B More Experimental Evidence for MOND

[Vanadium 50]

If you had an overlap region, experiments could test both theories and see which does better, and/or map the transition between them. But you really don't.

 

[Ibix]

If you had an overlap region, experiments could test both theories and see which does better, and/or map the transition between them. But you really don't.

So just to clarify, in #89 you meant "...there is a neat separation between rotation curves and every other test of gravity that has so far been performed"? Or is there something that makes rotation curves unique beyond their dependance on really low gravitational acceleration?

 

[vanhees71]

This makes MOND very suspicious then. It should make clear predictions about the phenomenology that it is supposed to describe (rotation curves without "Dark Matter") and then it should be possible to be tested against standard GR + "Dark Matter".

I thought there are also galaxies with no or very little Dark matter, and there the rotation curves are discribed by GR with only the visible matter. If MOND is a description of gravity as a universal interaction, then how does it explain that in this case no modification against GR + visible matter occurs?

 

[Vanadium 50]

Or is there something that makes rotation curves unique beyond their dependance on really low gravitational acceleration?

I don't think so.

All the terrestrial tests? Done with g > a0.
All the solar system tests? Done with g > a0.

That's the problem. And thinks we "know" about gravity may or may not apply to MOND. We "know" gravity affects all materials equally. Do we know that for MOND? Not really - there we look at pretty much the same material all the time: a mix of mostly hydrogen and some helium.

In fact, if soneone found a clever way to test MOND on earth with lead weights, and it failed, a fair conclusion is "well you tested it with lead. Stars are made mostly of hydrogen/"

 

[Structure seeker]

I thought there are also galaxies with no or very little Dark matter, and there the rotation curves are discribed by GR with only the visible matter. If MOND is a description of gravity as a universal interaction, then how does it explain that in this case no modification against GR + visible matter occurs?

With the EFE, usually a big enough other galaxy is nearby or may be nearby to explain these. And these are not easy to explain in Lambda-CDM either, since galaxies should only appear at high enough dark matter concentrations there.

Except for elliptical galaxies, there simply $g > a_0$

 

[Vanadium 50]

I thought there are also galaxies with no or very little Dark matter,

There are two. Or maybe three.

The amount of DM inferred depends on the distance. The distance of both is problematic. Indirect measures of their masses is also problematic.

One part of the astro culture I do not like is taking a distribution (spread can be either real, or measurement-driven, or both) and looking at the tails, and then declaring "Look! A new class of [whatever] !!" I understand why the culture developed this way, but I still do not like it.

Additionally, is difficult to strip a galaxy of its DM without disturbing its structure. It cannot be done in one interaction - it takes several. However, one does expect some DM variation and one sees that. Oddly, the variation always seems to match the MOND prediction.

 

[AndreasC]

Firstly, MOND describes what is and makes predictions of what we measure. This is no valid argument in my mind. It is constructed to do exactly this. It is a minimal requirement.

It is constructed to explain some galaxy rotation curves. That is similar to dark matter. BUT using it you can infer some other things that don't intrinsically have anything to do with these rotation curves, and indeed it seems it makes some correct predictions. The main problem is probably that it still can't explain some things without dark matter.

 

[ohwilleke]

McGaugh has an update on the wide binary debate.

 

[pinball1970]

McGaugh has an update on the wide binary debate.

I PMd you. This paper from the Gaia data,
Monthly Notices of the Royal Astronomical Society, stad3393, https://doi.org/10.1093/mnras/stad3393
Published: 3 November 2023
This goes against the MOND claims of the Chae paper.

 

[AndreasC]

Yep, this is the upcoming paper I alluded to with my previous post. Interesting to see what this means for MOND in the long run!

 

[PAllen]

Note this latest paper is by someone (Banik) who has long been a proponent of MOND, writing one of the major review papers in the field.

 

[Vanadium 50]

I don't see that as a problem. I have published several experimental papers supporting my side of a controversy. A few have even settled the controversy.

Am I biased? In don't know. I am certainly interested. We have controversy when people draw different conclusions from the same data. If N-1 experiments convice me but not everybody, and I do an Nth experiment that does convince everybody, where is the problem?

 

[Vanadium 50]

Where I do see a problem is, as I mentioned before, that we cannot test MOND in a terrestrial setting because the gravity of Earth obliterates the effect. But we can test it in wide binaries because for some reason the gravity of the planets does not obliterate the effect.

In Science, you and your worst enemy have to agree on what the predictions are. I don't think "Whatever Milgrom says it is" is a good basis for that.

