Chandra dark matter announcement could sink MOND

[Mike2]

Do we have the capability to determine the exact distribution of the matter necessary to give us the lensing effect in the dark matter region? An exact distribution of dark matter would probably distinguish between any kind of permanent matter which would continue to clump together and a vacuum energy effect which would tend to dissipate once free of the matter that formed it. I suspect computer simulations might show us that this distribution could not come from a form of matter that's gravitationally attracted to itself.

 

[ohwilleke]

Exact is a very demanding word. Resolution gets better and better, but it is never perfect, and is inherently limited by the number of lensed objects between Earth and the cluster whose lensing can be observed.

 

[SpaceTiger]

Markevitch is actually quite cagey in that quote. He leaves open the idea that DM might be specific to cluster level phenomena and that subcluster level phenomena might be MONDish. Given that almost all the contra-MOND evidence is at the cluster level, there is something to be said for that caution.

I suspect that wasn't his reason for being cagey. If there is dark matter on cluster scales, it would be very strange if there were no dark matter on galaxy scales as well. The caveat about modified gravity is most likely there to allow for large-scale, strong-field, or quantum modifications to GR.

 

[asciencebuff]

I suspect that wasn't his reason for being cagey. If there is dark matter on cluster scales, it would be very strange if there were no dark matter on galaxy scales as well. The caveat about modified gravity is most likely there to allow for large-scale, strong-field, or quantum modifications to GR.

can someone tell me (I'm 16 ) if this paper supports or contradicts MOND (it says it contradicts relativity but not a word on MOND!) ? http://arxiv.org/abs/physics/0608026" I am going to use it i n my science project on DARK MATTER DISCOVERY . this guy (or a lady) computes gravity on different scales like you guys say is possible after this historic NASA discovery. I would also need more papers like this-- what are my Google keywords here ?
I know Einstein proved Newton wrong long time ago but does this all mean that MOND is incorrect even though it doesn't say so? or is MOND no longer questioned?

also is it OK (ethical)to use geologic papers to disprove physics trheory like relativity (or MOND)? would my prof get mad if I used this paper ? THANKS!

 

[selfAdjoint]

can someone tell me (I'm 16 ) if this paper supports or contradicts MOND (it says it contradicts relativity but not a word on MOND!) ? http://arxiv.org/abs/physics/0608026" I am going to use it i n my science project on DARK MATTER DISCOVERY . this guy (or a lady) computes gravity on different scales like you guys say is possible after this historic NASA discovery. I would also need more papers like this-- what are my Google keywords here ?
I know Einstein proved Newton wrong long time ago but does this all mean that MOND is incorrect even though it doesn't say so? or is MOND no longer questioned?

also is it OK (ethical)to use geologic papers to disprove physics trheory like relativity (or MOND)? would my prof get mad if I used this paper ? THANKS!

{Added in edit} After wscanning it, I believe the paper you are citing is unsound. It is not absolutely unheard of that a local phenomenon like resonance could be extended over many orders of magnitude, but it is something that has to be shown in detail, not just by plugging numbers into an equation. Please find something else for your project.
The new observations are very strong evidence against MOND but not absolutely conclusive. The MOND partisans are trying to work around the physicality of dark matter. There are two papers containing the observations and their interpretation. What I'm sure your prof wants is not a blind acceptance of the new interpretations but a critical attitude showing independence of mind and ability to tell a hawk from a handsaw. (extra brownie points for spotting where the quote comes from).

MOND was never intnded as a serious contender for explaining the universe, rather it was in the spirit of "See if we can modify gravity a little to make these things (galaxy turning ratios) happen instead of positing matter that no-one can see".

Although as you say, GR reduces Newtonian gravity to a special case, yet that special case ("flat" spacetime) is a good approximation of how spacetime is on the scale of a galaxy. Individual stars have their gravity wells but the overall geometry, as analysis of the microwave background has suggested, is analogous to a flat plain with a lot of little pits scattered about it. The pits don't change the fact that overall, the landscape is flat. And in a flat spacetime, Newtonian gravity is an adequate approximation. So it was Newtonian gravity that they modified to make MOND.

I believe Marcus has a thread devoted to MOND papers, do a "search this forum" on MOND.

