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# Why are we so sure that there is a need for dark matter?

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Our scientists assume that there is not enough gravity in the galaxy to keep the stars in their orbital motion.

For example, in order to keep the Sun in its orbital motion around the SMBH, there is a need of 10^11 Sun mass.

However, the total mass of the SMB is only 4*10^6 Sun mass.

Therefore, the missing mass is called dark matter.

However, there is a severe mistake in this assumption

Somehow, the dark matter by itself can't explain the full structure of spiral galaxy.

It can't explain the Bulge, Bar, Ring and the disc shape.

It can't explain the spiral structure of the arm and why the thickness of the arm at the base (at 3KPC) is 3,000 LY while at the edge of the arm (12-15KPC) it is only 400LY.

It even can't explain the wobbling motion of the sun as it orbits around the galaxy.

Therefore, could it be that it was a sever mistake to assume that the Sun interact by gravity to the center of the galaxy?

We know that the moon interacts by gravity to the Earth.

The earth/moon are interacted by gravity to the Sun.

Therefore, as the moon interacts by gravity to the Earth, it wobbling while it orbits around the Sun.

Can we assume that spiral arm s gravitational arm?

The Sun is located at the Orion arm.

Therefore, why can't we assume that the Sun interacts by gravity to the local spiral arm and go with it wherever it goes?

Therefore, why can't we assume that as the moon interacts by gravity to the Earth, and it is wobbling while it orbits around the Sun, the Sun interacts to the Orion arm by gravity and it is wobbling as it orbits around the center of the galaxy.

Edited by Dandav

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On 11/25/2022 at 2:39 AM, Dandav said:

Therefore, the missing mass is called dark matter.

However, there is a severe mistake in this assumption

Somehow, the dark matter by itself can't explain the full structure of spiral galaxy.

It can't explain the Bulge, Bar, Ring and the disc shape.

I have wondered about that myself.Ā  Ā I came up with oneĀ  possible answer that I have not yet seen.

How about the combined mass of all black holes in the universe. Do we have an accurate estimate of the total mass of all black holes in the universe?

In a way that may be considered "dark matter", no?

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On 11/25/2022 at 5:39 PM, Dandav said:

Our scientists assume that there is not enough gravity in the galaxy to keep the stars in their orbital motion.

For example, in order to keep the Sun in its orbital motion around the SMBH, there is a need of 10^11 Sun mass.

However, the total mass of the SMB is only 4*10^6 Sun mass.

Therefore, the missing mass is called dark matter.

However, there is a severe mistake in this assumption

Somehow, the dark matter by itself can't explain the full structure of spiral galaxy.

It can't explain the Bulge, Bar, Ring and the disc shape.

It can't explain the spiral structure of the arm and why the thickness of the arm at the base (at 3KPC) is 3,000 LY while at the edge of the arm (12-15KPC) it is only 400LY.

It even can't explain the wobbling motion of the sun as it orbits around the galaxy.

Therefore, could it be that it was a sever mistake to assume that the Sun interact by gravity to the center of the galaxy?

We know that the moon interacts by gravity to the Earth.

The earth/moon are interacted by gravity to the Sun.

Therefore, as the moon interacts by gravity to the Earth, it wobbling while it orbits around the Sun.

Can we assume that spiral arm s gravitational arm?

The Sun is located at the Orion arm.

Therefore, why can't we assume that the Sun interacts by gravity to the local spiral arm and go with it wherever it goes?

Therefore, why can't we assume that as the moon interacts by gravity to the Earth, and it is wobbling while it orbits around the Sun, the Sun interacts to the Orion arm by gravity and it is wobbling as it orbits around the center of the galaxy.

Are we sure about existence of dark matter?

I think we are just using it as a placeholder to help hold our theories together.

Once we find out what is really going on, dark matter will be thrown on the scrap heap.

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17 hours ago, OceanBreeze said:

Once we find out what is really going on, dark matter will be thrown on the scrap heap.

Thanks

Why don't we consider Gravity as a perfect solution for the spiral galaxy?

However, instead of the imagination of direct gravity interaction between a star to the center of the galaxy, why can't we consider a gravity interaction between a star to its spiral arm?

Does the moon interact by gravity with the center of the galaxy?