 

[ohwilleke]

I've blogged Banik's new paper. If correct, it strongly disfavors simple toy-model MOND, but doesn't, for example, rule out Deur's gravitational self-interaction approach which replicates MOND in galaxy rotation curves, but does not predict a wide binary effect.

 

[Vanadium 50]

I will go a step further - since there is no agreement on either the data nor the predictions for wide binaries, it is not a good test.

 

[strangerep]

This debate continues to rage on a private MOND mailing list. Since it's private, I won't divulge details here, except to suggest that everyone "hang loose" for a bit longer as the science sausage continues to be made. The choice of quality criteria to be applied when selecting Gaia data is still controversial, and seems to be a significant theme underlying the current debate. No doubt more papers will appear soon.

 

[strangerep]

Where I do see a problem is, as I mentioned before, that we cannot test MOND in a terrestrial setting because the gravity of Earth obliterates the effect. But we can test it in wide binaries because for some reason the gravity of the planets does not obliterate the effect.

Huh? Which planets are you talking about? Planets that might be orbiting each of the stars in a wide binary pair?

 

[PAllen]

I don't see that as a problem. I have published several experimental papers supporting my side of a controversy. A few have even settled the controversy.

Am I biased? In don't know. I am certainly interested. We have controversy when people draw different conclusions from the same data. If N-1 experiments convice me but not everybody, and I do an Nth experiment that does convince everybody, where is the problem?

Not sure if you are referring to my post. The point I was making is that someone supportive of MOND has now published a paper that claims to very strongly rule it out. Banik still thinks lambda CDM is seriously flawed, but the new paper proves (in the authors view) that nothing close to MOND can be the answer.

 

[strangerep]

The point I was making is that someone supportive of MOND has now published a paper that claims to very strongly rule it out. Banik still thinks lambda CDM is seriously flawed, but the new paper proves (in the authors view) that nothing close to MOND can be the answer.

Heh, I hope you enjoy watching screeching U-turns in the near future.

Separately, Frederico Lelli (Astrophysicist at INAF) has recently re-emphasized a point he made near the end of this paper about how several different types of physical phenomena all reveal a universal acceleration scale of approximately the same value, although there is no a-priori reason for this.

Among others, he mentions these:

- The Baryonic Tully-Fisher relation,

- The Central Density Relation (applicable at small radii in galaxies),

- The Radial Acceleration Relation (applicable at large radii in galaxies).

In a non-MONDian universe there is no reason why the acceleration scales found in these phenomena should be the same. He points out that this is a strong reason to do research on MOND, analogous to how the appearance of $\hbar$ in disparate contexts was a compelling reason to explore quantum mechanics over 100 years ago.

 

[AndreasC]

I don't see that as a problem. I have published several experimental papers supporting my side of a controversy. A few have even settled the controversy.

Am I biased? In don't know. I am certainly interested. We have controversy when people draw different conclusions from the same data. If N-1 experiments convice me but not everybody, and I do an Nth experiment that does convince everybody, where is the problem?

It's the opposite here. Banik is a major MOND supporter, and now here he says MOND doesn't work.

 

[collinsmark]

Dr. Becky Smethurst chimes in on the new paper:

 

[pinball1970]

It's the opposite here. Banik is a major MOND supporter, and now here he says MOND doesn't work.

Yeah that's significant and shows integrity of the study?

 

[Vanadium 50]

I say again, wide binaries are a terrible test.

Let's go back to the basics. In the Newtonian word, I have two masses, M and m, separated by a distance r, and for simplicity, let's have them at rest. The heavier feels an acceleration Gm/r and the lighter GM/r and two lines of algebra should convince you momentum is conserved: no external force, and the center of mass doesn't move.

In MOND, the accelerations are GM/r and something else (assuming the acceleration is in the deep MOND domain). I think it is \sqrt{GMa_0/r} but it doesn't matter exactly what it is. The point is now that the center of mass starts to move, with no external force.

Nobody believes this is what happens. Nobody.

I think even the MOND proponents would argue that something must happen to prevent this, and that the equations we use for MOND are probably approximations for real, better-behaved ones.

This is part of the reason I say that MOND has problems with composite objects. (We can discuss why rotation curves are particularly ill-suited to sort this out).

So looking at wide binaries is exactly where we know that MOND prediction needs to be altered. It's just a bad test.

 

[strangerep]

In MOND, the accelerations are GM/r and something else (assuming the acceleration is in the deep MOND domain). I think it is \sqrt{GMa_0/r} but it doesn't matter exactly what it is. [...]

That's not how it works. You can't simply add MOND-adjusted fields from different sources -- that gives all sorts of nonsense along the lines you sketched (among others). This has been known for ~40 years (cf. Felten).

