perhaps "our bubble" is tilted by the gravity of many other bubbles, where "tilted" simply means that there is a gravitational potential gradient (slope) all across the observable universe, or even farther...

I wish I could offer commentary, but all I have are questions. First, thank you for this blog!

Regarding the gravitational potential gradient, is it speculated that the gradient has an "origin" at the "left" or "right" side of the observable universe? If so, what is the implication for the generalized Copernican principle, that there is no special place in the universe?

What, if any, are the implications of gravitational time dilation from one end of the gravitational potential gradient to the other?

Thanks Jorrie.

Hi GKC, you are welcome!

If I understand correctly, then the 'origin' of the gradient (the mass that causes it) must lie in the direction that the 'flow' is heading. However, this is no more 'non-Copernican' than the fact that Earth seems special to us, but may not be any more special than some other extra-solar planets. Likewise, our observable universe may just be one of a very large number of regions - after all, the total universe may be infinite in size. If so, we should not be too surprised that there are regions with higher density than our patch.

Gravitational time dilation? This 'dark flow signal', if not just an artifact, seems to be so small compared to the normal gravitational troughs and peaks, that we will probably never be able to determine its time dilation effects. Current data suggest that the 'dark flow' happens at roughly the same speed everywhere, so we do not even know if the gradient follows the normal inverse square-of-distance law. It may be so, but the source (origin) may be so far away that the tiny gravitational field just seems to be uniform. Future observations may be able to shed more light on this - it is really the "bleeding edge" of cosmology...

-J

I managed to calculate the rough order of magnitude of the possible gravitational redshift (associated with dark flow) over the radius of the observable universe. It amounts to one part in a thousand. The rom calculation goes like this.

The apparent dark flow velocity is around one million km/h, or ~ c/1000. Divide this by the age of the universe (~10¹⁰ years) to get peculiar acceleration (slope of the gravitational potential). Multiply by the radius of the observable universe (~10¹⁰ light-years) and you end up with an average gravitational redshift differential of one part in a thousand.

This is a rough upper limit, because the peculiar acceleration shortly after the BB should have been larger than today (areas were closer together), meaning the present slope should be smaller than the average. Granted, cosmic gravitational redshift may not quite work like this, but as a rom calculation, it's not too far-fetched.

-J

I recently saw a NASA Msnbc Photo collection of Space in which there was that one picture of our entire Galaxy top and bottom framed against the Black Space in the background with the large red floating clusters of some kind of matter .Have you seen that on-line already.DS

Hi Guest

Not sure which photo collection your refer to. Do you perhaps have a link or a title to search on?

BTW, if it was for our Galaxy, then one would expect 'floating clusters' against 'black space' outside of it, not so?

-J

Hello Jorrie. I would like to take a moment and say thank you for these blog entries. I seldom comment but always read; very interesting.

I believe guest may be refering to the ribbon and knot discovered by IBEX. I have seen it on the NASA channel lately. Even if this is an incorrect guess on my part, have you any observations about this?

Jorrie I would also like to extend my appreciation for your postings. I took several astronomy/astrophysics classes in high school and in college and I thoroughly enjoy reading your blog entries.

Jorrie, add my thanks to the others for your blog, I'm fascinated while failing to understand. As I understand it, dark matter/energy are not understood but are necessary to make the equations work; I am reminded, rightfully or not, of the æther, and I wonder if another Mr. Einstein will come along and tell us we don't need it, there is a perfectly rational explanation of the effect.

I remember my interest being revived when Carl Sagan had his TV program. One of the books or articles I read back then suggested that the structure of the universe was like a soapy foam, porous walls of matter around voids/bubbles of varying sizes with greater concentrations of matter in the corners between the multiple bubbles. It sounded odd, one immediately expects an homogeneous mixture, but then there are dust bunnies and dust webs. The stronger attraction of matter to closest of the surrounding matter suggests that the foam model may provide pathways for the flow, pathways that might give the wrong instantaneous reading on the general direction as the matter flows around a bubble.