 

[marcus]

can someone tell me (I'm 16 ) if this paper supports or contradicts MOND (it says it contradicts relativity but not a word on MOND!) ? http://arxiv.org/abs/physics/0608026" I am going to use it i n my science project on DARK MATTER DISCOVERY . this guy (or a lady) computes gravity on different scales like you guys say is possible after this historic NASA discovery. I would also need more papers like this-- what are my Google keywords here ?
I know Einstein proved Newton wrong long time ago but does this all mean that MOND is incorrect even though it doesn't say so? or is MOND no longer questioned?

also is it OK (ethical)to use geologic papers to disprove physics trheory like relativity (or MOND)? would my prof get mad if I used this paper ? THANKS!

we need a special thread to deal with your questions. I am not an expert in what this paper is about so i cannot judge it or predict whether your prof would give you a bad grade, if you use it. but I will tell you that this paper does not seem right for the topic of dark matter, to me.

Mensur is junior faculty at a Bosnian university. He is assistant prof of geophysics in the physics department of University of Sarajevo. He has a PhD in theoretical geophysics from the university of New Brunswick. He is a member of the American Geophysical Union. His email is
momerbasic@pmf.unsa.ba, and also omerbashich@yahoo.com
All that is proper and straightforward, but it doesn't indicate that his ideas in this paper are any good, and it doesn't indicate
that this paper have something to do with dark matter. It may just not be right for your project.
I hope there is still time for you to find better papers to talk about!

AFAICS based on a brief look, this Mensur paper is way out on a limb and speculative and although he has submitted it to a solid peer-reviewed journal (Annalen der Physik) I am betting dollars to donuts that it will not be accepted for publication.

Did you look at the Dark Matter links that Sean Carroll gave at his blog Cosmic Variance?
http://cosmicvariance.com/2006/08/21/dark-matter-exists/
He is a reputable wellknown guy and he was one of the people taking part in the NASA press conference.
He explained it in pretty simple terms. The first thing to get straight on is what Sean Carroll said

 

[marcus]

can someone tell me (I'm 16 )...

Hey buff!

what you should do is really look at this and understand it

http://www.astro.ucla.edu/~wright/blinking-1E0657-56.html

this is Ned Wright's special blinking combination graphic of the bullet cluster pictures

the blue is the dark matter
the red is the hot gas, the shockwaves of collision make it hot
and when both the red and blue are turned off you can see the clusters of galaxies (they are more orange than some of the stuff in the foreground because they are redshifted by distance). if you see the clusters you will notice that they are exactly where the blue WAS when the blue was turned on. the red, the hot gas, is in between.

Ned Wright is a senior cosmology faculty at UCLA. great teacher. world authority. there is lots more to learn at his website. but this graphic is a start.

 

[asciencebuff]

{Added in edit} After wscanning it, I believe the paper you are citing is unsound. It is not absolutely unheard of that a local phenomenon like resonance could be extended over many orders of magnitude, but it is something that has to be shown in detail, not just by plugging numbers into an equation. Please find something else for your project.
The new observations are very strong evidence against MOND but not absolutely conclusive. The MOND partisans are trying to work around the physicality of dark matter. There are two papers containing the observations and their interpretation. What I'm sure your prof wants is not a blind acceptance of the new interpretations but a critical attitude showing independence of mind and ability to tell a hawk from a handsaw. (extra brownie points for spotting where the quote comes from).

MOND was never intnded as a serious contender for explaining the universe, rather it was in the spirit of "See if we can modify gravity a little to make these things (galaxy turning ratios) happen instead of positing matter that no-one can see".

Although as you say, GR reduces Newtonian gravity to a special case, yet that special case ("flat" spacetime) is a good approximation of how spacetime is on the scale of a galaxy. Individual stars have their gravity wells but the overall geometry, as analysis of the microwave background has suggested, is analogous to a flat plain with a lot of little pits scattered about it. The pits don't change the fact that overall, the landscape is flat. And in a flat spacetime, Newtonian gravity is an adequate approximation. So it was Newtonian gravity that they modified to make MOND.

I believe Marcus has a thread devoted to MOND papers, do a "search this forum" on MOND.

Im trying to do a project on why there seem to be so many different views on what this NASA discovery means for relativity v. MOND.nobody seems to have a firm answer (even the CNN report looked sooo confusing) I hope its not just me who s confused? I plan on getting into college so hopefuly this should get me some extra credits.Im not going to pretend that I understand it so I thought it would be better if I asked around a little

OK thanks for explaining the relationship between MOND and Newton to me! but!-- if MOND was never meant to be THE theory how come is all over the news on NASA discovery??

If you don't mind asking: after this discovery do you consider yourself "MOND partisan" or "relativity partisan" or some say "x partisan", and why?

 

[asciencebuff]

we need a special thread to deal with your questions. I am not an expert in what this paper is about so i cannot judge it or predict whether your prof would give you a bad grade, if you use it. but I will tell you that this paper does not seem right for the topic of dark matter, to me.