The Moon interacts by gravity with the Earth, and go with it wherever it goes.

Does the Earth interact by gravity with the center of the galaxy?

The answer is - No (again).

The Earth (or actually the Earth/moon CoM) interacts by gravity with the Sun, and go with it wherever it goes.

So, why can't we assume that the Sun interacts by gravity with the spiral arm and go with it wherever it goes?

There is clear evidence for that.

It is the density of stars around us.

Do you know that there are 64 G stars in a 50LY sphere around us?

When we measured the sphere of 100LY around us we have found exactly 512 G stars.

Therefore, technically in each 50LY sphere there is exactly 64 G stars.

The thickness of the Orion arm is 1000Ly.

Therefore, theoretically, there are 512 * 10^3 = 512,000 G stars in a 1000LY sphere.

Don't you agree that this density is good enough to interact the Sun to the Orion arm by gravity?

Edited by Dandav
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23 hours ago, write4u said:

How about the combined mass of all black holes in the universe. Do we have an accurate estimate of the total mass of all black holes in the universe?

Black holes might represent perhaps 1% of the total mass density. That's a guess, dependent heavily on what you decide to include in the other 99%. Point is, it's not zero, and a positive percentage of an infinite universe makes for infinite combined massĀ of all black holes in the universe. It is probably best expressed as a density, not as total mass.

23 hours ago, write4u said:

In a way that may be considered "dark matter", no?

Black holes almost count as MACHO objects, which are almost dark matter of sorts, except they have a property of charge which actual dark matter does not.

21 hours ago, OceanBreeze said:

I think we are just using it as a placeholder to help hold our theories together.

That's quite the alternative opinion considering this is a no-speculation section.

3 hours ago, Dandav said:

Does the moon interact by gravity with the center of the galaxy?

The answer is indeed 'no' because the center of the galaxy doesn't have mass any more than the center of the solar system does. Right now, the center of the solar system (either the location of its center of mass, or the geometric center of the polygon formed by stretching a rubber band around all the planets) is vacant space. The moon does very muchĀ interact by gravity with every star, rock, bit-of-dark-matter, or free atom in the galaxy, and those in other galaxies as well. The moon is attracted to our sun, but not to the center of it. There's a difference, and the latter violates Newtonian law of gravity.

3 hours ago, Dandav said:

The Moon interacts by gravity with the Earth, and go with it wherever it goes.

The moon also interacts by gravity with the sun or the galaxy, and in both cases goes wherever it goes. But it going where it goes means the two are bound, which is very different from saying that they interact. So for instance, the moon may go where the galaxy goes, but the moon is not bound to Sgr-A, so it doesn't go where Sgr-A goes. But Sgr-A is bound to the galaxy just like the moon, so the moon goes where Sgr-A goes for the same reason it goes wherever Pluto goes, despite not being bound to Pluto.

3 hours ago, Dandav said:

So, why can't we assume that the Sun interacts by gravity with the spiral arm and go with it wherever it goes?

The sun is not bound to the arm, but (like Pluto) both are bound to the galaxy, so both go where the galaxy goes, even when the sun and the arm are nowhere near each other periodically.

3 hours ago, Dandav said:

Don't you agree that this density is good enough to interact the Sun to the Orion arm by gravity?

One pebble of mass, even in a different galaxy, is enough for the Sun to interact with it.

All that I've posted here follows directly from Newtons F=GMm/rĀ². Your suggestions violate it. In particular, there's no mention in that formula about centers of objects, especially centers of arbitrary human-designated sets of objects. Physics doesn't care what objects have been tied as a group by human language. Gravity cares about each bit of mass, so there is no 'star' or 'galaxy' or 'arm', all of which are just human groupings. There is just mass, each bit being where it is, and not elsewhere.

Edited by Halc
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Ā

Please look at the following image:

Ā Ā

Ā

Can you please explain that full spiral structure by using the dark matter idea?

1. Galactic disc -

As the dark matter is all about a sphere of matter that we can't see, then how it can set any sort of galactic disc?

Please remember that up to 1KPC the Bulge is a sphere. So how a sphere could be transformed into a disc (or spiral arms) at about 3KPC by the gravity power of the dark matter sphere?

2. Spiral arms -

Why at the base of the spiral arms (at 3KPC), the diameter of the arm is about 3000LY while at the edge it is only 400LY?

