[PmbPhy (OP)]

Is Dark Matter Real?

--------------------------------------------------------------------------------

Way too many times physics amateurs have posted claiming dark matter isn't real and we should listen to them etc. I've ignored those threads because they weren't credible. However there's an article on this subject in Scientific American this month entitled Is Dark Matter Real by two astrophysicists.

See: http://www.newenglandphysics.org/other/SciAmDarkMatter.pdf

Let me know what you think.

[Colin2B]

Hi Pete, the link doesn’t work I get a 404 error. I think there is a bit missing from the url

[PmbPhy (OP)]

Try it now.

[Bill S]

Nice one, Pete. 

I’ve been impressed by the small amount of Hossenfelder’s work I’ve had the opportunity to read.  A quick skim through this leaves me feeling that she and McGaugh have given the subject a balanced treatment.  Hopefully, I’ll be able to read it more thoroughly, and will, no doubt, have some questions.

[guest45734]

Many dark matter candidates have been cancelled over the years. I may be becoming biased, but am minded to think dark matter does not exist, and is nothing more than a mathematical fix to make observations fit predictions based on a set of equations.
I have been reading up on some of the MOND ideas, and am attracted to Verlindes entropic gravity ideas. Verlindes and the various MOND ideas do not require arbitrary amounts of Dark matter adding, which suggest they may be very close to the truth. DARK MATTER DOES NOT EXIST maybe

https://en.wikipedia.org/wiki/Entropic_gravity

I had wondered how time dilation could be included in entropic gravity and pulled this up https://arxiv.org/pdf/1602.05707.pdf which is also interesting

[evan_au]

MOND does not really deal with variations in the Cosmic Microwave Background Radiation, which Dark Matter does try to explain.
See: https://en.wikipedia.org/wiki/Lambda-CDM_model#Historical_development

[guest45734]

MOND does not really deal with variations in the Cosmic Microwave Background Radiation, which Dark Matter does try to explain.See: https://en.wikipedia.org/wiki/Lambda-CDM_model#Historical_development

Is it not still just adding random amounts of dark matter when other effects might also be the cause. Verlinde appears to be adamant we dont need dark matter, https://motherboard.vice.com/en_us/article/xwgk3j/theoretical-physicist-erik-verlinde-says-we-dont-need-dark-matter-to-explain-the-universe

You might find this linkl interesting in support of Verlindes claims www.scirp.org/journal/PaperInformation.aspx?PaperID=85930 4. Summary and Conclusions
The purpose of this paper has been to show how the CMB temperature anisotropy pattern could be a map of gravitational entropy as defined by Roger Penrose in his book entitled, “Fashion, Faith and Fantasy in the New Physics of the Universe.” This is particularly relevant with respect to Erik Verlinde’s theory that gravity is an emergent property of cosmic entropy. Verlinde’s theory dovetails nicely with the July 2018 Journal of Modern Physics paper entitled, “Clues to the Fundamental Nature of Gravity, Dark Energy and Dark Matter.”
In the present paper, the rationale for FSC calculations of gravitational entropy in the form of
S
−
−
√
S
is presented. These calculations indicate a tight correlation with the COBE DMR measurement showing CMB RMS temperature variations of 18 micro Kelvins. The COBE dT/T anisotropy ratio of 0.66 × 10−5 falls within the FSC gravitational entropy range calculated for the beginning and ending conditions of the recombination/decoupling epoch. Thus, the FSC model incorporating gravity as an emergent property of entropy suggests that the CMB temperature anisotropy pattern could simply be a map of gravitational entropy, as opposed to a magnified “quantum fluctuation” event at a finite beginning of time.
 
EDIT I found this lecture by Verlinde talking about his work which takes about an hour to watch. https://insidetheperimeter.ca/a-new-view-on-gravity-and-the-dark-side-of-the-cosmos-erik-verlinde-public-lecture/?__hstc=261081490.b20e624ce3bbf82fcde9c8f1a30c5bc1.1533466440658.1533466440658.1533466440658.1&__hssc=261081490.1.1533466440658&__hsfp=2495466239
 

[jeffreyH]

I hadn't responded to this thread since I have not studied this topic in depth. I am just watching with interest. If dark matter is the answer then that is fine but so is an alternative. If it matches observation.

[Bill S]

One thing which we can, probably, predict is that if the "Heavies" are questioning the existence of dark matter, there will be some lively discussion.

[guest45734]

 i dont know if anyone else is interested in Verlindes theories. The little i know about quantum entanglement suggests only information is transferred. Can forces(gravitational) be transmitted between entangled particles / qubits.

