy with material science were not measurable.

But then came general relativity, quantum fields, dark energy, etc., and we decided an empty vacuum wasn't actually empty after all.

FTFY (1, Funny)

justthinkit (954982) | about a year ago | (#44537591)

Dark energy, the Ether of the 21st century.

Re:Dark Matter (2)

K. S. Kyosuke (729550) | about a year ago | (#44537661)

Dark matter, the Ether of the 21st century.

Right you are, mate. I mean, have you tried sniffing that shit? That will get you tall faster than you can say Patrick Moore.

Re:Dark Matter (0)

Anonymous Coward | about a year ago | (#44537707)

Take it easy on the guy, if they'd tried to use the ligature slashcode would have just laughed derisively.

Re:Dark Matter (-1)

Anonymous Coward | about a year ago | (#44537799)

kyosuke, i've noticed your comments. you have become seriously annoying.

Re:Dark Matter, the Aether of the 21st century. (0)

mmell (832646) | about a year ago | (#44539907)

Agreed.

Y'know, Einstein himself once made the same mistake - called it the "cosmological constant" or some such. Needed a way to fudge his equations to jive with observed reality. I hear he was thrilled to hear 'bout Hubble's observations - made his equations work without nobtanium, unobtanium, adamantium, fudge factors, warp fudge factors or any other cheap cheats.

Mind you, I can't forward a better theory to explain why things have mass - but dark matter has always struck me as the modern equivalent of Russel's Teapot. Let me know when they find supporting evidence (which they may soon - or they may end up in the same place as Michelson and Morley).

The problem with dark matter (2, Insightful)

girlintraining (1395911) | about a year ago | (#44537447)

The problem with dark matter observation in this case is that science is based on empirical observation. If you can't see it, can't measure it, and can't even draw inferences from what you can see and measure to detect something indirectly... it's not science. What this is saying is that the effects are so miniscule that there is no equipment presently capable of separating an actual effect or observation from systemic inaccuracy in the equipment itself. That is, you can't tell whether it's just random 'noise' or an actual signal.

As I understand it, there's a big empty space in most of our theories and observations that says something should be filling it up, but we have very little in the way of actual data of what exists within this hole. We can infer something is needed to balance out our observations, but we haven't actually seen the 'something'. It's like a shy cat in an apartment. You won't see that cat again, and an exhaustive search of most of the rooms in the apartment comes up empty, but something keeps eating the cat food. Thus, we have concluded there's a cat in the apartment... but nobody has actually ever seen the cat.

Re:The problem with dark matter (3, Funny)

Ralph Spoilsport (673134) | about a year ago | (#44537467)

"hus, we have concluded there's a cat in the apartment... but nobody has actually ever seen the cat."

Or, your significant other has some weird cat food fetish thing going on...
Eeeek!
:-)

Re:The problem with dark matter (5, Informative)

buchner.johannes (1139593) | about a year ago | (#44537543)

The problem with dark matter observation in this case is that science is based on empirical observation. If you can't see it, can't measure it, and can't even draw inferences from what you can see and measure to detect something indirectly... it's not science. What this is saying is that the effects are so miniscule that there is no equipment presently capable of separating an actual effect or observation from systemic inaccuracy in the equipment itself. That is, you can't tell whether it's just random 'noise' or an actual signal.

But we do find it empirically. There is extra mass there, affecting other objects. We can detect it through it's gravitation, just not through light. It's a very strong signal, for example in the rotation velocity of galaxies. A lot of other science is, too, done without directly detecting the object of study, but through indirect effects and inference.

Everyone would like to get rid of Dark Matter. But its effects are clearly there. And we need to explain it. It does not have to be particles, or a kind of matter we know. You can call it something else than Dark Matter if you don't like the name. Anyone is welcome to come up with explanations. But they have to be in agreement with the observations.

Re:The problem with dark matter (1)

tqk (413719) | about a year ago | (#44537803)

The problem with dark matter observation in this case is that science is based on empirical observation. If you can't see it, can't measure it, and can't even draw inferences from what you can see and measure ...

But we do find it empirically. There is extra mass there, affecting other objects. We can detect it through it's gravitation, just not through light.

Am I the only one astonished to learn that regular astronomers are finally twigging to the fact that a lot of stuff out there can't be seen or detected by what we've got to work with? Why hasn't it been in your face obvious to everyone that there's a lot of stuff that doesn't radiate in the visible spectrum, or strong enough in an altogether different part of the spectrum for us to have seen or been able to describe before now. Of course we're going to finally wonder why that galaxy is spinning oddly based on the well known facts of such things such as the laws of motion.

Why invent exotic matter when the right combination of dust could be the answer?

Re:The problem with dark matter (5, Informative)

samkass (174571) | about a year ago | (#44537879)

Why invent exotic matter when the right combination of dust could be the answer?

