Dark Matter or Dark Force

[Strange]

Here: https://arxiv.org/abs/astro-ph/9811442

I can't see how Bligh gets the data he claims from that paper. But,as far as I can tell from his website, he doesn't have a clue what he is talking about so it is all moot. So we can just ignore that brown dwarf nonsense.

[swansont]

Web sites can be hard to evaluate, but when the very name tells you it's "alt", that's not a tough call.

[TakenItSeriously]

14 hours ago, Strange said:

I have not heard that before. Do you have a reference?

 

Here is the reference he gave for the relative motion of Brown Dwarfs..

Fuchs B., Jahreiss H., Wielen R., 1999,  Kinematics of Nearby Subdwarfs, Ap&SS,  265,  175

 

8 hours ago, Janus said:

Because the solar system has a high concentration of visible matter in it even compared to the local galactic neighborhood.  The local part of our galaxy has an average density of ~2e-9 kg/ km³.     If we take the total mass of the solar system and average it out into a sphere with a radius equal to Neptune's orbit, its average density works out to being ~5 kg/km³.  Much more tightly packed. The density of dark matter in the vicinity of the Solar system is ~6e-13 kg/km³.  Much less dense than even even the average galactic neighborhood. ( it works out that the expected amount of dark matter within the confines of the solar system is equal to about the mass of a small asteroid.

So if dark matter is so sparse, how can it have such a large effect on the galactic rotation curves?.  It's not confined to the galactic disk like the vast majority of the visible matter is;  it is spread out into a spherical halo in which the visible galaxy is embedded.  To work out how much gravitational effect it would have on a star orbiting a galaxy, you would need to calculate the total mass of DM contained in a sphere with a radius equal to the stars distance from the center of the galaxy.

With our own sun, some 26,400 ly out, and using the average density of DM in the local neighborhood, this work out to 2e10 solar masses, or a sizeable fraction of the galaxy's entire visible matter mass. (the real amount will actually be a bit more, since the dark matter density does increase a bit as you move towards the center of the galaxy.)

So while there would not be not enough dark matter in the solar system to measurably effect the motion of the planets, it would still add up to be more than enough to effect the galaxy as a whole.  

Solar system =  relatively heavy concentration of visible matter in a small region.  

Galaxy as a whole = lower concentration of visible matter, over a larger volume

 DM = even lower concentration of mass, but over even a huger volume.

Thanks for the detailed explanation.

I understand your points on the local sparsity of DM or how it creates a spherical halo surrounding galacies, which I assume have all been modeled to fit the rotation curves of visible matter. But that puts cause before effect which I don’t have a problem with if it results in resonable conclusions, except I dont see how the dispersal of DM could seem reasonable since gravity acting upon visible matter doesn't behave that way.

Its as if DM has one way properties of gravity that effects the motion of visible matter but is not itself effected by gravity or any of the laws of nature for that matter. Yet we know that the location of dark matter does seem to occupy roughly the same regions of space as visible matter in the very large scale based on the evidence of the lense effect so it must have some kind of tie to visible matter.

Now, if you take a step back and look at the described model as if it were a model of loop fields instead of particles of matter wouldn’t it seem to make more sense to you?

[Janus]

2 hours ago, TakenItSeriously said:

 

Here is the reference he gave for the relative motion of Brown Dwarfs..

Fuchs B., Jahreiss H., Wielen R., 1999,  Kinematics of Nearby Subdwarfs, Ap&SS,  265,  175

 

Thanks for the detailed explanation.

I understand your points on the local sparsity of DM or how it creates a spherical halo surrounding galacies, which I assume have all been modeled to fit the rotation curves of visible matter. But that puts cause before effect which I don’t have a problem with if it results in resonable conclusions, except I dont see how the dispersal of DM could seem reasonable since gravity acting upon visible matter doesn't behave that way.

Its as if DM has one way properties of gravity that effects the motion of visible matter but is not itself effected by gravity or any of the laws of nature for that matter. Yet we know that the location of dark matter does seem to occupy roughly the same regions of space as visible matter in the very large scale based on the evidence of the lense effect so it must have some kind of tie to visible matter.

Now, if you take a step back and look at the described model as if it were a model of loop fields instead of particles of matter wouldn’t it seem to make more sense to you?

The distribution of dark matter does match what you would expect given its properties. It does interact by gravity( both ways), but not by electromagnetic interaction. It is this difference that results in DM being spread out in a sphere while visible matter tends to collect into a more compact shape.   It means that dark matter can't 'collide' with visible matter or other dark matter. Dark matter just passes through everything, including other dark matter.    

