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"Dark Flow" Outside Observable Universe
Posted by
samzenpus
on Wed Sep 24, 2008 12:47 AM
from the here-comes-galactus dept.
from the here-comes-galactus dept.
DynaSoar writes "NASA astrophysicists have discovered what they claim is something outside the observable universe exerting an effect on the observable. The material is pulling clusters of galaxies towards a region of space known not to contain sufficient matter to create the effect. They can only speculate on what the material is and how space might differ there: 'In these regions, space-time might be very different, and likely doesn't contain stars and galaxies (which only formed because of the particular density pattern of mass in our bubble). It could include giant, massive structures much larger than anything in our own observable universe. These structures are what researchers suspect are tugging on the galaxy clusters, causing the dark flow.'"
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Great! (Score:4, Funny)
Re:Great! (Score:5, Funny)
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Re:Great! (Score:5, Insightful)
i think it's kinda cool. the idea that there are even more massive structures out there than what's in our observable universe is really quite mind-boggling. but without stars and galaxies i wonder what kind of emergent structures or phenomena could exist beyond our observable bubble.
i'm guessing it's probably not possible for biological life to form in such a radically different environment, but then again maybe i just lack the imagination to conceive of such possibilities. it seems like within our observable universe for any biological life to evolve it must follow certain patterns dictated by the laws of physics/chemistry. but if space-time in these regions is so different from our observable universe then who knows? our level of consciousness compared to what exists out there might be like comparing an amoeba with a blue whale. even the time scales experienced by other life forms could be drastically different from ours. entire civilizations could spring forth and flicker out of existence all in the blink of an eye.
but since we can't even observe what is out there maybe this is all pointless speculation.
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Re:Great! (Score:4, Interesting)
I would agree that if there is life, it is certainly not life as we know it.
But IMO the fundamental thing needed for life is an energy flow. Possibly you also need a state of matter corresponding to what we regard as solid i.e. one in which components tend to stay put without needing to expend energy. Given those two components, and enough time, I think that something that we could tentatively call life will emerge, occasionally, anywhere. How long it will take to get past the bacterial level is a much more complex question.
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Re:Great! (Score:5, Insightful)
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Re:Great! (Score:5, Insightful)
It's contradictory anyway. If we're seeing something influenced by it, then we ARE observing it. That's what observation MEAN.
If you're "watching" something, you're really interpreting electrical signals generated by your retina in response to chemical reactions triggered by photons, nothing "direct" about it whatsoever.
So saying we're seeing something being influenced by something outside the observable universe is nonsense.
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I think you're misinterpreting... (Score:5, Informative)
the word "observable". AFAIUI, in this case it means directly observable. Given an expanding universe -- since nothing can travel faster than light (and c is finite) and the universe has a finite age there is a limit to how far you can "see" in any direction from any given vantage point (see "horizon problem"). However, you might still be able to see an object at the very edge of "your" observable universe being influenced by something beyond your particular observation horizon -- that is, you can tell that it is being influenced by something and that it's not being influenced by something inside horizon. So essentially very talking about indirect observation here.
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Re:I think you're misinterpreting... (Score:4, Informative)
That is wrong I am afraid.
Nothing and that includes information can travel above the speed of light neither directly nor indirectly.
Yes, it it possible for something at the edge of our observable universe to be affected by something outside our observable universe right now.
But we do not (and cannot) observe what happens at the edge right now, but rather when light left that place heading in our direction a very long time ago.
So in effect we are seeing what happened at the edge in the past. This also means that the light from anything capable of affecting that part of the universe at that time would also by now had time to reach us and so we would be able to see it.
The summary is (as usual) a bit misleading.
What the article is suggesting is not that something outside the observable universe is affecting something else inside it right now and that we can see the effect but not the cause, but rather that something influenced a part of the universe around the time of the great inflation shortly after the big bang.
At that time those parts of the universe would have been close enough together that they could have affected each other. The inflation stage which was an extremely fast expansion of time and space itself has since moved some parts (in fact probably most of it) outside our observable universe so we cannot see this part.
What they see is something having a great speed due to an earlier influence by something we cannot see now, not that it is still being accelerated because that would have been a violation of the speed of light.