Simply put, because baryonic matter (ie. dust) radiates. This article would be titled, "Why our instruments are sensitive enough to detect all that dust that's affecting galaxies and superclusters rotation" if it was dust.

Here's a recent summary paper [arxiv.org] on the evidence for nonbaryonic dark matter. Dust has, alas, been hypothesized, tested, and rejected.

Re:The problem with dark matter (0)

Anonymous Coward | about a year ago | (#44537969)

How about planets?

Re:The problem with dark matter (0)

Anonymous Coward | about a year ago | (#44538181)

:facepalm:

Planets are just clumps of dust.

Re:The problem with dark matter (5, Informative)

khallow (566160) | about a year ago | (#44538559)

Planets are just clumps of dust.

But clumps of dust with a really low surface area for the mass involved. For example, Jupiter has a density of 1,330 kg per square meter and an average radius of almost 70,000 km (7*10^7 meters), a third more than water at STP. If instead, Jupiter were broken up into many equally sized balls of a smaller radius, then the mass stays the same, but the increase in surface area is inversely proportional to the decrease in radius.

For example a Jupiter-mass cloud of micron sized spheres, each with the density of Jupiter, would have a surface area 7*10^13 larger than Jupiter. That surface area incidentally happens to be roughly a twentieth of a square light year (roughly 4*10^30 square meters by my calculation) meaning at the right densities, such a cloud could intercept and radiate a lot more energy than Jupiter could, perhaps even be visible in small amateur telescopes at a few lightyears.

My point here is that some baryonic matter is a lot more visible, many orders of magnitude more visible, than other baryonic matter. And planet-sized objects are going to interact mostly by gravity as well meeting most of the desired characteristics of dark matter.

My take is having a significantly higher than expected fraction of the mass of your galaxies in rogue planets and similar things would be a way to account for dark matter.

But then there's the early universe observations. For example, the most damning evidence against dark matter hiding in planets and such, is observations of the cosmic microwave background [learner.org] (CMB), which is effectively the study of the period of the universe in which it started to become transparent to photons (about 400k years after the big bang according to the above link). That period of time is not a lot of time in which to create massive objects. And the fluctuations of the CMB yield dark to visible mass of roughly 5 to 1 (again according to claims in the above link).

So that indicates to me that there probably some sort of exotic matter out there which we haven't discovered yet.

Re:The problem with dark matter (2)

Anonymous Coward | about a year ago | (#44538425)

They were at one time one of the major contender's for dark matter under the title MACHOs (Massive Compact Halo Object). But they should've been observable by gravitational lensing as stars passed behind them. There were multiple surveys undertaken which didn't find them, so there aren't enough of them to be dark matter.

Re:The problem with dark matter (0)

Chemisor (97276) | about a year ago | (#44539115)

> Simply put, because baryonic matter (ie. dust) radiates.

I don't buy that. Dust around the solar system radiates because the sun is pumping a lot of energy into it. Hot interstellar gas you see in telescope images was warmed up the same way. Dust floating sufficiently far away from any star will be cold enough to not radiate anything, not infrared, not X-ray. An unilluminated piece of rock will be invisible to you in all ways except for its gravitational influence, which is precisely what we are seeing. As such, I see no evidence rejecting interstellar dust and rocks.

As for the additional arguments based on CMB and galaxy formation, they are based on speculative models of the big bang that have no empirical evidence backing them. Sure, speculate all you wish, but whenever you try to tell me your models rule out galaxy formation, I am far more likely to consider your models wrong than as any kind of proof of existence of exotic matter.

There is also some question of the validity of gravity estimations involved in velocity curve plotting. I find it very hard to believe that I'm smarter than every astrophysicist that looked at that paper, but I'd question why the paper assumes that the gravity at point in a galaxy is equal to the point-mass equivalent of the matter contained within that radius. That result would occur if you were to use the shell theorem, but that theorem is only valid when spherical symmetry exists. In a flat galactic disk of uniform density the gravity at every point except near the center and the edges would be proportional to the local matter density irrespective of the radius, producing flat rotational curves. Again, I find it very difficult to believe that nobody has seen this before, so please try to explain to me why the paper you have linked appears to be using the erroneous calculation.

Re:The problem with dark matter (3, Informative)

O('_')O_Bush (1162487) | about a year ago | (#44539239)

As others have pointed out, the local energy source (a star, solar system, galaxy) is not the only way that baryonic matter is detected from afar. What you are describing in your first paragraph is the MACHO theory ( massive compact halo objects, includes small rocks, dust, gases ), which has been tested and shown to be unlikely, in favor of the WIMP theory (Weakly Interacting Massive Particles).