Why the two main spiral arms looks so symmetrical?

Don't you agree that it is indication for tidal gravity force (which means gravitational arms)?

3. How can you explain the density of G stars by the dark matter?

19 hours ago, Dandav said:

Do you know that there are 64 G stars in a 50LY sphere around us?

When we measured the sphere of 100LY around us we have found exactly 512 G stars.

Therefore, technically in each 50LY sphere there is exactly 64 G stars.

The thickness of the Orion arm is 1000Ly.

Therefore, theoretically, there are 512 * 10^3 = 512,000 G stars in a 1000LY sphere.

Do you think that this unique density of 64 G stars per 50 LY in our current location in the Orion arm is just a random chance?

4. Stars outside the arms -Ā

As you calim that the stars are not bonded (or directly interacted by gravity) to the spiral arms, then do you agree that theoretically there should be stars outside the spiral arms?

If so there should be stars at the galactic discĀ between the arms and also after the edge of the spiral arms.

Therefore, why at the edge of spiral arms all the stars there are ejected from the galactic disc?

In other words, why the galactic disc ends exactly at the end of the spiral arms?

Ā

15 hours ago, Halc said:

The moon also interacts by gravity with the sun or the galaxy, and in both cases goes wherever it goes. But it going where it goes means the two are bound, which is very different from saying that they interact. So for instance, the moon may go where the galaxy goes, but the moon is not bound to Sgr-A, so it doesn't go where Sgr-A goes. But Sgr-A is bound to the galaxy just like the moon, so the moon goes where Sgr-A goes for the same reason it goes wherever Pluto goes, despite not being bound to Pluto.

Ā

1. Moon - Yes, the moon ALSO interacts by gravity with the Sun and the galaxy, but don't you agree that it mainly interacts by gravity with the Earth?

Why can't we agree that from the gravitational point of view of the moon it actually mainly effected by the gravitational interact of the Earth?

Why can't we accept the simple understanding that there are levels or stages of gravity impact/interact/bonding.

Therefore, can we agree that the first level of the moon gravity interaction is with the Earth, while the interaction with the Sun is just on the second gravity interaction level?

2. Wobbling motion:

Why can't we understand that the wobbling motion of the moon while it orbits around the Sun is a clear indication that the Moon does not directly interacted by gravity with the Sun, but with other point of gravity called earth.?

Theoretically, even if we shut down the light from the earth, (assuming that we look from outside the solar system) we could detect that there must be some gravitational point (or Com) that the moon orbits around it.

In the same token the Sun is wobbling while it orbits around the galaxy:

Therefore, why can't we understand that the Sun isn't directly interacted by gravity to the dark matter in the sphere around the center of the galaxy, but to some other gravitational point in the spiral arm that we just can't see.

Please also remember that we can't see or detect the dark matter.

Therefore, if you claim that the Sun orbits around the gravitational center of the dark matter sphere that we can't see, why it is impossible for the sun to orbit around some local point in the Orion arm that we can't see, but we can detect this point by its wobbling motion.

2.Ā Sgr-A -Ā

Do you agree that if we take out theĀ Sgr-AĀ  from the galaxy, there will be no galaxy?

Therefore, why do you claim that theĀ Sgr-A is bound to the galaxy? why not the galaxy is bound to theĀ Sgr-A?

15 hours ago, Halc said:

The sun is not bound to the arm, but (like Pluto) both are bound to the galaxy, so both go where the galaxy goes, even when the sun and the arm are nowhere near each other periodically.

We clearly see that the Sun is located in the Orion arm.

So, why can't we consider the arm as a gravitational arm?

Edited by Dandav
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14 hours ago, Dandav said:

Can you please explain that full spiral structure by using the dark matter idea?

Dark matter has little if anything to do with the apparent spiral structure. There are galaxies with much less dark matter (almost none) which still exhibit spirial structure.Ā  A mass of only dark matter would not form structure like that.

14 hours ago, Dandav said:

Why the two main spiral arms looks so symmetrical?

Mostly because you seem to have chosen one of the poorest depictions of our galaxy I've ever seen in what should be a reputable publication.

14 hours ago, Dandav said:

How can you explain the density of G stars by the dark matter?

