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Thread: The Search for Dark Matter

  1. #1
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    Post The Search for Dark Matter

    Dark matter . . . What is it? Nobody knows for sure, but it's definitely there. Or maybe it's not there, and we just need some redefinition of gravity at vast scales. ...

    Read the full blog entry

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    Lightbulb Just A Thought

    Hi Fraser....

    Recently I had a conversation with the very well known cosmotoligist, Russ Croman. He pitched the Question to him
    "What is Dark Matter" He promptly replied to me....
    "That's a Good Question!" and went on to say, "Nobody Knows!"

    I have posted my question about it many times and I never receive
    any replies! This is my theory about the unknown......

    I happen to believe in INFINITY! Infinity is primarally has two major componets: Endlessness and Timelyness, no beginning and no ending to either! There never has been a moment, when infinity was not existing! Why is it so difficult to believe that infinity does not have COLOR?? In other words, at night when we point our eyes away from Earth towards the sky and focus on the "Dark Matter" between any form of light, (stars,planets,etc.)
    and believe the "Darkness" is the color of Infinity...BLACK!

    The idea that the "Big Bang" theory that supossedly started the beginning of the Universe is absurd! What was existing before the Big Bang!?? Common sence tells us there had to be Something!
    If nothing else, there had to be infinity and Temporature!
    Note: the absence of heat, temporature will Drop! I don't think we know how far down temporature can drop?

    Much more, but it is after 4am and I'm ending here!

    Regards,
    Gary / searlesgold
    g-man=coin@sbcglobal.net

  3. #3

    Cool

    Quote Originally Posted by Fraser View Post
    Dark matter . . . What is it? Nobody knows for sure, but it's definitely there. Or maybe it's not there, and we just need some redefinition of gravity at vast scales. ...

    Read the full blog entry
    Dark matter i beleive is ther, i agree with astronemers, it is beleived it is there because objects are beleive to pass and then swing or turn as if ther was some planet or peice of matter using gravity to change it's route, i beleive in most cases that this would be a black hole, which is thought to have massive gravitional pull, even pulling light into itself as we all kno, hence making it impossible to shed any light at all to make even a slight prediction of wat is around it

  4. #4
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    Russ Croman will be overjoyed to learn that he is a beautician. All those years of education wasted trying to become a cosmologist.

    More constructive suggestion: write comments in a word processor and use the spelling and grammar checker, then copy to here. I make plenty of mistakes, this procedure catches most of them.

    Relevant to the discussion at hand, I have problems with the entire dark matter/dark energy scenario. Be back later after some source checking.

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    Hey Pamela.

    During the 'cast, you referred to the "ballet cluster" where the recent dark matter evidence was found. But it's spelled "Bullet" on APOD and other places. Just wondering.

    Great episode though.

    Also, Cosmic Variance has a great image about that cluster and dark matter, in the spirit of the classic demotivational posters...

    A friend of mine says that
    ...the astro community (which I find hard to comprehend oftentimes) would rather believe that we don't understand anything (e.g. MOND=general relativity is wrong for no good reason) than believe that new particles exist beyond those in stars...

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    Wimps?

    It seems to me that if Dark Matter (DM) is particulate and exerts gravitational influence, should it not agglomerate? Shouldn't we get DM planets, or at least planets and stars combined with DM? Or is it that WIMPS generate gravity, but are unaffected by it? Hmm!

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    what is dark matter?, that is a very dark matter.......
    ................................

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    Quote Originally Posted by Kevn View Post
    During the 'cast, you referred to the "ballet cluster" where the recent dark matter evidence was found. But it's spelled "Bullet...
    Hum,
    strangely i thought i heard it that way as well...
    i just put it down to a Freudian slip.

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    So that means Pamela secretly wants to be a ballerina? Cool!!

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    Hum,
    don't we all?
    , or she may have subconsciously spotted (for example) a tutu, during Frasers interview.

    BTW, there is more info about the bullet cluster (1E0657-56) on this thread.