The reason for this was that the MACHO theory made very specific predictions that could be tested using sensitive instruments, such as gravitational lensing (remember, there is supposed to be enough to dramatically effect the amount of gravity acting on a galaxy) and others (which I won't get in to). This was one of the first and most strongly believed in theories when dark matter was detected, so you can be sure that astronomers fought for it until the evidence against became too overwhelming.

That being said, there are still some astronomers researching MACHOs, since they have been detected, just not in the amount that accounts for the unexplained gravitational effects.

Re:The problem with dark matter (2)

dentin (2175) | about a year ago | (#44537947)

You're a fool if you think that regular astronomers are 'finally twigging' out about events that don't directly radiate in the visible spectrum. They are in fact painfully aware of the fact that they can only see the visible side effects of most events.

As for your question regarding exotic matter and dust, the opinion for many decades was that dust was the answer. That opinion has been replaced with exotic matter over time, for extremely good reasons which you apparently don't yet understand.

-dentin

Re:The problem with dark matter (1, Informative)

stenvar (2789879) | about a year ago | (#44538161)

As for your question regarding exotic matter and dust, the opinion for many decades was that dust was the answer. That opinion has been replaced with exotic matter over time, for extremely good reasons which you apparently don't yet understand.

"Extremely good reasons" is not the same as proof. And there are other possibilities, like large numbers of rogue planets, or multiple different mechanisms explaining different phenomena.

Don't get me wrong: weakly interacting dark matter is plausible, but until there is independent, direct evidence and observation, it remains just plausible speculation.

Re:The problem with dark matter (1)

dentin (2175) | about a year ago | (#44538249)

So long as you agree that it is not just plausible speculation, but currently the most likely plausible explanation, then we're on the same page.

Just because there are multiple plausible hypothesis, doesn't mean they're all equally probable.

-dentin

Re:The problem with dark matter (0)

stenvar (2789879) | about a year ago | (#44538877)

I strongly disagree. We simply don't know what is causing these effects, and anybody who assigns probabilities to such speculations is a charlatan, not a scientist.

Re:The problem with dark matter (1, Interesting)

Anonymous Coward | about a year ago | (#44539471)

Unless they are a scientist, like many astronomers, that have done surveys and placed upper bounds on the amounts of certain candidate forms of dark matter and shown that they cannot be any where near enough to be a significant contributor to the missing mass... The most mundane alternatives result in testable predictions about how much stuff is out there and how often it will be seen, either directly or indirectly, and in many cases, those tests failed. That places some pretty strong limits on those alternatives, except in the small chance that all of the observations were a fluke in the wrong direction.

Re:The problem with dark matter (1)

tqk (413719) | about a year ago | (#44538205)

You're a fool if you think that regular astronomers are 'finally twigging' out about events that don't directly radiate in the visible spectrum.

I may indeed be a fool. I've also run across many a science program on teevee hosting a distinguished representer who gushes over this subject. "We can't see *a lot of stuff!* Who knew?!?" Go figure.

Re:The problem with dark matter (2, Informative)

dentin (2175) | about a year ago | (#44538283)

[sarc]Naturally, everything you see on teevee is true and accurate, and all distinguished presenters are to be trusted, and all science program scripts are written for maximum accuracy and conveyance of relevant information. Why would we ever question something we saw on a tv program? Tune in for next week's "Ancient Aliens" for proof that the anti-TV conspiracy started in ancient Egypt![/sarc]

People interested in real science don't get their science from TV. People interested in real science learn from books written by scientists, from papers written by scientists, and by talking to real scientists doing real work in the actual field. Everything else is just the pop culture treatment.

-dentin

Re:The problem with dark matter (1, Redundant)

ceoyoyo (59147) | about a year ago | (#44538433)

Because the right combination of dust can't be the answer. That was thought of, tested, and it failed to explain observations.

Re:The problem with dark matter (4, Informative)

Bengie (1121981) | about a year ago | (#44539193)

You mean how this stuff is 100% transparent to all known frequencies from radio to gamma? Please, tell me what matter you know of that is 100% transparent to all forms of radiation. Enlighten us all knowing one.

Yes, we know, 100% that is is transparent. There are HUGE spots in the sky where there is gravitational lensing affecting background galaxies, but no obstructions in front of the galaxies. Something is causing the gravity, but it is letting the background light through perfectly clearly, minus the lensing.

We're not talking about small amounts of gravity either, whole galaxy masses worth. If you had a galaxy worth of gravitational lensing, you'd hope to find something causing it. Instead the background light comes through crystal clear, like nothing is there.. hmmmm...

Re:The problem with dark matter (1)

stenvar (2789879) | about a year ago | (#44538101)

But we do find it empirically. There is extra mass there, affecting other objects. We can detect it through it's gravitation, just not through light. It's a very strong signal, for example in the rotation velocity of galaxies.