Density of baryonic matterĀ  is not likely much of a function of non-baryonic matter.

14 hours ago, Dandav said:

As you calim that the stars are not bonded (or directly interacted by gravity) to the spiral arms, then do you agree that theoretically there should be stars outside the spiral arms?

Assuming there is space designated between the arms as not being part of the arms, then of course, the density of G stars in those places should be quite close to the density anywhere in the disk at a given radius. It's only the stars with lifespans shorter than the travel time between the arms that make the designated arm regions appear brighter.

14 hours ago, Dandav said:

Therefore, why at the edge of spiral arms all the stars there are ejected from the galactic disc?

You're the only one claiming this. I'm not repeating my answers. Look at your old topics for them.

Ā

14 hours ago, Dandav said:

Moon - Yes, the moon ALSO interacts by gravity with the Sun and the galaxy, but don't you agree that it mainly interacts by gravity with the Earth?

It mainly interacts by gravity with itself, which is why when an astronaut jumps on the moon with Earth above, he nevertheless falls back to the moon. And no, the main component of the acceleration of the moon is not from the mass of Earth, which you can easily compute if you actually did some mathematics now and then.

g=GM/rĀ²

Mass of Earth is 6e24 kg.Ā  r is 3.85e5 km, so acceleration due to Earth is 4e13 G

Mass of Sun is 2e30 kg.Ā  r is 1.5e8 km, soĀ acceleration due to Sun is about 9e13 G, or more than twice that of Earth's influence.

This fact has also been pointed out to you in the past.

14 hours ago, Dandav said:

Why can't we accept the simple understanding that there are levels or stages of gravity impact/interact/bonding.

There are not different kinds of gravity. Positing such would constitute new speculation. Newton's laws are sufficient to explain all motion of moon, rocks, stars, galaxies, etc. They are not sufficient to describe exceptional gravitational potentials, nor the expansion of the universe. For these one must invoke Einstein's mathematics.

14 hours ago, Dandav said:

motion of the moon while it orbits around the Sun is a clear indication that the Moon does not directly interacted by gravity with the Sun

That assertion is a direct violation of Newton's law of gravitation, which does not have the sun's gravity to to zero at 1 AU of distance. If gravity of the sun could not reach as far as the moon, then the Earth also would not be affected and it (and all the outer planets) would not orbit the sun. Your assertions contradict the most basic laws of gravity.

14 hours ago, Dandav said:

Theoretically, even if we shut down the light from the earth, (assuming that we look from outside the solar system) we could detect that there must be some gravitational point (or Com) that the moon orbits around it.

Your selected picture directly contradicts the mathematics. If the sun has a greater influence, the path of the moon can never curve away from the sun, as is depicted at each solid blue dot. The actual path of the moon is not a circle, but it still traces a concave path. Your picture even shows the Earth accelerating away from the sun, which is even more wrong.

If you want to base conclusions on a picture you find on the net, then at least find an accurate picture.

14 hours ago, Dandav said:

Therefore, why can't we understand that the Sun isn't directly interacted by gravity to the dark matter in the sphere around the center of the galaxy, but to some other gravitational point in the spiral arm that we just can't see.

The sun and everything else directly interacts with all matter, everywhere. That's it in a nutshell. That's what the mathematics says. It isn't attracted to abstract points, centers of anything, or any of the other fiction you make up. It's attracted to matter, and all of it, wherever it is.

Edited by Halc
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On 12/2/2022 at 9:42 PM, Halc said:

Black holes might represent perhaps 1% of the total mass density. That's a guess, dependent heavily on what you decide to include in the other 99%. Point is, it's not zero, and a positive percentage of an infinite universe makes for infinite combined massĀ of all black holes in the universe. It is probably best expressed as a density, not as total mass.

Black holes almost count as MACHO objects, which are almost dark matter of sorts, except they have a property of charge which actual dark matter does not.

That's quite the alternative opinion considering this is a no-speculation section.

The answer is indeed 'no' because the center of the galaxy doesn't have mass any more than the center of the solar system does. Right now, the center of the solar system (either the location of its center of mass, or the geometric center of the polygon formed by stretching a rubber band around all the planets) is vacant space. The moon does very muchĀ interact by gravity with every star, rock, bit-of-dark-matter, or free atom in the galaxy, and those in other galaxies as well. The moon is attracted to our sun, but not to the center of it. There's a difference, and the latter violates Newtonian law of gravity.

