It's impossible to explain something to you in simple fashion, because then you take it that way, and equally impossible to explain in more complex terms, because you are so distractible that you chase the first red herring.
How do stars follow Keplerian orbits when the galaxy they are in is itself turning end-over-end? That was the question. Looking at their pathways after numerous flips and flops of the parent galaxy, do you still think them to be following elipses? (No, I didn't accuse you of talking with a lisp.)
What makes you think whole intact spiral galaxies are doing pancake flips? That's a violation of the conservation of angular momentum.
I wouldn't accuse even planet Earth of traveling an absolutely perfect ellipse. That's just one component of its motion. It also wiggles back & forth, since Earth & the Moon both orbit a mutual barycenter, and that barycenter shares another barycenter with the Sun. Earth gets perturbed endlessly in small amounts as bits of meteoric dust zip by. It even gets perturbed by the passage of neutrinos through it. A body's instantaneous motion is a function of the sum of all the forces acting upon it. A body's actual path over a period of time is a function of all the variable forces acting upon it over time.
Yes, yes, of course. If anyone dares to think contrary to the Mighty Sefton, then they are to be dismissed as absent and unaccounted for.
I think he means that the cone-shaped jets driven by the radiation pressure of the accretion disk isn't the same cone as the cone you seem to have invoked for your conic section orbit deal.
I think he was only saying that, conceptually, the cone on which any orbit is inscribed is, itself, revolving (or maybe only rotating) about some other axis. I don't think he thinks there are physical cones in outer space with little planet tracks on them. ;-P
Ever since I can remember talking, one of my Grandpa's favorite questions was, "Can a wheel turn three ways at once?" And he'd start acting it out, with this imaginary wheel in front of him, spinning, then precessing, then, ... the game was afoot, so to speak. :-)
The world needs more of that kind of inspiration. :-)
So? What do you think each indivdual star/star cluster is doing? You think it's just sitting there? Hell no. It's orbiting with the mass center of the galaxy. If you were to run a movie of the halo very fast you'd see each such object wizzing along on its own geodesic.
Was this what Mark was saying was against the law? In this brief clip, rotating the bike wheel causes precession. This is what I think galaxies are doing. (Albeit very, *very*, slowly. (-: John
John, you're really making a major fool of yourself here. There's a major difference between a bike wheel and a spiral galaxy. Can you tell me what that difference is? I'll tell you what it is.
First, the bike wheel is a RIGID system. A galaxy is anything but. Second, the bike wheel is hanging on the end of a tense chord with its angular momentum vector at some angle to the vertical, within an approximately uniform gravitational potential. A galaxy is anything but.
As Mrs. Banks said, in Mary Poppins "Rather stooopid."
And classical physics explains this precession with the presence of an external torque that is not along the axis of rotation. (It is in fact perpendicular to both the axis of rotation and the axis of precession.) This explanation is neatly confirmed by changing the direction or magnitude of that torque and observing the appropriate change in the precession rate. And so if you think that galaxies precess, then you surely have an accounting of the external torque that is not along the axis of rotation.
What you're doing, John, is extrapolating similar *behaviors* to similar objects, without an understanding of the agent that is causing the behavior or the rules that govern that behavior. Thus you imagine that because galaxies and bicycle wheels both have rotation and moments of inertia, then whatever the bicycle wheel does the galaxy should do also.
Returning to the cats and dogs thing: Both are mammals, both are carnivores with sharp canine teeth and sensitive hearing, both have binocular vision, both walk on four feet and have claws, neither sweat and must lose extra heat through panting, and both have fur and tails that they use for balance in running. However, it would be a mistake to then assume that because dogs in the wild hunt in packs, then cats in the wild do the same.
You make the same mistake in a *profound* way in comparing galaxies to atoms. You extrapolate the similarities without understanding anything about the underlying causes that will also reveal their deep differences.
But stars within galaxies do not and cannot follow Keplerian orbitals. Why? Because spiral galaxies have *arms*. Their arms remain discrete. They are separated from the other arms by bands of dust.
If the stars followed Keplerian orbits the galaxies could not possibly have arms. The inner stars would quickly lap stars exterior to them. It was precisely *because* of this that Dumb...I mean Dark...Matter was proposed; to pull all the outer stars around faster!! (Who *was* the brainiac that belched out that one?)
No, galaxies aren't rigid. But they aren't fluid, either. They are definitely structured in a somewhat permanent way. And for whatever reason- DM or the real reason- the stars within DO NOT....and CAN NOT... follow Keplerian orbits. Who was the brainiac that said that? Sam? Was that you?
I think it is the Oct. 2005 issue of Scientific American that provides some layman level education about galactic spiral arms.... You, John, might benefit from reading about the phenomenon of spiral arms and stellar orbits.
Hi John, Sorry, but no banana. The 'arms' of a galaxy are not any type of permanent relationship. There is nothing 'holding' them together except for a tendency to gravitationally clump when a large number of separate large objects are spinning around a common center of mass. Star go into and out of the 'arms' constantly. It is more a 'chaos' effect than an actual structure.
If, by "Keplerian", you mean a nice, clean, uncomplicated ellipse, then I'll have to say "What ever gave you the idea that things in the Universe are even asserted to follow such ideal paths?" I already told you a few posts back that I already know that real things don't travel in clean ellipses. An ideal elliptical orbit is followed only by
*pairs* of gravitating objects. In this big Cosmos, there are no pairs. There are, in fact, g'zillions of things exerting forces upon each other, and gravity is only one of those forces. Kepler discovered elliptical orbits only by the grace of orbits which are sufficiently close to ideal ellipses as to be amenable to analysis by means available to him at that time. If they had been severely complicated, for example by our being in a binary star system, then he probably would not have had a chance.
Something you don't seem to grasp is that the arms are not equivalent to the individual stars within them. If I rig up a weak light source to shine through a pinhole, producing an Airy pattern (an interference pattern of concentric rings) on a screen, the image of the rings will be quite stable on the large scale. But if I look closely enough at the image I'll find that on the small scale it sparkles. Each sparkle is a single photon event on the screen. The large Airy pattern is not, from moment to moment, the same exact photons. The photons come & go. The spiral arms of a galaxy are not necessarily made up of the same exact individual stars from one eon to the next. The spiral pattern is not a function only of Keplerian orbits. There's something more complicated going on in spiral galaxies than *just" masses gravitating towards each other.
And if you don't know by now, at this late time in your carreer as a maverick physicist, why the anomalous periods of galactic stars suggests Dark Matter (which should then be investigated as a plausible hypothesis, *alongside* the hypothesis that gravity follows a law not yet understood by us)), then what the hell are you doing bashing it? You don't even know what it is that you're debunking.
There's an old saying, that "Things should be described as simply as possible, but no simpler." Your stuff is a perfect example of simpler.
I once saw a time-lapse artists' conception of how a spiral galaxy is structured, and it seems that the leading edges of the arms consisted of new, young stars and the trailing edges were old, burned-out stars, and the dark spaces between the arms were full of supernova dust ("star stuff") waiting to be conglomerated by the advancing gravity wave of the approaching arm, and become the new stars in the leading edge. It was kinda cool, actually.
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