Is there really dark matter?

[Helio]

.So a gap that needed plugging, which wasn't known about awhile back, now has "objective" evidence based on that gravitational need?

It was, actually, a while back (1933) that the strangeness was first detected. Zwicky found that galaxies revolved within a cluster much too quickly. No visible matter could be found to explain the additional gravity needed. Zwicky called the missing matter: dark matter.

But this was only one line of evidence.

Jumping forward several decades, Vera Rubin, with an improved spectrometer, measured the motion of stars moving in orbit around the center of the Andromeda galaxy. Keplerian motion, unexpectedly, was not found. A great deal of matter had to exist in a halo around the galaxy . This was now a second line of evidence.

Today, I think, there are only a small percentage of galaxies without this dark, but highly influential, matter.

There are also all those Einstein rings that add yet another line of evidence.

 

[whoknows]

It was, actually, a while back (1933) that the strangeness was first detected. Zwicky found that galaxies revolved within a cluster much too quickly. No visible matter could be found to explain the additional gravity needed. Zwicky called the missing matter: dark matter.

But this was only one line of evidence.

Jumping forward several decades, Vera Rubin, with an improved spectrometer, measured the motion of stars moving in orbit around the center of the Andromeda galaxy. Keplerian motion, unexpectedly, was not found. A great deal of matter had to exist in a halo around the galaxy . This was now a second line of evidence.

Today, I think, there are only a small percentage of galaxies without this dark, but highly influential, matter.

There are also all those Einstein rings that add yet another line of evidence.

All evidence for missing gravity, theory is fine, where is the objective proof for dark matter? My argument is not that dark matter is not real but that claims of objectivity that it is require justification.

 

[billslugg]

These are not evidence of missing gravity, they are evidence of missing mass. The only source of gravity, as we know it, is mass. We have excess gravity therefore there must be excess mass.
If you want to argue for new physics to explain it, that is fine but then you are just as unobjective as those of us positing missing mass.

 

[whoknows]

These are not evidence of missing gravity, they are evidence of missing mass. The only source of gravity, as we know it, is mass. We have excess gravity therefore there must be excess mass.
If you want to argue for new physics to explain it, that is fine but then you are just as unobjective as those of us positing missing mass.

I am not positing any new physics, just requesting that objective claims need to be justified.

 

[whoknows]

These are not evidence of missing gravity, they are evidence of missing mass. The only source of gravity, as we know it, is mass. We have excess gravity therefore there must be excess mass.
If you want to argue for new physics to explain it, that is fine but then you are just as unobjective as those of us positing missing mass.

How is/was it is determined that mass is missing or not, or in excess?

 

[billslugg]

We can see that galaxy clusters are orbiting some thing. We can see that galaxy stars are orbiting something we can't see. We can see Einstein Rings where there is no visible mass to cause the image. These are three independent indications of large masses we can't see.

 

[Helio]

What may be confusing is that the observations, though objective, are indirect evidence for DM. We always prefer direct observations of phenomena. But we are now beyond any reasonable doubt that DM is there and it’s not normal matter.

 

[G_x0a]

I think the current beautiful distances are enough to continue looking for the structure of space.
The dark matter hypothesis may be an observational error, going through many different derivatives (although I asked Grok and Grok concluded that scientists have considered most of the cases that lead to observational errors). But the way they came up with the quantitative number of 27% mass or 95% energy is amazing.

 

[Helio]

Observational evidence of the influence of DM on stars and galaxies since 1933 is likely in the thousands. Whatever DM actually is, its presence is “beyond a reasonable doubt”. Thus, alternative views are now ATM (Against The Mainstream) ones that will require significant argument to revise mainstream view.

 

[whoknows]

From my post#27

"All evidence for missing gravity, theory is fine, where is the objective proof for dark matter? My argument is not that dark matter is not real but that claims of objectivity that it is require justification."

-------

I phrased that wrongly/badly, better would have been "All evidence for a missing explanation for that excess gravity effect"

What I am trying to get at, is there any evidence for dark matter that does not rely on gravity?

How well understood is gravity?

 

[Helio]

From my post#27

"All evidence for missing gravity, theory is fine, where is the objective proof for dark matter? My argument is not that dark matter is not real but that claims of objectivity that it is require justification."

-------

I phrased that wrongly/badly, better would have been "All evidence for a missing explanation for that excess gravity effect"

What I am trying to get at, is there any evidence for dark matter that does not rely on gravity?

How well understood is gravity?

