wrote:
Eric Gisse wrote:
wrote:


On Mar 20, 1:34 pm, "Eric Gisse" wrote:
wrote:
There is _no_ reason to doubt that our interpretation of the weak
lensing results is false. There is matter there and it curves light
and we detect it. That is remarkably direct compared to other
cosmological observations that are *heavily* model-dependent.

Just remember that I am arguing that there is no DM within Galaxy
scales. ie MOND explains Galaxy rotation curves so obviously
Weak Lensing will need to be explained by a quantum theory that
will derive MOND. In my GR+DM cannot explain MOND.

Galactic/cluster scales are deeply classical - there is no reason to
expect a quantum theory would make any modifications at such
macroscopic distances. What we got is what we got, any modifications
to what we already know at large scales would have to be very subtle.

You can argue that there is no DM within a galaxy, but you can't argue
it from observational evidence. I can't argue against it, from the
same token - but I would think it odd that it all accumulates in the
halo.



Neutrinos avoid this problem by being hot, which prevents their
coupling together.

Neutrinos avoid the problem by having an insanely small scattering
cross section and by traveling within epsilon of light speed for
pretty much any plausible amount of energy. They avoid the problem so
well that they are horrible dark matter candidates - not enough of
them can be produced, and they are not capable of binding to galaxies
considering how fast they would be traveling. Neutrino dark matter
would form a background, not a halo.

True for Galaxy scales but not true for Cluster scales.
So whats your point?

What's another order of magnitude going to do?

Look, neutrinos travel _FAST_ - within an epsilon of c for all
realistic kinetic energies obtained from fusion reactions at the big
bang. There simply aren't any bound orbits - the best you can
reasonably expect is a weak background, which isn't going to influence
anything significantly.


KATRIN isn't and never will be a test of MOND. Neutrino oscillations
simply shift the flavors around - they do not add mass. Neutrino mass
is constrained to be very tiny, and if the L-CDM model is even close
to being reasonable the total masses of all neutrinos is less than an
eV.

I don't understand this, the three flavours are supposed to have
weight

mass =/= weight.

less than 2.2eV, 170KeV, and 15.5MeV. So even the lightest may be
heavier than 1eV. The others are much much more heavy.

No - those are the _least_ upper bounds on individual neutrino
masses. The individual measurements are gross measurements to say the
least - the spread is huge. However, the sum of neutrino masses is
quite small - on the order of an eV, as constrained by astrophysical
results [model dependent, but the consistency is very good across
varying data sets].

http://pdg.lbl.gov/2006/listings/s066.pdf

Do you mean to say that KATRIN will falsify LCDM if electron neutrino
happens to have a weight more than 1eV. I don't believe that DM
theories are falsifiable. They are just curve fitting exercises. Add
as
much DM as you need whereever you need. LCDM theories need not
apply to Galactic level and the NFW halos need not have any
cosmological significance.

If neutrino masses were observed directly to be far larger than a
fraction of an eV, I think it would be troublesome. But how exactly it
would be troublesome is less than clear to me.

Until some actual viable candidates are put forth, DM will be a bit
less than strong in its' foundation. However, something that preserves
our current theories of gravity and whose inclusion is supported by
modeling of the large scale structure of the universe is quite
compelling, especially when the only theory that is remotely competing
at this point is an even more ad-hoc theory.

Do not forget the supreme irony of neutrinos being anyway important in
finding dark matter. Neutrinos were postulated a full 25 years or so
before they were detected to explain the spectrum of energies in beta
decay and to explain why angular momentum was not conserved.


No! Neutrinos _can not do it_!

You mean that Neutrinos cannot make stable structures at Cluster
sizes.
This is as much an speculation as is my assertion as mine. We don't
yet know the masses and relative abundance of the three neutrinos.

Relative abundances can be gathered via big bang nucleosynthesis. I
gave you a link ...somewhere... that listed the top 10 or so most
common reactions, and neutrinos were in most of them.

It does not matter - the energies given to the neutrinos will be in
the MeV range. That is DEEPLY relativistic - E ~ pc for E mc^2.
Work backwards - how many zeros will be in your answer when you obtain
1 - v/c?

