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Space Science

Simulation Predicts Clumps of Dark Matter Within Galaxies 131

Posted by Soulskill
from the kind-of-like-normal-matter dept.
A team of researchers has simulated the gravitational interaction of dark matter particles over the course of a hypothetical 13.7 billion years. They found that the particles tended to form clumps large enough to assist in the formation of galaxies. The results contradicted observations from previous, smaller studies, but they lent support to an unrelated simulation of how the Milky Way formed. UCSC's press release is also available. Quoting ScienceNews: "The clumps of dark matter in the simulation have densities that are remarkably similar to densities that a University of California, Irvine research group found when simulating the formation of the Milky Way and its satellite dwarf galaxies, says James Bullock, the astrophysicist who leads the UC-Irvine group and was not involved in the new study. 'This is a remarkable success of the particular model simulated and adds strong support to the idea that the dark matter is made up of particles that are "cold." There are a number of planned experiments aimed at detecting the dark matter that are betting on it being cold, so this is generally good news for the community,' Bullock says. And, [study co-author Piero Madau] notes, larger simulations that might help constrain the nature of dark matter even more are already in the works."
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Simulation Predicts Clumps of Dark Matter Within Galaxies

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  • by Anonymous Coward

    Clumps of dark matter were predicted around Uranus.

  • Well... colder then light matter particles?
    • by BrentH (1154987) on Saturday August 09, 2008 @06:45AM (#24536403)
      Not necesarily (and this 'Cold' refers to something like mean velocity of the particles, not temperature), but current astrophysicists think that Dark Matter is predominantly cold. Otherwise it couldn't really clump together (it would 'boil' away so to speak) and we would be able to explain why we appear to detects clumps of unseen mattert (like in the Bullet cluster).
  • by Nazlfrag (1035012) on Saturday August 09, 2008 @01:54AM (#24535587) Journal

    I doubt this simulation did more than let them see what they wanted to see. "The researchers note that the simulation does not model any forms of normal matter such as stars or planets." Hardly a complete picture they drew.

    Why the obsession dark matter? Say with MOND, why are we so scared to think that perhaps Newtonian mechanics aren't quite enough to calculate with on galactic scales? Why do they think MOND is for cranks and crackpots? What of a static non-expanding universe and alternate redshift paradigms? Are they not just as feasible as exotic matter that only interacts gravitationally?

    That's a lot of questions, so I'll break it down to one. I'm just curious as to why dark matter is so widely supported, is it merely because breaking the standard model makes physicists too uncomfortable?

    • by Anpheus (908711) on Saturday August 09, 2008 @02:27AM (#24535659)

      I Am Not A Physicist, but the problem with MOND is that, well, it explains only one problem of gravity or cosmology, rather: galactic rotation. It fails to explain how spectacularly successful tests of general relativity have been. For example, where does MOND predict frame-dragging? Answer: it doesn't.

      MOND is what you get when you have a problem posed to amateur mathematicians and physicists, and they answer that problem (galactic rotation) with the simplest solution (let's just tweak this equation) without considering the fact that their modified theory is inconsistent with well-established theories that currently exist. MOND does not predict certain things that we see in nature, but this isn't seen by proponents. All the proponents see is, hey, it solves this problem. Well, yes, but it causes a whole lot more that you neglect to mention. Chiefly among those is, pretty much every quirk of relativity.

      • by anandsr (148302)

        Since MOND does revert to GR in high Gravity situations so it will support frame dragging. Anyway we have not much observations in the low gravity situations. The only problem with MOND is that it is not a proper theory. There is now a theory that models MOND called TeVeS which does support Frame Dragging, etc. The theory has not yet been studied to the extent that the really big questions like inflation, nucleosynthesis, WMAP, etc can be worked out.

        But one thing is for sure that TeVeS cannot be ultimately

        • Re: (Score:3, Informative)

          by Ambitwistor (1041236)

          Since MOND does revert to GR in high Gravity situations so it will support frame dragging.

          Don't confuse MOND and TeVeS. MOND is MOdified Newtonian Dynamics. It doesn't revert to GR or any relativistic theory in high gravity situations; in fact, it grows more different from those theories in strong gravity. TeVeS is a relativistic theory which has MOND as a particular limit (and Newtonian dynamics as another). It probably approaches GR in some other limit (decoupling of the scalar and vector fields?), but whether it agrees with all observations in strong gravity situations is, as you say, unk

    • Re: (Score:3, Insightful)

      by timmarhy (659436)
      because MOND hasn't been verfied by any pyshical tests. it's MOND that lacks evidence not dark matter. all dark matter is, is visible gravitational effects of matter we can't see just yet. it IS crazy to go modifying a verified theory of newton's laws to fit our results without being able to explain why.
      • by Nazlfrag (1035012)

        Why crazy to modify the laws if the empirical evidence deviates? I'd say that's a damn good reason to modify the laws.

