My solution to the conundrum of spiral galaxy rotation is that gravity increases towards the rotational plane of the spiral galaxy. The further the stars are from the central bulge, the closer they are to the plane of angular momentum of the galaxy. This seems to fit well with the general description of a spiral galaxy seen edge-on. Why hasn't anyone thought of this simple idea before? It even overcomes the problems associated with the second paragraph of the quote below:
Spiral Galaxy Dynamics: Gravity Increase of Rotational Plane (GIRP)?
- Thread starter common_sense_seeker
- Start date
Generally speaking, none of the attempts to modify gravity work very well. I don't know how many varieties there are, but a popular one I know of is called "Modified Newtonian Gravity". It explains the galactic rotation curves pretty nicely, but not too many of the other dark matter phenomena. In particular, modified gravity models have a hard time explaining the Bullet cluster (http://en.wikipedia.org/wiki/Bullet_cluster) and similar phenomena, in which dark matter appears to have seperated from the ordinary baryonic matter, while particle dark matter scenarios can usually handle it easily.
However I have no idea if something like your particular idea is out there already since I don't really know the details of any modified gravity theories.
However I have no idea if something like your particular idea is out there already since I don't really know the details of any modified gravity theories.
Hello all
The shape of the object (IE not spherical) that is producing the gravity is what needs to be incorporated into a more general gravity theory. You have changes in static electric theory to incorporate different shapes (sphere, infinite line, and infinite plane) and their resultant force equations (1/r^2, 1/r, 1) so why not gravitational theory.
The shape of the object (IE not spherical) that is producing the gravity is what needs to be incorporated into a more general gravity theory. You have changes in static electric theory to incorporate different shapes (sphere, infinite line, and infinite plane) and their resultant force equations (1/r^2, 1/r, 1) so why not gravitational theory.
Gravitation theory does do that, in a very similar way to classical electrostatic theory. Newtonian gravity and electrostatics are described by essentially exactly the same equations:
$$ F = k{qQ\over r^2} $$
$$ F = G{mM\over r^2} $$
True these are just for point masses and charges, but if you do the work you'll see that the other scenarios you describe work exactly the same way too.
It's just that most astrophysical bodies are very spherical so you really only see the 1/r^2 result. If you had an infinite line of mass it would have a 1/r force associated with it. Of course I am only talking Newtonian gravity here, but it would be similar in GR, just harder to calculate.
In fact the similarity goes a lot further than that, full classical electromagnetism and low-energy GR are both described by essentially the same equations as well. GR goes a bit different at higher energies because it is non-linear, but still, they are very similar. This is part of where Kaluza-Klein theories came from; if you change the spacetime of GR to be 5-dimensional and demand that it still obeys Einsteins equations, then electromagnetism arises as a natural part of the theory.
$$ F = k{qQ\over r^2} $$
$$ F = G{mM\over r^2} $$
True these are just for point masses and charges, but if you do the work you'll see that the other scenarios you describe work exactly the same way too.
It's just that most astrophysical bodies are very spherical so you really only see the 1/r^2 result. If you had an infinite line of mass it would have a 1/r force associated with it. Of course I am only talking Newtonian gravity here, but it would be similar in GR, just harder to calculate.
In fact the similarity goes a lot further than that, full classical electromagnetism and low-energy GR are both described by essentially the same equations as well. GR goes a bit different at higher energies because it is non-linear, but still, they are very similar. This is part of where Kaluza-Klein theories came from; if you change the spacetime of GR to be 5-dimensional and demand that it still obeys Einsteins equations, then electromagnetism arises as a natural part of the theory.
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Because people who've tried working on MOND realise there's more to solving a problem in physics than just giving arm waving explainations. If gravity increases as you get further away from the central bulge, how does it increase? How does it increase without implying the solar system should be different? Changing one part of the behaviour of a galaxy without changing any other part is quite difficult.
Did you not read my post? I'm saying gravity is stronger towards the rotational plane. Stars are closer to this the further away from the central bulge. This fits, agreed (just thinking abstractly for now)?