When visible matter collides ( or even makes a close approach) it interacts electromagnetically. It can either be deflected or the colliding matter could stick together.  In either case, there is an acceleration which causes the matter to emit electromagnetic waves which come at the expense of kinetic energy,  Colliding matter will give off heat and the resulting combined mass will have less momentum than it started with.  If there is a deflection, the individual components will separate at speeds lower than what they approached at.  This lower speed means that they will be more likely to be drawn into further interaction.  A large collection of visible matter will, through al these energy shedding interactions will tend to collapse into a denser arrangement before it becomes relatively stable.  

When DM makes a close approach, it may have its trajectory changed by gravity,  but this acceleration does not result in the production of EM radiation and thus no subsequent loss of energy. The participants of the encounter end up leaving with the same total momentum that they started with.  Without this mechanism for shedding kinetic energy, a DM cloud has no tendency to condense into a denser structure.

[TakenItSeriously]

30 minutes ago, Janus said:

The distribution of dark matter does match what you would expect given its properties. It does interact by gravity( both ways), but not by electromagnetic interaction. It is this difference that results in DM being spread out in a sphere while visible matter tends to collect into a more compact shape.   It means that dark matter can't 'collide' with visible matter or other dark matter. Dark matter just passes through everything, including other dark matter.    

When visible matter collides ( or even makes a close approach) it interacts electromagnetically. It can either be deflected or the colliding matter could stick together.  In either case, there is an acceleration which causes the matter to emit electromagnetic waves which come at the expense of kinetic energy,  Colliding matter will give off heat and the resulting combined mass will have less momentum than it started with.  If there is a deflection, the individual components will separate at speeds lower than what they approached at.  This lower speed means that they will be more likely to be drawn into further interaction.  A large collection of visible matter will, through al these energy shedding interactions will tend to collapse into a denser arrangement before it becomes relatively stable.  

When DM makes a close approach, it may have its trajectory changed by gravity,  but this acceleration does not result in the production of EM radiation and thus no subsequent loss of energy. The participants of the encounter end up leaving with the same total momentum that they started with.  Without this mechanism for shedding kinetic energy, a DM cloud has no tendency to condense into a denser structure.

It sounds like your describing matterless mass which is difficult for me to comprehend.

[Mordred]

Excellent explanation Janus, very accurate 

1 minute ago, TakenItSeriously said:

It sounds like your describing matterless mass which is difficult for me to comprehend.

 

No he is describing one of the distinctive differences between baryonic (normal matter) and weakly interactive matter. Both have mass but the key is the lack of the electromagnetic interaction with the WIMP family.

[TakenItSeriously]

6 minutes ago, Mordred said:

Excellent explanation Janus, very accurate 

 

No he is describing one of the distinctive differences between baryonic (normal matter) and weakly interactive matter. Both have mass but the key is the lack of the electromagnetic interaction with the WIMP family.

But without EM forces, whats the difference?

[Mordred]

Everyday objects like tables, chairs are held together by the the EM force. DM cannot bind the same way.

More importantly atoms themselves are held together by the EM force. So DM cannot form atoms

Edited December 5, 2017 by Mordred

[TakenItSeriously]

3 minutes ago, Mordred said:

Everyday objects like tables, chairs are held together by the the EM force. DM cannot bind the same way.

I understand but thats kind of my point. If you remove all properties of matter but its mass , how is it different from saying matterless mass?

 

[Mordred]

Mass isn't due to  just one force. All forces and energy density contribute to mass. DM has mass its simply due to the weak force which it does interact with much like neutrinos has mass via the same mechanism. Hence the sterile neutrinos Vmedvil and I were discussing earlier

I know this article will be too technical however as it is on topic it would be good to add here

"The next decade of Stetile neutrino studies"

https://arxiv.org/abs/1306.495

"We review the status of sterile neutrino dark matter and discuss astrophysical and cosmological bounds on its properties as well as future prospects for its experimental searches. We argue that if sterile neutrinos are the dominant fraction of dark matter, detecting an astrophysical signal from their decay (the so-called 'indirect detection') may be the only way to identify these particles experimentally. However, it may be possible to check the dark matter origin of the observed signal unambiguously using its characteristic properties and/or using synergy with accelerator experiments, searching for other sterile neutrinos, responsible for neutrino flavor oscillations. We argue that to fully explore this possibility a dedicated cosmic mission - an X-ray spectrometer - is needed."

now one of the key details in that article is that in order to account for the quantity of DM you would need at least 3 sterile neutrino flavors.

I will note this comes back to the conjecture Vmedvil posted earlier that I wanted clarity on.

Once he described what he was thinking in better detail. I knew this was what he was referring to.