    • Re: (Score:2, Informative)

      by Anonymous Coward

      First I want to clarify what dark matter is. It is just matter that cannot be seen directly, because it does not emmit light or radiation. But it can be observed by the gravitational effects it has on objects that can be seen. To an alien Saturn would be dark matter. Earth would be dark matter.

      So we have two options:
      1. We assume that our planets are the only ones in the universe, every other matter is light up and we can observe it by its radiations. Then we have to conclude that there is a fundamental erro

      • by Nazlfrag (1035012)

        Neither. As I asked initially, why the faith in dark matter? If there is only gravitational influence, where's the lensing?

        • by wanerious (712877)
          In case you don't get my response above, google for Bullet Cluster. There you'll see the lensing.
          • by Nazlfrag (1035012)

            Why do you attribute that to dark matter? It is an anomaly in Einsteins field equations sure, but evidence of unseen matter I doubt.

            • by wanerious (712877) on Saturday August 09, 2008 @10:27AM (#24537431) Homepage
              What?? Where in the field equations is there an anomaly? If it *were* some anomaly in the field equations, we'd see really bizarre effects everywhere else there are strong gravitational fields. We don't.

              The point is that it's not a strange theoretical solution, but a real, physical deflection of light by a gravitating mass. It is certainly evidence of unseen matter --- were there a cloud of unseen matter, this is exactly the effect it would have on passing light. To attribute it instead to a non-specific flaw in a theory we know *very* well is far more speculative than what you criticize others for.

    • by Hektor_Troy (262592) on Saturday August 09, 2008 @03:28AM (#24535829)

      Say with MOND, why are we so scared to think that perhaps Newtonian mechanics aren't quite enough to calculate with on galactic scales?

      It's not about being scared - it's about the scope of that theory. Using "stuff falls down" as a theory of gravity works, but only in very specific situations. It's not something you can use as a usable replacement for any of the accepted theories, like GR and Newton.

      Talking about scientists being scared of MOND is silly. Especially when you bring in Newtonian mechanics, which have long since been proven to fail in a large number of ways. The reason we still use Newtonian mechanics is that it's "good enough" for most things. Just like "stuff falls down" works great here on Earth, but not so well inside the ISS.

      • by Nazlfrag (1035012)

        I guess I should have used 'sacred' instead of 'scared'. It is good enough for things whithin a lightyear or less, but why should what we know about the small scale apply equally to the large scale? It doesn't work the other way round, perhaps there's an AU level quanta effect prevailing, perhaps many things.

        The blind dedication to the dark matter cause seems superfluous to the realisation that our local models of physics don't scale galacticaly.

        • If you read up on dark matter, you'd realise that it's merely a placeholder. We don't know WHAT it is, we just know it's there.

        • by Ambitwistor (1041236) on Saturday August 09, 2008 @11:57AM (#24537957)

          The blind dedication to the dark matter cause seems superfluous to the realisation that our local models of physics don't scale galacticaly.

          There is no "blind dedication to dark matter". And in fact, not scaling properly is exactly what's wrong with MOND. If you apply it to galaxies, it doesn't work for cosmology, and so on.

    • "I doubt this simulation did more than let them see what they wanted to see..[snip]..Why do they think MOND is for cranks and crackpots?"

      The first bit is wrong, to understand why it is wrong you need to answer the second bit yourself.
      • by Nazlfrag (1035012)

        Explain to me then how the experiment let them see more than which they analysed.

        The first experiment was wrong because they never even calculated the known variables, they just coaxed the unknowns into a verifiable pattern. Little science happened here, and a shitload of speculation took its place.

        Please give me your genuine answer for the second question, have you even considered MOND for yourself as an alternative, or are you just repeating that which has been foisted upon you?

        • You missed my point. The first thing your post did was disparage others for "seeing what they wanted to see". You then went on to tell us how you can see MOND making sense despite the fact that scientist can't get it to work.
    • by mazarin5 (309432) on Saturday August 09, 2008 @07:44AM (#24536623) Journal

      Say with MOND, why are we so scared to think that perhaps Newtonian mechanics aren't quite enough to calculate with on galactic scales?

      Nobody uses MOND for the same reason we don't use epicycles anymore: it's an unnecessary adjustment to an outdated system. Newton is a good approximation for low-speed and low-mass systems, but hasn't been considered perfect during the lifetime of anybody here.

      What of a static non-expanding universe and alternate redshift paradigms?

      Because it doesn't meet the observations. If you have to throw out everything else that does meet the observations to force fit your pet theory, then you're doing science incorrectly. Also, alternate redshift paradigms? Redshift is a very, very basic thing; it would take a lot of phenomenal evidence to change anything related to it.