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    I have a couple of questions for Pamela Day from the Dark Matter Podcast:
    1) Why do you refer to gravity bending light? Doesn't gravity warp space and light just travel along this warped space? Is this type of conceptual shortcut possibly responsible for our lack of understanding of what is going on with dark matter/energy?

    2) You mentioned that ther outer objects of galaxies and clusters are moving faster than expected, more like a rigid platter, rather than slowing down. I assume this slowing down is what we observe in spiral galaxies. Rather than additional dark matter, could there be an interaction between matter that we can only observe at this scale?

    Thank you in advance your attention to these questions.

  12. #12

    Arrow come on ppl

    some of u ppl r not even close to the subjusct, this is a space and astronomy forum about dark matter, don't talk about tutu's and other crap

  13. #13
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    Hehe,
    sry, got carried away on a musical thread posting day.
    Anyway, there is another exciting bit of research that has appeared recently that you may want to peruse.

    It seems we now actually have pieces of the puzzle

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    Nice show, once again.

    Trying to come up with suggestions for you.....Since I've gotten used to this place (BAUT), prior to air time, you might want to post any related images onto the respecitve thread and refer to them in your podcast so we can enjoy an even more colorful program.
    We know time flies, we just can't see its wings.

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    Quote Originally Posted by toneyvr View Post
    It seems to me that if Dark Matter (DM) is particulate and exerts gravitational influence, should it not agglomerate? Shouldn't we get DM planets, or at least planets and stars combined with DM? Or is it that WIMPS generate gravity, but are unaffected by it? Hmm!
    Hi toneyvr, welcome to the BAUT forum.

    A lot of people have the idea that gravity somehow can make things collect together, but it takes more than gravity. It takes some kind of force to stop the relative motions of two objects when they get collide. Dark matter doesn't get stopped when it goes by any other matter (dark or otherwise), except *very* rarely. We have a few mutually exclusive ideas about why, so we can't say we know yet. In short, dark matter will not agglomerate densely enough to form dark-matter planets.
    Forming opinions as we speak

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    dark matter

    If you can't see it, and you can't detect it, you can attribute any kind of properties you want to it.

    Let's look at the dark matter arguments again.

    1. The outer regions of spiral galaxies and galaxies in clusters move too fast to be held in orbit by the amount of gravitating matter that we detect.

    2. If Newtonian mechanics holds, a lot more of more or less evenly distributed gravitating mass is required.

    3. If a whole lot more mass is required, then it must be invisible and/or very difficult to detect. We certainly haven't had any luck so far, and I'm not impressed with the Bullet Cluster work.

    I'm not happy with the MOND work, either, but I think it has less smoke and mirrors than dark matter. Fundamentally, I think we're missing something. Remember what a stew physics was in after Michelson/Morley and before Einstein.

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    Hum,
    you are perhaps not aware of all the recent research that has basically discredited MOND as a viable alternative to DM.

    It is true that we haven`t see darkmatter, but we can detect it, and we can even attribute a few properties that it must have to fit with the observations.

    For example, researchers from the University of Cambridge Institute of Astronomy claim to have calculated that dark matter only comes in clumps larger than about 1,000 light-years across, implying an average speed of dark matter particles of 9 km/s, a density of 20 amu/cm³, and temperature of 10,000 kelvins.

    http://en.wikipedia.org/wiki/Dark_matter

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    Quote Originally Posted by Fraser View Post
    Dark matter . . . What is it? Nobody knows for sure, but it's definitely there. Or maybe it's not there, and we just need some redefinition of gravity at vast scales. ...
    I don't understand why dark matter halos wouldn't be subject to the same inertial tendencies as detectable matter. That is, why don't they slow down just as the outer stars are expected to according to the standard model. It seems to me that if dark matter halos explain the uniform rate of rotation of inner and outer objects in a spiral galaxy, then they must actually be dictating that rate of rotation. Perhaps that's why the ratio of dark matter to detectable matter is estimated to be about 5:1.

    Can anyone enlighten me on this?

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    Hum,
    indeed,
    by having massive amounts of `stuff` in halos it can explain away the linear (for the most part) rotation graph of the galaxy.

