Examining the Expected Effects of Dark Matter On the Solar System 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."
The problem with dark matter (Score:2, Insightful)
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 'noi
Re:The problem with dark matter (Score:4, Funny)
Or, your significant other has some weird cat food fetish thing going on...
:-)
Eeeek!
Re:The problem with dark matter (Score:5, Informative)
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.
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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 base
Re:The problem with dark matter (Score:5, Informative)
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.
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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 (Score:5, Informative)
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 (Score:4, Informative)
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.
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What's all this bullshit about paywalls? Could you provide me with a link to the papers that are being paywalled that you're bitching about? I'm on a university network -- I'll post the fucking things up myself if you want. Though since this is astronomy I'd be shocked if those papers aren't available through the arXiv or, if they're old enough, through adsabs. Have a hunt before you start accusing people who have devoted years of their lives to educating themselves on the topic of being religious zealots i
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Papers behind paywalls referencing non-public data.
If you want to pick on some field of science for doing this, astronomy is a bad choice. Just about every paper in astronomy gets put up on arxiv.org [arxiv.org], where it's available free of charge. And the data from government-funded telescopes, while usually held secret for 12-18 months to give the astronomer a chance to publish first (and hence an incentive to do the work of operating the telescope in the first place), is made public after that time. This is usually done on a per-telescope basis: for example, the
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Buy it or not but people smarter than I have spent decades modelling dust -- I know a good few people with PhDs and postdocs in the matter -- and what we expect to see from it. What we expect:
1) Radiation. Dust is heated, dust radiates. If nothing else, dust is bathed by the CMB, and therefore will still radiate.
2) Dust also scatters radiation. If nothing else, this is obvious in the CMB, but there *are* other things -- light from stars in our own galaxy, other galaxies, quasars, etc.
3) Dust is typically ch
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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
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"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
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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
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Estimating probabilities based on the best evidence we have available isn't being a charlatan; it's called being rational, and is the foundation of the scientific method. You can estimate based on strong evidence, but you can also estimate on weak evidence, and weak evidence is far from useless, especially if there's a lot of it.
You would do well to read up on the scientific method, and Bayesian probability estimation in particular, because I do not think you understand it at this point. Everything is pro
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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.
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[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
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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 (Score:5, Informative)
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...
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Due to Hawking Radiation, the smaller the black hole, the brighter it is, in fact becoming a net emitter of radiation under a certain size. That radiation also causes the black hole to evaporate over time, and the smaller the black hole is, the shorter its lifespan. At the size of a particle, a black hole should evaporate in a rather small amount of time.
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Well, you know that they do have radio and infrared telescopes, right? They already are checking other spectra. I'm not going to presume that they have it all covered, but I'd be very surprised to find it was just normal "dust" radiating in some very specific wavelength we just haven't checked yet. Let's not forget that while there is a wide spectrum of possibilities, you only radiate at certain wavelengths under specific circumstances such as being a product of high energy events. We've been looking at
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Although current theories of Dark Matter are pretty vague and ether-like at this point, weakly interacting particles have been demonstrated in the past, like neutrinos. It's far from being implausible or wild guessing.
I'm not saying that. It just seemed like extrapolating to new exotic particles wasn't called for if mere misunderstood dust might explain the phenomenon. I've since been informed that they indeed have thought of this and (rightly or wrongly) discarded it for various reasons.
[The /. bottom page quote: "You can not get anything worthwhile done without raising a sweat. -- The First Law Of Thermodynamics]
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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 i
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It presumes that we are talking about a single phenomenon and that our interpretation of our measurements is correct and consistent. I think it's more likely that "dark matter" as a single phenomenon doesn't even exist. A combination of modifying the laws of gravity, correct
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Although you're technically correct that there has historically been more than one cause of missing matter, we've managed to locate and calculate the amounts of extra planets or dust or brown dwarves and such already and found that while they do exist, they are in amounts that only explain something like 10% of the missing matter we needed to find when we started looking for "dark matter".