Borrowing from GR slightly, neutrinos are the massive equivalent of
light. They are the closest a massive particle can get to traveling on
a geodesic. Borrowing further, light only has closed [UNSTABLE!]
orbits around a mass when it is near [r ~ GM] the Schwarzschild
radius. Dark matter is out in the halos of galaxies and such - a shade
short.



Look back at that paper I linked to you the other day - remember how
everything was consistent with a HALO of dark matter? There are simply
not enough neutrinos and the ones whizzing around simply have too much
energy to be bound.

http://www.astro.ucla.edu/~wright/BBNS.html


Oh look there it is.


It doesn't give any neutrino abundance. I would think that there may
be
a huge amount of neutrino as it is a very important part of the
reactions
below one second timeframe. Also I do not expect that all of it will
be
absorbed. It is entirely plausible to have a large amount of
neutrinos.

Of course there will be a large number of neutrinos. They will for all
intents and purposes still be tooling around, barring ridiculously
rare absorbtion events.

They are very, very light and they are moving very, very fast. They do
not matter - neutrino-based dark matter has been long discredited even
before weak lensing results started coming in.



Both DM and MOND were hypotheses created to explain galactic rotation
curves. MOND, however, can't handle the large scale structure of the
universe while DM is an fundamental part in something that makes a
very, very good fit. Remember what you told me - something that fits
that well has to have some fashion of truth to it?

So give me one DM theory that works well at the large structure and
works well for the galaxies as well. We know that LCDM does not work
well at Galaxy level.

We don't have one as far as I know.

However, MOND seems like a good start. But I think Milgrom et al's
head would explode if the dark matter people co-opted MOND in that
fashion.


There is a difference between MOND and DM.
DM is a curve fitting exercise requiring the use of several free
parameters,
while MOND is a single equation that works well with a single
universal
parameter on all galaxies.

No.

If you read the papers I linked you, there is a direct correspondence
between dark matter and baryonic matter. The amount of free parameters
got very, very small.


TeVeS is making testable predictions. I personally don't like TeVeS,
but it is not a bad idea. We may come up with a law for weak lensing
through it. This work is also needed for convincing GR proponents that
DM in Galaxies is redundant.

I wish them the best of luck - they have some severe hurdles to pass
through.

They have to describe *all* of the following self-consistently:


Well GR has to explain MOND. Unless it does so, it is a suspect
theory.

G_uv = 8piG/c^2 T_uv

That is GR right there. Everything GR predicts is based upon what you
shove into T_uv - what do you suggest? Besides, the full machinery of
GR is un-needed. Newton works for this - deeply classical, remember?
GR is basically a few extra decimal places at 100AU distance - much
less hundreds of thousands of light years.

It needs to show how DM should be distributed to explain MOND.

This has been done by working backwards from the observed
distributions and Poisson's equation. MOND and DM play nice together.

http://www.journals.uchicago.edu/ApJ...610/58610.html

Seriously - did you read this?

It must show why it should have this distribution and not any other.
It must show why DM is required when the curves can be explained
based on only BM.

No, it doesn't. The question of "why" is not science's problem. The
best you can hope for is "how?"


1) Make dark matter irrelevant.
Why???

Making dark matter irrelevant is MOND's reason d'etre, that's why.

Bullet Cluster shows that DM exists at the cluster scale, which was
already expected from previous MOND fits to other cluster.
You can change it to Make dark matter irrelevent at the galactic
scale.
It is certainly not required at the galactic scales.

Bull**** it hasn't.

http://www.journals.uchicago.edu/ApJ...610/58610.html


I don't disagree with the rest of your list. They are certainly
required
by any quantum theory of gravity.

I'm not talking about a quantum theory specifically - I'm talking
about anything that seeks to supplant GR. The list is geared more
towards TeVeS and such.



MOND/TeVeS works well in strong gravity, as they are basically same as
GR. Works very well in Galaxies. Predicts HDM in Clusters, as required
by Bullet Cluster. Also is not against Dark Galaxies. It can be
falsified, but has not been falsified yet.

Careful when you say 'required'. I have been trying to distinguish
between things that are observationally true and which are required to
be true within a specific hypothesis.

