Dark matter ....

[joigus]

On the other hand, some of us have been quite stirred by @Markus Hanke's comments on non-linearity's potential to generate unexpected behaviours, when boundary conditions, global properties, etc may play a part in bringing about those.

I came a bit late to those comments and they've sent me into a whirlpool of thinking about how unusual it is for someone who's been trained in solving differential equations to extend these techniques to include:

1) The topological nature of the manifold itself in which one is solving the PDE.

2) The seemingly open-ended nature of how to deal with the sources and how simplification of those in order to make them tractable might make it impossible to capture properties of realistic solutions when the context is non-linear. 

It's rarely the case in general mathematical courses in ODE or PDE (linear or non-linear) that part of the problem itself is phrased like,

Oh, I almost forgot, as part of your assignment, you have to guess whether the problem is in R⁴ or maybe in some non-trivial topological space. That makes the problem insanely hard to solve.

Edited August 19 by joigus
added nuance

[DanMP]

2 hours ago, Eise said:

Where did I say scientists should stop? It is a critique on your position, that you already take DM for granted

The scientists trying to detect or explain DM have also taken DM for granted. Are they wrong?!?

 

I am open for other explanations, that's why I asked you about MOND, but your response was disappointing. 

2 hours ago, Eise said:

Where did I say scientists should stop? It is a critique on your position, that you already take DM for granted

The scientists trying to detect or explain DM have also taken DM for granted. Are they wrong?!?

 

I am open for other explanations, that's why I asked you about MOND, but your response was disappointing. 

[Mordred]

2 hours ago, joigus said:

On the other hand, some of us have been quite stirred by @Markus Hanke's comments on non-linearity's potential to generate unexpected behaviours, when boundary conditions, global properties, etc may play a part in bringing about those.

I came a bit late to those comments and they've sent me into a whirlpool of thinking about how unusual it is for someone who's been trained in solving differential equations to extend these techniques to include:

1) The topological nature of the manifold itself in which one is solving the PDE.

2) The seemingly open-ended nature of how to deal with the sources and how simplification of those in order to make them tractable might make it impossible to capture properties of realistic solutions when the context is non-linear. 

It's rarely the case in general mathematical courses in ODE or PDE (linear or non-linear) that part of the problem itself is phrased like,

Oh, I almost forgot, as part of your assignment, you have to guess whether the problem is in R⁴ or maybe in some non-trivial topological space. That makes the problem insanely hard to solve.

Hence the usage of supercomputers like Illustrus Millenium simulation which when they zoom in produced each galaxy type.

https://wwwmpa.mpa-garching.mpg.de/galform/virgo/millennium/

Even the NFW profile though requires using a PC as its formula is a power law though in that case one can factor that into a natural log function in the same manner as the scale factor for the FLRW metric.

Edited August 19 by Mordred

[Eise]

1 hour ago, DanMP said:

The scientists trying to detect or explain DM have also taken DM for granted. Are they wrong?!?

No, they aren't. DM is a viable hypothesis, so they are completely correct to search for it. You are the one who takes it for granted because your pet theory about relativity is based on it.

1 hour ago, DanMP said:

I am open for other explanations, that's why I asked you about MOND, but your response was disappointing. 

I think I will take your disappointment as a medal of honour.

[Markus Hanke]

17 hours ago, Eise said:

However, I am not sure if it could explain e.g. the separation of DM from normal matter.

I can not, of course, be sure about such specifics either, nor even about whether or not anything special would happen at all in an n-body problem. It’s really just an hypothesis, based on emergent dynamics in non-linear systems.

Basically I’m sceptical about both the particle as well as alternative-model options, so it’s good to have a third alternative.

I agree with DanMP’s earlier comment that DM is a big part of our current model of the universe, so this is a very important issue.

12 hours ago, joigus said:

someone who's been trained in solving differential equations

Well, I never have been trained. I simply base my thinking on what we do know - on situations with small n that can be exactly solved. For example the n=2 case; the spacetime of a binary body system is nothing like our naive idea of two Schwarzschild metrics superimposed. What happens for n= ~billions is anyone’s guess, because I don’t think those non-linearities smooth out.

So maybe DM is really a chaos-theoretic problem.

[DanMP]

I found an article ('Final parsec problem' that makes supermassive black holes impossible to explain could finally have a solution) suggesting that dark matter not only exists, but is also self-interacting. I learned about this few days/weeks ago, from a Sabine Hossenfelder video, but this article is better. 

 

 

On 8/19/2024 at 9:49 PM, Eise said:

No, they aren't. DM is a viable hypothesis, so they are completely correct to search for it. You are the one who takes it for granted

I wrote "detect or explain":

On 8/19/2024 at 7:53 PM, DanMP said:

The scientists trying to detect or explain DM have also taken DM for granted.

