Question Where moment of inertia came from? Interaction with primordial matter that may be dark matter?

[Catastrophe]

Yes, sorry for throwing the wrong word again. It is funny how brain works .. it is very difficult to root out an image that was already associated with a linguistic element

I totally agree with you. English is my native language, but I only found out today the more precise meanings of SPIN and ORBIT. Yesterday I still confused myself with the word ROTATION.

 

[vagor]

Btw, I very much like your motto - "There never was a good war, or a bad peace "

 

[Catastrophe]

Vagor, I am looking at your post #1. If you take the grenade analogy, the particles are flying straight out from the explosion. I can see that there will be a gravitational attraction between them, but surely that is minor compared with the blast from the grenade? Over time, the velocity of the particles will decrease and the grav attr will become greater in comparison, and this might introduce interaction - but in which direction. Clockwise or anticlockwise - bad words, but I think you see my point?

 

[Catastrophe]

Btw, I very much like your motto - "There never was a good war, or a bad peace "

Thank you. I try to live by it

 

[vagor]

Vagor, I am looking at your post #1. If you take the grenade analogy, the particles are flying straight out from the explosion. I can see that there will be a gravitational attraction between them, but surely that is minor compared with the blast from the grenade? Over time, the velocity of the particles will decrease and the grav attr will become greater in comparison, and this might introduce interaction - but in which direction. Clockwise or anticlockwise - bad words, but I think you see my point?

Yes, I see your point.
However:
1. That analogy was applied to cosmic era when forces of nature as we know them today did not exist. I don't think we can speculate at which point and distance gravity became prevalent
2. Without experiencing resistance and friction the particles (we can't even use the word particle in this context - that was a quark-gluon plasma or something like it) will fly away without losing energy and thus decelerating unless and until.
3. As they separate and forces of gravity kick-in, they will start to decelerate but everything is still along the continuum of radial directions from initial event. I don't see what interaction within this expanding plasma could possibly lead to introduction of non-zero Curl. I think it can be described within Divergence terms alone.
The point I was trying to make was what could possible cause the appearance or Curl or Rotor as used in Russian vector algebra and suggested the effect of interaction with dark matter that is essentially the matter of primordial universe into which our Universe was expanding.
This interaction may introduce gravitational attraction in direction normal to direction of expansion forcing vector field to Curl leading to turbulence and thus to rotations.

 

[Cat-Ret-Jet]

‘Your prediction of the university being like a grenade has one big problem and that is that the galaxies are speed up, this is not the case as that the grenade would still be increasing in explosion, and that is not the case.
The known fact that the galaxies are speeding up this would mean that there is something adding power to push it faster however there is one problem some of the galaxies are moving towards each other which goes against Neuton’s laws that a projected item will stay on the same course unless acted on by a separate force and there no hypotheses that could support this.

 

[Catastrophe]

The local galaxies are approaching because the force of gravity exceeds the tendency to expand. Gravity is diminished according to an inverse square law, which is small over local distances.

Cat

 

[IG2007]

It looks like spin should never be used in physics discussion as there is no fully isolated body in the Universe and all objects spin around something and not around their axis following a complex cycloid-like trajectory.

Well, I think, spin in Physics should only be used in the case of referring to the particle spin of bosons and fermions, as, if I remember correctly, rotation of those fundamental particles have been referred to as spin for almost a century. Please correct me if I am wrong.

 

[Catastrophe]

IG, of course there is a meaning of spin in particle physics, but the word is also needed in astronomy. What else can you use to mean a single body rotating about its axis? Certainly not the ambiguous word rotating!

Cat

 

[IG2007]

What else can you use to mean a single body rotating about its axis? Certainly not the ambiguous word rotating!

Rotation, maybe.

 

[Catastrophe]

IG, rotation is ambiguous. For clarity, it must be spin or orbit.

Cat

 

[IG2007]

IG, rotation is ambiguous. For clarity, it must be spin or orbit.

Cat

I consider the definition of rotation as a body of matter rotating around its own axis, you can also use the word "spinning" in "rotating around its own axis." Sure, it needs an observer but "rotation" sounds better to me than just spinning.

 

[Catastrophe]

IG, please see post #13 for definitions. The only safe way is to use spin or orbit respectively.