Hot neutrinos - it isn't something required by MOND, it is a
*hypothesis* that is added in to explain the bullet cluster within the
context of MOND.

It is *required* by MOND to fit Bullet Cluster or any Cluster data.
It may be that MOND is not the correct theory. But the Bullet Cluster
proves that there is dark matter at cluster scales.

There is no need to remove Dark Matter in Bullet Cluster. It is an
unambiguous observation that Dark Matter exists in Bullet Cluster.

Zuh?

Are folks folks going with the King Solomon approach and splitting the
difference? Arguing both dark matter *AND* MOND is a little
contradictory to me.

You have a lot of prejudice regarding MOND. I don't think I can rid
you
of your prejudice. You see the forest and cannot focus down to the
trees.

Of course I am prejudiced. The proponents of MOND seem to think it is
a theory of gravity unto itself rather than a model.

It is obvious that MOND and Dark Matter are not incompatible.
If you ask Milgrom himself, he will not agree with your statement.
The whole point of MOND is to show that a simple modification to
Newtons law can explain rotation curves of all galaxies. It doesn't
mean that we have seen everything, and that DM cannot exist in
clusters.

....then when a fair bit of evidence crops up which shows that it is an
actual matter distribution causing the funky rotation curves?


It only means that there is no need for DM in Galaxies. Nothing more
nothing less.

http://www.journals.uchicago.edu/ApJ...610/58610.html

READ IT


I don't think I can continue this discussion if you cannot grasp
this basic fact of MOND.


Also MOND has been predicting double the mass in most Clusters, which
should be the same Dark Matter which we see in Bullet Cluster. But
that doesn't mean that it has to be CDM, it could be HDM.

...and how many HDM candidates are there? There aren't that many
stable particles which don't interact electromagnetically...

And how many CDM candidates have been observed.

Viable? Zero.

At least Neutrino has been observed and has now been shown to
oscillate
with some flavours having huge masses. Since we don't know the
average
mass we cannot yet conclude that it cannot make stable structures
yet.

1 is less than 1 trillion. If my least upper bound is 1 trillion, 1 is
the possible true value.

Read the PDG link I gave you. The sum of masses appears to be less
than an eV.


Let me be clear - I accepted before and accept even more now thatMOND
is pointing to something important. What we seem to disagree on is
_what_ that important thing is.

Well now I can rejoice ;-). We have reached the most important part of
the discussion. You accept MOND effect as real.

Yes and no.

I accept that MOND is an accurate model over a surprisingly large
sample set. I rationalize it thusly: all galaxies appear to have
formed in the same way, more or less. So it stands to reason that DM
will be the same in each galaxy [less collisions and exotic
circumstances] if not more so due to the lack of interaction.

I do not accept that MOND is a physical theory unto itself. There are
too many results from weak lensing that make dark matter convincing in
my eye, as well as its' utility in cosmological modeling. The MOND
folkes probably would _not_ like that position.

Again the forest. Try to focus only on one aspect at one time. Looking
at trees only sometimes is useful.

It is obvious that MOND is not a physical theory. It is just a visible
artifact of the Quantum Theory of Gravity.

No. It isn't.

MOND was designed to, and continues to be, an exercise in curve
fitting that has served its' purpose very well. Getting the answer
right in one _limited_ regime does _not_ make it a viable theory of
gravity.


We know that Weak Lensing and Rotation Curves must have the same
origin. If it is GR+BM+DM then it is the same for both if it is QTG+BM
then it will be the same for both. Now if we can prove that GR+BM+DM
cannot fit the Rotation Curves as well or better than MOND, then we
have proved that GR+BM+DM is not the correct picture. And we must
look into finding a theory QTG that is compatible with MOND and also
explains weak lensing based only on BM.

http://www.journals.uchicago.edu/ApJ...610/58610.html

Dark matter and MOND share a large degree of correspondence. You
seriously need to read that paper.


The real solution is only to find a distribution of DM that has the
following
properties.
1) It can fit MOND at the currect epoch.
2) It can fit WMAP using a distribution that should be able to reach
the
MONDian distribution at the current epoch.

WMAP data is an observation of the background radiation - it is about
14 billion years short.

