New study shows Dark Matter isn't needed? Relativty explains it?

[Cosmo16]

new study shows Dark Matter mat not exist? Relativty explains it?

Look here
http://www.space.com/scienceastronomy/051010_dark_matter.html"

Is this valid reasoning? I noticed it hadn't been submitted to peer review.

 

[EL]

As said here:
https://www.physicsforums.com/showthread.php?t=92817&page=2 ,
the people I have talked to about this are all pretty sure there's an error somewhere in the paper. However, I'm not the one to judge it...

 

[Garth]

General Relativity Resolves Galactic Rotation Without Exotic Dark Matter has been submitted to Ap.J. it will be interesting to see if it passes peer review.

The case it makes is obvious; that the dynamics of a diffuse collection of orbiting masses, such as a spiral galaxy, has to be calculated in the non-linear theory of GR rather than the linear Newtonian theory. Apparently, and surprisingly, this has not been done before and the consequent mismatch between galactic dynamics and Newtonian theory has led to the invocation of galactic halo DM. However, Cooperstock and Tieu claim that when properly calculated there is no mis-match at all!.

However, in dismissing general relativity in favor of Newtonian gravitational theory for the study of galactic dynamics, insufficient attention has been paid to the fact that the stars that compose the galaxies are essentially in motion under gravity alone (“gravitationally bound”). It has been known since the time of Eddington that the gravitationally bound problem in general relativity is an intrinsically non-linear problem even when the conditions are such that the field is weak and the motions are non-relativistic, at least in the time-dependent case. Most significantly, we have found that under these conditions, the general relativistic analysis of the problem is also non-linear for the stationary (non-time-dependent) case at hand. Thus the intrinsically linear Newtonian-based approach used to this point has been inadequate for the description of the galactic dynamics and Einstein’s general relativity should be brought into the analysis within the framework of established gravitational theory. This is anessential departure from conventional thinking on the subject and it leads to major consequences as we discuss in what follows. We will demonstrate that via general relativity, the generating potentials producing the observed flattened galactic rotation curves are necessarily linked to the mass density distributions of the flattened disks, obviating any necessity for dark matter halos in the total galactic composition.

I think their calculations appear sound, although I have not checked them throroughly. However they conclude:

Moreover, it will be of interest to extend this general relativistic approach to the other relevant areas of astrophysics with the aim of determining whether there is any scope remaining for the presence of any exotic dark matter in the universe. Clearly the absence of such exotic dark matter would have considerable significance.

I cannot concur with the absence of DM as there is other evidence for extra-galactic DM from lensing and other effects in rich cluster IGM. However it may not be exotic, if Omega_baryon ~ 0.2 - 0.3, there would be no need to invoke hypothetical exotic non-baryonic DM to explain the mass detected within galactic clusters. Such a high Omega_baryon is predicted by the strictly linear expansion model.

Garth

 

[Garth]

Again:- If this analysis by Cooperstock and Tieu stands up then it would have profound implications for the 'mainstream model'. In particular there would be a problem with galaxy formation within the time scale that model allows.

The present model relies on the quick concentration of non-interacting DM to form the potential wells into which baryonic matter can fall, which then forms the visible galaxies. However if these galactic haloes are only an artifact of inappropriate Newtonian dynamics then more time would be required for the galaxies, now seen at high z to form.

The most extreme example of this is the Hubble ultra deep field object UDF033238.7-274839.8 aka HUDF-JD2 , a 6 x 10¹¹M_solar galaxy at z = 6.5 when the universe was only 860 Myrs old, (age given by Ned Wright's calculator allowing for DE). Also we have high-z quasars with significant iron abundances, and iron is the last element to be formed in fusion processes, such as APM 08279+5255at z = 3.91 whose age is 2.1 Gyr when the universe was only 1.6 Gyrs old (according to LCDM model expansion).

The strictly linear expansion model gives a universe age of 2 to 3 times the LCDM model.