Edited December 5, 2017 by Mordred

[TakenItSeriously]

1 hour ago, Mordred said:

Mass isn't due to  just one force. All forces and energy density contribute to mass. DM has mass its simply due to the weak force which it does interact with much like neutrinos has mass via the same mechanism. Hence the sterile neutrinos Vmedvil and I were discussing earlier

I know this article will be too technical however as it is on topic it would be good to add here

"The next decade of Stetile neutrino studies"

https://arxiv.org/abs/1306.495

"We review the status of sterile neutrino dark matter and discuss astrophysical and cosmological bounds on its properties as well as future prospects for its experimental searches. We argue that if sterile neutrinos are the dominant fraction of dark matter, detecting an astrophysical signal from their decay (the so-called 'indirect detection') may be the only way to identify these particles experimentally. However, it may be possible to check the dark matter origin of the observed signal unambiguously using its characteristic properties and/or using synergy with accelerator experiments, searching for other sterile neutrinos, responsible for neutrino flavor oscillations. We argue that to fully explore this possibility a dedicated cosmic mission - an X-ray spectrometer - is needed."

now one of the key details in that article is that in order to account for the quantity of DM you would need at least 3 sterile neutrino flavors.

I will note this comes back to the conjecture Vmedvil posted earlier that I wanted clarity on.

Once he described what he was thinking in better detail. I knew this was what he was referring to.

Well, this is where the real downside of my 2e condition kicks in. If I cant understand something as I’m reading it, I can’t retain it and Particle Physics seems like arbitrary facts to my mind. I understand that its not, mind you, I just can’t understand why its not.

[Mordred]

It takes a lot of effort to understand particle physics. Its not an easy topic. So don't feel bad about that.

Its one of primary reasons why I stress the importance of understanding correctly terms such as mass, energy, work, potential and kinetic energy..

The list goes on but any musunderstanding of the definitions will always prevent correct understanding of particle physics. (or physics in general)

[TakenItSeriously]

7 minutes ago, Mordred said:

It takes a lot of effort to understand particle physics. Its not an easy topic. So don't feel bad about that.

Its one of primary reasons why I stress the importance of understanding correctly terms such as mass, energy, work, potential and kinetic energy..

The list goes on but any musunderstanding of the definitions will always prevent correct understanding of particle physics. (or physics in general)

Yeah, but hard work I can handle, its just that without a short term memory I have to rely only on long term memory and LTM is apparently choosy about what it retains and just rejects stuff that has no meaning.

For example, if I’m reading something and come accross a paragraph that makes no sense to me I literally have no memory of its contents. I know I read it but couldn’t tell you a single word of what I read. It made academics a nightmare because, unless I could get a question answered in realtime, the rest of the lechture was just white noise.

1 on 1 I could learn practically anything very quickly because I could ask why and have it answered, but probably not with particle physics because knowing why something happens apparrently stops working at the fundamental levels below Quantum Mechanics and thinking “it just does” doesn’t help me to retain it.

[Mordred]

Ah gotcha, yeah that does present its challengs. I knew a few people that had that problem. It explains quite a bit so I will keep that in mind in the future.

Edited December 5, 2017 by Mordred

[TakenItSeriously]

6 minutes ago, Mordred said:

Ah gotcha, yeah that does present its challengs. I knew a few people that had that problem. It explains quite a bit so I will keep that in mind in the future.

I’m so glad you understand. Not everyone does and then I guess I just seem like an a*****e to them so I rarely bring it up.

[Vmedvil]

Ya, I still think there is a SNF interactions like mesons on Dark Matter as WIMPs while in Sterile Neutrino it would not have SNF interaction, but we can all say that any model with electric charge in DM is false because of Electroweak decoupling in W-, W+, and Z bosons along with lack of interaction with photons at all, even charged particles that make a neutral bound would be false.

Edited December 5, 2017 by Vmedvil

[Janus]

15 hours ago, TakenItSeriously said:

I understand but thats kind of my point. If you remove all properties of matter but its mass , how is it different from saying matterless mass?

 

What is it that makes "matter"?   We consider a table as being made of matter.  I can touch it and it feels solid. 

But what is really happening I "touch" the table.  My hand, and the table is made up of atoms with electrons in shells around a nucleus and these electrons have electric fields.  So what is happening is that my the electric fields of the electrons of the outer layer of my hand interact with the electric fields of the outer layer electrons of the table.  It is just an interaction of fields and nothing is really "touching" anything in the way we commonly think about it.  

The matter of the table is made of atom bound together by electromagnetic forces. Are the atoms themselves matter? We generally say that they are. Atoms are made up of electrons, protons and neutrons. Are they matter?  Again, we tend to say that they are. Protons and neutrons going further are made from quarks.

Quarks and electrons are considered fundamental particles, They are also considered matter particles.