      I'm just curious as to why dark matter is so widely supported,

      Dark matter is supported because it seems likely, fits the data, and doesn't contradict other observations. All it means is that we think there's some more mass out there, and we haven't seen it yet.

      is it merely because breaking the standard model makes physicists too uncomfortable?

      I get the willies just thinking about it! Or not.

      • Re: (Score:3, Informative)

        by Nazlfrag (1035012)

        Our models need to account for 90% more mass than empirical evidence proves exists. This only applies when considering galactic scales. Either our models are wrong, or there is a large mass of hidden matter that violates all the known properties of matter except one.

        I believe our models are wrong, and this study is flawed. Don't get the willies, just try to broaden your perspective.

        • by wanerious (712877)
          Why do you suppose DM violates all known properties of matter (save one)?
          • by Nazlfrag (1035012)

            It only interacts gravitationally right? Otherwise why is is dark?

            • by wanerious (712877)
              and perhaps weakly. Why is that of concern? It would be composed of neutral particles of small cross-section.
            • Dark matter is matter that doesn't interact electromagnetically (or does so very weakly). It can interact by any other interaction other than electromagnetism, including but not limited to gravity.

        • by mazarin5 (309432)

          Our models need to account for 90% more mass than empirical evidence proves exists.

          It's not necessarily as high as 90%, but that's one of the more extreme estimates in one of the models. Also, you have to understand that this is what the empirical evidence suggests exists.

          This only applies when considering galactic scales.

          Not especially true; dark matter, in many of its postulated forms, would be around us locally, but in concentrations (or distributions) that are inconsequential on the local scale. That is, its effect would be below our margin of error.

          Either our models are wrong, or there is a large mass of hidden matter that violates all the known properties of matter except one.

          Or there's something entirely at work that hasn't been considered yet. Dark matter is

          • Re: (Score:3, Informative)

            by Ambitwistor (1041236)

            We actually have a better chance of detecting the exotic particles than the rogue planets, so some people are focusing on that

            It's the other way around. Dark matter in the form of brown dwarves and such has actually been detected through gravitational microlensing observations. That's how we know that most of the dark matter isn't brown dwarves and other compact astrophysical bodies; it's there, but there isn't enough of it to explain the necessary gravitational effects.

    • by Goaway (82658) on Saturday August 09, 2008 @08:57AM (#24536985) Homepage

      Why the obsession dark matter?

      How about because MOND completely and utterly fails to describe the Bullet cluster [wikipedia.org]?

    • I think gravity is safe. Speaking as a layman, do we really know THAT much about the emissivity of the ordinary matter around us-- on galactic scales? I cannot help but think our theories of the emissivity of objects is not so robust that we have to come up with a new class of matter when this decade's calculations of gravity vs. emission don't add up. Seems like the simpler solution is to refit the emission theories. Q: And aren't there a whole bunch of reasons why emitted photons won't reach terrestri
    • by vertinox (846076)

      What of a static non-expanding universe and alternate redshift paradigms?

      A personal theory of mine is that redshift is affected by gravity and lack thereof.

      Gravity's effect is more apparent the close you are to a body. The closer you are to the earth the more you are affected by earth's gravity and the closer you are to the moon the more you are moon's gravity and so on.

      Hence, seeing light is affected by gravity, there might be something going off with the hand off between galaxies and other galaxies around

      • That's not a personal theory, that's a real theory: redshift is affected by gravity. (Google "gravitational redshift".) The explanation of cosmological redshift can be interpreted that way (expanding universe implies curved spacetime which implies gravitational redshift). But you can't explain cosmological redshift using a non-expanding flat universe by appealing to galaxies' gravity alone. It doesn't explain the distance-redshift relation, the luminosity-redshift relation, it would show a strong corre

    • by wanerious (712877) on Saturday August 09, 2008 @09:52AM (#24537257) Homepage
      I don't think "uncomfortable" is the right word. Certainly there is a huge upside to overturning the standard way of thinking, but also a huge risk in supporting ideas that seem untenable.

      Dark matter is inferred from a number of observations and calculations, including excess rotation speed of stars around galactic centers, excess speed of members of clusters of galaxies, and lensing of background galaxies not associated with luminous matter. While one may fiddle with MOND to possibly fit the first two phenomena (for a specific case, moreover --- one adjustment to Newton's laws had better account for *all* rotation curves), the last group of observations really seem to argue strongly against any reasonable form of MOND.

      If you google the Bullet Cluster image and description, you'll note that the blue region (most lensing of background) is tracing the highest density of matter, where the pink traces the density of luminous (here, X-ray cluster gas) matter. It is clear that there is a huge component of matter not identified with luminous matter. To account for this with MOND, it is not enough to increase the *strength* of the gravitational field, but also now the *direction*, since we observe the lensing in a direction roughly perpendicular to the axis of the cluster. Writing down such a gravitational law to account for this case would make any astrophysicist uncomfortable indeed.

