Talk:Dark flow

Distance of Particle Horizon?

Someone who truly understands this topic needs to do a major cleanup I believe. Unless I'm missing something, the particle horizon listed as being at a distance of 46 billion light years is pure claptrap. The universe is 14 to 16 billion years old. Therefore nothing can be further away than say 16 billion light-years. Did someone mistype a 4 instead of a 1? — Preceding unsigned comment added by 84.75.50.123 (talk) 22:51, 29 October 2011 (UTC)

Because of the expansion of the universe, there are distance measures which give distances appearing larger than the distance light could have been travelled since the beginning. See here for example; http://www.astro.ucla.edu/~wright/CosmoCalc.html --134.76.205.137 (talk) 08:22, 22 March 2012 (UTC)

I'm wondering about the inability for telescopes to see anything later than 380,000 years after the big bang. That is a relatively small period of time in universal and earth terms, so does that mean that if humans had evolved 380,000 years sooner than they did, they would have been able to see the big bang with their telescopes (ie our current level of telescopy)??

Content of page

This is not really a comment about notability or verifiability, but this stuff is silly. There are no physical effects from objects outside the observable universe, which is why it is called the observable universe. Although there are a few papers which keep claiming that a hypothetical external "eternally inflating" universe has some statistical or physical effects, if you can't see stuff electromagnetically, it can't suddenly gravitate on to you either.Likebox (talk) 22:08, 23 September 2008 (UTC)

Ok--- after reading the link--- this effect can be rephrased to apply to a single observable patch. The statement they make is that there are observable velocity fields of galaxy clusters today, which they believe are relics of primordial gravitational interactions in the inflating universe. What this means is that they are postulating that there are fluctuations of local velocity in the inflating universe (which requires a modified view of what kind of stuff can fluctuate back then), and this statement can be phrased as "gravitation from objects that have moved out of causal contact", but only if you insist on being purposefully obscure.Likebox (talk) 22:21, 23 September 2008 (UTC)

Well, thanks for clarifying. I wasn't quite sure if gravity can interact beyond this "observable universe" border (even if I was sure before), to be honest, I understood it that way. I'm only an amateur in astrophysics ;) But this way it makes a bit more sense, if I have understood it right this time ;) ColdCase (talk) 23:12, 23 September 2008 (UTC)

I was thinking about this all night. It's interesting--- there is no reason in principle that a non-minimal inflation mechanism couldn't generate a bulk flow of matter during reheating. Maybe it even occurs in minimal inflation models with just a scalar. I don't understand the perturbation calculations well enough to know if they just ignore any velocity effects or if they calculate them to be small. The way the calculations are done, you just look for scalar fluctuations and turn them into energy variations. But the thermodynamics in a flat space time allows for momentum fluctuations, although in a DeSitter space the momentum fluctuations would be centered around the preferred momentum at any position, but you need to know the variance not just the mean.

The stuff about "gravitational attraction past the horizon" is just hyperbole--- that's the kind of stuff you say to get the press and the general public interested. It doesn't help understanding, it just makes the proposed effect sound more magical than it is. they have a model where there are large scale flows of matter after reheating, and that's an interesting new idea.

I don't know what the answer is, and I didn't read the papers. But I am curious to know what the bulk flows of reheated matter is after inflation ends. I don't think that question has been asked before.Likebox (talk) 18:46, 24 September 2008 (UTC)

Lay interpretation

I am not going to comment on the section above which uses terminology and frames of reference with which I am wholly unfamiliar. That said, my understanding of what I read is that this phenomenon evidences the existence of a physical universe of which our known, so-called "observable universe", is a part, which is on a scale at least one order of magnitude larger than the measurements of the observable universe. __meco (talk) 06:35, 26 September 2008 (UTC)

read Observable universe. WAS 4.250 (talk) 19:03, 26 September 2008 (UTC)

: The "edge" of the observable universe is at a different location depending upon your own location. Although the mass that these clusters are accelerating towards lies outiside of the observable universe (from our perspective) it is not outside of the limit of the observable universe from the perspective of those clusters. Indeed, for illustrative purposes only, those clusters could lie closer to their attractor than we do to them.

