Re: LIGO.
- From: anandsr21@xxxxxxxxx
- Date: 28 Feb 2007 06:06:57 -0800
On Feb 25, 5:17 am, "Eric Gisse" <jowr...@xxxxxxxxx> wrote:
Juan R. wrote:
On Feb 21, 10:38 am, "Eric Gisse" <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.
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. 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.
Also to make matters worse for DM no theory works simultaneously
on LSB galaxies and giant Elliptical galaxies.
If you read your excerpt the paper says that DM also has trouble
with the structure formation aspects.
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.
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.
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.
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.
· 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;-).
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 think you should go to the site http://www.astro.umd.edu/~ssm/mond/
It will help you understand that MOND is not crackpot science.
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.
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.
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.
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.
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.
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.
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.
-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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