I hope I am not to unclear on this but English is not my first language so I find it a bit hard to explain any clearer.
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Re:I think you're misinterpreting... (Score:5, Informative)
Yes, it would. Gravity works at lightspeed also, so any gravitic effect on an observable object must be detectable at the observer, making the influencing object "observable".
Likewise, any other effect that we know of, all of which are limited to lightspeed. The only way that something outside the observable universe could affect something inside the observable universe and be seen by something else inside the observable universe is if the laws of physics that we know and love are basically a steaming pile of horse apples.
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Re:I think you're misinterpreting... (Score:4, Informative)
Because gravity works at the speed of light.
If gravity from B left there at some time in the past, and reached A, it then continued past A toward O.
Light from A went from A to O.
Light and gravity move at the same speed, so, the light from A reaches us at the same time as the gravity from B.
Therefore, B is within the "observable universe".
In order for the above to not work, some part of the process above must include "faster than light". Which, so far as current physics is concerned, isn't part of the picture.
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Re:I think you're misinterpreting... (Score:4, Informative)
Both of those are assumptions. If they were true, there wouldn't be a logical explaination for tachyons.
Who cares if there's a logical explanation for tachyons, since we don't have evidence for any?
Anyway, even if tachyons existed you'd never actually observe anything traveling faster than light; see this FAQ [ucr.edu].
In other dimensions things DO move faster then light.
Says who? In any relativistic quantum field theory or string theory, c is the limit in any dimension.
Furthermore, the speed of gravity is much greater then c.
van Flandern's website is a bunch of crackpot nonsense. He was pretty notorious on Usenet for years. He misapplies perturbation theory; if you apply his same arguments to electromagnetism, you "conclude" that light travels faster than light too (see here [arxiv.org]). In fact, you can rigorously prove in general relativity that the speed of gravity cannot exceed c (see here [arxiv.org], assuming that the gravitational waves aren't produced by weird things like negative mass). The 1993 Nobel prize in physics was awarded, in part, for an observational determination of the speed of gravity. (You can deduce it by the rate at which gravitational energy is radiated by orbiting bodies.) The measurements indicate that the speed of gravity is c, to within a few percent accuracy.
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Re:Great! (Score:4, Insightful)
Humans are insignificant for the terms of the universe, but we at least strive to understand it.
We haven't yet fully understood the universe, and even if we do it's so large that it's hard to fathom the span of it.
And did the universe really exist before the big bang or was it created by the big bang? How can one prove something that is hypothetical if we don't have something to measure it against?
Anyway - it is possible that what attracts matter is nothing more than an inert part of matter - or more specific a black hole that currently is invisible because it has consumed all matter near itself a long time ago.
The Big Bang wasn't a "perfect" explosion, and if it had been we wouldn't have had the distribution of galaxies that we have - it would have been a cloud of gas. And since we haven't had a perfect explosion it is possible that the black hole was created at a very early stage of our universe.
But who knows in reality?
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I'm no astronomer (Score:5, Funny)
But I'd say if lots of really big things are being affected, then there could be a bigger thing out there.
It's a theory I know. I'd like to call it Cen's Big Fucking Thing theory, it's a big ball of stuff, chairs, signs, tanks, gravel and so on, literally sucking the universe dry of interesting stuff. A universal suck, maybe even a multiversal suck mechanism. Either way, I'm pretty sure we'll not see it coming.
Re: (Score:3, Funny)
Flimflammery (Score:5, Insightful)
Dark matter to me has always smacked of a Victorian Era flimflam artist talking about the aether. And I don't care how dapper Mortimer T. Snerd is dressed, I'm not drinking his dark matter kool-aid until I can get a better explination for it than 'its invisible, supermassive, unobservable, and so totally there'. If you can't explain it to me, the interested layman, you may need to put your theory back in the crucible o' truth. Its probably not done yet.
Re:Flimflammery (Score:5, Interesting)
But I look forward to anything that seems to pin down the concept of 'dark matter'.
This new theory isn't an alternative to dark matter.
I'm not drinking his dark matter kool-aid until I can get a better explination for it than 'its invisible, supermassive, unobservable, and so totally there'.