There are unexplained gravitational effects, but that's all we really know. The idea that they are due to a single mechanism based on weakly interacting dark matter requires additional assumptions, foremost the assumption that all these effects have a single common explanation.

Weakly interacting "dark matter" is certainly a plausible explanation, but that's all it is for now. There is no actual direct evidence for it. The honest thing to do would be to choose a more neutral name than "dark matter" until we have direct evidence for some mechanism.

Re:The problem with dark matter (1)

sittingQuietly (935534) | about a year ago | (#44538267)

"Anyone is welcome to come up with explanations"

Fine. The stars on the edge of galaxies aren't there - they are images bent by the Shapiro effect. Their origins are stars close to the galactic center. The light is bent and appears to as as "stars" on the edge of galaxies. This would be why galaxies appear to rotate like wheels with spokes. The observed redshift and blueshifts (on the opposite edge of Andromeda, for example) would be retained. ... no dark matter necessary

Re:The problem with dark matter (1)

wonkey_monkey (2592601) | about a year ago | (#44540041)

they are images bent by the Shapiro effect

Assuming you're genuinely suggesting this as an alternative... The Shapiro effect is (as far as my understanding of it goes) an effect (the clue is in the name) caused by mass - and it's a delay effect, not a bending one. So what is the mass that's doing the bending? How does the light get bent in just the right way to make galactic discs look more spread out from all angles?

Re:The problem with dark matter (1)

Shavano (2541114) | about a year ago | (#44538391)

The problems with dark matter are on the "what is it" side. We can tell that it exists. What we can't tell is whether it's an effect of some particle we already know about or something else. Maybe it's extremely decelerated (barely moving) neutrinos left over from the condensation of matter in the big bang. That's presuming neutrinos have mass. Because if they're just about anything else that is known to exist, they'd be easier to observe. Or maybe it's that gravity ain't what we think it is. Maybe it's NOT QUITE inverse-square, but the difference only becomes observable at interstellar distances.

Re:The problem with dark matter (0)

Anonymous Coward | about a year ago | (#44538457)

What if dark matter actually has _no_ mass?

How much would that change things if it was entirely massless particles?
It certainly looks like the effect could be propagated at lightspeed, but there is a problem there in that we are missing a huge piece of the puzzle in relation to large scales anyway, the potential existence of a graviton that mediates the gravity side of things.
So until we were to actually find such a thing, we'd be even more clueless as to something we doubly and literally can't see.
So far all guesses put it as a massless particle too, which might explain the problems in finding it. Or it could be at energies below or beyond our abilities to detect presently. LHC might find it in the next decade, fingers crossed.
Maybe even as more research is done in to Higgs, it might reveal something else entirely.

There are a few theories around this I can see. And wacko-sites on it as usual. It's all about the vortices and wotsits!

Re:The problem with dark matter (1)

marcello_dl (667940) | about a year ago | (#44539973)

Until dark matter can be directly, or indirectly but consistently detected (e.g. we can take a bunch of dark matter and move it around, if it doesn't move it is a property of that particular region of space, not something contained in it), dark matter stays as an abstraction that helps our formulas to explain, pardon, model gravitational interactions.

That is, now you can either consider it an as yet undetected physical object, or the rationalization of an error, as you prefer, and orient your own research accordingly.

I point this out because "our models do not match our observations" can be either resolved by "therefore there is something more to be modelled" which in this case implies the dark matter hypothesis, or "therefore our models are wrong/too general/too limited", which would be strange but not impossible. Even after modeling every single past present and future aspect of reality, you cannot claim you completely know it, since you are speaking from the inside of it. It would be like testing every I/O combination in a unit test and then proclaiming you have achieved 100% code coverage. Those are two different things on two different levels.
Many scientists know this, not all of them unfortunately.

Re:The problem with dark matter (1)

wonkey_monkey (2592601) | about a year ago | (#44537827)

The problem with dark matter observation in this case is that science is based on empirical observation. If you can't see it, can't measure it, and can't even draw inferences from what you can see and measure to detect something indirectly... it's not science.

But we can measure it, and we do draw inferences from what has been measured, and that's exactly what they're doing here - using the measured large-scale behaviour of galaxies - from which we infer the existence of dark matter - to predict what might happen on a smaller scale, like a solar system - a scale on which we are currently not in the position to do observations of sufficient accuracy to disprove the inference (theory).

As I understand it, there's a big empty space in most of our theories and observations that says something should be filling it up

I wouldn't refer to problems in cosmological theories as "big empty spaces." That could get really confusing really quickly.

Re: The problem with dark matter (0)

Anonymous Coward | about a year ago | (#44538111)

I'm convinced you are a bot trying to catfish slashdot mods. Your programmer writes crappy AI.