      Now, especially since we can work backwards and calculate the distribution of dark matter needed to cause each observation, dark matter seems to be the *much* simpler explanation. Besides, we already have examples of matter that interact only gravitationally (and possibly weakly) --- neutrinos. As hard as it is to detect them, there may well be others we don't know about yet.

    • by pipingguy (566974) *
      On the other hand climate computer models that predict catastrophe are usually pretty reliable.

      Oh wait, we're not supposed to talk about that anymore.
    • by Ambitwistor (1041236) on Saturday August 09, 2008 @11:51AM (#24537915)

      Say with MOND, why are we so scared to think that perhaps Newtonian mechanics aren't quite enough to calculate with on galactic scales? Why do they think MOND is for cranks and crackpots?

      Who's this "they"? There is a really unpleasant meme running around Slashdot that reactionary scientists scorn and mock anything that isn't mainstream. In reality, MOND is not a mainstream theory (and for good reason), but it's still discussed seriously. Google around for Sean Carroll's presentation a year or two ago on MOND vs. dark matter (can't remember when that was when he was at U. Chicago or Caltech). This [cosmicvariance.com] is a good summary of his for why dark matter is likely to exist.

      What of a static non-expanding universe and alternate redshift paradigms? Are they not just as feasible as exotic matter that only interacts gravitationally?

      No, not even remotely. They are vastly less plausible than even MOND, which has problems of its own. But since this is about dark matter and its competitors, I'll stick to those.

      I'm just curious as to why dark matter is so widely supported, is it merely because breaking the standard model makes physicists too uncomfortable?

      Yeah, it's because theoretical physicists hate new theories. No theoretical physicist ever got fame and tenure by coming up with a new theory. They gotta stick to the old ones to survive.

      Seriously, tone down the paranoia. Dark matter also breaks the Standard Model by introducing new kinds of particles. (Well, unless you think it's axions, which are arguably part of the Standard Model). It's not like nobody has ever thought of an alternative gravity theory before. You can carpet a small moon with all the alternative gravity theories out there; scalar-tensor gravity, vector-tensor gravity, conformal gravity, chiral gravity, supergravity, and so on.

      The simple facts are that it's really hard to muck around with gravity in a way that simultaneously agrees with observations on tabletop, stellar, planetary system, galactic, and cosmological scales. With MOND it's easy to reproduce galactic rotation curves, but not much else. MOND also contradicts relativity; it's strictly Newtonian. There has been an attempt to correct that in the form of TeVeS (tensor-vector-scalar gravity). But TeVeS requires you to introduce two new gravitational fields, plus couple them together in just the right way, and even then it's far from certain whether it can explain dark matter evidence on all different scales (galaxies, clusters, cosmology, etc.). Furthermore MOND has difficulty explaining rather direct evidence of dark matter like the Bullet Cluster. Even if MOND is correct, it seems likely that you still need dark matter to explain everything.

      After all that, MOND looks far more ad hoc than just postulating the existence of a new kind of particle, especially since most of the new particle theories out there predict some kind of dark-matter like particle anyway for completely independent reasons. It's not like weakly interacting particles are terribly bizarre in the first place; neutrinos are dark matter, although they're too light to be most of the dark matter. The main difference between most of the dark matter and neutrinos is mass, and what's so odd something weak like a neutrino, only heavier? Such a particle, predicted by many theories, can (unlike MOND) simultaneously explain all the astrophysical phenomena which point towards dark matter.

      • by anandsr (148302)

        Well Bullet Cluster or any other cluster is a problem for MOND. But the Bullet Cluster is also a problem for Dark Matter. The velocity of the Cluster is much faster than GR can provide, which MOND can easily handle.

        I actually liken MOND to Keplers laws. It shows how the matter moves. If GR cannot reproduce it, then there is a need for a new theory. TeVeS is a patch which will not survive for very long.

        The other problem is that GR and QM don't work well. Possibly when we a proper Quantum Gravity theory then

        • Re: (Score:3, Insightful)

          by Ambitwistor (1041236)

          Well Bullet Cluster or any other cluster is a problem for MOND. But the Bullet Cluster is also a problem for Dark Matter. The velocity of the Cluster is much faster than GR can provide, which MOND can easily handle.

          (GR doesn't have anything to do with it per se; Newtonian gravity predicts the same thing as GR on galactic scales.)

          The Bullet Cluster is a much more severe problem for MOND than dark matter; you can't even qualitatively explain the divergence between the galaxy and the lensing with MOND. The Brownstein and Moffat paper you're alluding do doesn't even attempt to address that elephant in the room, which is the problem with MOND and the Bullet Cluster by far. I've also read comments on Cosmic Variance that

    • by Abcd1234 (188840)

      Say with MOND, why are we so scared to think that perhaps Newtonian mechanics aren't quite enough to calculate with on galactic scales?