    But it has to be said we don't know very much about the source of inertia,
    There are theories that make use of virtual photon/matter interactions to create mass/inertia, but how that may apply to darkmatter we don't know.
    Gravitational attraction and inertia (or even mass) may not be simply connected.

    It seems according to recent theories that dark matter has the same gravitational properties (± 10%) as normal matter. And the reason why it is in halos (rather than slowing down and clumping together at the centre of galaxies) seems to be that it is fasts moving and collisionless

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    Title: Spin alignment of dark matter haloes in filaments and walls
    Authors: Miguel A. Aragón-Calvo, Rien van de Weygaert, Bernard J. T. Jones, J.M. Thijs van der Hulst

    The MMF technique is used to segment the cosmic web as seen in a cosmological N-body simulation into wall-like and filament-like structures. We find that the spins and shapes of dark matter haloes are significantly correlated with each other and with the orientation of their host structures. The shape orientation is such that the halo minor axes tend to lie perpendicular to the host structure, be it a wall or filament. The orientation of the halo spin vector is mass dependent. Low mass haloes in walls and filaments have a tendency to have their spins oriented within the parent structure, while higher mass haloes in filaments have spins that tend to lie perpendicular to the parent structure.

    Read more (288kb, PDF)

    <attachment>
    Lefthand panel: Particles inside a sub-box of 37.5 × 75 × 100 h-1 Mpc. For reasons of clarity only a small fraction of the total number of particles is shown.
    Central panel: filaments delineated by a subsample of the particle distribution. At each particle location we have plotted the filament vector eF, indicating the direction locally parallel to the filament.
    Righthand panel: wall particles detected in the same sub-box: at each wall particle we plot the wall vector eW. Two walls can be clearly delineated: one seen edge-on (dashed outline) and one seen face-on (solid outline).
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  21. #21
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    Quote Originally Posted by Blob View Post
    Hum,
    indeed,
    by having massive amounts of `stuff` in halos it can explain away the linear (for the most part) rotation graph of the galaxy.

    But it has to be said we don't know very much about the source of inertia,
    There are theories that make use of virtual photon/matter interactions to create mass/inertia, but how that may apply to darkmatter we don't know.
    Gravitational attraction and inertia (or even mass) may not be simply connected.

    It seems according to recent theories that dark matter has the same gravitational properties (± 10%) as normal matter. And the reason why it is in halos (rather than slowing down and clumping together at the centre of galaxies) seems to be that it is fasts moving and collisionless
    I must say that, despite the recent observations, dark matter and dark energy strike me as black box explanations for phenomena that are anomalous with respect to mainstream theory. They seem like place-holders for huge unknowns in current cosmological thinking. While such constants have often been posited in the evolution of theory—witness Einstein's cosmological constant—I would expect them to just gently tweak the data to make it fit. The fact that dark matter and energy account for 94% of the universe seems an awful lot like the tail wagging the dog. Why are so many mainstream scientists prepared to make a leap of faith to something that seems so far-fetched? Is it possible that we're becoming too enamored of our own favorite theories?

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    Quote Originally Posted by Blob View Post
    Hum,
    It seems according to recent theories that dark matter has the same gravitational properties (± 10%) as normal matter. And the reason why it is in halos (rather than slowing down and clumping together at the centre of galaxies) seems to be that it is fasts moving and collisionless
    I recall seeing something about friction-produced static electricity in the earliest moments of the big-bang being required to initiate the accumulations of mass that have culminated in the large-scale structures of the universe.

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    Quote Originally Posted by eremon View Post
    I must say that, despite the recent observations, dark matter and dark energy strike me as black box explanations for phenomena that are anomalous with respect to mainstream theory. They seem like place-holders for huge unknowns in current cosmological thinking.
    Hum,
    indeed it is good to view the term `dark matter` as just a place-holder.
    However, having said that, there is little doubt nowadays amongst cosmologists that darkmatter exists - we can see through observation that it exists.

    The rule is that, to paraphrase Richard Feynman, "If the theories and mathematics do not match the observations, then they are wrong."

    As far as the current theories go, the only leaps needed are to what actual form that `shadow substance` takes.

