Thread: Mysterious Cosmic 'Dark Flow' Tracked Deeper into Universe

It seems to me that this particular observation is a fair indication that there is something very massive beyond our cosmic limit of being able to see, that is affecting the way a very large number of galactic clusters are moving. I'm pretty sure the current BB model of our universe is not able to to explain this observation. I do have my own ideas about it, but I'd very much like to know what others think on this subject?

NASA - Mysterious Cosmic 'Dark Flow' Tracked Deeper into Universe

Cosmic string ?

Great article, arKane.
Some feel that Kashlinsky's team that took the measurements didn't properly account for Anisotropy. Kashlinsky, however, defends his measurements well.

Maybe the Planck Satellite Data will very soon be released shedding some light on this little mystery.

If I'm not mistaken, wlminex and RealityCheck had asked about this specific issue on that other place in regards to their qualms with Big Bang theory and WMAP data interpretation.
Personally, I think the data is probably valid, but we have more to learn before jumping to conclusions.

I wonder what gift Max Planck will contribute with his namesake here, beyond the grave...

Originally Posted by Markus Hanke

Cosmic string ?

Sometimes not knowing the answer can be fun, but still, I'm not sure Cosmic strings would be high on my list of guesses. What about a behemoth massive black hole? After all there is no known size limit on BH's that I know of, and our view of the universe is somewhat limited. We really have no idea what's beyond our viewing limit, but we do know that for that many galactic clusters to be moving contrary to what's expected in an expanding universe, there must be a lot of gravity involved.

I wouldn't say the clusters are moving contrary to what's expected in an expanding universe, it is just that in addition to the expansion there seems to be a peculiar motion in a certain direction.

That would still be a black hole beyond epic proportions... Think about how big a galaxy is compared to the most supermassive of Black Holes, the BH still pales in shivering comparison. You're talking about clusters of hundreds of galaxies over an immense amount of space, here.
No, I wouldn't put much stock in that idea.

I think it's a dent in God's skull. Those clusters of galaxies are rollin' into the dent and that explains where he's been- He got knocked out (Maybe by the Big Bang...)

Originally Posted by Neverfly

Great article, arKane.
Some feel that Kashlinsky's team that took the measurements didn't properly account for Anisotropy. Kashlinsky, however, defends his measurements well.

Maybe the Planck Satellite Data will very soon be released shedding some light on this little mystery.

If I'm not mistaken, wlminex and RealityCheck had asked about this specific issue on that other place in regards to their qualms with Big Bang theory and WMAP data interpretation.
Personally, I think the data is probably valid, but we have more to learn before jumping to conclusions.

I wonder what gift Max Planck will contribute with his namesake here, beyond the grave...

I'm hoping the next generation of telescopes will help solve this problem. From the research I've done on them they will be truly awesome.

Originally Posted by arKane

From the research I've done on them they will be truly awesome.

Make a thread. C'mon- fill us in. Links. Details. Don't leave us hanging.

Originally Posted by SpeedFreek

I wouldn't say the clusters are moving contrary to what's expected in an expanding universe, it is just that in addition to the expansion there seems to be a peculiar motion in a certain direction.

But I'm sure you do think it's something that does need an explanation? Do you have any theories? Far out or otherwise.

Originally Posted by Neverfly

Originally Posted by arKane

From the research I've done on them they will be truly awesome.

Make a thread. C'mon- fill us in. Links. Details. Don't leave us hanging.

Glad you asked.

Very Big Telescopes

Originally Posted by arKane

Originally Posted by SpeedFreek

I wouldn't say the clusters are moving contrary to what's expected in an expanding universe, it is just that in addition to the expansion there seems to be a peculiar motion in a certain direction.

But I'm sure you do think it's something that does need an explanation? Do you have any theories? Far out or otherwise.

Yes, it needs an explanation, although one explanation is that it is a statistical fluke and that it corresponds to the primary anisotropies in CMB that we have already measured, something that Kashlinsky doesn't seem to feel is important. So rather than being a physical phenomenon in its own right, it would be the expected outcome in an expanding universe if the mass distribution in our local part of universe isn't as homogeneous as assumed by our cosmological model. Basically, even if the overall distribution of matter in the universe is generally homogeneous, there will always be lumpy areas and less lumpy areas at local scales, but our cosmology assumes homogeneity across the observable universe. Perhaps we live in a part of the universe that is actually lumpier on one side than the other!

