Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

WMAP data

  1. Feb 27, 2004 #1

    wolram

    User Avatar
    Gold Member

  2. jcsd
  3. Feb 27, 2004 #2
    I found funny the name that they gave to this algorithm: the friends-of-friends algorithm
     
  4. Feb 28, 2004 #3

    wolram

    User Avatar
    Gold Member

    I found funny the name that they gave to this algorithm: the friends-of-friends algorithm
    -------------------------------------------------------------------
    i suppose this just demonstrates that not everyone is
    happy with the first interpretation of the results, and
    weather right or wrong are manipulating the numbers to fit
    their own ends, something that goes on quite rampantly
    in cosmology.
     
  5. Feb 28, 2004 #4

    Nereid

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Well, "manipulating" data may be a bit strong, but yes, the normal process of science does involve (at a minimum) selecting which data to analyse, which analyses to do, which results to publish, ... and yes, the paper you end up writing may be worded in a way to best highlight the results you wish to convey. In this sense, scientists are no different from any other human beings.

    However, in the case of WMAP, 2MASS, SDSS, 2dF, HST, Chandra, Newton-XMM, Spitzer, CGRO, HIPPARCOS, ... *ALL* the data is released, even (in many cases) the pre-pipeline stuff. Further, most (all?) authors write about their methods of selection, analysis, etc, usually at some considerable length.

    So what you're seeing in this paper (which is a quite nice one, BTW) is a normal part of science, with some researchers taking the first year's WMAP results and doing a different analysis on them than those working directly on the project.

    Does the SZ effect extend to ~1o? or more?? Will the SZ imprints on the CMB from older, more distant superclusters cause us to substantially revise our estimates of the acoustic power spectrum in the CMB? Well, it won't be too long before the second year's WMAP results are released, and only a few more years before Planck is launched, and ...

    Stay tuned, it's an exciting time to be around; maybe someone can tell us what other period in modern science has seen so much happening (OK, quantum physics in the 1920s and 1930s).

    Oh, and almost lost in this is something quite nice - the SZ (Sunyaev-Zel'dovich) effect has been detected! And we may soon have another handle on (super)cluster masses, primordial intergalactic gas, distribution of dark matter in (super)clusters, ....
     
  6. Feb 29, 2004 #5

    wolram

    User Avatar
    Gold Member

    http://astro.uchicago.edu/SZE/primer.html

    The Sunyaev-Zel'dovich Effect (SZE) is a signature left in the cosmic microwave background (CMB) by collapsed structures containing baryons. This signature results from inverse Compton interactions between hot electrons in the collapsed structures and the low energy photons in the CMB. These interactions drive the population of electrons and photons toward equilibrium, resulting in a net transfer of energy from the electrons to the photons. In galaxy clusters the typical optical depth to Compton scattering is ~1%, so only 1 out of every 100 CMB photons that passes through the cluster suffers from these interactions. Therefore, rather than driving the electron and CMB photon populations all the way to equilibrium, the SZE results in a small distortion of the CMB spectrum.
     
  7. Feb 29, 2004 #6

    wolram

    User Avatar
    Gold Member

    http://www2.astronomy.com/Content/Dynamic/Articles/000/000/001/664kjbgi.asp

    Detailed measurements of the cosmic microwave background radiation — the "echo" of the Big Bang — appear to validate the idea that we live in a cosmos dominated by "cold dark matter" and "dark energy." But earlier this month, a group of astronomers at the University of Durham, England, published evidence that gas in nearby galaxy clusters may have altered the microwave signal during its 13 billion-year journey to Earth. If more distant galaxy clusters have the same effect, they say, our current ideas about the evolution of the cosmos may need substantial revision.
    The team, led by Tom Shanks, compared data from NASA's Wilkinson Microwave Anisotropy Probe (WMAP) to the positions of nearby galaxy clusters in three well-known catalogs. The clusters lie in regions of the sky where WMAP recorded lower-than average microwave temperatures. The average temperature of the microwave background is just 2.73 kelvins.

    In essence, galaxy clusters in the foreground may contaminate WMAP's view of the background radiation. "The power of this wonderful WMAP data is that it indicates that interpreting the microwave background 'echo' may be less straightforward than previously thought," says team member Sir Arnold Wolfendale.

