Dark Flow

[Chris Peterson]

From what I understand, if you sit right at the edge of the observable Universe, you can see 13.4 Billion Light Years in any given direction. So if you are on the edge of the observable universe does this mean that you can see things which we will never see. If this is the case, then it is perfectly concievable that there is something on the outside of "OUR" observable universe which we cannot see that is pulling space objects towards it.

While it is true that every point in the Universe is the center of its own, unique observable universe, it isn't the case that we can see the effects of things outside our own observable universe on objects that we can see.

There is no need for dark flow (if it exists... there remains a good deal of uncertainty about that) to be caused by anything pulling on it. All we seem to be observing is motion, and that requires no forces. The motion could be residual, from long ago. For instance, an area of high mass could have attracted the material early in the Universe- material that is now outside the observable Universe but was not then.

[wonderboy]

Did my post get deleted

[bystander]

No, it's on the previous page (4).

[wonderboy]

my bad, i didnt realise this topic was that many pages long. So are you saying Chris that our observable universe is only 13.4 billion light years. so I'm here (me) -------------------------------13.4 billion light years ------------------------------ (edge of obs uni)

If i was here

In my crude scale above, If I was half way through inbetween the n (in billion) and the l (in light) my observable universe would not be 13.4 billion light years but 6.7 billion light years?

[Chris Peterson]

So are you saying Chris that our observable universe is only 13.4 billion light years.
so I'm here (me) -------------------------------13.4 billion light years ------------------------------ (edge of obs uni)

Basically, yes. You need to be a little careful with the units. The light you see from the edge of the observable universe was produced 13.4 billion years ago; that doesn't mean the current distance to the edge of the observable universe is 13.4 billion light years. The actual distance is several times greater, due to the expansion of space over that 13.4 billion years.

In my crude scale above, If I was half way through inbetween the n (in billion) and the l (in light) my observable universe would not be 13.4 billion light years but 6.7 billion light years?

No. Everybody has their own sphere of visible universe, with its edges defined by 13.4 billion year old light. So if you were halfway out, you'd see part of the Universe that can't be seen from here (and we'd see some that would be invisible to you). But we couldn't see the effect on you of that part of the Universe inside your observable sphere but outside ours.

[The Code]

There is no need for dark flow (if it exists... there remains a good deal of uncertainty about that) to be caused by anything pulling on it. All we seem to be observing is motion, and that requires no forces. The motion could be residual, from long ago. For instance, an area of high mass could have attracted the material early in the Universe- material that is now outside the observable Universe but was not then.

http://en.wikipedia.org/wiki/Dark_flow

6 billion light years, A Dark Flow that expansion had no effect on. If the flow was at the speed of light, how long to start flowing? but its not at the speed of light. much slower. so how long to form the flow? more than 13.7 billion years?

http://www.popsci.com/science/article/2 ... e-galaxies

The facts are there for all to read. Discounting it, will not make it go away Chris.

[Chris Peterson]

The facts are there for all to read. Discounting it, will not make it go away Chris.

What is it you think I'm discounting? The POPSCI article is badly written, so I'll let that one go. The Wikipedia article, however, seems like a good summary of current thinking, and I don't see that it differs very much from what I said.

To summarize: assuming the so-called dark flow represents anything other than an initial anisotropy in the primordial Universe (which may certainly be the case), it is best explained as motion induced by the force of gravity from a part of the Universe that is no longer in our observable universe, but once was (which is why we can see its effects). Interesting, but not something that necessarily changes our understanding of cosmology in any fundamental way.

[The Code]

To summarize: assuming the so-called dark flow represents anything other than an initial anisotropy in the primordial Universe (which may certainly be the case), it is best explained as motion induced by the force of gravity from a part of the Universe that is no longer in our observable universe, but once was (which is why we can see its effects). Interesting, but not something that necessarily changes our understanding of cosmology in any fundamental way.

Right, Gravity. Now we got the logistics out of the way. we can ask the big question. What object can pull 1400 clusters of galaxies 4 to 6 billion light years, other than a new type of critical mass black hole which really does form a singularity, and the reason we can not see it, is because it is no longer there. In the soup of the early universe, I can not see Millions of Black Holes. I can only see One. Formed by the concentration of Matter/Gas. And it must have been huge. Is this Dark Flow a remnant Of that?

[Chris Peterson]

Right, Gravity. Now we got the logistics out of the way. we can ask the big question. What object can pull 1400 clusters of galaxies 4 to 6 billion light years...

