10 ms·

Could dark matter not exist?

211 points by strttn 11y ago

graycat 11y ago
Something has orbits around galaxies failing to follow the law of gravity from ordinary matter. The orbits are as if there there is some more mass with gravity, mass that doesn't interact with light. Something is in/near galaxies is bending light as if there were more mass there than there is from just ordinary matter. So, for that extra mass, call it dark matter. Seems simple enough. "Flaw in the theory of gravity?" Maybe, but that seems to be the hard way to get an answer.
- dandelany 11y ago
  Alternatively: The orbits around galaxies fail to follow the law of gravity of ordinary matter. The orbits are as if our gravity calculations, which seem to work well otherwise, are flawed. Something in/near galaxies causes them to bend light as if gravity were different. So, for that region, call it a flaw in the theory of gravity. Seems simple enough. "Unseen, never-before-detected form of matter which doesn't interact with any other matter except gravitationally?" Maybe, but that seems to be the hard way to get an answer. This is tongue-in-cheek of course, but it's hard to trust intuition in these realms, especially when one person's intuition is another person's "hard way" :)
  - rcxdude 11y ago
    Yeah, but AFAIK all the explanations based around adjusting our theory of gravity have failed to match the results, and tend to be pretty complicated and thus prone to overfitting.
    - AnimalMuppet 11y ago
      Whereas, since you can adjust the hypothetical distribution of dark matter to be whatever you need it to be to fit the data, you cannot falsify dark matter this way, since proving that no possible distribution of dark matter could fit the evidence is pretty much impossible. Still, to me there seems to be some level of equal implausibility in saying "our theory of gravity is wrong" and in saying "our theory of matter is wrong".
      - Retra 11y ago
        We have much more experience with matter, because we can interact with it on a variety of scales in a lab. Gravity is much harder to interact with, and thus much harder to explore. That's why it is quite a bit more likely that our understanding of gravity is incorrect.
      - bzbarsky 11y ago
        From my limited understanding, what's interesting about the dark matter approach is that if you pick the distribution of dark matter to fit the rotational velocity profiles of galaxies that also just happens to be the distribution that has a good fit to various other unrelated data sets (cosmic microwave background fluctuations, say). Now maybe there's a deep underlying reason we don't know about that makes those unrelated data sets in fact related to each other. Or maybe it just happens that the dark matter actually exists. But the point is that the dark matter theories we have were absolutely falsifiable, as the article points out. They made predictions that were then tested and so far the predictions have been correct.
        AnimalMuppet 11y ago
        I stand corrected.
- smil 11y ago
  Exactly. Dark matter and dark energy is just a symptom of the standard model of physics being incorrect. >Dark matter neither emits nor absorbs light or any other electromagnetic radiation at any significant level. According to the Planck mission team, and based on the standard model of cosmology, the total mass–energy of the known universe contains 4.9% ordinary matter, 26.8% dark matter and 68.3% dark energy.[2][3] Thus, dark matter is estimated to constitute 84.5% of the total matter in the universe, while dark energy plus dark matter constitute 95.1% of the total mass–energy content of the universe.[4][5][6] Science is literally religious faith.
  - apalmer 11y ago
    Ummm... this is kind of thing is well in line with the history of science. Clearly dark matter is a fudge factor to make the current model of physics work. Obviously there is a flaw here somewhere, so there are multiple competing theories of which dark matter & dark energy are but one for explaining this. Some theories are more popular than others... But pretty much within 5 years of a new falsifiable theory that can explain the situation which can be experimentally proven dark matter will go the way of the myriad of disproven theories... whereas religious faith would extend the belief in dark matter out for possibly thousands of years after it is shown to be experimentally incorrect. So not 'literally' religious faith at all...
  - dragonwriter 11y ago
    > Dark matter and dark energy is just a symptom of the standard model of physics being incorrect. Possibly, and if there was a better model -- one that was as good at predicting/explaining the observed effects for which the standard model works and did not require invoking dark matter and/or dark energy, the standard model would be dropped in a heartbeat. But right now the standard model + dark matter + dark energy is what works best, of the models that have been presented, at modeling what is actually observed in our universe. So it survives. For now. Whether it will be resolved by an as-yet-unproposed tweak to the basic model or finding out that "dark matter" and "dark energy" are real things is yet to be seen.
  - kleer001 11y ago
    > Science is literally religious faith. No it isn't. Not by a long shot. Faith requires that you confabulate to a reach a certain cognitive destination. Science only allows models that conform to reality upon repeated testing.
morsch 11y ago
I found the most interesting part of the article to be this image of a 1919 newspaper illustrating "Starlight bent by the sun's attraction": The Einstein theory. https://d262ilb51hltx0.cloudfront.net/max/847/1*LV-wtp9IclSx2-SZuP1FsA.jpeg https://d262ilb51hltx0.cloudfront.net/max/847/1*LV-wtp9IclSx... As for the rest of the article, well, Betteridge's law holds, though with the "as best we know"-suffix implicit to science and science journalism.
lordnacho 11y ago
It reads like a great example of how theory works. You have some evidence (old planets), and a model that predicts it well (Newton/Kepler). Then some new evidence comes in (Uranus), and the theory is almost right, but not quite. So we modify it a little, or we start searching for an extra mass to explain the error. Then some more experimental evidence comes in (galactic radial velocity), and we are thinking about modifying the theory a bit more (MOND). This is good for the radial velocity explanation, but not certain other things. We suppose there's some dark matter, and think about the consequences that would have. Then we see evidence consistent with that. Of course this is a boiled down version. Real science is rarely so clean.