AFAIK, the only objective evidence comes from only gravitational effects by DM. But there are many numerous hypotheses that are trying to discover the particle responsible, and perhaps non-particle ideas, as well.

Recall that the first universal law came from Newton and it modeled the behavior of gravity for mass objects. But he too admitted he had no idea what gravity is, only its actions on mass. Einstein took this to another level, but mystery still exists. The search for the graviton continues. So, science still gets to enjoy lots of hunting.

 

[whoknows]

AFAIK, the only objective evidence comes from only gravitational effects by DM. But there are many numerous hypotheses that are trying to discover the particle responsible, and perhaps non-particle ideas, as well.

Recall that the first universal law came from Newton and it modeled the behavior of gravity for mass objects. But he too admitted he had no idea what gravity is, only its actions on mass. Einstein took this to another level, but mystery still exists. The search for the graviton continues. So, science still gets to enjoy lots of hunting.

"AFAIK, the only objective evidence comes from only gravitational effects by DM."

Taking into account your previous posts are you saying

excess gravity effects require an explanation, these effects are caused by DM, therefore objective evidence?

Isn't this a circular argument? (apologies if I have misinterpreted or oversimplified)

 

[Helio]

excess gravity effects require an explanation,...

Yes, this is DM in a nutshell.

these effects are caused by DM, therefore objective evidence?

Scientists have simply put a label (ie DM) on whatever it is that is causing the excess gravitational effects. They are confident there is no normal explanation, such as dark clouds (e.g. Bok Globules).

I suspect it was assumed that the excess gravitational effects would be found when Zwicky first found it (1933) and coined the term "dark matter".

It took more and more evidence to convince scientists that normal matter of any kind could indeed not explain the three types of "excess gravitational effects". Vera Rubin's discovery in the Andromeda galaxy was more convincing, so this likely was when DM became mainstream, or soon thereafter with subsequent galactic observations.

It was very helpful to me years ago to learn the importance of determining what is objective and what is subjective. Objective evidence is actual measurements, especially repeatable measurements. Galileo's observations of the moons of Jupiter was objective evidence, but you'd be amazed how others not only disagreed but actively sought to discredit Galileo, especially from academia (not the Church, initially).

But Galileo seemed to not be too bothered by their false accusations. Why? Because he knew that eventually they, or important others, would obtain a scope and "measure" for themselves that his claims were accurate. He had objective evidence he knew would not disappear. That's the beauty of objectivity.

Science is fact-based, but often it's stated as being objective-based. They terms are synonymous. Philosophy & ideologies, and religion will often include facts but they are far more subjective-based realms that make arguments based on a number of grounds including argument by authority regardless of a few facts.

In the case of DM, we have not only an excess of gravity but an excess of observations revealing this excess, but no one yet knows what it is and if we can put it under an electron microscope or not.

Others think it may not be a particle of any kind, but something else. For instance, MOND (Modified Newtonian Dynamics) was introduced out of Israel, IIRC, a few decades ago and suggested that on larger scales Newton's laws require tweaking. They were able to show that their tweaking explained DM for certain circumstances, but it could not explain all circumstances. In order for MOND to explain all circumstance guess what additional item they need to get the job done..... DM. So you can see that this comes across as too ad hoc. But, I'm no expert so perhaps some new twists will produce an alternative to a particle model. I'm also no physicist, but I've studied astro history that helps me with these topics. Knowing the history, one learns the terms and explanations on how we got to where we are. This is not only helpful but fun.

 

[whoknows]

Yes, this is DM in a nutshell.


Scientists have simply put a label (ie DM) on whatever it is that is causing the excess gravitational effects. They are confident there is no normal explanation, such as dark clouds (e.g. Bok Globules).

I suspect it was assumed that the excess gravitational effects would be found when Zwicky first found it (1933) and coined the term "dark matter".

It took more and more evidence to convince scientists that normal matter of any kind could indeed not explain the three types of "excess gravitational effects". Vera Rubin's discovery in the Andromeda galaxy was more convincing, so this likely was when DM became mainstream, or soon thereafter with subsequent galactic observations.

It was very helpful to me years ago to learn the importance of determining what is objective and what is subjective. Objective evidence is actual measurements, especially repeatable measurements. Galileo's observations of the moons of Jupiter was objective evidence, but you'd be amazed how others not only disagreed but actively sought to discredit Galileo, especially from academia (not the Church, initially).

But Galileo seemed to not be too bothered by their false accusations. Why? Because he knew that eventually they, or important others, would obtain a scope and "measure" for themselves that his claims were accurate. He had objective evidence he knew would not disappear. That's the beauty of objectivity.