What makes you think anything was pulled 4 to 6 billion light years? There's no evidence at all suggesting how far any material has moved. The observation suggests that a grouping of galaxy clusters has a common velocity of about 600 km/s with respect to the CMB. That's all it suggests.

...other than a new type of critical mass black hole which really does form a singularity

I see no need to postulate some sort of new black hole type. Black holes aren't magic- they are simply gravitational sources. The most massive black holes known still mass less than a single galaxy. So a galaxy or galaxy cluster seems a much more likely gravitational source to have created some motion in one region of the Universe. This probably happened while the Universe was much younger, and regions were much closer together. This explains the relatively large velocity (because it was created when the attractive mass was much closer) as well as the absence of that mass in the observable universe today (it has moved beyond the horizon of what is observable from Earth).

[The Code]

This explains the relatively large velocity (because it was created when the attractive mass was much closer) as well as the absence of that mass in the observable universe today (it has moved beyond the horizon of what is observable from Earth).

The speed of light has, Would you say, a large velocity. Yet I can not see all the universe because of expansion. The speed of light was not fast enough to keep up. Yet this slower Dark Flow Escaped. Hows That?

[Chris Peterson]

The speed of light has, Would you say, a large velocity. Yet I can not see all the universe because of expansion. The speed of light was not fast enough to keep up. Yet this slower Dark Flow Escaped. Hows That?

Because it's moving at only a fraction of the speed of light (0.2%). It was never moving fast- it was just tugged on by something massive, which gave it a small common velocity with respect to the velocity we naturally see at that distance due to cosmological expansion. The thing that was tugging on it is simply in a part of the Universe that vanished over the horizon. Some material between what we can see and the now lost attractor certainly must be invisible to us now, as well. I don't see the problem.

BTW, we see these sorts of non-random motions in galaxy clusters everywhere. The only thing different about this one is that the attractive mass that the material is orbiting has moved outside the observable universe. Otherwise, there's nothing unusual here.

[neufer]

<<Dark Flow is a name given to a net motion of galaxy clusters with respect to the cosmic microwave background radiation which was found in a 2008 study. Analyzing the three-year WMAP data using the kinematic Sunyaev-Zel'dovich effect, the authors of the study found evidence of
a common motion of at least 600 km/s toward a 20-degree patch of sky
between the constellations of Centaurus and Vela.>>

Active galaxy Centaurus A is the pair of white radio jets just above the plane to the right of center:

The Vela Pulsar is the semi-detatched white radio blob along the plane somewhat further to the right of center

<<Vela is a constellation in the southern sky.
Its name is Latin for the sails of a ship, and it was originally part of a larger constellation,
the ship Argo Navis, which was later divided into three parts, the others being Carina & Puppis.>>

[list]The fair breeze blew, the white foam flew,
The furrow followed free;
We were the first that ever burst
Into that silent sea.[/list]

[wonderboy]

I mostly get this now, however what I don't understand is that I thought the universe was expanding and speeding up at the same time. So does that not mean that our sphere of observable universe is trundling along at the same speed therefore nothing could escape into the unobservable universe? I don't think there was a mass at one point within our universe then it escaped. there is a mass there, and its acting as a brake on the expansion of the universe, so it must be huge and more powerful than dark matter. It hasnt escaped our observable universe, its just always been outside it. I wonder what it is? Maybe its God? haha.

[wonderboy]

http://www.space.com/scienceastronomy/d ... 00326.html


Are these deformed galaxies what happens when you view a galaxy that is teetering on the edge of the observable universe? It must be.

[Chris Peterson]

Are these deformed galaxies what happens when you view a galaxy that is teetering on the edge of the observable universe? It must be.

The galaxies aren't actually distorted, they just appear so because they are so far away that the intervening matter deviates the light rays. Galaxies don't "teeter" on the edge of anything. If you were at those galaxies, they would be in the center of their own observable Universe, and it would be our position in the Universe that was very distant. Even so, these are still billions of light years from the edge of the observable Universe (as seen from here).

[Chris Peterson]

I mostly get this now, however what I don't understand is that I thought the universe was expanding and speeding up at the same time. So does that not mean that our sphere of observable universe is trundling along at the same speed therefore nothing could escape into the unobservable universe?

No. The farther away you get, the faster things are receding. So you reach a point where that speed is C, and that's where you stop being able to observe the Universe. There was a time when the entire Universe was causally connected; most of that Universe is now beyond our horizon. And material is still moving beyond our horizon.