Or perhaps the universe is lumpier somewhere just outside of our observable universe.

Or perhaps whatever it is that is causing the acceleration of the expansion in all directions, that which we call dark energy, is not as homogeneous as we naively assume. Perhaps dark energy has more influence in one place than in another.

Originally Posted by SpeedFreek

Or perhaps whatever it is that is causing the acceleration of the expansion in all directions, that which we call dark energy, is not as homogeneous as we naively assume. Perhaps dark energy has more influence in one place than in another.

Mmm... that's a bit of a stretch. Dark Energy is what's hypothesized to drive expansion.
This is something observed between galactic clusters and is overwhelmed by gravity making it negligible - a bit like you sneezing on a dust particle way out in space, or you sneezing on one while standing on the Sun (using super duper Sun Standing Boots).

ETA: Although... (snap)
If there was significant expansion from a vast expanse bordering the edge of one side of the cluster but little cumulative effect on the other due to nearby clusters damping out dark energy- it might make a twist-like distortion... The acceleration is only a matter of about a thousand km per second, right?
On these scales, that's pretty small.

I wanna see the raw data now.

Originally Posted by Neverfly

Originally Posted by SpeedFreek

Or perhaps whatever it is that is causing the acceleration of the expansion in all directions, that which we call dark energy, is not as homogeneous as we naively assume. Perhaps dark energy has more influence in one place than in another.

Mmm... that's a bit of a stretch. Dark Energy is what's hypothesized to drive expansion.

I was under the impression that dark energy is only hypothesised to be driving the acceleration of the expansion, rather than the expansion itself. For the first 7-8 billion years, the expansion was decelerating due to gravity, so how did it "accelerate" right at the beginning?

Originally Posted by SpeedFreek

I was under the impression that dark energy is only hypothesised to be driving the acceleration of the expansion, rather than the expansion itself. For the first 7-8 billion years, the expansion was decelerating due to gravity, so how did it "accelerate" right at the beginning?

Man, I gotta stop typing things.

Yes, what he said.

Originally Posted by SpeedFreek

Or perhaps whatever it is that is causing the acceleration of the expansion in all directions, that which we call dark energy, is not as homogeneous as we naively assume. Perhaps dark energy has more influence in one place than in another.

I've often wondered that myself and I'm thinking it wouldn't be to hard to prove one way or the other. At the very edge of our viewing range we would expect the red shift to be the same in all directions if the dark energy was the same all over the universe. So we only have to take measurements at many different points around the universe at the same max distance we can see. If there are differences in the red shift, I think we will have to assume the dark energy is coming from sources outside our viewing range.

Unfortunately, the higher the redshift, the larger the error margin for apparent recession velocity, and the "dark flow" is only a relatively small difference from the rest frame of the Hubble expansion.

To put this into context, we ourselves have a peculiar motion of around 600km/s relative to the CMB rest frame (which is as good a frame to be "at rest" in relation to expansion as any), but the dark flow is only in the thousands of km/s. The most distant galaxies we see have apparent recession velocities much faster than c, which is more than 300 times that figure. So if a distant galaxy has an apparent recession of, say, twice the speed of light, a difference of only a few thousand km/s will fall within the error margins of the estimate of apparent recession velocity.

Originally Posted by SpeedFreek

Unfortunately, the higher the redshift, the larger the error margin for apparent recession velocity, and the "dark flow" is only a relatively small difference from the rest frame of the Hubble expansion.

To put this into context, we ourselves have a peculiar motion of around 600km/s relative to the CMB rest frame (which is as good a frame to be "at rest" in relation to expansion as any), but the dark flow is only in the thousands of km/s. The most distant galaxies we see have apparent recession velocities much faster than c, which is more than 300 times that figure. So if a distant galaxy has an apparent recession of, say, twice the speed of light, a difference of only a few thousand km/s will fall within the error margins of the estimate of apparent recession velocity.

We may not have the instruments for that job at this time, but we are getting closer to a time when we will be able to cut the error margin down to a level we can work with. I'm just happy I'm not the only one that thinks the dark energy may not be as homogenous as has been assumed.

