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Dark flow

  1. Nov 7, 2008 #1

    wolram

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    http://www.sciencedaily.com/releases/2008/09/080923104410.htm

    ScienceDaily (Sep. 24, 2008) — Using data from NASA's Wilkinson Microwave Anisotropy Probe (WMAP), scientists have identified an unexpected motion in distant galaxy clusters. The cause, they suggest, is the gravitational attraction of matter that lies beyond the observable universe.

    The clusters show a small but measurable velocity that is independent of the universe's expansion and does not change as distances increase," says lead researcher Alexander Kashlinsky.
     
    Last edited: Nov 7, 2008
  2. jcsd
  3. Nov 7, 2008 #2

    wolram

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    Is this the first sign of a slippery balloon at extreme distance?
     
  4. Nov 7, 2008 #3
    Is this the first experimental sign for a pre-bigbang scenario, than it (might be)/is good news for both LQG bounce(s) and eventually also for also for stringtheories??!!

    Kind regards hurk4
     
  5. Nov 7, 2008 #4
    To me yet another sign of an already bankrupt model.
     
  6. Nov 7, 2008 #5

    mysearch

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    In the thread linked below, I have raised some questions regarding the scope of the accepted mainstream model of cosmology. Therefore, would be interested in the scope of differing opinions with respect to this model.
    https://www.physicsforums.com/showthread.php?t=269556
     
  7. Nov 7, 2008 #6

    wolram

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    I would say it is early to read to much into this yet, i thought it interesting rather than
    grand slam evidence of any thing.
     
  8. Nov 8, 2008 #7
    That will be exciting if they confirm it. Turns out the universe is not as homogenious as the simple LCDM model assumes it to be.
     
  9. Nov 8, 2008 #8
    The horizon is a long way out. So inverse square drop off in gravitation would detect how large of a mass 'beyond the horizon'? But how can one have an influence from beyond horizon? Even for our Local Group, if it's velocity in regards to CMB frame of reference is ~600 kms^-1, what mass would be required at what distance? Even the curvature from Virgo cluster is quite slight for our Local Group distance of ~50 Mlyrs.
     
  10. Nov 9, 2008 #9

    Chronos

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    The signal to noise ratio is not convincing.
     
  11. Nov 9, 2008 #10
    The FRW model, which is the basis for the LCDM model, assumes perfect not just approximate homogeneity. Once it is not perfect, extrapolations are suspect as we have no mathematical tools to predict the consequences of the introduced non-linearity. Current proponents of the model just intuititively believe that those non linear effects will magically cancel out. Experimental discrepancies are "explained" by introducing things like dark energy, dark matter, dark flows etc. They conveniently state that those dark things cannot be directly observed which makes it equivalent to posing that Angels or Pink Unicorns influence the distances of heavenly objects.
     
    Last edited: Nov 9, 2008
  12. Nov 9, 2008 #11

    marcus

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    You all might be interested in reading what Ned Wright had to say back in September about the two "Dark Flow" papers by Kashlinski et al. His note gives links to the papers
    http://www.astro.ucla.edu/~wright/dark-flow-errors.html
     
  13. Nov 10, 2008 #12
    Yes, Yes, and Yes again. To add to difficulties, it seems to me that almost everyone has now long forgotten how contrived is the resolution of the Horizon Problem, using The Inflationary Scenario (if Scenario is a still-accepted euphimism).

    As you say, Jennifer, the FLRW mode is the basis of LCDM cosmology. But the observed extent of homogeneity is glaringly incompatible with such cosmology --- that ]is the Horizon Problem. To resolve this impasse, then, one assumes that the observable universe was once only part of a homogeneous patch of a pre-inflationary universe. In this mad, unknowable universe the FRW model is thrown to the winds, seemingly without a thought, and replaced by what some folk happily postulate to be a multiverse seething with imhomogeneities that are conveniently now beyond our horizon ---- thanks to the inflationary device. This is where your Angels or Pink Unicorns come in, Jennifer, and is one reason why I cavil at writing about the consensus model as if it were dogma, Marcus.
     
  14. Nov 10, 2008 #13

    marcus

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    Have another look at my posts. I don't present consensus model as dogma. I have my own reservations about it (e.g. as one skeptical about inflation, I regularly report alternative solutions to horizon etc riddles---and I see no scientific reason to believe in the existence of a cosmological singularity since a onetime bounce model fits the data about equally well).

    Obviously everybody is free to think whatever they please about the universe, what I've been proposing is that we start off with a common minimal understanding of the standard mainstream picture. It makes communication a lot easier if everybody understands what they are deviating from. And what they are being skeptical about.

    You asked about inflation scenarios. AFAIK they are called scenarios to emphasize that they are not testable scientific theory---they solve some puzzles but in exchange present others---they have a certain mythical or speculative character at least for now. So they are called scenarios. Maybe ways to test and potentially rule out certain inflation schemes will be found, making them more like regular scientific theory.

    Jennifer referred to the absence of perfect homogeneity. I don't think this vitiates the FLWR. It can still be a damn good approximation, and enormously useful even with only approximate uniformity.

    If people are predisposed to utterly reject the standard model (rather than according provisional pragmatic partial acceptance) then they are likely to jump the gun when some news like Kashlinsky's "Dark Flow" comes out. Oh my! this shows how bankrupt the consensus model is! But I think it's probably wiser to wait before jumping, see Ned Wright's comment (I gave the link earlier.)