You believe neutrinos exist, right? How hard is it to believe that there's something else like a neutrino out there, but heavier?
Dark matter-like particles have been predicted for decades. Within the Standard Model, there's the axion which is supposed to solve the strong CP problem in QCD. In the supersymmetric extension of the Standard Model, there is the neutralino. In fact, most theories beyond the Standard Model naturally require some heavy scalar particle which could be a dark matter candidate.
Modifying gravity doesn't appear to consistently explain all the gravitational behavior we observe. The other alternative is modifying the source of gravity, i.e. there's something out there we can't see for some reason. And that does account for the gravitational behavior we observe.
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Smelloscope (Score:4, Funny)
Gravity Leech (Score:5, Interesting)
The third episode of Brian Greene's "Elegant Universe" documentary miniseries on PBS said that while matter is confined to the known dimensions, its possible that gravity isn't and so can move through dimensions. The example they feel is that we could possibly detect the gravity of 'something' in another Universe by its gravity, even though we could never actually touch it. Wonder if this is it?
http://www.pbs.org/wgbh/nova/elegant/ [pbs.org]
In other news... (Score:5, Funny)
The Dark Matter in US is pulling a ball busting amount of money away from tax payers to Large Banks.
In this area of Universe known as Capitol Hill and White House, the normal laws of space-time continumm is suspended so that banks which screw up your money get your money to bail out themselves.
The plot thickens (Score:4, Interesting)
ermmm... (Score:4, Interesting)
Re:ermmm... (Score:4, Insightful)
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Re:ermmm... (Score:5, Insightful)
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Re:ermmm... (Score:4, Insightful)
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Re:ermmm... (Score:4, Informative)
Yes but by the time those other ships were able to report to you the ships that they see that you can't, you can see those other ships, too.
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Re:ermmm... (Score:5, Informative)
Imagine points A-B-C to be gravitationally bound. Because of metric expansion, space between A-B and B-C expands. This can cause A to move away from C at larger than lightspeed. Since space between B-C only expanded half of A--C, B will be withing light distance from C and thus visible by observers on C. Light from A can reach B, but it will never reach C. By the time it would, space between B and C will have expanded so much that observers from C will no longer see B.
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Preprint Versions of the Papers (Score:5, Informative)
More general version (ApJL)
http://xxx.lanl.gov/abs/0809.3734 [lanl.gov]
More technical version (ApJ)
http://xxx.lanl.gov/abs/0809.3733 [lanl.gov]
Re:Preprint Versions of the Papers (Score:4, Interesting)
Either I'm confused or the write up and author of the space.com article are just confusing. Granted, I'm not a physicist but it seems to me that the papers are saying something very different from the write up and the article say. Instead of some mysterious new force from outside the universe, the two papers are based on an analysis of the Cold Dark Matter theory which has been around for some time.
The article is also confusing when it talks about the "known universe." The Inflationary Theory of the origin of the universe says that early on in its existence, the universe underwent a drastically fast expansion. When physicists talk about the "observable universe," they are referring to the idea that Inflation caused parts of the universe to expand so rapidly that their light cannot reach us in the age of the universe. Now those regions are still part of our universe, we just can't see them because they are "over the horizon" so to speak like a ship on the ocean which disappears from view once it gets so far away from shore that the Earth curves away from our field of vision.
In fact this last point appears to be the most interesting part of the papers if I understand them correctly. The papers suggest that it is possible to peak over the horizon and get an idea of what the universe looks like beyond the limits of what we can see with our telescopes. Like the mast of a ship peaking out from the edge of the horizon, clusters of galaxies that we could not see otherwise can be detected by carefully measuring the effects of their gravity on regions of the universe that we can see.
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It's Obvious (Score:5, Funny)
I forgot to say..... (Score:5, Informative)
I'd intended to add this to the summary, but forgot.
TFA has a very nice, if brief, explication on the "universe" vs. "observable universe". Too many people (science and science writing pros among them) make assertions about the former when they should specify the latter.
Go ahead and read it, it's only a space.com article (ie. very short).