Cat

 

[vagor]

Well, I think, spin in Physics should only be used in the case of referring to the particle spin of bosons and fermions, as, if I remember correctly, rotation of those fundamental particles have been referred to as spin for almost a century. Please correct me if I am wrong.

Spin of an elementary particle is a quantum number. This name was given to explain the observed behavior during spectrographic experiments in early 20-th century. In reality, all elementary particles are wave functions that manifest differently when interacting with physical environments. Elementary particles have no solid body and thus, using terms defined in #13 is probably inappropriate as well. However, I do not suggest that word spin shall not be used while describing quantum world. We probably should use rotate, revolute, etc. while discussing macro world and keep using spin for what it was originally intended by founders of QM.

 

[Catastrophe]

"and keep using spin for what it was originally intended by founders of QM."

I think that the word "spin" precedes QM.

Cat

 

[vagor]

"and keep using spin for what it was originally intended by founders of QM."

I think that the word "spin" precedes QM.

Cat

Yes, but in those early days they didn't know that electrons and nuclei are not classical solids. They also didn't think much about being linguistically proper. They simply saw spectral lines, new that electrons rotate around nucleus and new that electrons have charge. So, to explain what spectrometer showed, they assumed spectral variations to be due to rotation of electron around its axis and called it spin. They assumed that a particle can rotate clock - , counter clock wise, or do not rotate at all. Correspondingly they conjectured spin to be +1, 0, or -1. It was found later that some particles may have fractional spins.

 

[Catastrophe]

Yes, but I was posting about planets, not electrons.

Cat

 

[IG2007]

Yes, but I was posting about planets, not electrons.

Cat

Well, Cat, across modern history, the spin of planets around its own axis is referred to as rotation.

My emphasis.

 

[Catastrophe]

Well, IG, I was merely pointing out that spin and orbit respectively leave no room for ambiguity. You can see rotate, rotation, revolve (as in revolve about and revolve around) ambiguities all over the Internet, and beyond. I am not saying that they are all necessarily wrong, but ambiguous.

Cat

 

[IG2007]

Well, IG, I was merely pointing out that spin and orbit respectively leave no room for ambiguity. You can see rotate, rotation, revolve (as in revolve about and revolve around) ambiguities all over the Internet, and beyond. I am not saying that they are all necessarily wrong, but ambiguous.

Cat

Well, Cat, it's good enough for people to understand, TBH.

 

[Catastrophe]

IG, I find it easier to use unambiguous words, than to have to explain what I meant afterwards.

Cat

 

[vagor]

‘Your prediction of the university being like a grenade has one big problem and that is that the galaxies are speed up, this is not the case as that the grenade would still be increasing in explosion, and that is not the case.
The known fact that the galaxies are speeding up this would mean that there is something adding power to push it faster however there is one problem some of the galaxies are moving towards each other which goes against Neuton’s laws that a projected item will stay on the same course unless acted on by a separate force and there no hypotheses that could support this.

If you consider grenade explosion as not an instantaneous event, but is rather stretched in time, say for 14 B years or longer, then we are still within that explosion. Explosive substance that fills the grenade is still burning when its particles are already far away from point of singularity. In this scenario each particle is also exploding leading to acceleration of our Universe expansion,

Furthermore, if we are exploding into space occupied by primordial universe filled with what we call dark matter, than that dark matter may pull exploding particles from a grenade content to accelerate further in different directions defined by distribution of dark matter in primordial universe,

 

[Catastrophe]

"Celestial bodies often spin, from planets to stars to galaxies."

I must say, that I still cannot see how galaxies might spin. Where is the axis of rotation?

Cat

 

[vagor]

"Celestial bodies often spin, from planets to stars to galaxies."

I must say, that I still cannot see how galaxies might spin. Where is the axis of rotation?

Cat

Supermassive black hole found at the center of mass of each galaxy. As the matter of fact, you can actually see the axis of rotation as two (northern and southern) energetic jects shooting out from rotating black hole, https://www.google.com/url?sa=i&url...ved=0CAoQjRxqFwoTCMix6eu0pvECFQAAAAAdAAAAABAD

 

[IG2007]

IG, I find it easier to use unambiguous words, than to have to explain what I meant afterwards.

Cat

I don't find the word "rotation" to be ambiguous, really.