B Are Dark Matter Concentrations on Earth Seasonal?

[bluecap]

I'd like to ask something about modified gravity.. let me just quote sabine a bit (see her entire article) so I'd not mistakenly misrepresent her

http://backreaction.blogspot.com/2018/02/shut-up-and-simulate-in-which-i-try-to.html
"Shut up and simulate. (In which I try to understand how dark matter forms galaxies, and end up very confused.) "...

"And then there are the low surface-brightness galaxies. These are interesting because 30 years ago they were thought to be not existent. They do exist though, they are just difficult to see. And they spelled trouble for dark matter, just that no one wants to admit it.

Low surface brightness galaxies are basically dilute types of galaxies, so that there is less brightness per surface area, hence the name. If you believe that dark matter is a type of particle, then you’d naively expect these galaxies to not obey the Tully-Fisher relation. That’s because if you stretch out the matter in a galaxy, then the orbital velocity of the outermost stars should decrease while the total luminosity doesn’t, hence the relation between them should change.

But the data don’t comply. The low surface brightness things, they obey the very same Tully-Fisher relation than all the other galaxies. This came as a surprise to the dark matter community. It did not come as a surprise to Mordehai Milgrom, the inventor of modified Newtonian dynamics, who had predicted this in 1983, long before there was any data.

You’d think this would have counted as strong evidence for modified gravity. But it barely made a difference. What happened instead is that the dark matter models were adapted.

You can explain the observations of low surface brightness galaxies with dark matter, but it comes at a cost. To make it work, you have to readjust the amount of dark matter relative to normal matter. The lower the surface-brightness, the higher the fraction of dark matter in a galaxy."

I don't know if Sabine believes in modified gravity (MOND) or dark matter as particle. But something I don't understand. Let's say modified gravity is true.
How do you explain the following?

Is there a version of modified gravity (or MOND) that can explain the above too?

 

[bluecap]

I'd like to ask something about modified gravity.. let me just quote sabine a bit (see her entire article) so I'd not mistakenly misrepresent her

http://backreaction.blogspot.com/2018/02/shut-up-and-simulate-in-which-i-try-to.html
"Shut up and simulate. (In which I try to understand how dark matter forms galaxies, and end up very confused.) "...

"And then there are the low surface-brightness galaxies. These are interesting because 30 years ago they were thought to be not existent. They do exist though, they are just difficult to see. And they spelled trouble for dark matter, just that no one wants to admit it.

Low surface brightness galaxies are basically dilute types of galaxies, so that there is less brightness per surface area, hence the name. If you believe that dark matter is a type of particle, then you’d naively expect these galaxies to not obey the Tully-Fisher relation. That’s because if you stretch out the matter in a galaxy, then the orbital velocity of the outermost stars should decrease while the total luminosity doesn’t, hence the relation between them should change.

But the data don’t comply. The low surface brightness things, they obey the very same Tully-Fisher relation than all the other galaxies. This came as a surprise to the dark matter community. It did not come as a surprise to Mordehai Milgrom, the inventor of modified Newtonian dynamics, who had predicted this in 1983, long before there was any data.

You’d think this would have counted as strong evidence for modified gravity. But it barely made a difference. What happened instead is that the dark matter models were adapted.

You can explain the observations of low surface brightness galaxies with dark matter, but it comes at a cost. To make it work, you have to readjust the amount of dark matter relative to normal matter. The lower the surface-brightness, the higher the fraction of dark matter in a galaxy."

I don't know if Sabine believes in modified gravity (MOND) or dark matter as particle. But something I don't understand. Let's say modified gravity is true.
How do you explain the following?

View attachment 221242

Is there a version of modified gravity (or MOND) that can explain the above too?

I just learned the modified gravity is not same as MOND because modify gravity (Tensor–vector–scalar gravity) is relativistic generalization of MOND. In the bullet cluster, modified gravity can allegedly make the fields displace. Sabine explained in http://backreaction.blogspot.de/2017/01/the-bullet-cluster-as-evidence-against.html

"But modifying gravity works by introducing additional fields that are coupled to gravity. There’s no reason that, in a dynamical system, these fields have to be focused at the same place where the normal matter is. Indeed, one would expect that modified gravity too should have a path dependence that leads to such a delocalization as is observed in this, and other, cluster collisions. And never mind that when they pointed at the image of the Bullet Cluster nobody told you how rarely such an event occurs in models with particle dark matter."

Can these additional fields also be used to block gravity? Is this a prediction of Tensor–vector–scalar gravity too?