Mensur is junior faculty at a Bosnian university. He is assistant prof of geophysics in the physics department of University of Sarajevo. He has a PhD in theoretical geophysics from the university of New Brunswick. He is a member of the American Geophysical Union. His email is
momerbasic@pmf.unsa.ba, and also omerbashich@yahoo.com
All that is proper and straightforward, but it doesn't indicate that his ideas in this paper are any good, and it doesn't indicate
that this paper have something to do with dark matter. It may just not be right for your project.



I hope there is still time for you to find better papers to talk about!

AFAICS based on a brief look, this Mensur paper is way out on a limb and speculative and although he has submitted it to a solid peer-reviewed journal (Annalen der Physik) I am betting dollars to donuts that it will not be accepted for publication.

Did you look at the Dark Matter links that Sean Carroll gave at his blog Cosmic Variance?
http://cosmicvariance.com/2006/08/21/dark-matter-exists/
He is a reputable wellknown guy and he was one of the people taking part in the NASA press conference.
He explained it in pretty simple terms. The first thing to get straight on is what Sean Carroll said

I didnt know where to start so I just did a search on ARXIV.ORG (that's where the russian math wiz published his paper he's getting $1 million for!) so I searched for "MOND OR scale OR physics" and the search returned the above paper as the first one out of 300 or so (I think). So I (naively )assumed it was teh most popular or whatever. But the paper doesn't even mention MOND, strange that it got first on the list

But thanks a lot for the pointers as to how to actually judge a paper, and for the links to,I really appreciate that!

 

[marcus]

... I searched for "MOND OR scale OR physics" and the search returned the above paper as the first one out of 300 or so (I think). So I (naively )assumed it was teh most popular or whatever. But the paper doesn't even mention MOND, strange that it got first on the list

I strongly approve of your learning to use ARXIV.ORG and the search tool.
It is easy to get fooled especially at first. The arxiv search engine maxes out at 300 and gives stuff in no particular order

You would get a narrower search and fewer hits if you would say
"MOND AND scale AND physics". then the abstract (the brief summary) of the article would have to say all three things!

Or a moderately narrow search would be just to say "MOND" without any OR stuff. Then at least the abstract would have to say MOND for it to get hit.
===================

Basically in my view at least MOND has been ruled out now. I was at times very interested by MOND over the past 2 years. You could say that at least part of the time I was feeling like a MOND partisan, at least I wanted to make sure it got a fair hearing. Now I think it has been shot down. Time to move on.

the point is, buff, that IN A GALAXY CLUSTER MOST OF THE ORDINARY MATTER IS IN THE GAS BETWEEN THE GALAXIES.

so if there is no DM then the center of gravity, where gravity is pulling towards, and the center of the lens effect is going to be WHERE THE GAS IS.

but in that Ned Wright picture, or the other pictures,
ooops have to go, will be back later
============

I'm back. what they found was that the lens effect was NOT like one big lens in the middle centered on the (red) gas
instead it was acting like there were TWO lenses, each centered where the blue is in Ned's picture,
like a pair of goggles, or glasses, with not much lensing happening in between

THE LENSING WAS mostly NOT HAPPENING WHERE MOST OF THE ORDINARY MATTER WAS, there in the middle
=======
so there has to be some UNordinary matter, out there where the blue is, in Ned's picture
===========

you should try to understand how they detect lensing. In this business, whatever you are photographing there is ALWAYS SOME BACKGROUND of more distant galaxies. even if you are looking at clusters of galaxies like bullet that are already very distant there is always some that are MORE distant.
lensing is detected in several different ways, and one way is by the DISTORTION of background galaxies that should be circles or randomly oriented ellipses------lensing tends to make them more elliptical/ oblong and more pointed towards the center of the "lens"
----it is called the "weak lensing effect"

You can read a lot of this stuff in WIKIPEDIA and check in case i made a mistake. Always good to check :-)
there are more dramatic lensing effects, like getting double images etc. but the "weak lensing effect" is the stretching out of galaxy images on an axis pointing towards the center of the lens---and it is all they needed to plot the lens effect here
and that is how they got the BLUE blobs in Ned's picture

=============
If I said anything wrong, I hope someone will correct it. Also you Buff better make sure you understand what is going on in Ned Wright's picture. And also the other pictures that Sean Carroll put links to.
and then please come back if you have some specific question---something that doesn't make sense.