Garth

 

[Lapin Dormant]

Personally I suspect that the answer lies in the manner of Operation of Gravity, which is, to this date, seemingly, still unknown, in Completeness.

It may simply be that intergalactic gravity behaves slightly dfferently then the observable gravitational interactions seen at our local scale.

It may sum differently, it may simply be that in summing, it can drag much more of space around with it then had ever been previously thought of, if it can drag space around, then it can also drag around the contents of that space around without, persay, energy loss or general interactivity.

 

[Garth]

Personally I suspect that the answer lies in the manner of Operation of Gravity, which is, to this date, seemingly, still unknown, in Completeness.

It may simply be that intergalactic gravity behaves slightly dfferently then the observable gravitational interactions seen at our local scale.

It may sum differently, it may simply be that in summing, it can drag much more of space around with it then had ever been previously thought of, if it can drag space around, then it can also drag around the contents of that space around without, persay, energy loss or general interactivity.

You'll need to express your ideas with a mathematically described testable theory, GR, MOND and SCC are such examples.

But first we have to get the GR analysis right!

Garth

 

[Lapin Dormant]

Really so words won't do for you, interesting as that is the foundation of Mathematics, words.

ana one ana two ana three .. .. .. .. ..

But I appreciate your answer, for what it is worth.

 

[Garth]

Really so words won't do for you, interesting as that is the foundation of Mathematics, words.

ana one ana two ana three .. .. .. .. ..

But I appreciate your answer, for what it is worth.

Your concepts are fine, as points for discussion, but they will need to be quantified and not just 'hand waving'. I'm not criticising, my hands 'wave' as much as anybody's! However, having a mathematically described theory that makes testable predictions is way we separate out those ideas that 'work' and reflect reality in some way from those that are to fall by the wayside.

Modified gravity is MOND and your "if it can drag space around" is the gravitomagnetic effect being tested at this moment by Gravity Probe B, who knows what its answer will be?

Garth

 

[Pyro]

There has been a rebuttal of the paper that you can see here. The rebuttal basically says that the model is "unphysical". It's yet to be seen if this "unphysical" explanation is substantial or not.

 

[Garth]

There has been a rebuttal of the paper that you can see here. The rebuttal basically says that the model is "unphysical". It's yet to be seen if this "unphysical" explanation is substantial or not.

Welcome to these Forums Pyro! And thank you for that link.

We argue that in this model the gravitational field is generated not only by the galaxy matter, but by a thin, singular disk as well. The model should therefore be considered unphysical.

In fact I do not agree with its conclusion that the Cooperstock & Tieu galaxy model is 'unphysical', the galaxy does have a disk - the galactic disk in which the spiral arms are embedded, it consists of stars, dust and gas including massive molecular clouds. The total galactic mass Cooperstock & Tieu require is 21×10₁₀M_⊙ which is totally realistic.

Garth

 

[Lapin Dormant]

O.K. here it is, mathematically.

Your concepts are fine, as points for discussion, but they will need to be quantified and not just 'hand waving'. I'm not criticising, my hands 'wave' as much as anybody's! However, having a mathematically described theory that makes testable predictions is way we separate out those ideas that 'work' and reflect reality in some way from those that are to fall by the wayside.
Modified gravity is MOND and your "if it can drag space around" is the gravitomagnetic effect being tested at this moment by Gravity Probe B, who knows what its answer will be?

Garth

Thanks, I was aware of how science gets done, the answer mathematically would be ∞ = 1 (No, I am NOT joking) which needs to be broken down to be effective in it's descripton of reality, otherwise, no one will understand it, it needs explaining, sorry, but it is done with words, first, then math.

As Einstein himself stated, "Theory is that which shows us where to look" if I have a theory that is, ostensibly, complete and therefore shows 'what is' as such, then thereafter it would-could be mathematized, as to show it's validity, just that I do believe that it is not as simple as just one equation.