Science is fact-based, but often it's stated as being objective-based. They terms are synonymous. Philosophy & ideologies, and religion will often include facts but they are far more subjective-based realms that make arguments based on a number of grounds including argument by authority regardless of a few facts.

In the case of DM, we have not only an excess of gravity but an excess of observations revealing this excess, but no one yet knows what it is and if we can put it under an electron microscope or not.

Others think it may not be a particle of any kind, but something else. For instance, MOND (Modified Newtonian Dynamics) was introduced out of Israel, IIRC, a few decades ago and suggested that on larger scales Newton's laws require tweaking. They were able to show that their tweaking explained DM for certain circumstances, but it could not explain all circumstances. In order for MOND to explain all circumstance guess what additional item they need to get the job done..... DM. So you can see that this comes across as too ad hoc. But, I'm no expert so perhaps some new twists will produce an alternative to a particle model. I'm also no physicist, but I've studied astro history that helps me with these topics. Knowing the history, one learns the terms and explanations on how we got to where we are. This is not only helpful but fun.

Thank you Helio

Do you agree with my suggestion that your argument is circular?

----

"It was very helpful to me years ago to learn the importance of determining what is objective and what is subjective. Objective evidence is actual measurements, especially repeatable measurements."

I argue that the objective evidence is multiple examples of excess gravitational effects and that DM is a subjective interpretation of that.

 

[Helio]

Thank you Helio

Do you agree with my suggestion that your argument is circular?

No.

"excess gravity effects require an explanation, these effects are caused by DM, therefore objective evidence?"

You're trying to draw a conclusion that is illogical. The objective evidence is the stuff that establishes your first premise ("excess gravity effects") that, yes, these effects do require an explanation.

We don't know what DM is physically, but it is appropriate to give these excess gravity effects a label for the simple reason we will all know what is being addressed.

Perhaps this might serve better, "Our multiple lines of objective evidence establishing a mysterious presence of some sort of matter causing the excess in gravitational fields of both galaxies and galactic clusters is given the label of DM (Dark Matter)." There is no "therefore".

If you prefer a syllogism, perhaps...

Observational evidence reveals excess galactic speeds in clusters as well as non-Keplerian motions within galaxies, though no common matter can explain it.
Unobserved matter can produce such motions.
Therefore, DM exists.

This, I think, is a valid argument. But notice the 2nd premise didn't say "Only unobserved matter can produce such motions." This could invalidate the argument if another alternative is found.

 

[whoknows]

No.

"excess gravity effects require an explanation, these effects are caused by DM, therefore objective evidence?"

You're trying to draw a conclusion that is illogical. The objective evidence is the stuff that establishes your first premise ("excess gravity effects") that, yes, these effects do require an explanation.

We don't know what DM is physically, but it is appropriate to give these excess gravity effects a label for the simple reason we will all know what is being addressed.

Perhaps this might serve better, "Our multiple lines of objective evidence establishing a mysterious presence of some sort of matter causing the excess in gravitational fields of both galaxies and galactic clusters is given the label of DM (Dark Matter)." There is no "therefore".

If you prefer a syllogism, perhaps...

Observational evidence reveals excess galactic speeds in clusters as well as non-Keplerian motions within galaxies, though no common matter can explain it.
Unobserved matter can produce such motions.
Therefore, DM exists.

This, I think, is a valid argument. But notice the 2nd premise didn't say "Only unobserved matter can produce such motions." This could invalidate the argument if another alternative is found.

(Wrt the circular argument rebuttal you earlier wrote "AFAIK, the only objective evidence comes from only gravitational effects by DM")

re your

"If you prefer a syllogism, perhaps...
Observational evidence reveals excess galactic speeds in clusters as well as non-Keplerian motions within galaxies, though no common matter can explain it.
Unobserved matter can produce such motions.
Therefore, DM exists.
This, I think, is a valid argument. But notice the 2nd premise didn't say "Only unobserved matter can produce such motions." This could invalidate the argument if another alternative is found."

This again to me seems circular, and unscientific, especially when you are defining unobserved matter as DM, and also illogical when other possibilities might be allowed. Shouldn't the conclusion be therefore DM might exist?

 

[Helio]

This again to me seems circular, and unscientific, especially when you are defining unobserved matter as DM, and also illogical when other possibilities might be allowed. Shouldn't the conclusion be therefore DM might exist?

Do black holes exist? None have ever been observed, right?