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  #21  
Old February 25th 07, 05:56 PM posted to sci.astro.research
Jonathan Thornburg -- remove -animal to reply
external usenet poster
 
Posts: 24
Default Barred galaxies mass distribution

wrote:
MOND has been quite successful in fitting rotational speed data for
the galaxies. It has been tested on over 120 galaxies and there have
been no failures. Please see
http://www.astro.umd.edu/~ssm/mond/.

However, there also seem to be serious problems in trying to use MOND
as an explanation for galaxy rotation curves. See, for example,
http://fr.arxiv.org/abs/hep-ph/0105083
whose abstract reads:
Recently, several interesting proposals were made modifying the
law of gravity on large scales, within a sensible relativistic
formulation. This allows a precise formulation of the idea that such
a modification might account for galaxy rotation curves, instead
of the usual interpretation of these curves as evidence for dark
matter. We here summarize several observational constraints which
any such modification must satisfy, and which we believe make more
challenging any interpretation of galaxy rotation curves in terms
of new gravitational physics.


http://fr.arxiv.org/abs/astro-ph/0104435 is another critique, arguing
that trying to extend MOND to explain larger-than-galaxy phenomena
(particularly cosmology) runs into serious problems.

ciao,

--
-- "Jonathan Thornburg -- remove -animal to reply"
t = 28.Feb.2007: Max-Planck-Institut fuer Gravitationsphysik
(Albert-Einstein-Institut), Golm, Germany, "Old Europe"
http://www.aei.mpg.de/~jthorn/home.html
t = 1.Mar.2007: School of Mathematics, U of Southampton, England
"Washing one's hands of the conflict between the powerful and the
powerless means to side with the powerful, not to be neutral."
-- quote by Freire / poster by Oxfam
  #22  
Old March 2nd 07, 09:37 AM posted to sci.astro.research
[email protected]
external usenet poster
 
Posts: 19
Default Barred galaxies mass distribution

I don't know what happened to my response.
Retrying

On Feb 25, 9:56 pm, "Jonathan Thornburg -- remove -animal to reply"
wrote:
wrote:
MONDhas been quite successful in fitting rotational speed data for
the galaxies. It has been tested on over 120 galaxies and there have
been no failures. Please seehttp://www.astro.umd.edu/~ssm/mond/.


However, there also seem to be serious problems in trying to useMOND
as an explanation for galaxy rotation curves. See, for example,
http://fr.arxiv.org/abs/hep-ph/0105083
whose abstract reads:
Recently, several interesting proposals were made modifying the
law of gravity on large scales, within a sensible relativistic
formulation. This allows a precise formulation of the idea that such
a modification might account for galaxy rotation curves, instead
of the usual interpretation of these curves as evidence for dark
matter. We here summarize several observational constraints which
any such modification must satisfy, and which we believe make more
challenging any interpretation of galaxy rotation curves in terms
of new gravitational physics.


I understands the points 1, 2, and 4, and MOND works with them, as
the paper says. I don't understand the 3rd point it seems that it is
putting forward a theory that the potential in the disk plane will be
non-newtonian but perpendicular to it it will be newtonian, then uses
several observations to prove it. I don't know why is that. It should
have done the opposite. It also doesn't talk about MOND or any
other theory in that perspective, if they match the observations.


http://fr.arxiv.org/abs/astro-ph/0104435 is another critique, arguing
that trying to extendMONDto explain larger-than-galaxy phenomena
(particularly cosmology) runs into serious problems.


Well actually I have no problems with Dark Matter. We don't
really know the whole universe and there could be curiosities
that are too strange. We also know that MOND is not a
good theory. It is just a simple equation, which works very
well. I would say too well at the Galaxy level.

Even TeVeS is not a good theory. It is workable, but not
very good. It is ugly and ad-hoc. Which means that it will
not survive for very long.

What MOND does say that for most of the galaxies there
exists very little if any Dark Matter. It provides fits for galaxies
that no other theory, GR+DM or otherwise can match.

Also till date there have been no failures of MOND. I define
failure as in a body of mass that shows less gravitation
than MOND predicts. If there is more gravitation than MOND
predicts, it could be because MOND is wrong or because
there is some type of dark matter. But existence of DM
is not fatal for MOND. Unless you get very religious about
it, you can always admit that we don't know everything
about the universe and DM may exist.