The moon also interacts by gravity with the sun or the galaxy, and in both cases goes wherever it goes. But it going where it goes means the two are bound, which is very different from saying that they interact. So for instance, the moon may go where the galaxy goes, but the moon is not bound to Sgr-A, so it doesn't go where Sgr-A goes. But Sgr-A is bound to the galaxy just like the moon, so the moon goes where Sgr-A goes for the same reason it goes wherever Pluto goes, despite not being bound to Pluto.

The sun is not bound to the arm, but (like Pluto) both are bound to the galaxy, so both go where the galaxy goes, even when the sun and the arm are nowhere near each other periodically.

One pebble of mass, even in a different galaxy, is enough for the Sun to interact with it.

All that I've posted here follows directly from Newtons F=GMm/rĀ². Your suggestions violate it. In particular, there's no mention in that formula about centers of objects, especially centers of arbitrary human-designated sets of objects. Physics doesn't care what objects have been tied as a group by human language. Gravity cares about each bit of mass, so there is no 'star' or 'galaxy' or 'arm', all of which are just human groupings. There is just mass, each bit being where it is, and not elsewhere.

Ā On 12/2/2022 at 12:08 AM,Ā OceanBreezeĀ said:

"I think we are just using it as a placeholder to help hold our theories together"

Halc replied: "That's quite the alternative opinion considering this is a no-speculation section"

Ā

Since when did you start making up the site rules?

As I explained before, only when someone states something as a Fact, they are asked to back that up with a source.

By saying "I think etc." I am obviously expressing an opinion. I am entitled to have such an opinion since there is very little evidence for Dark matter, which by definition does not interact with anything. It does patch up and hold our Newtonian, and even modified Newtonian theories of gravity together. The existence of Dark Matter itself can be argued to be based more on opinion than Fact.

It seems you have an inclination towards debate and argue, rather than have a discussion. For example, you stated, rather factually, that "the sun is not bound to the arm, but (like Pluto) both are bound to the galaxy, so both go where the galaxy goes, even when the sun and the arm are nowhere near each other periodically."

I would like you to back up the claim that the there are times when the sun and the Orion arm are "nowhere near each other periodically". Since you stated it as a Fact, please provide your source(s).

Ā

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11 hours ago, OceanBreeze said:

Since when did you start making up the site rules?

My apologies. It was not my intention to leave that impression.

11 hours ago, OceanBreeze said:

there is very little evidence for Dark matter, which by definition does not interact with anything.

Well, it is posited to have mass, meaning it interacts with everything actually, but only via gravity. Dark matter has indeed not been 'proven', but neither has Einstein's relativity. The MOND theories are an alternative, but no MOND laws have been found that explain the motion of all galaxies, ones that appear to have more or far less dark matter than is typical.

11 hours ago, OceanBreeze said:

I would like you to back up the claim that the there are times when the sun and the Orion arm are "nowhere near each other periodically". Since you stated it as a Fact, please provide your source(s).

It is known as the winding problem. If all matter stayed in the same arm at all times, moving at the measured velocities, the galaxy shape would very quickly wind up so tight that all structure would be lost, leaving just a disk.

If the structure retains its general shape over multiple rotations and the stars maintain their general position in that structure, the matter in the galaxy would constitute approximate rigid motion, making the velocity of any star relative to the galaxy a linear function of its distance from the center. The measured rotation curve is not linear with distance:

This leaves some options as to what can be:

1) The arms distort and wind up per the first picture. We'd see many galaxies (anything not young) with tightly wound arms. This is not observed.

2) The arms break up frequently and new ones form after a while, lasting a fraction of a rotation at a time.

3) The stars don't move with the arms (density wave theory, not a proven thing) but rather travel between them.

4) The stars stay in their respective arms, but move outward along them as they fail to keep pace with the rotation rate of the pattern.

The first option can be falsified. The second one does not leave our sun in the Orion arm since the arm's existence is fleeting. I've not seen a theory proposing this, but there's probably one out there. The 4th option violates energy conservation.