The concepts I have in my head are not based upon mathematical reasonings, {Persay thought they include math knowledge} they are based upon observation{s} of reality and Lots of Currently known Scienctific evidence, after all, there is ony about ten percent of it left to know.

LD
.. .. .. .. Hops off .. .. .. .. .. Stage .. .. .. .. [/color]...[/color] {Whoooops!} .. .. .. .. .. ..I'll get off of this thread now, go find turtle, he should be back, any moment now[/color]

 

[Entropy]

has to be calculated in the non-linear theory of GR rather than the linear Newtonian theory.

W00t? I was under the impression that astronomers/astrophysists always used GR, I mean you'd think that there is a significant difference between the two when you're talking about these kind of things.

I'm shocked that no one has done this before.

 

[Chronos]

Thanks, I was aware of how science gets done, the answer mathematically would be ∞ = 1 (No, I am NOT joking) which needs to be broken down to be effective in it's descripton of reality, otherwise, no one will understand it, it needs explaining, sorry, but it is done with words, first, then math.

Agreed, words describe what the symbols represent in a mathematical formulation. The mathematical formulation part is what appears to be missing in this example.

 

[SpaceTiger]

There has been a rebuttal of the paper that you can see here. The rebuttal basically says that the model is "unphysical". It's yet to be seen if this "unphysical" explanation is substantial or not.

I love how the rebuttal paper cites "Introduction to Relativity". I'll let you guys know if we ever find dust disks distributed as a delta function in z.

 

[EL]

I love how the rebuttal paper cites "Introduction to Relativity".

Actually, isn't it possible that this singular disk models the galaxy quite good? Would a more realistic model really give a much different result? (I'm asking because I don't know...)

 

[Garth]

Actually, isn't it possible that this singular disk models the galaxy quite good? Would a more realistic model really give a much different result? (I'm asking because I don't know...)

I concur that's my point - even if their analysis leaves something to be desired the necessity of using GR rather than Newton to predict galactic rotation profiles would seem basic, don't you think?

Garth

 

[SpaceTiger]

Actually, isn't it possible that this singular disk models the galaxy quite good? Would a more realistic model really give a much different result? (I'm asking because I don't know...)

In some spiral galaxies, there are disks that are relatively thin, but certainly not well-approximated by a delta function. The point in the rebuttal paper was that there was an extra source of gravity in addition to that which they were using to model the luminous matter of a "real" galaxy. In other words, they were unknowingly including dark matter.

As for your latter question, I'm relatively sure (though I've not done the calculations myself) that the Newtonian approximation will be valid if GR is properly applied.

 

[EL]

In some spiral galaxies, there are disks that are relatively thin, but certainly not well-approximated by a delta function. The point in the rebuttal paper was that there was an extra source of gravity in addition to that which they were using to model the luminous matter of a "real" galaxy. In other words, they were unknowingly including dark matter.

Ah, that explains a lot! Thanks. (Have to admit I didn't read the rebuttal too carefully.)

As for your latter question, I'm relatively sure (though I've not done the calculations myself) that the Newtonian approximation will be valid if GR is properly applied.

Yes, that's what I think too.

Anyway, it's strange that CERN newsletter took it up after the rebuttal was written...
http://science.slashdot.org/science/...tid=160&tid=14

 

[Chronos]

I'm going to hide behind the skirt here, Garth... Can we say with any confidence what disc model might work? I think the observational evidence is really thin. Another objection: since when did CERN jump into the fray? I don't think that is even relevant to this conversation.

 

[SpaceTiger]

Anyway, it's strange that CERN put it on their webpage after the rebuttal was written...

Yeah, we were just talking about this at (very late) dinner. One of the guys here says he knows the people that wrote the CERN article and he says they're pretty distant from the mainstream. I wouldn't take it as an endorsement by everyone at CERN and, to my knowledge, nobody in the mainstream is taking it seriously.

 

[EL]

I'm going to hide behind the skirt here, Garth... Can we say with any confidence what disc model might work? I think the observational evidence is really thin.