The fact that it works as well as it does means that MOND
phenomenology is a fact at Galaxy levels. Which means
that no theory can be accepted unless it contains MOND
as an explanation. MOND cannot be ignored after fitting
120 galaxies which is probabilistically impossible if Dark
Matter could be distributed randomly.

The only way GR+DM can explain MOND by saying that
during structure formation DM and BM (baryonic mass)
where created so as to give MOND phenomenology. And
that the structures have diverged in a way so as to keep
MOND phenomenology at the galaxy scale.

Now this poses an obvious fine tuning problem, but we
may be able to live with it, if we can come up with a
possible structure theory that could explain MOND,
ie fit the observations based on the BM only, as
MOND does.

Currently the best CDM fits to the Rotation curves of
galaxies require two free parameters per galaxy.
This is way too inferior. MOND does much better with
a single universal parameter.

Now I will attempt to prove that there can be no
DM structure formation theory that can explain MOND.
For this I will use the excellent fits at
http://www.astro.umd.edu/~ssm/mond/n1560.gif
and other similar fits at
http://www.astro.umd.edu/~ssm/mond/mdlg.gif
and at http://www.astro.umd.edu/~ssm/mond/mdlg.gif_2

Now if you see these fits you will notice that most of
these galaxies have a lot of deviation from standard GR.
That is they require a lot of DM. Actually much much
more DM than there is BM in them.

You will also notice that MOND is also predicting the
wiggles in the rotation curve. This must mean that
the wiggles must also be present in the DM profile.

I believe that you will also agree that even if the
DM and BM evolved together, so as to maintain the
MOND phenomenology, it is still a tall order to
assume (and an even bigger fine tuning problem)
that they will evolve exactly the same. There will be
some deviations.

I also believe that at the time of structure formation
the rotation curves of the structure would be very
smooth, and the wiggles would occurr over
time due to irregularities getting magnified with time.

This means that the Wiggles in an otherwise smooth
curve would be due to the irregularities in the BM and
DM components. I would expect much less deviations
in the DM structure than the BM structure, because
DM does not interact much.

This will mean that the wiggles will be mostly due to
BM but will be quite a bit damped. ie the wiggle in
the BM structure will have quite a bit less effect on
the rotation curve. So that MOND will predict a much
bigger wiggle than in the rotation curve.

But these curves show that the wiggles are fit quite
well by the MOND theory. The magnitude of the
wiggles are also nearly the same. This would mean
very little DM if it exists. This is quite contrary to
the GR expectation.

Obviously if DM is not in these galaxies then GR
does not work well at these scales. And if GR does
not work at these levels, then we can't be sure of
its implication on Clusters, and cosmological scales.

We need a better theory. TeVeS may be a better
theory than GR, but it still needs more DM for
larger structures. It is ad-hoc and quite ugly, but
may be better to work with till we get a really good
theory.

I hope that my logic makes sense. Of course everything
depends on the fits at Stacy's site to be correct.
Which I believe they should be, because nobody refutes
them.

regards,
-anandsr
  #23  
Old March 12th 07, 06:37 PM posted to sci.astro.research
Nicolaas Vroom
external usenet poster
 
Posts: 216
Default Barred galaxies mass distribution

schreef in bericht
...

Now I will attempt to prove that there can be no
DM structure formation theory that can explain MOND.
For this I will use the excellent fits at
http://www.astro.umd.edu/~ssm/mond/n1560.gif
and other similar fits at
http://www.astro.umd.edu/~ssm/mond/mdlg.gif
and at http://www.astro.umd.edu/~ssm/mond/mdlg.gif_2


I have written a program to simulate galaxies using MOND.

For a more general discussion related to MOND which
includes your references See:
http://users.pandora.be/nicvroom/mond.htm
For a copy of the program see:
http://users.pandora.be/nicvroom/.prgmond.htm

You first url references NGC1560.
The url shows four rotation curves:
One Measured. One based on Newton's Law,
One based on MOND and one including Darkmatter.

