Re: MOND

anandsr21@xxxxxxxxx wrote:
On Mar 20, 8:42 am, "Eric Gisse" <jowr...@xxxxxxxxx> wrote:
On Mar 19, 12:56 am, anands...@xxxxxxxxx wrote:



On Mar 17, 9:05 pm, "Juan R." <juanrgonzal...@xxxxxxxxxxxxxxxxxxxx>
wrote:

On Mar 17, 5:35 am, anands...@xxxxxxxxx wrote:

On Mar 10, 11:28 pm, "Juan R." <juanrgonzal...@xxxxxxxxxxxxxxxxxxxx>
wrote:


It is not off-topic, if the question was "is there an interaction
which increases with distance", because there is an interaction.
It doesn't matter if it is microscopic or macroscopic. After all
microscopic does affect the macro world. And we know that the
microscopic makes up the world.

I should have been more clear. I knew about quark confinement, I just
expected a shade more thought to be given to the subject than was
actually given.

"microscopic" is still a half dozen orders of magnitude too large for
the strong force interactions. Strong force interactions are of the
femtometer range - and DO NOT EXIST outside it because the strong
force mediating particle [whatever the *** it is] is massive.

What I *meant* was name one verified macroscopic interaction which
_increases_ with distance with emphasis on both _verified_ and
_macroscopic_.


But when there are only four known interactions, if even one of them
increases with distance, why would you want to neglect that.

...because it *CAN NOT* interact with anything on a macroscopic scale.

I say "CAN NOT" as in "IT CAN NOT, IT IS NOT AN APPROXIMATION" sense.

Also QED (the Electro Magnetic interaction) also has a weird
interaction, called entanglement that does weird things even at a
huge distance, and instantly without coming into conflict with
superluminal expectations. I guess that is very macroscopic, and
it very much conflicts with GR. But you can chose to ignore that,
saying that some GR expectations like causality are not broken.

Entanglement does not exert a force, and does not transmit information
at anything faster than light speed.


I know that you actually mean only the gravitational interaction,
but in my opinion GR is already broken. I think the accelerated
expansion of the universe is due to repulsive force of gravitation,
and that will have to occur only if it increases with gravity. Its
all speculation, but you know that we don't have the quantum theory
of gravity.

A repulsive term is easily included in GR - cosmological constant AKA
dark energy.

The only problem is the quantum theory expectation of vacuum energy is
only about 120 orders of magnitude or so from the observed value. This
is a standing problem and I don't expect it to get resolved until a
halfway plausible quantum theory of gravity is formulated.

GR is broken in the "not a quantum theory" sense, *NOT* the "Whups we
are seeing something it cannot explain" sense.




[ii] My personal experience replying EricGisseposts recommended
avoiding advanced topics. I doubt he has studied QCD.

I wouldn't know about that. But when we are talking about the failures
of GR, then Quantum Theory definitely comes into the picture because
it is GR's biggest failure. Some may say that it is QCD's failure but
I doubt many will see it that way. It is definite that GR will be
found in the limit of a Quantum Theory of Gravity, rather than
QCD to be found in the limit of GR ;-).

I think it is premature to worry about GR being the limiting case of
anything because we haven't truly found it to be failing. I know your
position on dark matter and you know mine. That aside, it must break
down _somewhere_ but we haven't actually seen it happen yet.


GR has broken down and miserably. But you are turning a blind eye
to it. MOND is the indicator. You chose to ignore MOND because you
cannot explain it. If you could you would have done so. But it is a
fact that GR+DM cannot explain MOND LAW. It is not possible to
explain such a tight correlation between the Mass Discrepancies and
the observed accelerations. If you have a theory you can do so.
Nobody has done that till now. And nobody who has measured the
closeness of the correlation will believe that it can be done.

You are ignoring the very papers you have cited to me in researching
MOND - you know, the one you mentioned the other day which explicitly
says that dark matter is required in one form or another?

Personally I think MOND is indirectly mapping the actual dark matter
distribution. I have heard nothing that should dissuade me from that
notion.


You will again say that I am ignoring weak lensing. But I will say
what's so different about weak lensing, it also shows Mass
Discrepancy which is also an indication that GR has broken down, we
are again seeing Mass Discrepancies. Then you will say WMAP, again
the same Mass Discrepancy. Of course all these mean that there is
something wrong with GR, but you think that you are seeing different
confirmation of Dark Matter while the reason for all the
Mass Discrepancy, is the same. GR does not work in weak gravity
regimes.

