Educational diagram showing velocity curve

[Andrew Thornett]

Here is an educational diagram, which I am posting here so that anyone can use it without worrying about copyright. It is my copyright but I give permission for you or anyone else to use the diagram for any non-commercial purpose without needing further permission.

Andy

[Bruce Rout]

Hi Andrew,

Thanks for posting your diagram. There may be some disagreement regarding your assumptions. 

Respectfully,

Bruce 

On Mon, Jul 27, 2026, 7:02 p.m. 'Andrew Thornett' via Society of Amateur Radio Astronomers <sara...@googlegroups.com> wrote:

Here is an educational diagram, which I am posting here so that anyone can use it without worrying about copyright. It is my copyright but I give permission for you or anyone else to use the diagram for any non-commercial purpose without needing further permission.

Andy

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[Stephen Arbogast]

Not all  Physicists  agree about  'Dark Matter'    from  Sabine Hossenfelder.....   https://www.youtube.com/watch?v=Wdf5_vad9gM

Stephen

[Bruce Rout]

Stephen, I found Sabine's video hilarious. She does excellent critiques. She also supports MOND although that doesn't detract from her work. Again, it all appears to be the fallacy of the false premise.

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[Andrew Thornett]

Dear Stephen,

For what it is worth I also have problems with an explanation which relies of unidentified matter. However, I am not trained in physics and don't understand the maths, and get lost when folks on this group start talking about those things never mind Professors and the like. My diagram was meant to be an educational aid to explain what we look for in our H-line signals rather than contributing to the debate on the presence or otherwise of dark matter. Perhaps the diagram could be modified to be more fuzzy on the actual cause of the velocity curve!

Andy

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From: 'Stephen Arbogast' via Society of Amateur Radio Astronomers <sara...@googlegroups.com>
Sent: Tuesday, 28 July 2026 04:19:10
To: Society of Amateur Radio Astronomers <sara...@googlegroups.com>
Subject: Re: [SARA] Educational diagram showing velocity curve

 

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[Stephen Arbogast]

Andrew,

I understand....   Science  is  self correcting...  If  you have  young  students  it  is  important   that they understand   Science  does not   always   get  things  right  the  first time.

As you know from  Medicine many  mistakes  were  made along  the way.. we learn   and then we  progress!   Cool  stuff.

[Andrew Thornett]

Absolutely! As long as you understand that I dont disagree with you - I just dont consider myself qualified to add meaningfully to the debate.

Andy

Sent from Outlook for Android

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From: 'Stephen Arbogast' via Society of Amateur Radio Astronomers <sara...@googlegroups.com>

Sent: Tuesday, 28 July 2026 07:35:18

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[Jason Burnfield]

Whatever the cause ("dark matter" is just a place holder for "I don't know what it is"), the fact that the velocity curves of galaxies deviate substantially from Keplerian motion is not in dispute. 

There may debate about the cause, but the effect is clear as day.

Jason

[Whitham Reeve]

Hi Bruce - Agreed the video is funny. 

I did detect some artificial characteristics in both in the audio and video but there's no question a bullsh_t meter does exist ...

Whit

[Bruce Rout]

Hi Andy,

The diagram is fine as is because it shows the state of a certain segment of people studying galaxies and galactic structure. That is perfectly valid so long as the diagram, which is very clear and does show what the results would be if we assume that galaxies are Keplerian systems, clearly states where the information is coming from. That should be stated. Also, you state there is a curve which is actual, observed and with dark matter. The dark matter has never been directly observed. If it is a derived curve from a mathematical model assuming, or deriving, dark matter, then that should be stated. The curve is misleading. The curves derived from a dark matter model don't fit the data all that well from what I have seen so If you have new data derived curves from a fit, that would be excellent. I think the label should be the observed data with no reference to dark matter. Then put in a curve with the fit from whatever model is used, such as MOND, Halo model, or Top-Down Tree-search Algorithm. That would be very helpful. 

It is important to accurately state where the information comes from.

Also, the mass distribution graphs need to state where the information is coming from as well. The visible stars and gas curve is completely different than Shapely's measurements and other measurements from luminosity distribution in galaxies. The dark matter halo, if it is a halo, should have mass at the exterior of the galaxy rather than evenly distributed throughout the galaxy as I understand the theory. But any clarification you can give to the Halo theory as to its geometric distribution would be enormously helpful. The halo models I have seen have a disk geometry, a spherical geometry and both a disk and spherical geometry. It would also be nice to see what the MOND predictions are and what the mathematics is behind those models as well. I can see that there is no matter at all from 0 to about 7 kPc.