If you make such a comparison the galaxy should have
the same amount of baryonic mass.
The problem is you cannnot make a simulation where
the speed of the MOND curve is twice the speed
of the Newton curve based on the same mass distribution.

(There is the parameter a0 which you can adapt, but that
makes the whole MOND concept rather speculative)

The second url shows 16 galaxies.
The problem is that many of the MOND curves the speed
at a certain distance decrease.
IMO such curves are not possible with MOND.

Ofcourse my simulations can be wrong.

See also the discussion topic:
"Disk Stability MOND and Dark Matter" in this newsgroup.
Nicolaas Vroom

http://users.pandora.be/nicvroom/
  #24  
Old March 16th 07, 09:04 AM posted to sci.astro.research
[email protected]
external usenet poster
 
Posts: 19
Default Barred galaxies mass distribution

On Mar 12, 10:37 pm, "Nicolaas Vroom"
wrote:
schreef in ...

Now I will attempt to prove that there can be no
DM structure formation theory that can explainMOND.
For this I will use the excellent fits at
http://www.astro.umd.edu/~ssm/mond/n1560.gif
and other similar fits at
http://www.astro.umd.edu/~ssm/mond/mdlg.gif
and athttp://www.astro.umd.edu/~ssm/mond/mdlg.gif_2


I have written a program to simulate galaxies usingMOND.

For a more general discussion related toMONDwhich
includes your references See:http://users.pandora.be/nicvroom/mond.htm
For a copy of the program see:http://users.pandora.be/nicvroom/.prgmond.htm


I am not able to access your site.

I hope you took care to apply MOND correctly. It has non-local
affects.
You cannot replace all mass within a sphere with a point mass, for
measuring its effect outside the sphere. It gives non-intuitive
effects.
Check the explanation at
http://www.astro.umd.edu/~ssm/mond/mondnbody.ps

Other numerical approaches are necessary. For example, Brada's
thesis.
http://www.astro.umd.edu/~ssm/mond/brada.uu
See also MLAPM.
http://www.aip.de/People/AKnebe/MLAPM/

When we have a quantized Ads/CFT theory of gravity, which is the
equivalent of the other forces, nothing will work according to our
intuition. Time Dilation etc are intuitive compared to what we will
have ;-).

regards,
-anandsr
  #26  
Old March 19th 07, 11:25 AM posted to sci.astro.research
[email protected]
external usenet poster
 
Posts: 19
Default Barred galaxies mass distribution

On Mar 18, 3:18 am, Chris Mihos wrote:
wrote:
I hope you took care to applyMONDcorrectly. It has non-local
affects.
You cannot replace all mass within a sphere with a point mass, for
measuring its effect outside the sphere. It gives non-intuitive
effects.
Check the explanation at
http://www.astro.umd.edu/~ssm/mond/mondnbody.ps


hey, that's the boring version of the explanation i wrote. this one
is much more fun:

http://burro.astr.cwru.edu/ArnoldMOND/ahnoldmond.html

--
chris


ROTFL!!

Please do ask Stacy to replace the original one. This one is much
better.

thanks,
-anandsr
  #27  
Old March 22nd 07, 09:55 AM posted to sci.astro.research
Nicolaas Vroom
external usenet poster
 
Posts: 216
Default Barred galaxies mass distribution

schreef in bericht
...
On Mar 12, 10:37 pm, "Nicolaas Vroom"
wrote:

I have written a program to simulate galaxies usingMOND.

For a more general discussion related toMONDwhich
includes your references See: http://users.pandora.be/nicvroom/mond.htm
For a copy of the program see:
http://users.pandora.be/nicvroom/prgmond.htm


I am not able to access your site.


There was one . (point) too much.

I hope you took care to apply MOND correctly.

How do you apply MOND correctly ?

It has non-local affects.

What do you mean by that ?

You cannot replace all mass within a sphere with a point mass, for
measuring its effect outside the sphere.

I agree that that gives complications. IMO that is a problem with MOND.

It gives non-intuitive effects.

Why do you call the above effect non-intuitive ?

Check the explanation at
http://www.astro.umd.edu/~ssm/mond/mondnbody.ps

Yes I agree there is an issue.
See also my comments See: http://users.pandora.be/nicvroom/mond.htm
at Feedback #4.
At the end of that document is written:
"Note that this does not mean MOND is wrong,
just that this kind of calculation does not work"
IMO that is a serious problem.