3) There must be some observable departures from MOND which we
can see to discard MOND. In other words there can be no DM theory
that will be indistinguishable from MOND, because DM cannot have
zero degrees of freedom.

The bullet cluster is already an observable departure. You can't be
choosy and suddenly make MOND applicable only to galactic scales when
the entire theory is based around modifying gravity for low
accelerations.


2) We cannot be living in a special epoch, when DM matches MOND
everywhere. It must have been true for a very long time in the past.
And will
continue to do so for a very long time in the future.

I don't see why not - at least, the matching part. I am yet to hear a
convincing explanation as to why MOND *can't* be represenative of dark
matter.

We cannot be living in a special epoch because the galaxies we see are
in different stages of development. DM cannot fit MOND for all of them
unless it fits all of them at all times. So there can be no special
epoch.

They are not different.

Barring exceptional cases and galaxies that have suffered collisions,
they are all the same up to a parameter or three.


I thought it was obvious so did not give my reasoning.

4) If you see the 3 points above you see that DM in galaxies is
superfluous. It must satisfy too many features to be true, and top of
that it has no degrees of freedom, which makes it a superflous
concept. This is where Occam's Razor steps in to say that DM is not
simpler than MOND, and so must not be the true picture of the world.

I don't think you are applying Occam's razor properly. DM as a concept
is quite simple - there is matter we can't see that explains otherwise
contradictory observations. The concept is not superfluous because
there is no alternative _physical_ explanation, nor is there an
explanation of lensing results.

I think you are not applying it properly.

DM is simple but DM mimicking MOND is not. MOND is the real crux of
the problem. Without MOND, there is no trouble for DM at all.
With MOND it becomes totally superfluous (Just to remind only at the
galaxy level, MOND doesn't fit Cluster data, so DM is not superfluous
there).

DM is a simple concept.
MOND is a more complex concept.
DM mimicking MOND is a very complex concept.

http://www.journals.uchicago.edu/ApJ...610/58610.html

READ IT


On the contrary, MOND is expected to make a lot of Relativists very
angry when they find that no DM model can work ;-).

*points to weak lensing*

That is what it is all coming back to - weak lensing. Why does weak
lensing keep showing a distribution of dark matter if it isn't there?

Weak Lensing is irrevelent, and I am not ignoring it while saying
that.

Even 2 free parameters are too many when a competing theory can fit
the data without any free parameter. And most DM theories require 3 or
4 parameters. Remember that DM theories can fit the 20% cases where
the data is problematic. This indicates that the free parameters are
enough to fit any rotation curve even if they are not from a real
galaxy. This is what proves that there are too many parameters. Any
good model is one which is not able to work with bad data. DM models
are not good models.

What happens when the competing theory fails in an unambigious way in
a different case?

I don't think DM is anywhere near the point to where one could say "So
what? I can fit any arbitrary curve with a large enough amount of
parameters!"

Actually it is at that stage. I had seen somewhere can't remember
whether
it was a paper or article, in which they had created a pseudo galaxy
by merging data of two real galaxies. MOND would not fit that data,
while LCDM halos where able to fit it.

So how does that support your assertion that it has too many
parameters? The L-CDM model has a _highly constrained_ 6 dimensional
parameter space. I have linked you to the WMAP site and specific
papers before - the amount of freedom the parameters have are quite
small.

Do you know how many parameters I need to do a QM problem? Same order
of magnitude.


I and possibly all of the MOND proponents are dying to know an
entirely plausible distribution of DM that can fit MOND.

Read the papers I cited you previously. You will see where I'm coming
from.

Especially http://www.journals.uchicago.edu/ApJ...610/58610.html

Which one do you mean?
PseudoIsothermal Halo or NFW Halo.

Whichever.


I don't think there is any large scale formation theory for either of
them.

The most popular theory that explains large scale structure formation
is LCDM which fails badly on most Galaxies.

Does it...?

Reference?


You must understand that any distribution must have a valid formation
theory behind it. One is not complete without the other.

Interesting how dark matter is held up to the standard of "explain
anything and everything" [as it should] whereas MOND gets the "eh it
works sometimes - must be true" treatment.


Just remember that Occam's Razor is against you ;-).