- jfoutz 11y ago
  Real science is ugly because there are a bunch of theories that kinda sorta fit, but not really well. I think Maxwell had something like 40 equations for electricity. Give it a hundred years and hundreds of thousands of grad student hours, and something quite clean emerges. The unknown edges are messy, but as competing theories get winnowed out, merged and refined they become clear and concise.
  - AnimalMuppet 11y ago
    Maxwell had 20 equations for electromagnetism, because he didn't use vector notation, so he had to do the equations component by component. But that had nothing to do with having multiple theories. The current "Maxwell's equations" are exactly the same as Maxwell's 20 equations, merely expressed in a more convenient form.
    - cma 11y ago
      Wikipedia claims: "Less well known is that Heaviside's equations and Maxwell's are not exactly the same, and in fact it is easier to modify the latter to make them compatible with quantum physics.[25]"
    - zardo 11y ago
      In geometric algebra it's a single equation. ∇E=∂B/∂t
mixmastamyk 11y ago
Interesting, I always thought of dark matter as just a lot of extra "dust", the dust that clumps to make the stars that make up the universe. The asteroid belt, the extra mass in our kuiper or oort clouds, etc. The dust that blocks parts of our view of the Milky way. This article (and others I'm now skimming) point out that dark matter needs other magical properties however. Why is that the case? Why does simple "dark dust" not fit?
- aetherson 11y ago
  There'd have to be so much of it that we'd see it. There's way more dark matter than normal matter in the universe (stipulating that dark matter theories as we currently understand them are at a coarse level correct). If it were "dark dust," there would be enough of it that we would be able to detect it through means other than gravitational ones.
  - mixmastamyk 11y ago
    Thanks. Given that the Oort cloud is very sparse and we can't see it, and we can't (optically) see even the largest planets on other stars, why would we expect to be able to see it?
    - teraflop 11y ago
      The objects we know of are orders of magnitude too small to explain the missing mass. The Oort cloud is estimated to make up about 0.002% of the solar system's mass. If instead it was 5 times more massive than everything else put together (which would be required for it to make up our solar system's share of the galaxy's dark matter) it would be a lot more visible.
    - mtrpcic 11y ago
      There's one other thing that goes against the idea of "dark dust". if it was "dark dust" that was just a sparse cloud of standard elements, we would be able to detect the makeup of the cloud by pointing a Spectrometer at some of the darker (but seemingly "denser") parts of the cloud to detect what it's made of.
HillOBeans 11y ago
For those who are interested, physicist John Hartnett has developed a model that does not require dark matter. His work builds on that of Moshe Carmeli, who published "Cosmological Special Relativity". Hartnett's book is "Starlight, Time, and the New Physics" ISBN 978-0-949906-68-7. Disclaimer: I am not a physicist, and the math is way over my head, so I cannot double-check it. Hartnett has not made much, if any, headway with mainstream scientific publications, probably because he is a Biblical Creationist.
- gnufied 11y ago
  Just read one of his articles from his Website. He mixes physics and mythology with impunity. No wonder, his theories are not taken seriously.
  - cristianpascu 11y ago
    So, say, if someone comes to you with a clean demonstration of how and why something is happening in the world, people verify it and it proves correct, and (s)he says the idea was revealed while smoking pot in a mystical hotel in north canada, or france for that matter, you'd say no one should take the theory seriously? Good job!
    - dalke 11y ago
      I believe that gnufied is saying that this isn't a clean demonstration. If one paragraph of explanation is buried in 1,000 pages of dreck, then is the onus on the reader to find the nugget, or the author to emphasize the important part? If you've ever hung around a physics or astrophysics department you'll find that a lot of people send in explanations of how modern science is wrong. For example, http://www.universetoday.com/108044/why-einstein-will-never-be-wrong/ http://www.universetoday.com/108044/why-einstein-will-never-... comments: > One of the benefits of being an astrophysicist is your weekly email from someone who claims to have “proven Einstein wrong”. These either contain no mathematical equations and use phrases such as “it is obvious that..”, or they are page after page of complex equations with dozens of scientific terms used in non-traditional ways. They all get deleted pretty quickly, not because astrophysicists are too indoctrinated in established theories, but because none of them acknowledge how theories get replaced.
raverbashing 11y ago
There might not be dark matter, but we need a better explanation than MOND
cletus 11y ago
I'm no physicist but I've asked myself this question. It's a bit like string theory. String theory is a mathematical answer that solves some (all?) of the inconsistencies between quantum theory and gravity but has some implications that have no experimental evidence (eg extra dimensions). Dark matter always struck me as a kludge to explain the universe fit our model. There are many theories on it but no observed or experimental effects of dark matter to date. We say that there are four fundamental forces in the universe: weak nuclear, strong nuclear, electromagnetism and gravity. The first three are pretty adequately explained by quantum mechanics (AFAICT). The last of course isn't but is described pretty darn well by relativity. Thing is, what's always struck me as odd is the other forces, I believe, can both attract and repel. There is no observation or experimental evidence of "antigravity". It has always made me wonder if we're not making an error by trying to fit gravity into the Standard Model. Perhaps it's not a force like the others are and simply the result of the nature of space-time. Anyway, like I said: complete layman here. What I'm saying might be completely nonsensical to anyone with half a clue about physics. I know the LHC has looked and is looking for any evidence at the edges of the Standard Model of some violation that will hint at something that might explain all this. I also know minds far brighter than mine have spent a lot of time thinking about this. I'm still left wondering if dark matter/energy isn't simply another "string theory".
