Re: LIGO.

On Feb 28, 5:06 am, anands...@xxxxxxxxx wrote:
On Feb 25, 5:17 am, "EricGisse" <jowr...@xxxxxxxxx> wrote:



Juan R. wrote:
On Feb 21, 10:38 am, "EricGisse" <jowr...@xxxxxxxxx> wrote:
Quoted from the paper you just cited:

Whereas Angus, Famaey and Zhao consider it possibleto explain the
lensing with a reasonable purely
baryonic matter distribution, a later paper by Angus, Shan, et al.
[87] concludes that dark matter is needed after all. This is hardly
surprising; as we saw in Sec. 3, pureMONDdoes not fully account for
the acceleration discrepancy in the dynamics of quiescent galaxy
clusters [10]. But DM models of the bullet clusters within GR are not
without their problems. Farrar and Rosen [88] note that the relative
velocity of the clusters is too high as compared to those seen in DM
simulations of structure formation. To remove the contradiction they
propose that a non-gravitational attraction of a new sort acts only
between clumps of DM. But is assuming existence of DM together with a
new interaction specific to it more parsimonious than a modification
of standard gravity such asMOND?

You see the pure MOND is in trouble. But in my case I don't believe
that MOND is correct. It is just a manifestation of a breakdown of
GR that we see in all the Galaxies. It is like the Keplers laws,
they were correct but only worked for elliptical orbits. Similarly
MOND works only for Galaxies. I don't even expect it to be correct
at that scale, just that it matches the actual law quite nearly.

MOND is nonrelativistic curve fitting that abjectly fails in the case
of the bullet cluster. It never had a chance at being useful from the
beginning since it couldn't handle relativistic effects. The howitzer
shell that finally destroyed the fully nailed coffin was the bullet
cluster.


But DM is totally bunk. It does not work at all at the level of
Galaxies. If a equation (MOND) can fit all galaxies with a single
universal parameters then it has some truth in it.

MOND can't. If you think it can, back up the assertion with some
halfway decent references.

If you think DM is bunk, explain why the lambda-CDM [cold dark matter]
model fits the WMAP 1st and 3rd year data runs so well, as well as
being independently confirmed by the Sloan digital sky survey data.

No amount of nay saying will do any good. While no DM theory can fit the galaxies
without two parameters per galaxy. Two parameters per galaxy is
too much you can fit any two dimensional shape with it, incidentally
galaxy is a two dimensional shape.

It isn't as simple as that.


Also to make matters worse for DM no theory works simultaneously
on LSB galaxies and giant Elliptical galaxies.

If you say so.


If you read your excerpt the paper says that DM also has trouble
with the structure formation aspects.

Duh. We don't know what dark matter is or how it interacts with
itself, or anything else.


More talk about galaxies that are dark-matter free. I would think
those would be of great interest to astronomers, perhaps you have a
reference?

Please look into Giant Elliptical Galaxies. Some of them don't show
any evidence of DM. Astronomers who work on these abnormal galaxies
tend to find great solace in MOND, as it fits their data.

Think about the bullet cluster. Think about how an elliptical galaxy
is formed.

Knowing that dark matter will fly unbothered if two galaxies collide
[bullet cluster], would you really be surprised if the product of a
collision between two galaxies [an elliptical galaxy] is largely DM
free?


v) From an empirical point of view,MONDmodels using a single
parameter are often more precise in fitting data that GR+DM models,
even when later models use three or four parameters the fit to data is
poor that withMOND, doingMONDmore satisfactory [2].

MONDis a crap model even before the bullet cluster results, which at
the very least putMONDon the same ground as classical theory, are
taken into account. It does not take into account _any_ relativistic
effects - it is simply a rescaling of Gm/r^2.

Well TeVeS is Relativistic.

