"Dark Flow" Outside Observable Universe 583
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.'"
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!
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]
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).
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.
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.
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!!
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.
Re:Does this imply FTL? (Score:2, Informative)
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.
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.
Re:I think you're misinterpreting... (Score:2, Informative)
Would that object influencing the observed object not need to be inside your light cone for you to even observe the influencing that it is doing?
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.
Re:I think you're misinterpreting... (Score:3, Informative)
Your analogy is flawed, since speed of light does not play a role in it, while it does with this observable-object-influenced-by-object-outside-our-lightcone situation. For the information about the unobservable object to be able to travel to us, it must be within our lightcone, otherwise it would entail information travelling faster than light.
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.
Limit of knowledge (Score:1, Informative)
For my thoughts are not your thoughts, neither are your ways my ways, saith the LORD.
It's just more human arrogance to assume that what we can currently (or ever) observe constitutes the entire scope of existence. People laugh today at those who thought the earth was flat. Columbus thought he found the Indies. We've discovered that the solar system doesn't revolve around the earth and the galaxy doesn't revolve around the solar system. The reality is that our scientific observations are limited by our tools and our assumptions. Our imaginations are not so limited.
We can speculate all we want about what is "out there" and the effort to expand our knowledge and understanding of the world is a wonderful thing. I would just encourage those who feel it necessary to ridicule religion and/or faith to consider the idea that it is possible that our universe/universes are more complex and interesting than we could ever possibly comprehend. Not saying that we shouldn't try, just that you might want to consider the limits of our intelligence before deciding that the concept of God is such a silly idea.
Do I have 'proof'? Nope, but it is my contention that God is outside our ability to fully comprehend or observe. If God is truly the creator, and we consider the vastness, complexity, and beauty of our observable universe, I do not believe that that theory is really that much of a stretch.
Certainly no more so than "dark flows".
Re:Doesn't make much sense to me (Score:3, Informative)
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.
Yes, that's the idea here: the distant galaxies are still experiencing left-over motion due to a tug from matter long ago, which has by now expanded beyond our ability to see. This is a feature of the accelerating expansion due to inflation. Objects which were once within our causal horizon can be far, far away from it now. All we see is what effects remain from when they were near us.
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.
There was time for objects to gravitationally influence each other, if they were very close. Then they got blown far apart by the extremely rapid inflation. That's the whole point of inflationary theory: that objects used to be able to interact with each other (explaining the homogeneity and isotropy of the universe), but now they can't.
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;
The authors claim the velocity is too large to explain this way.
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.
They're too far apart to all be affected by a single cosmic event, unless it was in the very early universe when they were very close together (i.e., pre-inflation). That's what this theory proposes. The idea is that this all happened before there were galaxies or even atoms, just a plasma of high energy particles. During inflation some particles got tugged more in one direction than another if different regions of space were inflating at different rates, giving them a peculiar velocity relative to the average Hubble flow. After inflation, atoms, gas, stars, galaxies, etc. condensed from them, retaining the primordial peculiar velocity.
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.
Re:I think you're misinterpreting... (Score:3, Informative)
According to our current understanding of physics, the situation you describe can't actually occur. It is impossible for two pieces of matter to be moving apart at c. If we were moving at c/2 in one direction, RELATIVE to some piece of matter, and yet another piece of matter were moving at c/2 away from that reference matter in the opposite direction, that second piece of matter would be observed as moving away from us at 0.866c, and be well within our "observable universe".
Even if we assumed your case were valid, then we'd have to assume that the gravity from the object outside the observable universe (hereinafter the THING) could reach that far-flung galaxy (hereinafter, OVERTHERE), interact with it, and then the light from OVERTHERE could come here, and beat the light/gravity effects from the THING here, even though all of them (light/gravity from the THING, light/gravity from OVERTHERE) are moving at c. Can't happen unless something is moving ftl. In which case, we're back to using words like "quaint"....