Rather, one must first compute the total Newtonian field at the point of interest, and then apply the MONDian adjustment. That's more-or-less what AQUAL does. The problem you mentioned was a primary reason for inventing AQUAL. Unfortunately, it's non-relativistic so not much of a surprise that it's a bit off wrt gravitational lensing.

 

[AndreasC]

I say again, wide binaries are a terrible test.

Let's go back to the basics. In the Newtonian word, I have two masses, M and m, separated by a distance r, and for simplicity, let's have them at rest. The heavier feels an acceleration Gm/r and the lighter GM/r and two lines of algebra should convince you momentum is conserved: no external force, and the center of mass doesn't move.

In MOND, the accelerations are GM/r and something else (assuming the acceleration is in the deep MOND domain). I think it is \sqrt{GMa_0/r} but it doesn't matter exactly what it is. The point is now that the center of mass starts to move, with no external force.

Nobody believes this is what happens. Nobody.

I think even the MOND proponents would argue that something must happen to prevent this, and that the equations we use for MOND are probably approximations for real, better-behaved ones.

This is part of the reason I say that MOND has problems with composite objects. (We can discuss why rotation curves are particularly ill-suited to sort this out).

So looking at wide binaries is exactly where we know that MOND prediction needs to be altered. It's just a bad test.

I don't mean disrespect but I've noticed you have made a lot of posts where you say this or that is an obvious problem with MOND, or that this or that is not explained etc, whereas you could just read some basic review paper and find the answer. What you are saying here only applies to one formulation in the original, proof of concept paper on MOND. There is a bunch of well known theories that have been subsequently developed that do not violate conservation of momentum. People working on MOND are not so stupid that they didn't even notice the third law is violated for decades.

 

[Vanadium 50]

That's not how it works.

Which is exactly the point. You need to add something beyond just "here's what we see in rotationally supported galaxies" to get a working microscopic (insofar as one can call individual stars "microscopic")

And now you're trying to test two things.

 

[Vanadium 50]

you could just read some basic review paper

What makes you think I haven't?

There is a difference between not reading them and not being convinced by them. I find the arguments very epicyclical. Er...epicycular, Um...like epicycles.

One of PF's faults, especially in BSTM physics, is that it attracts a cheerleading mentality: "Go SUSY! Go MOND! Go X17!". It leaves little room for people to point out problems with both (or all) alternatives.

Wide binaries were a bad test when they supported MOND, and wide binaries were a bad test when they undermined MOND. Lining up on the sidelines based on this is a bad idea.

 

[strangerep]

One of PF's faults, especially in BSTM physics, is that it attracts a cheerleading mentality: "Go SUSY! Go MOND! Go X17!". It leaves little room for people to point out problems with both (or all) alternatives.

Rubbish. You seem to have no trouble pointing out such problems as you perceive them. No one is telling you to shut up. Quite the opposite, imho. I'm happy to listen carefully to (well considered, well informed, well explained) points of view.

 

[AndreasC]

What makes you think I haven't?

There is a difference between not reading them and not being convinced by them. I find the arguments very epicyclical. Er...epicycular, Um...like epicycles.

You're not convinced that what, AQUAL or TeVeS or whatever for example does not have the behavior you said? You can just reproduce the calculation, it's not that hard. Do you think this or the other papers on the WBT didn't address these different models of MOND? They did.

According to this paper, pretty much any kind of MOND people have come up with so far disagrees with the data. This may or may not be true, since there are lots of papers contradicting each other currently. Possibly this will only be conclusively resolved with the next Gaia release. Maybe even later than that. True, it doesn't mean the hard core of MOND is falsified, but, if true, all the models we have so far fail in that regime. This has nothing to do with the fact that MOND has to be modified to fit Newton's third law, because, well, this has been done a million years ago, and those models that recover the third law still fail.

In the same way, if we had the opposite result, it would show that current models of MOND do better than CDM in that regime. This would also be very important.

The fact of the matter is that the MOND law still works on galaxies, but if this is true, the hopes of it also working on slightly smaller scales (scales where people thought it would) are lost. That is, if this is correct. That's all there is to this, I don't understand where the controversy is.

 

[pinball1970]

This article today favouring a MOND model over ΛCDM, looking at the Hubble tension and Banik is one of the authors.

https://phys.org/news/2023-12-giant-void-puzzle-universe-expansion.html

EDIT: Paper here,(early Galaxy formation found by JWST is mentioned in the conclusion also) https://academic.oup.com/mnras/article/527/3/4388/7337338?login=false

So the paper favouring MOND 2.11.23 Void/ Hubble tension

Not favouring MOND using wide binary data 3.11.23