the details of MOND do not matter. the idea is there MIGHT have been some complicated explanation that didnt involve extraordinary matter, that would work just with ordinary type matter.
in fact there were several competing MOND-ish schemes that explained stuff with just ordinary matter (but complicating the laws of gravity)
Now none of that matters. All possible MOND schemes would have had the lensing centered in the middle where most of the ordinary type mass is. All existing and possible future MOND schemes are therefore dead. the details of the different schemes don't matter any more. Maybe that puts it too bluntly without proper qualifications and reservations etc. but that's how I see it.

finally we can be sure there is no other alternative possible explanation, there IS some kind of unusual matter we can't see as yet and it is where the blue blobs are in Ned's picture and it passes thru ordinary gas and stuff without colliding, and its gravity holds clusters together and does the observed lensing.

hope this not too longwinded and that it may be of use to you

here is the link to the Ned Wright picture

Hey buff!

what you should do is really look at this and understand it

http://www.astro.ucla.edu/~wright/blinking-1E0657-56.html

this is Ned Wright's special blinking combination graphic of the bullet cluster pictures

the blue is the dark matter
the red is the hot gas, the shockwaves of collision make it hot
and when both the red and blue are turned off you can see the clusters of galaxies (they are more orange than some of the stuff in the foreground because they are redshifted by distance). if you see the clusters you will notice that they are exactly where the blue WAS when the blue was turned on. the red, the hot gas, is in between.

Ned Wright is a senior cosmology faculty at UCLA. great teacher. world authority. there is lots more to learn at his website. but this graphic is a start.

 

[Chronos]

I'm trying to resist the urge to jump up and down. I've always been viscerally repelled by MOND - it violates GR and, more subtly, the laws of thermodynamics. 'Spooky action' at a distance implies a preferred reference frame, IMO. The mind numbing part of that experiment is it requires FTL communication to test the model. So what is the point?

 

[asciencebuff]

I strongly approve of your learning to use ARXIV.ORG and the search tool.
It is easy to get fooled especially at first. The arxiv search engine maxes out at 300 and gives stuff in no particular order

You would get a narrower search and fewer hits if you would say
"MOND AND scale AND physics". then the abstract (the brief summary) of the article would have to say all three things!

Or a moderately narrow search would be just to say "MOND" without any OR stuff. Then at least the abstract would have to say MOND for it to get hit.

thanks marcus! I did search with ANDs but guess what --it returned nothing, zero! So I tried with ORs and that worked. anyway my school bought software that scans student papers for plagiarism (checks againts Internet!) so I can't really use links you sent me even if I write it in my own words ( we were told the software crosschecks for words volumes and all sorts of logics). I did read the stuff you linked though--thanks very useful!

speaking of ARXIV.ORG how come that this russian math wiz I mentioned is getting his million (it was all over the news ) and he published his paper on ARXIV.ORG ? do you MUST publish in ajournal for your paper to hold true? you had a couple of email addresses for this guy,do you know him i s he a wiz like the russian guy ?? besides I don't have much time for this project plus I can understand tha paper quite all right . (plus as selfadjoint said he plugged numbers into equations and all works. it also speaks about dark matter a lot at the end actually!)

THANKS guys!

 

[marcus]

Go for it Buff! You are on your own, and seem to be doing fine.
I can't answer questions about Grisha, the Russian whiz. I actually don't know the latest about that.
Anyway time is short and you have your project to complete!

I'm trying to resist the urge to jump up and down. I've always been viscerally repelled by MOND - it violates GR and, more subtly, the laws of thermodynamics. 'Spooky action' at a distance implies a preferred reference frame, IMO. The mind numbing part of that experiment is it requires FTL communication to test the model. So what is the point?

Sometimes there's confusion because people talk about the 1980s version of MOND by Moti Milgrom. The kind of MOND people were considering in recent years AFAIK was typically Bekenstein relativistic MOND
(if anyone unfamiliar, look up Bekenstein on arxiv). that's what i mean by it.

the experiment proposed by Bekenstein and Magueijo to test MOND in the solar system, by a probe, did not require FTL. I don't know what "that experiment" means in the preceding post.

I have doubts that "spooky action at a distance" applies here----don't know what this could mean in Bekenstein MOND case.

Bekenstein MOND explicitly did NOT involve a preferred frame.

Bekenstein founded a branch of thermodynamics---black hole thermodynamics---and Hawking's black hole radiation conjecture stemmed from Bekenstein's original insight into black hole temperature and entropy. I never heard of Bekenstein's MOND violating thermodynamic laws and given his expertise in that area I think it's unlikely.

I don't think it is worth discussing MOND now. If anyone feels like jumping up and down with joy, my sincere advice is that they should do it, whether their reasons are based on fact or not, and whether their reasons make sense or not. True happiness is rare and should not be resisted!