- deciplex 11y ago
  > There are many theories on it but no observed or experimental effects of dark matter to date. FTFA: > And most spectacularly, you get an entirely new prediction: that when you get two clusters of galaxies colliding, the gas inside should heat up, slow down and emit X-rays (in pink, above), while the mass that we can see through gravitational lensing (in blue, above) should follow the dark matter, and be displaced from the X-rays. This new prediction has been borne out observationally and held up over the past decade, a spectacular indirect confirmation of dark matter.
- tjradcliffe 11y ago
  Dark matter is no more a kludge than phlogiston, or the lumineferous aether, or neutrinos. All of them were introduced as novel entities to explain experimental phenomena. The first two turn out not to exist, the latter does: http://www.tjradcliffe.com/?p=1801 http://www.tjradcliffe.com/?p=1801 Calling them kludges is to mistake the basic process of science for a hack. There are any number of confirmatory observations that fit the dark matter model, just as there were any number of confirmatory observations that fit the neutrio model. It's just that we haven't observed any dark matter particle interactions directly, just as we hadn't observed any neutrino interactions directly before Reines' experiment. It may be that dark matter turns out not to exist, and then we will know it was wrong. Until then it is perfectly ordinary science working in perfectly ordinary ways as it has been for over a century.
cristianpascu 11y ago
I graduated physics, but I'm almost a layman when it comes to general relativity. Still, I wonder if another possible explanation for stuff that don't match theory could be the basic assumption about our current cosmology. That the space is flat where there's no matter. Since there's a relation between the geometry of the space and the matter within, would it be unreasonable to believe that space itself could be curved independently of the matter we can observed? Maybe for other reasons, yet unknown?
InclinedPlane 11y ago
Sigh. Sure, it's possible, but very unlikely. These "MOND" gravity theories purport to explain observations better than the theory of dark matter, but they don't. They explain some things and leave gaping holes elsewhere. On the whole they are hugely inferior theories in terms of matching observational evidence. Their only advantage is that they lack the existence of massive, weakly interacting particles, which a lot of people seem to have strong objections to despite the fact that several types of such particles are already known to exist. Throughout the entire history of the development of the theory of dark matter the bias has always been against the idea of true dark matter, unseen particles that make up most of the mass of the Universe. But at every single step all of the other possibilities have been eliminated as realistic explanations of the evidence. The cold WIMP dark matter theory is the only one that explains the structure of the cosmic microwave background radiation, the large scale structure of the Universe, and the structure and behavior of galaxies and galaxy clusters. At this point the theory of dark matter is remarkably well hemmed in, it would be absolutely shocking to an extreme degree if it did not truly exist in the form we think it does. There's additionally a very elegant mechanism behind the formation of dark matter. It seems most likely to be composed of super-symmetric particles. Such particles would only be able to form in extreme, high-energy conditions. Precisely the sort of conditions that existed in the early era of the Universe immediately after the Big Bang. So the early Universe would have been creating huge quantities of such particles, which would then not interact much due to their weak interactivity. It wouldn't be until the Universe had expanded enough and cooled down enough to halt their production. This would neatly explain why so much of the mass of the Universe is in the form of dark matter rather than conventional matter.
- ajkjk 11y ago
  Did you read the article? It agrees with you.
- dkbrk 11y ago
  > These "MOND" gravity theories purport to explain observations better than the theory of dark matter, but they don't. MOND consistently fits the rotational velocity profile of galaxies better than dark matter. This isn't too surprising as MOND originated as an ad-hoc formula derived from observations of said rotational profiles, however MOND works very well over a very wide range of galactic profiles. The mass deficit observed in tidal dwarf galaxies is also quite strong evidence against just dark matter. I don't think anybody is seriously claiming that MOND is a complete theory, though of course there have been attempts by theorists at creating complete models, but they've failed to explain large-scale structural observation and the cosmic microwave background. This just means these attempts at creating a complete theory are probably wrong, not that there isn't something funky going on with galaxies that isn't completely accounted for by dark matter. > They explain some things and leave gaping holes elsewhere. This is a false dichotomy. MOND is not incompatible with dark matter. This "us vs them" mentality is really quite harmful. A combination of MOND and dark matter matches most observations very well, far better than dark matter in isolation. > Their only advantage is that they lack the existence of massive, weakly interacting particles, which a lot of people seem to have strong objections to despite the fact that several types of such particles are already known to exist. While I'm sure there are quite a few people for whom this is the case, you shouldn't dismiss the possiblity there are people who take MOND seriously because it legitimately fits the data better in some circumstances.