Hi passingtongreen, you are welcome. :)

As far as the æther is concerned, if I understand it correctly, the cosmic microwave background (cmb) acts as a reference against which the dark flow is measured. It is however not an æther of the Galilean/Newtonian kind.

In the case of dark flow, the "dust bunnies and dust webs" are apparently all 'swept along the floor', so to speak, at some constant rate, where the cmb is the 'floor'. It seems that the structure of the observable universe has little to do with it - the 'bubbles' are all moving in unison. This movement is over-and-above the cosmic expansion, where bubbles simply move away from each other.

Complex enough to give one a good headache... :(

-J

I sort of like the spongy image as wonderfully messy.

Been reading your Blog for 3 years now. Sortah too bad Roger Pink seems to have taken his ball and gone home.

Do I detect a greater openness to the multi universe theory, than you seemed to have in the past, Jorrie?

Sometimes thoughts get into the air, the mental landscape. Prior to reading this blog thread, I'd been wondering about what might be in the tv static picture we might not know yet how to isolate as meaningful.

Course my interest was in discovering TV from Spacey People in the other Dimension, or other Universe, that I imagine as having a different constant for the speed of light.

The discovery of the great Void of real nothing and vast makes me want to know if it is useful for a signal bounce for speed boost using reverse reality of what we know to be.

Can nothing be impenetrable as what is cannot be penetrated?

Hi,

I think I answered your 'openness' question in my prior reply to S.

As far as detecting signal from the static noise - it is one one of the great challenges of science (not necessarily out of TV static, but other noisy signals). Think about the Gravity Probe B frame-dragging test, that was effectively labeled a failure and the analysis stopped by NASA, until some private funding was obtained to continue the analysis. With that, the Stanford Group eventually did extract some very useful data out of the 'noisy gyro signal', confirming frame dragging to fair degree.

I do not understand what you are saying about the "great Void" and "signal bounce for speed boost"...

-J

I'll take that as confirmation that it is less fanciful to you now, than it was prior?

I am not at all familiar with the Gravity Probe B frame- dragging test.

The reference to the Great Void and any possibility of a signal bounce is a recent postulation on my part as I attempt to make use of known surprises about the universe predicted by String theory.

Recent means like "today", for I'd been thinking of other more mundane problems till piqued by the not yet explained.

Hi Transcendian, you wrote: "I am not at all familiar with the Gravity Probe B frame- dragging test".

I've written a little on GPB in this Blog entry and later some more in this one.

Some technical detail and references are also available on my website.

-J

Hi Jorrie,

Interesting blog. Are you saying that all matter in the observable universe has peculiar motion toward the purple ellipse? If so, that seems to be a stretch considering your comment "it is an artifact of the method of analysis, because it really boils down to digging up a signal out of the noise." Are you saying that all matter has the same velocity of peculiar motion, or is it faster for that closer to the elliptical area?

In your opinion, what is the probability that this is just a mathematical anomaly or programming error? Remember Pluto was discovered because of "perturbations" of the orbit of Neptune that later were found to be a mathematical anomaly or error ( if I remember the facts correctly).

You seem to be arguing with yourself: "Hence, it seems to be caused by the gravity of something outside⁴ of our observable universe." "...the observable universe may be influenced by something outside of it. Not exotically, like from other dimensions or other universes, but simply because there is a lot more universe than what we can observe." "There may obviously also be other universes out there, occupying other dimensions that we cannot observe, but possibly causing some warping of our own space." What, actually is your opinion here?

-S

P.S. There may be a 'dark intelligence" at work here.

Hi S,

You did leave out a few important words in the first quote, making it look slightly different. I wrote: "... it is possible that it is an artifact of the method of analysis, because it really boils down to digging up a signal out of the noise."

If confirmed, it surely means that all the observed galaxies have some component of common peculiar velocity - and AFAIK, that was over a large range of distances, some 1 to 4 Gly away. Only time will tell if it may still be an artifact of the method of analysis, but I suspect that if so, it would have been discredited by now, almost two years since first publication. As I wrote: "... there is reasonable confidence that something is going on there."