Doesn't make much sense to me (Score:5, Interesting)
Let's start with a recap of some statements that are true under current physical theories: (1) space itself is expanding (Hubble Expansion); (2) early in the history of the universe, the expansion of space was faster than the speed of light (Inflationary Big Bang theory); (3) nothing can exceed the speed of light, not even gravity or information (Special and General Relativity); and (4) we are confined our "observable universe": a bubble 92 billion light-years in diameter [wikipedia.org] (General Relativity plus Inflationary Big Bang theory — 13.7 billion light-years, plus inflation, plus 13.7 billion years of Hubble expansion).
Given these facts, neither gravity nor information from outside our observable universe can enter it.
Sure, parts of what we currently consider the observable universe might, in their own relativistic timeline, be "currently" experiencing a gravitational tug from parts of the universe that we can't currently observe, even in principle. However, if that is true, then either (a) such observable places will exit our field of observation before we observe that gravitational tug (i.e. the universe will expand faster than light), or (b) such unobservable places exerting a gravitational tug will enter our field of observation before we see the tug on things we can currently see (i.e. the universe will expand slower than light).
There's no way that information could take a roundabout path to us and arrive faster than information traveling in a straight line (or, more correctly in GR, a geodesic). Think about it: if light/gravity/information cannot travel directly to us, because the direct path is too long and too slow, how could it travel indirectly to us? The indirect path is, by definition, longer and slower than the direct path.
I suppose that, if a large mass was once observable but now is not (i.e. it tugged on some galaxies, then inflation happened), the theory in the article might make a certain amount of sense. But the timescale of inflation (fractions of a second after the Big Bang) doesn't really leave a lot of time for that to happen. It sounds much more plausible to my ears that either (a) there is a previously-undiscovered conglomeration of dark matter in that direction, but it still lies within our observable bubble; or (b) the galaxies in question are at high velocity but no longer accelerating, indicating leftover momentum from an ejection, collision, or some other high-energy event in the early universe.
OTOH, I'm no physicist, so maybe I'm missing something, or maybe the actual theory being promoted makes more sense than Space.com's rather awful writeup.
Re:Doesn't make much sense to me (Score:4, Informative)
You should read the abstracts of the articles, since it turns out you're right. From the abstract:
"This flow is difficult to explain by gravitational evolution within the framework of the concordance LCDM model and may be indicative of the tilt exerted across the entire current horizon by far-away pre-inflationary inhomogeneities."
They would, at least, find it less plausible to describe it with a huge mass of dark matter.
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Re:Since looking farther = further in time (Score:5, Informative)
Since no one reads TFA anyway, and since you clearly didn't:
The universe is thought to have formed about 13.7 billion years ago. So even if light started travelling toward us immediately after the Big Bang, the farthest it could ever get is 13.7 billion light-years in distance. There may be parts of the universe that are farther away (we can't know how big the whole universe is), but we can't see farther than light could travel over the entire age of the universe.
And then:
A theory called inflation posits that the universe we see is just a small bubble of space-time that got rapidly expanded after the Big Bang. There could be other parts of the cosmos beyond this bubble that we cannot see. In these regions, space-time might be very different, and likely doesn't contain stars and galaxies (which only formed because of the particular density pattern of mass in our bubble). It could include giant, massive structures much larger than anything in our own observable universe. These structures are what researchers suspect are tugging on the galaxy clusters, causing the dark flow.
Finally, on a side note, years of watching slashdot paid off in a truly interesting story!
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Are we alone? (Score:4, Funny)
Years of watching slashdot paid off in a truly interesting story
Yes and the editors missed the once-in-a-lifetime opportunity to run it under the heading "NASA SCIENTISTS DISCOVER GOD." Damn!
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Re:Are we alone? (Score:5, Funny)
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Re:Since looking farther = further in time (Score:5, Interesting)
What bugs me is that this "bubble" of the known universe really isn't a bubble at all, it's just the physical limit of our ability to observe; we have no means of determining the extent of this "bubble". Therefore, claiming that there could be "giant, massive structures much larger than anything in our own observable universe" just outside this bubble seems somewhat... convenient.
While I agree that this is one of the more interesting stories on slashdot in years, there are many aspects of contemporary cosmological theories that I remain highly skeptical of.