    (No-one is forcing anyone to jump)...

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    Quote Originally Posted by Kevn View Post
    During the 'cast, you referred to the "ballet cluster" where the recent dark matter evidence was found. But it's spelled "Bullet" on APOD and other places. Just wondering.
    Okay, here's where I admit a secret that bites me periodically. I have dyslexia, and sometimes I just read things wrong in really funny ways. I'm not sure how many times I read Bullet as Ballet, but it was a bunch, and it was just know that I realized that Bullet is not the same as Ballet when you had them side by side.

    Yes, I should have said Bullet. I just read it wrong a lot of times. Thanks for the excellent catch.

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    Quote Originally Posted by Blob View Post
    Hum,
    ...she may have subconsciously spotted (for example) a tutu, during Frasers interview.
    I now have an image of Fraser wearing a tutu skirt over normal cloths behind his mic...

    [shaking head clear]

    Nah - I just thought that light bending around galaxies was more of a ballet move than a bullet-like thing to do.

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    Quote Originally Posted by M. Mayer View Post
    I have a couple of questions for Pamela Day from the Dark Matter Podcast:
    1) Why do you refer to gravity bending light? Doesn't gravity warp space and light just travel along this warped space? Is this type of conceptual shortcut possibly responsible for our lack of understanding of what is going on with dark matter/energy?
    There are two schools of thought. One says that space is actually curved by mass and the light is going in a straight line through curved space. The other says that space is not actually curved, but gravity bends the light in a way that is observationally identical to curved space. I went with the "it's an analogy" school of thought. Since these are observationally identical schools of thought, I don't really have a hard and fast personal view, and I've found that most people understand the gravity bends light idea better, and understanding was my goal.

    [QUOUTE]
    2) You mentioned that the outer objects of galaxies and clusters are moving faster than expected, more like a rigid platter, rather than slowing down. I assume this slowing down is what we observe in spiral galaxies. Rather than additional dark matter, could there be an interaction between matter that we can only observe at this scale?[/QUOTE]

    The idea behind Modified Newtonian Dynamics is that gravitational interactions are different at really large distances. I'm actually going to refer you to a good review page rather than try and explain stuff here. Check out The MOND Pages

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    Fyi ...

    There is a BAUT Q&A thread devoted to DM (well, at least the observational basis of it ....).

    OK, OK, it's not complete; I will write another section soon, ... promise ...

    Oh, and the MOND pages? Just keep in mind, as you read the material therein, that it's highly partisan ... (an apparent example).

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    Quote Originally Posted by eremon View Post
    I recall seeing something about friction-produced static electricity in the earliest moments of the big-bang being required to initiate the accumulations of mass that have culminated in the large-scale structures of the universe.
    Hum,
    Big Bang nucleosynthesis and the production of Sterile Neutrinos?

  29. #29
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    Smile

    Dark Matter (and Dark Energy) have always mystified me. While this PodCast didn't really clear anything up, it at least showed that there are a lot of very smart people who are just as confused as I am.

    To be honest, I kind of view Dark Matter and Dark Energy as modern day Ether. We see things we don't truly uderstand so we theorize that there must be something there to make such and such happen. I wouldn't be surprised if we turned out to be completely incorrect and that Dark Matter and Dark Energy are simply aspects of the laws of Physics that we simply don't understand yet.

    Still, I enjoy following the research, even if I don't understand it all.

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    Quote Originally Posted by Eremon
    I recall seeing something about friction-produced static electricity in the earliest moments of the big-bang being required to initiate the accumulations of mass that have culminated in the large-scale structures of the universe.
    Quote Originally Posted by Blob View Post
    Hum,
    Big Bang nucleosynthesis and the production of Sterile Neutrinos?
    I think the idea was that something other than classical gravity is required to effect the minuscule initial agglomerations of particles that eventuated in objects large enough to exert gravitational influence. Friction between densely packed moving particles would have electrostatically produced the necessary attractive force.

    In googling I came across these:
    Gravity as the second order relativistic manifestation of electrostatic force.
    Quantum Cosmology With Decreasing Gravity.

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