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Thread: Dark Matter/Dark Energy

  1. #61
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    First let me point out that my formal physics education ended in high school (though I did have a college level Intro Astronomy course that included some astrophysics). I've tried to follow the dark matter/dark energy debate, within physics circles, as well as a layperson can, and I do keep a current subscription to Nature, which is probably one of the few subscriptions I actually read with any regularity. Still, I am well aware of my likely ignorance in the subtleties, particularly when it comes to defining what would qualify as either dark matter or dark energy.

    A few things have come to my attention recently, though, and I wonder to what degree these have been integrated into the physics mainstream? One, I read recently (and I wish I could recall exactly where) of an astronomer in (Georgia?) whose main project has been to complete a detailed census of objects within 10 parsecs of our solar system.

    Among the survey's more interesting findings have been a much higher than anticipated concentration of "relatively" dark bodies, including brown and red dwarfs. I've long wondered just how much of "dark matter" is simply ordinary matter that is not particularly luminous -- interstellar dust clouds that we do not pick up because there is no nearby star (or no star poised between us and the cloud) to reveal the existence of the matter in question. I'm sure this still leaves room for all sorts of other exotic particles, energies and whatnot, but if our assumptions about the composition of local space are significantly "off" it only stands to reason that some of this reassessment may be useful in recalculating our estimates of existing matter in the universe as a whole, and in particular sections of it.

    I also seem to recall reading recently that some investigators have questioned the calculations that led to the fairly recent assumption that there was a need for "dark energy" above and beyond the fairly accepted premise of needing dark matter to explain accelerating universal inflation.

    I've always tended to assume that "dark matter" etc. was a sort of "placeholder" value that astrophysicists used to account for effects and motion that would otherwise not be consistent with current theories of physics. It is always good to remember that multiple possibilities are open -- yes, the theories might be wrong (though it seems unlikely they can be entirely wrong -- Newtonian mechanics continues to be a perfectly valid way of predicting outcomes under most conditions, relativistic mechanics only have a noticeable impact at the extremes. Any future revisions are far more likely to apply to the extremes of the extremes than they are to entirely replace both Newton's and Einstein's theories.

    But, because nothing is ever entirely certain, it remains both wise and accurate to regard both Newton's and Einstein's laws in some regards as "theoretical." Observation so far continues to bear them out.

    I suppose I regard "dark matter" etc. as hypothesis rather than theory, and unless I'm mistaken, so does the rest of the physics "establishment." It is unfortunate that human frailty enters the picture and often prevents a revolutionary thinker and his theories from gaining general acceptance, but it is also understandable. I'm in no position to judge the merits of this "Electric Universe" concept (though it seems to me to be taking many self-evident aspects of physical reality and if I understand it correctly quite probably overextending them). For instance, I wouldn't deny that some weak electromagnetic forces apply across great distances, but the greater the distances, the more the inverse squares "law" tends to apply, I would think, implying that there impact would most likely be marginal at best. As for electrical current, wouldn't that be generated (and dispersed) locally, around those objects most likely to generate electrical fields, namely spinning objects with large iron cores, such as the Earth and some other planets, and most stars (and especially dim and basically dead ones . . . brown dwarfs or even deader stars that have converted all their fusionable matter to iron?)

    Perhaps I just can't follow the argument being made, and, to be honest, I don't feel equipped to make such evaluations given my current degree of (or lack of) expert knowledge in these areas. The best I can do is to read the abstracts of relevant research as it comes out and try to remain somewhat aware of where the generally accepted "gray areas" happen to be.

  2. #62
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    Well, Ebbixx
    I can only say that your thoughts and comments ring very true to me. The estimates that led to the "missing matter" theory could be off, but since no major change in the estimates has occurred in 70 years, I guess that the matter will stay missing. Whether the theories are wrong and need to be replaced, or whether some exotic stuff will be responsible for the behaviour of the visible (measurable) matter, ultimately it will lead to a better understanding of how the Universe works. The electric model is just that, a model and it needs to be proven to have merit (and this seems unlikely as the electric topic shows). Keeping an eye on the "grey areas" is exactly what will help us move towards this understanding, so my guess is that you're on the right track. Just keep asking questions, and make sure that we "assume nothing".
    Cheers.