AdieuToLogic 11y ago
> Could dark matter not exist? Sure.
- AdieuToLogic 11y ago
  I guess I need to elaborate on this answer. Perhaps our observations are a result of existing within two gravitational space-time distortions, one trivial and one not. The trivial one being the Sun and the non-trivial being the galaxy which we inhabit. If curvature of space-time theorized by General Relativity is accepted, then observing non-local energy will be affected by gravity in which the observation is being undertaken. Accounting for the Sun's influence has largely (if not completely) been addressed, but there lies a more difficult "elephant in the room" problem of determining what effect the gravitational curvature of the Milky Way has on any observations we can make. According to the University of Oregon[1], the observable mass of the Milky Way is 200,000,000,000 Solar masses. The same material indicates that visible stars account for 30% of that. Throw in a bit for singularities and lets call it "less than 50%" for the sake of discussion. In any event, there exists enough mass in this galaxy to plausibly state that the space-time we inhabit is affected. Yet a non-trivial amount considered "unaccounted for." Using the canonical 3d inverse-cone visualization of matter's effect on space-time, imagine our solar system exists on some point within the galaxy's gravitational cone yet not near its center. Making intra-galactic calculations may be influenced by compressed space-time instead of the presence of dark matter. And observations regarding other galaxies colliding (as mentioned in the article) migth be explained by gravitational phase shifting. Though all of this likely will be rebuked, it is why I originally said "sure." 1 - http://hendrix2.uoregon.edu/~imamura/123cs/lecture-2/mass.html http://hendrix2.uoregon.edu/~imamura/123cs/lecture-2/mass.ht...
ianamartin 11y ago
Of course dark matter doesn't exist. Hello, people. Dark matter is the eflourescent ether theory of the 21st century. There are things that we don't know how to explain right now. We have some ideas about how they can be explained. But they are really really bad. We will be laughing at dark matter theory in a few years.
- Sharlin 11y ago
  You might do well to familiarize yourself with the Dunning-Kruger effect.
- PhantomGremlin 11y ago
  Dark matter is the eflourescent ether theory of the 21st century. The quip I'm fond of is: Dark Matter is the Phlogiston of Contemporary Cosmology But, right now, dark matter is the best explanation we have of what we've observed.
- socceroos 11y ago
  That's my prediction as well, but I wouldn't have put it so....abrasively.
dschiptsov 11y ago
Most of concepts we are conditioned to take for granted does not exist outside our head.) The essence of scientific method is not in piling up concepts or in building up a support for a fancy theory. On the contrary, it is in exactly opposite - it is to refute and remove everything "mental" to see what remains, something which cannot be shaken by mere speculations or dismissed by any experience. That, perhaps, has something to do with what we call Truth. According to the ancients, who practiced this method, there is nothing but different forms of light. The question "what is between two Photons" makes no sense, because two Photons have nothing in common exept an imagination of an observer. Tracing them back "in time" makes no sense either, because time as a category is irrelevant to the light. It doesn't change.
madaxe_again 11y ago
Almost certainly not. Do epicycles exist? No. They were a handy tool/kludge. Our understanding of space-time is incomplete.
0xe2-0x9a-0x9b 11y ago
You can distribute dark matter in space to shape it in any pattern you like and give the dark matter any kind of property just to create a mathematical model that is consistent with observations. Dark matter is just a theoretical concept - for now or forever.
restalis 11y ago
"your theory has three burdens to meet:" ... "it must make new predictions that can be experimentally or observationally tested, and confirmed or refuted, that are unique to this new theory" ("MOND fails spectacularly, either offering no predictions...") I fail to understand the necessity for new predictions. This simply may or may not come out of new theories as a paradigm shift consequence and it is therefore just optional, not a must. In fact, I fail to fully understand even the first requirement (about reproducing all the successes of previous leading theory) - the current leading theory's explanation may happen to explain things somehow, but that may not be necessarily correct. I wouldn't dismiss a competing theory even with holes in it if there is a slightest chance that further work on it or on something closely related to it may come to cover those shortcomings in time.
- drpre 11y ago
  Disclaimer: far from a physicist. I think the point is that, for a new theory to become more favored than the current leading theory, the new theory must be consistent with at least as much scientific evidence as the leading theory. From there, the value of predictions is that they give a path for strengthening the theory further. I think you're right in saying that these are not hard-and-fast rules.
mpc755 11y ago
The notions of dark matter and the dark matter particle are incorrect. The mass which fills 'empty' space is beginning to be referred to as the 'dark mass' in order to distinguish it from the baggage associated with dark matter. 'Dark Energy/Dark Mass: The Slient Truth' https://tienzengong.wordpress.com/2015/04/22/dark-energydark-mass-the-silent-truth/ https://tienzengong.wordpress.com/2015/04/22/dark-energydark... "That is, all that we are certain about [is] the dark mass, not dark matter, let alone to say about the dark 'particle'." Particles of matter move through and displace the dark mass, including 'particles' as large as galaxies and galaxy clusters. The Milky Way moves through and displaces the dark mass. The Milky Way's halo is the state of displacement of the dark mass. The Milky Way moves through and curves spacetime. The Milky Way's halo is curved spacetime. The state of displacement of the dark mass is curved spacetime.