Again the silence...
Wait, so if I reply to a thread I'm trolling and if I don't I'm afraid to admit I'm wrong? What a nice catch 22 from you.
And you're obviously wrong because your implying that the further from the galaxy's sphere-like central bulge the closer stars are to the plane orthogonal to the axis of rotation. Except that there's stars in the plane of rotation near the bulge too. If you take a slice of the galaxy along that rotation plane you'll have stars all the way into the central region of the galaxy, not just some distance out, and their rotation curves will still need to be explained.
It's easy to see that stars will be in and around the galactic plane everywhere because if simple stellar mechanics. The centre of mass of a disk of material is at the centre of the disk. If a star is orbiting this disk then it'll actually be orbiting the centre of mass and so if the star beginning above the disk it'll be drawn downwards because there's a component of the gravitational force pulling it in the direction parallel to the axis of rotation of the disk. After some time it'll pass down through the plane of rotation, at which point it'll then be attracted back upwards. It'll continue this motion, moving up and down through the disk's plane of rotation in an oscillatory fashion. It's not possible for the star to start outside the disk and then it's orbital plane be parallel to the disk, it would imply there's no gravitational attraction between the disk and the star.
Again, this is something anyone whose done a bit of stellar mechanics should know. Infact you don't even need to know any of the equations, you just need to realise that a star would orbit a galaxy's centre of mass and if the star starts outside the galactic plane then it'll pass through it somewhere in it's orbit because its orbital plane is not parallel to the galactic plane.
You claim to have a degree in astronomy but this is yet another example of you seemingly having no clue about even the most simplistic of astronomical dynamical systems. Might I suggest that rather than try to be a smug patronising tool by saying "The silence is deafening" you spend that time more constructively, like reading a book on the topic you are talking about. Maybe then you'll stop believing you've got solutions to problems you don't even grasp.
And you're obviously wrong because your implying that the further from the galaxy's sphere-like central bulge the closer stars are to the plane orthogonal to the axis of rotation. Except that there's stars in the plane of rotation near the bulge too. If you take a slice of the galaxy along that rotation plane you'll have stars all the way into the central region of the galaxy, not just some distance out, and their rotation curves will still need to be explained.
It's easy to see that stars will be in and around the galactic plane everywhere because if simple stellar mechanics. The centre of mass of a disk of material is at the centre of the disk. If a star is orbiting this disk then it'll actually be orbiting the centre of mass and so if the star beginning above the disk it'll be drawn downwards because there's a component of the gravitational force pulling it in the direction parallel to the axis of rotation of the disk. After some time it'll pass down through the plane of rotation, at which point it'll then be attracted back upwards. It'll continue this motion, moving up and down through the disk's plane of rotation in an oscillatory fashion. It's not possible for the star to start outside the disk and then it's orbital plane be parallel to the disk, it would imply there's no gravitational attraction between the disk and the star.
Again, this is something anyone whose done a bit of stellar mechanics should know. Infact you don't even need to know any of the equations, you just need to realise that a star would orbit a galaxy's centre of mass and if the star starts outside the galactic plane then it'll pass through it somewhere in it's orbit because its orbital plane is not parallel to the galactic plane.
You claim to have a degree in astronomy but this is yet another example of you seemingly having no clue about even the most simplistic of astronomical dynamical systems. Might I suggest that rather than try to be a smug patronising tool by saying "The silence is deafening" you spend that time more constructively, like reading a book on the topic you are talking about. Maybe then you'll stop believing you've got solutions to problems you don't even grasp.
I haven't mentioned about any 'trolling'; that's what I do when I trail a line of hooks from my sea kayak to catch mackeral incidentally. That was QW. Yet another example of how we don't comprehend one another. I've given up reading your 'explanatory' posts from now on. Carry on replying if you wish, but I'm not interested enough to think about them.Wait, so if I reply to a thread I'm trolling and if I don't I'm afraid to admit I'm wrong? What a nice catch 22 from you.