I don't think there was a mass at one point within our universe then it escaped. there is a mass there, and its acting as a brake on the expansion of the universe, so it must be huge and more powerful than dark matter.

The mass of the Universe does act as a brake. But the "force" of cosmological expansion is stronger over large distances, which is why the Universe continues to expand. The "force" of dark energy increases even faster with distance, which is why the rate of expansion is increasing (that is, objects that are very distant are receding a little bit faster than you would expect if there was just a linear expansion of spacetime, as you would get with a truly constant Hubble constant).

[wonderboy]

I meant to strike out that full post because I did a bit of thinking and remembered that the universe is speeding up as it expands, and further and further away galaxies are actually moving away from us more quickly than those nearer to us. In saying that though. Surely the galaxies ("in front of us") are moving away from us more quickly than we can catch up, and some galaxies ("those behind us") must be getting more distant as we speed up? should we not be able to find in what direction we came from in the universe using that principle? or are we moving apart so slowly it would take millions of years?
obviously ages of galaxies could help as well. I have another idea brewing but im gonna try and refine it first, all together now ("not again!!!!" haha)




Just a quick question to add, does anyone have any idea at all in which way we are travelling through the cosmos? I wouldnt think so!

[Chris Peterson]

Surely the galaxies ("in front of us") are moving away from us more quickly than we can catch up, and some galaxies ("those behind us") must be getting more distant as we speed up? should we not be able to find in what direction we came from in the universe using that principle?

We aren't speeding up. We are the origin of our frame of reference. In a very real sense, we are at the center of the Universe and everything we see is expanding away from us. There is no preferential direction (although within our observable Universe, the motion isn't purely isotropic and random, so in a sense we can define a broader reference frame).

Just a quick question to add, does anyone have any idea at all in which way we are travelling through the cosmos?

Theory suggests that no point in the cosmos is moving with respect to the cosmos itself. You can only assess motion by comparing two points. Every point in the Universe is at the center of the Universe.

[neufer]

Way back in 1956, when I was ten, I bought a large war surplus horseshoe magnet formally used for radar. Among the many things one could do with this magnet was to hold it about a half foot away from a small metal toy car until it got started rolling really good and then pull the heavy magnet away as fast as one could while leaving the toy car still freely rolling along the floor at a constant speed.

Presumably, "God" played this very same trick on our universe with some large surplus gravitational object which he was able to rapidly pull away during the early inflationary expansion time period while leaving the matter in our universe still rolling along at a constant 600 km/s speed in the general direction of Centaurus/Vela.

Presumably, the microwave background is also moving in the same direction; however, relativistic time dilation makes the microwave background appear to be virtually stationary. The combination of the local motion vector of Local Group of Galaxies plus the overall motion vector of the universe at large results in the dipole pattern in the the microwave background radiation (warmer red in the direction of motion).

[Chris Peterson]

Presumably, the microwave background is also moving in the same direction; however, relativistic time dilation makes the microwave background appear to be virtually stationary.

I don't understand that comment. The CMB appears to be flying away from us at a good fraction of the speed of light. It is that large velocity that produces the huge redshift (z>1000) that has caused what started out as visible light photons to now have a wavelength of 1.9 mm. Of course, except for the high recessional velocities we infer from redshift measurements, everything in the Universe at cosmological distances appears stationary to us- which has nothing to do with relativistic mechanisms.

The combination of the local motion vector of Local Group of Galaxies plus the overall motion vector of the universe at large results in the dipole pattern in the the microwave background radiation (warmer red in the direction of motion).

I don't think any inference about the "overall motion vector of the universe" can be made from this data. I don't think there is even any accepted definition for the overall motion vector of the Universe.

[neufer]

Presumably, the microwave background is also moving in the same direction; however, relativistic time dilation makes the microwave background appear to be virtually stationary.

I don't understand that comment. The CMB appears to be flying away from us at a good fraction of the speed of light. It is that large velocity that produces the huge redshift (z>1000) that has caused what started out as visible light photons to now have a wavelength of 1.9 mm. Of course, except for the high recessional velocities we infer from redshift measurements, everything in the Universe at cosmological distances appears stationary to us- which has nothing to do with relativistic mechanisms.

The high recessional velocities we infer from redshift measurements caused primarily by relativistic time dilation:



By virtually stationary I am referring to the overall translation motion not the expansion motion.

