Singular disk of matter in the Cooperstock-Tieu galaxy model

[shalayka]

I wasn't certain if this topic strictly belonged in the GR forum.

I have read the article 'Singular disk of matter in the Cooperstock-Tieu galaxy model', by Mikolaj Korzynski (http://arxiv.org/abs/astro-ph/0508377). In it, the author finds that the singularity within Cooperstock & Tieu's model is not coordinate based.

What I don't understand is why the author takes the liberty of calling the solution questionable, when completely unphysical singularities of other types are clearly acceptable. ex: Cosmic strings being 1D singular filaments, and black holes being 3D singular spheres.

Does anyone know of any reason to consider 2D singularities any less reasonable than 1D or 3D singularities? Am I misinterpreting the author's use of the phrase "the model of galaxy they propose is questionable"?

Thanks for any insight.

 

[marcus]

Cooperstock-Tieu's idea has dropped out of sight for various reasons.

It came out in 2005 when people were more apt to be looking for alternatives to dark matter as an explanation of galaxy rotation curves.

It was criticized by many people in 2005, and then it disappeared. You don't hear about it much any more.

1. the main reason I think is that clouds of dark matter have been imaged by weak lensing and dark matter has become completely accepted.
Nobody is interested in alternative explanation of galaxy structure (whether by C-T or by MOND or whatever) because dark matter is there and provides a simple adequate explanation.

2. the second reason is that dark matter is required by clusters of galaxies and superclusters, to hold them together----and perhaps in the past also to promote their formation. My understanding is the C-T idea only applies to galaxies. So it does not cover all the bases---it doesn't offer an adequate substitute.

3. possibly a third reason that the C-T idea was dropped was because of all the criticism by people who claimed to find holes in it-----like this guy Korzynski.

Basically it doesn't matter whether Korzynski's crit is right or wrong because C-T is dead in any case.
Rightly or wrongly, Korzynski found that C-T would require there to actually be a massive disk in the galactic plane, the size of the galaxy. NO SUCH DISK IS OBSERVED.

He talks about the plane z=0. This would be like there is a sheet of metal slicing thru the Earth at the equator. unimaginably thin and dense metal. A disk with the same radius as the earth. What he means by z=0 is the equator plane of the galaxy.

If there would be a huge disk, it would be obvious to everybody it was there.
Stars bob up and down thru the z=0 plane of our galaxy all the time as part of their orbital motion. They would be crashing thru the disk, or the "singularity" if the disk were an actual singularity in nature.

========================

You question what Korzynski says by saying that black hole singularities are accepted.
I would say that they are where GR breaks down and they are only PROVISIONALLY accepted because we can't look past the event horizon and see what is really going on.

Last year there was a major workshop at Santa Barbara on what quantum gravity models to replace GR singularities with. All kinds of people participated from all over the world.
None of those people think singularities are real or exist in nature---the problem is what is really there. What really happened at the big bang, and immediately before. There are some models of this.

So I would say that ALL GR singularities are unphysical, but in the case of C-T galaxy size singularity it is ESPECIALLY unphysical because we can see that nothing is there. Whereas a BH singularity we know that something is there but we don't know what. So for the time being we talk about there being a singularity in the BH----or at the BB.
Something is there, we just need to get a better grasp of it. Meanwhile we refer to it as a singularity and what better temporary name?

 

[shalayka]

Thank you for the information.

Of course all singularities are unphysical. I was just having trouble recognizing why one type was questionable, but the other two are not.

Cooperstock & Tieu came out with a new paper in Nov 2007. In it they refute the claims of Korzynski, but I am not in the position to verify that their refutation is solid.

In any case, I thought that the Cooperstock & Tieu model was based on the idea of non-linear gravitation (feedback, I suppose it could be called?). As far as I know, this is also similar in concept to the method that Moffat & Brownstein used in their Bullet Cluster paper as well. Again, I'm not in the position to verify this. It's only my limited impression.

I remember reading a paper recently about black hole singularity replacement, by Pullin and others. That is definitely interesting stuff!

Thank you again for the information.

 

[Coin]

I don't think there's anything automatically out-of-bounds about a 2D singularity. Some of the old GUT cosmologies from the 80s and also some string theories have 2D singularities, in those contexts they are called "domain walls". If the existence of a 2D singularity caused the C&T theory to be discredited it would probably be because there was something unpalatable about the particular 2D singularity predicted (for example, as Marcus suggests, that it isn't observed).

Also, are you sure it is correct to call black holes 3D singularities? I don't know this stuff so well but I had always been told they were 1D [[EDIT: Sorry, you're right, I mean 0D]]. As far as I know it's not the black hole that is a sphere but its event horizon. Wouldn't a 3D singularity just be, like, spacetime?

 

[shalayka]

Thank you for the introduction to domain walls. I will look at my books tonight and see what I can find.

I see your point regarding whether or not it's correct to call a black hole a 3D singularity. I realize now that I should have been comparing event horizons, and that the singularity is indeed 0 dimensional.

 

[marcus]

Cooperstock & Tieu came out with a new paper in Nov 2007. In it they refute the claims of Korzynski, but I am not in the position to verify that their refutation is solid.

In any case, I thought that the Cooperstock & Tieu model was based on the idea of non-linear gravitation (feedback, I suppose it could be called?). As far as I know, this is also similar in concept to the method that Moffat & Brownstein used in their Bullet Cluster paper as well. Again, I'm not in the position to verify this. It's only my limited impression.

I remember reading a paper recently about black hole singularity replacement, by Pullin and others. That is definitely interesting stuff!

...

Oh ho! You are more up on this than I am. I did not remember about the new C-T paper of November 2007. So the C-T idea is still alive and kicking, after a fashion. I should say thanks to you for information.

I think I may have seen the paper you mention about black hole singularity replacement. there was one in late 2007 by Gambini and Pullin, if I remember right. Indeed it is interesting, and also confusing. Two groups both used LQG methods to study black holes and in both cases the singularity did not occur, but different things happened. IIRC in the Gambini and Pullin case there was an unambiguous bounce. The other authors were Vandersloot and somebody else.

I know that MOND people did answer the Bullet Cluster business, for example Moffatt and Brownstein. But there has been so much imaging of Dark Matter reported in the past year or two (anyway that's my impression) that I can't see how MOND can survive.

Since you are following the literature, perhaps you could start a thread on what you are interested in and keep us posted.

 

[shalayka]

Oh ho! You are more up on this than I am. I did not remember about the new C-T paper of November 2007. So the C-T idea is still alive and kicking, after a fashion. I should say thanks to you for information.

I think I may have seen the paper you mention about black hole singularity replacement. there was one in late 2007 by Gambini and Pullin, if I remember right. Indeed it is interesting, and also confusing. Two groups both used LQG methods to study black holes and in both cases the singularity did not occur, but different things happened. IIRC in the Gambini and Pullin case there was an unambiguous bounce. The other authors were Vandersloot and somebody else.

I know that MOND people did answer the Bullet Cluster business, for example Moffatt and Brownstein. But there has been so much imaging of Dark Matter reported in the past year or two (anyway that's my impression) that I can't see how MOND can survive.

Since you are following the literature, perhaps you could start a thread on what you are interested in and keep us posted.

I'm flattered indeed, but I don't think I'm ready to review the work of others. :)

I tend to stick to the more popular physics blogs for what's the "latest and greatest". The personalities themselves are highly entertaining at times.

If I do find anything that raises my antennae, I'll definitely post about it though!