And you're obviously wrong because your implying that the further from the galaxy's sphere-like central bulge the closer stars are to the plane orthogonal to the axis of rotation. Except that there's stars in the plane of rotation near the bulge too. If you take a slice of the galaxy along that rotation plane you'll have stars all the way into the central region of the galaxy, not just some distance out, and their rotation curves will still need to be explained.
It's easy to see that stars will be in and around the galactic plane everywhere because if simple stellar mechanics. The centre of mass of a disk of material is at the centre of the disk. If a star is orbiting this disk then it'll actually be orbiting the centre of mass and so if the star beginning above the disk it'll be drawn downwards because there's a component of the gravitational force pulling it in the direction parallel to the axis of rotation of the disk. After some time it'll pass down through the plane of rotation, at which point it'll then be attracted back upwards. It'll continue this motion, moving up and down through the disk's plane of rotation in an oscillatory fashion. It's not possible for the star to start outside the disk and then it's orbital plane be parallel to the disk, it would imply there's no gravitational attraction between the disk and the star.
Again, this is something anyone whose done a bit of stellar mechanics should know. Infact you don't even need to know any of the equations, you just need to realise that a star would orbit a galaxy's centre of mass and if the star starts outside the galactic plane then it'll pass through it somewhere in it's orbit because its orbital plane is not parallel to the galactic plane.
You claim to have a degree in astronomy but this is yet another example of you seemingly having no clue about even the most simplistic of astronomical dynamical systems. Might I suggest that rather than try to be a smug patronising tool by saying "The silence is deafening" you spend that time more constructively, like reading a book on the topic you are talking about. Maybe then you'll stop believing you've got solutions to problems you don't even grasp.
So the fact my post clearly explains how the claim of your central to the entire point of this thread is wrong isn't of interest to you?
In other words, you aren't interested in doing anything actually valid, you just want to talk acronyms with quantum_wave.
In other words, you aren't interested in doing anything actually valid, you just want to talk acronyms with quantum_wave.
You don't talk for the mainstream science community. What you're saying is just one person's opinion. I've read through Iain Nicholson's book 'Dark Side Of The Universe' 2007 and my ideas fit perfectly with the latest thinking and discoveries. For example, Nicholson concludes that the actual existence of dark matter haloes looks increasingly less likely when one studies the facts (Chapter 6: 'Does Dark Matter Exist at All?) (i) no detected density 'cusps' at the centers (ii) small satellite galaxies not seen but expected by computer simulation (iii) hierarchical galaxy formation scenario predicts that the smallest should have formed first and the largest, most massive, galaxies and clusters last - not seen (iv) random motions of stars in the outer parts of some (but by no means all) elliptical galaxies appear to decline with increasing distance from their centers in a way which suggests that they contain little, if any, dark matter at all. THESE ARE THE FACTS!
He has no answer..
I'm wondering if you're trying to troll or you're honestly so far up your own backside you can see out your mouth. This is the second time you'd done this in one thread and I'll say the same again, that you need to get over yourself. I get PMs from quantum_wave saying how I'm a jackass for replying to your threads, then I get a PM from him saying how I'm 'fanatical' and now that I'm not replying to your threads you whine that I have no answer.
Now either you want me to reply, in which case STFU about it when you don't like what I say or you STFU with you "He's got no answer". You have said nothing which requires a retort because you say nothing of value. You haven't answered any questions I've put to you. You claim to have an astronomy degree yet basic celestial mechanics, as I've explained in this thread, are beyond you.
Rather than making BS posts and whining "Oh look, he's got no answer" why don't you learn some science. Stop reading your pop science books and watching TV documentaries and pick up a textbook.
My explaination of how stars orbiting a galactic core would oscillate above and below the galactic plane isn't a matter of opinion, it's an unavoidable result of the behaviour of gravity. There's no 'it's my opinion', I'm telling you what Newton and Einstein say would happen, though if you aren't lying about an astronomy degree you should already know what I have had to explain to you.