  3. #63
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    I'm fairly new to the Universe Today forum, but thought I'd add my thoughts on this popular topic:

    Dark Matter - Something has to account for the gravity observed in galaxies. I haven't bought into the MOND theories yet. My understanding is that a major candidate for dark matter is some fairly heavy elementary particles that do not often interact with proton, electrons, etc. These might be the lightest supersymetric particle [if it exists]. These would have to have little enough kinetic energy that they are mostly orbiting around the galactic centers, and not free [neutrinos are not bound, and fly around at near light speed]. I am very willing to believe that supersymetric particles existed and devolved to these things during the first seconds of the univers's existence. Those were hot times that we'll never see again.

    Dark Energy - I look forward to knowing what is accelerating the expansion of the universe. Right now, I have trouble picturing anything doing this, but the evidence that it is happening seems pretty clear cut.
    Forming opinions as we speak

  4. #64
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    Has anyone been discussing the (fairly recent) "ghost condensate" hypothesis, that some claim may offer an all-in-one "entity" that would account for both the presumed effects of dark matter and dark energy?

    Refs:

    Seminar abstract on the ghost condensate - MIT, Nima Arkani-Hamed (a main proponent & Harvard faculty member)

    Univ. Illinois at Chicago High Energy Physics lecture series - abstract Hsin-Chia Cheng on ghost condensate

    Summary of New Scientist feature article, 7 Feb. 2004 -- scroll down for feature

    I'm sure a google (or other) search on "ghost condensate" will uncover further items, more detailed as time passes. I first read of this hypothesis sometime in late Feb. '04, in an issue (7 Feb? 2004) of New Scientist.

  5. #65
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    What a WIMP is I do not know.
    Well, I believe it's the opposite of a MACHO! :P (PS: What's a "macho"?)

    Ebbix, those links look real swell & I'm gonna take my time with them...

    I believe "brane (epkyrotic) theory" has a simple answer for dark matter. Whether it's true or not is another matter. And what it says about dark energy is another matter again. "Dark matter", supposedly, is the "watered-down" gravity from matter in higher (and bigger) dimensions than our 4D Universe.

    In other words, there is a whole Universe sitting right over the top of ours, and gravity is the only connecting force.

    So say the "experts" (not me&#33....

    Ah, hell... Too many theories, not enough FACT!!!

  6. #66
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    In other words, there is a whole Universe sitting right over the top of ours, and gravity is the only connecting force.
    What, in this context, is the meaning of "top". Such a semantic quagmire!! Why do the mighty thinkers founder in delusion! Why is Occam's razor given over to corruption! Why have the seekers of truth gone awhoring after fantasy and given themselves over to pseudological epicycling!!

    It's OK. I'll survive. Don't worry. I have been influenzed by Isaiah and Elijah.

  7. #67
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    Not only gravity, but the dark energy anti-gravity

    http://www.site.uottawa.ca:4321/astronomy/...nomicalconstant

    Newton's gravitational theory was inconsistent with relativity; in order to resolve this problem, Einstein replaced Newtonian gravity with the theory of general relativity (GR). GR predicted that gravity could be generated not only by mass but also by pressure - and that negative pressure could produce repulsive gravity. Unlike negative mass, negative pressure is not forbidden by any theory of modern physics, so repulsive gravity became at least a theoretical possibility.
    ::
    SCIENTISTS BELIEVE ANTI-GRAVITY ACCELERATES UNIVERSE
    > FULL STORY:
    http://www.astronomynow.com/breaking/9906/...grav/index.html
    >
    >


    ::An important adjunct to the debate over the Hubble constant is the notion that the universe cannot be older than its older stars, which appear to be those in globular clusters, spherical clumps of hundreds of thousands or millions of stars found near and around our galaxy
    http://www.space.com/scienceastronomy/hubb...ion_030410.html


    Ars reader D. Gaede noticed something in this CNN article that slipped my eyes earlier: Boeing is purportedly working on an anti-gravity propulsion engine. The article is actually just a glimpse into the world of so-called black technology -- tech research "secretly" funded by the US government. In it, however, the author considers the tensions between military development and public knowledge, between governmental silence and commercial deployment.