Re:The problem with dark matter (3, Informative)

ceoyoyo (59147) | about a year ago | (#44538459)

Dark matter, in various forms, is the hypothesis(ses) that explain empirical observations. For the last couple of decades we've been at the stage of hypothesizing various kinds of dark matter and testing them to see if they fit. The one that fits best so far, and is thus the leading contender, is a new kind of subatomic particle that interacts weakly and is fairly heavy. The dark matter story is an excellent example of how science is supposed to work.

Re:The problem with dark matter (1)

mmell (832646) | about a year ago | (#44539951)

Best concise explanation I've seen in a while. Nice job.

So we're basically talking about the modern version of WIMPS, tweaked to account for the WIMPS we haven't found yet.

While we're on the subject ... Higgs particles, Higgs field - sounds a lot like what they used to say gravitons were like (cue the bad Futurama jokes here...).

Re:The problem with dark matter (1)

Livius (318358) | about a year ago | (#44538693)

There are many good reasons to think that the dark matter hypothesis is on the right track. It provides many predictions that are borne out by observations, with a minimum of extrapolation from the properties of regular matter.

It's still a hypothesis.

There is no contradiction. I don't understand why people feel a need to disagree about it.

It is based on empirical observation (3, Insightful)

dbIII (701233) | about a year ago | (#44538785)

If you can't see it, can't measure it

You've got a bit mixed up here. The entire idea of dark matter is because we can measure something we can't see - there are gravitational effects but not electromagnetic ones that have been seen yet.
It's more like stepping on a black cat in the dark. You've felt it underfoot for an instant and it's run off somewhere, so while you don't know what it is or where it is you do have empirical evidence that you've stood on something.

Re:The problem with dark matter (1)

Anonymous Coward | about a year ago | (#44539395)

Umm, isn't most measurement done by "empirical observation"?

We know empirically that electric currents generate magnetic fields, and use them to turn a dial, thus we "measure" electrical current. Here, our observables are the rotation of galaxies, and the behavior of clusters of galaxies. That's equally measurement.

So we're seeing it, and measuring it, and drawing inferences. That is science.

We haven't *yet* found a way to measure quanta of dark matter.

And that's OK. Even up into Einstein's time (>= 1900) atoms were still hypothetical entities, never seen or measured, yet the theorists had several theories that only made sense if the atomic theory of matter was true. Einsteins' papers on brownian motion and (to a lesser degree) on the photoelectric effect both constituted indirect evidence for the atomic theory. Only later did it become possible to "see" and measure atoms, as experiments determined the size (X-ray experiments, ...) and characteristics (alpha particle experiments) of individual atoms.

General relativity (0)

mc6809e (214243) | about a year ago | (#44537493)

My bet is that the need for dark matter will disappear when relativistic effects are properly taken into account.

There seems to be the belief among astrophysicists that general relativity can be safely ignored when speeds are low. I'm not so sure.

Anyone that can integrate knows large values can be obtained when summing even the smallest values. Perhaps billions of otherwise ignorable relativistic effects become a large effect when acting together.

Re:General relativity (2, Informative)

Anonymous Coward | about a year ago | (#44537619)

Rebuttal: Bullet cluster.

Re:General relativity (4, Insightful)

wonkey_monkey (2592601) | about a year ago | (#44537703)

My bet is that the need for dark matter will disappear when relativistic effects are properly taken into account.

And I bet that at some point during the last few decades of thousands of observations, theories, and calculations by thousands of astronomers, physicists, and mathematicians (some with Nobel prizes, no less), someone would have already thought of this if it was an issue.

Re:General relativity (0)

mc6809e (214243) | about a year ago | (#44537777)

And I bet that at some point during the last few decades of thousands of observations, theories, and calculations by thousands of astronomers, physicists, and mathematicians (some with Nobel prizes, no less), someone would have already thought of this if it was an issue.

They're not gods (and there's no Nobel prize for mathematics).

And there has been some movement towards using relativity instead of dark matter to explain galactic rotation curves:

General Relativity Resolves Galactic Rotation Without Exotic Dark Matter [arxiv.org]

Re:General relativity (1)

wonkey_monkey (2592601) | about a year ago | (#44537967)

That paper's from 2005, but as they're still talking about dark matter I'm guessing it didn't satisfy many scientists.

They're not gods

No, but I think it's reasonable to assume they're a bit ahead of the average Slashdot poster in this department.

(and there's no Nobel prize for mathematics).

Two ways out of that one:

a) as it was meant to be read:

by thousands of [ astronomers, physicists, and mathematicians ] (some with Nobel prizes, no less)

b) I didn't say what they won the Nobel prizes for. Mathematicians have won Nobel prizes.

