New Attractor, New Repeller

Discussions ranging from space technology, near-earth and solar system missions, to efforts to understand the large-scale structure of the cosmos.

New Attractor, New Repeller

Postby BurtJordaan on March 14th, 2017, 2:51 am 

Thought the Great Attractor sounded formidable? Well, think again - the more distant Shapley Attractor is now dwarfing it. As redshift data of thousands of 'nearby' galaxies were compiled and refined, no sooner had Shapley claimed the superior role, or a new phenomenon showed up, one that seems to be even more powerful: the Dipole Repeller.

Dipole Repeller.png
Shapley Attractor and Dipole Repeller (https://vimeo.com/189355968)


OK, it seems that they work together, the one "pulls" and the other one "pushes" our local group of galaxies, with a 'peculiar flow vector' (the yellow arrow)[1] of 630 km/s, almost directly away from the Dipole Repeller. The vector is probably the result of a combination of the more local pulls and the big "pullers and pushers" farther out. So what is a 'pusher', or rather a repeller?

I'm no astronomer (not even an amateur one), but as I understand things, astronomers combine the redshift data of the area of interest with other observations, e.g. mass densities, into a computer program to provide a 3D density map, as in the colors of the image. Using this, together with observed redshifts, they then model the motion of near-massless particles that they "seeded" the background with. This gives the flow-arrows as pictured. The animation in https://vimeo.com/189355968 is stunning!

The Dipole Repeller is just the minimum average density point of a large area of under-density, called a 'void'. In terms of gravitational potential, the repeller is a local maximum (gravity 'bump') and the attractor a local minimum (gravity 'well') for the area of interest.

Enjoy! (before we discuss this amazing result further).

Notes:
[1] Peculiar flow is our motion relative to the local inertial frame in which the CMB temperature would be the same in all directions, i.e. isotropic,
Last edited by BurtJordaan on March 27th, 2017, 3:38 am, edited 5 times in total.
Reason: End notes, clarification
User avatar
BurtJordaan
Forum Moderator
 
Posts: 2434
Joined: 17 Oct 2009
Location: South Africa
Blog: View Blog (9)
dandelionDave_Oblad liked this post


Re: New Attractor, New Repeller

Postby BurtJordaan on March 15th, 2017, 1:31 am 

BurtJordaan » 14 Mar 2017, 08:51 wrote:The Dipole Repeller is just the minimum average density point of a large area of under-density, called a 'void'. In terms of gravitational potential, the repeller is a local maximum (gravity 'bump') and the attractor a local minimum (gravity 'well') for the are of interest.

If you look at the potential values on the video frame above, it looks like it is the opposite of what I wrote above. The potential of the Attractor is given as Phi = +955 and for the Repeller Phi = -650. I had to read the technical article to find out why, because the gravitational potential function Phi is normally maximally negative at the center of a mass (a local Attractor) and can at most be zero in distant, empty space.

It appears that they are using the gravitational field strength as a potential that they call Phi - the potential to cause a flow velocity. A positive Phi then causes inflow into an Attractor, while there is obviously a negative inflow for a Repeller.

It is good to note that the Repeller is not creating any force, it is just a flow from higher (gravitational) potential energy to lower potential. This is why I like my interpretation more - it is rather intuitive... ;)
Last edited by BurtJordaan on March 15th, 2017, 6:01 am, edited 1 time in total.
Reason: Added paragraph
User avatar
BurtJordaan
Forum Moderator
 
Posts: 2434
Joined: 17 Oct 2009
Location: South Africa
Blog: View Blog (9)


Re: New Attractor, New Repeller

Postby curiosity on March 26th, 2017, 6:34 pm 

I have been expecting a torrent of posts in regard to this.... "Come on guys, give me something good to read."
It's a fascinating subject, yet it has been met with a wall of silence ???
curiosity
Member
 
Posts: 351
Joined: 19 Jul 2012


Re: New Attractor, New Repeller

Postby BurtJordaan on March 27th, 2017, 3:40 am 

I think many of the usual contributors are still busy deciding how it all fits into their personal theories... ;)
User avatar
BurtJordaan
Forum Moderator
 
Posts: 2434
Joined: 17 Oct 2009
Location: South Africa
Blog: View Blog (9)


Re: New Attractor, New Repeller

Postby Eclogite on March 27th, 2017, 5:43 am 

curiosity » Sun Mar 26, 2017 10:34 pm wrote:I have been expecting a torrent of posts in regard to this.... "Come on guys, give me something good to read."
It's a fascinating subject, yet it has been met with a wall of silence ???
While I like to think of myself as open minded and far ranging in my beliefs and interests, I must confess to be being basically parochial.