Still, since gravity moves with the speed of light (and not faster), it is impossible we are seeing (!) that anything outside the observable universe can drag on them. It may be currently so, but at the point at time we are observing them (which is about 6 billion years ago) nothing can pull on them what we can't see, because by definition we would be able to see it, if we see the reaction of it on something other we see. That's the defenition of the observable universe. As far as I understood it, something HAS pulled on them before the universe expanded faster than light (space time is the only thing that can expand faster than light), so it was inside the observable universe at that time, but than it moved outside the observable universe. Now we see the aftereffect of the pull on this galaxies. That's how I'm understanding this. ColdCase (talk) 02:04, 27 September 2008 (UTC)

Yeah--- that was the charitable interpretation I gave in an overly jargonny way above. But that picture is not quite right. Stuff only moves out of view while inflation is going on. During inflation, stuff falls onto the cosmological horizon. But the moment the universe starts expanding normally, the horizon moves away and stuff comes out of it. So the only time that gravitational interactions from "beyond the horizon" (meaning from matter which later disappears from view) could matter is during inflation.

So I think the right way to state this (hopefully in a clearer way than before) is that during inflation, there are fluctuations in the inflaton field. Then there's a period where the energy is dumped into regular matter (called reheating). During this phase, one should calculate the momentum fluctuations of the regular matter, to see if they are small.Likebox (talk) 05:58, 27 September 2008 (UTC)

Couldn't it be that it's somthing that is behind the "haze" from the time when the universe was opaque, since light couldn't go thru but there was nothing stopping gravity from propagating? --TiagoTiago (talk) 14:07, 29 November 2011 (UTC)

This article shouldn't have been written

It's a paper and a press release. It might be something or it might not. The way to find out is to wait. We don't go writing an article based on the press release and linking it on the breaking news page and rewriting observable universe as though everything had suddenly changed. Space.com is not a reliable source for information about cosmology, and press releases are never reliable no matter how respectable the institution they come from. Science does not work this way. I'm not going to nominate the article for deletion because I hate deleting things, but I do think it shouldn't have been written. -- BenRG (talk) 23:40, 27 September 2008 (UTC)

But other newsworthy topics get prompt articles--- why not science too? It can be deleted later if it turns out to be wrong.Likebox (talk) 04:37, 28 September 2008 (UTC)

I can not sympathize with the sentiment offered by BenRG. We are not a scientific journal. We are not a print encyclopedia. We are not bound to review events only after a community-wide consensus has formed (in this case the community being a scientific one) or some community-established threshhold has been reached (publication in a peer-reviewed journal for example). We are completely free to sample whatever stirs the noosphere as long as it can be referenced with reliable sources. And whether Space.com is a reliable source for information on cosmology or not is irrelevant. It's definitely a reliable source for reflecting what moves the noosphere in the scinetific community in question.

And a short comment on what to do if the theory is thoroughly discredited: We certainly need not delete it. We will simply keep it and categorize it as one of the many scientific hypothesies and theories that didn't make it. That's how we usually do that. __meco (talk) 07:01, 28 September 2008 (UTC)

This isn't newsworthy, is what I'm saying. A published paper is not as important as you guys seem to think. Papers are just how physicists describe their work to each other. Passing peer review doesn't mean the work is correct, it means it meets basic standards of good research. The next step (as the press release mentions) is to repeat the analysis on a larger data set. It becomes news when the error bars get smaller, when the papers start to accumulate citations, when people start revising the cosmological models. Right now it's just a statistical anomaly which could be a fluke or even an error in the analysis. The astronomical community isn't abuzz with the news; I can't even find a mention of the paper in a blog written by a professional astronomer. Nothing in Ned Wright's News of the Universe, nothing in Cosmic Variance, nothing in Bad Astronomy.