So, what are these fundamental particles made of?  are they little balls of "something" that is imbued with the properties we measure the particle as having, or are they just the some total of the properties they exhibit?  Thinking of them in the first way seems like trying to extend the analogy of how the macroscopic world appears to be down to where it doesn't hold.

It seems much more likely that the second view is better, a fundamental particle is just "made up" of its combined properties. It has a mass and maybe a charge, etc. and fields associated with them, and the only way to interact with them is through these properties.  They are just entities with a collection of properties.

If this is the case,  Is there a single property that defines its "matterness".  If it can't interact through the electromagnetic force, is it not matter? 

Is the Neutrino matter? it has mass, but no charge, it also interacts with other matter rarely and only under certain conditions. A neutrino could pass through light years of lead without having one interaction.   Would you call a neutrino "matterless mass".   The WIMP model for dark matter just assumes that is is made up of particles like the neutrino, and which share like properties in some respects.

[Vmedvil]

Well, Electromagnetism would be the Solid part of matter then, as you get closer the negative and negative repel making it feel solid. That would make DM  non solid by that view which is what is found.

Edited December 5, 2017 by Vmedvil

[TakenItSeriously]

1 hour ago, Janus said:

What is it that makes "matter"?   We consider a table as being made of matter.  I can touch it and it feels solid. 

But what is really happening I "touch" the table.  My hand, and the table is made up of atoms with electrons in shells around a nucleus and these electrons have electric fields.  So what is happening is that my the electric fields of the electrons of the outer layer of my hand interact with the electric fields of the outer layer electrons of the table.  It is just an interaction of fields and nothing is really "touching" anything in the way we commonly think about it.  

The matter of the table is made of atom bound together by electromagnetic forces. Are the atoms themselves matter? We generally say that they are. Atoms are made up of electrons, protons and neutrons. Are they matter?  Again, we tend to say that they are. Protons and neutrons going further are made from quarks.

Quarks and electrons are considered fundamental particles, They are also considered matter particles.

So, what are these fundamental particles made of?  are they little balls of "something" that is imbued with the properties we measure the particle as having, or are they just the some total of the properties they exhibit?  Thinking of them in the first way seems like trying to extend the analogy of how the macroscopic world appears to be down to where it doesn't hold.

It seems much more likely that the second view is better, a fundamental particle is just "made up" of its combined properties. It has a mass and maybe a charge, etc. and fields associated with them, and the only way to interact with them is through these properties.  They are just entities with a collection of properties.

If this is the case,  Is there a single property that defines its "matterness".  If it can't interact through the electromagnetic force, is it not matter? 

Is the Neutrino matter? it has mass, but no charge, it also interacts with other matter rarely and only under certain conditions. A neutrino could pass through light years of lead without having one interaction.   Would you call a neutrino "matterless mass".   The WIMP model for dark matter just assumes that is is made up of particles like the neutrino, and which share like properties in some respects.

Yes, but youre forgetting one thing, all of the examples you gave are detectable by means other than it’s mass. Can we say the same for DM?

Matter we can detect directly.or at leas through it’s particle like evidence left behind.

DM is only detectable indirectly through it’s effect on matter.

Magnetic fields are also only detectable through their effect on matter

Edited December 6, 2017 by TakenItSeriously

[Mordred]

No we have to rely on indirect methods to detect DM. 

[Strange]

1 hour ago, TakenItSeriously said:

Magnetic fields are also only detectable through their effect on matter

Yep. It is quite hard to argue that anything is detected directly!

[TakenItSeriously]

7 minutes ago, Strange said:

Yep. It is quite hard to argue that anything is detected directly!

If you define DM as invisible non interactive matter, its true that we can only measure it indirectly through other matter.

If you define DM as a magnetic field, then the effects of the field on matter is direct evidence of the field.

So which would be real case?

Edited December 6, 2017 by TakenItSeriously

[Mordred]

The first case for DM, the indirect means, it is with its effects via gravity.

Edited December 6, 2017 by Mordred

[LaurieAG]

On 06/12/2017 at 11:21 AM, TakenItSeriously said:

If you define DM as invisible non interactive matter, its true that we can only measure it indirectly through other matter.

If you define DM as a magnetic field, then the effects of the field on matter is direct evidence of the field.

So which would be real case?

Why bother with indirect things when you can deal with the problem directly?

According to the latest PLANCK data total universal mass = 4.82% normal matter + 25.8% dark matter = 30.62% and the ratio between total calculated universal matter and total visible universal matter = 2*Pi +/- 1.1%.

It's easier to define our total universal matter as a polar or transformed variant of our ordinary matter (that puts the galactic rotation problem to bed as well) than continuing to believe the difference is something that cannot be clearly identified with our current physics. 

Edited December 19, 2017 by LaurieAG
remove duplicate word