In other words, the (presumably) 0.002c translation motion vector of the CBR
has virtually no effect on its 0.9999983c expansion motion vector.

The combination of the local motion vector of Local Group of Galaxies plus the overall motion vector of the universe at large results in the dipole pattern in the the microwave background radiation (warmer red in the direction of motion).

I don't think any inference about the "overall motion vector of the universe" can be made from this data. I don't think there is even any accepted definition for the overall motion vector of the Universe.

Our own motion vis-a-vis the bath of microwave radiation in which we are embedded is explicitly determined by the increase in CBMR radiation in the direction we are going. A large portion of that motion appears to be due to the "overall motion vector of the universe" vis-a-vis that same bath of microwave radiation which is slowly teased out using the kinematic Sunyaev-Zel'dovich effect.

At least, that's how I am interpreting it.
(Hopefully, our main disagreements are now & will continue to be in semantics.)

[Chris Peterson]

The high recessional velocities we infer from redshift measurements caused primarily by relativistic time dilation:

That isn't my understanding. When the photons we observe as the CMB were emitted, their sources had a low velocity with respect to our location. In the past 13+ billion years, the Universe between us has expanded, which has increased the wavelength of these photons while they were in flight. This redshift is the product of cosmological redshift, not relativistic redshift (that's my interpretation, anyway).

By virtually stationary I am referring to the overall translation motion not the expansion motion.
In other words, the (presumably) 0.002c translation motion vector of the CBR has virtually no effect on its 0.9999983c expansion motion vector.

I didn't know there were any measurements or estimates for translational motion of the CMB. Are you talking about what we'd see perpendicular to our apparent local motion? If so, there's is no need to invoke relativistic effects to explain the lack of apparent motion; we are simply moving too slowly with respect to the distance. We can't even see translational motion in the nearest galaxies, let alone things at cosmological distances.

Our own motion vis-a-vis the bath of microwave radiation in which we are embedded is explicitly determined by the increase in CBMR radiation in the direction we are going. A large portion of that motion appears to be due to the "overall motion vector of the universe" vis-a-vis that same bath of microwave radiation which is slowly teased out using the kinematic Sunyaev-Zel'dovich effect.

At least, that's how I am interpreting it.

Not me. I don't think there is any real concept of the overall motion of the Universe. All we can see is our own motion with respect to the CMB, which doesn't seem to have anything to do with the Universe as a whole, just our little observable bubble.

[The Code]

The plot Thickens
Quote:
''Kashlinsky speculates that the dark flow extends "all the way across the visible universe," or about 47 billion light-years, which would fit with the notion that the clusters are being pulled by matter that lies beyond known horizons''.

http://news.nationalgeographic.com/news ... ultiverse/

Any body remember back in the days when the end of the known Universe was the outer edges of our milky way?

Anybody know how to use a calculator?

Mark

[Chris Peterson]

''Kashlinsky speculates that the dark flow extends "all the way across the visible universe," or about 47 billion light-years, which would fit with the notion that the clusters are being pulled by matter that lies beyond known horizons''.

I expect that's a misquote. The material can't be pulled by something outside the observable universe. It was pulled by material that was inside the observable universe, but is now outside it. The material may be pulled now by material that is inside its observable universe, but outside ours; that doesn't break any rules. But we can't see the results of that, only the results of motion imparted long ago.

Any body remember back in the days when the end of the known Universe was the outer edges of our milky way?

There's nobody alive who remembers that far back.

[The Code]

Oh Right.

Here,s some more misquotes
''
Evidence Grows for Multiverse. The fact is that this latest discovery puts the final nail in the Big Bang model, even though the die-hard bangers will refuse to see it. What the evidence reported in the story is showing is that there is enough matter to create a gravity field detectable in the motions of the galaxies we can see from Earth, but the gravity field points to a source well outside the presumed edge of the universe which has been calculated from the observed red shift, which is assumed to be caused solely by relative velocity. But since the prime assumption is that our “banged” universe cannot reach that far, that there simply must be a wholly separate universe out there. Of course, since “universe” means “all that there is”, whatever is out there creating this gravity field is by definition part of this universe, which creates a paradox for the Big Bangers.''

http://www.prisonplanet.com/evidence-gr ... verse.html
http://news.branyvnimani.cz/?article_id=11362

dark flow extends “all the way across the visible universe,” or about 47 billion light-years.

Its everywhere. on the net.