As SpaceTiger pointed out, the model of the shape of the galaxy is really not the problem. The problem is that they seem to have invoked an extra source of gravity they didn't mean too...

 

[EL]

I wouldn't take it as an endorsement by everyone at CERN and, to my knowledge, nobody in the mainstream is taking it seriously.

Yes, that I'm pretty sure of too. Can we see the paper as debunked now, or do you think there could be some errors in the debunking?

 

[SpaceTiger]

Yes, that I'm pretty sure of too. Can we see the paper as debunked now, or do you think there could be some errors in the debunking?

Well, I pretty much ignored it from the get-go. There were two reasons for that. The first was that, if it were true, it would only explain one small part of the dark matter problem, leaving the rest horribly inconsistent. In other words, the same amount of dark matter that's needed to solve the dynamical problems is that needed to solve the problems of structure formation and the CMB power spectrum. If one part were solved in some other way, we would be left hanging on the other two.

The other reason was that I have a good bit of faith in the people that do these models. This is a pretty simple issue to have overlooked for so many years. I wouldn't be surprised if the same calculation had been done correctly many times before by other folks.

Anyway, yeah, it's debunked in my mind.

 

[Lapin Dormant]

O.k.

Agreed, words describe what the symbols represent in a mathematical formulation. The mathematical formulation part is what appears to be missing in this example.

Agreed so I would need the Latex equivalent of "The sum of all things, going to infinity, is equal to one"

But as I had already acknowledge it needs elucidation {mathematically as well} to fit into the minds of everyone else.

Till then, I will, probably, just shut up, Thanks

 

[Lapin Dormant]

curious

In some spiral galaxies, there are disks that are relatively thin, but certainly not well-approximated by a delta function. The point in the rebuttal paper was that there was an extra source of gravity in addition to that which they were using to model the luminous matter of a "real" galaxy. In other words, they were unknowingly including dark matter.

Just a question from the curious, is it not possible that gravity acts in some manner unseen to-or by us that could afford it a Disc of energy-alone that is {somehow} dragging around the rest of the Galaxy, with a variant in it's function pertinant to the elementals, timely available, of the construct of any given galaxy, calculated not 'across the board' of known galaxies but taking into account the relative ages, as per distribution, of the See-therefore 'known' galaxies and-or their respective centers?
Just a question, mind you.

 

[SpaceTiger]

Just a question from the curious, is it not possible that gravity acts in some manner unseen to-or by us that could afford it a Disc of energy-alone that is {somehow} dragging around the rest of the Galaxy

Gravity acting in a manner that we can't see is called philosophy. Gravity acting in a manner inconsistent with GR is possible only in the regimes in which the theory has not been tested. This includes the strong field and cosmological limits.

with a variant in it's function pertinant to the elementals

The "elementals" were, as far as I know, done away with in science hundreds of years ago.

timely available, of the construct of any given galaxy, calculated not 'across the board' of known galaxies but taking into account the relative ages, as per distribution, of the See-therefore 'known' galaxies and-or their respective centers?

Astronomers always make the appropriate considerations for age when taking their measurements. Of course, one can create arbitrarily complicated theories which are consistent with the observations and invoke, for example, time variations in the laws of physics. However, these theories will have no predictive power.

 

[Lapin Dormant]

Gravity acting in a manner that we can't see is called philosophy. Gravity acting in a manner inconsistent with GR is possible only in the regimes in which the theory has not been tested. This includes the strong field and cosmological limits.
The "elementals" were, as far as I know, done away with in science hundreds of years ago.
Astronomers always make the appropriate considerations for age when taking their measurements. Of course, one can create arbitrarily complicated theories which are consistent with the observations and invoke, for example, time variations in the laws of physics. However, these theories will have no predictive power.

Gravity already acts in a Manner that we cannot "see", what we "see" is the resultant of gravities Force acting-at work. A stationary car {Parked} is gravity acting, and no one can "see" it doing it, although you can, in your head, 'envision' it.