211 points by strttn 11y ago

Something has orbits around galaxies failing to follow the law of gravity from ordinary matter. The orbits are as if there there is some more mass with gravity, mass that doesn't interact with light. Something is in/near galaxies is bending light as if there were more mass there than there is from just ordinary matter. So, for that extra mass, call it dark matter. Seems simple enough. "Flaw in the theory of gravity?" Maybe, but that seems to be the hard way to get an answer.

dandelany 11y ago
Alternatively: The orbits around galaxies fail to follow the law of gravity of ordinary matter. The orbits are as if our gravity calculations, which seem to work well otherwise, are flawed. Something in/near galaxies causes them to bend light as if gravity were different. So, for that region, call it a flaw in the theory of gravity. Seems simple enough. "Unseen, never-before-detected form of matter which doesn't interact with any other matter except gravitationally?" Maybe, but that seems to be the hard way to get an answer. This is tongue-in-cheek of course, but it's hard to trust intuition in these realms, especially when one person's intuition is another person's "hard way" :)
- rcxdude 11y ago
  Yeah, but AFAIK all the explanations based around adjusting our theory of gravity have failed to match the results, and tend to be pretty complicated and thus prone to overfitting.
  - AnimalMuppet 11y ago
    Whereas, since you can adjust the hypothetical distribution of dark matter to be whatever you need it to be to fit the data, you cannot falsify dark matter this way, since proving that no possible distribution of dark matter could fit the evidence is pretty much impossible. Still, to me there seems to be some level of equal implausibility in saying "our theory of gravity is wrong" and in saying "our theory of matter is wrong".
    - Retra 11y ago
      We have much more experience with matter, because we can interact with it on a variety of scales in a lab. Gravity is much harder to interact with, and thus much harder to explore. That's why it is quite a bit more likely that our understanding of gravity is incorrect.
    - bzbarsky 11y ago
      From my limited understanding, what's interesting about the dark matter approach is that if you pick the distribution of dark matter to fit the rotational velocity profiles of galaxies that also just happens to be the distribution that has a good fit to various other unrelated data sets (cosmic microwave background fluctuations, say). Now maybe there's a deep underlying reason we don't know about that makes those unrelated data sets in fact related to each other. Or maybe it just happens that the dark matter actually exists. But the point is that the dark matter theories we have were absolutely falsifiable, as the article points out. They made predictions that were then tested and so far the predictions have been correct.
      - AnimalMuppet 11y ago
        I stand corrected.
smil 11y ago
Exactly. Dark matter and dark energy is just a symptom of the standard model of physics being incorrect. >Dark matter neither emits nor absorbs light or any other electromagnetic radiation at any significant level. According to the Planck mission team, and based on the standard model of cosmology, the total mass–energy of the known universe contains 4.9% ordinary matter, 26.8% dark matter and 68.3% dark energy.[2][3] Thus, dark matter is estimated to constitute 84.5% of the total matter in the universe, while dark energy plus dark matter constitute 95.1% of the total mass–energy content of the universe.[4][5][6] Science is literally religious faith.
- apalmer 11y ago
  Ummm... this is kind of thing is well in line with the history of science. Clearly dark matter is a fudge factor to make the current model of physics work. Obviously there is a flaw here somewhere, so there are multiple competing theories of which dark matter & dark energy are but one for explaining this. Some theories are more popular than others... But pretty much within 5 years of a new falsifiable theory that can explain the situation which can be experimentally proven dark matter will go the way of the myriad of disproven theories... whereas religious faith would extend the belief in dark matter out for possibly thousands of years after it is shown to be experimentally incorrect. So not 'literally' religious faith at all...
- dragonwriter 11y ago
  > Dark matter and dark energy is just a symptom of the standard model of physics being incorrect. Possibly, and if there was a better model -- one that was as good at predicting/explaining the observed effects for which the standard model works and did not require invoking dark matter and/or dark energy, the standard model would be dropped in a heartbeat. But right now the standard model + dark matter + dark energy is what works best, of the models that have been presented, at modeling what is actually observed in our universe. So it survives. For now. Whether it will be resolved by an as-yet-unproposed tweak to the basic model or finding out that "dark matter" and "dark energy" are real things is yet to be seen.
- kleer001 11y ago
  > Science is literally religious faith. No it isn't. Not by a long shot. Faith requires that you confabulate to a reach a certain cognitive destination. Science only allows models that conform to reality upon repeated testing.

morsch 11y ago

I found the most interesting part of the article to be this image of a 1919 newspaper illustrating "Starlight bent by the sun's attraction": The Einstein theory. https://d262ilb51hltx0.cloudfront.net/max/847/1*LV-wtp9IclSx2-SZuP1FsA.jpeg https://d262ilb51hltx0.cloudfront.net/max/847/1*LV-wtp9IclSx... As for the rest of the article, well, Betteridge's law holds, though with the "as best we know"-suffix implicit to science and science journalism.

