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  1. #1
    John Deer's Avatar
    John Deer Guest

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



    Take a look at the map folks:

    http://antwrp.gsfc.nasa.gov/apod/ap050925.html

    How the heck can scientists determine the age and makeup of the universe
    from this soup?

    JD

  2. #2
    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:


    Do you really want to know the answer or is this a rhetorical question
    revealing your own anti-science bias?

    Just thought I'd ask before I waste my time trying to point you toward
    an answer.

    ---
    Michael McCulloch

  3. #3
    John Deer's Avatar
    John Deer Guest

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

    Would an anti-science type be here and looking at APOD?
    Yes I would like to know.

    JD

    Michael McCulloch <michaelm@nospam.invalid.net> wrote in
    news:j3a5k11hljmcuavvn4l9ava00vof0cekro@4ax.com:



  4. #4
    Brian Tung's Avatar
    Brian Tung Guest

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

    John Deer wrote:

    I echo Michael's concern, but I'll give you my answer anyway.

    First of all, astronomers do not determine the age and makeup of the
    universe by just staring at that map any more than physicists determine
    the age of a radioactive sample by listening at the Geiger counter.
    Numerical analysis is done on the map, or the radioactive counts (and
    accompanying decay products).

    Secondly, what are astronomers looking for in the map, numerically?
    Even visually, you can see that the map is not random and without
    structure, the way a TV screen is on the (increasingly rare) occasions
    when the station isn't broadcasting. You can easily tell that there
    is a dark patch in the middle, and red patches (indicating, I *think*,
    higher density) at right, at lower center, and at far left. You can
    do spatial frequency analysis (in much the same way that your radio
    does temporal frequency "analysis") to find patches of smaller size.

    Now, these patches vary by size in two different ways. Generally, the
    smaller ones are more common, and they are less intense. That is to
    say, a smaller dark patch will not be as dark, and a smaller bright
    patch won't be as bright. The precise manner in which these patches
    vary by size (that is, by spatial frequency) tells astronomers much
    about the early history of the universe, before it became essentially
    transparent.

    I should point out that the trend that smaller patches are more common
    and less intense is only a general trend: I understand that there are
    certain spatial frequencies where that trend does not hold true, and
    just like emission lines in spectrographs, these are particular
    indicators of cosmological history.

    Thirdly, dark matter and dark energy cannot, at the present time, be
    detected indirectly (that's why they're called dark) in any event.
    There is no way to take this picture, or any other picture, and point
    to a certain feature and say, "Aha, there's the dark energy." (Or
    matter, for that--uh--matter.) Their effect, as far as we understand
    it at present, is only to modulate the expansion of the universe, and
    to affect the evolution of galactic clusters and superclusters. Both
    of these are reflected to some degree in the WMAP image.

    In short, there is much about astronomical work that can't be stuffed
    into a single APOD paragraph, and people should be wary of assuming,
    just because they can't understand how a conclusion is arrived at,
    that there is no understanding to be had at all.

    --
    Brian Tung <brian@isi.edu>
    The Astronomy Corner at http://astro.isi.edu/
    Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
    The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
    My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt

  5. #5
    Brian Tung's Avatar
    Brian Tung Guest

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

    John Deer wrote:

    I know your question is rhetorical, but actually the answer is yes.
    There are lots of people who would like to see establishment science
    get egg on their face, and they are only too willing to apply their
    poorly remembered fourth-grade science miseducation to that end.

    That's one reason why they say a little knowledge is a dangerous thing.

    --
    Brian Tung <brian@isi.edu>
    The Astronomy Corner at http://astro.isi.edu/
    Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
    The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
    My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt

  6. #6
    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?

    John Deer wrote:

    Certain characteristics of the universe are put into cosmological
    models such as how much dark energy and dark matter are in the universe,
    then the models are tweaked and tweaked until there is good agreement
    with the observables.