Edit this might be the paper Verlindes references in his lecture posted above.

https://arxiv.org/pdf/1611.02269.pdf

[yor_on]

Never liked 'gravitons' and 'dark matter', then again, that's a purely personal opinion. What is missing in your link though is a explanation of how they propose this 'modified gravity' is supposed to work, also how well it will fit Einsteins definitions of gravity
=

Actually it makes me think of 'phonons'

[guest45734]

Never liked 'gravitons' and 'dark matter', then again, that's a purely personal opinion. What is missing in your link though is a explanation of how they propose this 'modified gravity' is supposed to work, also how well it will fit Einsteins definitions of gravity
=

Actually it makes me think of 'phonons'

Remember its all just maths, and it may not explain the real world accurately. A curve fit can be made to make predictions based on a set of observations, once the model is stretched beyond its limits it develops errors. Einsteins equations have worked successfully for a long time, but they apply no intrinsic properties to space time except curvature, and arbitrary amounts of dark matter are required to make the model work. Einstein and others also wrote papers on wormholes EPR bridges to explain entanglement and quantum tunneling effects. The modern theories are trying to incorporate quantum effects to explain how gravity works.

What many of the new theories of gravity are exploring is that spacetime has properties arising from quantum theory and string theory. Verlindes approach and the Holographic approach both are exploring the nature of space time, and incorporate a wormholes. Verlinde claims his model does not require dark matter also I understand the Holographic model does not require it either.


The graviton is a undetectable spin 2 boson virtual particle that might stretch across a universe or might not and it might not exist either just like dark matter which could be anything you want it to be explain away the errors in equations, or observations that dont make sense.   

Edit.  Verlinde views space time geometry arises from the entanglement structure of the quantum state. Gravity emerges from this quantum information as a result of changes in entanglement caused by matter. For further info read Verlindes paper posted above.

Does Verlindes model look a little like a lattice of phonons also, are you maybe thinking down the same lines

[guest45734]

What have I missed does this link claim to put an end to the holographic universe idea or Verlindes version of emergent gravity.

3 days ago https://phys.org/news/2018-08-flaw-emergent-gravity.html

Edit If I am correct the holographic principle relies on an artificial anti de sitter space, which Verlindes version of imergent gravity does not.

A simpler link on Verlindes ideas https://darkmatterdarkenergy.com/2016/12/30/emergent-gravity-verlindes-proposal/

[yor_on]

Interesting dead cat, but I don't know what to think there. Just take this statement "If space is defined by the connectivity of quantum entangled particles, then it becomes almost natural to consider gravity as an emergent statistical attribute of the spacetime. After all, we learned from general relativity that “matter tells space how to curve, curved space tells matter how to move” – John Wheeler."

It seems you can get a mathematical model that allow space to exist without matter, and you can 'bend it' etc etc. All in accordance with relativity. But it makes sense to think of the universe as in some way entangled. There a key question could be how many entanglements a 'object' can have. If we presume only one at a time then a new 'bump' should replace the old, right?
=

Now that would be a good theoretical test of Verlindes proposal, wouldn't it? If he also can create a mathematical description of how a empty space/Universe can 'bend' and 'rotate', in accordance with the equations of relativity naturally.

"So in the AdS model, gravity is emergent and its strength, the acceleration at a surface, is determined by the mass density on that surface surrounding matter with mass M. This is just the inverse square law of Newton. In the more realistic dS model, the entropy in the volume, or bulk, must also be considered. (This is the Gibbs entropy relevant to excited states, not the Boltzmann entropy of a ground state configuration)." from your link.

What he says here should make it possible "Verlinde posits that the information and entropy content of space are due to the excitations of the vacuum state, which is manifest as dark energy."

Actually I joked about that here somewhere, suggesting that it was 'virtual particles' creating this 'extra mass' we needed looking at galaxies and the universe. So maybe? Then again, he's also using entropy for it, which makes it extremely theoretical to me. He's not easy to assimilate, I'll listen to that link you gave and see if I can make more sense of it , won't promise anything though, :)

[yor_on]

A universe of ideas dead cat :)
Information, I should write more about him
=

and yes, we're alike in that.
He do make sense
=

What I found frustrating before was the way he always referred to 'entropy', without me seeing exactly how he thought there. But in the 'lecture' he simplifies it to counting the number of bits, giving you a numerical expression of the amount of possibilities any given system can become in, defining that as the 'entropy' of the system. That's simpler and make sense. But if I get it right this numerical evaluation of bits are not what he means, it's just a safe starting stone from where we move to 'information', and uncertainty, itself, he's a deep thinker.