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Re:Since looking farther = further in time (Score:5, Informative)
And there are aspects of many contemporary theories (and lesser recognized works) that are equally skeptical of, and orthogonal to, each other. I personally don't know enough GR to talk confidently about why this is not exciting, but if it does turn out to be exciting, expect some very well written and insightful roundups here:
www.cosmicvariance.com
Small note: I have found Sean Carrol's [and team] work on the internet to be some of the most accessible stuff available from brilliant minds in science today. Of course, every time you read something dumbed down mathematically (even if only slightly), you end up hating yourself for not spending the time instead on understanding the 3 years worth of adv.math courses you need to really grasp what is happening. But the upside is that you can spend 15 minutes reading some well written summary by people like these, and end up getting a fairly good idea of the issue at hand all the same. Kudos to science "bloggers" (esp world-leading academics) everywhere. You make the internet suck a lot less.
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Re:Since looking farther = further in time (Score:4, Insightful)
If we are observing far-away galaxies being affected by the stuff too far away for us to observe directly, maybe we are observing the stuff outside our bubble indirectly? This visibility can be transitive?
Also, maybe we can also "observe" the stuff outside our bubble via the effects of "spooky action at a distance"?
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Re:Since looking farther = further in time (Score:4, Informative)
"Also, maybe we can also "observe" the stuff outside our bubble via the effects of "spooky action at a distance"?"
Well, then when we 'observe' this stuff, WE will have on our conscience whether the cat is dead or alive. :-)
But we still may never find out which one; which bubble^Wbox was/is in?
All joking aside, this is very interesting data to work with.
I can imagine a lot of theories to change/be scrapped/ be rewritten here in the near future.
I am really excited about this! (but somewhat befuddled-[I am not a physicist, much less an astrophysicist!]Astrophysics is a serious hobby for me) I hope some good info comes with further research.
That should open new 'doorways' and expand our understanding.
I don't think I can imagine all of the ramifications of this, but it strikes me as: 'Holy Cow, Batman...that cow lit her fart and flew over the moon!!!'
No doubt, this is the most exciting thing to happen with astrophysics (for me) in the past several years. The questions are ENDLESS!!!!!
Who knows 'what doors will open' for us, and the potential to find out what possible uses could arise from this.
P.S. I wish I knew enough to actually correctly answer your questions, but this news seems to sprout far more questions than can be accurately answered at this time.
Oh, and BTW, my head asplodes!!
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Re:Since looking farther = further in time (Score:5, Informative)
we have no means of determining the extent of this "bubble".
Effectively, we can: we can't see past the surface of last scattering where the cosmic microwave background radiation originates.
Therefore, claiming that there could be "giant, massive structures much larger than anything in our own observable universe" just outside this bubble seems somewhat... convenient.
Well, the chaotic inflationary theory has long predicted such structures should exist at all scales outside the observable universe. Anyway, we see matter near the boundary of the observable universe. There are almost certainly large structures outside the boundary too. We see some of that matter moving in a way it ordinarily wouldn't according to the usual cosmological expansion. It's not that big a leap to hypothesize that it's being pulled by something on the other side of what we can observe.
It's not a small leap, either — obviously it's hard to compile statistics on how these boundary clusters are moving, and thereby infer anything really solid about possible unseen gravitational sources. But it's not completely ad hoc. The explanation involves something that has been suggested by theory in the past for independent reasons, and observationally there don't appear to be any nearby sources of matter that could explain why the motion is so far from the Hubble flow. I suppose you could postulate a bunch of dark matter right near the boundary, but since (as you say) the cosmological horizon isn't some special physical place, but is just the region beyond which light hasn't reached us, that would be weird.
This should be taken with the usual grain of salt: it's a brand new paper and in a year or two could potentially be explained in a much more mundane way. I'd personally give it less than a 50% chance of being right. But it's not a priori ridiculous either. As another poster said, I hope that Cosmic Variance covers the result ... a real expert second opinion would be valuable.
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Here Be Dragons (Score:4, Insightful)
Therefore, claiming that there could be "giant, massive structures much larger than anything in our own observable universe" just outside this bubble seems somewhat... convenient.