On Mar 31, 11:41 pm, "Eric Gisse" wrote:

Do you say things like this after carefully ignoring evidence that
disagrees with your interpretation?

There exists an entire community discrediting you call evidences.

If dark matter is an artifact, why is it that including dark matter
makes for such a good model of the large scale of the universe?

That 'good' model (L-CDM) is based in many free parameters and
unproven assumptions and can fit almost anything by a change on the
parameters.

Why did MOND (you sometime called "crap model") predict a correct WMAP
second peak whereas your preferred "good model" (L-CDM 1997) predicted
a wrong peak?

Why that 'good' model introduces constrains are in disagreement with
analysis of dozens of galaxies (paper is in press)?

How
about explaining _all_ of the weak lensing results of the past 5 years
or so that explicitly map out the distributions of dark matter?

That 'explicit' map of dark matter is based in the prior _assumption_
dark matter is there. Therefore it is evidence of nothing.

[BLOCKQUOTE
Dark Matter is the craziest idea we've ever had
in astronomy. It can appear when you need it, it can do what
you like, be distributed in any way you like. It is the fairy
tale of astronomy.
]

MOND is a law, not a model nor a theory.

By what stretch of the imagination do you say that?

Again, just because you ignore stuff does not mean i invented. Even
Google knows about that!! a search by "MOND law" returns a million
items.

MOND _fails_ in the bullet cluster and it was invented as a _model_ to
explain rotation curves.

[i] What 'fails'? relativistic MOND? non-relativistic MOND? Any MOND?
None?

[ii] DM model was invented by the same motive. Did not you know?

[iii] We know GR + DM _fails_ in the bullet cluster and now a new kind
of mysterious interaction has been invented by DM theoreticians for
saving discrepancies.

Think about the weak lensing results - where is most of the dark
matter? Out in the halo. Ignoring weak lensing - where does the dark
matter need to be to smooth out the velocities? Out in the halo. What
is the domain of application for MOND? Out...in the halo, where
gravity is thought to be "weaker".

When R is larger the MOND law [1 / R] is stronger than [1 / R^2]. Why
do you claim gravity is weaker when is stronger?

It might be a good idea to explain what the hell you are talking
about.

You said the domain of application for MOND was where gravity is
thought to be weaker. It is just the inverse, is not?

The proponents think that if MOND works,
there is no dark matter while ignoring the extremely likely
possibility that MOND is mapping out dark matter.

You do not understand MOND nor its impressive empirical success.

GR+DM is not fine for galaxies and fails for bullet cluster unless
invoking now a unproven _ad hoc_ hypotesis about existence of a new
kind of interaction (NGI).

Go go gadget intellectual dishonesty.

Returning to your comical side again?

Are you the same Eric Gisse who did an entire series of biased
comments against MOND without taking some time to read literature on
the topic first? Is that your definition of "intellectual honesty"?

More about your unfounded accusation on NGI below.

You _KNOW_, assuming you actually read the paper, that the 'new kind
of interaction' is something that creeps in because the models they
picked can't quite explain how fast some parts of the bullet cluster
are moving by about 20%.

How can you use the bullet cluster data against MOND but favourable
towards GR + DM? The cluster is a problem for ***both*** MOND and GR
+DM.

That in no way means a 'new kind of
interaction' is necessary until a hell of a lot more research is done.

For avoiding any new misunderstanding by you part i will cite

[BLOCKQUOTE
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.
]

What do you understand by "To remove the contradiction [with GR+DM]
they propose that a non-gravitational attraction of a new sort acts
only between clumps of DM"?

And why my writing "a new kind of interaction (NGI)" is, in your own
words, intellectual dishonesty when I am reflecting current status of
DM models? Because you love DM disliking any kind of criticism?

Every time someone comes up with an idea that contradicts
relativity - no matter how flimsy - you take it as the gospel truth.

Could you offer a list of those supposed ideas or are you again
launching out balloons when lacking arguments?

Relativity has earned its' place in the scientific community.

Again, relativistic MOND exists!!!

MOND has gained its place on community during last decade. MOND will
remain with us in one or other flavour because rocks.