There's a huge disconnect between popular science reporting and real science. I wish it weren't so, but it is. Space.com gets its leads from press releases, not from astronomers, and what it reports is not what astronomers are thinking about but what its editors consider to have popular appeal. They reported on "dark flow" because it sounds cool. The actual science doesn't matter much; the important thing is that two-word phrases with the first word being "dark" are all the rage right now. And we seem to be guilty of the same thing. If the press release had described exactly the same research but without the words "dark flow," would we now have this article? What would it be called? Would it have reported the whole thing as though it were the new consensus of the experts, or would it have taken a more realistic view? I think that most likely we wouldn't have an article, just a brief and skeptical mention in Universe or Observable universe. That's the level of coverage I think this work merits at this stage, if we mention it at all. -- BenRG (talk) 14:23, 28 September 2008 (UTC)

I really appreciate the thorough and enlightening explanation you provide. It's something to consider, certainly. __meco (talk) 17:38, 28 September 2008 (UTC)

I think that BenRG might be missing the point. OK, it's true that the news media and serious professionals have different standards for what is "newsworthy", but the news media does consider this development newsworthy. I think Wikipedia should respect the media's decision, not belittle it, because it reflects what the mainstream public finds interesting. The fact that it is also science, and might one day merit a longer article on the data and methods and personalities, does not change that. I think its better not to include this in another general purpose article, because it is so strange and off topic.Likebox (talk) 19:25, 28 September 2008 (UTC)

Further, the term "dark flow" now has a designated meaning and can be said to either have evidence for it or not have evidence for it. If it turns out some mistake was made and there is no scientifically accepted evidence for dark flow at some time in the future, this article will have that added to it. So when someone talks about "dark flow" even if just to say "there is no dark flow", then peope can read all about it here. We have many articles about things that we now know do not exist. But in any case the current evidence is that dark flow exists. WAS 4.250 (talk) 20:18, 28 September 2008 (UTC)

Exactly. An example of an article on something we now know doesn't exist is planet X. We still have an article on it though, even though it's not real. YouthoNation (talk) 19:49, 29 September 2008 (UTC)

Ned Wright's News of the Universe now has an item on this saying that the methods used in the study are suspect. I trust his judgment, and I think this effect will probably turn out not to exist in the end. I don't think I've missed your point, but I think I have a different idea of what the point should be. I want to educate people about how science works, and one part of that is an understanding that science does not operate through press releases, and that there is no presumption of correctness for published peer-reviewed papers. I have a lot of respect for the press in principle, but I have no respect for "news" sources that don't employ anyone qualified to judge what's important in the area they claim to cover, and instead allow themselves to be manipulated by press releases. If press releases from science labs succeed in generating coverage then more of them will be written, and that could be enormously damaging to pure science in the long term. I don't think Wikipedia should be an accomplice to that, and usually it isn't. Even if you think it was appropriate to have an article, you should at least be bothered that we reported this effect as though it were an established fact. Even the authors' speculations about a possible cause were reported as fact. Look at the old version of the article, and at this edit to Observable universe, which is what brought me here. Okay, that was an anonymous editor, but I see this kind of thing a lot. Science doesn't work that way, and it worries me that so many people seem to think it does. -- BenRG (talk) 21:53, 29 September 2008 (UTC)

I think you are overreacting. Nobody here thought it was established fact (at least, I don't think any of them did), come on, it's one study a few months old. What people did do is get excited over a possibly important new discovery. Of course it might be nonsense. As for the edits you mentioned--- they got fixed, right? Maybe the authors of the study did that themselves. The media sometimes gets excited for mysterious reasons--- maybe it touches on some old point forgotten by specialists. It's always hard to tell why the media gets excited. What can you do? Just write about it (with careful caveats) and wait for more information.Likebox (talk) 22:58, 29 September 2008 (UTC)

Decay of Vector Perturbations in FRW cosmology

A grad student told me that there's an off-the-cuff reason to mistrust this type of thing. A cosmological momentum fluctuation is a vector perturbation, and he explained that the FRW solution suppresses these with a time dependent factor that is large. The (classical, but I didn't think of it) example he gave me is a hot gas of photons, with a random fluctuating momentum. The temperature of the gas goes down, and this is a photon-by-photon effect. I don't know what happens for slow moving massive stuff in FRW.Likebox (talk) 23:39, 16 December 2008 (UTC)

Dark Flow = Great Attractor?

Perhaps someone should compare this "recent find" with the Wiki page on the Great_Attractor. The area of space where this dark flow was discovered is the same area of space first reported in 1973. The Great Attractor appears to have been "rediscovered"!

NOTE: Placing a link in the "See Also" section may not be enough to explain this gross error on the part of the so-called "discoverers" of "Dark Flow".