"Elementals" refers to the reality of elements of Chemistry, (Periodic table of elements) as the state of matter, temperature and type of Atom-molecule (Ergo Composition) might just have more effect, gravitationally, then is currently thought, or known.
No need of time variation in the laws of physics, simply the notation that what is Observed, 13.5 Billion Light years away, is also that NEW.

Therefore perhaps operating on-in a manner that is yet not understood, from this perspective, as this perspective is where we have taken all of our Known {current} 'rules of physics' from, not from "there".
Could be some {very} Slight Differences we don't realize just yet, the View has some obscuring factors to it, doesn't it.

 

[Lapin Dormant]

Luminesence?

Lets try it this way, take a gas cloud 20 K in diameter, G^M/r so we will use M = 1 so all we have left is G/r {By the way there was an experiment, done in Germany, wherein the value of G has been brought into question, back in the 90's Last century (I love saying that)} so I will run into our gas cloud with a heating source, {this is, after all, a 'thought experiment', so I can do that, "run into a Gas cloud"} release several thousands of thousands of caloric values (BTU's) and the gas cloud will, upon the timing of the radiant exchange factors relevant to the type of Gas that it is, {Which chemical element(al) it actually is} expand it's r value, so does it's potential G/r value change, as well?

"What is there" {Liqid-solid-gas} is just as important, if not moreso, to "how it is functioning" as 'How it is functioning' is Based upon What is there!
Does that bring more "light" to your understanding of it?

 

[Lapin Dormant]

It's just "so" last Century

Whoops, got to fix some of this, the Gas cloud is 20 Kms, it's supposed to be G^m/r {not M the capitalisation} and let's say that when I expanded the Gas cloud (No Jokes about that please ) it became 40 Kms in Dia.

Asks' us the Question of; "Did the G value actually reduce, by half, of what it was-had been, even though our Mass has remained-remains the same?"

This question is so "last century" I' :!) saying that

 

[SpaceTiger]

Gravity already acts in a Manner that we cannot "see", what we "see" is the resultant of gravities Force acting-at work. A stationary car {Parked} is gravity acting, and no one can "see" it doing it, although you can, in your head, 'envision' it.

No, that's a measurable effect. In science, we're only concerned with measurable effects. If that's not what you mean by what we can "see", then I can assure that the distinction you're making is scientifically uninteresting.

"Elementals" refers to the reality of elements of Chemistry, (Periodic table of elements) as the state of matter, temperature and type of Atom-molecule (Ergo Composition) might just have more effect, gravitationally, then is currently thought, or known.

The noun form of "elemental" is not used in that way, so please use the word "element" in the future if you want people to understand you. Nobody is going to think that you're unintelligent if you use the standard meanings of words.

No need of time variation in the laws of physics, simply the notation that what is Observed, 13.5 Billion Light years away, is also that NEW.
Therefore perhaps operating on-in a manner that is yet not understood, from this perspective, as this perspective is where we have taken all of our Known {current} 'rules of physics' from, not from "there".
Could be some {very} Slight Differences we don't realize just yet, the View has some obscuring factors to it, doesn't it.

No idea what you're trying to say. The same applies to your other posts, which read more like a philosophy text than a scientific query. You need to be more precise if you wish to understand something scientific. For example, sentences like the following:

What is there" {Liqid-solid-gas} is just as important, if not moreso, to "how it is functioning" as 'How it is functioning' is Based upon What is there!

This would be completely ignored by most scientists if asked to them. I'm willing to make an attempt at answering your question, but you need to be more specific. The one question that sort of makes sense is the following:

Which chemical element(al) it actually is} expand it's r value, so does it's potential G/r value change, as well?

If a cloud of constant mass and density expands to a larger radius, then yes, its potential energy increases (all of the elements expand in approximately the same way). If you mean the gravitational potential on the surface, then your formula is correct. If you mean the total potential energy of the cloud, then it's given by:

U=\frac{3}{5}\frac{GM^2}{r}