[guest45734]

A universe of ideas dead cat
Information, I should write more about him
=

and yes, we're alike in that.
He do make sense
=

What I found frustrating before was the way he always referred to 'entropy', without me seeing exactly how he thought there. But in the 'lecture' he simplifies it to counting the number of bits, giving you a numerical expression of the amount of possibilities any given system can become in, defining that as the 'entropy' of the system. That's simpler and make sense. But if I get it right this numerical evaluation of bits are not what he means, it's just a safe starting stone from where we move to 'information', and uncertainty, itself, he's a deep thinker.

Mond and other theories like Verlindes seem to be gaining credibility. Hossenfelder seems to support Verlindes ideas in this paper https://arxiv.org/pdf/1703.01415.pdf also in the following later paper ref reddhift https://arxiv.org/pdf/1803.08683.pdf she adds further credence to Verlindes theories.

My conclusion is that Dark Matter is a result of over stretching Einsteins equations, it does not exist. ie It has never been detected because it does not exist.

I am going to reread Verlindes paper above, I may  have m i s s ed a lot. ie I did not get the impression ADs was a part of Verlindes ideas, whilst ds was, I also got the impression that his ideas were not derived from the holographic principle.   

Edit MOND, fudges the laws of gravity on large scales in such a way as to just give an accurate picture of the galactic rotation anomalies, allowing the maths to fit what is observed without dark matter. Verlinde’s idea gives a actual physical framework to consider modifications to the laws of gravity on very large scales. On very large scales the Holographic universe idea falls down, at least that is what I think Verlinde is banging on about and at very large scales ADs is not included, I also think Hossenfelder doesnot include Anti de sitter either in her analysis of Verlindes work. Clearly I still more reading to do.

@PmbPhy  do you have any comments to add to your initial post, on this thread, you are very very quiet it is very sTRANGE
                   

[guest45734]

What I found frustrating before was the way he always referred to 'entropy', without me seeing exactly how he thought there. But in the 'lecture' he simplifies it to counting the number of bits, giving you a numerical expression of the amount of possibilities any given system can become in, defining that as the 'entropy' of the system. That's simpler and make sense. But if I get it right this numerical evaluation of bits are not what he means, it's just a safe starting stone from where we move to 'information', and uncertainty, itself, he's a deep thinker.

This
link
tries
to
explains verlindes ideas
on
entropy
https://www.science20.com/hammock_physicist/it_bit_entropic_gravity_pedestrians

[alancalverd]

Not really my subject area, but I'd appreciate elucidation from those in the know.

As I understand it, the hypothesis of dark matter is invoked to explain that the outermost stars of some galaxies are orbiting the center more rapidly than can be accounted by the presumed mass of observable stuff in the galaxy.

Given that we only have about 100 years' observations of individual stars in distant galaxies, why do we think that they are in stable orbits and not just rushing towards the galactic centre from deep space? How good is the historic velocity data? Given that 100 years is a fleabite in galactic history, how accurate is the acceleration measurement? How do we know the gravitational centre of the galaxy hasn't moved with respect to the apparent centre if there are several light years between the outer star, say closer to us, and the gravitational centre, further away?

I'm always impressed by how much information astronomers manage to glean from a few ancient photons, but recorded history from geocentric flat earth to nebulae also shows that they are more often wrong than right, so why are they so sure about this year's invisible  turtles?

[PmbPhy (OP)]

As I understand it, the hypothesis of dark matter is invoked to explain that the outermost stars of some galaxies are orbiting the center more rapidly than can be accounted by the presumed mass of observable stuff in the galaxy.

Its not simply the outermost stars.

Given that we only have about 100 years' observations of individual stars in distant galaxies, why do we think that they are in stable orbits and not just rushing towards the galactic centre from deep space?

Take a look at a galaxy and notice how the matter looks like its in orbit. Then note that we get the same results no matter how far away (and thus how old) the galaxy is. And this holds for all stars in a galaxy, not just the outermost.

How good is the historic velocity data? Given that 100 years is a fleabite in galactic history, how accurate is the acceleration measurement?

Its the doppler that's measured and from that the speed.

How do we know the gravitational centre of the galaxy hasn't moved with respect to the apparent centre if there are several light years between the outer star, say closer to us, and the gravitational centre, further away?

The centers of the galaxies are all moving. In the centers frame the stars are in orbit of it. It's not accelerating with respect to its local inertial frame.

[alancalverd]

Quote from: alancalverd on Yesterday at 22:29:51How good is the historic velocity data? Given that 100 years is a fleabite in galactic history, how accurate is the acceleration measurement?

Its the doppler that's measured and from that the speed.

Yes, but the hypothesis of dark matter derives from acceleration, not speed. So you need two credible Doppler measurements some time apart.