What MOND predicts is that when you have two colliding BH's
(or large masses) that the speed of a star,
which circulates around the center of gravity of that BH,
after collision, will drastically change.
There will almost be no change when Newton is considered.

I have serious problems with MOND.
1. One is for example the above mentioned document.
2. A different one is the value of a0. This is more or less a free
parameter.
3. Third how do you go from Newton to MOND.
There are more or less three areas involved:
One with Newton at short distance between stars,
one with both Newton and MOND
and one with MOND only at large distances.

Other numerical approaches are necessary. For example, Brada's
thesis.
http://www.astro.umd.edu/~ssm/mond/brada.uu


I cannot access that url.

See also MLAPM.
http://www.aip.de/People/AKnebe/MLAPM/

When we have a quantized Ads/CFT theory of gravity, which is the
equivalent of the other forces, nothing will work according to our
intuition. Time Dilation etc are intuitive compared to what we will
have ;-).

Why do you again use the word intuition ?

Nicolaas Vroom
http://users.pandora.be/nicvroom/
  #28  
Old March 23rd 07, 09:42 AM posted to sci.astro.research
[email protected]
external usenet poster
 
Posts: 19
Default Barred galaxies mass distribution

On Mar 22, 1:55 pm, "Nicolaas Vroom"
wrote:
schreef in ...

On Mar 12, 10:37 pm, "Nicolaas Vroom"
wrote:


I have written a program to simulate galaxies usingMOND.


For a more general discussion related toMONDwhich
includes your references See:http://users.pandora.be/nicvroom/mond.htm
For a copy of the program see:
http://users.pandora.be/nicvroom/prgmond.htm


I am not able to access your site.


There was one . (point) too much.

I hope you took care to apply MOND correctly.


How do you apply MOND correctly ?

It has non-local affects.


What do you mean by that ?


Non-Local effects is explained below.


You cannot replace all mass within a sphere with a point mass, for
measuring its effect outside the sphere.


I agree that that gives complications. IMO that is a problem with MOND.


Yes, it is a problem with MOND. It is just slightly inaccurate. You
can
try to apply TeVeS if you want completely accurate results (according
to
MOND). But TeVeS is more complicated to apply. You will still have
non-local effects.

The bottom line is that MOND works. There are dozens of papers that
show you how to fit the data in galaxies.

I wouldn't recommend fitting clusters with it. Fitting Clusters is
much
more complicated as there is no nearly constant distribution of mass
so that you cannot simplify MOND effects.


It gives non-intuitive effects.


Why do you call the above effect non-intuitive ?


It is non-intuitive, if you are used to applying Newtonian gravity.


Check the explanation at
http://www.astro.umd.edu/~ssm/mond/mondnbody.ps


Yes I agree there is an issue.
See also my comments See:http://users.pandora.be/nicvroom/mond.htm
at Feedback #4.
At the end of that document is written:
"Note that this does not mean MOND is wrong,
just that this kind of calculation does not work"
IMO that is a serious problem.


It would seem as a serious problem, because we don't have a quantum
theory of gravity, which is bound to be a type of Quantized AdS/CFT
theory,
like the other forces. All AdS/CFT theories have non-local effects.

I believe that ultimately GR will be found to hold in a limit of the
Quantum
Theory of Gravity. And this limit will apply only to regions which are
Conformally flat. The gravity will be found to be conformally flat in
strong
gravitational regimes only. In weak gravity regimes non-local effects
will
become relevant, which should give rise to a MOND like phenomenology.

Another thing I expect is that like all other forces gravity may also
have
a repulsive factor, which will apply between all matter, only it will
apply
at a distance or will arise due to some other factor. This will result
in
the accelerating expansion of the universe, which has been observed.

Gravity is the only theory that does not seem to have any repulsive
factor, compared to other forces. QCD has three flavours, QED has
two types of charges, so it is OK for QGD(Quantum Gravitational
Dynamics) to have only one factor mass, but it must have a
repulsion, just like in QCD like flavours repell, and in QED like
charges
repell, so in QGD mass should also repell. Before QGD is formulated
it will not be known how it should happen.