The third option is the one I see most referenced/accepted, but it needs work, and I don't claim it as fact. I've seen some good simulations that generate nice bars and arms, but most of the simulations I see of say galaxy collisions don't use this model, and the winding problem shows in them.

Ā

The arms even look like waves, or more in particular, a wake. Water particles move from one wave to the next as waves pass. The waves of a wake are broken, looking like fallen dominoes.

Ā

That wake looks remarkably similar to the structure of one of the arms in the galaxy image you posted, a series of overlapping smaller waves rather than one long clean one.

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10 hours ago, Halc said:

My apologies. It was not my intention to leave that impression.

Apology accepted, no worries mate. Ā It rarely happens that someone apologizes instead of continuing to argue, so kudos to you for that. I may have misjudged you, in which case I am the one who should be apologizing to you.

Ā

Quote

Well, it is posited to have mass, meaning it interacts with everything actually, but only via gravity. Dark matter has indeed not been 'proven', but neither has Einstein's relativity. The MOND theories are an alternative, but no MOND laws have been found that explain the motion of all galaxies, ones that appear to have more or far less dark matter than is typical.

Quite right, I should have stated it this way: āThereās no evidence that dark matter interacts with any other force but gravityā. I suppose I just didnāt want to be stating the obvious.

Quote

It is known as the winding problem. If all matter stayed in the same arm at all times, moving at the measured velocities, the galaxy shape would very quickly wind up so tight that all structure would be lost, leaving just a disk.

I was under the impression that the density wave theory eliminated the winding problem but it did so by expressing the density wave as a standing wave.Ā
In other words, the stars within the arms are not necessarily stationary, though at a certain distance from the center, the corotation radius, the stars and the density waves move together.

Quote

Ā

The arms even look like waves, or more in particular, a wake. Water particles move from one wave to the next as waves pass. The waves of a wake are broken, looking like fallen dominoes.

That wake looks remarkably similar to the structure of one of the arms in the galaxy image you posted, a series of overlapping smaller waves rather than one long clean one.

Ā

I am glad I asked you to provide your source because researching the subject of density waves and the possibility of the wave decoupling from the physical material in the arm (stars and other matter), is something I find very interesting.

I am particularly interested in the corotation radius as it applies to our own galaxy and our solar system. What I am trying to find out, so far without success, is whether or not our solar system is located at the corotation radius of the Milky Way galaxy, which would make our solar system seem even more special in the scheme of things, by providing a stability point which perhaps supports the formation of life.

All of this is pure conjecture on my part; but I did find this interesting paper on Density Waves and the corotation point in some galaxies. Of course, it doesnāt answer my conjecture about the possible role of a special stability point which may allow for life to develop; but it is interesting in its own right.

Ā

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2 hours ago, OceanBreeze said:

I should have stated it this way: āThereās no evidence that dark matter interacts with any other force but gravityā. I suppose I just didnāt want to be stating the obvious.

Agree, but it would be a little more interesting if it was only EM interactions that were missing. I mean, neutrinos almost already qualify as dark matter, but they're sufficiently detectable (I'm unclear how they do it now, but I remember the early failed efforts) that their measured density is nowhere near that needed to account for dark matter density.

2 hours ago, OceanBreeze said:

I was under the impression that the density wave theory eliminated the winding problem but it did so by expressing the density wave as a standing wave.Ā
In other words, the stars within the arms are not necessarily stationary, though at a certain distance from the center, the corotation radius, the stars and the density waves move together.

Not sure what you mean by standing wave. I've seen what seem to be crude simulations where the wave doesn't move at all. No apparent rotation of the pattern, but the material goes around as usual. Most of the simulations have the spiral pattern move with trailing tips. Silly thing is that we've not had enough time to see the patterns move (have we?). It's not like you can measure the redshift of an effect, only of the matter comprising the effect, and that matter doesn't move with the effect.

2 hours ago, OceanBreeze said:

What I am trying to find out, so far without success, is whether or not our solar system is located at the corotation radius of the Milky Way galaxy, which would make our solar system seem even more special in the scheme of things, by providing a stability point which perhaps supports the formation of life.