      Because results like the Bullet Cluster have left even MOND theorists admitting that there must be at least some dark matter out there in order to explain the observations? Seriously, the least you can do is keep up with the latest science on the topic.

  • I've always wanted a pet Nibblonian...
  • by Abeydoun (1096003) on Saturday August 09, 2008 @02:01AM (#24535611)
    I've been curious... if there was an incredibly advanced civilization that was capable of building near perfect dyson spheres [wikipedia.org] around large expanses of space absorbing essentially all the radiation of the stars within it, wouldn't that look like "dark matter"?
    • by Anpheus (908711) on Saturday August 09, 2008 @02:35AM (#24535671)

      That is a "MACHO," which we have looked for and not seen enough of. MACHOs are unique in that they affect the light behind them (they are opaque and gravitationally lensing) and so while they could account for a lot of matter, we aren't seeing enough lensing and enough holes in the spectrum from "dark stars", areas where the sky is darker from an object blocking light behind it.

      And back of the envelope calculations say a dyson sphere wouldn't be anywhere near a black hole's mass, which is what we really would need to find quite a few of in order to find the missing mass.

      And this ignores any technical difficulties with actually constructing a dyson sphere.

      • Cosmic Smog? (Score:2, Interesting)

        by Tablizer (95088)

        It would certainly be interesting if dark matter turned out to be some kind of pollution from advanced civilizations.
             

      • Actually, a Dyson Sphere would have the same mass as a black hole around an equivalent star, as it encloses the star. Black hole mass = mass of solar system. Sphere mass = Mass of sun + mass of sphere = Mass of solar system.
        • by Anpheus (908711)

          I wasn't being particular enough, but there's a lack of "intermediate" size black holes from what we can see. We only find really stinking huge ones and then smaller ones, but still many times the mass of our solar sun.

          But what we need to find are -ridiculous- numbers of these smaller black holes, or still a ridiculous number of intermediate or supermassive black holes. We don't though. They apparently aren't there.

          And for the Sun to be a black hole, it would have to become a lot more massive. There's no wa

    • by Jugalator (259273)

      Not really, dark matter isn't black matter hiding light. It's only called "dark" in a metaphorical sense.

      Signs of it has been seen as being completely transparent and the only real visible sign of it being there thanks to it bending light due to gravitational lensing.

    • by dissy (172727)

      I've been curious... if there was an incredibly advanced civilization that was capable of building near perfect dyson spheres around large expanses of space absorbing essentially all the radiation of the stars within it, wouldn't that look like "dark matter"?

      Or perhaps even that incredibly advanced civilization consists of one or more Matrioshka Brains [aeiveos.com] which are living thinking entities with very similar characteristics as Dyson spheres have, as well as answer a number of unanswered questions about cosmology (assuming they exist, which statistics say not only should exist -somewhere- in the universe, but are actually likely, and perhaps even inevitable.
      Ok, that last one was my own wish more than anything else, perhaps the hopeless romantic in me, perhaps some s

    • I've been curious... if there was an incredibly advanced civilization that was capable of building near perfect dyson spheres [wikipedia.org] around large expanses of space absorbing essentially all the radiation of the stars within it, wouldn't that look like "dark matter"?

      Nice, that's one of the more creative ideas I've heard in a while.

      However, if the sphere absorbs the radiation of the stars inside of it, then the sphere will itself become heated and radiate back the energy it absorbs. It has been a while since I've taken thermal physics, but I'm fairly confident that an object that absorbs that much energy would be quite radiant, itself -- just in different wavelengths.

  • Kahn was right! (Score:3, Informative)

    by richie_the_toolman (1153737) on Saturday August 09, 2008 @02:05AM (#24535619)
    It is very cold in space!
  • ha (Score:2, Insightful)

    More cruft to add to the bogus hypothesis that is dark matter.

    I am a physicist.

    • I'm not a physicist and I'm not terribly well-informed on the whole dark matter thing. Are there any other hypotheses out there to do the same explanatory work as dark matter that's also less bogus?
    • Re: (Score:3, Informative)

      by BrentH (1154987)
      As a scientist you should know that there only are hypotheses. All you can do is find evidence or create tests that agree of disagree with a hyptothesis. As a bachelor student in a world renowned astrophysical institution, I started out as a sceptic (and still am). There are two branches of physics that sort of require the existence of dark matter. One is the theoretical side of astrophysics: the universe appears to require extra matter (and energy, which may well be vacuumenergy from particle physics) to h
    • by khallow (566160)
      Do you have anything to say about the nonbogus dark matter hypotheses too?
    • by Abcd1234 (188840)

      Well, either you're lying, or you're poorly educated on the topic. The Bullet Cluster [wikipedia.org] results have all but demonstrated the existence of dark matter.