Anyone that invested time, effort and/or money to detect or figure out what DM is or does, is taking DM as real, so I did the same. You can say that what I did is just garbage, but I did something. You, instead, just claimed that MOND is the correct explanation and, when asked about your favorite theory, you were unable and/or unwilling to respond. You consider this honorable? I think that it's quite the opposite.

 

This is a science forum, we are here to discuss science, not to claim that something is correct and, when asked for arguments, to become aggressive and offend the one who asked. Shame on you! 

Edited August 22 by DanMP

[Mordred]

The final parsec problem came up in another thread but we didn't have a reference so thanks for the link.

 

[kba]

On 8/19/2024 at 9:53 PM, DanMP said:

I am open for other explanations, that's why I asked you about MOND, but your response was disappointing. 

IMHO, MOND is speculative theory. Any theory should define law(equation, formula) of based on some model which explains why exactly such law physical value dependency was used. Does MOND do it? I'm not sure.

As I understand the philosophy of nature, we have to change the main paradigm of free(aka inertial) motion to understand DM phenomenon.

Any motion at any time isn't free (i.e. non enforced). Only forces support the motion. The motion by inertia is illusion that such motion is free (non enforced). Only the body, keeping in rest, forces do not act to.

As I have found, the gravity is a force which dynamically increasing during the motion. And such force makes any body or particle to accelerate its moving, if they are do not undergo for action of other forces. Thus, all bodies in the Universe have been accelerated, including stars. That's why their velocities do not decrease while they moving around the galaxy centre. The evolution of galaxy can be represented as stars moving around its center and slowly retires from it due to acceleration of [pseudo free] inertial motion. Such motion, actually, is provided by gravity of othe galaxies in the Universe. Rough calculation defines acceleration of any [free] motion equal to approximatelly 1E-9 m/s². DM doesn't hold the stars, as blocked inside the galaxy, on the stable orbit. That's why we observe various types of galaxies. Highly likely, galaxy evolution goes through various stages from quasars to scattered galaxies.

Edited August 23 by kba

[Eise]

23 hours ago, DanMP said:

Anyone that invested time, effort and/or money to detect or figure out what DM is or does, is taking DM as real, so I did the same.

Trying to find something is not the same as dogmatic stating that it exists. I would find it exciting if DM is found, and identified (axions? sterile neutrinos? WIMPS? something completely different?). And if Markus would be right, I could even say that the situation is similar to 'Vulcan or Neptune': the latter was the explanation of irregularities in the orbit of Uranus; the first  explained the irregularities in the orbit of Mercury by the limited validity of Newtonian gravity.

23 hours ago, DanMP said:

You can say that what I did is just garbage, but I did something.

Yes, you created a crackpot theory (e.g. your 2018 thread). Just as an analogy: a few years ago it was 'discovered' that neutrinos could travel faster than light. And suddenly there appeared many articles (if I remember correctly about hundred articles on Arxiv) that tried to explain this phenomenon. In the end it was a bad connection of the timer.

23 hours ago, DanMP said:

You, instead, just claimed that MOND is the correct explanation

I never did. I only said that it is a possible explanation for rotation curves of galaxies, i.e. it is a hypothesis why rotation curves are what they are. But it does not explain what is derived from e.g. the CMB or the bullet cluster. Otherwise show me where I claimed MOND is the correct explanation for rotation curves.

23 hours ago, DanMP said:

when asked about your favorite theory, you were unable and/or unwilling to respond.

But I did! DM!  

On 8/14/2024 at 5:23 PM, Eise said:

Ockham's Razor (slightly misused as Ockham originally meant it) suggests that having one single explanation for all phenomena that we connect to DM would be better.

On 8/18/2024 at 5:44 PM, Eise said:

I agree that 'one solution for all' phenomena that hint at there being more mass than we can see is the most 'beautiful' solution.

 So it is my favourite. But as I said already:

On 8/18/2024 at 5:44 PM, Eise said:

science is always in for a surprise.

And then there is @Markus Hanke's idea. Markus, are you aware of any physicists having similar ideas? 

Edited August 23 by Eise

[Mordred]

2 hours ago, Eise said:

 

And then there is @Markus Hanke's idea. Markus, are you aware of any physicists having similar ideas? 

I have come across papers using methods such as F(R) gravity to eliminate the need for DM they typically don't look far enough. Example they will focus on rotation curves but not look into early universe DM needs such as early universe LSS formation.

[MigL]

On 8/22/2024 at 6:44 AM, DanMP said:

I found an article ('Final parsec problem' that makes supermassive black holes impossible to explain could finally have a solution) suggesting that dark matter not only exists, but is also self-interacting.