Re:General relativity (0)

Anonymous Coward | about a year ago | (#44538293)

That paper was soon refuted. It sounded a little bit promising at first, but turned out to be useless. Since, much more evidence has emerged, such as the Bullet Cluster, that could not possibly be explained by the theory in that paper.

Re:General relativity (-1, Troll)

pjbgravely (751384) | about a year ago | (#44538387)

I am finding that dark matter has become a religion to some people. Saying there could be something else brands you an heretic and nothing you say after that matters. Yes they think the creators of the religion are gods.

Re:General relativity (4, Insightful)

ceoyoyo (59147) | about a year ago | (#44538477)

That's because when you say things like that you check off quite a few boxes on the crackpot criteria.

It's not a religion. Lots of different dark matter theories and alternatives have been proposed and tested. The problem is that when some random Slashdotter comes along and says "dude, it must be something else!" the actual astronomers, and the amateurs who can read, roll their eyes. When the same Slashdotter then says "dude, you're not taking me seriously because you can't get past your religious dogma!" said astronomers and literate amateurs roll their eyes harder.

Re:General relativity (1)

pjbgravely (751384) | about a year ago | (#44539019)

When people will not even imagine the possibility that what they believe could be wrong then I would call that a religion. I personally don't believe that dark matter exists, but that won't stop me from reading about it and studying the evidence if it is actually found and believing once I see the truth.

I keep my mind open, not closed to possibilities I have never imagined.

Re:General relativity (2)

ceoyoyo (59147) | about a year ago | (#44539043)

So who is it you're accusing of the religion of dark matter? The astrophysicists who've spent the last twenty years thinking up all sorts of crazy ideas for what it might be and then testing those ideas?

Re:General relativity (0)

pjbgravely (751384) | about a year ago | (#44539105)

I wasn't talking about the astrophysicists I was talking about their followers. Reread the parent to my first post.

By the way, thank you for proving my point.

Re:General relativity (4, Insightful)

ceoyoyo (59147) | about a year ago | (#44539345)

Ah, I understand. You're talking about people who are skeptical of your favourite off the wall theory. That's not religion. As the thread before your post said, when Slashdotter 214243 comes along with some theory from left field, along with an assertion that the experts (some of whom have Nobel prizes), who have put careers into looking into this question, are wrong (or religious), he better have some good evidence to support it. Every time I've seen it that "evidence" boiled down to a vague, usually incorrect understanding, usually with a healthy dose of conspiracy theory.

Maybe you've seen something a little more solid? Care to share?

Re:General relativity (1)

Anonymous Coward | about a year ago | (#44539683)

I find more and more that people trying to argue against dark matter are acting like dark matter is some religion to researchers, they think that proposing or discussing an alternative will brand them a heretic and things go undiscussed at the professional level (even if your charge here is not about actual scientists and only their followers). Way too many people act like the alternatives are completely ignored, and pushed away, despite their being whole research groups at many universities dedicated to some of the alternative theories, which are welcomed and frequently very popular talk givers because of their alternative views. Although nearly every such talk I've been to either directly, or in questions, has the talk giver say they still think dark matter has a better, more complete explanation of observations than their theory.

Re:General relativity (1)

Bengie (1121981) | about a year ago | (#44539209)

That still does not explain empty space having detectable mass in the form of gravitational lensing.

Priests (0)

Anonymous Coward | about a year ago | (#44538493)

That's correct. Only the priests of science have the right of thinking and conjecture.

If only people that have already done great things are allowed the opportunity to do great things, as all great things have obviously already been done by them, then the progress of civilization has already ended. I am glad that you are wrong.

Re:Priests (1)

sydneyfong (410107) | about a year ago | (#44538705)

If you never read the works of the "priests of science", you aren't qualified to say that they were wrong, or they have missed an obvious solution to a decades old problem.

Unless, of course, you actually solve the problem. But you're not going to get much respect by randomly throwing around some terminology from high school science classes and saying you're better than all those people who had spent years and years of studying the subject matter.

Re:Priests (0)

Anonymous Coward | about a year ago | (#44539263)

Unless you are a "priest of science" you really have no right to reject on their behalf. If you do, you simply cement their priesthood and your serfdom. Using your "logic", of course.

Re:Priests (0)

Anonymous Coward | about a year ago | (#44539795)

The issue is not that solutions can only come from scientists, and hence all else can be ignored, it is that too many arm-chair scientists are not aware of what has already been done. I don't work in astronomy, but of all the "great new idea that will challenge mainstream science", 90+% of them are things that can be proved wrong by constructing a simple desktop experiment with ~$10 of materials. And what makes it worse, is intro level textbooks would have provided the information they needed to know what to build that would show reality disagrees with their theory. The other 5-10% of ideas runs into other problems, just at a more advanced level than an intro textbook, and amounts to the author not realizing experiments had already been done addressing their question/idea.