The future of DM looks... dark. In an interview Milgrom states

[BLOCKQUOTE
It's been said that dark matter theory is beginning to resemble
the celestial mechanics of Ptolemy, who continually added epicycles
to his models as the observations failed to conform to a geocentric
universe. What would it take for scientists to abandon dark matter?

DM is encountering difficulties in the face of observations,
and people keep inventing new DM with new properties to try and
circumvent these difficulties. Over the years I have refrained
from attacking DM, but others have started finding faults with
it and that trend is increasing.
]

The very
tool that allows folks to probe the nature of dark matter -
gravitational lensing - is a relativity prediction.

[GR + visible-matter + dark-matter] --- Lensing

[Relativistic MOND + visible-matter] --- Lensing

Lensing is not proving DM and disproving MOND like you believe. The
analogy when Newtonian gravity failed is remarkable

[NG + visible-planets + hidden-planet] --- Mercury perihelion

[GR + visible-planets] --- Mercury perihelion

Eric Gisse [in reply to ] wrote:
It needs to show how DM should be distributed to explain MOND.

This has been done by working backwards from the observed
distributions and Poisson's equation. MOND and DM play nice together.

http://www.journals.uchicago.edu/ApJ...610/58610.html

Seriously - did you read this?

See below[*]

You can change it to Make dark matter irrelevent at the galactic
scale.
It is certainly not required at the galactic scales.

Bull**** it hasn't.

http://www.journals.uchicago.edu/ApJ...610/58610.html

See below[*]

You have a lot of prejudice regarding MOND. I don't think I can rid
you
of your prejudice. You see the forest and cannot focus down to the
trees.

Of course I am prejudiced. The proponents of MOND seem to think it is
a theory of gravity unto itself rather than a model.

Huge MOND literature contradicts you. MOND people knows that MOND is
not a theory but a law and this is well-explained in papers and
reviews. You did not read, true?

...then when a fair bit of evidence crops up which shows that it is an
actual matter distribution causing the funky rotation curves?


It only means that there is no need for DM in Galaxies. Nothing more
nothing less.

http://www.journals.uchicago.edu/ApJ...610/58610.html

READ IT

See below[*]

MOND was designed to, and continues to be, an exercise in curve
fitting that has served its' purpose very well. Getting the answer
right in one _limited_ regime does _not_ make it a viable theory of
gravity.

No. you are confounding MOND with DM. DM is curve fitting. MOND is a
law doing precise predictions. For the same systems GR does ***none***
prediction.

http://www.journals.uchicago.edu/ApJ...610/58610.html

Dark matter and MOND share a large degree of correspondence. You
seriously need to read that paper.

http://www.journals.uchicago.edu/ApJ...610/58610.html

READ IT

See below[*]

So how does that support your assertion that it has too many
parameters? The L-CDM model has a _highly constrained_ 6 dimensional
parameter space. I have linked you to the WMAP site and specific
papers before - the amount of freedom the parameters have are quite
small.

MOND-based models typically have 1/2 that freedom and predicted WMAP
data. L-CDM 1999 was wrong remember? And now its parameters are
changed to fit to WMAP data.

Moreover, several of L-CDM parameters do not agree with independent
tests for those values (however agreeing with MOND-based cosmology).
Those strange values are used in L-CDM because otherwhise L-CDM cannot
fit WMAP data (remember 1999). L-CDM is a truly forced _a posteriori_
fit.

MOND based cosmology, however was not _a posteriori_ fit, it predicted
first-second WMAP peaks.

The most popular theory that explains large scale structure formation
is LCDM which fails badly on most Galaxies.

Does it...?

Yes.

Reference?

Many, including a recent (APJ, in press) exhaustive analysis of 60
galaxies (i cited previously).

anything and everything" [as it should] whereas MOND gets the "eh it
works sometimes - must be true" treatment.

That is reason relativists invented DM. "eh GR works sometimes - must
be true and the galactic problem is in missed mass".

Remember Newtonians did the same mistake "eh NG works sometimes - must
be true and the perihelion problem is in a missed mass (planet)". But
Vulcan did never appear like dark matter is not doing it now...
[*] You cite that paper many times but you do not understand MOND (and
you distort the conclusion of the paper).