    Shanks and his colleagues suggest hot gas in the galaxy clusters interacted with Big Bang photons through a process known as inverse Compton scattering, in which fast-moving particles scatter low-energy radiation. Russian physicists R. A. Sunyaev and Ya. B. Zel'dovich predicted such an effect in the early 1970s, shortly after the cosmic microwave background radiation was discovered.

    Other teams have reported seeing the Sunyaev-Zel'dovich effect near a few rich galaxy clusters, and WMAP scientists observed it close to the centers of galaxy clusters.

    But the Durham team found the effect extended over a much larger area than previously detected — nearly one degree away from cluster centers. "If the galaxy clusters located several billion light-years from Earth also have the same effect, then we must consider whether it is necessary to modify our interpretation of the satellite maps of the microwave background radiation," Shanks says.

    The signature for both dark energy and dark matter lies in subtle ripples in the microwave background, tiny temperature variations imprinted on the universe when it was a thousand times smaller than it is today.

    "Our results may ultimately undermine the belief that the universe is dominated by an elusive cold dark matter particle and the even more enigmatic dark energy," Shanks explains. Both features appear in the models currently favored by cosmologists, but they introduce significant complications and, Shanks adds, constitute "undiscovered physics" because to date, neither one has been detected in the laboratory.

    A recurrent theme of the post-WMAP era is that such precision results may spell the end of cosmology. That end, Shanks suggests, may be greatly exaggerated.
     
    Last edited: Feb 29, 2004
  8. Feb 29, 2004 #7

    marcus

    User Avatar
    Science Advisor
    Gold Member
    2015 Award
    Dearly Missed

    I have to remark on another "PF click"
    Nereid says:
    ----------
    Oh, and almost lost in this is something quite nice - the SZ (Sunyaev-Zel'dovich) effect has been detected! And we may soon have another handle on (super)cluster masses, primordial intergalactic gas, distribution of dark matter in (super)clusters, ....
    -----------

    and then Wolram chimes in with:
    -----------

    http://astro.uchicago.edu/SZE/primer.html

    The Sunyaev-Zel'dovich Effect (SZE) is a signature left in the cosmic microwave background (CMB) by collapsed structures containing baryons. This signature results from inverse Compton interactions between hot electrons in the collapsed structures and the low energy photons in the CMB. These interactions drive the population of electrons and photons toward equilibrium, resulting in a net transfer of energy from the electrons to the photons. In galaxy clusters the typical optical depth to Compton scattering is ~1%, so only 1 out of every 100 CMB photons that passes through the cluster suffers from these interactions. Therefore, rather than driving the electron and CMB photon populations all the way to equilibrium, the SZE results in a small distortion of the CMB spectrum.

    --------------------

    And the effect for me is very educational, all of a sudden I know
    (and anyone else following the thread knows) some very interesting new things.

    It's called synergy I guess (an ancient buzzword from Bucky Fuller days) you have to have both nereids post and wolrams post and you mix them and you suddenly are aware of the SZE

    the beautiful thing is in 1900 Planck saw this thermal spectrum curve in the glow of a hot object----how the amount of energy in each wavelength is distributed in a lopsided bellcurve just so.
    a mound that sags off to the left a little as if by gravity.
    and sometime around 1990 the Cobe satellite found tht CMB was
    exactly following that thermal spectrum curve as if it was the glow
    of an object at 2.7 kelvin
    and the fit was very very exact out to like 4 decimal places

    so in 1900 planck found the formula of a curve
    and in 1990 his greatgrandchildren saw that the oldest glow in the universe exactly fits that formula

    and then in 2004 they said wait not it doesnt
    in certain directions of the sky where there is a heavy bunch of material
    we see that about one percent of the CMB photons have been given
    a small extra shot of energy
    so in the high energy tail of the thermal spectrum there is
    a little bit more than planck's formula says

    its this thing about measuring very accurately so you can discover
    a very fine deviation from an otherwise close fit---they are always doing this

    And where is this extra kick of energy coming from that effects one percent of the CMB photons coming from these particular patches of sky?