The answer's simple (Score:1, Informative)
It's outside our observable universe and is large...it must be God
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.
Re:I think you're misinterpreting... (Score:2, Informative)
If we see an object A (which is by definition inside our light cone) being influenced by another object B that we cannot observe, B is in our lightcone, but just occluded, because if it were outside our lightcone, it could not possibly have been observed, directly or indirectly.
See the other branch [slashdot.org] of this thread.
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.
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.
Re:But distances CAN increase quicker (Score:3, Informative)
As someone else pointed out this is exactly what the article is talking about.
Something influenced these galaxies around the time of inflation to give them a very high speed. Since then inflation has moved that something outside our observable universe (or lightcone if you will).
But what I was answering to was the claim that someone somehow was able to see something being influenced by something else outside our observable universe. I fail to see how this could be correct even considering inflation or the continuous expansion of time-space itself.
BTW: The article does not actually claim that anything outside our observable universe is still affecting these galaxies, only that something must have done at some time.
The article says that these far away galaxies are being observed to have an unexplained velocity not an unexplained acceleration.
The cause and effect took place a long time ago and that part of space time is probably not inside our observable universe anymore.
Re:But... (Score:3, Informative)
There are huge comment threads here arguing over the same question.
The answer is that their gravitational fields do not now have any effect on our observable universe. They used to. Pre-inflation, they could gravitationally influence us, and we could see them too. (Or we could, except for the fact that the universe was opaque back then.) Now we can't, because they expanded too far away.
Stupid stalker (Score:3, Informative)
Is someone following me around modding my stuff overrated? I wouldn't have minded if they had actually modded the factual parent post to which I referred up, or the incorrect ancestor +5 post down. As it is, they're just hiding the truth.
CrimsonAvenger, modded at 2 (the parent in my MOD PARENT UP comment), has it completely right. Warrax, modded at 5 Informative, has it completely wrong.
"Information can't travel faster than the speed of light" means just what it says. The impossibility of detecting changes outside your light cone is transitive - you can't detect changes outside your light cone, not even in the form of detecting changes to an object inside your light cone caused by an object outside your light cone.
At least, per relativity, you can't. If you can, then relativity is wrong.
Re:Silly trend in science (Score:3, Informative)
Sounds like you don't quite understand the concept of a light cone [wikipedia.org]... Let me simplify your example and see if I understand you:
*Galaxy A is within the Milky Way's observable universe.
*Galaxy B is outside the Milky Way's observable universe, but it's within Galaxy A's observable universe.
You are suggesting that even though we can't see Galaxy B, Galaxy B is still acting upon Galaxy A, and that we are seeing its perturbations here on Earth.
However, that doesn't work in an expanding universe. If Galaxy B is already past our observation horizon and continuing to recede, we will never see its effects on Galaxy A from our vantage point in the Milky Way.
You can read more on this fascinating topic at http://en.wikipedia.org/wiki/Observable_universe [wikipedia.org], and it's far better written there than I could ever hope to personally explain.
Re:Great! (Score:3, Informative)
Re:ermmm... (Score:3, Informative)
Think of it like this: they *expect* to see a certain red-shift from something at 6 billion light-years: it is moving away from us, and the radiation that we receive from it is "red-shifted" by a well-known amount. What they are apparently seeing is *more red-shift than they expect* and the vector of this extra red-shift points toward a certain section of space. Thus, they are deducing that "something out there" is *pulling* that group of galaxies, and the only force (that we currently know of) that operates at that scale is gravity.
Scientists are looking out past that group of galaxies at 6 billion light-years to *as far as they can see* (13.7 billion light-years), but they are not finding enough *matter* there to account for the gravitational action of this cluster of galaxies at 6 billion light-years. So whatever is pulling the galaxies is *beyond* 13.7 light-years.
The problem is that we have assumed -- until now -- that *everything in the universe* is within our little bubble with a radius of 13.7 billion light-years. Now, apparently, we've discovered that *this is not the case*. Something ... else ... is out there.