AFAIK, these observations were the first tentative evidence of what is going on outside of our observable patch, so I'll try and keep an open mind. In the past I tried to steer away from 'multi-verse' ideas, because there was no evidence whatsoever. I still prefer the idea of one very large universe, which may or may not be homogeneous at the very largest scale. It is something I can wrap my head around, but multiple 'bubbles', I don't know - but then, I'll not rule them out...

-J

Observed up to almost 4 billion light years distance, like the Bullet-Cluster (insert) on the right³ and moving between 1 and 2 million km/h relative to the normal Hubble flow for the distance, this peculiar (dark) flow seems to be independent of distance. Hence, it seems to be caused by the gravity of something outside⁴ of our observable universe. If confirmed, this is indeed very good news for cosmologists, because it gives them one more tool for measuring the 'bigger picture' - the cosmos at large.

Hi Jorrie,

This seems like it would be obvious, but I need to ask for verification anyway.

When we observe things that are almost 4 billion light years away, are we not observing what was happening 4 billion years ago in that part of the universe?

And whatever is happening right now, won't be observable by us until 4 billion years from now?

Thanks, Great blog

Hi kramarat, in the context of dark flow, this is a very interesting question.

The analysis of dark flow is done on the WMAP cosmic microwave background (CMB) data, which looks at what happened over 13 billion years ago (some 400 thousand years after the BB)¹. The CMB map is influenced by the scattering of the microwave photons through the hot X-ray emitting gas inside clusters, obviously at the time when the photons passed close to that cluster. For the Bullet Cluster, that was almost 4 billion years ago.

Now the very interesting part: the peculiar movements (dark flows) under consideration are apparently the result of what happened virtually at time zero (t ≤ 10^-32 sec), the inflation epoch - actually, it had to be before inflation started. It is thought that the pre-inflation cosmos must have been much more 'lumpy' than what it is today. One of these 'lumps' gravitationally tugged at our neighborhood (our observable cosmos) and gave it a 'bulk flow' in that direction.

Presently, our observable cosmos and that 'lump' are electromagnetically and gravitationally disconnected - due to inflation, they are farther from each other than what any influence could have traveled in the time. But, any speed relative to the background that did exist at t~0, will still exist today, not influenced by the gross expansion since then. That's the dark flow.

-J

1. Check it out with the cosmological calculator on my website. It also gives a lot of other parameters for that time.

Jorrie-

You have some very interesting materials available on your web site- I need some time to digest them, but, meanwhile, I have a few questions about the Standard Model that are related to the Dark Flow. Maybe you can help:

1- I am very disturbed by the concept of a singularity, which is how the Big Bang is normally presented to us lay persons. Especially disturbing is the lack of a cause and effect scenario- Dark Flow may have something to do with this...

2- The current value for the age of the Universe seems way too short to me. The Universe is supposedly only 13.9 billion years old. The Solar System is 4.5 billion years old. Life has apparently existed on earth for 3.75 billion years or so- and it took nearly all that time to get from the simplest form of prokaryote microbe to humans. When I look at the night sky, there is just too much there to have been created in only 13.9 billion years...

3- The microwave background is what the universe looks like from our very, very small corner- we don't even know what the other side of the Milky Way looks like. What does the background radiation look like from, say, Andromeda? How can we claim with any confidence that this is what the background looks like from anywhere in the universe?

4- The universe is very lumpy. How did it get that way from the Big Bang? Actually, I see the universe as being in a highly ordered state, with "matter" (whatever that is) clumped together in small regions, interspersed with regions of relatively low density.

5- The "speed of light in a vacuum" is an acceptable constant, but it does not describe the actual velocity of light through space, because space is not, generally, a vacuum. The actual velocity of light depends on the medium through which it passes. If we accept the concept of the "expanding universe", then it seems that one must also acknowledge that the early universe was much more densely packed then it is today, meaning light was traveling much slower through the denser medium than it does today. How does theory compensate for this? "Curvature of Space" is not my idea of a real explanation- it sounds more like an attempt to hide the fact that we really don't know what gravity is...