The 'final parsec problem' is not an observational problem; we know that SMBHs merge.
Computational modelling, however, fails to predict this, and SMBH merger simulations stall at about one parsec due to an effect termed dynamic gravitational drag. This suggests we don't have all the variables, or appropriate boundary conditions, in our computational model.
Dark matter, and its interaction in relation to dynamic gravitational drag, could be a solution. 

This in no way explains what dark matter is, but it might point to some properties of dark matter that allow for the overcoming of the final parsec problem, and help discriminate between possible dark matter contending models/particles.

It is akin to the galaxy rotation curve problem; dark matter is a possible solution.

Edited August 23 by MigL

[Markus Hanke]

18 hours ago, Eise said:

Markus, are you aware of any physicists having similar ideas? 

Sabine Hossenfelder, for instance - though I wasn’t immediately able to find a reference (have to look some more later). The idea isn’t new, and isn’t mine either, but I think never really came to the forefront, since it’s essentially untestable given the current limitations in computing power.

[DanMP]

On 8/23/2024 at 4:25 PM, MigL said:

The 'final parsec problem' is not an observational problem; we know that SMBHs merge.
Computational modelling, however, fails to predict this, and SMBH merger simulations stall at about one parsec due to an effect termed dynamic gravitational drag. This suggests we don't have all the variables, or appropriate boundary conditions, in our computational model.
Dark matter, and its interaction in relation to dynamic gravitational drag, could be a solution. 

This in no way explains what dark matter is, but it might point to some properties of dark matter that allow for the overcoming of the final parsec problem, and help discriminate between possible dark matter contending models/particles.

Yes, I agree.

 

The thing is that we may never directly detect dark matter particles, because of their low energy and/or other reasons, so the only thing we can do is to define DM models in such a way that they are in agreement with all the observations/aspects that are (or can be) related to DM. Even better would be to make/define a model that not only agrees with all the observations, but also makes predictions that can be tested by doing new observations or experiments. If I understood correctly, the same approach is used in order to model the structure of protons and neutrons.

 

On 8/23/2024 at 12:30 PM, Eise said:

On 8/22/2024 at 1:44 PM, DanMP said:

You, instead, just claimed that MOND is the correct explanation

I never did. I only said ...

This is what you said (the bold is mine):

On 7/31/2024 at 4:53 PM, Eise said:

Discussing DM, and not knowing what rotation curves are? One of the strongest empirical hints that DM exists (except the alternative, MOND, turns out to correct).

And a theory of gravity, like MOND, should cover all the aspects, not only the rotation curves, that’s why I asked you about gravitational lensing, Bullet cluster, gravitational time dilation and now gravitational waves. How is MOND explaining them?

 

On 8/23/2024 at 9:52 AM, kba said:

The evolution of galaxy can be represented as stars moving around its center and slowly retires from it due to acceleration of [pseudo free] inertial motion. Such motion, actually, is provided by gravity of othe galaxies in the Universe. Rough calculation defines acceleration of any [free] motion equal to approximatelly 1E-9 m/s². DM doesn't hold the stars, as blocked inside the galaxy, on the stable orbit.

If I understand correctly you are saying that the rotation of the stars around the galactic center is influenced by other galaxies in the Universe in the same way as the DM, if exists, would do? I really doubt that,  but you mentioned calculation. Can you elaborate or point to a credible source?

Edited August 25 by DanMP

[Mordred]

MOND does a better job than LCDM on Bullet cluster galaxies and for a time it did poorly on Spiral galaxies. However that has been dealt with in the case of MOND. What MOND needs to improve is galaxy clusters and early universe LSS formation processes where DM under LCDM is useful for that. AFAIK MOND makes no predictions on lensing.

Edited August 25 by Mordred

[Eise]

35 minutes ago, DanMP said:

This is what you said (the bold is mine):

On 7/31/2024 at 3:53 PM, Eise said:

Discussing DM, and not knowing what rotation curves are? One of the strongest empirical hints that DM exists (except the alternative, MOND, turns out to correct).

Wow, so much misunderstanding. I made red, what you are missing completely.

38 minutes ago, DanMP said:

And a theory of gravity, like MOND, should cover all the aspects

Not necessarily, here are my comments:

• gravitational lensing: is explained by GR
• Bullet cluster: that could be very well be DM. BTW, DM of the Bullet cluster is hypothesised on the basis of gravitational lensing.
• gravitational time dilation: is explained by GR
• gravitational waves: explained by GR

It's no use to go on. Especially because I said several times that I think that DM is the best explanation, as said, with citations of my own postings, and you do not seem to even see that. Let's wait for for what astrophysicists will discover, OK?