So yes, MACHOs are part of the equation for the original dark matter problem, and no doubt things like neutrinos and oth
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First of all, we can't put useful bounds on rogue planets at all; they are very hard to detect. Second, your reasoning still assumes that there is a single mechanism and that galaxies are largely all the same. We don't even know the rotation curve of our own galaxy very well; our local observations might simply not apply to most other galaxies. And different galaxies may have different kinds of dark matter.
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More than that we do have a hell of a lot of spectra of other spiral galaxies these days. Unless one takes the unsupportable view that the Milky Way is somehow unique -- compared to the thousands (or tens of thousands, or hundreds - I don't know how many we have) of galaxies we have examined in detail, we can immediately assume that the Milky Way has a similar rotation curve to other galaxies. The *details*, obviously, should be filled in and I'm glad people are examining it so carefully, but a good observa
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Yeah but since we can get much cleaner spectra from other galaxies, with far tighter error bars, we're going to learn more from those than we're likely to from the Milky Way. Observing the Milky Way we'll always have the problem that we're looking through the mess of our own dust. Viewing other galaxies we're not doing that and we can extract far cleaner data. I'm not saying that observing the Milky Way is unimportant but I will say that for this issue a large number of clean spectra from other galaxies is
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Oh, you might be meaning things like annihilation signals and the like, where we can actually get a handle on what dark matter is actually composed of, what it decays into, what it interacts with and how strongly. In which case, yes, I totally agree with you on that one. While it's still possible we're going to be lucky to find that (if a particulate dark matter exists) we can observe dark matter in the laboratory. If we're looking for something other than gravitational effects then yes, we have to look at
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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.
That would fail to explain thing like the bullet cluster and the fluctuations in the cosmic microwave background.
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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 a
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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.
Same thing can be said about gravity.
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Why is it so hard to imagine that there is a particle that interacts with gravity but not electromagnetically? That's really what this comes down to.
Remember you only touch that key on the keyboard because of photon interactions.
Are you happy with the existence of Neutrinos? These particles that barely interact with normal matter or do you think they are purely there to balance formulas too? (okay that's why they were originally there but not anymore)
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I have no issues in imagining that, the problem is indeed the opposite. If there COULD be a particle, everything is ok. If there MUST be a particle, there is lack of imagination. Sometimes that is good, speeds up the search for an explanation. Sometimes that makes the explanation difficult or impossible to reach. With neutrinos it was good.
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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?
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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
Re:The problem with dark matter (Score:4, Informative)
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.
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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...).
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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.
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I don't know about that. In Newtonian days, we definitely didn't know what gravity was, and we were very able to make use of our calculations based on our theories of its effects. Today, we presumably know more about gravity, but not everything, and we are able to make very useful calculations based on it.
Dark Matter probably does exist as some sort of WIMP, but even if it doesn't, we could still use our understanding of what we think it is for a useful effect.
In short, we can rely on it because we alread
It is based on empirical observation (Score:4, Insightful)
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.
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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.
Well, at this point, the cat food is being eaten, there is cat hair everywhere, the litter box is getting filled, and if somebody meows they will hear another meow come back in return from inside the wall. People can argue that it's not a cat, but whatever it is, it acts like a shy cat nobody has ever seen and any other explanations are a lot stranger than a cat that nobody has ever seen. Same thing for dark matter, either there is matter that only interacts via gravity, or there is something else out there
General relativity (Score:1)
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.
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Rebuttal: Bullet cluster.
Re:General relativity (Score:5, Insightful)
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.
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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 D [arxiv.org]
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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.
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Re:General relativity (Score:5, Insightful)
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.
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I keep my mind open, not closed to possibilities I have never imagined.
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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 (Score:5, Insightful)
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?
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Here's the thing. We "followers" may not be able to do the science ourselves, but we can both read the papers and look at who and how many scientists are working on X theory, and who and how many scientists are looking at Y theory, get a feel for it on a high level, and come to a conclusion. And that is assuming that we're all minimally proficient in science ourselves, when in reality, many of us have been carefully keeping up on these theories for decades on an amateur basis and have fairly good science
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> 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 re
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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 mas
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No it does not. Photons have no rest mass and their relativistic mass is negligible.