What MOND predicts is that when you have two colliding BH's
(or large masses) that the speed of a star,
which circulates around the center of gravity of that BH,
after collision, will drastically change.
There will almost be no change when Newton is considered.


I think you are ignoring that MOND only applies to weak
gravitational regimes. In strong regimes MOND is equivalent
to Newtonian Gravity.

Also Black Holes are inherently Relativistic objects and MOND
is not relativistic. You should really apply TeVeS.

Also remember that TeVeS is exactly equivalent to GR in
strong gravity.


I have serious problems with MOND.
1. One is for example the above mentioned document.
2. A different one is the value of a0. This is more or less a free
parameter.


It is no longer a free parameter. It is a universal parameter and
must have the same value for all observations. It has already
been fit to 1.21E-8 m/s^2. This cannot change as it has been
used to fit more than 100 galaxies. If it is changed it will no
longer fit that data. So it cannot have any other value now.

3. Third how do you go from Newton to MOND.
There are more or less three areas involved:
One with Newton at short distance between stars,
one with both Newton and MOND
and one with MOND only at large distances.


There is no distance scale in MOND. There is only an
acceleration scale, ie a0. Above a0 it is Newtonian,
below a0 it is MONDian. It doesn't matter now why it is so,
because we don't have a quantum theory of gravity. But it
has been proved with the enormous amount of data on
galaxies.

We still don't know precisely the function that should be
used at the boundary ie near a0, to predict the actual
gravity. It will need much more precise observations to
really fix the function.


Other numerical approaches are necessary. For example, Brada's
thesis.
http://www.astro.umd.edu/~ssm/mond/brada.uu


I cannot access that url.

See also MLAPM.
http://www.aip.de/People/AKnebe/MLAPM/


When we have a quantized Ads/CFT theory of gravity, which is the
equivalent of the other forces, nothing will work according to our
intuition. Time Dilation etc are intuitive compared to what we will
have ;-).


Why do you again use the word intuition ?


I don't understand your question. Don't you know what Intuition means?
Non-intuitive means that something does not follow your experiences
in the past. If you think that something should behave one way but it
turns out to behave in a different way then it is non-intuitive.

Before Einstein gave Relativity, would anybody think that it is normal
for time to dilate, or length to contract. So they were non-intuitive
results. Now after 100 years they can be considered intuitive for the
scientists, but still not for the rest of the world.

If now the quantum theory of gravity comes which says that gravity
does not follow Newtonian laws at some scale, then it will not be
intuitive. Although this is the expected outcome, but there may
be other effects that may be very counter intuitive. Like quantum
entanglement, or Quark Confinement, I am sure Quantum gravity
will have its own quirks.

regards,
-anandsr
  #29  
Old March 28th 07, 02:33 PM posted to sci.astro.research
Nicolaas Vroom
external usenet poster
 
Posts: 216
Default Barred galaxies mass distribution

schreef in bericht
...
On Mar 22, 1:55 pm, "Nicolaas Vroom"
wrote:
schreef in
...

On Mar 12, 10:37 pm, "Nicolaas Vroom"
wrote:


I have written a program to simulate galaxies usingMOND.


For a more general discussion related toMONDwhich
includes your references See:http://users.pandora.be/nicvroom/mond.htm
For a copy of the program see:
http://users.pandora.be/nicvroom/prgmond.htm


I am not able to access your site.


There was one . (point) too much.

I hope you took care to apply MOND correctly.


How do you apply MOND correctly ?

It has non-local affects.


What do you mean by that ?


Non-Local effects is explained below.


You did not explain it.

You cannot replace all mass within a sphere with a point mass, for
measuring its effect outside the sphere.


I agree that that gives complications. IMO that is a problem with MOND.


Yes, it is a problem with MOND. It is just slightly inaccurate.


What do you mean by that ?
Do you mean that a0 could have a different value ?

You can try to apply TeVeS if you want completely accurate results
(according to MOND).


For TeVeS See:
http://en.wikipedia.org/wiki/Tensor-...scalar_gravity
Why do I have to use TeVeS.

The bottom line is that MOND works.

If MOND works than why use TeVeS

There are dozens of papers that
show you how to fit the data in galaxies.