Oh wow, then you're much more in touch with the physics community than me. I only spend my days in a physics department of a university talking with professors and doing research, you reading a pop science book puts you miles ahead of me.
Except you have no work. You've got a total of about half an A4 page of waffling. No descriptions, no models, no justification, no methodology, no derivation, no results, no predictions, no quantitative framework, no logic, just BS you make up as and when you need it. Anyone can do that, it's literally childs play.
Oh well if someone is publishing their work in a pop science book, rather than submitting it for peer review in a journal, where they can do a detailed analysis which are avoided in pop science books because layman don't want to read journal articles, then he's bound to be right then, isn't he? Whenever someone avoids journals and peer review and published a pop science book instead it's an immediate redflag that their work wouldn't pass peer review and they just want money. Like I said to you before, why are you reading pop science books and not journals or textbooks? If you've got an astronomy degree then surely you're able to handle things a little more advanced than something you can buy in Walmart.
Other than the 14 (at least) around our galaxy alone. http://en.wikipedia.org/wiki/List_of_nearest_galaxies See, if you were reading papers and not pop science books you'd be able to check up on the claims made in the paper by using the references. Pop science books have no such requirement and clearly you don't put in any effort to check what you read, which is a terriblely bad habit to have if you have any intention of doing any science.
Says who? A pop science book author and you? It took me 7 seconds to find a list of dwarf galaxies in our local area, I remembered that the two Magellanic clouds are examples of such galaxies so I knew you were not correct. It's funny how you and q_w have had a go at Prom and myself for being defenders of the mainstream, for clinging too much to what other scientists say, yet you are accepting anything you read in a pop science book, which is at best written by the people you complain Prom and I listen to and at worst written by a crank hack who haven't ever done any science. Books do not need to be fact checked, like journal papers do, so they are less trustworthy than journals. And to top it off you're claiming to have an astronomy degree and yet you haven't ever heard of dwarf galaxies? Bloody hell, even people who only watch TV documentaries have usually heard there's two little partners (ie the Magellanic clouds) near the Milky Way.
You whine Prom and I state things like the fate of the universe as according to general relativity as fact, saying we should open our minds a bit and yet you swallow anything and everything you read in unreviewed, layperson-orientated books you bought in a shop, even when they should be setting off alarm bells in your head by conflicting with what you should have learnt during your astronomy degree.
Shake it off CSS. AN is the low life of the forum and not worth the sweat off your backside.
Damn. I will have to post more.
I didn't think you would resent not having that status.
It's not so much the label as the one who labels.
Meaning what exactly?
If I'm the low life why did you PM me in a very obvious attempt to wind me up? If you and CSS don't want me posting, why make posts which are a deliberate attempt to get a response from me?
CSS still hasn't responded to my explanation of how orbits will oscillate above and below the galactic plane. Do you think my explaination of why he's wrong is itself incorrect or do you agree with my explaination of why he's wrong? Or do you think it doesn't matter because nothing I say is worth reading, in your opinion?
You and CSS whine about Prom and myself, how we back one another up (the 'peanut group' or whatever you called us) yet you're swallow one anothers BS without a second thought. And, as I commented, CSS accepts stuff he reads in a pop science book blindly, yet when we show support for work in a textbook we're being narrow minded. Excellent hypocrisy. And the fact you've PM'd me in a clear attempt to wind me up shows how pathetic you are. You aren't aggravating, your pathetic attempts to delude yourself are humorous. Of course normally I wouldn't find pathetic things funny but then its no skin off my nose if you both continue wasting effort on coming up with acronyms for your waffle.
I bet in 12 months time you'll be exactly where you are now. Just like you were 12 months ago q_w. Funny how you've gotten nowhere and done nothing in a year. 2 years even. Perhaps close to 3 years. Well, funny to me.
You know what, that post smells. I doubt if anyone could stand to read it. And about personal hygiene; try to keep your mouth shut while you post and wash your hands before you type.
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