    • I'm a physicist too. Please stop embarrassing us. Your personal dislike for the theory is sadly irrelevant to the evidence in its favor.

  • One such clump was detected in the headquarters of the SCO corporation.

  • by YttriumOxide (837412) <yttriumox&gmail,com> on Saturday August 09, 2008 @04:14AM (#24535923) Homepage Journal

    For some time, I've been making random notes from articles relating to dark matter, string theory and quantum entanglement. I've been trying to form a hypothesis of dark matter with information from all of these three.

    Interestingly, this article has now given a lot more focus to one part of the idea that was forming that was a bit "wishy-washy" before (okay, it's still very wishy-washy, but less so now).

    The overall concept is basically along the lines of quantum entanglement being a property of the fact that two entangled particles are in fact just ONE string that's being bent through space in some rather unconventional ways (extra dimensions neither being "large and flat" nor "very very small and coiled", but rather "hideously complex monstrous things").
    This, combined with gravity ("graviton"strings) being freely able to travel through those dimensions rather than tied to an endpoint (hence appearing much weaker than the other forces, even though ALL forces have absolutely identical strength (another wild-ass guess, just because it would be "nice")) would lead us to an elegant idea about dark matter actually being gravity from perfectly normal matter that happens to be showing up in unexpected places.

    The fact that there are clumps of it definitely does not blow my ideas out of the water, but it does mean I need to re-work my idea of "hideously complex monstrous things" for the extra dimensions as I was assuming dark matter showed up "generally" in areas with other matter rather than specific clumps as "normal" does. It needs to be more structured than I had been thinking for a clump of matter in one place to form a "clump of dark matter" (e.g. the gravitational effect seen) elsewhere. That's actually a good thing though, because any structure lent to the process makes it closer to a testable hypothesis (anything completely unstructured could never become one, and having "no real clue" about the structure as I was, made it far too vague.)

    Note that this is still a very early infancy idea, and is somewhat around the "wild guess" point rather than even "hypothesis", so I'd be quite happy for people to comment on this - can anyone blow me completely out of the water on this line of thinking? Or can anyone offer ideas that support it? Or even just expand it a little? Does anyone know of any other research along these lines that I could read?

    • So, are you suggesting that dark matter gravity is actually gravity from matter in a parallel universe or from this universe folded in extra dimensions? Sounds fun, even if false.
      • Re: (Score:3, Insightful)

        by YttriumOxide (837412)

        My beginnings of a hypothesis are that it's gravity from THIS universe from folded dimensions. "Parallel Universe", while possible, seems to require too many further assumptions.

        Fun, yes. False, almost certainly, but not necessarily - that's the point of trying to formulate a hypothesis.

        • by Artifakt (700173)

          Are the extra dimensions actually limited to those of one of the current models (i.e. the most common 10 dimensional string theory model or one of its alternates?)
          (In other words, are you assuming the topology is the only thing that really matters, or just that you could find an interesting topology that shows some predictive power, and then refine both it and how many dimensions it applies to, and the tweaks needed would be easier to test and/or simpler and/or more beautiful than starting from the other en

          • Are the extra dimensions actually limited to those of one of the current models (i.e. the most common 10 dimensional string theory model or one of its alternates?)
            (In other words, are you assuming the topology is the only thing that really matters, or just that you could find an interesting topology that shows some predictive power, and then refine both it and how many dimensions it applies to, and the tweaks needed would be easier to test and/or simpler and/or more beautiful than starting from the other end?)

            Basically, I'm not YET making any assumptions about the topology, but it IS the most important factor in the idea itself. Once I think I have enough of an idea about what I need to be looking for, the first step will be to look at existing models (such as the more common string theory models) and see if they fit (or can be reasonably altered to fit without breaking other things), but if nothing does, I'll try to see if a topology could be described in any way that fits, whether it's a pre-existing idea or

    • The main problem with your theory is that entanglement just isn't that relevant on cosmological scales. On large scales, physics is pretty classical and entanglement irrelevant. That can change at small scales, so you might argue that it used to be relevant (near the Big Bang). But then temperature screws everything up: thermal excitation screws up the entanglement. Maybe it could have been relevant right at the Big Bang itself, due to poorly understood quantum gravity, but it has little to do with any

      • Re: (Score:3, Interesting)

        by YttriumOxide (837412)

        On large scales, physics is pretty classical

        Other than the large amount of seemingly "dark matter"...

        entanglement just isn't that relevant on cosmological scales

        Certainly true, but I wasn't really implying it needs to be. If we have a pair of entangled particles, they can THEN be separated by (apparently) quite any distance in classical space and nevertheless remain entangled. We haven't found a good way to use this as "faster than light communication", and there are very strong arguments that it can't be, however it seems to remain fact that these particles are somehow "connected" despite being physically

        • by Ambitwistor (1041236) on Saturday August 09, 2008 @11:31AM (#24537781)

          Other than the large amount of seemingly "dark matter"...