The problem is either of laziness, that someone pushing an idea hasn't bothered to take some basic steps to see what has been done before, and/or attitude. Many of the attitude issues almost amount to an attempt to what is a reversion back to natural philosophy before the scientific method, that someone can deduce the workings of the universe while ignoring observation.

The "priests" are not infallible and omniscient, but they have spent a lot more collective time on some problems that any one person, and that is all it comes down to.

Re:General relativity (1)

Chemisor (97276) | about a year ago | (#44539131)

> someone would have already thought of this if it was an issue.

Then please tell me who has already thought of explaining the expansion of the universe by considering the matter-to-energy conversion occuring within stars and realizing that the disappearing matter reduces space curvature, expanding it. Accelerating star formation and total power output would thus produce accelerating expansion of the universe. Do try to find any astrophysicists who has done these calculations. I'd be very interested to read their papers.

Re:General relativity (1)

wonkey_monkey (2592601) | about a year ago | (#44539891)

Then please tell me who has already thought of explaining the expansion of the universe by considering the matter-to-energy conversion occuring within stars and realizing that the disappearing matter reduces space curvature, expanding it.

Well, you have, so why don't you do the calculations, write a paper, and win a Nobel prize? From my point of view (that of not being an astrophysicist and only have an interested reader's grasp of the subject) you're the one making the claim, so it's on you to find the evidence.

Besides which, I was under the impression that energy warps space just as mass does (though perhaps you're referring to mass/energy being lost to the space around the star by radiation).

I was also not aware that if you remove mass from a volume of space the space within that volume begans to expand faster.

Re:General relativity (1)

tbid18 (2495686) | about a year ago | (#44538063)

My bet is that the need for dark matter will disappear when relativistic effects are properly taken into account.

There seems to be the belief among astrophysicists that general relativity can be safely ignored when speeds are low. I'm not so sure.

The situation you are talking about, where speeds are low, concerns special relativity, and it's obvious [wikipedia.org] that low speeds do not make much of a difference. This isn't some "guess" that astrophysicists are making. It's a direct result of what special (and therefore) general relativity says. And astrophysicists do [arxiv.org] use general relativity.

Re:General relativity (1)

mc6809e (214243) | about a year ago | (#44538523)

The situation you are talking about, where speeds are low, concerns special relativity, and it's obvious that low speeds do not make much of a difference.

Obvious?

A coil of wire with electrons moving at mere centimeters per hour is enough to exhibit relativistic effects (magnetism).

Re:General relativity (0)

Anonymous Coward | about a year ago | (#44539719)

Except at those slow speeds you can find electromagnetism is consistent with Galilean relativity, so you can't really argue that is relativistic. This only breaks down at higher velocities like other relativistic effects, where the connection between the Lorentz transformation and Maxwell's equations become much more obvious. You can't really argue that magnetism is a purely a relativistic effect, even if the two theories are intertwined now in modern physics.

Re:General relativity (0)

Anonymous Coward | about a year ago | (#44539497)

The effect may be small, integration of a bunch of small things can result in a large thing. I think he's trying to say is: the error you get from ignoring Lorentz factors on slow moving objects may add up to a lot when you integrate over the entire solar system, and that might be a large chunk of what we call "dark matter."

Majorana or Dirac? (1)

Pro-feet (2668975) | about a year ago | (#44537497)

It can't collide with itself? Good to know that the Majorana versus Dirac particle question is settled then. Oh, wait...

Of course, I didn't bother to RTFA...

Re:Majorana or Dirac? (0)

ceoyoyo (59147) | about a year ago | (#44538481)

It's extremely difficult or impossible for it to collide with itself. Better, pedantic man?

everything old is new again (0)

Anonymous Coward | about a year ago | (#44537875)

dark matter is the new aether

Dark matter, dark energy, and M-theory (4, Interesting)

blincoln (592401) | about a year ago | (#44537977)

This is probably a dumb question, but I've been wondering about it for something like a decade, and I never see it referenced (even to debunk it) in legitimate science discussions.

A mysterious effect which looks like matter, but is invisible except for its gravitational effect. A second mysterious effect which causes the rate-of-expansion of the universe to increase.

I grow more and more skeptical of string theory and its relations every year, but the first of those definitely sounds to me like matter that's in another brane. The second one seems (to my non-physicist mind) like it could also be explained by the same thing, just a different set of matter in a different position relative to the first.

If our universe really is a 3D brane in a hyperdimensional space with others, isn't this exactly the sort of thing we'd expect to see? Further, wouldn't we see related effects like neutron stars unexpectedly flashing into black holes when they come into close-enough contact with dense clumps of matter in adjacent branes (IOW, when there's not enough observed mass in our own to explain the change to a black hole)?