I first learnt about dark flow from a BBC Horizon program “is everything we know about the universe wrong” that can be seen here. I very soon thought it must be an effect of the expansion of the universe; not just expanding but expanding ever faster. I thought that if the universe had always had this type of accelerating expansion then the Hubble sphere will not be near our particle horizon or our visible horizon but somewhere much closer. In an expanding universe the Hubble sphere is a distance from an observer where the recessional velocity of distant galaxies will be equal to the speed of light. There is nothing special about the actual geodesic location of our Hubble sphere it is just a location relative to us. Another observer in a different galaxy will have a Hubble sphere at different locations; we will be receding at the speed of light relative to some other observers.

My initial reasoning for equating dark flow to accelerating expansion was quite a simple one. Because light has a finite velocity when we look further and further away we are looking further back in time. Light takes 100,000 years just to get from one side of our galaxy to the other and the term look back time is often used as a measure of distance. Thinking that time in our universe had a beginning then this would limit our look back time. A non-accelerating expansion would put the Hubble sphere at the big bang moment but in an accelerating expansion that interface between luminal recession and super-luminal recession will be somewhat closer and the stuff of the universe will appear to disappear at our visible horizon as the accelerated expansion puts once visible objects beyond our visible horizon.

If we were to observe a distant galaxy for a long enough period of time we would see that the increasing recessional velocity will give the appearance of slowing down events there as the look back time increases. At the Hubble sphere this slowing down will cause events to come to a standstill. In an accelerating universe where we can see beyond the Hubble sphere events will appear in reverse time order.

In a universe where time is transfinite past time ran relatively faster but light had the same velocity making past distances longer. This means we can see less in our horizon as future distances get smaller.

I made my first YouTube video; it is explaining “Dark Flow” a difficult task in less than 15 minutes (my You Tube limit). It can be found here:

Dark Flow

To first make the video I had to teach myself PowerPoint so I apologize for this post being a bit late.

Your skill at producing that YouTube video was impressive. If you do any others please let me know. But my impression of the Dark Flow is that those groups of 1000's of galaxies are moving contrary to the expansion of the universe. As if they were under the influence of a very large gravitational source we have yet been unable to identify as it lies somewhere past the limit of what we can see.

I don't know if your ideas are on the right track or not, but I suspect not or we would see Dark Flow like events in all directions.

Originally Posted by arKane

Your skill at producing that YouTube video was impressive. If you do any others please let me know. But my impression of the Dark Flow is that those groups of 1000's of galaxies are moving contrary to the expansion of the universe. As if they were under the influence of a very large gravitational source we have yet been unable to identify as it lies somewhere past the limit of what we can see.

I don't know if your ideas are on the right track or not, but I suspect not or we would see Dark Flow like events in all directions.

Thank you arKain I find a bit of animation can get my message across and better indicate what I do or do not understand.

I think that this dark flow effect can be seen behind many other bullet clusters, it did at one time say that they had discovered many more on the Wikipedia site. The point is it is only a visual effect, when it comes to actually detecting the motion they are unsure now as what direction they are travelling. I think that when we can detect galaxies Z = 2 and further without the aid of gravitational lensing then we will indeed see this effect everywhere we look. It will then be a little more difficult to explain it away with dark energy etc…..or maybe not.

That's a very nicely made video, Ricewind, and it begins very well indeed, but as I watched further certain misconceptions about how the expansion relates to the Hubble horizon started to creep in.

We can see galaxies that have always been receding faster than light and have never been inside our Hubble sphere, but we do not receive their photons reversed!

Have a read of the paper below (it is the standard explanation of our current cosmology), and if you have any questions about it feel free to ask!
[astro-ph/0310808] Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the Universe

If you have trouble with the text, the diagrams alone can tell you a lot!

Thank you Speed Freek, I am familiar with that and it explains well how super-luminal recession is possible due to inflation where very rapid early expansion happened. I think though that there could a bit of a problem with it as it would need an expansion that was initially faster than light through the space that the light later travels through to reach us now. Would that not be against the law of physics? If it then slowed down where did the kinetic energy go? If inflation was early rapid expansion; where things were carried along with the stretching space then that stretching space would still be super-luminal, even though the expansion stopped accelerating it never stops expanding.

I think though that there could a bit of a problem with it as it would need an expansion that was initially faster than light through the space that the light later travels through to reach us now. Would that not be against the law of physics?

space can expand faster than light and not be in violation of relativity.

If it then slowed down where did the kinetic energy go?

no kinetic energy involved as far as i can see as it wasn't the mass in the universe moving through space.

ps, i'm an amateur so take what i post with caution.