97.103.58.89 (talk) 10:53, 25 January 2009 (UTC)Paine Ellsworth [email protected]

I compared both and found that they are both in the Centaurus region (although the Dark Flow article didn't mention distances), seeing as the "Great Attractor" is obscure enough for me not to of heard of it or seen it in most articles about Astronomy on WP (only found it one time in the Dark Energy section), it could be possible, but highly unlikely, that they have just never heard of it and neither had the press. But i don't think it is likely.GundamMerc (talk) 03:18, 20 February 2009 (UTC)

It is certainly possible, although it may as well be a coincidence; a "patch in the sky" is two-dimensional whereas space is 3d. From the Dark Flow article, it seems to me that the Dark Flow targets something "further out". Either way, it is not our "job" to decide on that - Wikipedia does not do original research. I think this Dark Flow thing is just one of those articles where we have to wait & see what happens, surely someone will tackle this discovery over time and either confirm or discredit it. -- Nils (talk) 05:19, 6 May 2009 (UTC)

The Great Attractor article mentions that it lies in the direction of Centaurus and Hydra. The Spacedaily article mentions the exact same directions for Dark Flow, I think this is more than enough coincidence to mention it. ykhan (talk) 22:19, 28 September 2010 (UTC)

Absurd new section not supported by sources

Okay, the new sections recently added to this article (The universe as a gravitational drainage basin, The location of the Great Attractor in a small closed universe) are fairly quirky and likely OR, but the latest (Why the universe's gravitational field is geocentric) is just absurd:

"By virtue of its being the summit of the universe's organized complexity, the Earth's biosphere is the absolute centre of the universe's quantum-gravitational potential (also known as the quantum potential) ... Therefore, the intensity of the universal dark flow is a function of mankind's informational progress."

The passage quoted from David Bohm clearly says nothing of the sort. Unless a reliable source is provided quickly to show that this is not just crackpot nonsense, I will remove it. Gandalf61 (talk) 10:59, 3 October 2010 (UTC)

I agree. --dab (𒁳) 20:23, 3 October 2010 (UTC)

2011 paper

I don't have time to add http://www.astro.auth.gr/~tsagas/Publications/Journals/PRD/PRD14.pdf in the text so I'm just going to put it in the references. Given the authorship and recent Nobel prize in physics, I think it's important enough for the introduction. Dualus (talk) 04:09, 9 October 2011 (UTC)

That had to be moved to the external links section for now. As soon as you have the time to use the link as an inline citation, that is when it can be seen in the References section. Thank you very much! – Paine Ellsworth ( CLIMAX )  23:35, 10 October 2011 (UTC)

Planck data

Should we perhaps mention lack of support from Planck data be mentioned in the opening section? at the moment it seems to lean too much towards "this is a confirmed as real thing".Geni (talk) 21:40, 3 June 2013 (UTC)

It is in the lead Bhny (talk) 21:48, 3 June 2013 (UTC)

ah right. How did I miss that?Geni (talk) 21:58, 3 June 2013 (UTC)

You were correct though that the rest of the lead made dark flow seem confirmed. I just made some more changes that I think makes it clearer Bhny (talk) 22:07, 3 June 2013 (UTC)

Thankyou. That looks good.Geni (talk) 22:51, 3 June 2013 (UTC)

Notability

There's already a section on whether this article should have been written. As I understand it the criterion for keeping an article is not whether it's factually correct, but also WP:NOTABILITY. Is the theory of "Dark Flow" notable? AadaamS (talk) 13:55, 29 August 2013 (UTC)

Yes, the concept of dark flow is notable. "If a topic has received significant coverage in reliable sources that are independent of the subject, it is presumed to be suitable for a stand-alone article or list" - it received significant coverage along with other current topics in books and documentaries about popular cosmology [1] and [2]. Whether dark flow actually exists is of course a different question: it seems increasingly unlikely here: [3]. --Cedders^tk 15:14, 19 December 2013 (UTC)

Planck data and Atrio-Barandela's paper

Is anyone disputing that Planck found no evidence for dark flow? The paper by Atrio-Barandela only seems to say that Planck data doesn't contradict WMAP data. Also we shouldn't be relying on a wp:primary arXiv source. If this paper is important it should have been written about somewhere. Bhny (talk) 23:51, 5 July 2014 (UTC)