So...when weak lensing manages to show dark matter that doesn't mean
that there is actual matter there, it just means GR is yet again
breaking down in yet another way consistent with there being matter
that doesn't interact via electromagnetism?

I find that even harder to believe. Something is bending light - and
nobody has an even remotely plausible explanation as to take into
account the lensing while simultaneously removing the need for dark
matter. No, TeVeS does not count until it predicts something solid.


To you it doesn't matter that the Mass Discrepancy is increasing
with the scale. At the Galaxy level it depends on the size and
density (basically the weakness of gravity), at the cluster level
it is 10 times. At the Cosmic level it is 100 times. But you will
see all these similar failings as confirmation of Dark Matter.

Oh come on. The larger the scale under consideration is, the more
visible matter there is.


You will also ignore the only thing that can open your mind.

Versus a preconceived notion [no dark matter] that isn't even agreed
upon by the very papers you cite me?

Denying the weak lensing results is even more closed minded than me
disagreeing with what you think MOND means.

Because it is so much more easy to live with the status quo.
You don't want to face the possibility that we don't know any
theory that can account for weak gravity regimes. This is
actually a great time for theoretical physicists to try and
find the correct theory, and quite a few are working towards
them, and I am not talking about crackpots. Search for papers
on TeVeS, Conformal Loop Quantum Gravity, AdS/CFT gravity.

Start paring the list down.

Of these, how many of them make testable predictions? No, I don't mean
"soon", I mean "right here <link to paper".

Of these, how many match _already verified_ predictions by general
relativity?

Of the remaining, if any, match up with the area O' interest that is
the bullet cluster while removing the need for dark matter?


But it is a difficult thing to do, you have to be great at
mathematics. These theories are much more difficult to work
with mathematically than GR.

Considering how hard it is to use GR without making a large series of
approximations, I can't help but wonder how many of these theories are
at the point where they can make useful predictions rather than
sweeping statements from toy models.


Why don't you study MOND results. The MOND people cannot be
pulling numbers out of thin air. You can test them out. You can
try to make a model of DM that will fit MOND. But you won't do
that, you will simply ignore all the evidence, because that's
the easy thing to do.

Of course they aren't.

Keep in mind that MOND offers no explanation as to _why_ gravity is
being screwy, just that it _is_ screwy and that it _is_ a model of the
screwyness. There is no reason offered as to why dark matter can't
simply be modeled by MOND. It isn't as if MOND is based off of bedrock
principles - it is an ad-hoc notion that fits the bill in certain
places.

I'm curious as to what the experiment described here will say.

http://physicsweb.org/articles/news/11/3/12/1




So we start with the statement that GR is true in a limit of a
Quantum Theory of Gravity, which means that GR is not the true
picture. So I don't know why Relativists find it so difficult to
come to terms with the fact thatMONDworks and proves that the
Limit of GR is a few kilo parsecs. Although Pioneer may mean that
something is wrong there too. But Pioneer seems to be a fluke
rather than an indication of something wrong.

My money is on outgassing and/or asymmetric RTG heat reflection.

MONDworking, for suitable definitions of working, does not prove
anything other thanMONDis a halfway decent model under certain
conditions.

I beg to differ here. MOND is not a "halfway decent model", as a
model it is pathetic. It is simply a law, just like Kepler's
Laws, that for some underlying reason works well on the galaxy
scales. We need somebody like Newton or Einstein to explain MOND,
just like Newton explained Kepler's laws and Einstein explained
precession of Mercury. I guess they had it easier, because there
was no scientific establishment to fight with.

[I swear to god, if google eats this post...]

Do _NOT_ try to pull that "I'm fighting the establishment!" bull***
with me. The papers you cite are published in reputable journals.
Considering how _often_ MOND is referred to in popular and technical
scientific articles, MOND is decidedly mainstream. The folks in here
who also cry about persecution have wet dreams about being given the
kind of attention that MOND gets in the literature.

MOND is not a law. MOND is a model - it was designed as such, and
remains as such. The fact that it has any sort of success means
something - I think it means that it is keying in on the dark matter
distribution in galaxies at some level.

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".


http://www.astro.umd.edu/~ssm/mond/daverussellletter.html
The above is a letter that gives 8 reasons why CDM should be
considered falsified within Galaxy limits.