    The First Detailed Full Sky Picture of the Oldest Light in the Universe
    http://map.gsfc.nasa.gov/m_mm.html

    Also see Ned Wright's Cosmology Tutorial
    http://www.astro.ucla.edu/~wright/cosmolog.htm
    http://www.astro.ucla.edu/~wright/cosmology_faq.html

    WMAP: Foundations of the Big Bang theory
    http://map.gsfc.nasa.gov/m_uni.html

    WMAP: Tests of Big Bang Cosmology
    http://map.gsfc.nasa.gov/m_uni/uni_101bbtest.html


    PHYSICS NEWS UPDATE
    The American Institute of Physics Bulletin of Physics News
    Number 624 February 13, 2003 by Phillip F. Schewe, Ben Stein, James
    Riordon

    A PINPOINT PRECISION MAP of the cosmic microwave background, reported this
    week at a press conference by scientists associated with the orbiting
    Wilkinson Microwave Anisotropy Probe (WMAP), brings the early universe into
    sharper focus. The credibility of WMAP's pronouncement rests on three
    things: its angular resolution is some 40 times better than that of its
    microwave predecessor, the Cosmic Background Explorer (COBE); it
    comprehensively surveyed the entire sky for a whole year (3 more years of
    data is yet to come); and it measures the polarization of the microwave
    radiation; the orientation of the radiation arises partly from the last
    scattering of light at the time of "recombination," when stable atoms
    formed for the first time, and partly from the time when ultraviolet
    radiation strewn by the first generation of stars ionized once again a lot
    of atoms in space. Here are a few of the salient numbers coming out of the
    WMAP analysis: the time of recombination was 380,000 years after the big
    bang; the era of the first stars was about 200 million years along
    (surprisingly early); the age of the universe is 13.7 billion years; and the
    accounting of matter in the universe is as follows: atomic matter makes up
    about 4%, dark matter about 23%, and dark energy 73%. (Websites:
    http://map.gsfc.nasa.gov/;
    http://www.gsfc.nasa.gov/topstory/20...apresults.html)

    Ref: http://www.astro.ucla.edu/~wright/cosmolog.htm#News

    MAP Data Released!

    11 Feb 2003 - The results from the first year of observing by the
    Wilkinson Microwave Anisotropy Probe were announced today at a Space
    Science Update in the auditorium of NASA HQ. Important results
    include:

    o The satellite has been renamed in honor of the late David T.
    Wilkinson of Princeton University, a key member of the project from
    its conception.

    o The polarization of the microwave background anisotropy coming
    from scattering by electrons 200 million years after the Big Bang
    has been detected. This is evidence for an early generation of
    stars existing 4 to 5 times earlier than any object yet observed.

    o The WMAP data agree with previous work showing the Universe is
    flat and in an accelerating expansion.

    o The WMAP data give the most precise values for the density of
    ordinary [baryonic] matter made of protons and neutrons and for the
    dark matter: 0.4 and 2.5 yoctograms per cubic meter. These
    correspond to omega_b = 0.0224 +/- 0.0009 and omega_m = 0.135 +/-
    0.009.

    o The WMAP data give the most precise value for the age of the
    Universe: 13.7 +/- 0.2 Gyr. The Hubble constant is Ho = 71 +/- 4
    km/sec/Mpc, and the vacuum energy density corresponds to lambda =
    0.73 +/- 0.04. 13 papers by the science team and the maps and
    power spectra are available by clicking on the image above.

    See: http://www.astro.ucla.edu/~wright/cosmolog.htm#News

    Ref: http://www.aip.org/enews/physnews/2003/659.html
    Physics News Update Update #659 (October 28, 2003)

    A Map of the Universe

    A map of the universe produced by the Sloan Digital Sky Survey contains
    200,000 galaxies at distances of up to two billion light years, and
    spread out across 2400 square degrees of sky. According to Sloan
    astronomer Michael Blanton (NYU), this is "the best three-dimensional
    map of the universe to date." The Sloan effort uses a telescope in New
    Mexico optimized to record spectra from many galaxies at the same time.
    One of the standout features of the map is the Sloan Great Wall of
    galaxies, some 1.37 billion light years long and the "largest observed
    structure in the universe" (preprint:astro-ph 0310/0310571) Combined
    with data from other telescopes, such as the Wilkinson Microwave
    Anisotropy Probe (WMAP), the new Sloan observations help tamp down
    uncertainties in several pivotal astronomical numbers. The new best
    value for the Hubble constant is 0.70 with an uncertainty of about
    0.04; the amount of energy in the universe vested in matter is 30% with
    an uncertainty of 4%; the upper limit on neutrino mass is 0.6 eV; and
    the age of the universe is 14.1 billion years with an uncertainty of 1
    billion (Preprint astro-ph/0310/0310723; visit Sloan website).