In the conclusions, I read in the paper you cite:

[BLOCKQUOTE
The possibilities are limited. Either (1) MOND is essentially
correct,
or (2) dark matter results in MOND-like behavior in disk galaxies.
]

You. of course, ignore posibility 1 and take 2 as being proved...

The author of that paper is Stacy S. McGaugh. He is one of multiple
folks abandoning DM and taking MOND seriously. He contradicts you in
so a clear way I will cite it.

[BLOCKQUOTE
Issues for Dark Matter:

Does the stuff we call Dark Matter really exist?

Can a dark matter based theory explain the MONDian phenomenology
observed in
rotation curves?

My gut reaction to all these questions is negative.
]

[BLOCKQUOTE
The problem is, all of the dark matter theories fail, including my
own.
]

Of course, you cite a old paper. Let me take a more recent paper by
that same author [1]:

[BLOCKQUOTE
In stark contrast to the situation for CDM, MOND fits rotation
curves well (Fig. 6).
That is does so is well established (Sanders & McGaugh 2002). What
this means
is open to debate.

Like most astronomers, I ignored MOND for a long time, thinking it
so unlikely
as to not warrant consideration. I was obliged to reconsider when
the fine-tuning
problems with dark matter became severe (McGaugh & de Blok 1998a),
and the
predictions of MOND came true in my data. Milgrom (1983) made a
series of spe-
cific predictions for low surface brightness galaxies, all of which
were subsequently
realized (McGaugh & de Blok 1998b).

This must mean something. The question, of course, is what. There is
a
widespread myth that MOND is somehow designed to fit rotation
curves, and is
guaranteed to do so. This is demonstrably false (de Blok & McGaugh
1998). Quite
the contrary, MOND fits have only one fit parameter, ⋆, and are
considerably
better constrained than fits with dark halos. This is a non-trivial
fact: if you
write down the wrong force law, it fails (and fails badly) quite
quickly. Many
other modifications of gravity have been attempted, and suered just
such a fate.
]

[BLOCKQUOTE
Many models are possible with dark matter,
which provides no unique null hypothesis: there is a wide variety of
things rotation
curves might reasonably be expected to do. In MOND, there is
precisely one thing
rotation curves can do, and that is what they do.
]

About the cluster results i already said you that popular news cluster
is evidence of DM against MOND is nonsense (or typical GR marketing).
In a recent preprint (April) i read [2]:

[BLOCKQUOTE
Taken at face value, a collision velocity of 4700 kms−1
constitutes a direct contradiction to CDM. Ironically, this
cluster, widely advertised as a fatal observation to MOND
because of the residual mass discrepancy it shows, seems to
pose a comparably serious problem for CDM. It has often
been the case that observations which are claimed to falsify
MOND turn out to make no more sense in terms of dark
matter.
]

[1] http://arxiv.org/pdf/astro-ph/0510620

[2] http://arxiv.org/pdf/0704.0381

On Apr 5, 9:43 am, "Eric Gisse" wrote:
wrote:
Eric Gisse wrote:
wrote:
It needs to show how DM should be distributed to explainMOND.

This has been done by working backwards from the observed
distributions and Poisson's equation.MONDand DM play nice together.

http://www.journals.uchicago.edu/ApJ.../v609n2/58610/...

Seriously - did you read this?

And Seriously did you??

You think that MOND and DM play nice. But the author of the paper
doesn't think so. So how did you come to that conclusion from this
paper.

There can only be one of two options at the galactic scale.
1) There is a difference between MOND and GR+DM. In this case we
know that MOND works better than GR+DM for all theories of GR+DM.
So obviously MOND is the correct law.
2) There is no difference between MOND and GR+DM, in which case
DM does not exist and MOND is wrong. Because there can be no
matter that has no degrees of freedom.

If you think that a kind of matter can exist without any degrees
of freedom. You are entitled to your opinion, but it is not a
scientific opinion.

There are only two realistic options.
1) You can ignore MOND, and believe that MOND proponents are
crackpots.
2) You have to accept MOND, and the failure of GR.

There is no middle way. GR+DM cannot model MOND.

I think we are at a stalemate. There is no point in arguing further.

regards,
-anandsr