There isn't jack *** about TeVes other than lots of promises. People
whine that dark matter is a 'kludge' and then, inexplicably, turn to
theories like MOND or TeVes which are even more of a kludge. TeVes is
merely a more complicated form of curve fitting. A scalar field,
vector field, and metric gives lots of wiggle room in terms of free
parameters.




Your reference is interesting, but it is more interesting that the
Lamba-CDM model is the one that makes the best fit with the WMAP 3
year data. It should be noted that the L-CDM model has 6 free
parameters, rather than 3 or 4. Familiarize yourself with the topics
you seek to argue about.

Lets leave Cosmology behind please. L-CDM is not working at a much
smaller scale. First lets get it to work at the Galaxy level. There
is no DM theory yet that can fit Galaxies satisfactorily. First we
should get that right and then talk about cosmology. If there
is something wrong with GR you will see much larger artifacts at
cosmic levels.

Of course it doesn't work at a smaller scale - it isn't meant to. It
is meant to model large scale stuff. When I say large, I mean much
larger than individual galaxies. Nobody knows what dark matter is.
Lots of guesses, no solid data.

Nobody uses GR for large scale structures like a galaxy. Everything is
very, very Newtonian at that range. Since GR reduces to Newton under a
set of conditions which a galaxy satisfies, that's ok.




http://arxiv.org/PS_cache/astro-ph/pdf/0603/0603449.pdf

Here is something moderately interesting as well:

Page 14

Table 3 shows that the power-law CDM is a significantly better fit
than the simpler
models. If we reduce the number of parameters in the model, the
cosmological fits significantly
worsen:

I didn't know that to get a fit you can even increase or decrease
number of parameters. So much for the scientific method. And then
you think that it is the best thing since the big bang.
Is it any better than a high level curve fitting exercise.

Yes. The number of parameters is small, and reasonable.

http://en.wikipedia.org/wiki/Lambda-CDM_model

It is a model of the universe that makes a very good fit with 6
numbers. Think about that for a minute.






· Cold dark matter serves as a significant forcing term that amplifies
the higher acoustic
oscillations. Alternative gravity models (e.g.,MOND), and all baryons-
only models,
lack this forcing term so they predict a much lower third peak than is
observed by
WMAP and small scale CMB experiments (McGaugh 2004; Skordis et al.
2006). Models
without dark matter (even if we allow for a cosmological constant) are
very poor
fits to the data.

Far from a common misconception between relativists,MONDis not more
empirical than GR+DM. It is true that the ***original***MONDlaw was
derived from direct empirism from a kind of observations but since
MONDformulae has been _applied_ to cases for which was not initially
considered and has continued to work when applied in the new
situations.MONDhas done several ***serious*** predictions in places
where GR has done _none_.

MONDis CURVE FITTING.

I agree. CDM is also curve fitting. Now we are even;-).

L-CDM is a *model* with specific falsifiable assumptions about what is
being modeled. MOND is a "dunno. fit it to a curve" theory.




Can you name even one thing thatMOND[or TeVes] has predicted that
turned out to be true? I'm talking about predictions that aren't
fitting to already-known results. I want to know if there is somethingMONDhas predicted that was never seen before, and was validated by
observation.

Have you heard of LSB galaxies, the low surface brightness galaxies
that apparently have too much DM. These are the ones that were
predicted by MOND. And then when the data came in over the next
decade it fit MOND very well. Actually it is a cornerstone of
MOND. So it scores better there than DM, which has never
predicted anything.

I have no answer for this.


I think you should go to the sitehttp://www.astro.umd.edu/~ssm/mond/
It will help you understand that MOND is not crackpot science.

Of course not. I just don't like it and think some of the arguments
for it are moderately hypocritical. The original incarnation of MOND
is dead and buried, and the latest iteration is a metric, scalar
field, and vector field stacked ontop of eachother. Yet somehow that
is supposed to be better than dark matter.

It is just not beautiful. But then creating a beautiful theory
is the work of scientists, and almost all of them are astronomers,
who have lost their faith in DM, and GR.