    well in 1923 arthur holly compton noticed that when you shine a ray of photons (in his case the light was Xray) at some material
    there is a small fraction of the light which actually interacts with the electrons in the atoms
    it bounces off them and gives them a little kick of energy and looses the same amount
    so a small fraction of the light gets drained slightly
    by a collision or "scattering" process

    and in physics almost everything is reversible (at least at a microscopic level) so you can have a
    REVERSE compton process where a very hot bunch of electrons
    hit a small fraction of the photons passing thru
    and give some of the photons little shots of energy

    the transfer of energy can go from the electrons to the photons (backwards from what compton observed in 1923)

    and in 2004 according to what Nereid and Wolram say
    (which I did not know) they actually observed that tiny fraction of slightly heated up microwave background light
    as a deviation from the planck thermal radiation curve

    please correct me if I am wrong.

    if this is right then what I especially like is the connection
    of 1900 and 1923 and COBE circa 1990 and 2004
    it makes me feel proud of my species
     
    Last edited: Feb 29, 2004
  9. Feb 29, 2004 #8

    wolram

    User Avatar
    Gold Member

    BY Nereid.


    So what you're seeing in this paper (which is a quite nice one, BTW) is a normal part of science, with some researchers taking the first year's WMAP results and doing a different analysis on them than those working directly on the project.
    --------------------------------------------------------------------
    this is what i meant by "manipulating the numbers", maybe i should
    ask, how many ways can they be interpreted, and if any whos method
    is best?
     
  10. Feb 29, 2004 #9

    wolram

    User Avatar
    Gold Member

    MARCUS, if anyone is interested i found this in WIKIPEDIA
    ----------------------------------------------------------------------
    This radiation is regarded as the best available evidence of the Big Bang (BB) theory and its discovery in the mid-1960s marked the end of general interest for alternatives such as the steady state theory. The CMR gives a snapshot of the Universe when, according to standard cosmology, the temperature dropped enough to allow electrons and protons to form hydrogen atoms, thus making the universe transparent to radiation. When it originated some 300,000 years after the Big Bang -- this point in time is generally known as the "last scattering surface" -- the temperature of the Universe was about 6000 K. Since then it has dropped because of the expansion of the Universe, which cools radiation inversely proportional to the fourth power of the Universe's scale length.


    Features
    One of the microwave background's most salient features is a high degree of isotropy. There are some anisotropies, the most pronounced of which is the dipole anisotropy at a level of about 10-4 at a scale of 180 degrees of arc. It is due to the motion of the observer against the CBR, which is some 700 km/s for the Earth.

    Much smaller variations due to external physics also exist; the Sunyaev-Zel'dovic-Effect is one of the major factors here, in which an cloud of plasma scatters the radiation. The phenonomena that radiant cosmic microwave background radiation (CMB) interacting with the dirac sea of "electron" clouds distorts the spectrum of the radiation (analogous to the Compton effect via the photon).

    Even more interesting are anisotropies at a level of roughly 1/100000 and on a scale of a few arc minutes. Those very small variations correspond to the density fluctuations at the last scattering surface and give valuable information about the seeds for the large scale structures we observe now. These density fluctations arise because different parts of the universe are not in contact with each other.

    In addition, the Sachs-Wolfe effect causes photons from the Cosmic microwave background to be gravitationally redshifted. These small-scale variations give observational constraints on the properties of universe, and are therefore one important test for cosmological models.


    Detection, Prediction and Discovery
    The CBR was predicted by George Gamow, Ralph Alpher, and Robert Hermann in the 1940s and was accidentally discovered in 1964 by Penzias and Wilson, who received a Nobel Prize for this discovery. The CBR had, however, been detected and its temperature deduced in 1941, seven years before Gamow's prediction. Based on the study of narrow absorption line features in the spectra of stars, the astronomer Andrew McKellar wrote: "It can be calculated that the 'rotational' temperature of interstellar space is 2 K."

    Because water absorbs microwave radiation, a fact that is used to build microwave ovens, it is rather difficult to observe the CMB with ground-based instruments. CMB research therefore makes increasing use of air and space-borne experiments.


    Experiments
    Of these experiments, the Cosmic Background Explorer (COBE) satellite that was flown in 1989-1996 is probably the most famous and which made the first detection of the large scale anisotropies (other than the dipole). In June 2001, NASA launched a second CBR space mission, WMAP, to make detailed measurements of the anisotropies over the full sky. Results from this mission provide a detailed measurement of the angular power spectrum down to degree scales, giving detailed constraints on various cosmological parameters. The results are broadly consistent with those expected from cosmic inflation as well as various other competing theories, and are available in detail at NASA's data center for Cosmic Microwave Background (CMB) [ed. see lin

    A third space mission, Planck, is to be launched in 2007. Unlike the previous two space missions, Planck is a collaboration between NASA and ESA (the European Space Agency).