    "GRASP," or Gravity Research for Advanced Space Propulsion, was only recently reported in Jane's Defence Weekly, but the U.S. military may have had the technology for years.
    ::
    http://www.princeton.edu/~chirata/mmr/m020701.html

  8. #68
    Faulkner Guest
    Boeing claim that "GRASP" was merely the name of a paper submitted at a conference, not the codename for secret "anti-gravity" research. (See here)

    Also NASA experiments in this area, despite some promising results at the start, still remain inconclusive...apparently...

    So who knows what really is going on? So much secrecy, disinformation, contradictory statements, etc....

  9. #69
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    Originally posted by Faulkner@Mar 5 2004, 05:49 AM
    > What a WIMP is I do not know.

    Well, I believe it's the opposite of a MACHO! :P (PS: What's a "macho"?)
    WIMP is a Weakly Interacting Massive Particle. This would be something that interacts less often than neutrinos, but weighs more than a proton. We have no proof that such particles exist, but proof would be hard to come by. Many proposed particles fit this bill. The current favorite of theorists is the Neutralino which is the lightest decay product with a supersymetry quantum number that is non-zero.


    MaCHO is a Massive Compact Halo Object. This is any of a class of object originating from familiar matter that are dark, and drifting around the galaxy. Examples are old-cold neutron stars, free planets, black-holes. Red dwarfs so dim they can't be seen, very old white dwarfs, unpaired socks from my laundry.

    Note that the WMAP data implies that only a small fraction of the missing mass can be composed of MaCHOs, the bulk must be WIMPs of some sort or another. Studies of micro-lensing events draw the same conclusion, i.e. there are MaCHOs, but not enough to account for the speed of stellar orbits around the galaxy.
    Forming opinions as we speak

  10. #70
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    That's really neat don't you think? On the one hand there is the assumption of a particle that we can't measure with our instruments, on the other is matter that we can measure, but isn't there because we assume that gravity is the only force acting on cosmological scales.
    How to proceed?

    Cheers.

  11. #71
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    Here's a quote from my input to a thread in: -> Everything Else in the Universe-> Cold or Hot. Is it true that the driving force for estimating the dark matter is to satisfy the condition that omega must equal one ?

    Let's examine this problem from the most basic observations we know about.

    The emotional factor that makes dark matter appealing is that we would like the universe to neither collapse nor cool (thin out) to an extremely small density (i.e., discover an omega equal to one). Lay this aside; the universe can't care at all.

    The observed phenomenon that we are trying to explain with dark matter is that stars in orbit about galaxies and galaxies in orbit about their groups and clusters of groups have a line of sight velocity component as observed on earth as manifested by the blue shift of the atomic spectra that seems too high for the gravitational field associated with the presumed mass of the objects. Also, I assume the tangential velocity of the peripheral stars/galaxies is somehow not commensurate with that of the stars/galaxies orbiting nearer to the respective mass centers; although I have not seen this concluded/stated by an expert in the field.

    Where can one find definitive quantitative analyses that present the details of this dilemma such as: galaxy XXXX with mass YYYY megasols has peripheral stars with tangential velocity VVVV where velocity V'V'V'V' should have been observed? Are the observers certain that gravitationally coupled stars in various star cluster sizes in the periphery have not added their cluster orbiting velocities to that of the orbiting star cluster center of mass. In the galactic periphery their mutual gravitational attraction could be more overwhelming than that of stars closer to the mass center (and therefore subject to cluster disruption by the gravitational effects of the galactic mass center) due to their distance from the galactic center of mass thus generating more star clusters in the periphery. A similar argument applies to galaxies with respect to their groups and groups with respect to their clusters etc., Emission spectral line broadening should be an indication of peripheral star clustering since a number of stars in the cluster will have receding velocities within the star cluster while others will be traveling such that their star cluster orbiting velocity will have no line of sight to earth component.