    How was the Indian Ocean?
     
    Last edited: Nov 10, 2008
  15. Nov 10, 2008 #14
    I support both comments. As to the Indian Ocean (at Umhlanga Rocks N. of Durban): Pretty good!
     
  16. Nov 11, 2008 #15

    Chronos

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    I concur with marcus. The Kashlinsky papers take considerable liberties with mainstream interpretations to draw extreme conclusions. Strangely enough, they rely on rigidly defined mainstream interpretations as their footings. I found this objectionable in their initial paper on this basis alone. Having now seen Ned Wright's comments, I am comfortable with my instincts on this one. I view it as a shotgun objection to mainstream physics - to wit, some underlying assumptions must at least be subtley flawed [or misinterpreted] to allow me to draw such a conclusion. I do not find that particularly shocking.
     
  17. Nov 11, 2008 #16
    If I understand this correctly, gravitational waves from the “unobservable” part of the Universe are thought to be causing the dark flow in the observable part. But, the reason given for one part of the Universe to be unobservable is that the distance is so great that light cannot reach us; it is over the horizon. In that case, how is it that gravity is reaching us, if gravity travels at the speed of light?
     
  18. Nov 11, 2008 #17

    marcus

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    It's basically a good question.

    There was a time when matter that is now too far to see
    was much closer to us
    And then the pull of that matter might have started us drifting in some direction and we just continued by inertia.

    If there is some lopsidedness, some unevenness in the distribution of matter, with some slight overdensity in some direction beyond our current horizon, well maybe we are not feeling that bunch of matter NOW but maybe it started us drifting back at a time when we did feel it.

    But be careful! The current dark flow proposal has been poo-pooed and given the brush-off. Ned Wright is a pretty good authority and he found mistakes in the Kashlinsky paper. He says don't trust it. My advice it would be good not to talk as if you believe Kashlinksky. Don't start assuming that it is real. I gather others of us agree.

    One thing to notice in any case is that the standard cosmo model is rather ROBUST in the sense that it can absorb some perturbations like this without being invalidated. George Ellis (an early collaborator of Hawking who is now a recognized cosmo expert) did an analysis back in 1998 of the robustness of the usual FLWR model. It is pretty tough and resilient. So if some future study does find evidence of some slight largescale inhomogeneity, and some slight drift, well this will be extremely interesting but probably will not change our basic outlook very much.

    ===========
    as a matter of vocabulary, when I hear people talking about "gravitational waves" they usually are talking about some little temporary ripples, not the overall steady pull. I agree with the idea that changes in the gravitational field travel at c, or no faster than light. I'm not being very clear about this, but I don't feel entirely comfortable with your phrasing your question in terms of gravitational waves. Maybe someone else will help clear this up. News doesnt travel faster than c. Information doesn't....I have to leave it here.
     
    Last edited: Nov 11, 2008
  19. Nov 11, 2008 #18

    mysearch

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    Schroder, your question raises some additional issues in my mind, which may be relevant to this thread. First, for clarification, I am assuming that the observable universe broadly aligns to the particle horizon associated with CMB decoupling. I believe this is estimated to be ~46 billion lightyears rather than the visible horizon at 13.7 billion lightyears?

    However, I would have thought, in a homogeneous model, that these horizons are subjective to the position of the observer. As such, if I could magically and instantly transport to position-X some 47 billion lightyears in distance, I would be beyond our observable horizon, so what would this part of the universe look like? As I understand it, the homogeneous model would suggest that it would be similar to what we see from our current position, although from position-X, our home galaxy would be beyond their observable horizon.

    o Therefore, I wouldn’t have thought that photons and gravity waves see our perception of a horizon as any form of a barrier. As such, couldn’t a remote galaxy within our observable universe be affected by structures that appear to be beyond our observable horizon, but within their subjective definition?

    o In a perfect homogeneous model, all galaxies would be at rest with CMB. The fact that galaxies exist suggests that gravitational `anomalies` do exist and, as an extreme example, I understand that `The Great Attractor` is believed to account for a peculiar velocity of some 700 km/s. If so, could some enormous gravitational source beyond our observable horizon not conceptually be the source of another peculiar velocity, which the original article cited in #1 has dubbed `dark flow` even withstanding Ned Wright’s cited errors?

    o Finally, as a general question, any thoughts on how many times I could repeat the conceptual jump of 46 billion lightyears, i.e. 46+46+46 etc, or does spatial geometry have something to say about this accumulating distance?​
     
  20. Nov 11, 2008 #19

    It seems you are describing some form of cascaded gravity. I had not thought of that, but it does seem possible.
     
  21. Nov 12, 2008 #20
    The homogeneous model (the FLRW model that relies on the cosmological principle) --- by itself --- can't explain homogeneity on a scale larger than halfway to our observable horizon, let alone to multiples of the horizon radius, because of the limited scale of causal contact inherent in the model. So even the observed scale of homogeneity is in conflict with the plain vanilla everywhere-isotropic model.

    To resolve this problem one must incorporate inflation into the mix of speculation, thus extending the scale of homogeneity out to at least twice beyond what is observable. And who knows what lies beyond this? Boundaries, topological defects and a broken model? Or sea-serpents?
     
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