          There's nothing non-classical (i.e., quantum) about the behavior of dark matter. At least nothing we've observed so far. It's just matter, maybe like a neutrino but heavier. You don't need to appeal to quantum entanglement or anything exotic to explain it.

          If we have a pair of entangled particles, they can THEN be separated by (apparently) quite any distance in classical space and nevertheless remain entangled.

          In theory, yes. In practice, they need to be extremely isolated from everything else in the universe to remain entangled. That's why it's so difficult to maintain long-range entanglement for purposes like quantum encryption. You may think space is "empty", but it just takes a single photon to ruin the entanglement.

          This is why my hypothesis considers that they may actually not be physically separate at all - they are "right beside each other" through twisted "extra" dimensions, just in some way that we currently do not have the ability to measure or understand particularly well.

          Now you're mixing up two different ideas, quantum mechanics and extra dimensions. If they're interacting through other dimensions, fine, but you don't need entanglement to explain that either.

          This leads on to the idea of "dark matter" being gravity from "nearby" objects that are classically quite distant, but in reality quite "close".

          All the above problems notwithstanding, it's easy to come up with more. Even if you ignore the fact that these particles can't plausibly remain entangled, you have to explain how all these distant particles got entangled with each other in the first place. (If you're tempted to say "the Big Bang", you really can't ignore the previous fact given the extreme temperatures involved. Maintaining entanglement requires no outside interaction with other particles at any time over the intervening 14 billion years.) Furthermore, entangled particles interact with each other, but that interaction in general doesn't look anything like the vector or tensor field theories that give rise to what we think of as "forces" such as gravity or electromagnetism. (Why should this purported "entanglement force" act like gravity anyway?) And there's no explanation for the astrophysical observations like how entanglement with distant particles can simulate the effects of a spherical cloud of dark matter enclosing a disc galaxy.

          Basically, it seems like a very bizarre hypotheses that, all the physical evidence against it aside, doesn't even seem to have much to commend it over the alternatives. It's not like the idea of there being weakly interacting particles out there is so crazy; plenty of particle theories predict them for completely independent reasons including possibly the Standard Model, and there are other weakly interacting (though less massive) particles out there already, like neutrinos.

          • Hmmm... I think you're latching on to my mention of entanglement a bit much and that's causing a misunderstanding - looking back at my last posts, I can see how I gave that impression... sorry. I'm not saying that there's any relationship between entangled particles and my ideas about dark matter directly - I'm not positing an "entanglement force" of any kind. I was simply giving two somewhat separate ideas with a related core idea - that of the twisted dimensions allowing for distant objects to be in rea

            • I was simply giving two somewhat separate ideas with a related core idea - that of the twisted dimensions allowing for distant objects to be in reality "right beside each other"

              Okay, ignore for the moment quantum mechanics and just talk extra dimensions. It's still really hard to explain dark matter by appealing to distant normal matter being nearby in extra dimensions. Think about how these dimensions need to be connected. The standard scenario has them curled up small, which means that matter only interacts with itself through them, not with distant matter. Or you could postulate that they hook up to distant parts of the universe, but doesn't explain how galaxies consistentl

              • that doesn't explain a gravitational force that acts like dark matter does; it would probably be more like putting two galaxies on top of each other

                Yes, I've had to really think about this - it's simply "not enough" to postulate that all of the "leftover" gravity from one relatively large place is displaced somewhere else - that just wouldn't work - a galaxy that had an extra galaxy's worth of gravity (or MUCH MUCH more if it's all the "leftover" gravity from a gravity force that's as strong as the other forces) would simply collapse immediately and we'd very much notice it.

                Or you could also postulate that matter is connected up randomly with other matter, but with that it would hard to explain any consistent attractive effective force, let alone one that is attractive in the manner required.

                I don't see that's necessarily the case. Rather than saying "random", I prefer

                • Rather than saying "random", I prefer to say "not obvious" - that is, the "extra" gravity from Earth (just as an example) isn't necessarily projecting an Earth sized blob of gravity (or Earth * 10^36 sized blob) at one other point in space. More that much smaller parts of Earth are projecting much smaller blobs of gravity at various locations.

                  I don't see how you're going to get an effective central force out of that without a lot of fine tuning. And I don't know what mechanism is supposed to hook local portions of space up to distant locations in any manner other than random. At least in quantum cosmology you could imagine some kind of chaotic spacetime foam.

                  Who's to say we'd see "huge" apparent violations?