"giant, massive structures much larger than anything in our own observable universe" is the new "here be dragons".
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Re:Since looking farther = further in time (Score:4, Funny)
by definition, expansion of space is Imperial, not metric.
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Re:The Universe goes on Forever (Score:5, Funny)
" If the known universe is expanding outward, that means that it has to have someplace to go, right?
Or am I just high right now?"
I'd say it's a little of both.
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Re:The Universe goes on Forever (Score:5, Insightful)
The bang wasn't an explosion in spacetime, it was an explosion of spacetime. The expansion of space just means that the metric which measures distance between two points that stay at the same location changes. As time passes, two points which stay at the same location on some hypothetical reference grid will first measure one foot apart, then two, then five, etc. They aren't going anywhere, they're being carried along on space itself.
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Re:which space? between galaxies or atoms? (Score:5, Informative)
What is happening is that the underlying geometry of space is expanding. Best estimate of the rate of expansion is something like 72 kilometres per second per megaparsec. So if two objects are one million parsecs apart (that's 3.26 million lightyears), then one second later they'll be one million parsecs and 72 kilometres apart.
In addition, objects in that space are free to move within it, and so if they are subject to mechanical forces they'll follow those forces just as normal. So atoms and apples are held together by their internal electromagnetism, and the Solar System by the gravitational attraction between the Sun and the planets. Objects like these drift along with cosmic expansion, but do not themselves expand.
It's only on the cosmic scale that the universal expansion becomes significant. Remember, we're talking kilometres per second per megaparsec - on such a huge scale, forces pulling objects together drop to tiny levels, while the expansion of space becomes greater and greater. The Andromeda Galaxy is only two-thirds of a megaparsec away, and so the cosmic expansion is small compared to the local motion of the galaxies - indeed, we're on a collision course with Andromeda. The largest known object in the Universe, the Great Wall, is maybe a hundred times more distant; on this scale, the cosmic expansion becomes significant. It's really the distance between galactic clusters and superclusters which is being expanded.
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Re:bah (Score:5, Insightful)
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Re:Wow, lets just add another hypothical entity (Score:5, Funny)
Seriously guys, the place is a red-taped bureaucracy waste. They're too busy running background checks on people in non-sensitive jobs to do research.
This just screams, "I got fired from my NASA cleaning job for using meth".
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Re:Does this imply FTL? (Score:4, Interesting)
True.
However the radius of the observable universe increases with time.
The time it took for light to travel from these distant galaxies should equal the additional time it will take for light from the cause of the movement to travel from the galaxies to us.
This means that if we can see the action we should also be able to see the cause.
Information cannot travel faster than light neither directly nor indirectly.
The only explanation I can see is that this speed (or flow) was caused by a gravitational tug that happened around the time of inflation.
But if this is the case we should not register any current (or rather at the time we see now light departed from the galaxies toward us) acceleration of these distant galaxies apart from what can be expected from the general expansion of the universe.
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Re:Punk science (Score:5, Funny)
You know, I've been wondering for a long time just exactly what is the secret ingredient in a tall, cool glass of Shut the Fuck Up.
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Re:insufficient data (Score:4, Insightful)
First, the region that these clusters are supposedly moving towards are pretty close to being in line with the heart of the Milky Way. What this means is that the attractor object may simply be obscured by our own galaxy.
It's not just the lack of an attractor object, it's the unusual velocities.
Second, the motion is not unusually large for superclusters.
They argue otherwise: "If produced by gravitational instability within the concordance LambdaCDM model, the motion would require the local Universe out to ~ 300h^1 Mpc to be atypical at the level of many standard deviations of the model", and argue that even a 100 km/sec motion due to local gravitation alone would be excluded by observations. I confess that I don't know enough cosmology to understand why. Either you expect smaller motions in the earlier universe or else there are additional constraints at work (they mention having to explain why the dipole is approximately constant with depth). I'd have to do more background reading to understand what's going on here, but the point is that they say they have reason to believe that the motion is unusually large.
What really bothers me here is the claim that these bodies are still experiencing forces from the long departed rest of the universe.
I don't think they are. From my reading of the paper, it sounds like this motion is left over from the inflationary phase.
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