[DanMP]

4 minutes ago, Eise said:

Wow, so much misunderstanding. I made red, what you are missing completely.

It is possible, after all, to misunderstood you, so I apologize. 

 

8 minutes ago, Eise said:

58 minutes ago, DanMP said:

And a theory of gravity, like MOND, should cover all the aspects

Not necessarily, here are my comments:

• gravitational lensing: is explained by GR
• Bullet cluster: that could be very well be DM. BTW, DM of the Bullet cluster is hypothesised on the basis of gravitational lensing.
• gravitational time dilation: is explained by GR
• gravitational waves: explained by GR

I don't understand, MOND is not competing GR? They don't exclude each other? 

 

15 minutes ago, Eise said:

Let's wait for for what astrophysicists will discover, OK?

Ok 😀

 

19 minutes ago, Mordred said:

MOND does a better job than LCDM on Bullet cluster galaxies

Do you have a link on this? 

[Mordred]

That was over a decade ago it would be tricky to find those earlier comparisons. The bullet cluster and Spiral galaxies were often used in arguments of which is the better treatment between LCDM and MOND. Most of the recent papers are now using later versions of MOND which has undergone numerous changes over the last decade. Some versions of MOND include DM as well.

If I recall it tied into the cusp core core problem which MOND required extensions to handle.

So nowadays the first question one has to address when doing comparisons is "which version of MOND ?"

 Though I don't keep up with MOND research I do occasionally examine their articles in the interest of looking for mathematical methodologies. It's one of the primary reasons I examine alternative theories as more often than not one cones across treatments that can be useful in other applications.

For example one alternate theory not mentioned yet was Poplowskii BH universe origin papers if I recall he tried addressing both DM and DE using torsion. However the constraints on a torsion component in our universe global metric is nowadays far too stringent.

The mathematical techniques come in handy with certain aspects of particle characteristics. Not to mention toy universe modelling 

 

Just an aside it took me awhile to recall a MOND treatment involving GR which was one of your earlier questions.

One such model is TeVeS it's been considered an alternative possible replacement of GR. Where it stands nowadays I couldn't tell you it does tie into gravitational lensing as part of its examinations 

Edited August 25 by Mordred

[MigL]

2 hours ago, Mordred said:

One such model is TeVeS it's been considered an alternative possible replacement of GR. Where it stands nowadays I couldn't tell you it does tie into gravitational lensing

If that was J Bekenstein's TeVeS ( Tensor/Vector/Scalar gravity ) generalized relativistic version of MOND, then, being relativistic, it would be able to handle lensing.
However it does have its problems; one large problem being stellar gravitational stability with Bekenstein's parameters.

[Mordred]

47 minutes ago, MigL said:

If that was J Bekenstein's TeVeS ( Tensor/Vector/Scalar gravity ) generalized relativistic version of MOND, then, being relativistic, it would be able to handle lensing.
However it does have its problems; one large problem being stellar gravitational stability with Bekenstein's parameters.

It was and your likely correct on that. It's been quite a few years since I last looked at any TeVeS literature.

[kba]

On 7/31/2024 at 1:47 AM, julius2 said:

The aim of my posts is to "stitch together" the "right theory"

Is it means that I can suggest my idea for DM here?

Edited August 26 by kba

[Mordred]

28 minutes ago, kba said:

Is it means that I can suggest my idea for DM here?

!

Moderator Note

Personal theories belong in their own thread in Speculations and must adhere to the Speculation guidelines in the pinned threads at the top of the Speculation forum.

 

 When answering questions in other posters threads all answers are required to be mainstream answers. To answer with personal theories amounts to thread hijacking which is just one of the reasons for that rule.

 

That being stated your more than welcome to ask any related questions were happy to help you learn. If your not particularly familiar with DM as understood by current research.

Edited August 26 by Mordred

[Markus Hanke]

8 hours ago, MigL said:

However it does have its problems

This is the trouble, really; all the known and proposed alternative models of gravity have some form of problem. Generally speaking, they tend to be able to model one particular (class of) phenomenon better than GR, but then fail spectacularly in other situations. Most of them are also mathematically complicated, and unwieldy to work with, and oftentimes they rely on additional assumptions (extra fields etc) for which we have no evidence.

[Eise]

Well, @Markus Hanke, it seems we have to wait for a cluster of quantum computers, each with 1 TB of QBits, before this is getting solved... Slowly I get to think that your idea about the problem of solving the n-body problem with GR might have a lot of truth in it. 

[Mordred]

 It would certainly help as there are numerous formulas needing good testing related to galaxy rotation curves and the core cusp problem.