I 'm not too interested in anything beyond the Local Group of galaxies, or further back in time than when the first planetary systems started to form. It's within that milieu that life as we know it evolved and intelligence emerged. The rest is as relevant as plate tectonic mechanisms to a Mayan high priest.

Brilliant work, but it doesn't turn me on. (Loved the graphic.)
Eclogite
Forum Moderator
 
Posts: 1388
Joined: 07 Feb 2007
Location: Around and about


Re: New Attractor, New Repeller

Postby vivian maxine on March 27th, 2017, 8:32 am 

Well, the cat holding it all together gets my attention. How many see him?

Seriously, though, one of us really is interested. Why? I don't understand it. I'm strange, I know, but I love digging into something I have absolutely no understanding of and see if I can make some little sense of it. It's just me. Anything new gets my attention at least long enough to see what I can make of it. That and the fact that "what's out there?" keeps me awake nights. :-)

All that is no help to the OP at all. I'm sorry.
vivian maxine
Resident Member
 
Posts: 2837
Joined: 01 Aug 2014


Re: New Attractor, New Repeller

Postby vivian maxine on March 27th, 2017, 12:22 pm 

Burt, after reading more - the article and some things from Wikipedia - I am wondering something. Does every supercluster have an attractor that pulls on nearby clusters which, in turn, pull in nearby galaxies with their own lesser attractors? And maybe those galaxies also have still lesser attractors that bring in stars and solar systems from nearby? In other words, is this part of a universe-wide system? And - more important - is all of this a picture of what gravity is doing?

Yet, if that is fact, we lose the theory that the entire universe is expanding, don't we? Instead, we have the theory of the final crush at a center.

Am I making sense?
vivian maxine
Resident Member
 
Posts: 2837
Joined: 01 Aug 2014


Re: New Attractor, New Repeller

Postby BurtJordaan on March 28th, 2017, 1:52 am 

vivian maxine » 27 Mar 2017, 18:22 wrote:Does every supercluster have an attractor that pulls on nearby clusters which, in turn, pull in nearby galaxies with their own lesser attractors?

Yes, all astronomical bodies "pull on one another", but they are not called 'attractors' - rather just gravitational centers (gc's). And we have a whole hierarchy in astronomy, normally ending with the smallest astronomical bodies. The Earth's gc sits near the center of Earth and our Moon's near its center, but then the Earth/Moon system also has a gc, which sits inside Earth, about a two-thirds from the center. For our system it is called the Barycenter.

Superclusters are defined by the fact that the mutual gravity of a group of clusters holds them in some form of orbital motion around their common gravitational center (it is a gravitationally bound structure). Outside that supercluster, cosmic expansion overwhelms the (weak) mutual gravity there and the distances to other superclusters are increasing over time (it is no longer a gravitationally bound structure).

This increase in distance between superclusters roughly follows Hubble's law. At the distance of the Shapley Attractor, it amounts to a recession speed of over 13,600 km/s. So we are not being drawn closer to the Attractor, but the recession rate is just being decreased by some 630 km/s.

This is a pretty complex system, so please ask if things are not clear to you.
User avatar
BurtJordaan
Forum Moderator
 
Posts: 2434
Joined: 17 Oct 2009
Location: South Africa
Blog: View Blog (9)


Re: New Attractor, New Repeller

Postby Dave_Oblad on March 28th, 2017, 6:18 am 

Hi all,

I admit to finding this extremely interesting. Mostly because it conforms to my personal explanation for the mechanics of Gravity. I predicted many years ago that large voids would have a repulsive effect on semi-nearby clusters of Matter. I was thrilled when some female student at some University discovered that Voids have the opposite effect on Light as a Gravitational lens. It will take some hunting to find my post that predicted such. I was dismayed that I never found any followup to that observation by this student.

I seem to remember some article that suggests this was predicted by GR as the difference between Concave and Convex light distribution due to Gravitational effects. It falls in line with my Personal Hypothesis that the Planck Length has variable Scale when separated by distance.. as a Gradient Scale.

So yes, I'm very happy someone has shown that Deep Voids can have a repulsive effect on Matter, as Inverted Gravity. (I hypothesized that Space-Time Curvature as being a Planck Length Scale Gradient)

Best Regards,
Dave :^)
User avatar
Dave_Oblad
Resident Member
 
Posts: 3208
Joined: 08 Sep 2010
Location: Tucson, Arizona
Blog: View Blog (2)


Re: New Attractor, New Repeller

Postby vivian maxine on March 28th, 2017, 6:20 am 

Burt Jordaan wrote:Outside that supercluster, cosmic expansion overwhelms the (weak) mutual gravity there and the distances to other superclusters are increasing over time (it is no longer a gravitationally bound structure).


