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  1. #21
    Michael McCulloch's Avatar
    Michael McCulloch Guest

    Default How do astronomers know how much dark energy and dark matter in the universe from a radio map?



    On Tue, 04 Oct 2005 11:52:34 -0400, John Deer <JD@nowhere.com> wrote:


    Here is my attempt to answer along with references that you can dig
    into to get more meat regarding your specific question.

    The prevailing cosmological theory (i.e. the Big Bang) is largely
    based on a mathematical model of the Universe called the Lambda-CDM
    model:

    http://en.wikipedia.org/wiki/Lambda-CDM_model

    This model has been developed over the years from observational data
    and the input of many scientists. However, this is only a model of the
    Universe and is only useful as long as the model makes predictions
    that can be verified from observational data.

    WMAP provided a data set that allowed astronomers to test the
    predictions of the Lambda-CDM model at a scale and resolution
    previously unavailable from various other cosmic background radiation
    maps.

    The WMAP team, and various other scientists I assume, analyzed the
    WMAP data and combined it with other available observational data
    sets. What they came up with among many things are these graphs:

    http://lambda.gsfc.nasa.gov/product/...pectrum_ss.gif

    Parent page:
    http://lambda.gsfc.nasa.gov/product/...t/m_images.cfm

    As others have stated in this thread, the graph shows the relationship
    of the observed spectral variations in the WMAP (and other) data for
    the cosmic background radiation. The red line shows the curve that is
    generated for the Lambda-CDM model using the parameters identified by
    the WMAP team as the best fit.

    Back to the Lambda-CDM model, the six main parameters (again read the
    Wikipedia reference above) "measured" by the WMAP team result in a
    mathematical prediction of the age of the Universe. An example of how
    the various ratios of dark energy and dark matter affect the
    calculation of the age of the Universe is illustrated here:

    http://map.gsfc.nasa.gov/m_uni/101bb2_1.html

    You may ask: where is the affect of ordinary matter in the graph?
    Well, the amount of ordinary matter according to the Lambda-CDM model
    is so insignificant as to be practically inconsequential!

    So, observing the red line of the expansion graph (using the currently
    preferred ratios derived from WMAP) shows it intersects the zero
    Universe size at approximately 13-14 billion years.

    Note that the red line also shows that the Universe will expand
    forever.

    Does this mean that the determination by the WMAP is not open to
    revision or challenge? Of course not. But any competing theory has to
    also account for the observed data and offer a model that can make
    testable predictions as well or better than the current model(s) such
    as the Lambda-CDM.

    We had a local astronomy professor visit our astro club last fall and
    present two detailed talks about the WMAP data and the implications
    for cosmology. He had several interactive computer programs which
    would allow him to input the various parameters and show the resulting
    graphs. It was great fun to "play god" with the parameters and watch
    how the Universe responded! ;-)

    ---
    Michael McCulloch

  2. #22
    Chris L Peterson's Avatar
    Chris L Peterson Guest

    Default How do astronomers know how much dark energy and dark matter in the universe from a radio map?

    On Tue, 04 Oct 2005 22:36:58 -0600, Tim Killian <TJK@notmyrealemail.com>
    wrote:


    Could you provide an example of such "erroneous" observations, or of a
    serious cosmological theory that ignores observed data by considering it
    erroneous?

    _________________________________________________

    Chris L Peterson
    Cloudbait Observatory
    http://www.cloudbait.com

  3. #23
    Bob's Avatar
    Bob Guest

    Default How do astronomers know how much dark energy and dark matter in the universe from a radio map?

    Sometimes observations and experiments in the lab get goofed up, and
    that's something scientists have to be careful of. But if the
    observations or experiments are goofed up, whatever it is that people
    think was the defect in the observing or experimental method or
    procedure has to be corrected and another set of observations and
    experiments has to be run. So when a new theory and experiments to
    verify it are done, and you get essentially a "mismatch" (that is, they
    don't jive) you have to look at both to see where the problem is. And
    then fix it and do the experiments over again. Oh, it's happened where
    a bad theory and bad experiment happen to match and thus "confirm" the
    bad theory, but that's rare, and usually gets caught by other
    scientists in the field. You really don't want that to happen else you
    end up looking like a scmuck....


  4. #24
    Thomas Womack's Avatar
    Thomas Womack Guest

    Default How do astronomers know how much dark energy and dark matter in the universe from a radio map?

    In article <1128460433.212029.273490@g44g2000cwa.googlegroups .com>,
    canopus56 <canopus56@yahoo.com> wrote:


    Is it showing illuminated _gas_ rather than very diffuse starlight?
    The Web page suggests that most of the intra-cluster light they detect
    in that spectacular image is from stars scattered out of the Virgo
    galaxies; I suppose it's a moot point, since spectroscopy of something
    magnitude 28 and that diffuse isn't really practical (though I believe
    people have detected intra-cluster planetary nebulae, and even stars
    using long Hubble exposures), and repeating the very long exposure in
    H-alpha would be a tedious task.