Your Key Point that "the observed flat rotation curve cannot be explained by visible matter alone" is dependent upon assuming the galaxy is a Keplerian system. That system has an overwhelming source of a gravitational field at the centre, such as the Sun in our solar system, and there is no gravitational interaction whatsoever between stars and interstellar dust and gas, such as is assumed between planets in our solar system. (actually, deviations from the Keplerian model is how we found outer planets, like Uranus, Neptune and Pluto). If the galaxy is not structured as a solar system, such as having a massive central body and non-interacting orbiting stars and material, then the entire dark matter and MOND universe collapses and the observed distribution of matter explains the flat rotation curve perfectly.

I appreciate the amount of work you have put into this diagram, but it needs clarification to eliminate its misleading aspects.

Thank you for your patience in going through this.

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[Alfred Aburto]

Absolutely!

Eventually the BS meter will shift over to the green.

Al

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[Andrew Thornett]

Gosh, Bruce! Looks like I have accidently opened a can of worms! All I was trying to do was produce a simple diagram to demonstrate the key difference between galacfic curve with and without dark matter that could be used as beginner educational diagram for example in talks to local astronomy societies where there is little or no knowledge of the subject nor practical radio astronomy nor cosmology.

I wasn't trying to produce a scientific treatise on the subject!

Also, it can be difficult to find copyright free images to use in talks so I wanted to provide one for SARA members - hence why I posted the image in the first place.

Anyway, errors noted and will be addressed in the next iteration of the diagram.

Andy

Sent from Outlook for Android

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From: sara...@googlegroups.com <sara...@googlegroups.com> on behalf of Bruce Rout <bruc...@gmail.com>
Sent: Tuesday, 28 July 2026 19:14:18
To: sara...@googlegroups.com <sara...@googlegroups.com>

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[Bruce Rout]

 Hi Andrew,

I’m afraid every time anyone deals with Dark Matter they are opening a can of worms. And I appreciate your efforts to demonstrate the key difference between galactic rotation curves with and without dark matter. The controversy is about the methods used and assumptions made rather than concerning the person trying to figure out what is going on. I thought this is a great opportunity to have a little poster in response, which is also public domain as far as copyright is concerned and is meant for teachers to use in order to teach about assumptions. This is a diagram of the Michelson-Morley experiment which proves irrefutably that the Earth is not rotating. This is a Socratic method and it involves a logical trap.

Again, thank you for opening up this discussion.

-Bruce

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[Andrew Thornett]

Thanks for sending that poster.

Talking about rotation, are you (or someone else) able to answer a question for me on rotation?

This is it: Cosmology and particle physics talks about effect of rotation, rotating black holes behave differently to non-rotating ones. But, surely rotation is measured relative to an external reference - so if your black hole, particle, etc., was located in a universe with nothing else around, then how could it be determined whether it was rotating and would rotation have any meaning?

Clearly, I am missing something important. I presume it has to be something internal in the system as rotation affects the radio emissions of that system or particle - but for life of me I don't know what.

Answers please using small words with maximum three letters (or not much more) in them and no complex terminology or equations!

I will then post the answer on my website for other befuddled would-be amateur radio astronomers!

It is becoming a mission of mine to help untrained dolts like myself, without any background in physics or engineering, and for who reading the equations is like trying to understand some strange foreign language, to grasp enough of the relevant concepts to get involved and excited about our hobby!

Andy

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From: sara...@googlegroups.com <sara...@googlegroups.com> on behalf of Bruce Rout <bruc...@gmail.com>

Sent: Wednesday, 29 July 2026 04:13:50

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[Andrew Thornett]

Thanks for sending that poster.

Talking about rotation, are you (or someone else) able to answer a question for me on rotation?

This is it: Cosmology and particle physics talks about effect of rotation, rotating black holes behave differently to non-rotating ones. But, surely rotation is measured relative to an external reference - so if your black hole, particle, etc., was located in a universe with nothing else around, then how could it be determined whether it was rotating and would rotation have any meaning?

Clearly, I am missing something important. I presume it has to be something internal in the system as rotation affects the radio emissions of that system or particle - but for life of me I don't know what.

Answers please using small words with maximum three letters (or not much more) in them and no complex terminology or equations!

I will then post the answer on my website for other befuddled would-be amateur radio astronomers!

It is becoming a mission of mine to help untrained dolts like myself, without any background in physics or engineering, and for who reading the equations is like trying to understand some strange foreign language, to grasp enough of the relevant concepts to get involved and excited about our hobby!