  7. #7
    Ed T's Avatar
    Ed T Guest

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


    "Brian Tung" <brian@isi.edu> wrote in message

    That's a good point but there's a counter point: even though a cosmologist
    says it, it might be erroneous. <g>

    As a non-physicist, I am often left with the *impression* that dark matter
    and dark energy are concepts that have arisen as fudge-factors to preserve
    current theories. In other words, their existence is postulated to "make the
    math work" within the current cosmological paradigm. It leaves me
    wondering whether the underlying theory is in need of this patch because it
    is flawed.

    I'm not disputing their existence, only relaying my *impressions*. It is
    likely, as Brian points out, the advocates of dark matter/dark energy theory
    have formed their ideas with the help of a superior understanding.

    Ed T.



  8. #8
    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 17:55:58 GMT, "Ed T" <reply@thegroup.thx> wrote:


    In spite of similar sounding names, dark matter and dark energy are
    totally different things. While the existence of dark matter has
    cosmological implications, its observation is much less cosmological. We
    can observe the effects of dark matter locally- in the motion of our own
    galaxy and in galaxies nearby. We also have some fair understanding of
    the sort of particles that could constitute dark matter. Because of
    this, its existence is pretty widely accepted. Dark matter doesn't
    necessarily require a lot of new physics.

    Dark energy, on the other hand, is only inferred from the motion of the
    Universe on a cosmological scale, and the underlying physics is almost
    completely undeveloped. Dark energy is much more a "fudge factor" than
    dark matter. The existence of dark energy is much more uncertain- there
    are cosmological theories that can potentially explain the way the
    Universe is expanding without requiring dark energy.

    _________________________________________________

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

  9. #9
    Chuck Taylor's Avatar
    Chuck Taylor Guest

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

    John Deer wrote:

    Actually, we have anti-science trolls here all the time.

    That said, the simplest answer is to say that there are
    different theories about the makeup of the universe. Think of
    them as different recipes to make a universe. You take each
    recipe and project the kind of universe it would produce. With
    the photo you mentioned, they project each theory (recipe) to
    see how uniform a universe it would form at the point in time
    when light was able to travel through the universe. You are
    looking not only at how uniform it is, but the size and
    distribution of various clumps of matter.

    So imagine we have theories A,B and C. Each is a different
    recipe for creating a universe. You work each recipe to see
    what kind of distribution it produces. Then you look at the
    map and see which theory matches the reality.

    Hope this helps.

    Chuck Taylor
    *********************************************
    Do you observe the moon? If so, try
    http://groups.yahoo.com/group/lunar-observing/

    If you enjoy optics, try
    http://groups.yahoo.com/group/ATM_Optics_Software/
    *********************************************


  10. #10
    Brian Tung's Avatar
    Brian Tung Guest

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

    Chris L Peterson wrote:

    Right--the distribution of dark matter isn't what's mysterious. By
    observing cluster dynamics, we can tell it hangs around ordinary matter.
    The only thing about it that's dark is that we can't see it; it doesn't
    interact very strongly with electromagnetic radiation the way that
    ordinary matter does.


    I point out, however, that although it's a fudge factor, it's not wholly
    arbitrary. It's sort of like precession, which was observed long before
    it was explained by Newton. It wasn't a random, aimless wandering; it
    was systematic change, with a smooth trend over time. So, in a way, is
    dark energy.

    --
    Brian Tung <brian@isi.edu>
    The Astronomy Corner at http://astro.isi.edu/
    Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
    The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
    My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt

 

 
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