Bullet cluster, bullet cluster, bullet cluster. Until the anti-dark
matter crowd adequately explains the bullet cluster, dark matter has a
serious point in its' favor. The anti-DM crowd also needs to explain
why the L-CDM model does such an excellent job. As well as why the
dark matter assumed by the L-CDM model [cold non-interacting _non-
baryonic_ dust] is such a good model for something that they claim is
an artifact of gravitation.




See also extensive comparison ofMONDvs GR+DM in [3] from ayone who
initially worked in DM theories until experimental data tired out him.

You expect me to take that seriously when he does not support his
claims at all?

Which claims does he not support. I think that the site is very
easy to understand.

Um, all of them?

The claims he makes are easy to understand, but the support for the
claims isn't there so I have no means of evaluating it for myself.




Of course,MOND***alone*** cannot be the last reply.MOND(including
relativisticMOND) may be posted in a firm theoretical basis, (I
disagree with AQUAL, TeVeS, and all that).

As a historical remark, I would point that dark matter is today
playing the same role that missing planet (that planet never found) in
the Newtonian theory of Solar system gravity.

We call that planet Pluto these days.

He actually meant Precision of Mercury. Which was supposed
to be caused by some hidden planet, and was fit by special
relativity.

Nobody seriously thought it was a planet, or somesuch. Everything that
was considered [Vulcan, dwarf star companion, shell of dust between
the sun and Mercury, etc] ended up failing for various reasons. The
final explanation was done by *general* relativity, which is a theory
of gravitation. Not special relativity, which is explicitly not a
theory of gravitation.

The analogy stopped being valid when the bullet cluster results were
published.


I don't understand the god like reverence that GR holds in
the minds of Relativists. If things can behave differently
at high speeds, why can't they do so at low accelerations.

Can you name one interaction effect that gets stronger as distance
increases? No, please don't argue that gravity is like a harmonic
oscillator.

GR is highly accepted by PHYSICISTS [relativists is a crank term used
by those who wish to dilute the language in order to make their
position appear more valid] because of the extreme validity of the
predictions it makes.

After all we haven't directly tested anything at these
low accelerations. At least MOND by working on almost
all galaxies makes a very strong case that something is
wrong with gravity at galaxy scales. And if there is
something wrong at these scales it cannot be correct
at higher levels.

I disagree with the assertion that MOND works everywhere. It most
certainly fails to take into account any relativistic effects, and I
am yet to see evidence for the assertion that it predicts the way
galaxies rotate correctly. I expect that it is a different scaling
parameter for each galaxy.


MOND indeed does not work at cluster levels and above,
but thats probably due to the fact that we don't know
how MOND arises. It is stupid to try to fit WMAP data
to it. As it cannot make any sense at the cosmological
level, when it doesn't even fit Clusters. But that doesn't
mean that GR is correct. MOND is just a tool that proves
that GR is not correct.

Ah, interesting.

MOND doesn't work on the small scale [planets, star systems, star
clusters] and it doesn't work on the large scale [superclusters,
clusters]. It only works on galaxies, and even that is debatable.

Even then, a theory that is broken from the beginning somehow proves
GR wrong! Even though observation is entirely consistent with dark
matter being real actual matter that doesn't electromagnetically
interact.


I like to think that the low acceleration effect
arises due to the curvature of the Universe. And GR
does suffer from the flatness problem. If big bang
happened then the Universe must have a curvature.
MOND simply exposes the problems of GR.

What flatness problem?

Observation says that the universe is not curved. Now or ever.

Spend some time familiarizing yourself with the results published in
the last 2 years. They are very interesting and put forth some serious
challenges for both camps of thought, along with the minor outliers.


-anandsr



[1] http://arxiv.org/abs/astro-ph/0701848

[2] http://www.astro.umd.edu/~ssm/mond/fit_compare.html

[3] http://www.astro.umd.edu/~ssm/mond/mondvsDM.html


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