                  If dark matter is affecting galactic dynamics so strongly that we have to postulate that 90% of the matter out there is dark matter, I can't see how you're going to avoid strong violations

                  • I don't see how you're going to get an effective central force out of that without a lot of fine tuning. And I don't know what mechanism is supposed to hook local portions of space up to distant locations in any manner other than random. At least in quantum cosmology you could imagine some kind of chaotic spacetime foam.

                    "Chaotic" != "Random"... But if you prefer to call it random, then okay, let's work with that definition. The mechanism is the main thrust of my idea - "twisted" dimensions.

                    If dark matter is affecting galactic dynamics so strongly that we have to postulate that 90% of the matter out there is dark matter, I can't see how you're going to avoid strong violations.

                    Work with the word "random" - Quite "at random", our local area doesn't have any large clumps, and it's distributed so finely that we don't see it. This is also the case for most of the universe in general, so we're nowhere special in that regard. The areas that ARE special are those where it's "at random" clumping up the endpoints t

  • No one has much clue as the nature of dark matter in the way that we do about standard matter: What happens when it clumps together, does it get hot ? Does that heat help to counteract gravity ? Without knowing fundemental things like this - how is it possible to do detailed simulations ?
  • So now do we need to worry about dark matter colliding with Earth? Can't this stuff be detected by looking at areas where the cosmic background radiation is lower than usual? I suppose if it were moving it would have some sort of heat signature to it...

    • Dark matter probably collides with the Earth all the time and we don't notice since it interacts so weakly with us. It's the same with neutrinos. I don't know why dark matter would make the cosmic background cooler than usual, but people have looked for its imprint in the fluctuations found in the cosmic background (places where the fluctuations are denser than usual due to its clumping). That's one of the lines of evidence in its favor, actually.

  • I am not convinced that MOND or the related TeVeS are the proper approaches to take. The evidence seems to weigh more in the camp for dark matter, but there could be even more exotic explanations that could exlain the gravitational lensing such as what is seen in the Bullet Cluster. Perhaps space-time itself gets a bit "wrinkly" in some parts of space, or perhaps there's a parallel universe that only interacts with ours through gravitation. Of course, verification of this would be difficult at best, so ther
  • Research like this makes a number of assumptions about "Dark Matter," for instance that it exists at all (at least in the conventional sense), and I think the biggest assumption is that "Dark Matter" is actually some kind of particle. The fact of the matter is we know Jack and Shit about "Dark Matter," and Jack just left town. All we have seen is gravitational effects on observable materials in our universe with no obvious cause... to assume that there's some magical particle out there doing this is just
    • Research like this makes a number of assumptions about "Dark Matter," for instance that it exists at all

      Yeah, duh. That's how you do science. Propose a hypothesis, see what it predicts if you assume it's true, and see if that prediction holds in the real world.

      I think the biggest assumption is that "Dark Matter" is actually some kind of particle.

      How is that a big assumption? It explains the observations easily, most leading theories of particle physics predict such a particle for independent reasons, similar particles (though lighter) are known to exist already, and competing assumptions (brown dwarfs or other compact bodies, modified gravity, etc.) fail to explain the observations.

      • Well I assume the Flying Spaghetti Monster did it all then. That explains the observations easily. I guess it must be true!
        • You really have no clue how science works, do you?

          Dark matter is not some ad hoc "explanation". There are good reasons to believe it exists entirely independent of astrophysics, as I mentioned. Beyond that, it explains a number of very different astrophysical phenomena in a consistent way. Most other explanations fall short; they can explain one gravitational anomaly but are silent on or often inconsistent with others. Furthermore, dark matter is not a unfalsifiable band-aid that can explain anything; it

          • And the Flying Spaghetti Monster theory passes all of them with flying colors as well. All Dark Matter theories boil down to "Something must be causing this, lets say Dark Matter is!" when Dark Matter has never, ever been observed and there's no more validity to its existence than the FSM (which also has never been observed but in theory fill all the same roles as Dark Matter). It's silly science to be saying "Dark Matter does it!" when there is literally no evidence that this nebulous "Dark Matter" even
            • And the Flying Spaghetti Monster theory passes all of them with flying colors as well.

              So, no, you don't understand how science works.

              The FSM isn't falsifiable, it doesn't make any specific quantitative predictions, its existence is not a natural consequence of other physical theories.

              It's silly science to be saying "Dark Matter does it!" when there is literally no evidence that this nebulous "Dark Matter" even exists.

              Think for a minute.

              If a weakly interacting massive particle existed, what evidence would we see that it exists?

              Gravitational anomalies of a very specific quantitative character on scales from galaxies to clusters to cosmology. These anomalies would not be totally independent but would relate to each other in a

            • by Urkki (668283)

              These "very specific predictions" are manufactured by scientists trying to explain the unexplainable

              And how is that different from, say, General Relativity?

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