Originally Posted by Ricewind

Thank you Speed Freek, I am familiar with that and it explains well how super-luminal recession is possible due to inflation where very rapid early expansion happened. I think though that there could a bit of a problem with it as it would need an expansion that was initially faster than light through the space that the light later travels through to reach us now. Would that not be against the law of physics?

The universe is always receding faster than light at some distance or other and that paper actually explains why this is not against the laws of physics. This is the standard cosmology - the observable universe has a radius three times larger than the age of the universe. The edge of the observable universe would have had to have receded at an average of three times the speed of light to have reached that distance in the time available, which would be impossible for an object travelling through space. But the universe is not travelling through space when it expands.

Originally Posted by Ricewind

If it then slowed down where did the kinetic energy go?

When you throw a ball up into the air and it slows down the higher it gets, where did the kinetic energy go? Into gravitational potential. It is gravity which slowed down the expansion of the universe over the course of the first 7 - 8 billion years, too. But if you are referring to the initial inflation it was the other way around - the potential energy of the inflaton field was turned into that "kinetic energy" in the phase transition when inflation ended and "normal" expansion continued on from there. But this is not kinetic energy in the usual sense, as objects aren't actually moving in relation to their local enviroment - nothing ever overtakes a photon, anywhere, even if distant galaxies recede superluminally.

Originally Posted by Ricewind

If inflation was early rapid expansion; where things were carried along with the stretching space then that stretching space would still be super-luminal, even though the expansion stopped accelerating it never stops expanding.

Not sure what you are getting at here. If you want to use the "expanding space" analogy, then space only expands between things, which carries those things further apart. It is the cumulative effect of this expansion, over distance, which causes an apparent recession speed faster than light. There is always a distance where the apparent recession speed is superluminal. Right now that distance is around 14 billion light-years. At the time the CMB was released distances at less than 1 million light-years were receding superluminally. And during inflation, it was distances down at the atomic scale that were increasing superluminally.

Originally Posted by Chrispen Evan

I think though that there could a bit of a problem with it as it would need an expansion that was initially faster than light through the space that the light later travels through to reach us now. Would that not be against the law of physics?

space can expand faster than light and not be in violation of relativity.

If it then slowed down where did the kinetic energy go?

no kinetic energy involved as far as i can see as it wasn't the mass in the universe moving through space.

ps, i'm an amateur so take what i post with caution.

That seems right to me. I only skimmed over speedfreek's link, so I may be asking a question that's already been answered.

Take two points A & B with the two points passing the point at which the space between the two points is expanding faster than the speed of light. B emits a photon back towards A. My question is this, The photon will be traveling towards A at the speed of light. While the total distance between A & B is expanding faster than light, it seems to me that the photon (point C) moving towards A will reach a point where the distance between A & C will not be expanding faster than light, and the photon will now be able to reach point B at some future date?

Originally Posted by arKane

Take two points A & B with the two points passing the point at which the space between the two points is expanding faster than the speed of light. B emits a photon back towards A. My question is this, The photon will be traveling towards A at the speed of light. While the total distance between A & B is expanding faster than light, it seems to me that the photon (point C) moving towards A will reach a point where the distance between A & C will not be expanding faster than light, and the photon will now be able to reach point B at some future date?

Yes, that is quite correct, although the acceleration of the expansion does introduce a cosmological event horizon, but this event horizon is always more distant than the Hubble horizon (where an object recedes at c) except when the accelerating expansion is exponential. There, that clears that up!

Thank you all for replying. I was wrong in post 22 and my objections were not valid. I was not objecting to galaxies having faster than light recessional velocities but the objections I did make were wrong.

Originaly posted by Speed Freek "We can see galaxies that have always been receding faster than light and have never been inside our Hubble sphere, but we do not receive their photons reversed!"

That is true for the CDM model although I still think the photons will arive in reverse time order due to a look back time delay that causes a greater than stationary event sequence delay past the Hubble sphere.In my original post I was thinking of a model where time is slowing down relative to the past; and in that model we get inflation in the very distant past very fast relative to now and getting faster as our now time slows in the future. The difference between the two models here is the inflation has always been constant but always relatively faster in the past, with the expansion a function of time, compared to an inflation rate that has changed from fast to stopped and then increases to the not so fast now.

As the Space is growing and expanding the dynamics of the space are also changing with the time.

Could dark flow be caused by gravity from another universe?