 

[Chronos]

Unlike light, gravity cannot be shielded or blocked any known means. To the best of our knowledge bosons, like the photon and putative graviton, completely ignore other bosons. This is evident when you shine a light through a magnetic field. the light is not deflected irrespective of magnetic field strength.

 

[mfb]

To the best of our knowledge bosons, like the photon and putative graviton, completely ignore other bosons.

Various bosons couple to each other. ATLAS recently observed light-by-light scattering, associated production and vector boson fusion as Higgs production modes (seen by ATLAS and CMS) are examples. Radiative penguin diagrams (also seen) have W/photon interactions.
And so on.

Gravitons should interact with all bosons, but we don't have experimental results for that yet of course.
Your statement is completely wrong.

This is evident when you shine a light through a magnetic field.

Delbrück scattering

 

[bluecap]

I just learned the modified gravity is not same as MOND because modify gravity (Tensor–vector–scalar gravity) is relativistic generalization of MOND. In the bullet cluster, modified gravity can allegedly make the fields displace. Sabine explained in http://backreaction.blogspot.de/2017/01/the-bullet-cluster-as-evidence-against.html

"But modifying gravity works by introducing additional fields that are coupled to gravity. There’s no reason that, in a dynamical system, these fields have to be focused at the same place where the normal matter is. Indeed, one would expect that modified gravity too should have a path dependence that leads to such a delocalization as is observed in this, and other, cluster collisions. And never mind that when they pointed at the image of the Bullet Cluster nobody told you how rarely such an event occurs in models with particle dark matter."

Can these additional fields also be used to block gravity? Is this a prediction of Tensor–vector–scalar gravity too?

I'd like to ask about modified gravity.. first.. how accurate is Sabine statements in the following found at the url above:

"Cyberax,

The idea of modifying gravity is that there's no particle dark matter. I mean, strictly speaking it could be both, but if you have particle dark matter anyway, you don't need modified gravity, so it's kinda pointless to combine them. So, you modify gravity instead of adding particle dark matter.

Then the question is what's the difference? Well, if you add particle dark matter you add quantum fields to the standard model of particle physics. If you modify gravity otoh, you add classical fields to general relativity. The main difference is (besides the one being quantized and the other not) the way that the additional fields couple. For what is relevant here, however, is only that there is a priori no reason for the focus of the additional fields in modified gravity to be located where the 'normal' dark matter is.

I say 'a priori' because to figure out where it is you have to solve the dynamical equations. Which I haven't done. On that matter I can merely tell you that people working on modified gravity claim they can fit the Bullet Cluster without too many problems. I haven't looked into this too deeply and can't say much about this. Hence, all I am saying here is that at least for what the theoretical structure is concerned the focus of gravity can be offset from the normal matter distribution in modified gravity too.

B. "

To avoid having quantized particles (and hence particulate dark matter) required by QFT.. Sabine said you added classical fields to general relativity in modified gravity. So there is no particle. Is this correct? And you can shift fields even when there is no matter like in the bullet clusters where the gravitational field are at the sides while the matter is at center... is this correct?

 

[Chronos]

Agreed, mfb, QFT is not my forte. A little checking corroborated boson boson interactions do sometime occur - e.g. ,https://physics.aps.org/synopsis-for/10.1103/PhysRevLett.111.080405 notes:
"
"Despite what movie lightsabers suggest, light beams pass through each other without effect. However, two photons will, on rare occasion, bounce off each other. This elastic photon-photon scattering, which occurs via intermediate particles, has never been observed directly, but a new analysis in Physical Review Letters shows that the Large Hadron Collider (LHC) at CERN could detect around 20 photon-photon events per year

Photons only interact with charged particles, so they shouldn’t interact with themselves. But quantum physics allows for a photon to temporarily fluctuate into a particle-antiparticle pair (such as an electron-positron pair), and one of these charged particles can absorb a second photon. When these intermediate particles recombine, they emit two photons. The whole process appears as two photons ricocheting off each other, but it has only been observed indirectly by its effect on the magnetic moments of the electron and muon."

I'll even cop a plea on magnetic fields bending light since technically a sufficiently powerful magnetic field could have have enough stored energy to induce gravitational lensing.. I chimed in with this because I vividly recall from years ago a professor waving a big magnet under his nose before asking if we saw it wiggle before launching a spiel about boson boson interactions. But, unless I missed a major breakthrough, gravitational shielding is still doing hard time at sci fi penitentiary.

 

[mfb]

Well, an article from 2013 can't have results from 2016-2017 of course:
ATLAS observes direct evidence of light-by-light scattering