lordnacho 11y ago

It reads like a great example of how theory works. You have some evidence (old planets), and a model that predicts it well (Newton/Kepler). Then some new evidence comes in (Uranus), and the theory is almost right, but not quite. So we modify it a little, or we start searching for an extra mass to explain the error. Then some more experimental evidence comes in (galactic radial velocity), and we are thinking about modifying the theory a bit more (MOND). This is good for the radial velocity explanation, but not certain other things. We suppose there's some dark matter, and think about the consequences that would have. Then we see evidence consistent with that. Of course this is a boiled down version. Real science is rarely so clean.

jfoutz 11y ago
Real science is ugly because there are a bunch of theories that kinda sorta fit, but not really well. I think Maxwell had something like 40 equations for electricity. Give it a hundred years and hundreds of thousands of grad student hours, and something quite clean emerges. The unknown edges are messy, but as competing theories get winnowed out, merged and refined they become clear and concise.
- AnimalMuppet 11y ago
  Maxwell had 20 equations for electromagnetism, because he didn't use vector notation, so he had to do the equations component by component. But that had nothing to do with having multiple theories. The current "Maxwell's equations" are exactly the same as Maxwell's 20 equations, merely expressed in a more convenient form.
  - cma 11y ago
    Wikipedia claims: "Less well known is that Heaviside's equations and Maxwell's are not exactly the same, and in fact it is easier to modify the latter to make them compatible with quantum physics.[25]"
  - zardo 11y ago
    In geometric algebra it's a single equation. ∇E=∂B/∂t

mixmastamyk 11y ago

Interesting, I always thought of dark matter as just a lot of extra "dust", the dust that clumps to make the stars that make up the universe. The asteroid belt, the extra mass in our kuiper or oort clouds, etc. The dust that blocks parts of our view of the Milky way. This article (and others I'm now skimming) point out that dark matter needs other magical properties however. Why is that the case? Why does simple "dark dust" not fit?

aetherson 11y ago
There'd have to be so much of it that we'd see it. There's way more dark matter than normal matter in the universe (stipulating that dark matter theories as we currently understand them are at a coarse level correct). If it were "dark dust," there would be enough of it that we would be able to detect it through means other than gravitational ones.
- mixmastamyk 11y ago
  Thanks. Given that the Oort cloud is very sparse and we can't see it, and we can't (optically) see even the largest planets on other stars, why would we expect to be able to see it?
  - teraflop 11y ago
    The objects we know of are orders of magnitude too small to explain the missing mass. The Oort cloud is estimated to make up about 0.002% of the solar system's mass. If instead it was 5 times more massive than everything else put together (which would be required for it to make up our solar system's share of the galaxy's dark matter) it would be a lot more visible.
  - mtrpcic 11y ago
    There's one other thing that goes against the idea of "dark dust". if it was "dark dust" that was just a sparse cloud of standard elements, we would be able to detect the makeup of the cloud by pointing a Spectrometer at some of the darker (but seemingly "denser") parts of the cloud to detect what it's made of.

HillOBeans 11y ago

For those who are interested, physicist John Hartnett has developed a model that does not require dark matter. His work builds on that of Moshe Carmeli, who published "Cosmological Special Relativity". Hartnett's book is "Starlight, Time, and the New Physics" ISBN 978-0-949906-68-7. Disclaimer: I am not a physicist, and the math is way over my head, so I cannot double-check it. Hartnett has not made much, if any, headway with mainstream scientific publications, probably because he is a Biblical Creationist.

gnufied 11y ago
Just read one of his articles from his Website. He mixes physics and mythology with impunity. No wonder, his theories are not taken seriously.
- cristianpascu 11y ago
  So, say, if someone comes to you with a clean demonstration of how and why something is happening in the world, people verify it and it proves correct, and (s)he says the idea was revealed while smoking pot in a mystical hotel in north canada, or france for that matter, you'd say no one should take the theory seriously? Good job!
  - dalke 11y ago
    I believe that gnufied is saying that this isn't a clean demonstration. If one paragraph of explanation is buried in 1,000 pages of dreck, then is the onus on the reader to find the nugget, or the author to emphasize the important part? If you've ever hung around a physics or astrophysics department you'll find that a lot of people send in explanations of how modern science is wrong. For example, http://www.universetoday.com/108044/why-einstein-will-never-be-wrong/ http://www.universetoday.com/108044/why-einstein-will-never-... comments: > One of the benefits of being an astrophysicist is your weekly email from someone who claims to have “proven Einstein wrong”. These either contain no mathematical equations and use phrases such as “it is obvious that..”, or they are page after page of complex equations with dozens of scientific terms used in non-traditional ways. They all get deleted pretty quickly, not because astrophysicists are too indoctrinated in established theories, but because none of them acknowledge how theories get replaced.