I have also studied those curves.
As I have mentioned I have two major problem.

First if the rotation curve is not flat but decreases
at larger distances than you can not simulate those
with MOND.
(MOND can only be used if the speed increases.)

Secondly starting point is a certain visible (baryonic) mass
distribution.
With Newton you can calculate the rotation curve
but this curve does not match the measured curve.
Solution add an halo of darkmatter.

With MOND you should start with this same mass
distribution.
The problem is that the speeds (rotation curves) calculated
based on that assumption with MOND
(assuming that MOND is applicable at scales
larger than 0.1 ly See below) are far too much.

Check the explanation at
http://www.astro.umd.edu/~ssm/mond/mondnbody.ps


Yes I agree there is an issue.
See also my comments See:http://users.pandora.be/nicvroom/mond.htm
at Feedback #4.
At the end of that document is written:
"Note that this does not mean MOND is wrong,
just that this kind of calculation does not work"
IMO that is a serious problem.


It would seem as a serious problem, because we don't have a quantum
theory of gravity, which is bound to be a type of Quantized AdS/CFT
theory,
like the other forces. All AdS/CFT theories have non-local effects.


The rest removed.

The fact that you say that we should use a different theory
IMO is prove that with MOND we have a serious problem.

What MOND predicts is that when you have two colliding BH's
(or large masses) that the speed of a star,
which circulates around the center of gravity of that BH,
after collision, will drastically change.
There will almost be no change when Newton is considered.


I think you are ignoring that MOND only applies to weak
gravitational regimes. In strong regimes MOND is equivalent
to Newtonian Gravity.


My question is more related to two large masses.
If the star is outside the range where a=a0
than with Newton when the two masses collide there
is (almost) no change in the speed of the test object
but with MOND there is.

I have serious problems with MOND.
1. One is for example the above mentioned document.
2. A different one is the value of a0. This is more or less a free
parameter.


It is no longer a free parameter. It is a universal parameter and
must have the same value for all observations. It has already
been fit to 1.21E-8 m/s^2.

I expect you mean 1.21E-8 cm/s^2

This cannot change as it has been
used to fit more than 100 galaxies. If it is changed it will no
longer fit that data. So it cannot have any other value now.

3. Third how do you go from Newton to MOND.
There are more or less three areas involved:
One with Newton at short distance between stars,
one with both Newton and MOND
and one with MOND only at large distances.


There is no distance scale in MOND. There is only an
acceleration scale, ie a0. Above a0 it is Newtonian,
below a0 it is MONDian.


For the Sun the distance for a to get smaller than a0
(1.21E-10m/s^2) is roughly 0.1 ly.
The distance between then sun and the nearest star
is 1.3 pc or 4.3 ly.
That means the behaviour between almost all the stars
in our Galaxy is described by MOND.
Only when two stars become very close the description
becomes Newton.

Is that the correct application of MOND ?

It doesn't matter now why it is so,
because we don't have a quantum theory of gravity. But it
has been proved with the enormous amount of data on
galaxies.

We still don't know precisely the function that should be
used at the boundary ie near a0, to predict the actual
gravity. It will need much more precise observations to
really fix the function.


Other numerical approaches are necessary. For example, Brada's
thesis.
http://www.astro.umd.edu/~ssm/mond/brada.uu


I cannot access that url.

See also MLAPM.
http://www.aip.de/People/AKnebe/MLAPM/


When we have a quantized Ads/CFT theory of gravity, which is the
equivalent of the other forces, nothing will work according to our
intuition. Time Dilation etc are intuitive compared to what we will
have ;-).


Why do you again use the word intuition ?


I don't understand your question. Don't you know what Intuition means?
Non-intuitive means that something does not follow your experiences
in the past. If you think that something should behave one way but it
turns out to behave in a different way then it is non-intuitive.


Science has nothing to do with (my or your) intuition.
Science has to do with experiments under carefully defined
conditions.
There is no personal "dimension" in science.

Nicolaas Vroom
http://users.pandora.be/nicvroom/
  #30  
Old April 3rd 07, 01:37 PM posted to sci.astro.research
[email protected]
external usenet poster
 
Posts: 19
Default Barred galaxies mass distribution

Nicolaas Vroom wrote:
schreef in bericht
...
On Mar 22, 1:55 pm, "Nicolaas Vroom"
wrote:
Non-Local effects is explained below.