    CBR and Non-Standard Cosmologies
    During the mid-1990's, the lack of detection of anisotropies in the CBR led to some interest in nonstandard cosmologies (such as plasma cosmology) mostly as a backup in case detectors failed to find anisotropy in the CBR. The discovery of these anisotropies combined with a large amount of new data coming in has greatly reduced interest in these alternative theories.

    Some supporters of non-standard cosmology argue that the primodorial background radiation is uniform (which is inconsistent with the big bang) and that the variations in the CBR are due to the Sunyaev-Zel'dovich effect mentioned above (among other effects).
     
  11. Feb 29, 2004 #10

    Nereid

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Oh my goodness The number of ways to take data, analyse it, and publish it is probably close to infinite, in the sense of ordinary human understanding!

    But it's not so sinister as it sounds.

    First, the data (let's talk about just the CMB):
    - how many photons in the (waveband) per second arrive from an x' (or y") circle centred on ([tex]\alpha, \delta[/tex])? That's pretty unambiguous, and there are multiple sources, for different wavebands and x (y). The major advance that WMAP brought us, over COBE and even BOOMERANG, is the resolution - minutes of arc rather than degrees.
    - how many of these photons are from Milky Way 'contamination'? Well, first the sources and nature of 'contamination' need to be understood - and they're a fascinating study in their own right - and there can be real disagreement over this. How important is it? For all CMB studies, very. How much room is there for reasonable disagreement, esp in WMAP? Not much.
    - next, what are the differences between the observed number of photons per second and a dipole CMB? In other words, if the CMB is a blackbody with a dipole (which is interpreted as the motion of the Milky Way/Local Group towards the Great Attractor) and the really interesting parts, how to 'remove' the blackbody and dipole? First, the WMAP satellite is moving wrt the solar barycentre, and that motion is well characterised (so little disagreement on that correction). Next, the blackbody temperature and dipole (location of hot and cold poles, 'speed' of local motion) are well studied and not much room for disagreement.
    - this gives us a map of deviations, i.e. numbers for each y" circle on the 4[tex]\pi[/tex] sphere
    - oh, I forgot one step; photons per y" in waveband A is the result of a 'pipeline' - the inputs are signal strengths from instruments at times t ... the outputs are photons per second per y" in waveband A. Room for disagreement? Sometimes, but this part of the work is almost always done very well these days, by 'engineers', the unsung heros of modern science. In the case of the HST, the historical data is further processed years after it was first recorded, by teams who examine the physics of the instruments in great detail, based on poking and prodding the instruments returned from the HST by Shuttle astronauts
    - now, after a great deal of work, we're ready for the 'real' science!

    [to be continued]
     
  12. Feb 29, 2004 #11

    Nereid

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    You're pretty much right marcus (any deltas would be mere quibbles). And it goes much further ...

    First, how do the 100 GeV-1 TeV (and up?) gammas observed by CANGAROO (etc) arise? Well, a leading source is inverse Compton scattering by relativistic electrons (much more than 'very hot') off the CMB! (I might add that if you visit Theory Development, you'll see that quite a number of ideas put forward would have a tough time explaining the inverse Compton effect).

    Next, what is the most perfect blackbody we've observed (including all lab experiments)? You guessed, the surface of last scattering, the CMB!

    Finally, how about going all the way back to Plato? One way to describe the SZE is to say it's a 'shadow' of (ionised) gas in the gravitational well of a (super)cluster.

    Oh, and BTW, at least one of the papers linked on the WMAP site does mention the SZE (and the paper which wolfram gave a link too discusses this too), saying that it likely can be seen in the direction of the Coma cluster, at the 2.5[tex]\sigma[/tex] level.
     