raverbashing 11y ago

There might not be dark matter, but we need a better explanation than MOND

cletus 11y ago

I'm no physicist but I've asked myself this question. It's a bit like string theory. String theory is a mathematical answer that solves some (all?) of the inconsistencies between quantum theory and gravity but has some implications that have no experimental evidence (eg extra dimensions). Dark matter always struck me as a kludge to explain the universe fit our model. There are many theories on it but no observed or experimental effects of dark matter to date. We say that there are four fundamental forces in the universe: weak nuclear, strong nuclear, electromagnetism and gravity. The first three are pretty adequately explained by quantum mechanics (AFAICT). The last of course isn't but is described pretty darn well by relativity. Thing is, what's always struck me as odd is the other forces, I believe, can both attract and repel. There is no observation or experimental evidence of "antigravity". It has always made me wonder if we're not making an error by trying to fit gravity into the Standard Model. Perhaps it's not a force like the others are and simply the result of the nature of space-time. Anyway, like I said: complete layman here. What I'm saying might be completely nonsensical to anyone with half a clue about physics. I know the LHC has looked and is looking for any evidence at the edges of the Standard Model of some violation that will hint at something that might explain all this. I also know minds far brighter than mine have spent a lot of time thinking about this. I'm still left wondering if dark matter/energy isn't simply another "string theory".

deciplex 11y ago
> There are many theories on it but no observed or experimental effects of dark matter to date. FTFA: > And most spectacularly, you get an entirely new prediction: that when you get two clusters of galaxies colliding, the gas inside should heat up, slow down and emit X-rays (in pink, above), while the mass that we can see through gravitational lensing (in blue, above) should follow the dark matter, and be displaced from the X-rays. This new prediction has been borne out observationally and held up over the past decade, a spectacular indirect confirmation of dark matter.
tjradcliffe 11y ago
Dark matter is no more a kludge than phlogiston, or the lumineferous aether, or neutrinos. All of them were introduced as novel entities to explain experimental phenomena. The first two turn out not to exist, the latter does: http://www.tjradcliffe.com/?p=1801 http://www.tjradcliffe.com/?p=1801 Calling them kludges is to mistake the basic process of science for a hack. There are any number of confirmatory observations that fit the dark matter model, just as there were any number of confirmatory observations that fit the neutrio model. It's just that we haven't observed any dark matter particle interactions directly, just as we hadn't observed any neutrino interactions directly before Reines' experiment. It may be that dark matter turns out not to exist, and then we will know it was wrong. Until then it is perfectly ordinary science working in perfectly ordinary ways as it has been for over a century.

cristianpascu 11y ago

I graduated physics, but I'm almost a layman when it comes to general relativity. Still, I wonder if another possible explanation for stuff that don't match theory could be the basic assumption about our current cosmology. That the space is flat where there's no matter. Since there's a relation between the geometry of the space and the matter within, would it be unreasonable to believe that space itself could be curved independently of the matter we can observed? Maybe for other reasons, yet unknown?

InclinedPlane 11y ago

Sigh. Sure, it's possible, but very unlikely. These "MOND" gravity theories purport to explain observations better than the theory of dark matter, but they don't. They explain some things and leave gaping holes elsewhere. On the whole they are hugely inferior theories in terms of matching observational evidence. Their only advantage is that they lack the existence of massive, weakly interacting particles, which a lot of people seem to have strong objections to despite the fact that several types of such particles are already known to exist. Throughout the entire history of the development of the theory of dark matter the bias has always been against the idea of true dark matter, unseen particles that make up most of the mass of the Universe. But at every single step all of the other possibilities have been eliminated as realistic explanations of the evidence. The cold WIMP dark matter theory is the only one that explains the structure of the cosmic microwave background radiation, the large scale structure of the Universe, and the structure and behavior of galaxies and galaxy clusters. At this point the theory of dark matter is remarkably well hemmed in, it would be absolutely shocking to an extreme degree if it did not truly exist in the form we think it does. There's additionally a very elegant mechanism behind the formation of dark matter. It seems most likely to be composed of super-symmetric particles. Such particles would only be able to form in extreme, high-energy conditions. Precisely the sort of conditions that existed in the early era of the Universe immediately after the Big Bang. So the early Universe would have been creating huge quantities of such particles, which would then not interact much due to their weak interactivity. It wouldn't be until the Universe had expanded enough and cooled down enough to halt their production. This would neatly explain why so much of the mass of the Universe is in the form of dark matter rather than conventional matter.

ajkjk 11y ago
Did you read the article? It agrees with you.
dkbrk 11y ago
> These "MOND" gravity theories purport to explain observations better than the theory of dark matter, but they don't. MOND consistently fits the rotational velocity profile of galaxies better than dark matter. This isn't too surprising as MOND originated as an ad-hoc formula derived from observations of said rotational profiles, however MOND works very well over a very wide range of galactic profiles. The mass deficit observed in tidal dwarf galaxies is also quite strong evidence against just dark matter. I don't think anybody is seriously claiming that MOND is a complete theory, though of course there have been attempts by theorists at creating complete models, but they've failed to explain large-scale structural observation and the cosmic microwave background. This just means these attempts at creating a complete theory are probably wrong, not that there isn't something funky going on with galaxies that isn't completely accounted for by dark matter. > They explain some things and leave gaping holes elsewhere. This is a false dichotomy. MOND is not incompatible with dark matter. This "us vs them" mentality is really quite harmful. A combination of MOND and dark matter matches most observations very well, far better than dark matter in isolation. > Their only advantage is that they lack the existence of massive, weakly interacting particles, which a lot of people seem to have strong objections to despite the fact that several types of such particles are already known to exist. While I'm sure there are quite a few people for whom this is the case, you shouldn't dismiss the possiblity there are people who take MOND seriously because it legitimately fits the data better in some circumstances.