Concerning the corotation radius (zero for the former 'stationary wave'), that radius seems to be where the bar changes to a ring/arm pattern (around 3kpc). I'm not stating this as fact, and there might be different models that put it at different radii. Putting it at 3kpc seems to make sense, but then spirals lacking any kind of bar need to be explained. If it's there, then the arms go faster than the matter and we get overtaken by the next arm in line, the Sagittarius-Carina arm. Closer in (2kpc say), the matter rotates faster than the bar. This may again not be the case since the rotation curve is hardly constant.

The graph I showed in my prior post has a low point near that 3kpc point where I suspect is that corotation radius. It goes up from there with smaller radius, somewhat like inverse-square orbital ratesĀ of planets. But then, around 0.6 kpc it drops off sharply, suggesting perhaps that density of the inner galaxy is fairly uniform and there's no significant mass around which to drive any appreciable orbital speed. Sure, we have that black hole in there, but only a hundred or so stars actually orbit it, and the mass of the black hole just isn't enough to move the material a little further out. Most galaxies our size (Andromeda in particular) have central black holes far more massive.

No, I don't think we're anywhere near the special radius. What's special about being here is stability. The stars are sufficiently sparse way out here in the rural section of the galaxy that we can go 5 billion years without significant change to our environment. Close in (especially around the 3kpc ring) you have close encounters with other stars which might suddenly thrust planets into new orbits or even new suns, the resulting climate jolt eliminating all but the most primitive life.

Even 5 billion years is a close call for us. It took that long (maybe 4.5 actually) for humans to appear, and yet we've less than 1 billion years to go before the planet can no longer support multicellular life. The oceans will boil away, etc. This is not opinion, just what I read. I can get sources if you want.

I personally suspect that the environment here was significantly different even a short time (50 million years) ago. One clue is the paradox of the dinosaurs and the square cube law, but that's a whole different topic.

2 hours ago, OceanBreeze said:

I am glad I asked you to provide your source because researching the subject of density waves and the possibility of the wave decoupling from the physical material in the arm (stars and other matter), is something I find very interesting.

It wouldn't be a wave if it was coupled to the material medium. The density wave theory is hardly universally accepted, but what other options are there which match the observations?

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8 hours ago, Halc said:

Agree, but it would be a little more interesting if it was only EM interactions that were missing. I mean, neutrinos almost already qualify as dark matter, but they're sufficiently detectable (I'm unclear how they do it now, but I remember the early failed efforts) that their measured density is nowhere near that needed to account for dark matter density.?

If Sterile right hand neutrinos are ever found through the seesaw mechanism they would be extremely heavy and still fill the requirement of being non relativistic (cold). That's the theory anyways.Ā

Edited by Shustaire
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On 11/25/2022 at 3:39 AM, Dandav said:

Our scientists assume that there is not enough gravity in the galaxy to keep the stars in their orbital motion..

I'm going to start hereĀ  if you calculate via Newtons gravitational laws. The baryonic mass distribution should give us a Kepler decline in rotation curves. The outer region stars would not rotate at the same rate as the internal region.

Ā I'm sure you have heard this before. However it has little to do with the BH at the center. If you look at the r^2 relation of [tex] f=\frac{GMm}{r^2}/[tex]you will see the force of gravity will quickly reduce to effectively zero as the radius increases.Ā

This is also true with the galactic bulge...

Ā So what matter distribution us required to keep the rotation curves in a non Kepler decline such as we see in spiral galaxies ?

The answer is you need a uniform mass distribution that envelopes the spiral galaxy sufficient to offset the bulge as well.

This is given by the NFW profile

This is the most popular solution involving mass.

Dark matter does not determine the structure of a Galaxy. If you want to understand that then studyĀ

Density wave theorem.

Edited by Shustaire
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55 minutes ago, JeffreysTubes8 said:

I feel that what is waving between particles are gravtiational microwaves. The reason they entangle is because of retrocausality imho.Ā

Any chance you could give some evidence to back up your beliefs? Your empty assertion show a distinct lack of respect for the forum and the people who are using it.Ā  Your feels do not play into the truth in anyway.Ā

Edited by Moontanman
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12 hours ago, JeffreysTubes8 said:

I have a whole mathematical model in the Historical Codex Thread. I had started my hypothesis in explaining the SMBH formation issue, there were other hypotheses to explain the problem, direct collapse of primordial gas clouds, blue giant stars, etc. However, they don't give time enough to form such large black holes so early in the universe. In my model everything gravitates to one center almost immediately forming SMBHs but these objects themselves can create enough dark energy to prevent the universe from becoming a black hole due to the superluminal gravity within the event horizon proximity and launching galaxies FTL as we observe them to be traveling. -e particles, or even down quarks, would represent the local strength of gravity, the up quarks or positively charged particles would be experiencing similar pulls from another direction due to the higher gravitational frame-drag rate, even though the frame-drag magnitude is infinitesimal to a local source by comparison. So the opposing pull of a local object like the SMBH against dark energy particle collisions from far away forms the first atoms. This is before light is free to move about the cosmos.Ā

The model's logic base is Murphy's law, a sphere is the product of what can happen in a dimensional body. Infinite spheres are then likely to occur with every possible velocity in every possible direction, and due to the constant of c we observe, these graviton spheres should be about a planck length. So when they make contact they emit a gravity wave which tugs (frame-dragging) everything within the vicinity of the wave by a planck length, then as the wave expands this gravitational magnitude decreases by the inverse square law. A black hole is just many gravitons inseparably combined into one, each time a new graviton combines with the black hole a very strong gravitational wave is released. Inside the eh a graviton that is not combined will continue to move by this frame drag rate of millions or billions of planck lengths in a planck time long after it outraces the expanding gw of the black hole, it is now a dark energy particle. When it collides with another graviton the gw emitted may not pull by more than a planck length, but it will do so in millionths or billionths of a planck time, inverse of the gw that created it, but the effect is the same on an object experiencing this gravity. Fast gravity = strong gravity. Which is why I believe anti-gravity crafts observed, like the Gimbal Video, are real.Ā

Ā

11 hours ago, JeffreysTubes8 said:

When I speak of "what is waving between particles"Ā

When one sees this the immediate question that comes to mind is, what is waving? What is this particle pond? If particles aren't bullets that is, as originally thought, and they are as observed in that diagram, as a microscopic fluid. Apropos a gravitational fluid. Two up quarks and one down quark, the hydrogen atom, that's a pattern held in place by external gravitational influences converging at a local cosmic region in such a way that it creates the specific structure of a specific type of matter. So in my theory matter is a holoprojection of what's going on at the heart of galaxies and collisions between galaxies - as these forces converge at the spiral discs of the galaxy, or the spherical gas cloud back before the CMB.Ā

So again all you give is meaningless word salad... still trying to baffle us with bullshit due you having no brilliance.Ā Ā

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On 12/4/2022 at 8:35 AM, Halc said:

It is known as the winding problem. If all matter stayed in the same arm at all times, moving at the measured velocities, the galaxy shape would very quickly wind up so tight that all structure would be lost, leaving just a disk.

If the structure retains its general shape over multiple rotations and the stars maintain their general position in that structure, the matter in the galaxy would constitute approximate rigid motion, making the velocity of any star relative to the galaxy a linear function of its distance from the center.

The winding problem is an indication that our scientists have considered a possibility for gravitational arm "whereĀ all matter stayed in the same arm at all times".

However, this idea of gravitational arm had been rejected not due to any error in the gravity force that can bond the stars in the arm, but due to the winding problem.

Do you agree with the above?

Edited by Dandav
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5 hours ago, Dandav said:

The winding problem is an indication that our scientists have considered a possibility for gravitational arm "whereĀ all matter stayed in the same arm at all times".

There was never a theory of 'gravitational arm'. A galactic arm is a human abstraction, an arbitrary subset of material. There is no valid physics that suggests that an arbitrary subset of matter like that can exhibit gravity in isolation of other gravity. It's like asserting (as you do) that Earth's pull on the moon somehow negates the pull of the sun on it. That was shown to be wrong, despite the fact that the moon tends to stay in Earth's vicinity.

So yes, there was a time when the prevailing view suggested that most stars tended to stay in the same 'arm'. It was never a 'gravitational arm' theory since an abstraction does not have gravity of its own. Each bit of matter everywhere (not just in the galaxy, which is just another abstraction in the end) exerts pull on all other bits. The acceleration of any given particle is due to the sum of these forces, including local interactions through forces other than gravity. An arm isn't a mass at a location, so it adds nothing to the above description.

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