    Is the distribution configuration of the dark matter such that it is additive to that of the center of mass of the visible matter? Does guessing at a larger mass for the galactic central black hole assist in the resolution of this problem? How does assuming that the dark matter hovers just outside the galactic halo in either a toroidal shape or a spherical shape help? Would the axiomatic constancy of the speed of light result in light coming from a star inside the dark matter shell cause it to be blue-shifted as it traveled toward the shell and subsequently red-shifted after it has passed through the shell and is on its way to earthbound observers?
    Is the shifting required to be symmetrically distributed?

    Do we have substantive evidence for dark matter or do we just hope it may be there to support a favorite "set of epicyclic musings".
    Can anyone answer the questions?

  12. #72
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    Originally posted by GOURDHEAD@Mar 7 2004, 08:31 PM
    Can anyone answer the questions?
    Personally, I'm not offended by cold dark matter. Something happened in the first few seconds of the universe that must have produced a lot of very high energy particle interactions. I can believe that 80% of the matter in the universe is stuff that can't be seen because the universe is now way to cold and empty to light it up.

    Where can one find definitive quantitative analyses that present the details of this dilemma such as: galaxy XXXX with mass YYYY megasols has peripheral stars with tangential velocity VVVV where velocity V'V'V'V' should have been observed?
    There are frequent articles in arXive concerning this sort of thing. Typically, they look at a nearly edge on spiral galaxy and measure the red-shift on many small zones. Most of these articles recently have focussed on the implied dark mater distribution from the measured velocities. The zones avoid confusion with stars with less line-of-sight motion.

    Are the observers certain that gravitationally coupled stars in various star cluster sizes in the periphery have not added their cluster orbiting velocities to that of the orbiting star cluster center of mass.
    Most of these studies look at large groups of stars, and so a a few close binaries would not alter the result. Also, for scale, note that the sun goes around the galaxy about 8 times faster than the earth goes around the sun.


    Is the distribution configuration of the dark matter such that it is additive to that of the center of mass of the visible matter?
    Yes. Cold dark matter is graviationally bound to the galaxy or cluster. Typically, a significant fraction of it is close to the center of the galaxy. There are loads of papers about this. They are a little heavy on the math. I haven't yet bothered plowing through the analysis, just the discussion and conclusions.

    Does guessing at a larger mass for the galactic central black hole assist in the resolution of this problem?
    No. The central black holes of galaxies are very small in mass compared to the total dark mater of the galaxy. Our galaxy has a central black hole of about 3 or 4 million times the mass of the sun [if you include matter that hasn't quite fallen in yet]. The mass of the galaxy is about 300,000 times that much.

    How does assuming that the dark matter hovers just outside the galactic halo in either a toroidal shape or a spherical shape help?
    I don't think that would help. The observed velocities are best explained by a smoother distribution, increasing in density toward the center of the galaxy.

    Would the axiomatic constancy of the speed of light result in light coming from a star inside the dark matter shell cause it to be blue-shifted as it traveled toward the shell and subsequently red-shifted after it has passed through the shell and is on its way to earthbound observers?
    Yes, light is blueshifted as it falls into a gravitational potential well. This is a small but measured affect. I didn't really follow what observation was intended to be explained away with this.

    Do we have substantive evidence for dark matter or do we just hope it may be there to support a favorite "set of epicyclic musings".
    I'd place it as better than epicycles, but still waiting for some unambiguous physical data. The fact is that the implied density of this matter can be measured in clusters and galaxies through a variety of means such as lensing and velocity studies. These measurements will become increasingly accurate in the years ahead, and if they require some hard to swallow ideas to explain what we see, new ideas will be advanced. So far WIMPs of some sort or another are doing great at supplying a plausible explanation with the fewest rash assumptions. Hopefully some kind of accelerator experiment will start turning up super-symetric particles soon, or some other direct cosmic detection of supersymetric anihilations will be seen. Until then, we are talking about the most plausible model to explain something that the material we see can't explain.
    Forming opinions as we speak

  13. #73
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    Suppose dark matter doesn't exist; no exotic particles will be found and all the dead stars are accounted for and still don't add up to explain the orbital behaviour of galaxies. Do we have a plan B, that would have to be evaluated as a next step? And if we have a plan B, maybe we could discuss that one first (MOND comes to mind, but I haven't heard much about it lately).
    I'd hate to wait 50-odd years until we exhausted every possible way of proving something that doesn't exist.
    Anyone?
    Cheers.