But not zero. And in case you hadn't noticed the bright shiny orb in the sky, you get a lot of photons when you convert matter to energy, and their total energy will be equivalent to the total mass converted. I'm sure there's a formula for it somewhere...
Convert that matter to light and space unwarps itself, expanding the universe.
If that's the case - and I'm not at all clear why you've concluded that the universe would expand in any real sense just because some part of space is less warped than it used to be - it's only because the light leaves the local area. But then that light w
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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.
E=MC2 is an equivalence, not a transformation.
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You're making a classic mistake there. When matter gets converted into energy gravitation doesn't care. It cares about the total mass-energy. Which doesn't change. So while the emitted photons do not have mass they do have energy which of course has a mass equivalent.
In a closed system* even if there are nuclear reactions taking place the mass-energy of the system does not change.
*to actually do this you'd have to contain all the mass and photons and neutrinos, which we don't know how to do, but the point s
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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.
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Obvious?
A coil of wire with electrons moving at mere centimeters per hour is enough to exhibit relativistic effects (magnetism).
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Except that electromagnetism IS a relativistic effect. You don't have electromagnetism without relativity.
Majorana or Dirac? (Score:2)
Of course, I didn't bother to RTFA...
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But hey, what do I know, I'm not even one of them.
Dark matter, dark energy, and M-theory (Score:5, Interesting)
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)?
Another interpretation (Score:1)
"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.
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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.
At first there was nothing then it exploded (Score:3)
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,
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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 (Score:2)
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.
Wrong summary? (Score:2)
So, it can't collide with itself, meaning that it has no way of getting hotter[...]
Wouldn't gravitational interactions count as "colliding", at least for the purpose of exchanging energy? And the fact that it can't radiate away energy has more to do with it not interacting electromagnetically than its ability to collide with itself, hasn't it?
Pioneer anomaly (Score:2)
If there is a constant density of dark matter in the solar system it will have a too small effect on Neptune to be detected. When moving further away from the sun the effect of the dark matter becomes stronger. So if we want to detect its gravitation we have to go as far away from the sun as possible. We should see something like the Pioneer anomaly, but we probably have to send a probe much farther out to detect any effect.
Re:Dark Matter (Score:5, Insightful)
As opposed to the ether of the 19th century, quantum fields, which are what we currently use to explain everything?
Relativistic space under tension? (Score:3, Interesting)
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 r
Re: (Score:2)
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: (Score:2)
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 w
Re: Dark Matter (Score:4, Funny)
Re: Dark Matter (Score:5, Funny)
Re: (Score:2, Insightful)
Re: Dark Matter (Score:4, Interesting)
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 (Score:4, Insightful)
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.
Just the opposite (Score:5, Insightful)
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: (Score:1, Funny)
Slight change in perspective (Score:2)
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.
Re: (Score:3)
In contrast, scientists started by measuring orbital velocities and could only explain them with dark matter.
That's why I think dark matter is more like epicycles than the ether.
Re: (Score:2)
Good points.
Re:Just the opposite (Score:5, Funny)
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 (Score:5, Informative)
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: (Score:2)
Old science? As in "not my personal theory I just invented"?
Einstein had a perfectly valid alternative to postulating an Ether, i.e. he used Special Relativity to explain the things that used to be explained (with more and more problems) by postulating an Ether. So, using Occam's Razor, the existence of an Ether is no longer a useful scientific theory - unless you can show there is a physical reality that is explained best by postulating an Ether. In which case, we'll need to take a long, hard look at SR ag
FTFY (Score:2, Funny)
Re: (Score:3)
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: (Score:2)
Re:Dark Matter, the Aether of the 21st century. (Score:5, Informative)
Let me know when they find supporting evidence [of dark matter]
You mean like the rotational curves of galaxies, the velocity dispersion of stars in galaxies (including observations of globular clusters with very little dark matter, leaving MOND with even more problems), gravitational lensing (including the bullet cluster), fluctuations in the cosmic microwave background etc. [wikipedia.org]?
Mind you, I can't forward a better theory to explain why things have mass
Dark matter has nothing to do with why things have mass. That would be the Higgs field (or, rather, why fundamental particles have mass. Most of the mass of normal matter has another explanation).