STVG & Rotation curves vs Dark Matter

[DyerWolf]

Guess this goes here...

Braunstein and Moffat offer an alternative to CDM for the rotation curves: called (IIRC) Scalar, Tensor, Vector Gravity. According to an article I read, the theory did very well in predicting the curves for a variety of galaxy types - without resorting to the use of CDM.

I haven't read much about their theory here (although I do recall a vigorous debate re: MOND/TeVeS). What is the general consensus?

Anyone here familiar with their theory who can point me to articles accessible to the informed amateur? (I've read the New Scientist piece)

Thanks

[publius]

Moffat and Brownstein's STVG gravity is not the typical type of ATM that gets posted here. It is "merely" an alternate theory of gravity in keeping with the grand tradition of physics (and within in a mathematical framework, I remind some of our ATM friends, here). It makes predictions.

We've discussed this in a couple or three threads. Search on "Moffat" and STVG (or some permutation of those letters -- I got it mixed up a lot ).

Iorio put out a paper claiming to rule it out from outer solar system data, very accurate data of the motion of the outer planets. IIRC, STVG according to Iorio calculations at least, predicted a component of motion that, while incredibly small, was in the precision of the latest measurements, at least according to him. Such a component wasn't there.

Iorio always seemed pretty good to me, but he did get in sort of a food fight about a Mars probe orbit demonstrating frame dragging. Others said his error constraints were laughable, apparently.

-Richard

[Iori Fujita]

First of all, I would like to present this fundamental working hypothesis. It is the universal force which unifies gravity and separator into one. No one ever knows about the separator force. So now, I give a definition of the law of universal separation at first.

Fs = - Sp Ea Eb / r^2 F ; the separation force
Ea ; Energy which belongs to the point a
Eb ; Energy which belongs to the point b
r ; the distance between a and b
Sp ; the separation constant
This force will not be detected on the Earth. It can be negligible even in the solar system. But it will work in the galactic scale.
Next step is to unify Gravitation and Separation into one law.

Fg = G Ma Mb / r^2 -----------------Then,
Fg+s = G Ma Mb / r^2 - Sp Ea Eb / r^2


And assume that Sp = G / c^4, because E = mc^2.

Fg+s = G Ma Mb / r^2 - (G / c^4) Ea Eb / r^2

One step forward by using the complex number formula.

F = G ( Ma + i Ea / c^2 ) ( Mb + i Eb / c^2 ) / r^2
F = G Ma Mb / r^ - (G / c^4) Ea Eb / r^2 + i ( G Ea Mb / ( r^2 c^2 ) + G Ma Eb / ( r^2 c^2 ))
The real part is Re( F ) = Fg+s, but I don't know how to deal with the imaginary part ; Im( F ) = G Ea Mb / ( r^2 c^2 ) + G Ma Eb / ( r^2 c^2 ).

So an existing substance is to be described as S = M + i E / c^2 .
In a certain independent area, if M + E / c^2 = constant ( in other words when M decreases by ΔM, E will increases by ΔE = ΔM c^2 ), then abs( S ) = will be minimum when M = E / c^2, because abs( S ) = root( M^2 + E^2 / c^4 ).

Iori Fujita

[Tim Thompson]

Braunstein and Moffat offer an alternative to CDM for the rotation curves: called (IIRC) Scalar, Tensor, Vector Gravity.

Spelling. It's Brownstein, specifically The Bullet Cluster 1E0657-558 evidence shows Modified Gravity in the absence of Dark Matter; Brownstein & Moffat,
February 2007; accepted for publication in Monthly Notices of the Royal Astronomical Society, July 2007. The results are too new, not even really "published" yet, to have much reaction. Still, there are 5 citations to the preprint, and the latest may be significant. The speed of the `bullet' in the merging galaxy cluster 1E0657-56; Springel & Farrar, MNRAS 380(3): 911-925, September 2007. The authors argue that a better hydrodynamical model of the cluster merger reduces the relative velocities of the galaxy clusters, which velocity was previously estimated from the shock velocity. That changes the relative masses. And that means the collision is completely compatible with a standard CDM model. It does not necessarily mean that Brownstein & Moffat are wrong, but it does mean that there is no reason at hand to prefer one explantion over the other, all other things being equal. There is, not surprisingly, more work to do here.

These papers linked here are the best I can do. They are not intended for amateurs, so the extent to which you find them accesible is for you to decide.

[DyerWolf]

Richard, Tim: thanks very much for the responses (Tim - thanks also for the spelling catch - I hate errors - especially my own).

The abstract looks very interesting. One problem: how do I open it to see the full document? Do I need to sign up with a library somewhere?

[Tim Thompson]

The abstract looks very interesting. One problem: how do I open it to see the full document? Do I need to sign up with a library somewhere?

Follow the arXiv e-print link. That is an archive of pre-prints, all of which can be downloaded in PDF or PostScript format free of charge. I prefer to link to the NASA ADS entry, rather than directly to the arXiv entry, because ADS will show if the paper has been published, which arXiv sometimes does not do, and because ADS tracks citations, so we can see which papers have cited the paper of interest, and thus follow the literary train.

And add this paper: Galaxy cluster masses without non-baryonic dark matter; Brownstein & Moffat, MNRAS 367(2): 527-540, April 2006. This may have been the intended source for Brownstein & Moffat.

[czeslaw]

According to Dark Matter problems Milgrom proposed a MOND idea as change of the acceleration by a distance.
Beckenstein proposed the tensor-vector-scalar gravity theory (TeVeS) of gravity.

In 1979, Moffat made the observation that the antisymmetric part of the generalized metric tensor need not necessarily represent electromagnetism; it may represent a new, hypothetical force. Later, in 1995, Moffat noted that the field corresponding with the antisymmetric part need not be massless, like the electromagnetic (or gravitational) fields. To distinguish his work from Bekenstein's, Moffat calls this version of his theory Metric-Skew-Tensor Gravity (MSTG).
http://en.wikipedia.org/wiki/Nonsymm...ational_Theory

Beckenstein's and Moffat's theories are based on the idea that a Gravitational Field posses its energy and a relativistic mass which has its weight and interacts gravitationally.

A good discussion on MTG possibility shows an article of 2006 :
http://arxiv.org/PS_cache/gr-qc/pdf/0611/0611005v1.pdf

[DyerWolf]

I've been poring over T. Van Flandern's ideas and Carlip's response. While the site I found Van Flandern's paper on seems a bit "woo", his paper was intruguing. Carlip's response brought forth the quadropole nature of gravity that Richard has mentioned elsewhere.

Yet this issue got me to thinking: do the Galaxy Rotation Curve equations / observations presume c_g = c? (Did I write that correctly? I mean speed of gravity = speed of light) Or do they make a Newtonian-esque presumption that the effect of gravity is instantaneous?

It seems to me that a galaxy is big enough that the speed of gravity (c_g = 2x10^10c) Van Flandern suggests could be falsified by observation.

Is that possible?

[publius]

Dyerwolf,

While at first blush you would think the size of a system would directly affect this, it doesn't. What matters (using appropriate coordinates and other considerations) is the ratio (v/c) of the system. Think of the ratio of "where it is instantaneously" vs. "where it would be if the acceleration didn't change over the light travel time". That will scale with distance easily.

And that's tied to radiation. If this system isn't radiating significantly, then the effects of propagation delay are being cancelled, no matter how big it is.

So Newtonian gravity works well even for the Galaxy as a whole.

-Richard