That explains it. Thank you very much. So, what is being found is one after another of these superclusters and the story of what they are doing makes a good mystery worth watching. They aren't pulling on each other but are pulling on other clusters, thus maybe increasing their wizes. I see the makings of separate universes with us trying to travel from one to the other. There is a great novel in there somewhere. :-)

Ignore my fantasizing. You did answer my question and thank you. I understand now.
vivian maxine
Resident Member
 
Posts: 2837
Joined: 01 Aug 2014


Re: New Attractor, New Repeller

Postby BurtJordaan on March 28th, 2017, 7:54 am 

Dave, the effect of a void is a much a 'repulsive effect' as the aircraft is to a parachutist when she jumps out of it.

But you are right that light bends around voids in the opposite direction than around denser clusters, but that effect has the same cause as with the parachutists above. Just normal gravity, without any dark energy, make voids grow larger over long time periods.
User avatar
BurtJordaan
Forum Moderator
 
Posts: 2434
Joined: 17 Oct 2009
Location: South Africa
Blog: View Blog (9)


Re: New Attractor, New Repeller

Postby BurtJordaan on March 28th, 2017, 11:34 am 

curiosity » 27 Mar 2017, 00:34 wrote:I have been expecting a torrent of posts in regard to this.... "Come on guys, give me something good to read."
It's a fascinating subject, yet it has been met with a wall of silence ???

I noticed that the authors have used the term "cosmography" early on in their video (~20s). This is a very old term, originally used in the 1550s. According to this Wiki: "Cosmography is the science that maps the general features of the cosmos or universe, describing both heaven and Earth (but without encroaching on geography or astronomy)."

Since the 1970s, it did start to get a special significance in the above two subjects, almost as a sort of phase transition between astronomy and modern cosmology. The former could mostly be done with ordinary Newtonian gravitational theory as basis, but when we go to very large distance scales, Einstein's theory needed to be used for a model that agrees with observations.

Around 2004, a paper by Mathematician Matt Visser, "Cosmography: Cosmology without the Einstein equations developed a math description that is independent of both Newton's and Einstein's theories, but simply based on observables. He wrote: "Indeed, a surprising amount of modern cosmology is pure kinematics, what Weinberg [2] refers to as cosmography, and is completely independent of the underlying dynamics governing the evolution of the universe."

Visser closed by saying (marginally snipped for simplicity):

"Thus all comments made in this article are completely independent of one’s favorite choice of matter model for the cosmological fluid. There are currently very many quite radically different models for the cosmological fluid under active consideration. Though these models often make dramatically differing predictions in the distant past, .... there is considerable degeneracy among the models in that many physically quite different models are compatible with present day observations."

This should do it for the 'curious cats'...
User avatar
BurtJordaan
Forum Moderator
 
Posts: 2434
Joined: 17 Oct 2009
Location: South Africa
Blog: View Blog (9)


Re: New Attractor, New Repeller

Postby BurtJordaan on March 30th, 2017, 2:51 am 

I quoted Matt Visser in my prior reply:
There are currently very many quite radically different models for the cosmological fluid under active consideration. Though these models often make dramatically differing predictions in the distant past, .... there is considerable degeneracy among the models in that many physically quite different models are compatible with present day observations.

This is a crucial difference. The Planck mission's results on the CMB anisotropy (and other parameters, like acoustic modes) are better explained by the standard LCDM cosmo-model than by any competing model.

Due to the late dominance of the cosmological constant (accelerating expansion curve), as shown by the plot below, the scale factor (a) curve is fairly linear during the last 5 billion years or so.

expansion rate.png
Decelerating/accelerating expansion


In this region, even a very simple model can give predictions that are within the error bars of the observations. Not so for much earlier times. At the scale shown here, the CMB lies almost at the origin and the Visser-cosmography model only operates in the near-linear regime.

-=-

PS: The curves were obtained by setting LigtCone7 as follows (with rest at defaults):

LightCone7 setupX.png
Click on picture for better resolution


After opening LightCone7, click the Chart Option and Column Selection boxes to change those defaults.
Last edited by BurtJordaan on March 30th, 2017, 2:54 am, edited 1 time in total.
Reason: Typos
User avatar
BurtJordaan
Forum Moderator
 
Posts: 2434
Joined: 17 Oct 2009
Location: South Africa
Blog: View Blog (9)



Return to Astronomy & Cosmology

Who is online

Users browsing this forum: No registered users and 6 guests