    I really hadn't expected the halos of M84 and M86 (the galaxies on the
    right of that image) to overlap!

    I'd be very interested to see how far out you can detect the halos
    using a fast wide-field amateur instrument like the Epsilon 180
    astrograph.

    Tom

  5. #25
    Bob's Avatar
    Bob Guest

    Default How do astronomers know how much dark energy and dark matter in the universe from a radio map?

    IIRC, one of the features of dark matter particles is that they don't
    clump together like ordinary matter does. So you never get dark matter
    asteriods, planets and so on. Or dark matter molecules. And dark
    matter particles pass thru the Earth and other clumps of regular matter
    and not be impededed at all. Heard it said that there is likely about
    2 kilograms of dark matter particles passing thru the Earth right now,
    but none of it clumps with the Earth. Maybe a little of it orbits the
    earth's center of mass, but none clumps with Earth's regular matter.
    But taking the dark matter density of 2Kg/(volume of an 8000 mile
    sphere (that of the Earth) and then figure that's the density thruout
    the solar system, the mass of all that still comes out too small to do
    anything much to the orbits of planets and such. But look at the
    volume of a galaxy, then it becomes important. Or at least that's how
    I misunderstand it..... :-)


  6. #26
    Bob's Avatar
    Bob Guest

    Default How do astronomers know how much dark energy and dark matter in the universe from a radio map?

    Oh and we don't know how many different types of dark matter particle
    there are. Maybe it's one or two, or maybe it's a big mess of 'em like
    the hundred or so sub-atomic ordinary mass partilces we know about.
    But if none of the dark matter ever clumps like regular ordinary matter
    does, then you'd never have any dark matter chemistry or biochemistry
    and additional fun like we have with regular matter.


  7. #27
    canopus56's Avatar
    canopus56 Guest

    Default How do astronomers know how much dark energy and dark matter in the universe from a radio map?

    Thomas Womack wrote:


    Thomas, that's a good catch. The web page <<
    http://astroweb.case.edu/hos/Virgo/ >> states the extended glow is from
    the galactic halo:

    "Many long streamers of stars can be seen, along with very faint
    extended halos surrounding the bright galaxies, . . ."

    Galactic halos typically consist of stars, gas and dark matter. I'm
    interpreting the glow to be diffusion of starlight off the gas. As you
    point out, that is not entirely correct - some of the diffuse light
    comes directly from the stars.

    - Canopus56


  8. #28
    Tim Killian's Avatar
    Tim Killian Guest

    Default How do astronomers know how much dark energy and dark matterin the universe from a radio map?

    Dark matter is composed mostly of unmatched socks that have migrated
    from drawers and laundry baskets through an inter-dimensional
    singularity, and are now floating in the void, untouchable by photons or
    normal atomic particles. Crazy you say? My theory has as much
    observational data to back it up as any of the rest.

    Bob wrote:

  9. #29
    Sam Wormley's Avatar
    Sam Wormley Guest

    Default How do astronomers know how much dark energy and dark matterin the universe from a radio map?


    Just a note about Dark Matter...

    Particle Dark Matter: Evidence, Candidates and Constraints
    http://arxiv.org/abs/hep-ph/0404175

    Scientists Map Dark Matter, Prove Einstein Right
    http://www.space.com/news/cosmic_shear_000512.html

  10. #30
    Tim Killian's Avatar
    Tim Killian Guest

    Default How do astronomers know how much dark energy and dark matterin the universe from a radio map?

    Five years and counting as we await "really strict tests"...

    From the 2000 article: "At the same time, astronomers admit that their
    new method for finding dark matter has not yet been tested enough to
    allow experts to make a definitive generalization about the fate of the
    universe. "Since our approach is new, its not very precise yet," said
    Wittman. 'Really strict tests of the theory will come in the next few
    years as astronomers measure the [weak] lensing more and more accurately.'"

    And from the recent Bertone paper:

    "We observe in large astrophysical systems, with sizes ranging from
    galactic to cosmological scales, some “anomalies” that can only be
    explained either by assuming the existence of a large amount of unseen,
    dark, matter, or by assuming a deviation from the known laws of
    gravitation and the theory of general relativity."

    In other words, the observed anomalies could be due other causes, but
    the authors like dark matter theories and so off they go.

    "Although it is definitely clear that the slope of the density profile
    should increase as one moves from the center of a galaxy to the outer
    regions, the precise value of the power-law index in the innermost
    galactic regions is still under debate. Attention should be paid when
    comparing the results of different groups, as they are often based on a
    single simulation, sometimes at very different length scales."

    Yes, there is nothing like disparate "single simulation" results and
    some marginal supporting observational data to cement the theory - I
    hope the Nobel Committee is paying attention - LOL! But then Alan Guth
    has held them in suspense for 25 years while they await a plausible
    explanation of his inflation daydream. These authors can surely count on
    some measure of patience as they seek those magic, unseen, unobservable
    particles of dark matter.


    Sam Wormley wrote:

 

 
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