  14. #74
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    Originally posted by VanderL@Mar 7 2004, 11:42 PM
    Do we have a plan B
    The journals are full of ideas being explored, including a few MOND articles every month, plus things that deal with the gravitational influence of nearby parallel universes. There are other ideas that I see expressed to, which to my eye seem like crackpot ideas, but that doesn't rule them out. Some of them are pretty entertaining reads.

    People love thinking about this stuff, so there is no shortage of plan B material.

    Going back to your original question about flat omega, that's another option.

    Currently, however, I'd have to say that for observation matching theory, and theory predicting observation, the LCDM theory is worked out to the greatest level of detail of all options present so far.
    Forming opinions as we speak

  15. #75
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    Originally posted by Faulkner@Mar 5 2004, 05:49 AM
    I believe "brane (epkyrotic) theory" has a simple answer for dark matter. Whether it's true or not is another matter. And what it says about dark energy is another matter again. "Dark matter", supposedly, is the "watered-down" gravity from matter in higher (and bigger) dimensions than our 4D Universe.
    Those who've forwarded the -- let's call it a ghost condensate hypothesis, in the hope of retaining some clarity -- are not prepared to contend that this is or isn't the explanation for all those observations that have tended to be accounted for by the intentionally vague terms "dark matter" and "dark energy." I think their only claim is that a "ghost condensate" would serve as a sort of unified factor that could account for all of the unanticipated anomalies. While logically attractive, and, if it stands, perhaps a better "answer" at least in terms of applying Occam's razor, until it can be relatively proven by some of the proposed tests that would potentially prove or disprove its existence, it remains at the very most a hypothesis, a classification which I expect it's originators would agree with wholeheartedly.

    No scientist I know of likes to wind up with egg on their face because they jumped the gun and declared a problem solved or a question answered, without adequate proof. Despite what by now have been many observations that support the theory of special relativity, physicists and astronomers continue to seek additional confirmation, and also at least try to remain open to the possibility that another theory might one day take the place of the present hybrid we use of Newtonian mechanics and relativity.

    I have trouble wrapping my head around the idea of "brane theory" but I'll be certain to look for current studies etc.

  16. #76
    Faulkner Guest
    Do we have a plan B
    No, but I've got a "Plan 9 from Outer Space", buddy! :P

    The trouble is, how are we to differentiate between crackpot theories & "science"? I think "science" is an ambiguous term. Just look at quantum mechanics, string theories, etc. I won't mention relativity theory because I believe you can follow that through in a logical way (if you're smart & patient enough; I'm not! :P ). But these new "esoteric" scientific theories defy common-sense and don't even TRY to paint a rational picture in our minds.

    But we believe in them...because they come from a physics journal, or something...even tho' they are stating outright absurdities...

    I've read MANY physicists saying how they know if they're on the right path, because the theory is "aesthetic" and "feels right". String theory is an example. It is mathematically "beautiful" (so they say, I wouldn't know&#33...

  17. #77
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    Originally posted by Faulkner@Mar 8 2004, 12:34 PM
    But we believe in them...because they come from a physics journal, or something...even tho' they are stating outright absurdities...
    Yes, a lot of the theories seems pretty wacky. I agree that being elegant doesn't make it real. I prefer reading papers that describe what we are seeing, and provide concrete ways to describe it. I find the popular articles that try to summarize theories and explain String [or M-Brane] thoeries, or describe collapsed coiled dimensions in layman's terms kind of off-putting. These articles hide real [but more tedious] science work being done.

    Here's a pointer to an article describing Dark-Matter Halo Structure. [requires Acrobat reader, and takes part of a minute to download] Don't be thrown off by the term six dimensional phase-space. The six dimensions are simply three normal dimensions for the positions of particles, and the same three dimensions again for their momentum. It has nothing to do with stuff we can't see or measure or imagine easily.