1) 'Renzo's Rule' indicating that light traces mass.

Why is this a failure? It is important, but I fail to see the
"failure" part.

This explains Renzo's rule, plus it is an example someone working
backwards from Gauss' law [or equivalently, as done in the paper,
Poisson's equation] which I wanted to do previously to finding out
that it was already done. It was done, in my opinion, very nicely as
well!

http://www.journals.uchicago.edu/ApJ/journal/issues/ApJ/v609n2/58610/58610.html

I found this paper to be very, very informative in both explaining
both MOND and dark matter as applied to galactic scales. The nature of
the fits is now less opaque, which I found helpful. Plus it gave
support and a direct reference to that large number of MOND fits you
alluded to previously.

You will find the paper very informative as well, so I'm not going to
try to summarize it. But both our positions allowable - either MOND is
correct as-is or the distribution of dark matter in galaxies gives
rise to MOND.

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

2) Disk-Halo conspiracy

http://arxiv.org/PS_cache/astro-ph/pdf/9610/9610188.pdf [PDF is
slightly glitchy...]

One of the conclusions I thought was most intriguing was that the dark
matter halo shape under that model was something that was reasonably
constant.

It [disk halo conspiracy] is touched on indirectly as well by the
previous paper. Given there is an alternative explanation that is
entirely plausible, I don't see why folks are adopting the CDM
WROOOOOOOOONG stance. So far, it looks like the worst case is that the
CDM model needs tweaking - which doesn't surprise me, I do not believe
it was even geared as a model for scales so small.

3,4) No idea what is even being talked about since I don't have that
paper onhand.

5-8) Talked about with _extensive_ detail in the first paper I linked
you.

The linked paper has the same content - same equations, same data,
same conclusions as the first paper as well.

What folks seem to be missing is that success of MOND and success of
dark matter are not mutually contradictory goals. MOND seems to lend
itself fairly easily to a dark matter explanation, despite how angry
that probably makes the MOND crew.

The constant inclusion of the virial mass [200x universe critical
density] and the size associated with it amuses me for some odd
reason...I don't find anything wrong or objectionable, it just amuses
me.


The above also links to an interesting paper. In the initial
version, it concluded that DM+GR cannot explain the correlation.
But by the time it got published the conclusion had changed a
lot. I guess the referee convinced them of the utility of not
ignoring DM in any case ;-). This is a case where the
establishment does prevent publishing of unbiased papers.

That is BULL*** and you know it.

The conclusions reached thus far do not eliminate dark matter. In
fact, they refine dark matter as a concept because the only thing
really used is the fact that MOND is, observationally, a good fit.


http://www.citebase.org/abstract?id=oai%3AarXiv.org%3Aastro-ph%2F0403206
(Cores of Dark Matter Halos Correlate with Disk Scale Lengths)

Yes, yes. More of the same.


I don't know what you mean exactly by "suitable definitions of
working", but MOND works very well without any exceptions on the
scale of galaxies. In 80% of galaxies it gives very good fits,
for the rest of the 20%, it is known that there are problems with
the data. And the important thing is that it cannot fit those 20%,
as would be expected for a theory with no free parameters, a0 is
no longer free. Another important thing is that DM models can fit
those 20% cases also to the same degree of accuracy as the other
80%, because of the large number of free parameters.

The number of free parameters isn't that big and you know it, if you
have actually been reading the papers you have been citing me.

My remark of "suitable definitions of working" was _before_ I saw the
first paper I linked - it was exactly what I was looking for. I wanted
something that gave me a broad overview of MOND results, rather than
personally stitching together a hundred results. I was unable to
determine how much of the swooning was over fanboyism or actual data,
which now I know and I adjust the remark accordingly.


The onus is on theoretical physicists to find the underlying reason.
Ignoring MOND does not help.

That much is now obvious. MOND is an excellent model for individual
galaxies, though I _suspect_ it fails for galaxies that are products
of or are in various stages of collision [eg, bullet cluster].

Keep in mind that nothing you have shown me or what I have found
conclusively, or even most likely, makes dark matter an incorrect
model. In fact, everything I have seen thus far either supports or
refines dark matter. Using the MOND fits along with the empirical data
gives some nice constraints on entirely plausible distributions of
dark mater where there were none before, which is quite useful.


regards,
-anandsr

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