I see that the LHC is being shut down for a year or so- I guess that means we have to wait a while longer for news of the Higgs boson...

Hi cwarner7_11, you are welcome. I'll try, briefly...

1. Singularities are things science does not understand yet, because no current theory explain them - they are part of ''dark science''. There is hope that some form of Quantum Gravity Theory will eventually be successful and provide an explanation for the beginning.

2. There are so many independent observations that converge on this 13.7 Gy age that it has a high probability, I think. True, without dark matter, the structures we see could not have formed in this time, if ever.

3. We can never be sure, but fitting all our validated observations into a model for the large-scale universe and that is what we get - it should look the same from anywhere in our observable cosmos. You may have to take out different peculiar flows for different locations though...

4. Cluster/galaxy formation is well understood today. The CMB has exactly the right sort of lumpiness in it to drive the lumpiness that we see today - granted, we need dark matter for that. Although we do not know what dark matter is made up of, it must be there; otherwise we would not observe what we do.

5. Yes, the speed of light (c) is just a constant that represents the local speed of light in vacuum. It is not valid over the large scale-cosmos, where the expansion has a major influence on the average speed of light. It is taken into account in cosmic models.

It is somewhat like the speed of light inside a medium: in the empty space between atoms, the speed is c, but not on average for the medium. AFAIK, it has to do with the delay in absorbing and re-emitting photons by the atoms of the medium. Massive bodies in space also delay the passage of photons somewhat, decreasing the average speed for the distance, but the effect is minor and easy to account for, where necessary.

Hope this helps :)

-J

Thank you for taking me seriously, Jorrie- a lot of modern physicists would brush off anyone who questions the Standard Model...

Now, would we not get exactly the same measurements if, instead of the Universe expanding, our particular little neighborhood is actually shrinking? For example, if our solar system were actually accelerating toward the Black Hole in the center of the Milky Way, we would likely start getting squeezed, but since everything locally iss getting squeezed the same amount, we would not be able to detect any local effects (although, from my experience, I have to say the world most definitely seems to be getting smaller!). Now, if there is a relative, uniform acceleration between us and the rest of the universe, how can one say with any confidence that the universe is accelerating away from us, rather than us away from the universe (i.e., sinking into a black hole). I have often wanted to crunch the numbers to figure out what the universal constant would predict regarding how long before we fall through the event horizon- or would we even notice (other than that the rest of the universe has suddenly gone dark). The nice thing about this approach, I don't have to concern myself with Dark Energy- it is all gravity.

I think ultimately, we may find that a Grand Unified Theory is not possible, because it is very possible that gravity is something totally different than the other forces we deal with. There have been some interesting theories put forth lately that might actually suggest this (I am thinking of MOND, and another one I just read recently, but don't have a link readily at hand).

As I said, it looks like we're going to have to wait a couple more years for confirmation of the Higgs boson (which would really put a big hole in my "alternative" thinking)...

A better understanding of gravity, and of what really distinguishes mass from other energetic matter is what is needed.

Hi CW,

Many people have pondered the fact that we may be shrinking (not falling towards a black hole though), rather than that the cosmos is expanding. Apart from some technical and philsophical difficulties, we would have observed exactly what we do today. It is just another measurement system (set of rods for distance, that also shrinks).

In a way, astronomers already do that with their co-moving coordinates,¹ where the distance to a remote galaxy remains constant, while the universe is expanding. It means that the proper distance of all nearby things (that do not follow the expansion) must decrease. This is just an arbitrary, useful coordinate system and has no bearing on how things work.

We know for sure that we are not falling towards our galaxy's central BH, because the Sun is in orbit around it (in free-fall, yes, but not falling in). The distance to the central BH is so vast that there are absolutely no detectable tidal gravity effects in our neighborhood (which would have been a radial stretching en tangential squeeze). So, forget that idea!