  13. Feb 29, 2004 #12
    DOn't know if this will be interesting (as I never heard before about the magnetic Sunyaev-Zeldovich effect), but just appeared today in arxiv
    "Magnetic Sunyaev-Zeldovich effect in galaxy clusters"
    http://arxiv.org/abs/astro-ph/0402669
     
  14. Mar 1, 2004 #13

    wolram

    User Avatar
    Gold Member

    a bit of topic but i thought this interesting, its one of the
    things that fired my interest way back.
    ----------------------------------------------------------------------
    searching for the BB.
    ---------------------
    Arno Penzias and Robert Wilson were puzzled. The two scientists at Bell Labs in Holmdel, New Jersey, had ruled out everything they could think of that could create the static their satellite communications antenna was picking up. Pigeons had taken to roosting in the radio antenna's large horn. They thought that perhaps heat from pigeon droppings was the cause.

    They set out a trap to catch the pigeons, but that didn't resolve the mystery either. No matter where in the sky they pointed their radio antenna, they kept picking up that faint, persistent hiss.

    Their determination in 1964 that the entire sky seemed to be dimly glowing with radio light confirmed physicists' predictions and later earned Penzias and Wilson a Nobel Prize. The two scientists had, quite by accident, discovered the fading flash from the big bang.

    im sure not a single pigeon was harmed.
     
    Last edited: Mar 1, 2004
  15. Mar 1, 2004 #14

    wolram

    User Avatar
    Gold Member

    the thing I'm not sure about is the margin in the numbers,
    one number will give dark energy, another will disprove it,
    i wont go as far as one paper mentioned, "that no dark
    energy will be the end of cosmology", or words to that
    effect, but it has me thinking how will research continue
    without it ??
     
  16. Mar 2, 2004 #15

    Nereid

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    If you've had a chance to take a look at the diagrams with the confidence limit (CL) regions shaded in, you'll get a quick idea of what the formal margins are from one analysis. I doubt whether any paper could present CL regions that are significantly smaller.

    If you have time, it would also be helpful to bone up a bit on just what a 'CL of 95%' means (and what it doesn't mean!)

    I'll be returning to dark energy and observations later, when I have more time.
     
  17. Mar 4, 2004 #16

    wolram

    User Avatar
    Gold Member

    by NEREID>
    If you've had a chance to take a look at the diagrams with the confidence limit (CL) regions shaded in, you'll get a quick idea of what the formal margins are from one analysis. I doubt whether any paper could present CL regions that are significantly smaller.

    If you have time, it would also be helpful to bone up a bit on just what a 'CL of 95%' means (and what it doesn't mean!)

    I'll be returning to dark energy and observations later, when I have more time.
    --------------------------------------------------------------------
    i know i am a bonehead, but people of science may not understand
    that little if any interest is shown for this subject by the
    general population, they are more into soaps and football and have
    a very short attention span for anything like dark energy, its sad
    but true, can anything be done to capture the public attention?
    well maybe dark energy is to unintuitive to bring up in conversation
    until its "ghostly" character is resolved.
     
  18. Mar 5, 2004 #17

    Nereid

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    IMHO, wolfram, you have no cause to be so harsh to yourself - you ask good questions, you are persistent, and are not easily dissuaded by arguments based purely on authority, and more.

    How to excite Joe Sixpack (and Joan CabSav)? Get them interested in the awesome splendor of life on Mars, or the Dark Force (aka dark energy)? This is surely worthy of a subforum in its own right, and I know that marcus, wolfram and Nereid (at least) have briefly discussed this before. Maybe SelfAdjoint would consider adding a subforum in Mkaku? I feel such discussions would be out of place in GA&C.
     
  19. Mar 5, 2004 #18

    selfAdjoint

    User Avatar
    Staff Emeritus
    Gold Member
    Dearly Missed

    Great idea Neried. I'll do it!
     
  20. Mar 6, 2004 #19

    Nereid

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    IMHO, there's still quite a 'large margin in the numbers' for dark energy, [tex]\Lambda[/tex], dark matter of different kinds, topological defects, and much, much more. :smile:

    Sometimes the early understanding of a set of observations turns out to be 'right'. For example:
    - Hubble's distance-redshift (if his paper had been submitted today, it would surely have failed peer-review, the signal was so poor)
    - quasars as being cosmologically distant (it took several decades to get multiple sets of independent corroboration, and to finally rule out serious alternatives)

    ... and sometimes it doesn't.

    [later]
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: WMAP data
  1. WMAP two-year data? (Replies: 10)

  2. New WMAP data released (Replies: 1)

  3. Wmap and razors (Replies: 6)

  4. WMAP and big crunch (Replies: 1)

Loading...