Re:Dark matter, dark energy, and M-theory (0)

Anonymous Coward | about a year ago | (#44539957)

Don't mix up observations and theories that try to explain those observations.
Those effects are being observed. They are very real. And for lack of a better explanation we refer to the causes of these observations as "dark matter" and "dark energy", without knowing what those actually are. It is just that it needs a name.

And as far as string theory goes. All the critiques are correct, but it is also true that string theory is still the best theory we have to even get close to answer to what is going on.
You may not like it, it may not make sense to you, but nature doesn't care what we think.
Just accept that we understand very little about all this and that you are looking at our first feeble attempts to come to an understanding and it all makes more sense :-)

Another interpretation (0)

TheSkepticalOptimist (898384) | about a year ago | (#44537985)

"a diffuse mess, with a density that is ridiculously low, to the point where detecting its local effects is likely to remain... challenging for the foreseeable future"

In other word something irrelevant we can safely ignore and not invest any more money or resources into.

Re: Another interpretation (0)

Anonymous Coward | about a year ago | (#44538367)

That's pretty much 90% of quantum physics and cosmology.

Re:Another interpretation (1)

joe_frisch (1366229) | about a year ago | (#44538935)

Understanding the universe has been a good investment in the past. There is good evidence for something that behaves like dark matter on galactic scales. If it isn't dark matter it might be something more interesting.

Re:Another interpretation (0)

Anonymous Coward | about a year ago | (#44539871)

Umm, "understanding the universe" has yielded no tangible results since 1945.

It's mental masturbation, plain and simple.

At first there was nothing then it exploded (2)

Trax3001BBS (2368736) | about a year ago | (#44538509)

This is a sig I've seen someone use on /. the article says to me dark matter was here, then nothing exploded.

The 2dF Galaxy Redshift Survey http://scienceblogs.com/startswithabang/files/2013/07/kozm_LSS.jpg [scienceblogs.com]
shows stuff coming towards us. I've heard so many space programs say everywhere you look everything is moving away from us,

Re:At first there was nothing then it exploded (0)

Anonymous Coward | about a year ago | (#44538973)

Maybe the problem of understanding is the human race is still dumb. Give it a few thousand more years for our understanding to advance. Dark matter, dark energy and other strange things will be solved someday. When that wisdom arives I have another puzzle to solve. Ghosts. That's right, a fuckn ghost that I don't believe in. I keep telling myself that I don't hear foot steps once-in-a-while when no one is around. I had another person visit one day that heard it too. Maybe ghosts are part of dark matter too.

Re:At first there was nothing then it exploded (0)

Anonymous Coward | about a year ago | (#44539243)

The 2dF Galaxy Redshift Survey http://scienceblogs.com/startswithabang/files/2013/07/kozm_LSS.jpg [scienceblogs.com]
shows stuff coming towards us.

No, it doesn't. Perhaps the color coding was chosen poorly, but it doesn't show things moving towards us at all. Quite the opposite.

Re:At first there was nothing then it exploded (1)

Trax3001BBS (2368736) | about a year ago | (#44539445)

The 2dF Galaxy Redshift Survey http://scienceblogs.com/startswithabang/files/2013/07/kozm_LSS.jpg [scienceblogs.com]
shows stuff coming towards us.

No, it doesn't. Perhaps the color coding was chosen poorly, but it doesn't show things moving towards us at all. Quite the opposite.

Tossed that out for a response, thank you.

I did search it out first
http://www.aao.gov.au/2df/manual/2df_manual.html [aao.gov.au]
and
http://www2.aao.gov.au/2dFGRS/Public/Publications/colless_specz.pdf [aao.gov.au]

source: http://en.wikipedia.org/wiki/2dF_Galaxy_Redshift_Survey [wikipedia.org]

I couldn't find anything to grab on to, other than "8.2 Simple redshift completeness mask" of the PDF but figure I was on the wrong track
(ie: made no sense to me).

Serious Question (1)

dorpus (636554) | about a year ago | (#44539561)

This may or may not relate to dark matter, but the other day, an electrical storm was passing over my house, and I momentarily saw a dark spot on the wall. Is there a scientific explanation for such phenomena? I've never had visual disturbances like that otherwise.

Dark matter is soooo dark... (0)

Anonymous Coward | about a year ago | (#44539913)

...it can only be observed as a giant hole in our theory.

If Star Trek has taught us anything... (0)

Anonymous Coward | about a year ago | (#44540001)

Having just finished watching Star Trek TNG Season 4 in lovely high definition, it appears that the effects of dark matter in the solar system will be A) Objects disappearing and reappearing at random, and B) A large increase in the amount of women wanting to date androids.

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