You did not explain it.


A non local effect is one that does not allow dis-regarding external
factors. Something that does not reduce with the square of distance.
Basically you cannot replace a sphere with a point mass.

Yes, it is a problem with MOND. It is just slightly inaccurate.


What do you mean by that ?
Do you mean that a0 could have a different value ?


No. Just that MOND the equation is not completely accurate.
The world is not newtonian so any newtonian formulation will
not be entirely accurate, and you will have effects that don't
make sense. Just read the n body document I gave you.
The reason it doesn't make sense is because of the newtonian
formulation of MOND. It explains things better as TeVeS, which
will not have such wierd aspects.

So you cannot apply it simply. You must think of where you
are applying it and then derive a form which will apply in that
case. eg. In a galaxy you must assume a disk with simple non-
uniformity and then derive a form that can be used. That is what
the accompanying papers do.

If you have to use individual stars for your application then you
must use TeVeS.

There are dozens of papers that
show you how to fit the data in galaxies.


I have also studied those curves.
As I have mentioned I have two major problem.

First if the rotation curve is not flat but decreases
at larger distances than you can not simulate those
with MOND.
(MOND can only be used if the speed increases.)


Don't talk about distances. MOND does not work
with distances, it works with acceleration scale a0.

Are there any galaxies where rotation curves decrease
at distances where accelarations are less than a0?

If you have found one, please publish your results,
Scientists have been searching for such results for
the last 25 years.


Secondly starting point is a certain visible (baryonic) mass
distribution.
With Newton you can calculate the rotation curve
but this curve does not match the measured curve.
Solution add an halo of darkmatter.

With MOND you should start with this same mass
distribution.
The problem is that the speeds (rotation curves) calculated
based on that assumption with MOND
(assuming that MOND is applicable at scales
larger than 0.1 ly See below) are far too much.


Again you are talking about distances. Distances don't
matter in MOND. MOND regime does not start for
100s of Lightyears within our own galaxy, at the center.

For our SUN it would start at much below 0.1ly. Actually
at a distance of a couple of days.

The fact that you say that we should use a different theory
IMO is prove that with MOND we have a serious problem.


And what would be that problem?
It just means that you don't understand MOND. You must
understand it first before you can apply it correctly.

My question is more related to two large masses.
If the star is outside the range where a=a0
than with Newton when the two masses collide there
is (almost) no change in the speed of the test object
but with MOND there is.


How do you collide to stars such that a a0.
I believe even if you where to collide two marbles the
acceleration between them will be more than a0, at the
point where they are about to merge.

Also remember MOND is applicable only when *all*
gravitational forces are considered. Basically you cannot
do these tests on earth, or near the SUN. There is only
one point between Earth and the Sun where the
gravitational force between them cancells exactly, where
we can test for MOND.

There is no distance scale in MOND. There is only an
acceleration scale, ie a0. Above a0 it is Newtonian,
below a0 it is MONDian.


For the Sun the distance for a to get smaller than a0
(1.21E-10m/s^2) is roughly 0.1 ly.


I would think it would be more like 0.01 ly.

The distance between then sun and the nearest star
is 1.3 pc or 4.3 ly.
That means the behaviour between almost all the stars
in our Galaxy is described by MOND.
Only when two stars become very close the description
becomes Newton.

Is that the correct application of MOND ?


That is correct. But it will not apply near the center of
the galaxy.

Science has nothing to do with (my or your) intuition.
Science has to do with experiments under carefully defined
conditions.
There is no personal "dimension" in science.


I don't understand your rejection of intuition. After all science
progresses due to intuition. You cannot make a new equation
without intuition. You first think up an equation based on your
intuition, and then test it out. The intuition is not infallible,
actually it is wrong more times than correct, when working
on unknown things, but you couldn't proceed without it.
Inventions are born out of intuitions, and that includes
discovering laws of nature.

Remember the story of the Benzene ring. How it was
dreamt, before understanding its nature. That is a very
obvious example of intuition playing a role in science.


Nicolaas Vroom
http://users.pandora.be/nicvroom/

 




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