Andy

Sent from Outlook for Android

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From: sara...@googlegroups.com <sara...@googlegroups.com> on behalf of Bruce Rout <bruc...@gmail.com>

Sent: Wednesday, 29 July 2026 04:13:50

To view this discussion visit https://groups.google.com/d/msgid/sara-list/CAKczWimV2e3HPNUVzEA2gmRLDRmuUjmxFF9WZj_sGuA130Ad1g%40mail.gmail.com.

[Dave Typinski]

Short answer: nobody knows. Mach's principle -- the name for this line of
inquiry -- remains a matter of debate in our understanding of the universe.
--
Dave

[Bruce Rout]

You are being way too hard on yourself. There can be no knowledge without understanding. If you are rotating you are accelerating and you can tell if you are accelerating using a string and a nut tied to one end. The nut will point to where you are accelerating from. If the string stays slack, you're not accelerating. However, if you're not accelerating there's heaps of stuff you don't know without an external reference. But if you are accelerating, that effects stuff and you are in, what is called, an accelerating reference frame, and certain directions behave differently than other directions.

On top of all that, there is spin. If you want to slow down physicists just mention the effects of heat and spin. With spin there are preferred directions, like outwardly from the centre of spin and the axis of spin and so on. 

Radio waves, light, etc. are quickly fluctuating electric and magnetic fields. But these fields are not oriented with any preferred directions. If a source of a radio wave or light, like excited atoms for example, are in an accelerated region, like spinning or so on, there will be a preferred direction to the orientation of electric and magnetic fields. So if your antenna is set one way to incoming waves from an accelerating source you'll get a different reading than if the antenna is set in a different direction. 

That is one way light or radio waves can be polarized.

There are other things happening with spin but I have slowed down now.

I am sure others can do a much better job explaining this.

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[Andrew Thornett]

Very helpful! Thanks Bruce.

Andy

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From: sara...@googlegroups.com <sara...@googlegroups.com> on behalf of Bruce Rout <bruc...@gmail.com>

Sent: Wednesday, July 29, 2026 3:25:36 pm

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[Alfred Aburto]

Hi Bruce,

Your attachment is not the Michelson-Morely experiment of 1877.  It's fake. A really bad joke? The point of the Michelson-Morley experiment was to "prove" there was NO "aether", the supposed, at the time, medium through which light traveled. It had nothing to do with the Earth's rotation which was an effect that was too small for the experiment to measure.  Perhaps that was the point you were making? The Socratic method?

What interests me is why some people take the time and effort to generate charts like the one you attached. :-(

Best Wishes,

Al

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[Bruce Rout]

Andrew, I'm glad you received the poster in the way it was intended. It is tongue in cheek and is intended to create discussion regarding assumptions. As you correctly identified the real core of the problem, it is not relativity or the speed of light that is the issue in the poster; it is whether or not the Earth is spinning. The challenge to students of any leel is: How can we prove the Earth is rotating without going outside the classroom? The answer of course is with a gyroscope or Faucault pendulum. Have one gyroscope for the boys and one for the girls and a couple of stopwatches. There is a stopwatch on your phone. Then the fun begins. Then you can ask if the rotation of the galaxy has any effect. And what is the difference between being in an accelerating or npn-accelerating environment? And how can we tell? 

You have created a very good ciil discussion. That is rare with this subject matter.

To view this discussion visit https://groups.google.com/d/msgid/sara-list/bd500f7a-3da9-439c-9b6e-5751d167a1c5%40san.rr.com.

[Bruce Rout]

Hi Alfred. You have caught me. The poster is AI generated and was not made in 1877. The apparatus of M&M was aimed along the line of the supposed rotation of the Earth and also along the line towards the theoretical pole. And the experiment should definitely be able to detect the difference. But, of course, it detected no difference, which proves that the Earth is not rotating. The experimenters had wrongly assumed that the Earth was rotating and that led to the failure of the experiment.

I was in a discussion with Andrew regarding assumptions made in Dark Matter theories. The observations cannot be explained not because of any failure of physical theory aka General Relativityy, gravity and so on, but because of assuptions that have been taken for granted and should be carefully examined and questioned. Using assumptions without question leads to all sorts of humerous results, such as the Earth not rotating and Dark Matter and MOND for example.

It is tongue in cheek in a friendly discussion regarding posters and teaching science using simplified ideas. That was the point of poster: to confuse people and make them smile.