    You can see that this article pretty much assumes only that we have gravity much as Newton described it. The article describes the density of dark matter [as observed by gravitational forces] as a function of its distance from the center of the galaxy. It gives a snapshot of where we stand at understanding dark matter today, without claiming to know more than we do. A year from now more refined measurements will have allowed scientists to say a little more. Slowly the constraints on what we are looking for in the laboratory will be narrowed enough to make a successful search possible.
    Forming opinions as we speak

  18. #78
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    I don't think that our technology is good enough just yet to see everything thats out there.... we can see far out into the Universe, but can't really ZOOM in on any one spot other than whats in our own solar system.... and thats not even that great... I dont see any pictures of the insides of Jupiter, or topographical terrain maps of Pluto or the orbits of all the objects floating around the Kuipier(sp?) Belt... we can't even track how many comets or Death NEO's are out there, just waiting to find our little habited world.

    gonna take Time... and patience... and newer technology more than likely....

    Plus the courage to update any outdated theories floating around.... like is the CMB really the edge of our Universe, or just a Wave spreading out, with mores waves infront of it, like ripples in water when a stone drops into it... the waves ripple outwards... and maybe we arent the only 'dropped stone' out there....
    we could be within a massive 'lake/ocean' with many 'stones' being dropped in....

    =P

    . ..-={A}=-.. .

  19. #79
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    String theory is not what I see as a "plan B", it is more an effort to explain everything at once. What I would like to know is what would happen if we assume that what we see is what we get. We can measure photons and spectra, some radiation (in 2-D) and everything else depends on assumptions. We assume that stellar movements (and galaxies as well) are only governed by gravity, mostly Newton's description of it.
    When we look at how most galaxies rotate, there is something missing from the equations; mass. Either we can't see this mass (hence dark matter) or we need something else that can account for the rotation (or gravity can be fudged, as MOND would have it). There are some galaxies that do not show this missing mass component, this only deepens the mystery. Are there other ways to move matter around that are not incorporated in Newton's equations? That is the line of thought that led me to include the plasma model as a possible way to explain the missing mass. But there must be more options, I guess. I'll do some googling, maybe there is more to find.

    Cheers.

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    heh... good ol' google....

    I wouldn't want to think that Einstein knew it ALL.... but, he did think of equations that have stayed constant to today...
    But, I'm sure that there are many things that we don't know about, and that our technology can't pick up everything.... just what our senses can perceive... Wavelengths, Spectras, etc, with the help of instruments. But I think that it may take us to actually be in the IGM to tell what it is truelly made of... maybe our instruments can't detect certain anamolies such as intergalactic gravitational forces other than how they interact with eachother, and not really how a system of galaxies may be interacting within a more vast area of clusters of galaixes, over millions of lightyears wide.... and being within our own galaxy, its kind of hard to look from the outside in, to see whats happening right here, right now, with the surround environment, while our Galactic Center may be putting certain nudges upn our instruments that may be giving us 'warped/blurred/inconsistent' answers, or answers that are not truelly 'Factual', but just hypothetical, because we can't be in the best place to view what is really there....
    Astronomers throw these factors in there, to better help their equations make sense, but who's to say one factor is too much or not... or that its being used in the wrong fashion.

    We're trudgin along =)

  21. #81
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    Dark matter is now carefully defined as matter that can only be detected by gravitational means, and not by its own or reflected radiation. Thus planets, rocks, sand, dust, gas, and other ordinary matter cannot be dark matter. It's origin is not really Fritz Zwicky, since he probably meant that what he needed was ordinary matter that he couldn't detect with the instruments he had. The most referenced paper is by van Albada et al (1985), and they tried to find the mass distribution in NGC 3198, by first assuming an exponential mass distribution for the disk. When that did not produce the rotation speeds to match experiment, they added spherical shells centered on the galaxy and called them dark matter, since no such shells could be detected (then or since). Since they are quite bright, and probably knew they were making a mistake, dark matter may be a hoax.

    They probable wanted to add the extra mass needed in the plane of the disk, but didn't know how. Actually gravity would cause such shells to collapse into the disk.
    When done right Newton's law works fine and dark matter is not needed to find the mass distribution in the disk that causes the rotation speeds (www.galaxymethods.net).