What is happening, is that our whole Galaxy is falling towards our Andromeda cousin and at the same time, the whole Local Group and Local Cluster are falling towards the very massive Shapley Supercluster. This movement is readily detectable as a 'dipole' in the CMB temperature and when taken out, we get the true picture of the CMB temperature map. A lot of what we know today comes from that WMAP data set.

Remember that the Higgs Boson really belongs to quantum theory, not quite to gravitation theory, although there is some hope that it may provide some insight in how to link the two diverse theories (as quantum gravity). If the Higgs exists, it would be the mechanism by which particles acquire mass, not quite how mass causes gravity. Its connection with cosmology may be in giving dark matter a predictable mass, but I don't think it has any connection with vacuum energy, dark energy or dark flow per se.

-J

1. For definitions of cosmic distances, take a look here: http://cr4.globalspec.com/blogentry/8864/Blast-From-The-Past

You are much more knowledgeable in this field than I could ever hope to be...However, "...the distance to the central BH is so vast that there are absolutely no detectable tidal gravity effects..." is an issue that is related to the MOND model, which, if I understand it correctly, is a modification of the traditional picture which suggests that gravitational effects at great differences are not what one would expect from standard theory, based on the fact that many distant stars in the outer regions of distant galaxies are moving much faster than standard theory would predict- and MOND provides a simple model that does not require any magical Dark Energy to explain- or maybe not (one winds up with yet another "constant", the physical meaning of which still must be defined...)

I think if we are to fully grasp the nature of gravity, we must first have a better handle on just exactly what is mass, which is why I focus on the Higgs boson. Apparently, one can not have gravity without mass. It may well be that the properties of the Higgs boson, if it is finally confirmed, will provide more questions than answers, which is what keeps life interesting.

Meanwhile, I must rely on gurus such as yourself to help keep my rambling thoughts within reasonable bounds (although I am not quite ready to give up on the falling in to a black hole concept).

Hi CW, you wrote: "" [me]...the distance to the central BH is so vast that there are absolutely no detectable tidal gravity effects..." is an issue that is related to the MOND model..."

I don't think so. MOND or not, the tidal gravity effects (stretch and squeeze) are absolutely negligible at our distance from the Galactic center (or from any other body that is not inside our own Solar system). Then also, MOND is on shaky ground because it does not fit some significant observations, e.g. the Bullet Cluster mass separation, where dark matter works just fine.

It seems to me that MOND can be tweaked to fit certain observations, but then it does not fit others. BTW, MOND only attempts to replace Dark Matter, not Dark Energy, which is pushing the universal expansion in the opposite direction than gravity. I agree on the Higgs - found or not found, both results will have profound implications on our understanding of mass and forces in the quantum sphere.

"(... although I am not quite ready to give up on the falling in to a black hole concept)"

Problem is that there is absolutely no evidence pointing towards it and I think that if modeled like you postulate, we will get a result totally different to what we observe today. Generally, things do not fall into BHs, they rather orbit them. It is only when the immediate neighborhood of the BH is fairly crowded and friction or other perturbations between orbiting matter cause them to lose mechanical (orbital) energy, that they fall in.

If you want to push this idea further, maybe start a new thread under General, so that it will be more visible to other readers. Only so many are prepared to slog through this Blog of mine.

-J

I wrote: "But, any speed relative to the background that did exist at t~0, will still exist today, not influenced by the gross expansion since then."

Oops! The latter part of my statement is not true - just as inflation presumably ironed out the 'wrinkles in spacetime' to a large degree, it also reduced any peculiar movements by roughly the same degree. I discussed something related to this in a previous Blog: "Particle Momentum Decay"

This does not nullify the hypothesis - it possibly explains why the dark flow is so tiny. When the universe had extreme energy density, the gravitational forces must have been immense, possibly resulting in large relative flows between regions of different density. These have been reduced by inflation and to lesser extent also by the expansion after inflation.

-J