AdieuToLogic 11y ago

> Could dark matter not exist? Sure.

AdieuToLogic 11y ago
I guess I need to elaborate on this answer. Perhaps our observations are a result of existing within two gravitational space-time distortions, one trivial and one not. The trivial one being the Sun and the non-trivial being the galaxy which we inhabit. If curvature of space-time theorized by General Relativity is accepted, then observing non-local energy will be affected by gravity in which the observation is being undertaken. Accounting for the Sun's influence has largely (if not completely) been addressed, but there lies a more difficult "elephant in the room" problem of determining what effect the gravitational curvature of the Milky Way has on any observations we can make. According to the University of Oregon[1], the observable mass of the Milky Way is 200,000,000,000 Solar masses. The same material indicates that visible stars account for 30% of that. Throw in a bit for singularities and lets call it "less than 50%" for the sake of discussion. In any event, there exists enough mass in this galaxy to plausibly state that the space-time we inhabit is affected. Yet a non-trivial amount considered "unaccounted for." Using the canonical 3d inverse-cone visualization of matter's effect on space-time, imagine our solar system exists on some point within the galaxy's gravitational cone yet not near its center. Making intra-galactic calculations may be influenced by compressed space-time instead of the presence of dark matter. And observations regarding other galaxies colliding (as mentioned in the article) migth be explained by gravitational phase shifting. Though all of this likely will be rebuked, it is why I originally said "sure." 1 - http://hendrix2.uoregon.edu/~imamura/123cs/lecture-2/mass.html http://hendrix2.uoregon.edu/~imamura/123cs/lecture-2/mass.ht...

ianamartin 11y ago

Of course dark matter doesn't exist. Hello, people. Dark matter is the eflourescent ether theory of the 21st century. There are things that we don't know how to explain right now. We have some ideas about how they can be explained. But they are really really bad. We will be laughing at dark matter theory in a few years.

Sharlin 11y ago
You might do well to familiarize yourself with the Dunning-Kruger effect.
PhantomGremlin 11y ago
Dark matter is the eflourescent ether theory of the 21st century. The quip I'm fond of is: Dark Matter is the Phlogiston of Contemporary Cosmology But, right now, dark matter is the best explanation we have of what we've observed.
socceroos 11y ago
That's my prediction as well, but I wouldn't have put it so....abrasively.

dschiptsov 11y ago

Most of concepts we are conditioned to take for granted does not exist outside our head.) The essence of scientific method is not in piling up concepts or in building up a support for a fancy theory. On the contrary, it is in exactly opposite - it is to refute and remove everything "mental" to see what remains, something which cannot be shaken by mere speculations or dismissed by any experience. That, perhaps, has something to do with what we call Truth. According to the ancients, who practiced this method, there is nothing but different forms of light. The question "what is between two Photons" makes no sense, because two Photons have nothing in common exept an imagination of an observer. Tracing them back "in time" makes no sense either, because time as a category is irrelevant to the light. It doesn't change.

madaxe_again 11y ago

Almost certainly not. Do epicycles exist? No. They were a handy tool/kludge. Our understanding of space-time is incomplete.

0xe2-0x9a-0x9b 11y ago

You can distribute dark matter in space to shape it in any pattern you like and give the dark matter any kind of property just to create a mathematical model that is consistent with observations. Dark matter is just a theoretical concept - for now or forever.

restalis 11y ago

"your theory has three burdens to meet:" ... "it must make new predictions that can be experimentally or observationally tested, and confirmed or refuted, that are unique to this new theory" ("MOND fails spectacularly, either offering no predictions...") I fail to understand the necessity for new predictions. This simply may or may not come out of new theories as a paradigm shift consequence and it is therefore just optional, not a must. In fact, I fail to fully understand even the first requirement (about reproducing all the successes of previous leading theory) - the current leading theory's explanation may happen to explain things somehow, but that may not be necessarily correct. I wouldn't dismiss a competing theory even with holes in it if there is a slightest chance that further work on it or on something closely related to it may come to cover those shortcomings in time.

drpre 11y ago
Disclaimer: far from a physicist. I think the point is that, for a new theory to become more favored than the current leading theory, the new theory must be consistent with at least as much scientific evidence as the leading theory. From there, the value of predictions is that they give a path for strengthening the theory further. I think you're right in saying that these are not hard-and-fast rules.

mpc755 11y ago

The notions of dark matter and the dark matter particle are incorrect. The mass which fills 'empty' space is beginning to be referred to as the 'dark mass' in order to distinguish it from the baggage associated with dark matter. 'Dark Energy/Dark Mass: The Slient Truth' https://tienzengong.wordpress.com/2015/04/22/dark-energydark-mass-the-silent-truth/ https://tienzengong.wordpress.com/2015/04/22/dark-energydark... "That is, all that we are certain about [is] the dark mass, not dark matter, let alone to say about the dark 'particle'." Particles of matter move through and displace the dark mass, including 'particles' as large as galaxies and galaxy clusters. The Milky Way moves through and displaces the dark mass. The Milky Way's halo is the state of displacement of the dark mass. The Milky Way moves through and curves spacetime. The Milky Way's halo is curved spacetime. The state of displacement of the dark mass is curved spacetime.