    It is a fair bet that dark energy is also the invention of someone that made a math mistake.

  22. #82
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    What if the invisible force keeping a galaxy in it's form is what's coming from the supermassive blackhole at it's center... the pressure in the middle could be sucking at in extreme force, and releasing in extreme force, the IGM keeps the galaxies in their 'bubble' through extreme temperature changes and the blackhole expands the 'bubble' while it feeds on the star masses closest to it, expelling the heated gaseous/plasma that makes our Galaxies so damn hot... kind of like a helium balloon, except its one in an ocean instead of in the sky.. and the helium is ionized hydrogen. =/

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    That dark energy, etc, is about the color of fudge, in the first place, in analogy.
    http://community.webtv.net/hotmail.com/pri...ingsofthePlasma

    Prime

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    Maybe dark matter is something from another dimention that projects into our universe and we, in our limited 3D perception, just see it as dark matter.

  25. #85
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    Hi All,

    I have some observations and some questions too.

    Dark matter:

    1. Just consider : a) Our inability to detect even massive planets around nearby stars sometime back, it is only indirect method of detecting the wobbling caused by gravity that is helping us now to detect them B) Sedna and other objects beyond Ku belt are being discovered so late c) many more dwarfs are appearing in the vicinity than earlier expected. So in short we are all learning and finding many more objects in close proximity to our solar system itself. Their mass may not add up much but we could not notice them till recently in such a close proximity!

    2. We are located in one arm of the milky way galaxy, far from its center, our understanding of what it is like at the center is limited. What we know is limited to signatures in the electromagnetic spectrum – all about active hot matter – visible or indirectly detected. The occurrence of cold dead and simple matter, as simple as Iron (not exotic elements) may be very high there – at the center of a galaxy. We know the celestial void is just too large between active stars, just imagine how many dim and dead matter like dead stars can fit in between?

    3. Has anyone actually counted hairs in the scalp? It is very homogeneous and therefore we can count a Sq cm and extrapolate. What about a balding person like me? I hope the same method is used to calculate the number of stars in a galaxy. The sun is unfortunately near the balding patch. When we look around the sun, which is not at the center of the galaxy, we could always go wrong in our calculation for the mass of milky way by a large factor.

    4. Only recently we have figured out that there is something as large as double the size of the moon that would have been visible if we had x-ray eyes.

    So we have a milky way that has large number of visible stars, radio telescope visible stars and dead/cold/feeble IR detectable stars. In addition we have lots of ‘dust’ like the Earth and Jupiter, which do not weigh much in our solar system but could be significant elsewhere. If some assumptions of a few decades back are reviewed afresh with new scientific inputs, will it be difficult to explain 80% missing mass of our milky way or we still have to look for exotic matter? I am not sure it may still be there! So we need to look for the exotic thing as well as not so exotic thing and review our every hypothesis on the ‘missing matter’

    For my understanding can anyone update me on: If we just consider the milky way galaxy, why is extra mass required to hold it together? If its mass were just 20% of what it is, why will it fall apart? Is it required at the center or almost uniformly? Where is the missing mass more prominent as per calculations?

    Dark Energy:

    1. Since we have had limited scientific observation, are we so sure that the universe is expanding just by observing nine supernovae?

    2. Why is Andromeda going to collide with milky way if we are all going apart? Why is cannibalism amongst galaxies seen nearby if galaxies are spreading out? At what distance this dark energy becomes prominent – beyond the distance of milky way from Andromeda for sure?

    3. Why is this dark energy not affecting spreading within a galaxy? Within our solar system?

    4. Can there be a form of energy which behaves just the opposite of inverse square of distance? More prominent as you go further?

    Maybe we are all being pulled towards what we see as the edge of the universe as we are all part of a ripple in the pool.

    I really look for some enlightenment on above.

    Cheers

  26. #86
    Join Date
    Nov 2004
    Posts
    90
    Again I recommend www.galaxymethods.net for an easy explanation about dark matter and why it probably doesn't exist.

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